A novel specimen design to establish the forming limit diagram (FLD) for GFRP through stamping test

Abstract

Inspired by metal forming tests, the conventional forming limit diagram (FLD) was employed to characterize the forming properties of the Glass Fiber Reinforced Polypropylene (GFRP) composite in this study. The strain history of GFRP specimens was captured by using a 3D digital image correlation (DIC) system. Since the conventional metal FLD is established by major and minor strains only, which is inadequate to characterize the formability of different components in the pre-consolidated woven composites. Therefore, this study proposes a new notch design, where the specimens have two long notches with different aspect ratios on the both sides, to ensure that the failure is dominated by fiber breakage mode while retaining the fiber continuity in specimens. For comparison, the conventional hourglass specimens and the newly-proposed notch specimens with different widths were both tested through a series of stamping experiments to investigate the formability of the GFRP materials. The equivalent fiber strains based FLD from the conventional narrow hourglass specimens with 45°,-45° shows an abnormal value of equivalent fiber strain around 40% in the shear deformation region, which was far beyond the tensile limit of glass fibers. On contrary, the FLD from the proposed notch specimens presented a limiting strains around 5%, involving all possible deformation modes. Thus, the FLD of the notch specimens was established in the form of parallel line here, which can be used as a criterion to characterize the formability of GFRP in which the fiber breakage was a dominant failure mode. Note that this criterion takes into account the influence of different components on the formability of GFRP and combined deformation history with failure mechanism, implying more suitable for GFRP. This study provided an effective way to establish the design criteria and FLD for other woven pre-consolidated GFRP materials.