Test and Evaluation for Robustness
Test and Evaluation for robustness of a product is an involved process. For electrical and electronic equipment an evolution of design engineering evaluation has been required to meet acceptable failure rates for fielded product. Instituting these test methodologies requires looking beyond a test to pass approach.
Robustness in Military Applications
In the military this requirement was apparent following World War II where new materiel had often failed to meet performance criteria when introduced to its operational environment. This led to the creation of AAF Specification 41065 in 1945. This specification was comprised of ten methods for developmental product evaluation with preset parameters. This standard later became MIL-STD-810 Environmental Engineering Considerations and Laboratory Tests.
As this standard evolved, it became more and more apparent to those writing it the limitations of a cookie cutter approach. Environmental issues are far too complicated and nuanced to be easily defined in a manner that is appropriate for all applications. Because of this, every revision of the standard has increasingly stressed the need for tailoring tests to meet the anticipated environmental stresses in the lifetime of the product.
Because industry largely ignored the requirements for tailoring, a tailoring process was created in revision G in 2008. Despite this though, developmental test and evaluation of products has often not been adequately performed. This has led to costly redesigns in operational testing phases and caused delays in final systems.
Part one of MIL-STD-810 now details the creation of a design and evaluation management system. This system identifies environmental stressors expected to be encountered in the life cycle of the product including logistical transport, tactical transport, storage, and operational. Proper implementation of these processes allows for release of product that is capable of meeting its mission requirements.
Robustness in Automotive Applications
As electronics were first introduced in automobiles failure rates were excessive. These failures were caused by climatic, mechanical, chemical, electrical, and electromagnetic stresses in vehicle applications. As the industry moved towards longer warrantied products, emphasis shifted from the detection of failures at the end of the development process to prevention of failures throughout the full life cycle.
This prevention requires designing for ruggedness at concept development with a Zero-Defect Strategy. Here again developmental test and evaluation is seen as essential for success. A test to pass approach that does not return useful data is not desirable. A detailed analysis of this approach can be found in SAE J1211: 2012 Handbook for Robustness Validation of Automotive Electrical/Electronic Modules.
Like MIL-STD-810, SAE J1211defines a Robustness Validation process that involves both the user and the supplier to define and establish requirements and acceptance criteria based on the end vehicle’s specific application. These requirements and criteria are based on a defined Mission Profile with the goal designing out susceptibility to failure mechanisms.
This Robustness Validation process relies first on knowledge-based modeling simulation and analysis methods in the design phase. These designs are then to be verified and validated testing protocols including test-to-failure and failure/defect susceptibility testing to confirm or identify Robustness Margins
The standard categorizes these failure mechanisms as follows:
- Electromagetic Compatibility (EMC)
As with MIL-STD-810 the automotive industry’s approach examines the synergetic effect of environmental stressors. This approach requires a comprehensive analysis when a test and evaluation program is initiated.
Understanding Environmental Stresses
For any application of ruggedness design, an understanding of the environmental stresses involved is essential. This therefore requires an assessment and identification of all probable environmental factors, their frequency of occurrence, and intensities. In MIL-STD-810 parlance this is accomplished through the development of a Life Cycle Environmental Profile (LCEP).
For automotive applications this is done through a Mission Profile. These profiles should include all phases of product life including transit and storage. They should also include lessons learned from similar product histories.
Once these stressors have been identified, their criteria can be used for development of design specification. These criteria are also used to develop a test master plan with relevant stress values to be used in robustness tests.
Military and automotive applications require design and test methods that ensure ruggedness. The development of a test and evaluation program that will verify a design and return significant data must be initiated at the concept stage of product development. This is true when ruggedness is required of any product.
CVG Strategy has experience in developmental test and evaluation for a wide variety of industries including military and automotive. Because of this we understand looking beyond a test to pass perspective. We can help develop a test program that will return meaningful data and verify a products ability to survive harsh environments.