3-DIMENSIONAL STRESS RELIEF DISPLACEMENT RESULTING FROM DRILLING A BLIND HOLE IN ACRYLIC

Analyses of optically based, hole-drilling stress measurements require accurate knowledge of the three-dimensional relaxation displacements induced by the drilling of a blind hole into the surface of a stressed object. These displacements are calculated using two closed-form solu tions proposed earlier and a numerical finite element technique. Doubl e exposure holographic fringe patterns calculated from the analytic di splacements are in poor agreement with those observed in a controlled laboratory calibration experiment on a block of acrylic subject to a k nown uniaxial compressive stress. However, the fringe positions predic ted by the finite element modeling match those obtained from the obser ved fringe pattern using image-processing procedures, although some dr illing-related discrepancies remain near the stress-relieving hole. Th e stress-strain behavior of acrylic is extremely temperature sensitive ; the discrepancies near the stress relief hole may result from drilli ng-induced heat. Despite these near hole disagreements between the pre dicted and observed fringe patterns, the overall correspondence indica tes that the finite element method adequately provides the desired thr ee-dimensional relaxation displacements necessary for determination of stress magnitudes in some blind hole drilling measurements employing coherent optical recording.