MODELING STRENGTH DEGRADATION OF HYPERVELOCITY IMPACTED WINDOWS FOR THE SPACE SHUTTLE

摘要

The shallow surface pits created by hypervelocity impact damage on fused silica windows were modeled as a spherical cap surrounded by a circumferential crack to develop a probabilistic model between pit measurements and residual strength predictions. Using finite element analysis, the stress concentration of a spherical cap was determined as a function of the radius and depth of the cap. This stress concentration was then taken into account in developing the appropriate stress intensity factor for this idealized pit-crack geometry. By accounting for fatigue crack growth, the pit-crack model was then used to analyze fatigue strength data of hypervelocity impact-damaged windows to obtain the initial, effective circumferential crack size and the corresponding strength of the windows. The use of this pit-crack model in formulating a probabilistic strength prediction scheme for the windows of the Space Shuttle is discussed.