# Quantitative Accelerated Life Testing Data Analysis

## Introduction to Common Stress Loading Schemes and Stress Profiles  in Accelerated Life Testing

As a supplement to the Accelerated Life Testing Data Analysis Basics quick subject guide, this document presents an overview of some common stress loading schemes and stress profiles used in accelerated life testing. This subject is covered in more detail in ReliaSoft's Accelerated Life Testing Online Reference on Weibull.com. See also Stress Loading

### Stress is Time-Independent (Constant Stress)

When the stress is time-independent, the stress applied to a sample of units does not vary with time. For example, if temperature is the stress type, each unit will be tested under the same accelerated temperature for the duration of the test.

Constant Stress Profile

### Stress is Time-Dependent (Time-Varying Stress)

When the stress is time-dependent, the stress applied to a sample of units varies with time. For example, if temperature is the stress type, each unit may be tested at 100K for 10 hours then increased to 150K for 10 hours then increased to 200K for 10 hours over the duration of the test. Time-dependent stresses can be applied in a variety of ways, including step-stress, ramp-stress, etc. Some common stress profiles are shown next.

 Step-Stress Profile Ramp-Stress Profile Progressive Stress Profile Completely Time-Dependent Stress Profile

### Analyzing Data from Time-Dependent Stress Conditions

ReliaSoft's ALTA PRO software is capable of analyzing accelerated life data when the accelerated stress level(s) and/or the use stress level(s) vary with time. You can use the Stress Profile folio to define the profile by time segments (start and end), with a stress level defined for each time segment. The stress can be a constant value (e.g.,200K) or an equation that describes the stress behavior as a function of time, S(t).

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