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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.14, #5-6)

Study of Abrasive Wear Volume Map for PTFE and PTFE Composites by H. Unal; U. Sen; A. Mimaroglu (pp. 287-306).

The potential of this work is based on consideration of wear volume map for the evaluation of abrasive wear performance of polytetrafluoroethylene (PTFE) and PTFE composites. The fillers used in the composite are 25% bronze, 35% graphite and 17% glass fibre glass (GFR). The influence of filler materials, abrasion surface roughness and applied load values on abrasive wear performance of PTFE and PTFE composites were studied and evaluated. Experimental abrasive wear tests were carried out at atmospheric condition on pin-on-disc wear tribometer. Tests were performed under 4, 6, 8 and 10 N load values, travelling speed of 1 m/sec and abrasion surface roughness values of 5, 20 and 45 µm. Wear volume maps were obtained and the results showed that the lowest wear volume rate for PTFE is reached using GFR filler. Furthermore, the results also showed that the higher is the applied load and the roughness of the abrasion surface, the higher is the wear rate. Finally it is also concluded that abrasive wear process mechanism include ploughing and cutting mechanisms.

Keywords: Abrasive; Wear volume map; PTFE composites

Effect of Bonder at Skin/Core Interface on the Mechanical Performances of Sandwich Structures Used in Marine Industry by C. Borsellino; L. Calabrese; G. Di Bella (pp. 307-323).

The present work is aimed to extend the knowledge of mechanical properties of sandwich structures used for marine applications focusing on the possibility to increase the performances of such structures by adding a bonder at the skin/core interface. Therefore, three sandwich structures that are utilised in different structural components of a yacht were realised by manual lay-up. The mechanical characterisation was performed by flatwise compressive, edgewise compressive and three point flexural tests. The tests execution has allowed both to determine the mechanical performances and to understand the fracture mechanisms that take place when the bonder is added in the stacking sequence of the samples.

Keywords: Sandwich; Glass fibres; Bonder; Mechanical properties

Progressive Failure of Composite Hollow Sections with Foam-Filled Corrugated Sandwich Walls by D. Zangani; M. Robinson; A. G. Gibson (pp. 325-342).

The aim of this paper was to model the progressive failure of foam-filled twin-walled composite hollow box sections with internal reinforcement. The effect of different corner designs, and different arrangements of the corrugation inside the core were investigated. The numerical model developed to simulate quasi-static compression tests involved integrating a progressive failure criterion into an explicit dynamic analysis code. The model provided very good correlation with experimental crush force data and effectively described the progressive material failure. It also enabled the energy absorption contribution of each of the main structural components to be determined. It was concluded that this particular approach had the potential to be used in the design and optimisation of crashworthy composite structures containing similar features to those involved here.

Keywords: Crushing; Finite element; Box section; Energy absorption

Impact Damage of 3D Orthogonal Woven Composite Circular Plates by Changgan Ji; Baozhong Sun; Yiping Qiu; Bohong Gu (pp. 343-362).

The damages of 3D orthogonal woven composite circular plate under quasi-static indentation and transverse impact were tested with Materials Test System (MTS) and modified split Hopkinson bar (SHPB) apparatus. The load vs. displacement curves during quasi-static penetration and impact were obtained to study the energy absorption of the composite plate. The fluctuation of the impact stress waves has been unveiled. Differences of the load-displacement curves between the quasi-static and impact loading are discussed. This work also aims at establishing a unit-cell model to analyze the damage of composites. A user material subroutine which named VUMAT for characterizing the constitutive relationship of the 3-D orthogonal woven composite and the damage evolution is incorporated with a finite element code ABAQUS/Explicit to simulate the impact damage process of the composite plates. From the comparison of the load-displacement curves and energy absorption curves of the composite plate between experimental and FEM simulation, it is shown that the unit-cell model of the 3D woven composite and the VUMAT combined with the ABAQUS/Explicit can calculate the impact responses of the circular plate precisely. Furthermore, the model can also be extended to simulate the impact behavior of the 3D woven composite structures.

Keywords: 3D orthogonal woven composite; Unit-cell; Transverse impact; FEM simulation; User subroutine

Experimental and Numerical Analysis of Composite Folded Sandwich Core Structures Under Compression by S. Heimbs; P. Middendorf; S. Kilchert; A. F. Johnson; M. Maier (pp. 363-377).

The characterisation of the mechanical behaviour of folded core structures for advanced sandwich composites under flatwise compression load using a virtual testing approach is presented. In this context dynamic compression test simulations with the explicit solvers PAM-CRASH and LS-DYNA are compared to experimental data of two different folded core structures made of aramid paper and carbon fibre-reinforced plastic (CFRP). The focus of the investigations is the constitutive modelling of the cell wall material, the consideration of imperfections and the representation of cell wall buckling, folding or crushing phenomena. The consistency of the numerical results shows that this can be a promising and efficient approach for the determination of the effective mechanical properties and a cell geometry optimisation of folded core structures.

Keywords: Folded core; Sandwich structures; Compression testing; Numerical simulation

Head Shape and Winding Angle Optimization of Composite Pressure Vessels Based on a Multi-level Strategy by A. Vafaeesefat; A. Khani (pp. 379-391).

This paper presents a multi-level strategy for the optimization of composite pressure vessels with nonmetallic liners. The design variables for composite vessels include the head shape, the winding angle, the layer thickness, the number of layers, and the stacking sequence. A parameter called “modified shape factor” is introduced as an objective function. This parameter takes into account the effects of the internal pressure and volume, the vessel weight, and the composite material properties. The proposed algorithm uses genetic algorithm and finite element analysis to optimize the design parameters. As a few examples, this procedure is implemented on geodesic and ellipsoidal heads. The results show that for the given vessel conditions, the geodesic head shape with helical winding angle of nine degrees has the better performance.

Keywords: Filament wound vessel; Optimization; Genetic algorithm; Multi-level strategy; Stacking sequence; Shape factor; Geodesic

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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.14, #5-6)