Measurement of Residual Stresses by the Hole-Drilling Strain Gage Method

Boring Numerous studies on the effects of hole size and shape and machining procedures have been published. Rendler and Vigness specified a specially dressed end mill which is compatible with the residual stress rosettes . The end mill is ground to remove the side cutting edges, and then relieved immediately behind the cutting face to avoid rubbing on the hole surface. It is imperative that the milling cutter be rigidly guided during the drilling operation so that the cutter progresses in a straight line, without side pressure on the hole, or friction at the noncutting edge. These end mills generate the desired flatbottomed and square-cornered hole shape at initial surface contact, and maintain the appropriate shape until the hole is completed. In doing so, they fulfill the incremental drilling requirements as stipulated in ASTM E837. Specially dressed end mills offer a direct and simple approach when measuring residual stresses on readily machinable materials such as mild steel and some aluminum alloys. The RS-200 Milling Guide with the microscope removed and the end-mill assembly in place is shown below. The end mill is driven through the universal joint at the top of the assembly, by either a hand drill or variable-speed electric drill.

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