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Multiaxial loading on mechanical products is very common in the automotive industry, and how to design and analyze these products for durability becomes an important, urgent task for the engineering community. Due to the complex nature of the fatigue damage mechanism for a product under multiaxial state of stresses/strains which are dependent upon the modes of loading, materials, and life, modeling this behavior has always been a challenging task for fatigue scientists and engineers around the world. As a result, many multiaxial fatigue theories have been developed. Among all the theories, an existing equivalent stress theory is considered for use for the automotive components that are typically designed to prevent Case B cracks in the high cycle fatigue regime.

Effects of roller diameter and number on the contact pressures, subsurface stresses and the fatigue lives of cam roller follower bearings are investigated in this paper. Finite element analyses under plane strain conditions were conducted to identify the effects of the diameter and number of the rolling elements and the thickness of the outer ring. The fatigue life of the inner pin generally increases as the roller diameter increases. But, reducing the number of rollers to accommodate larger rollers does not necessarily increase the fatigue life. The inevitable decrease of the thickness of the outer ring due to the increase of the roller diameter results in the increase of compliance for the outer ring. This increase of compliance leads to excessive deformation of the outer ring and consequently more load must be carried by fewer number of rolling elements.

This paper introduces a methodology to calculate confidence bounds for a normal and Weibull distribution using Monte Carlo pivotal statistics. As an example, a ready-to-use lookup table to calculate one-sided lower confidence bounds is established and demonstrated for normal and Weibull distributions. The concept of one-sided lower tolerance limits for a normal distribution was first introduced by G. J. Lieberman in 1958 (later modified by Link in 1985 and Wei in 2012), and has been widely used in the automotive industry because of the easy-to-use lookup tables. Monte Carlo simulation methods presented here are more accurate as they eliminate assumptions and approximations inherent in existing approaches by using random experiments. This developed methodology can be used to generate confidence bounds for any parametric distribution. The ready-to-use table for the one-sided lower tolerance limits for a Weibull distribution is presented.

In this paper, the development of random vibration testing schedules for durability design verification of engine mounted products is presented, based on the equivalent fatigue damage concept and the 95th-percentile customer engine usage data for 150,000 miles. Development of the 95th-percentile customer usage profile is first discussed. Following that, the field engine excitation and engine duty cycle definition is introduced. By using a simplified transfer function of a single degree-of-freedom (SDOF) system subjected to a base excitation, the response acceleration and stress PSDs are related to the input excitation in PSD, which is the equivalent fatigue damage concept. Also, the narrow-band fatigue damage spectrum (FDS) is calculated in terms of the input excitation PSD based on the Miner linear damage rule, the Rayleigh statistical distribution for stress amplitude, a material's S-N curve, and the Miles approximate solution.

Elastomers have large reversible elastic deformation, good damping and high energy absorption capabilities. Due to these characteristics along with low cost of manufacturing, elastomeric components are widely used in many industries and applications, including in automobiles. These components are typically subjected to complex multiaxial and variable amplitude cyclic loads during their service life. Therefore, fatigue failure and life prediction are important issues in the design and analyses of these components. Availability of an effective CAE technique to evaluate fatigue damage and to predict fatigue life under complex loading conditions is a valuable tool for such analysis. This paper discusses a general CAE analytical technique for durability analysis and life prediction of elastomeric components. The methodology is then illustrated and verified by using experimental fatigue test results from an automobile cradle mount.

In this paper, constant amplitude strain-life fatigue data from a variety of sheet steel suppliers is examined. The data is processed to remove unsatisfactory test results, and the median curves for both the elastic and plastic strain-life relationships are determined. Statistical single-sided elastic and plastic strain-life design curves are generated using the approximate Owen lower tolerance limit method. The resulting statistical total strain-life design curves are then compared to an established theoretical single-sided statistical tolerance limit to assess the validity of using the approximate Owen lower tolerance limit method for the generation of single-sided design curves for strain-life fatigue data.

The staircase fatigue testing method is a recognized method for determining the fatigue limit of powertrain components. The purpose of this paper is to improve upon existing standards by adding common practices that will ensure a higher degree of statistical accuracy in the data. This includes specifying appropriate sample sizes, stress increments and initial load conditions, as well as making suggestions for appropriate methods of analyzing the data. Two methods (Dixon and Mood method and probit analysis method) are selected and compared in terms of relative percent difference on four parameters (mean, standard deviation, B10 fatigue strength and B50 fatigue strength). The staircase data are obtained by simulations from normal and lognormal fatigue limit distributions.

An analytical load distribution solution for calculation of the loads exerted by the rolling elements on the outer raceway in cylindrical roller bearings under radial loading is proposed in this paper. The loads exerted by the rolling elements are obtained based on an assumption that the profile of the maximum contact pressures of rolling elements resemble the profile of the contact pressure of the corresponding lumped cylinder. Based on this assumption, an analytical load distribution solution which gives the loads exerted by the rolling elements on the outer raceway is derived based on the non-conforming contact solution of Hertz and the conforming contact solution of Persson. These loads can be calculated from the analytical solution with the total applied load and the normalized contact pressure profile of the corresponding lumped cylinder. Two-dimensional finite element analysis was conducted to validate the proposed analytical solutions.

This report explores the relationship of different failure criteria - specifically, surface cracks, stiffness changes, and two-piece failures - on rolled, ductile, cast-iron crankshafts. Crankshaft samples were closely monitored throughout resonant bending fatigue testing and were taken to near complete fracture. By monitoring resonance shifts of the samples during testing, stiffness changes and cracks were monitored. These data showed that an accelerating frequency shift was sufficient to indicate imminent two-piece failure and that this condition can be used as a failure criterion. Fatigue studies on two different crankshafts using this failure criterion were compared to those using a surface crack failure criterion. This comparison showed that using the surface crack failure criterion erroneously decreased the apparent fatigue life of the crankshaft significantly.

Two popular critical plane models developed by Fatemi-Socie and Smith-Watson-Topper were derived from the experimental observations of the nucleation and growth of cracks during loading. The Fatemi-Socie critical plane model is applicable for the life prediction of materials for which the dominant failure mechanism is shear crack nucleation and growth, while the Smith-Watson-Topper model, for materials that fail predominantly by crack growth on planes perpendicular to the planes of maximum tensile strain or stress. The two critical plane models have been validated primarily by in-phase and 90° out-of-phase loading, and few, on the complex, non-proportional loading paths. A successful critical plane model should be able to predict both the fatigue life and the dominant failure planes. However, some experimental studies indicate the 304 stainless steel has the two possible failure modes, shear and tensile failure dominant, depending on the loading mode and stress and strain states.

Joining technology is a key factor to utilize dissimilar materials in vehicle structures. Adaptable insert weld (AIW) technology is developed to join sheet steel (HSLA350) to cast magnesium alloy (AM60) and is constructed by combining riveting technology and electrical resistance spot welding technology. In this project, the AIW joint technology is applied to construct front shock tower structures composed with HSLA350, AM60, and Al6082 and a method is developed to predict the fatigue life of the AIW joints. Lap-shear and cross-tension specimens were constructed and tested to develop the fatigue parameters (load-life curves) of AIW joint. Two FEA modeling techniques for AIW joints were used to model the specimen geometry. These modeling approaches are area contact method (ACM) and TIE contact method.