The defects in thick S2-glass/polyester woven composite laminates and their effect on the mechanical properties were studied using ultrasonic tests. Moreover, a suitable NDT(Non-Destructive Testing) parameters proper to detect delaminations and void contents were proposed for thick laminates. The UT(Ultrasonic Test) was chosen to be a proper method to detect delaminations and void contents simultaneously using the reflection and attenuation of ultrasonic waves. We used a 5 MHz probe made by Krautkramer to detect the through-the-thickness location of delaminations using A-scan method and showed the size and through-the-width location of delaminations using C-scan method.
These defects degrade the mechanical strength of thick composite laminates especially the matrix-dominant properties. The result of the short-beam test with the beam that has the artificial defects shows that the interlaminar shear strength was degraded by 7.4% for 12.5%-delaminated beam and 19.8% for 25%-delaminated beam. In the case of compressive test, void contents of the specimen was 5.04% and compressive strength was degraded by 9.5%.