How fast is too fast? Accelerated Life TestingApril 28, 2014
When planning a test program, one of the most important variables is determining how long the testing will take. There is a great deal of pressure to compress timelines in order to deliver to market, and liability for field failures has proved disastrous even for major companies. This double-whammy makes it critical to have the tools available for selecting a test that accurately represents the life cycle of a component while reducing development time in order to deliver on schedule.
How to Decrease Time? Simple. Increase stress to reduce the number of cycles needed. Stress is easily increased by adding more force, more extreme temperatures, higher g-levels, more pressure, more speed… More power!
The Catch? Each of these variables tends to interact with the others. For example, increasing temperatures may cause plastics to become brittle, so they no longer fatigue along their designed s-n curve. Isolating one or two variables might be ok for a material test, but becomes more complicated at the component level. Using the same example on a motor, maximizing the temperature and stress may generate known failures on the plastic housing, but could cause premature failure of the bearings due to the higher temperatures. This would require an additional test that is more representative for the bearings, adding to the cost and complexity of development. A gain in one area is lost in another, illustrating it is not so simple.
The Solution? Stand on the shoulders of giants. Build on the existing engineering knowledge rather than trying to start from scratch. Research your industry and discover the specifications that others have developed for applications similar to yours. MIL-STD-810 is a broad scope military specification that describes how to tailor testing to environmental conditions a component is likely to see in the field. GMW3172 is a common automotive specification that takes this idea a step further and actually provides guides for development testing of electrical components at an accelerated pace based on empirical and statistical data.
The best way to get the most out of your testing is to be prepared at the planning stage. Using a well-established specification or development guideline is one way to prevent unrealistic expectations from sabotaging an otherwise successful development program. Having an industry standard can help ensure good engineering practices are followed, and balance the pressures of program management. NTS has experience in a wide variety of markets, and can assist with test plan development in order to create a schedule that is achievable and will be a success for everyone.
By Randy Cobb, Climatics Department Manager at NTS Detroit. For more information please visit the NTS Detroit webpage or call the lab directly at 313.835.0044 .