Scratch and wear resistance of transparent topcoats on carbon laminates

The present investigation deals with the application of low-curable powder paints on epoxy–carbon laminates. Carbon laminates were first peened to corrugate their surface, hence increasing the wettability and allowing a better adhesion of the overlying coatings. Powder coatings were then electrostatically sprayed onto peened and unpeened substrates and baked into a convection oven. Their aesthetic and tribological performance was comparatively evaluated. Powder coated peened carbon laminates exhibited good adhesion and visual appearance as well as noteworthy scratch resistance and tribological performance.     

Corrugated laminate homogenization model

This work addresses the problem of finding a substitute material model for describing the load response of globally flat corrugated sheets made from multidirectional laminates. Exact solutions of the equations governing thin singly curved shells give the displacements, strains and stresses within a unit cell extending over one period of the corrugation pattern. The forces reacting to enforced unit deformations determine the constitutive law of the substitute material model. The analytical results are compared with those of finite-element models.     

Geometrically non-linear analysis including shear deformation of composite laminates

Geometrically non-linear deformations of composite laminated plates are computed using the perturbation finite element method (PFEM). The PFEM is more economic in terms of computational time than conventional finite element iterative procedure, and results in semi-analytic solutions because deformations are polynomial functions of external loads, and vice-versa. To account for the transverse shear effect on deformation of a laminated plate, a discrete-layer shear deformation theory is introduced. This approach predicts more accurately the distribution of displacements and stresses through the thickness than single-layer theories. Detailed derivation of the theory is presented in the paper. A three-node triangular element model and computer program have been developed and implemented as part of this study. Computed numerical results of several examples show that the perturbation finite element solutions are in good agreement with exact solution, experimental data and calculated numerical result from other investigators.     

水环境对热塑性复合材料层合板分层疲劳裂纹扩展的影响

本文研究了水环境对ICIAPC-2热塑性预浸料(AS4/PEEK)制成的单向复合材料层合板分层疲劳裂纹扩展的影响.用双悬臂梁试件进行了I型张开位移加载试验.试验环境为23℃水中和50℃水中.水环境未引起很大的不利影响.用电子显微镜和机理分析讨论了水环境对CF/PEEK和CF/环氧两种层合板的差异.     

Transmission electron microscopy of interfaces in structural ceramic composites

Ceramic composites based either on a particulate, fibre or a lamellar architecture are potentially useful as damage-tolerant high-temperature engineering materials. The ability of the interfaces in such systems to deflect cracks is vital to the damage tolerance of these materials. Transmission electron microscopy techniques enable the chemical and physical characterization of these interfaces, providing information on interlayer thicknesses, chemical species, local bonding and the microstructural features which give rise to the interfacial properties, thereby enabling a full understanding not only of composites after processing, but also after exposure to aggressive environments such as air at high temperature. Examples of the application of transmission electron microscopy to all three composite architectures are described.     

Mesh design in finite element analysis of post-buckled delamination in composite laminates

The role of mesh design in the post-buckling analysis of delamination in composite laminates is addressed in this paper. The determination of the strain energy release rate (SERR) along the crack front is central to the analysis. Frequently, theoretical analysis is limited to treatment of the problem in two dimensions, since considerable complexity is encountered in extending the analysis to three dimensions. However, many practical problems of embedded delamination in composite laminates are inherently three-dimensional in nature. Although in such cases, the finite element (FE) method can be employed, there are some issues that must be examined more closely to ensure physically realistic models. One of these issues is the effect of mesh design on the determination of the local SERR along the delamination front. There are few studies that deal with this aspect systematically. In this paper, the effect of mesh design in the calculation of SERR in two-dimensional (2D) and three-dimensional (3D) FE analyses of the post-buckling behavior of embedded delaminations is studied and some guidelines on mesh design are suggested. Two methods of calculation of the SERR are considered: the virtual crack closure technique (VCCT) and crack closure technique (CCT). The 2D analyses confirm that if the near-tip mesh is symmetric and consists of square elements, then the evaluation of the SERR is not sensitive to mesh refinement, and a reasonably coarse mesh is adequate. Despite agreement in the global post-buckling response of the delaminated part, the SERR calculated using different unsymmetrical near-tip meshes could be different. Therefore, unsymmetrical near-tip meshes should be avoided, as convergence of the SERR with mesh refinement could not be assured. While the results using VCCT and CCT for 2D analyses agree well with each other, these techniques yield different quantitative results when applied to 3D analyses. The reason may be due to the way in which the delamination growth is modeled. The CCT allows simultaneous delamination advance over finite circumferential lengths, but it is very difficult to implement and the results exhibit mesh dependency. Qualitatively, however, the two sets of results show similar distributions of Mode I and Mode II components of the SERR. This is fortunate, since the VCCT is relatively easy to implement.     

Hybrid‐stress solid elements for shell structures based upon a modified variational functional

In this paper, we start with a modified generalized laminate stiffness matrix that serves as a remedy to resolve the thickness locking and some abnormalities encountered by solid‐shell elements in laminate analyses. A modified Hellinger–Reissner functional having displacement and a set of generalized stresses as independent fields is devised. Based upon the functional, eight‐node and 18‐node hybrid‐stress solid‐shell elements are proposed. A number of benchmark tests on homogenous and laminated plates/shells are conducted. The accuracy of the elements is promising. Copyright © 2002 John Wiley & Sons, Ltd.     

Fracture Process in ± θ Laminates Subjected to Mode II Loading

This work studies the behavior of a multidirectional laminate under Mode II loading. We describe the process of delamination in a reinforced composite of glass/epoxy. The stacking sequence (plies orientation [± ] was selected to minimize the coupling effects. The Mode II interlaminar test under three-point bending and cantilever flexure using ENF (End Notch Flexure) and ELS (End Load Split) specimens, respectively, was performed and analyzed. The test procedures and the results of strain-energy-release rate study for crack initiation are presented. The fracture process and the mechanical behavior of the two types of specimens are analyzed. The analysis clearly shows a close link between the angle , the ratio a/L, and the thickness h of the specimen. Fracture by delamination can be obtained only with an optimal choice of these parameters. The analysis of the states of stresses at the tip of crack allows us to explain the phenomenon of bifurcation between plies and is confirmed by the experimental results.     

挠性覆铜板

主要介绍挠性覆铜板的组成、制造方法及技术发展。     

CFRP片材加固混凝土连续梁长期受力性能与极限承载力试验

制作了3根钢筋混凝土矩形截面连续梁,考虑了CFRP片材加固、温度等因素影响,对3根梁进行长达648d的长期荷载试验,研究了长期荷载作用下的徐变性能,并对3根梁进行了极限承载力试验。