The effect of pre-heat temperature on the formability of a glass-fibre/polypropylene and steel-based fibre–metal laminate

This paper presents an experimental and numerical investigation into the effect of pre-heat temperature on stretch forming of a fibre metal laminate (FML) comprised of alternating layers of steel and woven (0/90) glass-fibre polypropylene in a 2:1 configuration. Hourglass sample geometries were formed in an open die and real-time photogrammetry was used to measure the evolution of strain fields over the lower surface of each sample. The sample pre-heat temperatures were 140 °C (above the crystallization temperature) and 170 °C (melt temperature of polypropylene). For each temperature, a forming limit curve (FLC) was determined based on ISO 12004-2:2008 and compared to the FLC of the steel skin. The experimental results demonstrate that pre-heat temperature of 140 °C enables sufficient matrix flow such that the formability of the FML is comparable to the formability of the steel sheet. Furthermore, the FML stretch-forming process was simulated using commercial finite element software, LSDYNA, with an explicit solver. The glass-fibre polypropylene material behaviour was simulated with a curve fitting technique of material characterization test results. A user-defined subroutine (UMAT) was developed for the composite material modelling through all process temperatures. The simulation, justified with experiments, provided a numerical model of the hybrid material to utilise for forming complex shapes.