Strength wearout

Shenoy et al. (2009b) proposed a modified version of this equation that they termed the normalized nonlinear strength wearout model (NNLSWM), which is given by ... 

The normalized nonlinear strength wearout model applied to aluminum-epoxy single lap joints tested at different loads (Shenoy et al. 2009b]... 

Shenoy et al. (2009c) proposed various further modifications to this approach, which they applied to aluminum alloy-epoxy single lap joints subjected to various forms of VAR The application of the cycle mix factor to predict strength wearout and cycles to failure for VAF is illustrated inO Fig. 33.8. The figure shows two strength wearout curves, showing the reduction... 

The end of the bathtub curve occurs when the strength of the product declines (susceptibility increases). This is commonly known as "wearout." Wearout occurs after several years but the mechanisms vary considerably depending on the type of component. 

Process qualification tests can be the same set of accelerated wearout tests used in design qualification. As in design qualification, overstress tests maybe used to qualify a product for anticipated field overstress loads. Overstress tests may also be exploited to ensure that manufacturing processes do not degrade the intrinsic material strength of hardware beyond a specified limit. However, such tests should supplement, not replace, the accelerated wearout test program, unless explicit physics-based correlations are available between overstress test results and wearout field-failure data. 

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