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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.

Fatigue behavior of laser welds in lap-shear specimens of high strength low alloy (HSLA) steels is investigated based on a fatigue crack growth model. Fatigue experiments of laser welded lap-shear specimens were conducted. Analytical global stress intensity factor solutions are developed and compared with finite element computational results. A fatigue crack growth model based on the analytical local stress intensity factor solutions of kinked cracks and the Paris law for crack growth is then adopted to estimate the fatigue lives of the laser welds under cyclic loading conditions. The estimated fatigue lives are compared with the experimental results. The results indicate that the fatigue life predictions based on the fatigue crack growth model are slightly longer than the experimental results.

We have developed new CAE tools in the concept design process based on First Order Analysis (FOA). Joints are often modeled by rotational spring elements. However, it is very difficult to obtain good accuracy. We think that one of the reasons is the influence of the nonlinear behavior due to local elastic buckling. Automotive body structures have the possibility of causing local buckling since they are constructed by thin walled cross sections. In this paper we focus on this behavior. First of all, we present the concept of joint analysis in FOA, using global-local analysis. After that, we research nonlinear behavior in order to construct an accurate joint reduced model. (1) The influence of local buckling is shown using uniform beams. (2) Stiffness decrease of joints due to a local buckling is shown. (3) The way of treating joint modeling considering nonlinear behavior is proposed.

A new method for crashworthiness optimization of vehicle structures is presented, where an early design exploration is done by the optimization of an equivalent mechanism approximating a vehicle structure. An equivalent mechanism (EM) is a network of rigid bodies connected by prismatic and revolute joints with special nonlinear springs. These springs are designed to mimic the force-displacement characteristics of thin-walled beams often found in the vehicle body structures. A computer software is implemented that allows the designer to quickly construct an equivalent mechanism model of a structure using a graphical user interface (GUI) to optimize the model for given objectives prior to final tuning using finite element (FE) models. A case study of a vehicle front substructure consisting of mid and lower rails is presented, which demonstrates that the new approach can obtain a better design with less computational resources than the direct optimization of a FE model.

The fundamental relationship between semi-solid processing and microstructure and their effect on the flow characteristics of semi-solid metals have been studied for several years. However, how the process related microstructure influences fatigue properties has not been given the same attention. This study examines the influence of process-related microstructure on the fatigue properties of semi-solid formed A357 alloys. High-solid-fraction (62% solid) and low-solid-fraction (31% and 36% solid) semi-solid formed A357 was tested in axial fatigue with a stress ratio (R) equal to -1. The high solid fraction (HSF) material had better fatigue properties than the low solid fraction (LSF) material. This is attributed to the fatigue crack initiation mechanisms, as related to the fatigue crack initiation features and the strengths of the materials.

The automobile industry has been using high-density polyethylene (HDPE) as a material to fabricate fuel tanks. Because untreated HDPE is permeable to the primary constituents of gasoline, these fuel tanks are now being produced with various barrier technologies that significantly reduce this permeation rate. Four currently available barrier technologies are fluorination, sulfonation, coextrusion, and the laminar barrier technology. These technologies have successfully proven to decrease the permeation rate of pure gasoline. However, it is suspected that their effectiveness may be reduced when alcohols are introduced into the fuel blend. In this work, we determine the permeation rates of gasoline-alcohol fuel blends through HDPE by conducting tests on 22-gallon HDPE fuel tanks and on small HDPE bottles fabricated with and without these barrier technologies. The goal of this study is to provide a comprehensive evaluation of these four barrier technologies.

THIS paper reports work begun in 1935 at the instigation of the Murray Corp. of America. Methods used in studying the relations between the automobile seat cushion and its function in transporting passengers with greater comfort and less fatigue are described. Constructed for this purpose was a piece of apparatus called the Universal Test Seat, whose dimensions were completely adjustable with arrangements to vary the distribution of the supporting pressure in any manner which seemed most comfortable to the passenger. The authors describe tests made by use of this apparatus, present summaries of some of the results recorded and conclude that, to give the passenger the maximum comfort and least fatigue, the following mechanical objectives should be attained by the cushion: 1. To support the passenger over a large area to get the smallest unit pressure on the flesh; 2.