The benefits of stress testing

Weak products may exhibit failures or degrade only under certain stress conditions. Stress testing includes testing after stressing the incipient defects to hard defects and testing during stressing to show marginal defects, which are followed by root cause analysis and corrective actions. A given unit of a product has a probability of encountering a maximum stress X during its product life. It also has a probability of possessing a product yield strength Y, which is the maximum stress the unit ran survive without failure. A convenient picture is the contour map of the joint probability distribution of X and Y. Units in the Y<X region in this contour map will fail during the product life, whereas stress testing at a maximum stress level of X ^ST will capture the units in the Y<X^ST region. Therefore the lines X=Y and Y=X^ST divide the units into four regions, each with its cost and benefit from stress testing. The value of X^ST may be adjusted to vary the relative size of each region, and therefore to maximize the net benefit