Three-Dimensional Finite Element Analysis of Free Edge Stresses and Delamination of Composite Laminates

Abstract

A 24-node, 64-degree-of-freedom, solid hexahedronal finite element is used to analyze the interlaminar free edge stresses and delamination of composite laminated plates. The difficulty due to the requirement of large storage space which is frequently encountered in the modeling of contoured delamination problems is resolved by using the preconditioned conjugate gradient method. One of the advantages of this method is that there is no need to store the fill-in elements in the stiffness matrix decomposition process, which leads to a significant reduction in storage space required, thereby making the numerical analysis of the complicated contoured delamination problem feasible as well as effective. To evaluate the accurateness of the present formulation, numerical algorithm and computer program, free edge stress analyses are performed for a [0/901 cross-ply and a [+ 45], angle-ply laminated plate. Both plates are subjected to an axial tensile strain loading. The present three-dimensional results are found to be in good agreement with those obtained using an alternative quasi-three-dimensional methods. To further demonstrate the applicability of the present development, the strain energy release rate of a [+25/90], graphite-epoxy rectangular laminated plate subjected to tensile strain is studied. Two initial delaminations are assumed to be located in the midspan of the two opposite free edges and also at the middle of the thickness. The delamination contour is assumed to be a straight line segment joined by two circular arcs. The strain energy release rates along the delamination front are calculated using the modified crack closure method. As a step beyond the solution using quasi-3D assumption, the present results show the non-uniform distribution of mode I strain energy release rate G1 along the boundary of the delamination front which fluctuates to a maximum value when approaching both ends at the free edge of the laminate.

Estimation of transverse/interlaminar stresses in laminated composites – a selective review and survey of current developments

“…The third layer quadrilateral element (LQ3) is of 24 nodes with 64 dof and improves upon the LQ2 element by allowing both terms in the transverse shear displacement expression to vary linearly through the layer thickness. Later Yang and He [85] used the LQ3 element for the analysis of free-edge stresses in cross-ply and angle-ply laminate. They used the preconditioned conjugate method to solve the system of linear equations.…”

Aeroelastic Control of Smart Composite Plate with Delaminations

“…It can be seen that maximum applied voltage is less than 80 volts. This figure also shows that the applied voltages to the actuators (1,2,5) and (3,4) are in the same phase. This combination of the control voltages can efficiently control the higher bending mode (second bending mode) which causes the model to flutter.…”

“…However, this displacement field does not necessarily satisfy the condition that the transverse shear stresses (s 4 and s 5 ), vanish at the top and bottom surfaces of the plate (z = ±h/2) as well as on the delamination interface surfaces (z = h 1 , Figure 1) in the delaminated region. That is, (4) in which the superscript r corresponds to either the nondelaminated region (u), or the regions above and below the delamination (d 1 and d 2 ), respectively. For orthotropic plates, these conditions are equivalent to the requirement that the corresponding strains be zero on these surfaces.…”

“…A significant amount of research has also been performed in modeling defects such as delamination in composites. Although three dimensional approaches [4,5] are more accurate than two dimensional theories [6][7][8][9], their implementation can be very expensive for practical applications. The layer-wise approach [10] is an alternative since it is capable of modeling displacement discontinuities.…”

Residual Stress Analysis and Expansion of Plastic Zone in Clamped Supported Aluminum Metal-Matrix Laminated Plates with a Circular Hole Under Transverse Loading

“…Linear or nonlinear finite element method can be used to analyze the laminated composites [11][12][13][14][15][16].…”