Analysis on the turning point of dynamic in-plane compressive strength for a plain weave composite

Experimental investigations on dynamic in-plane compressive behavior of a plain weave composite were performed using the split Hopkinson pressure bar. A quantitative criterion for calculating the constant strain rate of composites was established. Then the upper limit of strain rate, restricted by stress equilibrium and constant loading rate, was rationally estimated and confirmed by tests. Within the achievable range of 0.001/s-895/s, it was found that the strength increased first and subsequently decreased as the strain rate increased. This feature was also reflected by the turning point(579/s) of the bilinear model for strength prediction. The transition in failure mechanism, from local opening damage to completely splitting destruction, was mainly responsible for such strain rate effects. And three major failure modes were summarized under microscopic observations: fiber fracture, inter-fiber fracture, and interface delamination. Finally, by introducing a nonlinear damage variable, a simplified ZWT model was developed to characterize the dynamic mechanical response. Excellent agreement was shown between the experimental and simulated results.

Acoustic emission characterization methods of damage modes identification on carbon fiber twill weave laminate

In order to get a deep understanding of composite failure mechanisms, the new advanced signal processing methodologies are established for the analysis of the large number of acoustic emission (AE) data obtained from the quasi-static tension test of carbon fiber twill weave composite. For this purpose, AE signals have been collected and post-processed for tension test, and are analyzed with three signal processing methods: Empirical Mode Decomposition (EMD), Hilbert-Huang Transform (HHT) and modified energy entropy algorithm. AE signals can be decomposed into a set of Intrinsic Mode Functions (IMF) components, results from this study reveal that the peak frequency of IMF components based on Fast Fourier Transform (FFT) corresponds to different damage mechanisms of composite. HHT of AE signals can clearly express the frequency distribution of IMF component in time-scale in different damage stages, and can calculate accurate instantaneous frequency for damage modes recognition. The energy entropy based on EMD is introduced to act as a new relevant descriptor of composite damage modes in order to improve the characterization and the discrimination of the damage mechanisms.

Analytical Solution for Predicting In-plane Elastic Shear Properties of 2D Orthogonal PWF Composites

This paper proposes a new analytical solution to predict the shear modulus of a two-dimensional（2D） plain weave fabric（PWF） composite accounting for the interaction of orthogonal interlacing strands with coupled shear deformation modes including not only relative bending but also torsion,etc.The two orthogonal yarns in a micromechanical unit cell are idealized as curved beams with a path depicted by using sinusoidal shape functions.The internal forces and macroscopic deformations carried by the yarn families,together with macroscopic shear modulus of PWFs are derived by means of a strain energy approach founded on micromechanics.Three sets of experimental data pertinent to three kinds of 2D orthogonal PWF composites have been implemented to validate the new model.The calculations from the new model are also compared with those by using two models in the earlier literature.It is shown that the experimental results correlate well with predictions from the new model.