Failure Analysis

• 3D optical profile plot of ball bearing surface wear scar

Failure of materials surface metrology

Failure analysis, cracks and fissures

The 3d optical profiler measurement contains reliable two dimensional cross-sections in any direction across the surface. The volumetric accuracy of three dimensional measurements can be used to produce precise calculations of the volume of voids, wear, pits, grooves and failure cracks and fissures.

Surface roughness data (Ra) and texture metrology can be used to analyze surfaces at shear points, joints and contact points, at the point of failure, and can characterize the shape and depth of cracks and fissures.

Fatigue failure

Interference microscopes make three dimensional maps that have been used in scientific research as well as research and development to improve processes and determine the effect of various finishing processes on fatigue failure.

One study of fatigue in mechanically fastened joints in airframes and metallic aerospace structures, (Cindie Giummarra and Harry R. Zonker, Alcoa Inc. published in ICAF 2005 Proceedings, Hamburg Germany) noted that interference surface profiling was useful in characterizing the original, as-machined surface roughness (Ra), as well as the surface roughness after various surface finishing techniques such as anodizing, shot peening, laser peening and proprietary chemical finishing techniques.

Residual stress, particularly compressive stress caused by the finishing techniques, was measured by examining fretting cracks which nucleated in the hole bore of joint specimens. Inducing fatigue failures and determining the nucleation source and depth of the joint or fretting fatigue results helped to specify the advantages and disadvantages of various surface finishing techniques in reducing fatigue failure, depending on the type and depth of stresses the specimen is to undergo.

Results helped determine that surface treatments may improve fretting resistance and joint fatigue life through various features of surface finishing, including increasing surface roughness to limit the surface-to-surface contact (which is a necessary element in nucleation of fretting cracks).

Wear marks

Scratches, wear and voids can be measured and their characteristics determined that help to diagnose the nature of the failure event.

The software provided with the vertical scanning interferometer is able to remove the surface curvature and present the wear or defect independent of the surface figure.