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Efficient Random Vibration Analysis Using Markov Chain Monte Carlo Simulation

SAE International Journal of Materials and Manufacturing

Univ. of Toledo-Mahdi Norouzi, Efstratios Nikolaidis
  • Journal Article
  • 2012-01-0067
Published 2012-04-16 by SAE International in United States
Reliability assessment of dynamic systems with low failure probability can be very expensive. This paper presents and demonstrates a method that uses the Metropolis-Hastings algorithm to sample from an optimal probability density function (PDF) of the random variables. This function is the true PDF truncated over the failure region. For a system subjected to time varying excitation, Shinozuka's method is employed to generate time histories of the excitation. Random values of the frequencies and the phase angles of the excitation are drawn from the optimal PDF. It is shown that running the subset simulation by the proposed approach, which uses Shinozuka's method, is more efficient than the original subset simulation. The main reasons are that the approach involves only 10 to 20 random variables, and it takes advantage of the symmetry of the expression of the displacement as a function of the inputs. The paper demonstrates the method on two examples.
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Material Microcrack Failure Effects Based on Residual Stress Evaluations

SAE International Journal of Materials and Manufacturing

Olgun Celik-Mustafa Karaagac, Murathan Soner
Olguncelik-Alper Togay, Kasim Sevimli
  • Journal Article
  • 2012-01-0187
Published 2012-04-16 by SAE International in United States
The leaf spring manufacturer must supply high quality raw material at required strength for ensuring endurance rig tests. It's very important to maintain both inside and surface cleanliness of raw material.This study presents micro crack effects on material surface by evaluating residual stress values. Residual stress values on leaf springs are measured with X-ray diffractometer and different residual stress values are classified on the same raw material batch which have also the same material failures.Finally, micro cracks are measured in metrics. Micro crack standardization is performed considering the residual stress values and rig tests. The outputs in metrics which correlated with endurance rig tests can be taken as reference by the manufacturers of leaf spring and original equipment manufacturers.
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Balancing Manufacturability and Performance Attributes in Lean Design

SAE International Journal of Materials and Manufacturing

Kettering Univ.-Mohamed El-Sayed, Jacqueline El-Sayed
  • Journal Article
  • 2012-01-0512
Published 2012-04-16 by SAE International in United States
Implementing the Voice of the customer is one of the main challenges during the Vehicle Development Process. The variety of desired vehicle attributes requires well-defined processes that include manufacturability along with the voice of the customer in all aspects of the product development process. Customer's defined attributes along with regulations and manufacturability requirements should flow through all process phases starting from the early concept development phase.This paper discusses a lean design approach to assure that the voice of the customer attributes are addressed and balanced through the product development process from concept to production. The lean approach includes architectural, performance, and manufacturability as key development attributes. A case study of Automotive Modular Door System is presented to demonstrate the application of the lean approach in the design and development of complex automotive systems. In this case study safety and manufacturability are considered as the key attributes shaping the system.
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Scuffing Behavior of 4140 Alloy Steel and Ductile Cast Iron

SAE International Journal of Materials and Manufacturing

Missouri Univ. of Science and Technology-Nancy Kelley
Oakland University-Jiman Han, Gary Barber, Qian Zou, David Schall
  • Journal Article
  • 2012-01-0189
Published 2012-04-16 by SAE International in United States
Scuffing is a failure mechanism which can occur in various engineering components, such as engine cylinder kits, gears and cam/followers. In this research, the scuffing behavior of 4140 steel and ductile iron was investigated and compared through ball-on-disk scuffing tests. A step load of 22.2 N every two minutes was applied with a light mineral oil as lubricant to determine the scuffing load. Both materials were heat treated to various hardness and tests were conducted to compare the scuffing behavior of the materials when the tempered hardness of each material was the same. Ductile iron was found to have a consistently high scuffing resistance before tempering and at tempering temperatures lower than 427°C (HRC ≻45). Above 427°C the scuffing resistance decreases. 4140 steel was found to have low scuffing resistance at low tempering temperatures, but as the tempering temperature increases, the scuffing resistance increased. Ductile iron and 4140 steel had the same scuffing resistance at a tempering temperature of about 538°C (ductile iron HRC 35-36; 4140 steel HRC 40). The scuffed specimens were studied using…
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Correlation between Scatter in Fatigue Life and Fatigue Crack Initiation Sites in Cast Aluminum Alloys

SAE International Journal of Materials and Manufacturing

Ford Motor Co-Carlos Engler-Pinto, Xuming Su
Nanjing Univ. of Aero. & Astro., China-Xin Zheng, Haitao Cui, Weidong Wen
  • Journal Article
  • 2012-01-0920
Published 2012-04-16 by SAE International in United States
High cycle fatigue tests at a constant positive mean stress have been performed on a Al-Si-Cu cast aluminum alloy. The Random Fatigue Limit (RFL) model was employed to fit the probabilistic S-N curves based on Maximum Likelihood Estimate (MLE). Fractographic studies indicated that fatigue cracks in most specimens initiate from oxide films located at or very close to specimen surface. The RFL model was proved to be able to accurately capture the scatter in fatigue life. The cumulative density function (CDF) of fatigue life determined by RFL fit is found to be approximately equal to the complementary value of the CDF of the near-surface fatigue initiator size.
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Optimal Fastener and Preload Selection

SAE International Journal of Materials and Manufacturing

Flexion Engineering Inc.-Paul Barker
MDA-Jim Olmstead
  • Journal Article
  • 2012-01-0478
Published 2012-04-16 by SAE International in United States
Selecting fastener pre-load and strength for tension fastened joints has traditionally been an iterative tradeoff between separation, strength and slip requirements. In this paper, equations are presented for the maximum external load that a fastened joint can support and the optimal pre-load to achieve this load while simultaneously satisfying safety factors for separation, strength and slip. The equations are based on linear joint theory and joint stiffness. The optimal equations account for variations in joint stiffness due to variations in joint geometry and materials. Furthermore the equations account for variations in joint preload, load-plane factor, friction coefficients and thermal loading. The external load may be axial, shear or a combination of both. The equations can be plotted to create a 3D “Fastener Design Space” that represents the maximum acceptable joint external tension and shear loads as a function of the joint preload. The design space is normalized by fastener strength to make it applicable to any fastener. Any combination of preload, tension and shear that falls within the fastener design space represents a safe joint…
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Fatigue Life Assessment of Welded Structures with the Linear Traction Stress Analysis Approach

SAE International Journal of Materials and Manufacturing

Tenneco Inc-Zhigang Wei, Fulun Yang, Limin Luo
The University of New Orleans-Pingsha Dong
  • Journal Article
  • 2012-01-0524
Published 2012-04-16 by SAE International in United States
Structural stress methods are now widely used in fatigue life assessment of welded structures and structures with stress concentrations. The structural stress concept is based on the assumption of a global stress distribution at critical locations such as weld toes or weld throats, and there are several variants of structural stress approaches available. In this paper, the linear traction stress approach, a nodal force based structural stress approach, is reviewed first. The linear traction stress approach offers a robust procedure for extracting linear traction stress components by post-processing the finite element analysis results at any given hypothetical crack location of interest. Pertinent concepts such as mesh-insensitivity, master S-N curve, fatigue crack initiation and growth mechanisms are also discussed. Then, fatigue life assessment of automotive exhaust systems is conducted and the data correlation with a recently developed equilibrium data analysis method is provided and compared. Finally, the needs for further development of more physically sound analysis approaches are indicated.
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System Topology Identification with Limited Test Data

SAE International Journal of Materials and Manufacturing

Oakland Univ.-Vijitashwa Pandey, Zissimos Mourelatos
  • Journal Article
  • 2012-01-0064
Published 2012-04-16 by SAE International in United States
In this article we present an approach to identify the system topology using simulation for reliability calculations. The system topology provides how all components in a system are functionally connected. Most reliability engineering literature assumes that either the system topology is known and therefore all failure modes can be deduced or if the system topology is not known we are only interested in identifying the dominant failure modes. The authors contend that we should try to extract as much information about the system topology from failure or success information of a system as possible. This will not only identify the dominant failure modes but will also provide an understanding of how the components are functionally connected, allowing for more complicated analyses, if needed. We use an evolutionary approach where system topologies are generated at random and then tested against failure or success data. The topologies evolve based on how consistent they are with test data. We demonstrate the proposed methodology by approximately identifying the topology of an electric motor.
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Estimation of High-Cycle Fatigue Life by using Re-analysis

SAE International Journal of Materials and Manufacturing

Univ. of Toledo-Mahdi Norouzi, Efstratios Nikolaidis
  • Journal Article
  • 2012-01-0066
Published 2012-04-16 by SAE International in United States
In design of real-life systems, such as the suspension of a car, an offshore platform or a wind turbine, there are significant uncertainties in the model of the inputs. For example, scarcity of data leads to inaccuracies in the power spectral density function of the waves and the probability distribution of the wind speed. Therefore, it is necessary to evaluate the performance and safety of a system for different probability distributions. This is computationally expensive or even impractical. This paper presents a methodology to assess efficiently the fatigue life of structures for different power spectra of the applied loads. We accomplish that by reweighting the incremental damage calculated in one simulation. We demonstrate the accuracy and efficiency of the proposed method on an example which involves a nonlinear quarter car under a random dynamic load. The fatigue life of the suspension spring under loads generated by a sampling spectrum is calculated. Then, the fatigue life for different spectra is estimated by using re-analysis. We compare the results with those from simulation to validate the method.
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Quality Inspection of Spot Welds using Digital Shearography

SAE International Journal of Materials and Manufacturing

Chrysler LLC-George Harmon
Oakland Univ.-Nan Xu, Xin Xie, Randy Gu, Lianxiang Yang
  • Journal Article
  • 2012-01-0182
Published 2012-04-16 by SAE International in United States
Spot Welding is an important welding technique which is widely used in automotive and aerospace industry. One of the keys of checking the quality of the welds is measuring the size of the nugget. In this paper, the Shearographic technique is utilized to test weld joint samples under the thermal loading condition. The goal is to identify the different group of the nuggets (i.e. small, middle, and large sizes, which indicate the quality of spot welds). In the experiments, the sample under test is fixed by a magnet method from behind at the four edges. Thermal loading was applied in the back side and the sample is inspected using the digital Shearographic system in the front side. Results show the great possibility of classifying the nugget size into three groups and the measurement is well repeatable.
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