Analysis on the detection sensitivity of laser shearography of foam sandwich structure under vacuum loading

In order to explore the detection sensitivity of laser shearography of foam sandwich structure under vacuum loading, two types of foam sandwich structure bonding defect test blocks were designed and prepared. The defects were debonding defects between skin and foam and debonding defects between foam and matrix. Laser shearography was performed on two different types of defect specimens using different vacuum pressure differentials. The results showed that the laser shearing technology could effectively detect the bonding quality between skin and foam, and between foam and matrix. For the bonding quality of PMI foam and quartz fiber skin, when the skin thickness was about 1 mm and the vacuum pressure difference reached 6 kPa, the debonding (length×width) defect of 10 mm×10 mm could be detected. For the bonding quality of PMI foam and matrix, when the thickness of foam was 5 mm and the vacuum pressure difference reached 5 kPa, the debonding defect of 10 mm×10 mm could be detected. When the thickness of foam was 20 mm, the detection sensitivity decreased significantly, and only when the vacuum pressure difference reached 9 kPa the debonding defect of 30 mm×30 mm could be detected. If the vacuum pressure difference continued to increase, the noise interference in the speckle image would increase, seriously affecting the recognition of defects.