Browse Topic: Advanced high-strength steels

Items (313)
Find
High-Strength Carbon and Alloy Die Drawn SteelsJ935_202606 (Current)6/22/2026
This SAE Recommended Practice is intended to provide basic information on properties and characteristics of high-strength carbon and alloy steels which have been subjected to special die drawing. This includes both cold drawing with heavier-than-normal drafts and die drawing at elevated temperatures.
Metals Technical Committee
Comparison of Formability Performance Between CR550LA and CR590DP2026-01-01784/7/2026
While rapid development of advanced high strength steels (AHSS) for a safer and lighter vehicle has been a primary focus in the automotive industry, the application of traditional high strength low alloy (HSLA) steel continues to be actively supported and developed. AHSS are often used to replace HSLA steels for downgauging while maintaining similar or better performance in crashworthiness and durability. However, recent developments have enabled the availability of higher strength, cold-rolled HSLA steels that could offer opportunities for a more balanced solution between material cost and material performance. Certain higher strength HSLA steels not only offer a cost-effective way to increase the strength-to-weight ratio but also provide comparable formability and better weldability to AHSS. In this study, cold rolled HSLA grades of CR420LA and CR550LA are evaluated in overall formability and in-use performance when compared to CR590 dual phase (DP) grade. The evaluations performed include both global and local formability tests such as forming limit curve (FLC) testing, true fracture strain, half specimen dome and hole expansion tests. Experimental results indicate that CR550LA tends to have a slightly better local formability but slightly lower global formability than CR590DP. The results demonstrate these higher strength, cold-rolled HSLA steels can potentially be used to replace CR590DP for certain components.
Shih, Hua-Chu, Brown, Lindsay, Pednekar, Vasant, Shi, Ming, Tedesco, Sarah
Optimization of Global and Local Formability Properties through Nb Microalloying2026-26-03031/16/2026
David Martin, CBMM Asia Bernardo Barile, CBMM Europe BV Caio Pisano, CBMM Europe BV Automotive high strength steels have specific microstructure-dependent forming characteristics. Global formability is generally associated with high uniform strain values which imply good drawability and stretch forming properties driven by pronounced work hardening. Local formability on the other hand is often measured by various fracture strain values—generally higher in single phase steels. In this respect, the so-called ‘local/global formability map’ concept has been established not only to provide a comprehensive methodology to characterize existing automotive steels but also to enable improvement strategies toward more balanced forming characteristics. Niobium (Nb) microalloying is a powerful tool to achieve both property improvement in general and property balance in particular. More than two decades of research has demonstrated that Nb-induced microstructural optimization is applicable to HSLA steels, AHSS (DP, CP, TRIP, TWIP) and PHS, and it has been realized in commercial production of such steels. This contribution details the underlying metallurgical and processing effects of Nb microalloying in automotive high-strength steels and highlights achieved global and local formability improvements. Respective optimization vectors are demonstrated through intrinsic formability mapping, where the possibilities and limitations are indicated.
Barile, Bernardo
Experimental Study on the Role of Hole Expansion Ratio in Enhancing Crashworthiness of Advanced High Strength Steel2026-26-02951/16/2026
To meet light weighting and safety targets, the automotive industry is increasingly using advanced high strength steel (AHSS) materials and advanced manufacturing techniques for complex body parts. To improve energy absorption of automotive body parts, various steel grades are developed by steel manufactures with variety of properties (YS, UTS, EL %, HER). Also, the formability of AHSS grades (TS > 980 MPa) is challenging due to its limited edge ductility. This study focuses on role of hole expansion ratio (HER) in energy absorption of AHSS material. In the study, different AHSS material with variety of microstructure and properties are experimented, with the aim to identify the optimum properties that can help to enhance crash worthiness of formed part. From experimentation, it is evident that hole expansion ratio plays an important role in determining edge ductility, as well as energy absorption. This study may not only help to improve crash performance but also help for light-weighting of automotive body parts.
Jain, Vikas, Bandru, Shreenu, Nadarge, Harshad, Misal, Swapnali, Deshmukh, Mansi, Paliwal, Lokesh
Influence of Microstructure on the Mechanical Properties of Laser-Welded Joints between Different Classes of Automotive Steels2025-36-004912/18/2025
The need to reduce vehicle weight without compromising safety drives the use of advanced high-strength steels (AHSS) in the automotive industry. Laser welding is a widely employed technique for joining dissimilar materials due to its high precision and small heat-affected zone (HAZ). However, differences in the chemical composition and thermomechanical properties of the materials can create heterogeneous microstructures in the fusion zone (FZ) and HAZ, directly impacting the mechanical properties of the welded joint. This study aims to evaluate the relationship between microstructure and mechanical properties in laser-welded joints of dissimilar automotive steels. The objective is to understand how microstructural transformations affect weld strength, ductility, and toughness, contributing to process parameter optimization and improved structural performance. Microstructural analysis will be performed using optical microscopy, and mechanical tests, such as tensile testing and microhardness, will be conducted to correlate microstructural changes with the mechanical properties of the welded joint. It is expected that laser welding will result in a hardened HAZ due to the high cooling rate, which may reduce ductility and increase hardness in the welded region. Differences in the chemical composition of the base materials may lead to the formation of brittle phases in the FZ, affecting the joint's strength and toughness. The findings of this study will provide essential insights for improving the welding process and ensuring greater structural reliability in automotive applications.
Santos, dos Flávio Nunes, Reis de Faria Neto, dos Antonio, Dias, Erica Ximenes, Martins, Marcelo Sampaio, Santos Pereira, dos Marcelo
Advanced High Strength Steels in Rear Underrun Protection Devices2025-36-03108/1/2025
A Rear Underrun Protection Device (RUPD) is a safety feature installed on the rear end of chassis of trailers, designed to prevent smaller vehicles from sliding underneath the rear of the trailer in the event of a collision. Therefore, it plays a critical role in reducing the risk of serious injuries or fatalities. The RUPD standard is updated aiming to improve the strength and resistance of these devices, therefore improving the road safety. This paper shares the author’s experience with the latest standards and regulations for Rear Underrun Protection Devices (RUPD), with a focus on the use of Advanced High Strength Steel (AHSS). It provides a general overview of RUPD standard requirements and suggests several AHSS steel tube sizes suitable for the main longitudinal member, serving as a starting point for design. Key design parameters and potential failure points in RUPD structures are discussed, along with possible solutions. Finite Element Modeling (FEM) is commonly used in the design phase to assess structural performance before physical testing. Given the high costs of prototyping, FEM accuracy is crucial. The paper highlights common sources of inaccuracy—mainly related to modeling techniques—and suggests ways to improve reliability.
Rad, Nima Asadi
Material Characterization of Newly-Developed Advanced High Strength Steels for Prediction of Crash Performance2025-01-82204/1/2025
New highly ductile advanced high strength steel (AHSS) grades with tensile strength greater than 980 MPa have been developed with the aim of achieving a combination of high strength and excellent formability. The new jetQTM-Family [1, 2] offers high local and global ductility, which is expected to contribute to the improvement of vehicle crash performance. For the reliable design and management of vehicle crash performance, material modeling, including work hardening behavior and material failure strain, plays an important role in numerical simulation. Especially, the accuracy of material failure prediction is important for the development of crash performance. In this study, the fracture behaviors of 980jetQTM, 1180jetQTM, and conventional Dual-Phase (DP) steels are investigated through simple tensile and V-bending fracture tests incorporating experimental-numerical hybrid ductile fracture analysis. Based on the experimental results, the ductile fracture parameters in the Hosford-Coulomb fracture model [3] are determined for numerical crash simulation. To investigate the validity of the calibrated ductile fracture model, axial crushing tests of hat-shaped square columns are performed for the 980 MPa grade. Numerical simulations of axial impact are also performed by ANSYS LS-DYNA [4] under the same conditions as in the experimental tests, and three-point bending tests are carried out for the 1180 MPa grade to simulate side crash deformation. Both the numerical simulations of the axial crash and the three-point bending crash show good agreement with the experimental results. The developed material model can express the excellent local elongation performance of the jetQ materials. The crash simulation with the material model shows good crash performance with a low risk of fracture during crash deformation.
Sato, Kentaro, Sakaidani, Tomohiro, Ohnishi, Yoichiro, Paton, Adrian, Roesen, Hartwig
Elevated Fracture Resistance of Q&P1180 Steel after Forming and Paint-Baking2025-01-82214/1/2025
According to several precedent studies, most of the cold-forming advanced high-strength steel (AHSS) grades can obtain reinforced yield strength from the automotive forming and paint-baking treatments without losing their fracture resistance like some aluminum alloys. Concisely, the mechanism of such behavior can be mainly attributed to the ‘Cottrell Atmospheres,’ some thermally mobilized interstitial atoms that cluster around and impede mobile dislocations during only the yielding stage of the plastic deformation but cannot continue durably enough to affect the fracture. Nevertheless, an exception, Q&P1180, was discovered from precedent studies and characterized in this work. Different from other AHSSs, this grade exhibited distinctively elevated fracture resistance and yield strength after the pre-straining and baking. Such uniqueness was speculated to be caused by 1) no soft ferrite in the microstructure and 2) the transformed fresh martensite induced by the plastic deformation being tempered-softened by the paint-baking cycle. Such two microscopic features narrowed the micro-hardness differences among the neighboring multi-phases in the deformed and baked Q&P1180 microstructures, which consequently retarded the micro-voids creation and coalescence to the macroscopic fracture. To support this speculation, a series of mechanical experiments were conducted, including various treatment conditions, stress-state, and strain-rate dependencies, on the pre-strained and baked Q&P1180 samples. As a comparison, other multi-phase AHSS grades, such as Q&P980 and DP980LCE, were also tested to indicate their lack of such behavior. Eventually, the test results characterized the consistently elevated fracture resistance of Q&P1180 under all the investigated conditions and accordingly highlighted this target material’s advantageous crashworthiness in the automotive applications.
Hu, Jun, Sun, Yeting, Thomas, Grant
Understanding Forming Characteristics of Different Microstructure Steels within 980MPa and 1180MPa2025-01-82224/1/2025
For electrical vehicle (EV) automotive body-in-white (BIW) structures, protection of passengers and battery in crash event becomes equally important. In addition to energy absorption, intrusion protection for battery and vehicle becomes extremely important and GPa advanced high strength steels (AHSS) including press hardened steels (PHS), DP/MP/CP/GEN3 steels have become material of choice for design for those components. Higher yield strength materials especially in 980/1180MPa MP and CP category are chosen for part design over conventional low yield strength DP. In this study, the forming characteristics including both global and local formability are evaluated and compared among 980 DP/MP grades. Formability test such as forming limit curve (FLC), true fracture strain, V bend, half dome, and hole expansion tests are conducted. Microstructure analysis to understand the effect of different grain structure and phases of DP/MP grades is also accomplished. A T-shape laboratory die trials are carried out to compare and understand the global formability of these steels. Experimental results indicate MP grades tend to have better local and equivalent global formability than DP steels. Some best practices are recommended when AHSS (MP) is used to form 980DP type parts in terms of both global and local formability performances.
Shih, Hua-Chu, Pednekar, Vasant, Shi, Ming, Singh, Jatinder, Tedesco, Sarah, Wu, Wei
TOC99-07-01-0TOC2/17/2025
TOC
Tobolski, Sue
Laser Welding Applied to Complex Phase Steel2024-36-015912/20/2024
The development of advanced high-strength steels has become essential in the production of lightweight, safe, and more economical vehicles within the context of the automotive industry. Among the advanced high-strength steels, complex phase steels stand out, characterized by their high formability and high energy absorption and deformation capacity. Laser welding is a technique that applies laser using high energy density as a heat source. It has the advantages that the high welding speed and low heat input compared to other welding methods cause a decrease in deformation, and the narrow width of the weld bead and heat-affected zone allows for the welding of complex parts that would be difficult for other welding methods. Based on a study of a complex phase steel, an analysis was made of the microstructures observed by optical microscopy, the grain boundaries and certain phases contained in this microstructure, as well as the microstructures of each area in the laser welding region observed by scanning electron microscopy. Presenting as results the microstructures of the welded region, such as martensite and bainite phases are the dark phases and retained austenite and ferrite phases are the light phases.
Dias, Erica Ximenes, Reis de Faria Neto, Antonio, Castro, Thais Santos, Martins, Marcelo Sampaio, Santos Pereira, Marcelo
Performance Optimization of Ti-Steel Laser-Welded Joints Based on Optimized Support Vector Machine and Multi-Objective Salp Swarm Algorithm05-18-02-001011/7/2024
The dissimilar welding of titanium to steel enables the integration of the advantageous properties of both metals, facilitating the design of lightweight, corrosion-resistant, and high-strength multifunctional composite structures. However, significant differences in their thermophysical properties pose substantial technical challenges in practical welding scenarios, necessitating careful selection of process parameters to enhance the quality and performance of the weld joint. This article establishes a support vector machine (SVM) model with laser power, welding speed, and laser spot diameter as independent variables, and the maximum residual stress and minimum yield strength of the weld joint as dependent variables. To improve prediction accuracy, the SVM model is optimized using the beluga whale optimization (BWO) algorithm. Taking the established model as the objective function, the multi-objective salp swarm algorithm (MSSA) is employed to optimize the laser welding process parameters for titanium–steel dissimilar metal welding. Simulation experiments validate the efficacy of this optimization approach.
Zhu, Yubin, Meng, Xiangli, Zhang, Xinran
Comparison of Bake Hardening Effects on AHSSs and Extruded Aluminum Alloys Applied in BEV Reinforcement Structures2024-01-22404/9/2024
At the dawn of battery electric vehicles (BEVs), protection of automotive battery systems as well as passengers, especially from severe side impact, has become one of the latest and most challenging topics in the BEV crashworthiness designs. Accordingly, two material-selection concepts are being justified by the automotive industry: either heavy-gauge extruded aluminum alloys or light-gauge advanced high-strength steels (AHSSs) shall be the optimal materials to fabricate the reinforcement structures to satisfy both the safety and lightweight requirements. In the meantime, such a justification also motivated an ongoing C-STARTM (Cliffs Steel Tube as Reinforcement) Protection project, in which a series of modularized steel tube assemblies, were demonstrated to be more cost-efficient, sustainable, design-flexible, and manufacturable than the equivalent extruded aluminum alloy beams as BEV reinforcement structures. Tangent to this comparative study, the present work shed some light on the bake hardening (BH) effects during a paint-baking cycle, which was a necessary processing procedure for a body-in-white (BIW), on some representative AHSSs and extruded aluminum alloys via various coupon-level mechanical experiments under precise in-situ strain/displacement and temperature control conditions at multiple strain rates and stress states. The corresponding material mechanisms were also reviewed and explained. Eventually, the test results revealed some tremendously distinct changes induced by the BH effects on the two types of metallic materials: the baking-induced Cottrell atmosphere could effectively enhance the strength without weakening the local ductility of the target AHSS, while the baking-induced precipitation slightly hardened the selected aluminum alloy yet lowered its fracture limit. Such a distinction further indicated the advantages of the AHSSs in this application. The ultimate objective of this work was to provide relative references for future finite element simulations and BEV structural designs.
Hu, Jun, Sun, Yeting, Yu, Miao, Wang, Yu-Wei, Thomas, Grant
Effect of Local Ductility on Crash Performance of Automotive Structures Considering Press Forming Strain of Advanced High Strength Steels2024-01-22414/9/2024
A fundamental study on the ductility of high strength steels in crash deformation is carried out to investigate the effect of the local ductility of various materials on automobile crashworthiness, considering the prestrain induced by press forming in the manufacturing process. In this study, a newly developed 980 MPa-grade steels [1], ‘jetQTM’, is investigated to clarify its advantage in term of crashworthiness in comparison with the conventional DP (Dual Phase) and TRIP steels. Quasi-static axial crushing tests are performed to evaluate the crashworthiness of the different types of steel. Based on the experimental results, the effect of the local ductility of high-strength steel on the risk of material fracture is discussed. In this paper, a new bending test method, orthogonally reverse bending, (ORB), is proposed to simulate the fracture that occurs during crash deformation considering press-forming strain. The test method is developed using a combination of the V-bending process and the tight radius bending method (based on VDA 238-100). The V-bending process is used to induce the pre-strain in the test sample, simulating the strain caused by press-forming, and the second bending process is performed to evaluate the fracture angle and local ductility of the high strength steel after the press-forming process. The proposed ORB method shows that the local ductility of TRIP steel is decreased by the press-forming due to transformation of the microstructure, while jetQ steel displays higher local ductility even after press-forming. A numerical simulation model is also developed to understand the fracture behavior in the ORB process. The simulation shows that fracture strain occurs in the local bending area with prestrain by the V-bending process. Finally, the applicability of the developed high strength steel to automobile body structures to realized light-weight body structures is discussed.
Sato, Kentaro, Sakaidani, Tomohiro, Komine, Shinsuke, Wang, Fangyi, Nakagaito, Tatsuya
Experimental Study on Bendability of Advanced High Strength Steels2024-01-28604/9/2024
Fracturing in a tight radius during bending is one of the major manufacturing issues in forming Advanced High Strength Steels (AHSS). The study investigated the bendability of AHSS under two forming conditions: bending with and without stretched over the die radius. The bendability was evaluated by conducting modified Bending Under Tension (BUT) test for stretch bending and 90o v bend test for bending without stretch. The study also examined the effect of material properties on the limiting bend ratio. Various strength high strength steels, range from 420 MPa to 1700 MPa tensile strength, were selected in the study. Results indicated that critical radius-to-thickness ratios between the two tests are different but correlated in a relationship which was depicted in the bendability diagram. The map and constitutive relation curve derived from limiting bend ratios identified the multiple bendability (stretched and no-stretch) of each strength grade of test steel, which is recommended as the guideline for design-evaluate the bendability performance of the AHSS. The determined limiting bending strains could serve as the die radius thinning criterion, while further field validations are needed to verify the robustness.
Shih, Hua-Chu
Springback Control through Post-stretching Using Different Hybrid Bead Designs with Tonnage Consideration2024-01-28594/9/2024
Multiple hybrid bead designs were investigated in this study to control the springback on DP780 samples using post-stretching technique. The performance of the four different hybrid bead designs was evaluated by measuring the minimum blank-lock tonnage required to control the springback during a U-channel stamping process. A finite element (FE) model of the U-channel stamping process was developed to simulate the process and predict the minimum blank-lock tonnage required for springback control using each of the hybrid bead designs. It is shown that the developed FE model predicts both the required minimum blank-lock tonnage for post-stretching, and the springback profile, with good accuracy.
Nazari, Sobhan T., Zhu, Feng, Makrygiannis, John, Zhang, Jimmy, Wang, Yu-Wei
Categorization and Properties of Advanced High Strength Automotive Sheet SteelsJ2745_202402 (Current)2/23/2024
This SAE Recommended Practice defines various grades of continuously cast high-strength sheet steels and establishes mechanical property ranges. These sheet steels can be formed, welded, assembled and painted in automotive manufacturing processes. They can be specified as hot-rolled or cold-rolled sheet. Furthermore, they can be coated (hot-dipped galvanized, hot-dipped galvannealed, and electrogalvanized) or uncoated. Not all combinations of strength, dimensions and coatings may be commercially available; consult your steel supplier for details.
Metals Technical Committee
TOC99-06-01-0TOC2/12/2024
TOC
Tobolski, Sue
Effect of Spot Weld Parameter on HAZ of Advanced High Strength Steel Joint2024-26-01871/16/2024
To meet different target of light-weighting, lower fuel economy, crash safety and emission requirement, advanced high strength steel (AHSS) is commonly used in automotive vehicles and has become popular now a days. AHSS material up-to 1500 MPa is commonly used for structural components and major reinforcement of automotive BIW. Manufacturing of AHSS material requires precise control of chemical composition, and subsequent rolling and heat treatment to get optimum combination of required phases In most of the AHSS material microstructure, martensite is present along with ferrite or other phases. Hot stamp steel with strength level 1500 MPa strength also have martensite phase in microstructure after press hardening. However during heating and cooling cycle in resistance spot welding, martensite phase tempering affects hardness at Heat Affected Zone (HAZ). Softness at HAZ lower downs shear and tensile strength of joint which impacts fatigue properties of the joint and energy absorption during vehicle crash. Base material and spot weld joint’s fatigue strength and energy absorption at high strain rate are two important properties and performance criteria. These are generally considered while designing automotive parts and their joining. This paper discusses HAZ softening while spot welding of AHSS, impact of weld parameters (welding current, weld time, electrode force) on microstructure, micro-hardness and derivation of optimum spot weld parameter for spot welding with AHSS material.
Jain, Vikas, Misal, Swapnali, Paliwal, Lokesh
TOC99-05-06-0TOC12/18/2023
TOC
Tobolski, Sue
Influence of High-Strength, Low-Alloy Steel on Fatigue Life at a Non-Load-Bearing Transverse Welded Attachment05-17-01-000211/17/2023
This study investigated the influence of high-strength low-alloy steel on the fatigue life of a load-bearing member with a non-load-bearing transverse welded attachment (T-joint). It compared high cycle fatigue data to two fatigue design codes, namely BS 7608 and Eurocode EN 1993-1-9. Different base and filler material combinations of varying material strengths were investigated, resulting in a total of three different specimen configurations. Two material combinations had a high-strength steel (Strenx® 700 MC D) for the base material, with one combination having a matched filler material and the other having an undermatched filler material. The third material combination had a lower-strength steel (S 355 JR AR) for the base material, with a matched filler material. Tensile tests were performed to confirm the base material mechanical properties and weld quality of the manufactured specimens. The investigation showed that there was no significant benefit to using high-strength steel as the base material for a fatigue loaded T-joint with a non-load-bearing welded attachments.
Ramsay, Gareth Allan, Venter, Gerhard, Bredell, Johann
Constructing bus structures with stainless steel23TOFHP08_038/1/2023
Outokumpu and collaborators show a possible weight reduction of up to 35% by using high-strength stainless steel in place of carbon steel. The weight of a typical bus could be reduced by up to 35% - more than 1,000 kg (2,205 lbs.) - by using high-strength stainless steel to replace tubular bus-frame elements traditionally manufactured in carbon steel. That is the conclusion of a first-of-its-kind project carried out by stainless-steel manufacturer Outokumpu, together with CAD/CAE solution specialist FCMS, the Munich University of Applied Sciences and RotherCONSULT. Corrosion-resistant stainless steel could offer sustainability combined with reduced maintenance time and costs. In addition, high-strength stainless steel grades have become commercially available that offer significant weight savings. The aim of this project was to examine what that could mean in terms of lower weight and reduced material costs.
Schuberth, Stefan, Rother, Klemens, Pohl, Werner
Computational Material Modelling for Damage Prediction of Advanced High Strength Steel2023-28-13095/25/2023
FEA based simulations are extensively used in automotive industry for improving the product design and reducing the time taken for design and prototyping. FEA based simulations require material data as an input in form of material models. Most commonly used material models for simulation of metallic materials are elastic models and elasto-plastic models, which provide very good correlation till ultimate tensile strength (UTS). For simulation beyond UTS value, elasto-plastic material model has to be used along with material model considering the damage accumulation post UTS. For crash like event in automotive crash, required material models should consider the effect of various stress state conditions (Triaxiality) and strain rate sensitivity of materials along with damage accumulation. In LS Dyna solver, MAT_ADD_EROSION material model (GISSMO) along with MAT_024 is widely used for these applications. This paper will focus on development of GISSMO material model card for advanced high strength steel. Various stress state conditions will be considered along with strain rate sensitive properties. Paper will also cover the MAT_024 material model card which is used in association with MAT_ADD_EROSION for elasto-plastic region. Simulated data of coupons and component will be validated with experimental results.
Mulla, Suhail Mahanmad Hanif, Nemade, Sanket, Vhanaje, Manoj G, Nigade, Sachin Rajendra, Mahajan, Rahul, Santosh Jambhale, Medha
Lightweight Swivel Seat Frame Concepts Using Advanced Steel Grades2023-01-50214/21/2023
The seat frame to be applied to future autonomous vehicles is expected to be rotatable considering various seating configurations. For the rotatable or swivel seat frame, it might be more difficult to secure passenger-related safety performances including seat belt anchorage (SBA) strength than a conventional seat frame because the conventional seat frame has two seat belt anchoring points on the body center pillar whereas those points of the swivel seat frame should be all located within the rotating structures in the seat frame. Since the swivel seat frame adds a structure for rotation, the mass of the swivel seat frame significantly increases compared to the nonrotatable seat frame, which may become an obstacle to reducing the mass of the vehicle. Currently, there are not many cases of mass production of rotating vehicle seats, and there are hardly any reports of mass reduction through advanced steel materials or corresponding numerical safety performance. In this study, the mass of the swivel assembly, the core part of the swivel seat frame, was reduced by more than 22.8% by establishing a baseline model of the swivel seat frame through benchmarking, applying advanced steel materials to it, and improving the structural design. In addition, a swivel assembly concept with an improved structure for better safety performance was derived, and the steel grade and gauge of the relevant core parts were optimized using a commercial program LS-OPT and various libraries of Python, an open-source programming language. The lightweight concepts and various solutions derived from this study are expected to be a good starting point for applying advanced steel grades to future seat frames.
Kim, Jaehyun
Characterization and Modeling of Anisotropic Fracture of Advanced High-Strength Steel Sheets2023-01-06134/11/2023
As an engineering approach of balanced complexity and accuracy, the Generalized Incremental Stress-State dependent damage Model (GISSMO) in LS-DYNA® has now been widely adopted by the automotive industry to predict metallic materials’ fracture occurrences in both forming and crashworthiness simulations. Calibration of the nominal GISSMO is typically based on material characterization data along a certain representative material orientation. Nevertheless, many rolled or extruded metallic materials, such as advanced high-strength steel (AHSS) sheets, exhibit accentuated anisotropic fracture behavior, even though, notably, some of these materials show comparatively weak anisotropic plasticity in the meantime. Accordingly, in this work, the deformation and fracture behavior of a selected AHSS grade, Q&P980 steel, was first characterized based on a series of mechanical experiments under simple shear, uniaxial tension, plane strain, and equi-biaxial tension conditions. Then, material models were calibrated based on the plasticity and fracture data. Two fracture models, either stress- or strain-based, were applied to fit the fracture loci of the target material, which then could be directly implemented into the material cards in LS-DYNA®. Particularly, to simulate the anisotropic fracture behavior of the target material, an extended GISSMO material card (eGISSMO) was introduced and highlighted in this work. Unlike the nominal GISSMO, the eGISSMO integrated the different anisotropic fracture loci and damage accumulation along three material orientations (longitudinal, diagonal, and transverse) into a single material card. In the subsequent validation based on a customized three-point-bending (3PB) testing setup on hat-section samples, only the finite element (FE) model using the calibrated eGISSMO successfully simulated the anisotropic fracture bifurcation observed in the actual experiments.
Hu, Jun, Pan, Hao, Pavlina, Erik, Thomas, Grant
Effect of Local Ductility of Advanced High Strength Steels in 980MPa and 1180MPa Grades on Crash Performance of Automotive Structures2023-01-00814/11/2023
A fundamental study on the ductility of high strength steels under impact deformation is carried out to investigate the effect of the local ductility of various materials on crash performance. In this study, newly developed 980 and 1180 MPa grade steels are investigated to clarify their advantages in term of crash performance compared to conventional DP (Dual Phase) steels. The features of the developed steel, named as jetQ are higher yield strength and higher local ductility due to an optimized microstructure by the quenching and partitioning process (QP) [1, 2]. The bending test according to VDA 238-100 is performed while observing the fracture propagation during the bending test. Fracture strain in the tensile tests is evaluated by a three-dimensional shape measurement technique for the fracture surface. Both three-point bending tests and axial impact tests are performed to evaluate the crashworthiness of different types of steel. The three-point bending test simulates the “structural bending and intrusive deformation” that occur in the automotive side impact test. In the axial impact test, the “folding deformation” and energy absorption during the automotive front crash test are simulated in a laboratory testing machine. In this study, the fracture behavior and energy absorption performance of the high strength steels are investigated under both deformation modes. Based on the experimental results, the effect of the local ductility of the high strength steel on the risk of material fracture is discussed. The experimental results show that high strength steels with higher ductility of thickness strain can improve crash deformation with lower risk of crash fracture. The jetQ steels of grades over 980 MPa have excellent local ductility compared to conventional DP sheets. The jetQ steel also shows higher crash performance due to its higher yield strength. Considering these advantages, the applicability of the jetQ steel to automobile body structures is discussed from the viewpoint of light weight body structures.
Sato, Kentaro, Sakaidani, Tomohiro, Toji, Yuki, Takajo, Shigehiro, Paton, Adrian, Manuela, Irnich, Thiessen, Richard
The Jetq-Family - New Highly Ductile AHSS Steel Grades with Improved Technological Properties2023-01-00804/11/2023
New highly ductile AHSS steel grades with tensile strength greater than 980 MPa have been developed with the aim of combining high strength and excellent formability. The new jetQ-Family offers high local and global ductility while still fulfilling standards for resistance towards hydrogen embrittlement and weldability. These improved properties are based on their specifically engineered microstructure, which utilize the TRIP-mechanism in a strengthened matrix. This work shows how the microstructure plays a significant role for the tensile testing as well as hole-expansion. Based on the increased yield strength a better crash performance compared to conventional DP steel grades can be attained. The local ductility is demonstrated with excellent hole expansion ratios and high resistance to sheared edge failure. In combination with improved bending angles and thickness strain at fracture a robust process for manufacturing of components can be achieved. The results are completed by the characterization of resistance spot welding and the resistance towards hydrogen embrittlement. The jetQ-Family with its optimized property profile will contribute to greater safety and efficiency in vehicle bodies.
Irnich, Manuela, Thiessen, Richard, Paton, Adrian, Sato, Kentaro, Toji, Yuki, Minami, Hidekazu
A Method for Measuring In-Plane Forming Limit Curves Using 2D Digital Image Correlation05-16-03-00194/10/2023
With the introduction of advanced lightweight materials with complex microstructures and behaviors, more focus is put on the accurate determination of their forming limits, and that can only be possible through experiments as the conventional theoretical models for the forming limit curve (FLC) prediction fail to perform. Despite that, CAE engineers, designers, and toolmakers still rely heavily on theoretical models due to the steep costs associated with formability testing, including mechanical setup, a large number of tests, and the cost of a stereo digital image correlation (DIC) system. The international standard ISO 12004-2:2021 recommends using a stereo DIC system for formability testing since two-dimensional (2D) DIC systems are considered incapable of producing reliable strains due to errors associated with out-of-plane motion and deformation. This work challenges that notion and proposes a simple strain compensation method for the determination of FLCs using a low-cost single-camera (2D) DIC system. In this study, formability tests are performed on an automotive-grade 6xxx series aluminum alloy using the Marciniak in-plane FLC testing method. The tests are performed on a custom setup that enables simultaneous optical strain measurements using a stereo DIC as well as a 2D DIC system. The results show how 2D DIC FLC points match those obtained by stereo DIC using two popular FLC approaches: ISO 12004-2 section-based spatial method and a time-dependent linear best fit (LBF) method.
Agha, Akshat, Abu-Farha, Fadi
Hydrogen Embrittlement Testing of Ultra High Strength Steels and Stampings by Acid ImmersionJ3215_202303 (Current)3/8/2023
This standard describes a test method for evaluating the susceptibility of uncoated cold rolled and hot rolled Ultra High Strength Steels (UHSS) to hydrogen embrittlement. The thickness range of materials that can be evaluated is limited by the ability to bend and strain the material to the specified stress level in this specification. Hydrogen embrittlement can occur with any steel with a tensile strength greater than or equal to 980 MPa. Some steel microstructures, especially those with retained austenite, may be susceptible at lower tensile strengths under certain conditions. The presence of available hydrogen, combined with high stress levels in a part manufactured from high strength steel, are necessary precursors for hydrogen embrittlement. Due to the specific conditions that need to be present for hydrogen embrittlement to occur, cracking in this test does not indicate that parts made from that material would crack in an automotive environment. Results from this test should be considered in conjunction with the strain state of the material and the operating environment of the part when selecting any UHSS. Since this test method is comparative, the most information can be gained if a control sample of known performance is evaluated along with the material being studied.
Metals Technical Committee
BIW Lightweight Potential Applying Uncoated UHS Hot Forming Steel with Increased Tensile Strength2022-36-00192/10/2023
Weight reduction and safety are key factors on the automotive market. Lightweight materials have been widely discussed as an alternative to reduce CO2 emissions levels and fuel efficiency. Press-hardened steels (PHS), such as 22MnB5 steel, are known to combine high ultimate strength resistance and low thickness. To improve this correlation, new generations of ultra-high strength (UHS) hot forming steel grades are under development. Once the mechanical properties improve after the hot forming process it is possible to decrease the thickness keeping the same performance. An example is the 37MnB5 steel which has some adjustments in terms of chemical composition, increasing its hardenability and providing a more refined quenched martensite. A simulation study of weight reduction for a body in white (BIW) application will be presented considering a 37MnB5 steel grade. Additionally, some preliminar results of this steel are discussed. The heat treatment, performed in laboratorial scale, results in as expected phase transformation, being the microstructure composed by a martensitic matrix. The studied grade shows high potential as lightweight solution once it offers ultimate strength values up to 1900 MPa, allowing studies of thickness optimization, keeping the ductility of the first-generation of PHS steels. Depending on the application the weight reduction could reach approximately 10 to 15 percent, compared to parts produced using 22MnB5.
Santana, Dr. Jessica, Gomes Pallu, Lucas, Curti, Gustavo, Hirota, Frederico
A Method for Measuring In-Plane Forming Limit Curves (FLC) using 2D Digital Image CorrelationSAE-PP-003222/5/2023
With the introduction of advanced lightweight materials with complex microstructures and behaviors, more focus is put on the accurate determination of their forming limits, and that can only be possible through experiments, as the conventional theoretical models for forming limiting curve (FLC) prediction fail to perform. Despite that, CAE engineers, designers, and tool makers still rely heavily on theoretical models due to the steep costs associated with formability testing, including mechanical setup, a large number of tests, and the cost of a stereo digital image correlation (DIC) system. The International Standard ISO 12004-2:2021 recommends using a stereo DIC system for formability testing since 2D DIC systems are considered incapable of producing reliable strains due to errors associated with out-of-plane motion and deformation. This work challenges that notion and proposes a simple strain compensation method for the determination of FLCs using a low-cost single camera (2D) DIC system. In this study, formability tests are performed on an automotive-grade 6xxx series aluminum alloy using the Marciniak in-plane FLC testing method. The tests are performed on a custom setup that enables simultaneous optical strain measurements using a stereo DIC as well as a 2D DIC system. The results show how 2D DIC FLC points match those obtained by stereo DIC using two popular FLC approaches: ISO 12004-2 section-based spatial method and a time-dependent Linear Best Fit (LBF) method.
Agha, Akshat, Abu-Farha, FADI
Effectiveness of 2D Digital Image Correlation in Capturing the Fracture Behavior of Sheet Metal Alloys05-16-02-000912/14/2022
It is a consensus in academia and the industry that 2D digital image correlation (2D-DIC) is inferior to a stereo DIC for high-accuracy material testing applications. It has been theoretically established by previous researchers that the 2D-DIC measurements are prone to errors due to the inability of the technique to capture the out-of-plane motion/rotation and the calibration errors due to lens distortion. Despite these flaws, 2D-DIC is still widely used in several applications involving high accuracy and precision, for example studying the fracture behavior of sheet metal alloys. It is, therefore, necessary to understand and quantify the measurement errors induced in the 2D-DIC measurements. In this light, the presented work attempts to evaluate the effectiveness of 2D-DIC in mechanical testing required for the generation of fracture strain vs. triaxiality curve for sheet metal. This work presents a direct comparison of fracture strains obtained by 2D-DIC and stereo DIC for four loading conditions (uniaxial tension, plane strain, shear, and balanced biaxial tension) on two materials with very diverse mechanical and fracture properties—CR4 and DP800 steel. The comparisons are done for full-field strain contours, fracture strains, and strain paths/triaxialities generated using the two DIC systems. A simple technique is proposed to compensate for the effects of out-of-plane motion in the 2D measurements. It is shown that 2D-DIC can capture the material deformation with sufficient accuracy not only for planar specimens but also for certain scenarios involving out-of-plane motion (such as balanced biaxial tension) by theoretical compensation of the strains.
Agha, Akshat
Hole Expansion Characteristics of Advanced High Strength Steel (AHSS) Grades and Their Effects on Manufacturability in Automotive Industry2022-28-035010/5/2022
Currently, automotive industries are using Advanced High-Strength Steels (AHSS) sheet grades to achieve key requirements like light weighting and improved crash performance. But forming of AHSS grades becomes key challenge due to its lesser ductility and edge fracturing tendency during forming. In general, most of the automotive components undergoes shearing operations like blanking and punching which affects the edge ductility of the steel. AHSS grades possess limited edge ductility compared with conventional steel grades which results in edge fracturing due to tensile strain during stretch flanging operation. Stretch flange-ability is an important formability characteristic, which aids in material selection to avoid edge fracturing of complex shaped parts. Material with better stretch flange-ability possess better edge ductility and hence perform better in stretch flanging of sheet metal. Various test methods have been developed to predict stretch flange-ability behavior of the steel grades. Among that, Hole Expansion test is a one of the effective method to predict the stretch flange-ability of sheet metal. The present work investigates the effect of microstructure and tensile properties on hole expansion characteristics of different AHSS with different process conditions. Steel grades with varying chemical composition, varying tensile strength and varying microstructure are evaluated: Dual phase steel grades (DP590, DP780, DP980), Transformation Induced Plasticity Steel (TRIP 780), Micro-alloyed High Strength Low alloy grades (E34, E46, SPFH590, S700MC). Hole Expansion Ratio (HER) measurement is done as per the ISO16630 standard. Results shows that the HER% decreases linearly with increase in tensile strength below 700MPa. Steel with tensile strength greater than 700-1000 MPa, results in HER of 20-30%. Also, the importance of HER in the AHSS grades selection for the manufacturability of complex parts is demonstrated.
Udhayakumar, Thendralarasu, Paliwal, Lokesh, Misal, Swapnali, Ponkshe, Shripadraj
TOC99-04-04-0TOC9/7/2022
TOC
Tobolski, Sue
Categorization and Properties of Steel Sheet for Automotive Cold Forming ApplicationsJ2947_202204 (Current)4/1/2022
This SAE Recommended Practice establishes and defines requirements for grades of continuously cast automotive steel sheet that can be formed, welded, assembled, and painted in automotive manufacturing processes. These sheet steels can be specified as hot-rolled, cold-rolled, uncoated, or coated. Steel sheet can be coated by hot dipping, electroplating, or vapor deposition of zinc, aluminum, or organic compounds. Not all combinations of material types, strength levels, and coating types may be commercially available. Consult your steel supplier for availability.
Metals Technical Committee
True Fracture Strain Measurement and Derivation for Advanced High-Strength Steel Sheets2022-01-02373/29/2022
The importance of true fracture strain was initially highlighted in the context of local versus global formability considerations used in material selection among advanced high strength steels (AHSSs) of similar tensile strength. Inspired by the relative studies, a precedent work compared the fracture strain results via either digital image correlation (DIC) based method or optical fracture surface measurement on different AHSS samples. It concluded that the DIC-based testing results generally underestimated the fracture strain. As a continued study, the present work further analyzed the DIC-based testing procedure and attributed such an underestimation mainly to the volume constancy assumption. Furthermore, this work pointed out that also because of the same assumption, the optical fracture surface measurement to some extent overestimated the fracture strain. Nevertheless, it was also observed that different AHSS grades were affected discrepantly by the two methods. Therefore, scanning electron microscope (SEM) was applied to inspect the morphology of various micro-voids and dimples on different fracture surfaces to explain the discrepancy. To bypass the volume constancy assumption, this work also proposed two alternative methods, including a DIC-based thinning measurement method and a hybrid method, and discussed their limitations. In addition, the effects of DIC measurement frame rate and anisotropic plasticity based on the Hill-1948 yield function were also studied in this work. Last but not the least, by substituting the different fracture strain results based on all the introduced methods into an early stage of calibration of the Generalized Incremental Stress State dependent damage Model (GISSMO) for forming and crash simulations, the importance of the fracture strain accuracy was further highlighted.
Hu, Jun, Thomas, Grant, Campbell, Cynthia
A Novel Tensile Testing Method to Characterize the Weld Metal Properties for Laser Welded Blank (LWB) with AHSS2022-01-02433/29/2022
The automotive industry applies Laser Welded Blanks (LWB) to increase the material utilization and light-weighting of the vehicle structure. This paper introduces a novel tensile testing method to characterize the hardening behavior of the weld material with a digital image correlation (DIC) and apply it as a constitutive hardening model in forming simulations with the LWBs of GEN3 steel. Formability tests under biaxial conditions were performed with LWB of GEN3 steel. Experimental results were correlated with finite element analysis (FEA) predictions that were conducted with and without the weld material model. The results show the weld material model for the LWB improves the accuracy of FEA predictions of both necking failures on the base metal as well as cracking on the weld.
Kim, Minki, Gu, Jiahui, Kim, Hyunok
Efficient Processing of Material Property Definition to Predict Fracture of AHSS in Crash Analysis2022-01-02363/29/2022
Advanced High Strength Steel (AHSS) with high strength and deformation resistance is applied to automotive components and plays an important role in protecting passengers in the event of a crash, as well as contributing to fuel economy improvement by reducing the weight of the car body. However, due to the low ductility of the AHSS, there is an issue about the occurrence of fracture during a vehicle crash. In order to cope with these problems from the early design stage, preliminary verification is made through crash CAE analysis, but a high level of material property definition is required for fracture prediction. To predict fracture, many tests are required to secure the base data for parameter calculation of a complex fracture model, and a lot of physical time is required to verify the model. This paper aimed to semi-automate the material parameter calculation and verification process for efficient and reliable fracture prediction of AHSS. To this end, a user interface program was developed and its effectiveness was verified. The GISSMO fracture model in LS − DYNA® was used for fracture prediction, and 1.0GPa grade cold-rolled steel was examined. The existing method of calculating GISSMO parameters may have many error factors because it relies on the engineer's engineering judgement or the trial and error method. To reduce these error factors, LS − OPT® and LS − DYNA®, which are optimization tools, were linked to calculate and optimize parameters. Uniaxial tension, simple shear, notched tension and biaxial tension tests were conducted to evaluate the fracture characteristics of various load paths during crash events, and a drop weight impact test was performed for component-level verification. Finally, the validity of the method proposed in this study was reviewed by comparing the test and CAE analysis results.
Lee, Kang Hee, Jun, ChulWoong, Choi, Sunyong, Lee, Kyoungteak, Lee, Dong Yul, Kim, Dae Young
Development of New Vehicle Safety Structures by Using Third-Generation Steels05-15-02-00111/6/2022
Research and development efforts in the automotive industry have been long focused on crashworthy, durable vehicles with the lowest mass possible as higher mass requires more energy and, thus, causes more CO2 emissions. One way of approaching these objectives is to reduce the total vehicle weight by using higher strength-to-weight ratio materials, such as Advanced High-Strength Steels (AHSS). Typically, as the steel gets stronger, its formability is reduced. The steel industry has been long developing (so-called) third-generation (Gen3) AHSS for the automotive industry. These grades offer higher formability compared to first-generation (Gen1) and cost less compared to the second-generation (Gen2) AHSS. Transformation Induced Plasticity (TRIP)-aided Bainitic Ferrite (TBF) and Quenching and Partitioning (Q&P) steel families are considered to be the Gen3 AHSS. These grades can be cold-formed to more complex shapes, compared with the Gen1 Dual Phase (DP) and TRIP steels at equivalent strength levels. In this article, new single-piece A- and B-pillar reinforcements were designed using a Gen3 AHSS, TBF980. Spot-welding operations were eliminated due to part consolidation with the more formable steel. These parts will be the first structural automotive parts which were manufactured with cold-forming technology using TBF steels with a sstrength level close to 1 GPa or even more. Weight and cost reductions were realized by the new design while improving the crash performance.
Erzincanlioğlu, Samet, Aydiner, Tamer, Aras, Firat, Çelik, Hafize, Billur, Eren, Karabulut, Semih, Gümüs, Iskender Onder
Optimization of Body-in-White Weld Parameters for DP590 and EDD Material Combination2021-28-021510/1/2021
Body in White (BIW) of an automobile serves as the shell, on which all the components that make up a vehicle, are mounted. The BIW is an assembly of press formed sheet metal components. The sheet metal composition of each component varies based on the form and functionality requirement of that component. The resulting assembly has multiple weld joineries with dissimilar compositions. The weld integrity of the joineries is crucial in maintaining the geometrical and structural integrity of the BIW. The primary welding method used in BIW assembly is Resistance Spot Welding (RSW). The quality of the weld is an outcome of a combination of multiple weld parameters. These parameters are majorly estimated based on the joinery thicknesses and material combinations. Multiple welding and testing iterations are done to fine tune the parameters for an optimum weld joinery. This is a very tedious process which increases the process time of a BIW assembly. This paper studied the impact of critical weld parameters and recommended the optimum parameter combinations. Real world combinations were emulated by evaluating dissimilar material combinations. Advanced high strength steel (DP590) with Extra deep draw (EDD) joineries with varying material thicknesses were considered for the study to represent the commonly used dissimilar composition combination. The optimized parameters for multiple combinations were concluded and results were discussed. The optimized parameters enable quick selection of optimum weld program for a given joinery or weld station and eliminate material wastage and time.
Thiruppathi, R, Selvam, Ganesan, Kannan, Muniya Gounder, voppuru, Naga Sheshank Reddy, Baskaran, V
Acura TLX is HONDA'S NEW BODY-BUILD BENCHMARK21AUTP09_039/1/2021
All-new for 2021, Acura's midsize sport sedan gets an exclusive platform to go with its structural, materials and dynamic advancements. Body development leader Jeremy Lucas explains. Honda body-engineering presentations have become a much-anticipated highlight of the annual Great Designs in Steel (GDIS) conference in Michigan. Honda's “ACE” vehicle structures are considered by competitors to be benchmarks in overall integrity, occupant protection and mass efficiency. The newest iteration - that of the all-new 2021 Acura TLX - adds dynamic behavior to the other ACE attributes. The TLX's body development leader, Jeremy Lucas, deems the new sport sedan to be “the most exciting project I've been involved with in my 23 years at Honda.” In a recent interview with SAE Media, he also praised the GDIS event, as “an environment in which we in the body-engineering and materials communities can learn from each other.”
Brooke, Lindsay
Effects of Heat Input on Microstructure and Mechanical Properties of Dissimilar Laser-Welded Dual-Phase and Boron Steel Joints05-15-01-00058/31/2021
Heat-affected zone (HAZ) softening occurs during the laser welding of many Advanced High-Strength Steels (AHSS) that are used for body-in-white (BIW) of automobiles, leading to degradation in the mechanical properties of the welded joints. The microstructure and mechanical properties of dissimilar laser-welded AHSS comprising of as-received 22MnB5 with dual-phase (DP) steels (DP600, DP800, and DP 1000) were investigated in this study. Welds were made at welding speeds ranging from 1 m/min to 3 m/min. Irrespective of welding speed, the DP600-22MnB5 joints fractured in the base metal (BM) of 22MnB5 during tensile tests. Likewise, welded joints of DP800-22MnB5 and DP1000-22MnB5 made at 1 m/min and 2 m/min failed in the BM; however, at 3 m/min the failure location of these joints shifted to the fusion zone (FZ). The fractured surfaces of all the welded combinations were characterized by optical and scanning electron microscopy (SEM). Based on fracture energy, joints welded at 2 m/min were optimal due to a compromise of minimizing the weld size and formation of hard phases within the weld FZ and HAZ.
Aderibigbe, Isiaka Akanbi, Popoola, Patricia Abimbola, Sadiku, Rotimi Emmanuel, Biro, Elliot
Lightweight steel on a (COLD) ROLL21AUTP06_026/1/2021
A newly developed high-strength steel for cold stamping aims to beat aluminum for EV battery enclosures and other vehicle applications. Automotive OEMs are faced with the difficult task of significantly improving fuel economy and safety, while maintaining a competitive position in the market - as well as investing in the electrified future. This, among other benefits, can be accomplished by utilizing higher-strength steel in the production process. A newly developed and patented cold-roll high-strength steel for cold stamping, known as ColdStamp-Steel, is ideal for producing vehicle body-structure and safety components, including battery enclosures of electric vehicles (EV). The microstructure of ColdStamp-Steel consists of one or more of martensite, ferrite, and retained austenite in different percentages, depending on the steel composition and heat treatment. Also, one or more of carbides, nitrides and carbonitrides are part of the microstructure. The resulting material offers high strength at moderate ductility and ColdStamp-Steel features a higher strength-to-weight ratio than commercial cold-rolled steels. Applications include vehicle bumper reinforcement beams, pillars, door impact beams, rocker panel inners and reinforcements, side-sill reinforcements, roof frame, beltline reinforcements and clips.
Vartanov, Gregory
Constitutive, Formability, and Fracture Characterization of 3rd Gen AHSS with an Ultimate Tensile Strength of 1180 MPa2021-01-03084/6/2021
The superior formability and local ductility of the emerging class of third generation of advanced high-strength steels (3rd Gen AHSS) compared to their conventional counterparts of the same strength level offer significant advantages for automotive lightweighting and enhanced crash performance. Nevertheless, studies on the material behavior of 3rd Gen AHSS have been limited and there is some uncertainty surrounding the applicability of developed methodologies for conventional dual-phase (DP) steels to this new class of AHSS. The present paper provides a comprehensive study on the quasi-static and dynamic constitutive behavior, formability characterization and prediction, and the fracture behavior of two commercial 3rd Gen AHSS with an ultimate strength of 1180 MPa that will be contrasted with a conventional DP1180. The hardening response to large strain levels was determined experimentally using tensile and shear tests and then validated with 3-D simulations of tensile tests. In general, the strain rate sensitivity of the two 3rd Gen AHSS was significantly different as one grade exhibited larger transformation-induced behavior. The in-plane formability of the three 1180 MPa steels determined using Marciniak tests was similar but with a stark contrast in the local formability for the 3rd Gen AHSS. The forming limit curves could be accurately predicted using the experimentally measured hardening behaviour and the modified Bressan-Williams through-thickness shear model. An efficient experimental approach to fracture characterization for AHSS was developed that exploits tool contact and bending to obtain fracture strains on the surface of the specimen by suppressing necking. Miniature conical hole expansion and biaxial punch tests are used along with the VDA 238-100 bend test.
Noder, Jacqueline, Gutierrez, Jon Edward, Zhumagulov, Amir, Khameneh, Farinaz, Ezzat, Hesham, Dykeman, James, Butcher, Cliff
Strain Amount and Strain Path Effects on Instrumented Charpy Toughness of Baked Third Generation Advanced High Strength Steels2021-01-02664/6/2021
Third generation advanced high strength steels (AHSS) that rely on the transformation of austenite to martensite have gained growing interest for implementation into vehicle architectures. Previous studies have identified a dependency of the rate of austenite decomposition on the amount of strain and the associated strain path imposed on the sheet. The rate and amount of austenite transformation can impact the work hardening behavior and tensile properties. However, a deeper understanding of the impact on toughness, and thus crash performance, is not fully developed. In this study, the strain path and strain amounts were systematically controlled to understand the associated correlation to impact toughness in the end application condition (strained and baked). Impact toughness was evaluated using an instrumented Charpy machine with a single sheet v-notch sample configuration. The instrumented striker provides a load - displacement curve as well as a total impact energy measurement, which is the integration of the load - displacement curve. Using these measurements, this study intends to understand any potential correlation between amount of retained austenite transformation, through the varying of strain paths and amount of strain, and resulting impact toughness after paint bake.
Hodges, Adam D., Tedesco, Sarah, Anderson, Shane M., Golem, Lindsay, Huang, Gang
Formability Characterization of 3rd Generation Advanced High-Strength Steel and Application to Forming a B-Pillar2021-01-02674/6/2021
The objective of this study was to assess the formability of two 3rd generation advanced high strength steels (3rd Gen AHSS) with ultimate strengths of 980 and 1180 MPa and evaluate their applicability to a structural B-Pillar for a mid-sized sport utility vehicle. The constitutive behavior including strain-rate effects and formability were characterized to generate the material models for use within AutoForm R8 software to design the B-pillar tooling and forming process. An extended Bressan-Williams instability model was able to deterministically predict the forming limit curves obtained using Marciniak tests. The tooling for the representative B-pillar was designed and fabricated with Bowman Precision Tooling and forming trials conducted for both 3rd Gen steels that had a thickness of 1.4 mm. The 3rd Gen 980 B-pillar was successfully formed in accordance with the predictions of the numerical models while the 3rd Gen 1180 was predicted to have significant failure based upon the in-plane FLC. Most areas of splitting were concluded to be false-positive predictions since the 3rd Gen 1180 B-pillar only fractured in one location of approximately in-plane uniaxial tension. The predicted splitting regions were in areas of local bending and tool contact that are currently not well accounted for in the traditional approach to formability evaluation using an in-plane FLC. To fully exploit the enhanced formability of 3rd Generation steels, the dynamic nature of forming limits in light of bend severity and contact pressure effects need to be considered.
Gutierrez, Jon Edward, Noder, Jacqueline, Paker, Neil, Bowman, Jamie, Zhumagulov, Amir, Dykeman, James, Malcolm, Skye, Ezzat, Hesham, Butcher, Cliff
Letter from the Guest Editor05-13-03-001510/29/2020
Letter from the Guest Editor
Weiler, Jonathan
Letter from the Guest Editor05-14-01-000110/14/2020
Letter from the Guest Editor
Weiler, Jonathan
Materials and Technologies for Lightweighting of Structural Parts for Automotive Applications: A Review05-14-01-00079/14/2020
Reducing the weight of automotive components is one of the most achievable solutions for lowering the transport carbon footprint. This is the reason for the rapid increase over the last few years in the replacement of conventional alloys (i.e., steel and cast iron) with low-density materials (i.e., aluminum alloys, composites) and in the redesign of components shape in order to remove the unnecessary material (e.g., related to the introduction of additive manufacturing or high-strength materials). Despite this general trend, the use of higher-density metals and massive geometries is still predominant in the production of structural components, especially for heavy vehicles and safety-relevant parts. Aim of the present review is to summarize how this current situation can be overcome. The analysis started with an investigation about the materials that can be used for the production of structural parts, the potential reduction of the component weight and its costs. The scenarios analyzed foreseen by 2030 an improved weight reduction combined with additional cost. Both the parameters increased when moving from medium/small vehicles to luxury vehicles (from -18% to -35% weight and from €3 to €8-10 per kg saved, respectively) as a direct consequence of an increased usage of lighter materials. Then, the research reports some relevant actual applications, which succeeded in the weight reduction of these kind of components. The identified materials and technologies discussed were: advanced high-strength steel, carbon fiber-reinforced polymer, aluminum, additive manufacturing technologies, and alternative joining techniques.
Cecchel, Silvia
The Effect of Current Mode on the Crack and Failure in the Resistance Spot Welding of the Advanced High-Strength DP590 Steel05-14-01-00029/9/2020
The causes of failure due to cracking in the resistance spot welding of the advanced high-strength steels dual-phase 590 (DP590) were investigated using scanning electron microscopy (SEM), optical microscopy, and the tensile-shear test. The results showed that by increasing the current amount, the formation of the melting zone occurred in the heat-affected zone (HAZ), leading to the cracking in this area, reducing the tensile strength and decreasing the mechanical properties; the initiation and growth of cracking and failure in this region also happened. In the HAZ, by increasing the current amount with the softening phenomenon, the recrystallized coarse grains also occurred, eventually resulting in the loss of mechanical properties. The results of the tensile-shear test also indicated that by increasing the current up to 12 kA, the strength was raised, but the ductility was reduced. At a higher current, the decrease in mechanical properties, strength, and ductility was noticeable. The optimum current amount and pressure were 10 kA and 4.2 kN, respectively; in this case, the maximum force was 22,000 N, and the maximum displacement was 10 mm.
Ghandi, Arian, Shamanian, Morteza, Salmani, Mohamad Reza
Items per page:
1 – 50 of 313