Detection and analysis of micro cracks in low modulus materials with thermal loading using laser speckle interferometry

Micro-defect detection is an essential field of failure analysis for the assessment and reliability of engineering materials under various loading conditions. This paper illustrates the effect of thermal loading on micro crack formation in certain low modulus materials used for aerospace applications and further analysis. The demands of increased performance of polymeric materials have created a need for new experimental techniques for accurate measurements of their structural defects through non-destructive ways. The present work employs one such optical non-destructive technique such as Laser Speckle Interferometry (LSI) to study the micro crack formation in the low modulus material used as an insulator in solid rocket motors. The low modulus material used is a nitrile based rubber compound which, when thermally loaded to a differential temperature in the range of 20°C to 28°C generates an optimum fringe pattern for the analysis of defects. Extremely small defects in the micrometer scale can be detected by analyzing the anomalies in the generated fringe pattern.