Crack Detection and Monitoring Crack Growth in Fastener Holes Using the DMI Optical SR-2 Strain Measurement Technology

Results are presented for crack initiation detection and crack growth monitoring using DMI SR-1 Strain Gages and DMI SR-2 Reader in two Northrop Grumman aluminum test coupons subjected to cyclic loading. Results demonstrate the utility of the technology to detect cracks and crack growth in holes. The DMI SR-1 strain gage is applied so that it frames the hole in the test coupon. This results in strain measurements at tangents to hole and associated shear strains. A differential strain reading between gage lengths on parallel and opposing sides of a hole, resulting from discontinuities in the material surrounding a hole, indicates crack initiation and as the crack grows the differential reading increases.© 2007 ASME

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