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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.20, #2)
Manufacturing Aspects of Advanced Polymer Composites for Automotive Applications by Klaus Friedrich; Abdulhakim A. Almajid (pp. 107-128).
Composite materials, in most cases fiber reinforced polymers, are nowadays used in many applications in which light weight and high specific modulus and strength are critical issues. The constituents of these materials and their special advantages relative to traditional materials are described in this paper. Further details are outlined regarding the present markets of polymer composites in Europe, and their special application in the automotive industry. In particular, the manufacturing of parts from thermoplastic as well as thermosetting, short and continuous fiber reinforced composites is emphasized.
Keywords: Polymer composites; Manufacturing; Automotive
Fracture Model of Bimaterial under Delamination of Elasto-Plastic Structured Media by V. M. Kornev; V. D. Kurguzov; N. S. Astapov (pp. 129-143).
Delamination of bimaterial composed of two structured materials is considered. A crack is located at the interface between two media. Under tension applied at infinity, I mode fracture is implemented. The improved Leonov-Panasyuk-Dugdale model (LPD model) is proposed to be applied in combination with the Neuber-Novozhilov approach. The case when elastic material characteristics are identical and strength ones essentially differ is analyzed in detail. Analytical description of plotting the fracture diagram of quasi-brittle bimaterial for the plane stress state is given. Numerical modeling of the plasticity zone in bimaterial under quasi-static loading has been performed. The updated Lagrange formulation of solid-state mechanics equations is used in a numerical model. This formulation is most preferable for modeling of bodies made from elasto-plastic material subjected to large strain. Using the finite element method, a plastic zone in the vicinity of a crack tip has been described. It is shown that the shape of the plastic zone in bimetal essentially differs from that in a homogenous medium. Numerical experiments are in good agreement with the proposed analytical model of the pre-fracture zone in the weakest material.
Keywords: Fracture criteria; Pre-fracture zone; Stress intensity factors (SIFs); Crack opening; Crack blunting; Quasi-brittle fracture diagram
Fatigue Behaviour of Glass Fibre Reinforced Composites for Ocean Energy Conversion Systems by A. Boisseau; P. Davies; F. Thiebaud (pp. 145-155).
The development of ocean energy conversion systems places more severe requirements on materials than similar land-based structures such as wind turbines. Intervention and maintenance at sea are very costly, so for ocean energy supply to become economically viable long term durability must be guaranteed. Cyclic loading is a common feature of most energy conversion devices and composites are widely used, but few data are available concerning the fatigue behaviour in sea water of composite materials. This paper presents the results from an experimental study to fill this gap. The fatigue behavior of composite materials reinforced with different types of glass fibre is characterized in air and in sea water; the influence of testing in sea water rather than air is shown to be small. However, sea water ageing is shown to reduce the fatigue lifetime significantly and strongly depends on matrix formulation.
Keywords: Composite material; Fatigue behaviour; Sea water ageing; Failure mechanism; Tidal turbine
How to Prepare SMC and BMC-like Compounds to Perform Relevant Rheological Experiments? by Olivier Guiraud; Pierre J. J. Dumont; Laurent Orgéas (pp. 157-169).
The study of the rheology of injected or compression moulded compounds like SMC or BMC is made particularly difficult by the high content and the intricate arrangement of their fibrous reinforcement. For these two types of compounds, inappropriate rheological testing protocols and rheometers are often used, which leads to a very large scatter of the experimental data. This study describes specific sampling and specimen’s preparation methods, as well as dedicated rheometry devices to test their rheology. Following the proposed protocols, it is possible to obtain rheological measurements showing low scatter of the recorded stress values: about ±10% for SMC and about ±15% for BMC-like compounds.
Keywords: Polymer composite materials; Rheology; Measurements scatter; SMC; BMC; Fillers
The Displacement Perspective During Ultimate Failure of Composite Laminates by P. Pal; A. Bhar (pp. 171-183).
This paper deals with the studies on the state of displacement of symmetric and anti-symmetric angle-ply and cross-ply laminated composite plates during its ultimate failure, subjected to transverse static load. First-order shear deformation theory (FSDT) is employed in conjunction with the finite element approach using eight-noded quadratic isoparametric element. The free vibration analyses of isotropic and laminated composite plates are carried out to ensure the overall validity of the present finite element formulation. The mid surface of the laminate is considered as the reference plane. The principal material directions in different laminae are oriented to produce a laminated structural element capable of resisting loads in several directions. The stiffness of a composite laminate is obtained from the properties of the constituent laminae. The affected stiffness of the failed lamina is discarded completely after the failure of weakest ply. The rigidity matrix of the laminate with remaining laminae is re-established. The re-evaluation process continues until the laminate fails completely. To investigate the displacement behaviour of laminates during the ultimate failure, parametric studies are carried out for different cases by varying the stacking sequences, fiber orientations, layer thicknesses, aspect ratios and the number of layers in the laminate. The comparison of results in terms of non-dimensional natural frequencies and ply-by-ply failure analyses obtained from the present investigation are made with those available in the reported literature.
Keywords: Isotropic plates; Laminated composite plates; Free-vibration analysis; First-ply failure; Ultimate failure; Finite element method (FEM)
Effect of Hybridization on Stiffness Properties of Woven Textile Composites by Liliana Bejan; Nicolae Taranu; Adriana Sîrbu (pp. 185-194).
The present study focuses on stiffness properties of woven textile reinforced polymeric composites with respect to hybridization, and geometry of reinforcement. The analyzed composites represent combinations of different fibre materials (E-glass, Kevlar 49, carbon HM) in a predetermined fabric geometry (a plane weave embedded in thermosetting polymeric resin) serving controlled properties and required performance. The effects of hybridization on the stiffness properties of woven textile composites have been studied with respect to the fibres materials, the unbalancing degree of fabrics, and the variation of compactness and undulation of yarns. Some undesirable effects in fabric geometry can be overcome by the combined effects of hybridization and compactness.
Keywords: Composite materials; Hybrid reinforcement; Woven fabric; Textile composites; Elastic stiffness
Characterisation of Ductile Prepregs by F. Pinto; A. White; M. Meo (pp. 195-211).
This study is focused on the analysis of micro-perforated prepregs created from standard, off the shelf prepregs modified by a particular laser process to enhance ductility of prepregs for better formability and drapability. Fibres are shortened through the use of laser cutting in a predetermined pattern intended to maintain alignment, and therefore mechanical properties, yet increase ductility at the working temperature. The increase in ductility allows the product to be more effectively optimised for specific forming techniques. Tensile tests were conducted on several specimens in order to understand the ductility enhancement offered by this process with different micro-perforation patterns over standard prepregs. Furthermore, the effects of forming temperature was also analysed to assess the applicability of this material to hot draping techniques and other heated processes.
Keywords: Ductility; Forming; Prepregs