Analysis of the transverse cracking in hybrid cross-ply composite laminates

A modified shear-lag analysis, taking into account the concept of interlaminar shear stress, is employed to evaluate the effect of transverse cracks on the stiffness reductions in different glass/epoxy and graphite/epoxy hybrid cross-ply laminates. The modified shear-lag model is proposed that assumes interlaminar adhesive layer between two neighbouring layers transferring not only interlaminar shear stress but also normal stress. The stress distribution is solved by the used model which rigorously satisfies the stress equilibrium equations, boundary conditions and the traction continuity at interfaces between layers.     

Artificial immune system for optimal design of composite hydrogen storage vessel

Based on the clonal selection principle in the biological immunology, an artificial immune system (AIS) is proposed to optimize the weight of Al-carbon fiber/epoxy composite hydrogen storage vessels under burst pressure constraint. The AIS simulates the generation of the antigens, the combination of the antigens and antibodies, and the selection, cloning and hypermutation of B cells, the maintenance of diverse antibody cells, the generation of the memory cells with high affinities and the death of the antibody cells with low affinities. Effects of the antibody size and the iterative number on the optimization results are explored. By comparison, the AIS shows higher search velocity and precision than the genetic algorithm and simulated annealing.     

Simulations of delamination in CFRP laminates: Effect of microstructural randomness

Due to their high specific strength and stiffness, fibre-reinforced composite materials are being increasingly used in structural applications where a high level of performance is important (e.g. aerospace, automotive, offshore structures, etc.). Performance in service of these composites is affected by multi-mechanism damage evolution under loading and environmental conditions. For instance, carbon fibre-reinforced laminates demonstrate a wide spectrum of failure mechanisms such as matrix cracking and delamination. These damage mechanisms can result in significant deterioration of the residual stiffness and load-bearing capacity of composite components and should be thoroughly investigated. The delamination failure mechanism is studied in this paper for a double cantilever beam (DCB) loaded in mode I. Several sensitivity studies are performed to analyse the effects of mesh density and of parameters of the cohesive law on the character of damage propagation in laminates. The microstructural randomness of laminates that is responsible for non-uniform distributions of stresses in them even under uniform loading conditions is accounted for in the model. The random properties are introduced with the use of Weibull’s two-parameter probability density function. Several statistical realisations are carried out which show that the effect of microstructure could significantly affect the macroscopic response emphasizing the need to account for microstructural randomness for accurate predictions of load-carrying capacity of laminate composite structures.     

Mode I Fracture Resistance of a Laminated Fiber-Reinforced Ceramic

The mode I fracture resistance of a ceramic matrix composite has been measured. Simultaneous observations have revealed that the resistance is dominated by frictional dissipation upon the pullout of fibers that fracture in the crack wake off the crack plane. Numerical and analytical crack growth simulations have been compared with the experimental results. One important feature in this comparison concerns the occurrence of large-scale bridging. With these effects taken into account, the simulations and the experiments are found to be in good correspondence for acceptable magnitudes of the interface sliding stress.     

Enhanced Fracture Toughness in Layered Microcomposites of Ce-ZrO2 and Al2O3

Laminar composites, containing layers of Ce-ZrO₂ and either Al₂O₃ or a mixture of Al₂O₃ and Ce-ZrO₂, have been fabricated using a colloidal method that allowed formation of layers with thicknesses as small as 10 μm. Strong interactions between these layers and the martensitic transformation zones surrounding cracks and indentations have been observed. In both cases, the transformation zones spread along the region adjacent to the layer, resulting in an increased fracture toughness. The enhanced fracture toughness was observed for cracks growing parallel to the layers as well as for those that were oriented normal to the layers.     

Mechanical behavior of a composite printed-wiring-board material

This paper describes an experimental investigation of the mechanical behavior of a paper-filled-phenolic laminate widely used in the electronics industry. Uniaxial tensile tests in three directions, sandwich-beam bending tests to determine the compressive behavior, and cylindrical-punch punchability tests were conducted. Interesting phenomena observed included difference in tensile and compressive behavior, consistent crack branching in tension, and strain mismatch during punching. Based upon a thesis submitted by the first author in partial fulfillment of the requirements for the M.S. degreee in Mechanical Engineering at the University of Oklahoma, December 1976.     

Vibration of axisymmetric composite piezoelectric shells coupled with internal fluid

This paper presents the theoretical and finite element formulations of piezoelectric composite shells of revolution filled with compressible fluid. The originality of this work lies (i) in the development of a variational formulation for the fully coupled fluid/piezoelectric structure system, and (ii) in the finite element implementation of an inexpensive and accurate axisymmetric adaptive laminated conical shell element. Various modal results are presented in order to validate and illustrate the efficiency of the proposed fluid–structure finite element formulation. Copyright © 2007 John Wiley & Sons, Ltd.     

冲击载荷下复合材料层板断裂韧性的实验研究

利用Hopkinson杆加载装置,对带有单边切口的CFRP、GFRP层板试件进行冲击拉伸加载实验。根据一维应力波理论求得作用于试件上的载荷P(t)和试件加载点的位移δ(t)。根据试样中应力随时间的变化历史σ(t),再结合断裂韧性测试原理,建立动态应力强度因子KI(t)响应曲线。利用柔度变化率方法确定起裂时间,分别得到在2种加载速率下CFRP、GFRP层板的动态断裂韧性。     

Lagged strain of laminates in RC beams strengthened with fiber-reinforced polymer

Based on the theory of concrete structure, a new expression was derived for lagged strain of fiber-reinforced polymer （FLIP） laminates in reinforced concrete （RC） beams strengthened with FRP. The influence of different preloaded states and nonlinear stress-strain relationship of compressed concrete were both taken into account in this approach. Then a simplified expression was given by ignoring tensile resistance of concrete. Comparison of analytical predictions with experimental results indicates satisfactory accuracy of the procedures. The errors are less than 8% and 10% respectively when the tensile resistance of concrete is or not considered. While the maximum error of existing procedures is up to 60%.