Abstract
The strain rate-dependent behavior of a unidirectional non-crimp fabric (UD-NCF) carbon fiber/snap-cure epoxy composite loaded along the transverse direction under quasi-static and dynamic conditions was characterized. Transverse tension and compression tests at quasi-static and intermediate strain rates were performed using hydraulic testing machines, while a split Hopkinson pressure bar (SHPB) apparatus was used for transverse compression tests at high strain rates. A pulse shaper was used on the SHPB apparatus to ensure dynamic equilibrium was achieved and that the test specimens deformed homogenously with a nearly constant strain rate. The transverse tensile strength at a strain rate of 16 s−1 increased by 16% when compared to that at quasi-static strain rates, while distinct localized fracture surface morphology was observed for specimens tested at different strain rates. The transverse compressive yield stress and strength at a strain rate of 325 s−1 increased by 94% and 96%, respectively, when compared to those at quasi-static strain rates. The initial fracture plane orientation for the transverse compression tests was captured with high-speed cameras and found to increase with increasing strain rate. The study provides an important data set for the strain rate-dependent response of a UD-NCF composite material, while the qualitative fracture surface observations provide a deeper understanding of the failure characteristics.
Highlights
Composite materials comprising heavy-tow non-crimp fabric (NCF) reinforcements are increasingly considered for use in primary load-bearing structures due to their excellent specific mechanical properties and relatively low cost when compared to other liquid composite molded materials reinforced with woven or braided fabrics
High strain rate transverse compression tests were performed on a compression split Hopkinson pressure bar (SHPB) apparatus, which consisted of a striker bar, incident bar, and transmitted bar (Figure 5)
Hydraulic testing frames were used for tests conducted under quasi-static and intermediate strains rates, while a split Hopkinson pressure bar (SHPB) apparatus was used for high strain rate tests
Summary
Composite materials comprising heavy-tow non-crimp fabric (NCF) reinforcements are increasingly considered for use in primary load-bearing structures due to their excellent specific mechanical properties and relatively low cost when compared to other liquid composite molded materials reinforced with woven or braided fabrics. Schaefer et al [4] studied the transverse tensile strain rate-dependent response of IM7–8552 (58% fiber volume fraction), a toughened carbon/epoxy system, and reported a slight increase in the ultimate strength and strain-to-failure. Schaefer et al [4] observed an increase in the transverse compressive strength and modulus with the increase in strain rate for IM7/8552; a noticeable decrease in the strain-to-failure was reported. Yokoyama et al [7] found a significant increase in the transverse compression strength and elastic modulus of the carbon fiber/epoxy material system T700/2521 (65% fiber volume fraction); a significant decrease in the strain-to-failure was observed, which contradicts the results reported in [6]. The present work aimed to characterize the strain rate-dependent behavior of a UDNCF carbon fiber/snap-cure epoxy composite material manufactured using a high-pressure resin transfer molding (HP-RTM) process. The current study addresses a major gap in the literature by characterizing a high-performance automotive NCF composite for the first time, while establishing a suitable dynamic testing protocol
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