LAUSR

Abstract Ammonium polyphosphate (APP) is one of the most widely used halogen-free flame retardant, added in various resins to improve the fire properties, such as flame and smoke spread ratings and LOI, of fiber-reinforced polymer (FRP) composites. This paper experimentally investigates the effects of using APP, as a fire-retardant filler, on mechanical properties (i.e. ultimate tensile, flexural, and bond strength) of glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP) composites. Based on two fiber types (i.e. carbon and glass) and three different APP mass fractions in resin (i.e. 0, 20, and 40% of total weight of matrix), six sets of specimens were prepared for each test (i.e. tensile, flexural, and lap shear) and they were tested at ambient and elevated temperatures ranging from 25 to 500 °C. For each specimen, five repetitions were prepared to ensure reliable results, and therefore a total of 660 specimens were tested. The SEM and ANOVA analyses were also carried out. In general, the test results indicated that as the exposure temperature increased, the mechanical strength of specimens decreased significantly with loses up to 95%. However, the strength degradation rate of APP filler-containing composites was considerably less than those of their filler-free counterparts. Based on the experimental results three novel empirical models were developed to predict the mechanical strength retention of different composites.