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1.
In the present study, the initiation and evolution of the interphase damage and their influences on the global stress-strain relation of composite laminates are predicted by finite element analysis on a micromechanical unit cell model. A thin layer of interphase elements is introduced and its stress-strain relation is derived based on a cohesive law which describes both normal and tangential separations at the interface between the fiber and matrix. In addition, a viscous term is added to the cohesive law to overcome the convergence difficulty induced by the so-called snap-back instability in the numerical analysis. The matrix behavior is described by a recently developed nonlinear viscoelastic constitutive model. As application examples, glass fiber/epoxy unidirectional laminates under off-axis loadings are analyzed. One-quarter of the unit cell is used in the analysis accounting for the geometrical symmetry of the model, and the corresponding periodic boundary conditions for combined global shear and normal loading are derived. Results show that the initiation and evolution of the interphase damage can be well simulated and the predicted global stress-strain responses are in good agreement with the experimental results. 相似文献
2.
A new discrete layer finite element (DLFE) is presented for electro-mechanically coupled analyses of moderately thick piezoelectric adaptive composite plates. The retained kinematics is based on layer-wise first-order shear deformation theory, and considers the plies top and bottom surfaces in-plane displacements and the plate transverse deflection as mechanical unknowns. The former are assumed in-plane Lagrange linear, while the latter is assumed in-plane full (Lagrange) quadratic; this results in a nine nodes quadrangular (Q9) DLFE. The latter is validated in free-vibrations, first numerically against ANSYS three-dimensional piezoelectric finite elements for a cantilever moderately thick aluminum plate with two co-localized piezoceramic patches, and then experimentally against a free quasi-isotropic transverse composite thin plate with four piezoceramic patches. The obtained short-circuit and open-circuit (OC) frequencies were satisfactory for both benchmarks, while the post-treated modal effective electromechanical coupling coefficients agreed well with ANSYS results (first benchmark) but only fairly with the experimental ones (second benchmark). Once validated, the Q9-DLFE was used to assess numerically the equipotential (EP) physical condition influence on the OC sensed electric potential; for this purpose, the above first benchmark, but with the top piezoceramic patch only, was finally analyzed. It was found that the EP condition homogenizes and lowers the sensed potential on the OC electrode. 相似文献