The structural intensities of composite plates with a hole

The structural intensities in isotropic and orthotropic laminae and composite laminated plates with and without a hole of different rim conditions are studied using the finite element method. Patterns of superposition among structural stress fields, intensity vectors, mode shapes and streamlines of energy flow are obtained for the various cases. It is found that the hole completely changes the distributions of the stress and energy flow path in plates. Despite its nature of mode dependent the pattern of energy flow may be different from each other despite having similar structural mode shapes, moreover the position of maximum stress is not corresponding to the position of maximum structural intensity.     

叠片式吊钩的强度计算

用于铸造起重机的龙门钩除了受到起吊载荷的作用，还受到吊运的液态金属的高温辐射，不仅承受弯曲应力、扭转应力、剪切应力还有高温钢水辐射产生的热变应力等，通过对几个危险截面的强度分析，以最终确定吊钩组的截面尺寸。     

层压复合工艺优化

文章采用正交组合实验,对复合织物的剥离强度、耐静水压、透湿和透气性能进行分析。利用灰色近优综合评定,得出最优工艺。     

Stochastic nonlinear failure analysis of laminated composite plates under compressive transverse loading

This paper present the second ordered statistics of first-ply failure response of laminated composite plate with random material properties under random loading. The basic formulation is based on higher order shear deformation plate theory (HSDT) with the geometrically nonlinearity in the von-Karman. The direct iterative based C⁰ nonlinear finite element method combined with mean centered first order perturbation technique developed by the authors are extended and successfully applied nonlinearity for failure problem with a reasonable accuracy to predict the second order statistics (standard deviation) of first-ply failure response using Tsai-Wu and Hoffman failure criterion with macroscopic analysis. Typical numerical results for various combinations of boundary conditions, plate thickness ratios, aspect ratios, laminates scheme and layers, elastic modulus ratios have been presented to illustrate the application of developed procedure. Some new results are presented and examined which clearly demonstrated the importance of the randomness in the system parameters in the failure response of the structures subjected to transverse loadings.     

Effects of vertically aligned carbon nanotubes on shear performance of laminated nanocomposite bonded joints

Abstract

The main objective is to improve the most commonly addressed weakness of the laminated composites (i.e. delamination due to poor interlaminar strength) using carbon nanotubes (CNTs) as reinforcement between the laminae and in the transverse direction. In this work, a chemical vapor deposition technique has been used to grow dense vertically aligned arrays of CNTs over the surface of chemically treated two-dimensionally woven cloth and fiber tows. The nanoforest-like fabrics can be used to fabricate three-dimensionally reinforced laminated nanocomposites. The presence of CNTs aligned normal to the layers and in-between the layers of laminated composites is expected to considerably enhance the properties of the laminates. To demonstrate the effectiveness of our approach, composite single lap-joint specimens were fabricated for interlaminar shear strength testing. It was observed that the single lap-joints with through-the-thickness CNT reinforcement can carry considerably higher shear stresses and strains. Close examination of the test specimens showed that the failure of samples with CNT nanoforests was completely cohesive, while the samples without CNT reinforcement failed adhesively. This concludes that the adhesion of adjacent carbon fabric layers can be considerably improved owing to the presence of vertically aligned arrays of CNT nanoforests.     

Comparisons of buckling-to-weight behavior of cylindrical shells with composite and metallic stiffeners

The present research deals with the study of buckling pressure-to-weight ratio of cylindrical shells with laminated ring stiffeners. The research introduces a strain energy formulation for laminated rings, in which each ring stiffener may be treated individually and the geometrical dimensions and material properties of the stiffeners may be different from one another. In a parametric study, the impacts of various geometrical parameters of rings on the buckling pressure-to-weight ratio of shells for composite and metallic stiffeners are compared. The results show that the buckling-to-weight behavior of the shells with Steel stiffeners generally differs from the shells with stiffeners made of Aluminum, E-glass/epoxy, Graphite/epoxy, or Kevlar49/epoxy.     

Critical heat flux and mass loss rate for extinction of flaming combustion of timber

The critical mass loss rate and critical heat flux for self-extinction of flaming combustion during steady-state burning of timber was measured in this study for a range of timber species. A vertical mass loss calorimeter was used to provide the external heat flux and to measure the mass loss of the timber samples. The results showed that the critical mass loss rate was dependent upon the timber species but did not show a clear dependency with the timber density. Critical mass loss rates and heat fluxes for self-extinction exist for each of the timber species tested for both the solid timber and cross laminated timber (CLT). Debonding of both the char layer and the individual lamella of the CLT caused increased mass loss rates, re-ignition after self-extinction and increased flame lengths. Both char and ply fall-off were observed.     

Properties of solid wood and laminated wood lumber manufactured by cold pressing and heat treatment

Physical, mechanical, and morphological properties of solid wood lumbers which were cold pressed in a press and then heat treated in a kiln. Two different kinds of domestic thinning small-diameter softwood (Ginko biloba L.) and hardwood (Tilia amurensis Rupr.) were used in this study. First 50 mm thick lumbers were cold pressed until 35 mm (30% of control lumber) using a stopper for 5 min. Then the cold pressed lumbers were heat treated in an electric kiln at 180 °C for 6, 12, 24, or 48 h. To increase the utilizability of woods, the LVLs were produced from 4 mm thick veneers prepared from the heat treated lumbers using a veneer saw. Each LVL sample consisted of 5 layers which were subsequently 48 h-, 24 h-, 12 h-, and 6 h-treated veneers and untreated veneer (from top layer to bottom layer). The shrinkage rates of softwood and hardwood were considerably decreased with increasing temperature. The mechanical properties of heat treated samples were better than those of unpressed control samples. The bending strength and modulus of elasticity of the LVLs manufactured from cold pressed and then heat treated lumbers were slightly lower than those of untreated woods. The colour values obtained from the heat treated wood samples showed a clear effect of the temperature on the colour changes.     

铜铝层状复合板中性盐雾腐蚀行为研究

采取模拟大气环境的室内中性盐雾腐蚀实验,探讨了铜铝层状复合材料的腐蚀行为。通过扫描电镜(SEM)观察腐蚀后铜铝界面形貌,结合X射线衍射仪(XRD)和能谱仪(EDS)分析腐蚀产物成分,并通过电化学检测分析试样经过不同时间盐雾腐蚀后的表面腐蚀状态,探讨铜铝复合板在服役环境下的腐蚀机制。结果表明:铜铝复合板在盐雾环境下铜铝构成腐蚀原电池,Al为阳极铜为阴极,阴阳极面积比越大,腐蚀速率越大。随着腐蚀的不断进行,铜铝界面的Cu一侧发生腐蚀,且靠近界面的位置腐蚀最为严重,随着腐蚀时间延长,铝基体出现严重的剥蚀现象,Cu几乎无变化。腐蚀产物成分为Al2O3,Al(OH)3和AlO(OH),电化学结果显示:铜铝复合板在腐蚀的过程中,腐蚀速率呈现先增加后减小再增加的趋势。