共查询到20条相似文献,搜索用时 15 毫秒
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《Acta Materialia》2008,56(18):5138-5146
A symmetric and interconnected skeleton structural (SISS) model is proposed for predicting the thermal and electrical conductivities and Young’s modulus of open-cell foams with hollow and solid struts. The model predicted the effective thermal and electrical conductivities of solid-strut aluminium foams and other open-cell foams for the entire porosity range. The SISS model provided upper and lower bounds for the effective thermal conductivity and Young’s modulus of hollow-strut open-cell nickel foams. The SISS model was also found to predict the effective thermal conductivity of closed-cell graphite foams, and the effective electrical conductivity and Young’s modulus of closed-cell aluminium foams with reasonable accuracy. By analogy, the SISS model might also be applied to other physical properties. 相似文献
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Foams are more and more widely used because of their high mechanical properties relative to their low density. Most available mechanical models are based on idealised unit-cell structures. A significant disadvantage of the unit-cell modelling approach is that it does not account for the natural variations in microstructure that are typical for most foam structures. Our objective has been to investigate how the cell irregularity affects the elastic properties of open-cell foams. We generated periodic, three-dimensional (3D), random samples with different degrees of irregularity, and used finite element analysis (FEA) to determine the effective elastic properties. The geometrical properties were investigated for 3D random open-cell foams and related to the elastic properties. The results indicate that the more irregular the foams, the larger will be their effective Young's modulus and shear modulus at constant overall relative density. On the other hand, the bulk modulus reduces with increasing degree of cell irregularity, while the Poisson's ratio is largely independent. 相似文献
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A repeating element composed of four cell struts in a pentagonal dodecahedron model is used to analyze the creep-buckling of open-cell foams. The solid making up the cell struts is assumed to follow power-law creep. As a result, the theoretical expression for describing the failure time for the onset of creep-buckling of open-cell foams under uniaxial compression is obtained. Theoretical results indicate that the creep-buckling of open-cell foams depends on their relative density and microstructural imperfection and the creep parameters of solid cell struts. Furthermore, a simple relationship between creep strain rate and failure time is proposed for the creep-buckling of open-cell foams and then compared to the existing experimental results; they agree well. In addition, cell-strut creep-buckling is the dominant failure mechanism when the imposed compressive stress is close to the elastic buckling strength of open-cell foams. However, cell-strut creep-rupturing is more likely to occur when the imposed compressive stress becomes smaller. Moreover, the transition of failure mechanism from cell-strut creep-buckling to cell-strut creep-rupturing is discussed. 相似文献
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Ni–Sn alloy intermetallic coatings with different Sn contents, were electrodeposited on Vanadis 23 steel substrates. Structural and chemical characterisation of these coatings was performed by x-ray diffraction, scanning electron microscopy and electron dispersive x-ray analysis. The as-plated Ni–Sn coatings were found to consist of a crystalline Ni solid solution with dispersed Ni–Sn intermetallic phases, whereas in certain cases bulk intermetallic coatings were obtained. The addition of Sn as an alloying element into electrolytic Ni coatings led to a significant increase of hardness and Young’s modulus of these coatings. In addition, the effect of a post-deposition heat treatment at 400°C for 1?h on the microstructure and mechanical characteristics of these electrolytic Ni–Sn alloy coatings was investigated. 相似文献
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有限元网格模型的质量是决定塑性成形有限元模拟结果的精度和可靠度的关键因素之一。文章提出了基于实体模型几何特征六面体网格自适应生成算法,在表面曲率较大和厚度较小的区域实现局部加密;提出了穿插法边界拟合方法,避免特征边界点的反复搜索,提高有限元网格生成的效率,实现网格与实体模型表面精确拟合。几个复杂几何模型的网格自动划分结果,验证了该算法的实用性和有效性。 相似文献
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《Acta Materialia》2008,56(10):2283-2289
A repeating element consisting of four straight and uniform-thickness cell struts in a pentagonal dodecahedron model is employed to analyze theoretically the creep-rupturing of open-cell foams. In the repeating element, the solid making up cell struts is assumed to follow power-law creep and the Monkman–Grant relationship. Consequently, the theoretical expressions for describing the steady-state creep strain rate and creep-rupturing time of open-cell foams are obtained. It is shown that the creep-rupturing of open-cell foams can also be described by the Monkman–Grant relationship. Moreover, the Monkman–Grant parameters m1 and B1 of open-cell foams depend on their cell structure and those of solid cell struts. The Monkman–Grant parameters determined from the existing experimental results on the creep-rupturing of open-cell aluminum alloy foams are compared to those calculated theoretically from the proposed pentagonal dodecahedron model. The difference between theoretically calculated and empirically determined B1 is attributed to some pre-existing cell structural imperfections in open-cell aluminum alloy foams. 相似文献
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J. ChenK. Chandrashekhara C. MahimkarS.N. Lekakh V.L. Richards 《Journal of Materials Processing Technology》2011,211(2):245-255
Cold rolling is used to eliminate void defects in cast materials thus improving the material performance during service. A comprehensive procedure is developed using finite element analysis and neural network to predict the degree of void closure. A three-dimensional nonlinear dynamic finite element model was used to study the mechanism of void deformation. Experiments were conducted to investigate void closure during the cold flat rolling process. Experimental results are compared to the three-dimensional finite element predictions to validate the model. The void reduction predictions from finite element analysis are in good agreement with experimental findings. Plastic strain, principal stress distribution around the void and void reduction ratio are presented for various case studies. As finite element simulation is time-consuming, a back-propagation neural network model is also developed to predict void closure behavior. Based on the correlation analysis, the reduction in sheet thickness, the dimension of the void and the size of the rollers were selected as the inputs for the neural network. The neural network model was trained based on results obtained from finite element analysis for various simulation cases. The trained neural network model provides an accurate and efficient procedure to predict void closure behavior in cold rolling. 相似文献
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Lingfei Zhang José M.F. Ferreira Susana Olhero Loic Courtois Tao Zhang Eric Maire Jens Chr. Rauhe 《Acta Materialia》2012,60(10):4235-4246
Bulk and cellular cordierite ceramics were prepared from a non-stoichiometric powder consisting of corundum, talc (triclinic), α-quartz, K-feldspar, kaolinite, mullite and a small amount of a glass phase. The optimal sintering processing route was evaluated to obtain good mechanical properties. A high flexural strength of 120 MPa and a Young’s modulus of 99 GPa were achieved. The ceramic foams were fabricated by impregnation of polymer preforms with the optimized stock suspension. The mechanical properties of ceramic foams were studied by impulse excitation and compression tests. The Gibson–Ashby model predicted the ceramic foam’s effective modulus and its elastic limit strength well, as measured experimentally. In addition, the actual three-dimensional (3-D) structure obtained from X-ray computed tomography (CT) coupled with the finite element method (FEM) was used to calculate the Young’s modulus and the elasticity limit of the ceramic foam; however, this did not produce aby better agreement between the calculated values and the experimental results. The discrepancy between the Gibson–Ashby model and FEM could probably be attributed to the accuracy and small volume of representative reconstructed 3-D cellular structure. Taking account of the effect of the internal hollow structure on the stress localization in the ceramic struts, the CT–FE modeling provides a good measure of the adaptability and predictability of actual ceramic foam structures for realistic damage modeling. 相似文献
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F. Nematzadeh S. K. Sadrnezhaad 《Journal of Materials Engineering and Performance》2013,22(11):3228-3236
Nitinol stents are used to minimize improper dynamic behavior, low twistability, and inadequate radial mechanical strength of femoral artery stents. In this study, finite element method is used to investigate the effect of crimping and Austenite finish temperature (A f) of Nitinol on mechanical performance of Z-shaped open-cell femoral stent under crimping conditions. Results show that low A f Nitinol has better mechanical and clinical performance due to small chronic outward force, large radial resistive force, and appropriate superelastic behavior. 相似文献
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Xiaochuan Sun Luiz F. Kawashita Tino Wollmann Sebastian Spitzer Albert Langkamp Maik Gude 《Production Engineering》2018,12(2):215-228
Braiding is an attractive manufacturing method for tubular elements such as hollow shafts and struts. One of the main challenges however is the integration of suitably performing end-fittings. Recent advances in additive layer manufacture have enabled the fabrication of end-fittings which can be ‘co-impregnated’ or ‘co-cured’ with the fibre preform in a single step, i.e. without the need for secondary adhesive bonding. This requires the introduction of protrusions onto the surface of the end-fitting to promote mechanical interlocking with the fibres. However, the lack of accurate modelling tools for the simulation of this manufacturing process means that much empiricism is currently used in the design of such structures. A novel numerical framework is presented here for the full-scale simulation of the braiding process over structured end-fittings. Nonlinear finite element analysis is applied at the meso-scale, with strands of beam elements representing individual yarns and meshed surfaces modelling the mandrel and tooling. Penalty-based contact formulations are then used to simulate all inter-yarn and yarn-metal interactions, enabling detailed predictions of fibre paths around surface protrusions. In order to verify and validate this numerical framework, a series of full-scale braiding experiments was conducted using additively-manufactured thermoplastic mandrels. Final braid patterns as well as the occurrence of braid imperfections were investigated and compared to model predictions. It is shown that the proposed modelling strategy reproduces well the trends observed experimentally in terms of final braid quality. A parametric study was then conducted on the effects of initial end-fitting alignment with respect to oncoming yarns, suggesting that better control over this parameter could reduce considerably the occurrence of braid imperfections. 相似文献
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螺栓连接是工程结构的重要连接方式。优化螺栓连接结构的布局可以提高结构的力学性能。建立螺栓连接结构的有限元参数化模型,对连接板和螺栓进行有限元力学分析。运用萤火虫算法对螺栓布局进行优化设计,得到合理的螺栓排布尺寸,减小了孔周应力。当螺栓数量为4个时,与初始设计方案相比,优化后螺栓的分布更加合理,最大孔周应力明显下降。当螺栓数量为6个时,对三排和双排的初始设计方案进行优化,得到相同的双排最优螺栓布局。数值算例表明了萤火虫算法在螺栓连接结构布局优化中的有效性,研究结果可供机械设计参考。 相似文献
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采用第一性原理赝势平面波方法研究了合金元素Cr、V对Ti-Al系合金电子结构的影响,计算了含Cr、V的Ti-Al系合金的总能量、结合能、力学性能、电荷密度、态密度,从理论上解释了在Ti-Al系合金中固溶合金元素Cr、V后其性能得到改善的原因。计算结果表明,随着合金元素Cr(0~25at%)、V(0~25at%)含量的增加,合金的结合能绝对值逐渐增大,结构稳定性逐渐增强;切变模量G和杨氏模量E都逐渐增大,但提高的幅度逐渐减小。原因主要是固溶的Cr使合金中Cr3d、Al3p和Ti3d电子相互杂化,V使合金中V3d、Ti3d和Al3p电子相互杂化,合金的结合能力增强。 相似文献
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Al/SiC nanolaminates possess an excellent combination of mechanical strength and flexibility. While nanoindentation provides a reasonable estimate of the mechanical properties such as Young’s modulus and hardness of these materials, the stress state under nanoindentation is extremely complex. Micropillar compression has become an attractive method of studying the mechanical properties of materials at small length scales in a nominally homogeneous stress state. In this work, micropillars of Al/SiC nanolaminate were fabricated using focused ion beam milling. Compression testing was carried out using a flat-end nanoindenter head. The actual displacement of the pillar during micropillar compression was deconvoluted by subtracting the “extraneous” displacements of the system. Fractographic analysis showed that Al squeezes out between the SiC layers and that a mutual constraint is observed between the hard and soft layers. Numerical finite element modeling was also employed to provide physical insight into the deformation features of the multilayered pillar structure and agreed well with the experimental observations. 相似文献
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Fadi Al-Badour Nesar Merah Abdelrahman Shuaib Abdelaziz Bazoune 《Journal of Materials Processing Technology》2013,213(8):1433-1439
A 3-dimensional localized finite element model (FEM) is developed to predict likely conditions that result in defect generation during friction stir welding (FSW). The workpiece is modeled using Eulerian formulation, while the tool is modeled using Lagrangian. Coulomb's frictional contact model is adopted to define the tool workpiece interaction, while the welding speed is defined by material inflow and outflow velocities. The numerical results show that the coefficient of friction has a major effect on void formation; the lower the friction coefficient is applied, the larger the void is formed. Furthermore, welding using force control (FC) at lower welding speed results in smaller void size and wider plastic zone, leading to higher quality weld. 相似文献