Showing papers on "Composite laminates published in 2008"

Variable stiffness composite panels : Effects of stiffness variation on the in-plane and buckling response

Abstract: Descriptions of fiber orientation variation for flat rectangular composite laminates that possess variable stiffness properties are introduced. The simplest definition employs a unidirectional variation based on a linear function for the fiber orientation angle of the individual layers. Analyses of variable stiffness panels for in-plane and buckling responses are developed and demonstrated for two distinct cases of stiffness variations. The first case assumes a stiffness variation in the direction of the loading, and numerical results indicate small improvements in buckling load for some panel configurations due to favorable distribution of the transverse stresses over the panel planform. The second case varies the stiffness perpendicular to the loading, and provides a much higher degree of improvement due to the re-distribution of the applied loads. It is also demonstrated that the variable stiffness concept provides a flexibility to the designer for trade-offs between overall panel stiffness and buckling load, in that there exist many configurations with equal buckling loads yet different global stiffness values, or vice versa.

Porosity reduction using optimized flow velocity in Resin Transfer Molding

Abstract: Liquid Composite Molding (LCM) regroups a number of well known manufacturing techniques of polymer composites based on resin injection through fibrous reinforcements. LCM processes such as RTM (Resin Transfer Molding) have been increasingly used to manufacture parts for a wide range of industrial applications and were shown to be cost effective in the low to medium range of volume production. To improve the performance of these processes, more scientific knowledge of the impregnation phenomena is required. In LCM processing, injection pressure dominates the impregnation of the fibers. In RTM, the formation of macro/micro-voids entrapped between or within the fiber tows is a function of the capillary pressure, the porosity of the fiber bed and the local fluid velocity. The presence of these voids within the laminate is a common source of micro-cracking that reduce short and long term mechanical properties. In this work, an experimental analysis is carried out on different types of fibrous reinforcements to study the optimal impregnation conditions by relating the content of macro/micro-voids to the local capillary number. Finally, a study demonstrating the impact of voids on mechanical properties of composite laminates is carried out.

Progressive failure analysis of carbon fiber/epoxy composite laminates using continuum damage mechanics

Abstract: Based on the CDM theory, an energy-based stiffness degradation method is proposed to predict the progressive failure properties of the Al–carbon fiber/epoxy composite laminates. For carbon fiber/epoxy composites, three failure modes: fiber breakage, matrix cracking and fiber/matrix interface failure are included in the present model. A 3D finite element technique including the multiframe restart analysis and the arc-length algorithm is developed to perform the progressive failure analysis. The calculated load–displacement curve and the final failure strength of structure are compared with those obtained from experiments and other existing models. This work provides a progressive understanding of the damage initiation and propagation behaviors of composite laminated structures above.

A ballistic material model for cross-plied unidirectional ultra-high molecular-weight polyethylene fiber-reinforced armor-grade composites

Abstract: The known fiber and polymeric-matrix material properties, unit-cell microstructural characteristics and unit-cell level finite-element analyses are used to construct a new ballistic material model for 0°/90° cross-plied oriented polyethylene fiber-based armor-grade composite laminates. The model is constructed in such a way that it can be readily integrated into commercial finite-element programs like ANSYS/Autodyn [ANSYS/Autodyn version 11.0, User Documentation, Century Dynamics Inc., a subsidiary of ANSYS Inc., 2007] and ABAQUS/Explicit [ABAQUS version 6.7, User Documentation, Dessault Systems, 2007] as a user material subroutine. To validate the model, a series of transient non-linear dynamics simulations of the transverse impact of armor-grade composite laminates with two types of bullets/projectiles is carried out. The results obtained are next compared with their experimental counterparts. This comparison revealed that a relatively good agreement is obtained between the experimental and the computational analysis relative to: (a) the success of the armor panels of different areal densities in defeating the bullets at different initial bullet velocities; (b) post-mortem spatial distribution of damage within the panels; (c) the temporal evolution of a bulge at the back-face of the armor; and (d) the existence of three distinct armor-penetration stages (i.e. an initial filament shearing/cutting dominated stage, an intermediate stage characterized by pronounced filament/matrix de-bonding/decohesion and the final stage associated with the extensive bulging of the armor panel).

A Three-dimensional Damage Model for Transversely Isotropic Composite Laminates

Abstract: This article proposes a fully three-dimensional continuum damage model, developed at the sub-ply level, to predict in an integrated way both the intralaminar and the interlaminar failure mechanisms that occur in laminated fiber-reinforced polymer composites The constitutive model is based on the assumption that the composite material is transversely isotropic, and accounts for the effects of crack closure under load reversal cycles The damage model is implemented in an implicit finite element code taking into account the requirement to ensure a mesh-independent computation of the dissipated energy The comparison between the model predictions and published experimental data indicates that the model can accurately predict the effects of transverse matrix cracks on the residual stiffness of quasi-isotropic laminates, the interaction between transverse matrix cracks and delamination, and final failure of the laminate

Delamination Behaviour of Composites

Abstract: Part 1 Delamination as a mode of failure and testing of delamination resistance: Fracture mechanics concepts, stress fields, strain energy release rates, delamination initiation and growth criteria Delamination in the context of composite structural design Review of standard test procedures for delamination resistance testing Testing methods for dynamic interlaminar fracture toughness of polymeric composites Experimental characterization of interlaminar shear strength. Part 2 Delamination: detection and characterization: Integrated and discontinuous piezoelecrtric sensor/actuator for delamination detection Lamb wave-based quantitative identification of delamination in composite laminates Acoustic emission in delamination investigation. Part 3 Analysis of delamination behavior from tests: Experimental study of delamination in cross-ply laminates Interlaminar mode II fracture characterization Interaction of matrix cracking and delamination Experimental studies of compression failure of sandwich specimens with face/core debond. Part 4 Modeling delamination: Predicting progressive delamination via interface elements Competing cohesive layer models for prediction of delamination growth Modeling of delamination fracture in composites: a review Delamination in adhesively bonded joints Delamination propagation under cyclic loading Single and multiple delamination in the presence of nonlinear crack face mechanisms. Part 5 Analysis of structural performance in presence of delamination and prevention/mitigation of delamination: Determination of delamination damage in composites under impact loads Delamination buckling of composite cylindrical shells Delamination failure under compression of composite laminates and sandwich structures Self-healing composites Z-pin bridging in composite delamination Delamination suppression at ply drops by ply chamfering Influence of resin on delamination.

Seismic Rehabilitation of Reinforced Concrete Frame Interior Beam-Column Joints with FRP Composites

Abstract: An experimental research program is described regarding the use of externally applied carbon fiber-reinforced plastic (CFRP) jackets for seismic rehabilitation of reinforced concrete interior beam-column joints, which were designed for gravity loads The joints had steel reinforcement details that are known to be inadequate by current seismic codes in terms of joint shear capacity due to the absence of transverse steel hoops and bond capacity of beam bottom steel reinforcing bars at the joint Lap splicing of beam bottom steel reinforcement at the joint using externally applied longitudinal CFRP composite laminates is investigated Improvement of joint shear capacity using diagonal CFRP composite laminates is another strengthening scheme employed Concrete crack widths for the as-built specimens and the extent of CFRP delamination for the rehabilitated specimens at various drift ratios are reported The test results indicate that CFRP jackets are an effective rehabilitation measure for improving the seismic performance of existing beam-column joints with inadequate seismic details in terms of increased joint shear strength and inelastic rotation capacity In addition, CFRP laminates are effective rehabilitation measures for overcoming problems associated with beam bottom steel bars that have inadequate embedment into the beam-column joints

Indentation mechanics and fracture behavior of metal/ceramic nanolaminate composites

Abstract: Composite laminates on the nanoscale have unique properties, such as high strength, high wear resistance, and biocompatibility. In this paper we report on the nanoindentation behavior of a model metal–ceramic nanolaminate consisting of alternating layers of aluminum and silicon carbide (Al/SiC) processed by PVD on a Si substrate. Composites with different layer thicknesses were fabricated and the effect of layer thickness on Young’s modulus and hardness was quantified. The effect of indentation depth on modulus and hardness was studied. The damage that took place during nanoindentation was examined by cross-sectioning the samples by focused ion beam (FIB) technique and imaging the surface using scanning electron microscopy (SEM). Finite element modeling (FEM) of nanoindentation of nanolaminates was conducted. The damage patterns observed in experiments were qualitatively supported by the numerical simulations.

Design and manufacture of all-PP sandwich panels based on co-extruded polypropylene tapes

Abstract: This paper describes the creation of polypropylene sandwich panels, based on all-polypropylene (all-PP) composite laminates combined with a polypropylene based honeycomb or foam core. These all-PP composite laminates are based on high modulus polypropylene tape reinforcing a polypropylene matrix. Sandwich panels containing these all-PP composite laminate faces are compared with sandwich panels containing conventional glass fibre reinforced polypropylene laminate faces, and the mechanical properties, failure modes, and design requirements of these different materials are discussed.

Effect of drilling induced damage on notched tensile and pin bearing strengths of woven GFR-epoxy composites

Abstract: Analytical and experimental studies were made to evaluate the notched tensile and pin bearing strengths of the woven glass fiber reinforced (GFR)-epoxy composite laminates. The symmetric glass/epoxy woven mat cross-ply laminates containing 16 woven mats were prepared using hand lay-up technique with 45% of volume fraction. The laminates were cut into specimens as per ASTM standards. The experiments were done at three different feed rates, spindle speeds and hole diameters to examine the influence of drilling parameters on the notched tensile strength and bearing strengths of the laminates. The design of experiments and analysis of variance (ANOVA) techniques of Taguchi, were utilized to study the statistical influence of the drilling parameters on the extension of delamination. The fracture data of center-hole tensile specimens were correlated using a modification in one of the stress fracture criteria viz., the point stress criterion (PSC). The bearing strength was correlated with notched and un-notched tensile strengths of the woven fabric composite laminates.