Accelerated Life Testing: Principles, Acceleration Factor and Life Extrapolation
What is Accelerated Life Testing?
Accelerated life testing (ALT) raises stress — temperature, voltage, humidity or vibration — so that failure mechanisms are exposed in a short time, then uses stress-life models to extrapolate the high-stress failure data back to normal use conditions and estimate lifetime and reliability at rated operation. It targets high-reliability, low-failure-rate products and is the approach recommended by IEC 62506 and MIL-HDBK-781A. Run a small pilot first to confirm the failure mode under acceleration matches service conditions.
When to Use It
Use it for lifetime verification of semiconductor devices, LEDs, capacitors, batteries, connectors and relays; for new-product reliability verification; and for competitor comparison or supplier incoming-reliability assessment. Choose the model by stress type: Arrhenius for temperature, the inverse power law for voltage or current, Peck for temperature-humidity, and Norris-Landzberg for thermal cycling or vibration. Where verification time is limited, ALT shortens the test considerably.
How to Use It (Step by Step)
Select the stress model, enter the use stress, test stress and model parameters such as activation energy, and the tool returns the acceleration factor AF and the equivalent test time at normal stress. Design the plan with 3–4 stress levels and at least 3–5 samples per level, then model the failure data with a Weibull analysis tool for a complete picture. Validate the model with an intermediate stress group when the extrapolation span is large.
Key Formulas / Example
Temperature (Arrhenius): AF = exp[(Ea/k)(1/Tu − 1/Ts)], with k = 8.617×10⁻⁵ eV/K and temperatures in kelvin. Example: Ea = 0.7 eV and a step from 25 °C to 105 °C gives AF ≈ 300, so 1,000 test hours represent about 300,000 use hours. The activation energy must come from failure-mechanism data, and accelerated stress must not exceed material limits or change the failure mechanism.