Browse Topic: Fatigue
Qualification of new aerospace alloys requires extensive mechanical testing to capture anisotropy and ensure reliable performance under complex loading conditions. This process is costly and time-consuming, particularly with emerging manufacturing routes such as additive manufacturing. Advanced yield surface prediction offers a route to reduce test campaigns by linking microstructural features to macroscopic constitutive models. In this work, Digimat is employed as a multi-scale material modeling platform to generate yield surfaces of polycrystalline metals using computational homogenization. Representative volume elements (RVEs) are constructed from experimental texture and grain morphology data, and their response under multiaxial loading is simulated using a crystal plasticity framework. The computed yield loci are then fitted with phenomenological functions (e.g. Yld2000-2D), enabling calibration of anisotropic yield models from virtual testing. As a case study, an AA6016-T4 sheet
Traditional safe-life methodologies for rotorcraft structural components rely on deterministic safety factors to account for uncertainty in loads, material properties, and operational usage. While effective for ensuring safety, these approaches lead to early retirement lives and reduced aircraft availability. This paper presents an updated digital twin-based probabilistic framework for rotorcraft component fatigue life assessment that integrates a probabilistic stress–life (S-N) material model, machine learning-based load estimation from flight data, and Monte Carlo uncertainty propagation. The approach is demonstrated for a critical location on the CH-146 Griffon main rotor yoke. Compared with earlier work, the present study advances the framework through independent validation of the load-estimation model and application to available in-service flight data from multiple mission categories. A probabilistic sensitivity analysis is used to examine the separate and combined effects of
This presentation focuses on evaluating the fatigue life of the TAV-8B aircraft using a more realistic, data-driven structural assessment approach. Flight-by-flight data recorded from individual TAV-8B aircraft were then combined with the regression models and FEA-based load-to-stress transfer functions to generate aircraft-specific stress spectra and fatigue damage predictions using the CI89 fatigue analysis program. The results showed a 95% probability that the aircraft would exceed the projected SLAP fatigue life of 9,500 flight hours.
This paper presents a high-fidelity fatigue damage modeling framework for composite structures with ply drops, incorporating several key advancements to capture localized fatigue behavior. The approach includes: (1) computation of local stress ratios at each fatigue cycle; (2) an R-ratio-dependent fatigue damage accumulation model; (3) implementation of a constant load diagram to construct S–N curves at arbitrary R-ratios; and (4) a cycle-jumping technique to account for the evolving rate of fatigue damage accumulation due to progressive stiffness redistribution. A combined experimental and numerical study was conducted on tapered composite beams subjected to mixed axial tension and vertical bending. A custom-designed fatigue test fixture was developed to capture displacement at the loading end, which was then used as a boundary condition in the fatigue life prediction model. To guide the selection of fatigue test peak loads, static failure analyses were first performed on
Rolling-element bearings in rotorcraft dynamic systems are critical components susceptible to rolling contact fatigue (RCF), a dominant degradation mechanism manifesting through subsurface-initiated spalling, surface micropitting, and fatigue fractures. Robust inspection strategies compliant with EASA and FAA requirements are therefore essential. Traditional methods are often invasive, requiring disassembly, and are susceptible to human-factor errors. Smart Duplex introduces a design-for-monitoring architecture integrating in-situ videoscopic and coherence scanning interferometry (CSI) for high-resolution 3D surface mapping, including under partial grease coverage. This paper details a repeatability and reproducibility (R&R) framework ensuring metric consistency; a maintainability assessment projecting significant man-hour reductions and high availability; certification rationale emphasizing airworthiness improvements via enhanced detectability, workload reduction, and digitized
This work presents the development and application of a methodology for predicting fatigue life, implemented within the modern progressive failure analysis software tool CDMat, developed at the Advanced Materials and Structures Laboratory of the University of Texas at Arlington. CDMat is designed as an extension to the general-purpose finite element analysis program ABAQUS/Explicit. The set of user-defined subroutines for describing material behavior can be expanded by adding new subroutines. A recent development in CDMat is a computational model capable of predicting delamination crack growth under quasi-static and fatigue loading, based on a fracture mechanics approach using the J-integral. The J-integral is calculated by integrating stresses and displacements along a line defined by the negative gradient of displacements in the cohesive interface. Due to the large integration path, the J-integral allows for a highly accurate estimation of the energy release rate, which makes it
This work evaluates the long-term fatigue life and structural compatibility of integrated optical fiber sensors (OFS) within an H145 (or BK117 D-3) helicopter flexbeam. Utilizing fiber Bragg grating (FBG) arrays, the study compares different deployment techniques under a 100,000-cycle fatigue test: embedded, surface-integrated, and surface-applied. A validated three-dimensional (3D) finite element model (FEM) was developed to reconstruct cross-sectional loads and correlate experimental strain data. Validation against conventional electrical strain gauges (SG) confirms that embedded FBGs significantly outperform SGs in durability, maintaining functionality beyond the operational limit of traditional sensors. Furthermore, the methodology successfully tracks global stiffness evolution and degradation throughout the fatigue life. Micro-computed tomography (µCT) scans verify that the integrated fibers do not compromise structural integrity. These findings demonstrate the potential of
Due to the spot weld and mechanical fastener share the similar characteristics to join sheets together with differences in deformation behavior around joint region, a novel spot joint element (user-defined element) consists of regular Mindlin shell elements and equations for different kinematic constraints is proposed to simplify the spot joint representation in lightweight automotive structures. The novel spot joint element can not only provide accurate deformation behavior around joint region but also output mesh-insensitive structural stresses at virtual nodes with the use of traction-based structural stress method for fatigue failure analysis. In this investigation, the structural stress distributions around joint circumference in the lap-shear specimens with spot weld or fastener are first calculated to validate the accuracy of the novel spot joint element. Then, the structural stresses along different cross-sections emanating from joint are also calculated for the specimens with
In recent years, computer-aided engineering (CAE) has become an essential practice in design and durability analysis of industrial components such as weldments. The current analytical trend for CAE-based fatigue life prediction of weldments includes procedures based on design guidelines, mesh-sensitive methods (e.g., local strain-life approach) and mesh insensitive methods (e.g., Volvo and Verity methods). As an inherent characteristic of weldments, the geometry of the weld is often simplified in failure analysis and important hotspots such as start/stop of the weld beads are not considered in the design process. However, such critical locations cannot be avoided in complex welded structures. Therefore, incorporating main geometrical details of the weld can improve the accuracy of critical regions identification and damage calculation using mesh-sensitive CAE-based methodologies. Herein, a framework for life prediction of welded components including the weld geometry is discussed and
Carbon fiber-reinforced polymers (CFRPs) have become essential in modern aerospace structures, from fuselage skins and wing components to nacelles, interior structures, and a growing range of primary load-bearing parts. Their high strength-to-weight ratio delivers major benefits in fuel efficiency, payload capacity, and fatigue performance. Yet achieving reliable adhesive bonds on CFRP surfaces remains a persistent engineering challenge. The low intrinsic surface energy of composites - particularly under thermal cycling, vibration, and moisture exposure - limits bond durability unless surfaces are properly prepared. Plasma surface treatment has emerged as a pivotal solution, offering a fast, controllable, and non-destructive way to increase surface energy, improve wettability, and enhance adhesion across complex geometries. This is especially important as the aerospace industry transitions from thermoset to thermoplastic composites (TPCs), which enable faster processing, lower
The high-pressure steering hose in a hydraulic steering system carries pressurized hydraulic fluid from the power steering pump to the steering gear (or steering rack). Its main function is to transmit the force generated by the pump so that the hydraulic pressure assists the driver in turning the wheels more easily. The high-pressure hydraulic pipeline in the power steering system is a vital component for ensuring optimal performance. During warranty analysis, leakage incidents were observed at the customer end within the warranty period. The primary factors contributing to these failures include pipe material thickness, material composition, mechanical properties, and engine-induced vibrations. This study investigates fatigue-related failures through detailed material characterization and Computer-Aided Engineering (CAE) based on real world usage road load data collected. The objective is to identify the root causes by examining the influence of varying pipe thickness on fatigue life
In heavy-duty tippers, where challenging conditions demand high torque, planet carriers play a crucial role by enabling efficient load distribution and torque transmission while supporting gear ratio and speed variation in space-constrained systems such as automatic transmissions, hybrid drivetrains, and electric vehicles. This paper focuses on the comprehensive durability performance assessment of planet carrier housing (PCH) using duty cycles derived from road load data acquisition (RLDA) measurements for a heavy-duty tipper gearbox development program. The existing Design Validation Plan (DVP) for the planet carrier considers first gear utilization of 10-15% at 40% vehicle overload, in line with historical data. However, recent trends in mining applications revealed vehicle overloads of 55-65%, leading to an increase in first gear utilization (25-35%). This shift presents challenges for original equipment manufacturer (OEM) to enhance design durability while incorporating additional
This study addresses the challenge of ensuring the durability of closed couple exhaust manifolds in the compact engine bays of modern vehicles, focusing on a longitudinally mounted 1.2L 4-cylinder engine. The original sheet metal Exhaust manifold design failed the thermal fatigue bench durability test, requiring a complete redesign to improve strength without changing materials. Initial simulation predictions significantly deviated from physical test results, with repeated cracks observed during accelerated thermal fatigue bench testing, despite simulations predicting a higher number of cycles before failure. This difference highlighted the need for a deeper understanding of the manifold's failure modes, primarily thermal fatigue, and mechanical vibration during engine transients. The design of experiment (DOE) approach was used to find the effect of different parameters e.g., gas temperature, surface temperature, air flow, thermal gradient, on the durability result & also to
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