SHEAR CRACKS IN FOAM CORE SANDWICH PANELS - NONDESTRUCTIVE TESTING AND DAMAGE ASSESSMENT

Shear cracks in the core of foam core sandwich panels may be found as a result of overloading, impact, or fatigue. These are subsurface flaws and are therefore hard to find nondestructively and may act as initiation points for final failure. Hence, it is of vital interest to detect these flaws and compute their influence on the load-bearing capacity of the panel. In the present paper, different types of shear cracks are simulated in foam core sandwich panels. They are inspected with a thermal nondestructive testing (NDT) method based on an infrared (IR) detector. It is found that all types of simulated cracks can be satisfactorily detected. An engineering approach is used to estimate the residual strength of the panels caused by the shear cracks. The panels are analyzed with the finite element (FE) method to compute fracture mechanics parameters. By using fundamental material data, such as the fracture toughness, the strengths of the panels in presence of the cracks are predicted. Finally, all panels are tested in four-point bending, and it is found that the experimentally measured and the predicted strengths agree well.