Design and application of accelerated life test of grating ruler based on step stress loading

Combined with the actual project, a grating ruler accelerated life test device is designed, which can simulate the actual loads, including temperature, humidity and speed stress. An accelerated life test scheme based on stepped stress loading is proposed, and 6 grating rulers are tested based on time-censored test method. An accelerated life model based on Weibull distribution used for evaluating the lifetime is established. Related experimental techniques also can be typical application cases for innovative practical teaching.

Fatigue Life Modeling Using Nitinol Data

Nitinol is a shape memory alloy that has become very popular for medical applications. Specifically, Nitinol tubing is used as peripheral stents, cardio stents and other medical implant devices. Medical implants subjected to blood pressure experience approximately 40 million cycles per year, which necessitates a life expectancy of at least 600 million cycles. Consequently, modeling the fatigue life of Nitinol is critical because failure could result in severe consequences, if not death. The purpose of this work is to model a rather robust set of fatigue data for Nitinol tubes. A phenomenological distribution function for fatigue life is considered. The form of the distribution function includes a kernel that incorporates time dependent loading, mechanical breakdown, and statistical behavior. The approach is a form of the classical accelerated life model in which covariates are included to account for physical attributes that directly influence lifetime. Because of the generality in the formalism, the model is applicable for a variety of loading conditions. The modeling for the Nitinol data is a combination of traditional stress–life methods with a Weibull distribution function. The proposed approach incorporates stress dependencies in the distribution parameters. Also, the Weibull distribution is assumed to be in the form of a three–parameter distribution rather than the more frequently used two–parameter. To assess the validity of the proposed methodology confidence bounds will be estimated for the data.

Composite GM (1, 1) Model for Treating Data of Constant Stress Amplitude Accelerated Life Tests

An accelerated life model is an important factor affecting the evaluation of test data. Avoiding the existent difficulties of treating mixed data and based on the grey theory with composite GM(1,1) model, approach is presented for treating fatigue data under constant stress amplitude accelerated life tests. Availability of the approach has indicated by an example.