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Vishay Measurements Group
Interactive Guide
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RS-200 System
RS-200 Milling Guide
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Strain Gages and Instrumentation for Residual Stress Measurements |
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Introduction
A predominant factor contributing to the structural failure of machine parts, pressure vessels, framed structures, etc., may be the residual "locked-in" stresses that exist in the object prior to its being put into service. These residual stresses are usually introduced during manufacturing, and are caused by processes such as casting, welding, machining, heat treating, molding, etc. Residual stress cannot be detected or evaluated by conventional surface measurement techniques, since the strain sensor (strain gage, photoelastic coating, etc.) can only respond to strain changes that occur after the sensor is installed. The most widely used practical technique for measuring residual stresses is the hole-drilling strain gage method described in ASTM Standard E837. With this method, a specially configured electrical resistance strain gage rosette is bonded to the surface of the test object, and a small shallow hole is drilled through the center of the rosette. The local changes in strain due to introduction of the hole are measured, and the relaxed residual stresses are computed from these measurements. Vishay Measurements Group Tech Note TN-503, Measurement of Residual Stresses By The Hole-Drilling Strain Gage Method , presents a detailed discussion of the theory and application of this technique. 
The hole-drilling method is generally considered semi-destructive, since the drilled hole may not noticeably impair the structural integrity of the part being tested. Depending on the type of rosette gage used, the drilled hole is typically 0.062 or 0.1 25 in (about 1.5 or 3.0 mm), both in diameter and depth. In many instances, the hole can also be plugged, if necessary, to return the part to service after the residual stresses have been determined. The practicality and accuracy of this method is directly related to the precision with which the hole is drilled through the center of the strain gage rosette. The Vishay Measurements Group RS-200 milling guide provides a practical means to accomplish this task.
Measurement
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