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Using Accelerated Stress Testing to Obtain High Product Reliability
DN Staff
July 1, 2015
3 Min Read
In product development, each step of the process requires decisions to be made. From design feasibility, to development, to production, having the right information to make good decisions can ultimately keep a product from failing validation. The key is highly focused information that doesn't come from conventional, statistics-based tests but from accelerated stress testing (AST).
Conventional Versus Accelerated Testing
Conventional tests determine the pass/fail point for a group of product samples that are subjected to a single stress point. Such tests need to be repeated for each different state of stress. They yield statistical data and are necessary to demonstrate compliance with customer requirements and industry regulations. They are validating tests, however, and don't necessarily identify weaknesses in designs, concepts, or end products.
Accelerated stress testing determines the failure modes for a small group of samples when subjected to different levels of multiple, simultaneously applied stress sources (such as vibration and temperature). One well-designed test determines weak points in a product, makes determinations about material selection, and provides considerations for improving overall product design, warranty options, and overall lifespan of the product. AST can be a valuable tool in product development.
AST Methods
There are several methods for running AST on products:
Failure Mode Verification Test (FMVT): FMVT reveals inherent design weaknesses and can be used to validate failures predicted by the failure mode and effects analysis (FMEA) process. By exposing a design to a combined set of amplified environments/stresses, multiple failure modes (and their sequence and distribution) are produced. Intended to provide context to the failure modes relative to the design (or compared with similar designs), FMVT examines what will fail, what will cause the failure, and how the failure ranks against other failures. FMVT is a popular testing method for mechanical and electron mechanical.
Highly Accelerated Life Test (HALT): During the HALT process, a product is subjected to increasing stress levels of temperature and vibration (independently and in tandem), rapid thermal transitions, and other stresses specifically related to the operation of a product. Structured to provide context to the failure modes relative to the operational and destruct limits of a product, HALT looks at not only what will fail and what causes the failure but also how the failure ranks against specific specifications. HALT is commonly used for testing electronics.
Key Life Test (KLT)/Full System Life Test (FSLT): Similar to a traditional reliability test, KLT/FSLT uses a full system to apply all service stresses to a product to evaluate changes and ensure its reliability. By putting objects through simulated real-life conditions, these tests determine whether a product can meet a determined minimum life.
Accelerated Reliability Test: In an accelerated reliability test, several sets of parts are tested at much higher stress levels than the expected service level until enough data is collected to extrapolate the service condition time to failure. These tests determine the expected minimum life of a product.
MORE FROM DESIGN NEWS: Identifying and Reducing Stresses in Pressure Vessels
Other test methods include:
Mini tests for HALT and FMVT, which are run in shorter time spans for quicker, lower-cost information.
Multiple Environment Over Stress Test (MEOST), a variant of FMVT.
Specialized AST methods for certain industries and environments.
HALT and FMVT are both failure identification methods, which work well at providing failure mode information as the primary output. These methods are suitable for challenges that require failure mode information (design iteration, warranty problems). FMVT can determine the product margin for improvement, so it's useful for design iterations or to compare the relative robustness of competing designs. HALT provides the margin of design to service conditions.
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