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PRISM determines residual stress using the hole drilling technique and laser interferometry. The stress relief brought about is measured in the form of surface displacements by digital photography of speckle patterns before and after drilling. This method is much quicker and easier-to-use than strain-gage methods. The paper introduces the measurement system and discusses depth profiles obtained from different materials and their correlation with x-ray diffraction results.

PRISM is a new residual stress measurement system that uses hole drilling combined with electronic speckle pattern interferometry. Since it doesn’t require the application of strain gages, measurements can be performed without much preparation effort. The instrument evaluates a continuous surface area around the hole rather than three or six locations as with strain gages. Stress depth profiles with a dozen depth increments or more can be obtained within about half an hour. PRISM measurements captured the basic differences between the two types of stress profiles existing in the camshafts examined, which are in agreement with x-ray diffraction (XRD) measurements also performed. Thus PRISM is an option for quick stress testing of camshafts. Not all details of the XRD measurements were detected, though, specifically the very thin surface compressive layer (<30μm) could not be identified.

Hole drilling is a very common technique for measuring residual stresses. Adding an orbiting motion of the drill was found to improve hole quality in difficult to drill materials and has been in practice for decades. This study compares measurements using various orbiting amounts. Each measurement was repeated twice to evaluate measurement statistics. There is a distinct, though relatively small, effect of the hole shape when no orbiting is used. It disappears already when the hole is 50% larger than the tool size. Different orbiting amounts also produce systematically different results. These may be related to the absolute hole size.