Applied Composite Materials (v.22, #4)

Quasi-static Load Sharing Model in the Case of Moulded Glass Fibre Reinforced Polyamide 6 Gears by Julien Cathelin; Michèle Guingand; Jean-Pierre de Vaujany; Laurent Chazeau; Jérôme Adrien (343-362).
This paper presents a fast and efficient computational method to predict the mechanical behaviour of plastic cylindrical gears made of fibre reinforced polyamide 6. Based on this method, an investigation on the relation between the fibre orientation and the gear behaviour is done. The numerical method uses a viscoelastic model accounting for the temperature, humidity and rotational speed dependence of the gear. This model is developed under the assumption that the material is stressed in its linear domain. The method is performed in three steps: the first one consists of defining the fibre orientation from simulation and experimental results. The second step characterises the viscoelastic behaviour of the material. The third step consists in calculating the load sharing with local meshing, which integrates the viscoelastic model over the entire surface of the tooth. This model permits computation of the load sharing between instantaneously engaged teeth and provides results such as contact pressure, tooth root stress and transmission error. Three fibre orientation models with an increasing complexity are compared. Simulation results show a limited influence of the fibre orientation on the contact pressure and tooth root stress, nevertheless difference up to 10 % are observed on the transmission error amplitude.
Keywords: Plastic gears; Viscoelastic behaviour; Glass fibre; Polyamide 6

Permeability Tests of Fiber Fabrics in the Vacuum Assisted Resin Transfer Molding Process by Wang Changchun; Bai Guanghui; Wang Yang; Zhang Boming; Pan Lijian (363-375).
A special device is designed to measure the in-plane and through-thickness permeability of a preform for the vacuum assisted resin transfer molding (VARTM) process. The device is composed of pressure control module, aluminum experimental platform, thickness test module, and pressure test module, which is controlled by a computer. Two kinds of experiments were conducted for carbon fiber noncrimp biaxial fabrics to verify the reliability of the new device based on constant pressure injection. The two experiments are composed of: (1) testing of in-plane permeability for 1, 5, 10 and 20 layers with the method of the line injection by comparing the two conventional methods; (2) testing of the through-thickness permeability for the laminate denoted as [±45] 20 with the central injection method. The results show: (1) the in-plane permeability decrease with the increase of layer number and the permeability for 20 layers is only 62 % of the one layer; (2) the in-plane permeability is an order of magnitude greater than through-thickness permeability based on experimental results of laminate denoted as [±45] 20. A good agreement obtained between the device and two comparison methods proves the validity of the device.
Keywords: VARTM process; Permeability test; Impregnation process; Novel device

Modelling Strategies for Simulating Delamination and Matrix Cracking in Composite Laminates by Frederic Lachaud; Christine Espinosa; Laurent Michel; Pierre Rahme; Robert Piquet (377-403).
The composite materials are nowadays widely used in aeronautical domain. These materials are subjected to different types of loading that can damage a part of the structure. This diminishes the resistance of the structure to failure. In this paper, matrix cracking and delamination propagation in composite laminates are simulated as a part of damage. Two different computational strategies are developed: (i) a cohesive model (CM) based on the classical continuum mechanics and (ii) a continuous damage material model (CDM) coupling failure modes and damage. Another mixed methodology (MM) is proposed using the continuous damage model for delamination initiation and the cohesive model for 3D crack propagation and mesh openings. A good agreement was obtained when compared simple characterization tests and corresponding simulations.
Keywords: Composite materials; Delamination; Finite element analysis; Crack propagation; Matrix cracking; Mixed mode

The Influence of Geometrical Parameters on the Buckling Behavior of Conical Shell by the Single Perturbation Load Approach by Maria Francesca Di Pasqua; Regina Khakimova; Saullo G. P. Castro; Mariano A. Arbelo; Aniello Riccio; Richard Degenhardt (405-422).
Since the development of the first theories to predict the buckling induced by axial compression in shells sensitive to imperfections, a significant discrepancy between theoretical and experimental results has been observed. Donnell and Koiter are among the first authors demonstrating, for these structures, the relevant influence of the geometrical imperfections on the reduction of the buckling load. Currently, the preliminary design of imperfections sensitive shell structures used in space applications is carried out according to the NASA SP-8007guideline. However, several studies have proven that this guideline leads to over-conservative design configurations when considering the geometrical and material imperfections existing in real cones. Since the pioneer work of Arbocz, alternative methods have been investigated to overcome this issue. Among the different approaches, in this paper, the Single Perturbation Load Approach (SPLA), originally developed byHühne as a deterministic way to calculate the knock-down factor of imperfection sensitive shells, is further studied. Indeed, a numerical investigation about the application of the SPLA to the simulation of the mechanical behavior of imperfection sensitive composite conical structures under axial compression is presented. This study is related to part of the work performed in the frame of the European Union (EU) project DESICOS.
Keywords: Buckling; Conical shells; Composite; Knock-down factor

Mechanical Performance and Failure Mechanism of Thick-walled Composite Connecting Rods Fabricated by Resin Transfer Molding Technique by Gang Liu; Chuyang Luo; Daijun Zhang; Xueqin Li; Peng Qu; Xiaochen Sun; Yuxi Jia; Xiaosu Yi (423-436).
A resin transfer molding technique was used to fabricate thick-walled composite connecting rods, and then the mechanical performance of the connecting rod was studied experimentally, at the same time the stress and failure index distributions were simulated numerically. The experimental results show that under a tensile load, the connecting rod first cracks near the vertex of the triangle areas at the two ends, and then the damage propagates along the interface between the main bearing beam and the triangle area as well as along the round angle of the triangle area. Whereas under a compressive load, the delamination primarily occurs at the corner of the U-shaped flange, and the final destruction is caused by the fracture of fibers in the main bearing beam. The simulated results reveal that the tensile failure is originated from the delamination at the round angle transition areas of the T-joints, and the failure strength is determined by the interlaminar strength. Whereas the compressive failure is caused by the fracture of fibers in the main bearing beam, and the failure strength of the structure is determined by the longitudinal compressive strength of the composite material. The simulated results are basically consistent with the experimental results. Hence the mechanical performance and failure mechanism of the complicated composite structure are revealed in great detail through the coupling of the two kinds of research methods, which is helpful for the optimal design of composite structures.
Keywords: Composite Material; Connecting Rod; Mechanical Performance; Failure Mechanism; Resin Transfer Molding

Numerical Investigation of the Ballistic Performance of Metal-Intermetallic Laminate Composites by Yang Cao; Shifan Zhu; Chunhuan Guo; Kenneth S Vecchio; Fengchun Jiang (437-456).
Metal-intermetallic laminate composites (MIL) based on the Ti-aluminide system are a new class of lightweight structural materials that can be used as either appliqué or structural armor. The explicit 2D finite element code LS-DYNA was employed to investigate the ballistic performance and failure mechanism of MIL composite plate subjected to impact loading. For comparison’s sake, the penetration simulation was also conducted for a monolithic intermetallic Al3Ti sample under the same conditions. Damage tolerant abilities of the two targets were evaluated based on the analysis of the projectile tail velocity, crack density and absorbed material energy. The simulation results indicated that when cracks initiated in the Al3Ti matrix propagated to the interface between the matrix and reinforcement, their directions changed due to the bridging effect of the reinforcement Ti, which enabled the MIL composite to consume more energy as a result of the increase of the crack path lengths created by the crack deflection and bifurcation. Additionally, some other energy-absorbing mechanisms, such as deflection of cracks, plastic deformation of the ductile Ti also play important roles in enhancing the energy-absorbing capacity of the MIL composites.
Keywords: Metal-intermetallic laminate composites; Finite element method; Damage evolution; Crack density