Crack Propagation for Glass Fiber Reinforced Laminates Containing Flame Retardant: Based on Single-Edge Tensile Loading

Research on crack propagation for fiber reinforced composites containing flame retardant is rare. The micro-cracks propagation is a reason for delamination and debonding failure of fiber reinforced composites. To study the crack propagation of continuous glass fiber reinforced epoxy resin laminates that contained ammonium polyphosphate flame retardant (GFRP-APP), the quasi-static single-edge tensile loading (SETL) experiments for the end-notched GFRP-APP specimens were carried out by MTS universal electronic testing machine. The crack propagation of the end-notched 90 degrees GFRPAPP specimen includes two types, both of which belong to opening type (mode I). Namely, one type is mode I multi-cracks propagation without preexisting crack, and the other is mode I fiber bridge propagation with preexisting crack. The intralaminar fracture toughness along fiber direction of GFRPAPP is approximately 4.2 N/mm, which is calculated by area method. The opening displacement-tensile force curves can be divided into three stages for 90 degrees GFRP-APP specimen without crack, i.e., crack gestation, crack birth and crack propagation. However, the 90 degrees GFRP-APP specimen with crack not contains the crack birth stage. Additionally, the microscopic morphology for the fracture face of pure epoxy resin and GFRP-APP, and the phase analysis for GFRP-APP were performed by scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). As a conclusion, the pores and interfaces in materials were the guiding factors of micro-crack propagation, and the ammonium polyphosphate flame retardant particle contributed extra interfaces.