Reliability and
Maintenance
Management
Accelerated Life
Testing ALT
Dr. Hazem Smadi
April 2012
Accelerated Life Testing ALT
• The concept of accelerated life testing is to subject
certain sample of a product to a test with sever
conditions relative to normal usage condition, and
applying certain stresses in the test, based on each
case. The test is accelerated in order to save the
testing time.
Areas of Life Testing
• Qualitative test: yields failure information (modes).
• Types:
o Elephant test.
o Torture test.
o Shake and bake test.
Areas of Life Testing
• Quantitative test: designed to quantify the life
characteristics of the product, component or system under
normal use conditions and provide reliability information.
• It can take the form of usage rate acceleration or overstress
acceleration. These forms are known as accelerating
methods.
Accelerating Methods
• Usage rate acceleration: Applied on units that are not
continuously operated.
• Overstress acceleration: Applied on units that are
continuously operated.
• The mentioned methods are usually applied by testing the
items of interest between their specific limits and their
design limits.
Stresses to be known before performing ALT
• Mechanical Stress.
• Electrical Stress.
• Environmental stress.
ALT Models
• Statistics-based models: failure time, PDF, CDF, and failure
rate.
• Overload stress model
•
Two possible test outcome (success and fail), binomial test is
applied.
ALT Models
• Deterioration-monitoring model
•
Measure certain property that varies with time, by applying normal
stress level on a product unit for a period of time t1.
•
Calculate the rate of change for this property per unit of time.
•
Increase the stress level, and keep testing the same product unit.
•
Calculate the rate of change for the same property per unit of time
under this stress level.