Behavior Of Cross-ply Laminates Research Articles

Describing the Flexural Behaviour of Cross-ply Laminates Under Cyclic Fatigue

The objective of this work is to derive modelling of the fatigue behaviour of cross-ply laminates from the experimental results obtained in the case of three-point bending tests. Modelling the fatigue behaviour is based on the stiffness reduction of test specimens. Firstly, experimental results are described using interpolation functions. Then, the characteristic coefficients of these functions are studied as function of the laminate properties and loading conditions. This approach allows to predict the fatigue life of composite laminates while avoiding a large number of fatigue tests. Wohler curves are used to compare the experimental and analytical results, and a good agreement is found between the results. Next, a simple approach is considered to define a damage parameter. It is based on the analogy between the mechanical behaviour and the fatigue damage evolution of composite laminates during fatigue tests. The developed models are applied to analyse the influence of constituents on the fatigue behaviour and damage development of composite materials under fatigue loading.

Flexural Fatigue Behavior of Cross-Ply Laminates: An Experimental Approach

Within an experimental approach we describe the mechanical behavior of different resin-epoxy laminates reinforced with cross-ply Kevlar and glass fibers under conditions of static and cyclic three-point bending. In static tests, we consider the effect of stacking sequence, the thickness of 90°-oriented layers, reinforcement type on the mechanical behavior of laminates under loading and on realization of various damage modes leading to rupture. Cyclic loading studies have been performed in two steps. In the first stage, we inquire into the dependence of the behavior and durability of four glass fiber-reinforced laminate-types on the stacking sequence; the second stage is devoted to studying the dependence of cyclic strength and fatigue behavior of laminates on the reinforcement type. Fatigue tests are carried out in load-control regime for glass and hybrid (Kevlar + glass) fiber laminates. Fatigue curves are constructed in coordinates “stress – number of cycles until fracture” from the criteria corresponding to a drop in stiffness by 5 and 10%. Analysis of the results obtained permits evaluation of the effect of the stacking sequence and the reinforcement type on the behavior of cross-ply laminates in cyclic loading. The presence of Kevlar fibers accounts for nonlinear behavior of laminates in static tests and for low cyclic strength in fatigue tests under three-point bending.

Modeling a creep behavior of cross-ply laminates with progressive transverse cracking

A creep model is established for a cross-ply laminate in which the transverse crack density is increasing. Viscoelasticity theory and shear lag analysis are employed for this creep model and the transverse crack density is expressed as a function of both time and stress, based on a probabilistic failure model. The creep compliance of the cross-ply laminate is determined from creep tests of [90°8] specimens. The creep strain and transverse crack density of [0/90°3]s cross-ply laminates are measured during the creep tests and predicted creep strains using the present model agree well with the experimental ones.

Interlayer shear slip theory for cross-ply laminates with nonrigid interfaces

In the conventional analysis for laminated composite materials, the composite interface is always assumed to be rigidly bonded. However, due to the low shear modulus and poor bonding, the composite interface can be nonrigid. Based on the previously developed inter laminar shear stress continuity theory and a linear shear slip law, this study presents a so-called interlayer shear slip theory to investigate the effect of the interfacial bonding on the behavior of cross-ply laminates. Closed-form solutions for the cases of the cylindrical bending of long composite strips with [0/0] and [0/90] sequences are obtained. Numerical results for the laminates with different length-to-thickness ratios are presented. They reveal that the interlayer shear slip theory is valid for cross-ply laminates with rigid and nonrigid interfaces. It is also concluded from this study that at some special locations, namely, singular points, the transverse shear stress or in-plane normal stress remains insensitive to the condition of interfacial bonding.

Non-linear vibrations of simply supported rectangular cross-ply plates

A method of direct numerical integration of the frequency-ratio expression is proposed to study the non-linear free vibration behaviour of rectangular cross-ply laminates. The proposed method, even with single-term approximations for the admissible functions, yields results that agree very well with the existing perturbation solutions. Non-linear behaviour of the cross-ply laminates is also studied with the harmonic oscillations assumption, by using the conservation of energy and the modal equation. The results are found to be lower and upper bounds to those obtained from the direct numerical integration method. It is also observed that the arithmetic mean of the two solutions with the harmonic oscillations assumption matches very well with that of the direct numerical integration method. Non-linear vibration characteristics are obtained for several configurations of cross-ply plates. Results for orthotropic and isotropic plates are also obtained as special cases.