Materials Engineering Department
BS in Materials Engineering
Fracture toughness, or the ability of a material to resist fast fracture by crack propagation is an important property in the use of composite materials for structural designs. Other mechanical tests such as tensile, flexure, and compression are more established and practical than testing fracture toughness. Fracture toughness testing is less commonly used because it requires specific specimens and non-conventional test methods. In composite materials specifically, delamination of the plies of materials is tested for GIC and GIIC values to find the critical strain energy release rate of the two types of fracture modes. The common two tests for these values are the double cantilever beam (DCB) and the end-notched flexure (ENF) tests. Both tests require a complex loading scheme, compliance calibration, and Excel calculations to achieve the final maximum strain energy release rate values. This project aimed to simplify the preexisting testing methods and the calculations that follow. In an attempt to simplify these test methods, a USB microscope recorded the crack propagation throughout the laminate for the compliance calibration as either test method proceeded. DCB tests were run to determine average GIC values of 1318 J/m2 and 145 J/m2 for the AS4/ PEEK thermoplastic and TR50s/TC275 thermoset material, respectively. ENF tests were also run to find average GIIC values being 1428 J/m2 for the thermoplastic matrix material and 455 J/m2 for the thermoset matrix material. Along the way to these calculations, the USB microscope was found to be extensively useful in monitoring crack growth and a new Excel template for both tests was developed to make calculations simpler.