Effect of strain rate and fibre rotation on the in-plane shear response of ±45° laminates in tension and compression tests

Abstract

This work focuses on the effect of strain rate and fibre rotation on the in-plane shear properties of composite laminates. The effect of fibre rotation on the measured shear properties, was for the first time experimentally quantified with the comparison between compression and tension tests of the ±45° laminate samples. Significant increase of shear strength and decrease of final failure strain was observed with the increase in strain rate from 5e-4 1/s to 1300 1/s. The nonlinear constitutive model was developed to simulate the large deformation process, in which the fibre orientation was updated as a function of the in-plane shear strain. The results of this investigation should motivate the updating of procedures for experimental characterization as well as analytical and numerical modelling of in-plane shear response of laminates.

Bridging mechanisms of through-thickness reinforcement in dynamic mode I&II delamination

“…Considering the fact that the peak forces in dynamic tests were underestimated due to inertia effect, the maximum bridging forces may increase with loading rate more significantly than shown in Fig.7b. The sharp drop after peak force is indicative of the fracture of the pin-composite bond, and the significant rate dependence of matrix dominated shear strength [31] is likely to be responsible for the higher of peak bridging force in dynamic tests. All Z-pins were pulled out gradually after this interfacial failure.…”

“…Micro cracks on the failure plane tend to be more closely spaced during dynamic fracture, and the size of shear cusps decreases due to the limited volume between neighbouring cracks [31]. This relatively smooth fracture surface may result in less frictional resistance at the pin-laminate interface.…”

Combined shear/tension testing of fibre composites at high strain rates using an image-based inertial impact test

“…where σ 12 l is the average shear stress over the angled section at x 0 (dashed line in figure 1), S is the surface area of the trapezoidal shape up to the angled section (shaded area in figure 1), l is the length of the angled section and a 1 S is the average acceleration over the trapezoidal area. Equation 4 can be evaluated at any angled section x 0 provided that the section does not intersect the impacted edge as this would introduce the contribution of the impact force F(t). The area S can be calculated for any valid angled section x 0 , using:…”

“…Current high strain rate data for the matrix dependent properties of composites has been obtained using the split-Hopkinson pressure bar (SHPB) [1][2][3][4][5][6] . The SHPB technique requires that several assumptions are satisfied in order to infer the material properties from the strain gauge measurements on the bars [7].…”

“…Consequently the strain rates in [5] were limited to below 500 s −1 . * e-mail: l.c.fletcher@soton.ac.uk Off-axis specimens have been used in the SHPB apparatus to study the strain rate dependence of the shear properties of composites [2][3][4]8]. These studies generally focus on combined compression/shear testing as this removes experimental difficulties associated with gripping the specimen.…”