Effect Of Ply Thickness Research Articles

Damage characterization in thin-ply composite laminates under out-of-plane transverse loadings

Composite laminates with thin-ply layers are expected to exhibit superior damage resistance to the standard composite laminates. This study investigated the damage characteristics of carbon fiber/toughened epoxy thin-ply laminates subjected to transverse loadings. Quasi-isotropic laminates were prepared using both standard prepregs and thin-ply prepregs in order to examine the effect of ply thickness on the damage accumulation processes. Clear difference on damage accumulation process between standard laminates and thin-ply laminates was identified; fiber fractures were susceptible to formation in thin-ply laminates. Finally, the reason of the difference on damage process was investigated using finite element analyses, and it was clarified that the accumulated delamination position has a significant effect on the fiber fractures during the indentation.

Evolution of ply cracks in multidirectional composite laminates

This paper treats evolution of ply cracks in multidirectional composite laminates subjected to a quasi-static tensile load in the longitudinal direction. Starting with pre-existing ply cracks in off-axis plies, the formation of additional cracks is analyzed by an energy-based approach. A critical laminate energy parameter associated with formation of these cracks is defined and is evaluated using experimental data for a reference cross-ply laminate. The modeling approach requires crack surface displacements, which are calculated by a three-dimensional finite element (3-D FE) analysis performed on a suitable representative volume of the given cracked laminate. The model predictions agree well with experimental data for [ 0 / ± θ 4 / 0 1 / 2 ] s and [ 0 / 90 / ∓ 45 ] s laminates. A parametric study is conducted to evaluate effects of ply thickness and ply stacking sequence on damage evolution in [ 0 m / 90 n / ∓ θ p ] s laminates.

Investigation of the Free Edge Interlaminar Stresses Dependence on the PLY Thickness and Orientation

Among the principal damage modes in composite laminates, is delamination. Design details, such as free, straight or curved, edges, induce large local out-of-plane loads, generating interlaminar stresses. In the present work, the effect of ply thickness and the angle between two adjacent layers on the interlaminar stresses developed at the vicinity of straight and curved free edges in composite laminates under thermomechanical loading is examined. The results are obtained by the application of a 3-dimensional Finite Element Analysis.

Prediction of Delamination Growth and Opening Near Intersection of Transverse Matrix Cracks and Delamination

The use of advanced composite materials for cryogenic fuel tanks reduces the mass of the structure but microscopic damage can cause fuel leakage. The amount of leakage depends on the connectivity of the damage and crack opening displacements. In this paper, the damage growth and the opening near the intersection of transverse matrix cracks (TMC) and a delamination are discussed. Three-dimensional finite element analysis (FEA) was used to analyze cross-ply and angle-ply graphite/epoxy laminates. The strain energy release rates (SERR) along the delamination front were calculated based on the virtual crack closure technique. The strain energy release rate has a very large variation along the delamination front and is sensitive to a variety of geometric and load parameters. There is an extreme gradient of the strain energy release rate near the intersection of the delamination front and the TMC. Based on the SERR results, likely delamination shape and size for cross- and angle-ply laminates were determined. Prediction of the likely shape and size will help one to understand the conduit for leakage. The opening near the intersection of the TMC and the delamination was calculated. The effect of ply thickness on the SERR and the opening is also discussed.

Effects of layup angle and ply thickness on matrix crack interaction in contiguous plies of composite laminates

Abstract Matrix microcracking behaviors in constrained plies adjacent to a cracked ply are highlighted. Quasi-static tension tests of [0/ θ /90]s and [0/ θ 2 /90]s laminates with θ =30, 45 and 60° were conducted in order to investigate effects of the ply thickness and the intersecting angle of the cracked plies on the crack development in the adjacent plies. Matrix cracks developed along the fiber direction were the dominant damages observed in 30° plies of [0/ θ 2 /90]s laminates, whereas a high density form of matrix microcracking was mainly observed in θ ° plies of the other laminates. The difference of the matrix cracking behaviors in the adjacent plies among laminate configuration is characterized by calculating energy release rates associated with θ ° ply crack growth in the presence of 90° ply cracks using finite element analysis. It is clarified that microcracking in plies adjacent to a cracked ply is susceptible to formation in the cases of thin θ ° ply thickness and small intersecting angles of the cracked plies.

Evaluation of long-term durability in high temperature resistant CFRP laminates under thermal fatigue loading

Thermal fatigue tests were conducted on high temperature resistant carbon fiber reinforced plastics cross-ply laminates to evaluate microscopic damage progress which affects macroscopic mechanical behavior of the laminates. Materials system used were thermoplastic polyetheretherketone based, AS4/PEEK and thermoset bismaleimide based, G40-800/5260. Several types of laminate configuration were used to clarify the effect of ply thickness on microscopic damage progress. Microscopic damages were observed using optical microscopy and soft X-ray radiography. Energy release rate associated with transverse cracking was calculated using variational analysis. The modified Paris law was used to predict transverse cracking. From comparison to mechanical fatigue test results, it is clarified that transverse crack accumulation rate was larger under thermal fatigue loading at same energy release rate range due to the dependence of the fracture toughness on temperature.

Experimental and analytical characterization of transverse cracking behavior in carbon/bismaleimide cross-ply laminates under mechanical fatigue loading

Abstract Transverse cracking behavior in high temperature bismaleimide-based carbon fiber reinforced plastics (CFRP) laminates under fatigue loading was observed. Three types of cross-ply laminate, [0/90 2 /0], [0 2 /90 3 /0 2 ] and [0 2 /90 4 /0 2 ], were tested to study the effect of ply thickness. Damage observation was conducted using two methods. Optical microscopy and soft X-ray radiography were used for edge and internal damage observation, respectively. Variational approach was used to derive the energy release rate associated with transverse cracking. Multiplication of transverse cracks was modeled based on modified Paris-law approach.

多方向強化複合材料積層板の層内樹脂割れ解析手法の提案

A new analytical method for calculation of transverse lamina cracking in multidirectionally laminated composites has been proposed in the present paper. Both energy balance criterion and stress criterion have been applied simultaneously for evaluation of initiation and extension of transverse lamina cracks with special consideration of residual stress. A micro model of [ θ/90 ] s laminate with a transverse crack in 90 deg. layer has been numerically analyzed and the results have been applied to evaluate the stress distribution and the stiffness reduction of a multidirectional laminate. Mixed mode fracture criterion based on Mode I and II energy release rates and Hashin's stress criterion were used to predict the initiation and extension of transverse lamina cracks in the multi layers. The analytical results were compared with experimental results of the cross-plied and quasi-isotropic laminates. Effects of ply thickness and stacking sequence on behavior of transverse lamina cracking were well explained by the present method. The present method has been expected to be a useful analytical tool for damage tolerance design of laminated composite structures.

Damage-mechanics analysis of matrix cracking in cross-ply CFRP laminates under thermal fatigue

Microscopic damage development in high-temperature CFRP, AS4/PEEK cross-ply laminates under thermal cycling has been investigated. Two types of laminate configurations were tested to discuss the effect of ply thickness. Matrix cracks initiated in both 0 and 90° plies and the number of cracks increased as the number of cycles increased. The number of cracks in the stable growth region were twice as great as in a 90° ply. To discuss these experimental results, a damage-mechanics analysis was used to evaluate the energy-release rate associated with cracking and thermal residual stress in cracked ply. It was clear that a modified Paris law approach is effective for thin plies and an average-stress approach is effective for thick plies.

Experimental characterization of microscopic damage progress in AS4/PEEK cross-ply laminates under thermal cycling

Microscopic damage progress in high temperature CFRP cross-ply laminates under thermal cycling was investigated. Two types of laminate configuration were tested to study the effect of ply thickness. Matrix cracks initiated in both 0° and 90° plies and the number of cracks increased as the number of cycles increased. The saturated number of cracks in 90° plies was twice as large as that in 0° plies. To discuss these experimental results, shear-lag analysis was used to evaluate both the energy release rate associated with matrix cracking and the thermal residual stress in cracked plies. It was implied that the effect of the maximum thermal residual stress as well as the energy release rate range were significant in the quantitative evaluation of the matrix cracking induced by the thermal cycling.

Effect of Ply Thickness and Fibre Orientation on Delamination Initiation in Broken Ply Composite Laminates

The present study examines the delamination initiation at the interface of broken and continuous plies in case of GR/E and GL/E laminates with broken central plies. A full 3D FE analysis has been performed with each layer of the laminate modelled as homogenous and orthotropic. The interface between the broken and continuous plies has been modelled with a thin resin rich layer. Eight-noded isoparametric layered elements have been used to model the laminate specimen. Also, 3D contact elements are used to prevent the interpenetration of delaminated faces at the interface. Based on the results of 3D FE analysis, GI, GI, and GI,, have been calculated at the delamination front using Irwin's Crack Closer Integral. It has been observed that the delamination initiation is a mixed mode phenomenon even in the case of uniaxial loading. Brewer and Lagace's Quadratic Stress Criterion has been used in conjunction with Linear Elastic Fracture Mechanics (LEFM) to calculate the delamination initiation strain and the critical strain energy release rate (Gc). The effects of various factors such as ply thickness, fiber orientation, resin stiffness on Gc have been studied for GR/E and GL/E laminates having broken central plies.

Effect of Ply Thickness on Fracture of Notched Composite Laminates

The effect of ply thickness on unnotched and notched strength of fiber-dominated laminates is investigated. Experiments are conducted to examine the effect of subcritical damage on fracture toughness of AS4/3501-6 graphite/epoxy laminates with cross-ply and quasi-isotropic configurations. It is observed that ply thickness has a significant effect on the notched behavior of cross-ply laminates but less so for quasi-isotropic laminates. The experimentally observed crack-tip damage in the form of axial splitting in the 0-deg plies and delamination is modeled by a two-dimensional finite element analysis using Mindlin plates, and the criterion that controls damage (split) growth is established. The role of such damage on crack-tip stress distribution is investigated, and inferences are drawn to determine the circumstances under which a fracture mechanics type of failure model can be used to predict the notched response of these laminates.

Effect of ply thickness on fracture of notched composite laminates

Effect of ply thickness on fracture of notched composite laminates

The behaviour of cross-ply hybrid matrix composite laminates: Part 1: Experimental results

Two types of cross-ply laminate have been made from prepreg: (a) hybrid matrix laminates consisting of longitudinal plies of glass fibres in epoxy resin and transverse plies of glass fibres in epoxy resin/urethane elastomer blend; and (b) uniform matrix laminates with the same resin in both the longitudinal and transverse plies. The presence of the urethane in the transverse plies increases the applied strains necessary for the initiation and development of transverse cracking during the extension of both hybrid matrix and uniform matrix laminates. The effect is greater with increasing amounts of urethane. The cracking data, stress/strain behaviour, acoustic emission response and ply thickness effects on crack development are discussed in the light of existing theories concerning transverse cracking.