Woven Composite Plates Research Articles

Polymer Matrix Woven Fabric Composites Subjected to Low Velocity Impact: Part III—Effect of Incident Impact Velocity and Impactor Mass

The studies have been carried out on the damage initiation behavior of polymer matrix woven fabric composite plates subjected to a transverse central low velocity point impact load. Specifically, the effect of incident impact velocity and impactor mass for the same incident impact energy on the impact behavior has been investigated with a square plate of 150 mm × 150 mm × 6 mm. The material systems considered are: E-glass/epoxy and T300/5208 carbon/epoxy woven fabric composites. Inplane failure of the layers in the form of matrix cracking / lamina splitting and delaminations were the primary objectives of the study. The studies have been carried out using an in house Finite Element Analysis code. The inplane failure functions and the interlaminar failure functions have been predicted using quadratic failure criteria. It is observed that the use of incident impact energy alone as a parameter to characterize the impact behavior is inadequate. Instead, the effect of both incident impact velocity and impactor mass should be considered separately.

Fatigue behavior of 3D multi-layer angle interlock woven composite plates

This study was aimed at investigating the fatigue behavior of three-dimensional (3D) multi-layer angle interlock woven composite plates. Tensile cyclic stress was applied to the specimen along the weft yarn direction. Unnotched three-layer and five-layer plates were used in this work in order to compare their fatigue properties and damage processes. The effect of a center hole on the fatigue behavior was also investigated by using notched three-layer and five-layer plates. The experimental results showed that the three-layer specimen exhibited higher static ultimate tensile strength (UTS), but lower fatigue limit strength or higher fatigue sensitivity than the five-layer specimen for both the unnotched and notched plates. Normalized S/N curves of the unnotched and notched specimens, the maximum cyclic stress being divided by the appropriate UTS, were observed almost to coincide on a single line for both the three-layer and five-layer plates. This indicated that a center hole did not affect the fatigue sensitivity of these plates. Metallography was employed to study the microscopic fatigue damage process. According to the observations, the fatigue process could be divided into five stages. The fatigue damage mechanism primarily involved transverse cracks in the warp yarns, debonding between the warp and weft yarns, debonding extension and deflection into the matrix, and weft fiber breakage.

Numerical and experimental determination of in-plane elastic properties of 2/2 twill weave fabric composites

This paper presents the in-plane elastic properties of 2/2 twill weave, T300 carbon/epoxy, woven fabric composite plates, obtained by both finite element analysis and experiments. A micromechanical, three-dimensional (3D) finite element model of the single layer unit cell of a 2/2 twill weave fabric composite is built, and a homogenization process is implemented. A unit cell is chosen such that it encloses the characteristic periodic repeat pattern in the fabric weave. Detailed geometry together with construction procedures for this new model are developed by using ANSYS Parametric Design Language (APDL). In this respect, the scope for altering the weave and yarn parameters is facilitated. Standard tensile and rail shear tests with modifications are performed for this kind of woven fabric composite. Elastic mechanical properties determined by experiments are presented, and the finite element model is verified. Satisfactory correlation between the predicted and experimental results are obtained.

Material-smart analysis of textile-reinforced structures

A methodology of the material-smart structural analysis proposed in this paper links micromechanical modelling of a complex fibrous reinforcement to a three-dimensional analysis of a structural part. The geometry of the reinforcing textile varies throughout the entire volume of a part, thus its stiffness characteristics are dependent on the spatial coordinates. The methodology addresses this by determining elastic properties of the textile composite in a local region (a ‘meso-volume’) through a processing science model. The ‘global’ structural analysis incorporates a variational formulation of the three-dimensional elasticity problem for an inhomogeneous anisotropic body, a division of the body into meso-volumes having individual elastic properties, further partition of each meso-volume into sub-elements, and application of special deficient spline functions for a local approximation of displacements with respect to all three coordinates. All the necessary external and internal boundary conditions can be satisfied with any prescribed accuracy in the proposed numerical procedure. Several numerical examples for woven and braided composite plates are considered to illustrate the applicability of the methodology and the calculational procedure.

Notched Strength and Fracture Criterion in Fabric Composite Plates Containing a Circular Hole

The effects of the hole size and the specimen width on the fracture behavior of several woven fabric composite plates are experimentally investigated in tension. It is shown in this paper that the characteristic length ( d o) in the Point Stress Criterion (PSC) depends on the hole size and the specimen width. A modified PSC for predicting the notched strength is proposed. An excellent agreement is found between the experimental results and the analytical predictions using the modified PSC. When the unstable fracture occurred, the equivalent critical crack length ( a c) corresponding to the damage zone size is about twice the characteristic length. The characteristic length decreases with an increase in the notched strength. The critical energy release rate ( G c) corresponding to the unstable fracture criterion is independent of the hole size for the same specimen width. G c increases with an increase in the specimen width. These results can be explained by the correlation between the G c and the notch sensitivity factor (k).

Three-dimensional analysis of anisotropic spatially reinforced structures

The material-adaptive three-dimensional analysis of inhomogeneous structures based on the mesovolume concept and application of deficient spline functions for displacement approximations is proposed. The general methodology is demonstrated on the example of a brick-type mosaic parallelepiped arbitrarily composed of anisotropic mesovolumes. A partition of each mesovolume into sub-elements, application of deficient spline functions for a local approximation of displacements and, finally, the use of the variational principle allows one to obtain displacements, strains and stresses at any point within the structural part. All of the necessary external and internal boundary conditions (including the conditions of continuity of transverse stresses at interfaces between adjacent mesovolumes) can be satisfied with requisite accuracy by increasing the density of the sub-element mesh. The application of the methodology to textile composite materials is described. Several numerical examples for woven and braided rectangular composite plates and stiffened panels under transverse bending are considered. Some typical effects of stress concentrations due to the material inhomogeneities are demonstrated.