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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.

Crankshaft fillet is subjected to a cyclic bending stress during operation. Fatigue cracks are observed at the fillet during the fatigue test. Compressive stresses are generated by deep-rolling process in order to increase the surface hardness and improve the fatigue strength. To examine the deep-rolling effect, the residual stresses at the fillet need to be investigated. Incremental hole drilling and ISSR (interferometric strain/slope rosette) method is applied to measure the residual stresses at the bottom of the fillet. Incremental hole drilling process is to gradually remove material and mill a hole on the specimen surface in order to relax stress. The ISSR is composed of three micro-indentations, which are indented near the hole and would generate interferometric fringe patterns upon incident laser beam. With incremental drilling, stress relaxation causes the relieved strains, which in turn cause the shifts of interferometric patterns.

Spot Welding is now widely used in the fabrication of sheet metals, mainly due to the cost and time considerations. Spot welds are found in nearly all products where sheet metal is joined. Examples range from a single metal toolbox to nearly 10,000 spot welds found in a typical passenger car. Obviously the quality of the spot weld has a direct impact on the quality of the product. The problem of estimating the spot-weld quality is an important component in quality control. If the weld nuggets are improperly or incompletely formed, or the area surrounding the nugget is smaller than required, the structural integrity of the entire part may be uncertain. Furthermore these inconsistencies are usually internal and are seldom visible to Optical Inspection. This study is focused on the non-destructive evaluation of the spot welds using “Digital Shearography”.

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.

Dang Van (Dang Van et al., 1982 and Dang Van, 1993) states that for an infinite lifetime (near fatigue limit), crack nucleation in slip bands may occur at the most unfavorable oriented grains, which are subject to plastic deformation even if the macroscopic stress is elastic. Since the residual stresses in these plastically deformed grains are induced by the restraining effect of the adjacent grains, it is assumed that the residual stresses are stabilized at a mesoscopic level. These stresses are currently approximated by the macroscopic hydrostatic stress defined by the normal stresses to the faces of an octahedral element oriented with the faces symmetric to the principal axis; mathematically they are equal to each other and they are the average of the principal stresses.