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在单向晶须增强树脂基复合材料的三维单胞模型的基础上,利用细观力学有限元分析方法研究复合材料中SiC晶须体分比的变化对材料整体力学性能的影响.研究表明:在单向SiC晶须增强树脂基复合材料中,晶须体分比对晶须应力作用明显大于对基体的影响;随着晶须体分比的增加,界面剪切应力分布曲线下移;晶须体分比的变化对轴向弹性模量的影响远大于对横向弹性模量的影响. 相似文献
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应用二维平面模型和有限元分析方法研究了晶须在不同取向角单向排列和随机排列时对晶须增强树脂基复合材料应力应变和弹性性能的影响.结果表明:在晶须体积分数和外加应力相同的条件下,取向角θ的变化对应力应变集中系数有较大影响;晶须随机排列时,应力集中系数远大于单向排列时的应力集中系数,而应变集中系数同θ=30°时的系数接近;复合材料弹性模量随晶须取向角的增加而减小,当晶须取向角θ>45°时,弹性模量受晶须取向角的影响较小,晶须随机排列时的弹性模量值介于θ=30°和θ=45°的弹性模量值之间. 相似文献
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高雷诺数下有限长圆柱绕流阻力特性研究 总被引:1,自引:0,他引:1
针对不同长径比的有限长圆柱模型,采用大涡模拟及雷诺平均的方法,对高雷诺数下有限长圆柱绕流阻力特性进行数值模拟和分析,得到了圆柱阻力系数随长径比和雷诺数的变化规律,讨论端面效应对绕流阻力系数的影响。结果表明:在亚临界区内,相同雷诺数下阻力系数随长径比的增大而增大,呈线性变化规律,L/D的对阻力系数的影响明显大于Re对阻力系数的影响;在阻力危机区内,相同雷诺数下阻力系数随长径比的增大而增大,呈二次函数的变化规律,但各工况达到阻力系数“转折点”对应的雷诺数各不相同,基本呈现随雷诺数的增大向前推移的趋势,Re对阻力系数的影响明显大于L/D对阻力系数的影响;在阻力回升区,阻力系数回升的“转折点”随着雷诺数的逐渐增大而向后推移。在各分区内,端面效应对阻力系数的影响随雷诺数增大而更加明显,在高度方向上的最大影响区域约占圆柱总高度的16%。研究结果对有限长圆柱绕流特性的研究及应用具有重要意义和价值。 相似文献
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硫酸钙晶须填充UHMWPE复合材料的摩擦磨损性能 总被引:2,自引:0,他引:2
以硫酸钙晶须(CSW)作为填料填充改性超高分子量聚乙烯(UHMWPE),采用热压成型法制备了不同硫酸钙晶须含量的UHMWPE/CSW复合材料;在销-盘摩擦磨损试验机上考察了硫酸钙晶须对UHMWPE/CSW复合材料摩擦学性能的影响,利用扫描电子显微镜对UHMWPE复合材料的磨损表面进行了微观分析。结果表明:随着硫酸钙晶须填充量的增加,复合材料的硬度逐渐增大,耐磨性能逐渐增加,摩擦因数逐渐减小;当硫酸钙晶须填充质量分数为20%时,UHMWPE/CSW复合材料的摩擦学性能最好。 相似文献
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水润滑轴承在工作中存在表面粗糙峰接触等摩擦问题,而合理的长径比可以改善轴承润滑状态。以重载水润滑轴承为研究对象,建立水润滑轴承混合润滑热模型,通过有限差分法计算求解,研究长径比对重载水润滑轴承性能的影响。结果表明:在相同载荷条件下,增大长径比可增强水膜承载力、提高最小膜厚进而改善轴承润滑状态,可使轴承压力分布均匀、削弱应力集中效应从而提高轴承使用寿命;低速时增大长径比可降低摩擦因数,但高速时摩擦因数随长径比的增大而增大;增大长径比还可降低轴承温度,但不利于水流的轴向端泄排出。 相似文献
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Aluminium-based composites, reinforced with low volume fractions of whiskers and small particles, have been formed by a powder route. The materials have been tested in tension, and the microstructures examined using transmission electron microscopy. The whisker composites showed an improvement in flow stress over the particulate composites, and this was linked to an initially enhanced work-hardening rate in the whisker composites. The overall dislocation densities were estimated to be somewhat higher in the whisker composites than the particulate composites, but in the early stages of deformation the distribution was rather different, with deformation in the whisker material being far more localized and inhomogeneous. This factor, together with differences in the internal stress distribution in the materials, is used to explain the difference in mechanical properties. 相似文献
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分析了弯曲剪应力对弯扭组合变形轴主应力强度的影响,推出了考虑该因素影响时第三、第四强度理论的相当应力,并给出了设计公式。结合实例进行了分析比较,指出当轴中传动点距支承较近且扭矩比弯矩大时,剪应力对轴的强度有较大的影响。 相似文献
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Hong Gun Kim 《Journal of Mechanical Science and Technology》1994,8(4):475-484
It is well known that the shear lag theory is not to provide sufficiently accurate strengthening predictions when the fiber aspect ratio is small. This is due to its neglect of stress transfer across the fiber ends and the stress concentrations that exist in the matrix regions near the fiber ends. In this paper, a new approach to investigate stress transfer mechanisms in shear deformable discontinuous composites is proposed to overcome the shortcoming of shear lag theory. The modification scheme is based on the replacement of the matrix between fiber ends with the fictitious fiber to maintain the compatibility of displacement and traction. Thus, the proposed model takes fiber end effects into account and results in fully closed form solutions. It was found that the proposed model gives a good agreement with finite element results and has the capability to correctly predict the values of interfacial shear stresses and local stress variations in the small fiber aspect ratio regime. 相似文献
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采用Ansys/Ls-dyna平台,基于动态接触理论建立发动机气门-气门座冲击接触仿真分析模型,探讨发动机复层气门座材料匹配性对其接触特性的影响。研究结果表明:复层气门座摩擦副匹配对其接触应力影响较大,特别是反映材料弹性特征的模量E和密度ρ。当弹性模量匹配比Ec/Eq小于0.5时,等效应力σN随Ec/Eq的增大而增大,但当Ec/Eq大于0.5以后,σN的变化速率显得较平缓;密度匹配比ρc/ρq对σN的影响规律与E相似,其中σN随ρc/ρq变化速率的改变大约发生在0.5,当ρc/ρq超过0.5时,σN的变化速率也呈现平缓趋势。复层厚度h对σN的影响也较大,且存在非线性现象。一般地,h的增加可缓冲冲击接触,使σN降低,但当h达到0.6 mm时,σN显现反弹上升的现象,且其增幅与复层材料特性有关,并且h较小时,气门的反弹较小,接触应力较平缓。 相似文献
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Effects of filler crystal structure and shape on the tribological properties of PTFE composites 总被引:1,自引:0,他引:1
In this paper, effects of filler crystal structure and shape on the friction and wear properties of potassium titanate whisker (K2Ti4O9 whisker, K2Ti6O13 whisker), TiO2 whisker and TiO2 particle filled polytetrafluoroethylene (PTFE) composites under dry friction conditions were studied. Meanwhile the influence of filler content, sliding duration, test speed and load were also investigated. Experimental results show that the friction coefficients of various PTFE-based composites are weakly dependent on filler shape but they are more strongly dependent on filler crystal structure. However, for improving the anti-wear property of PTFE, filler crystal structure has less importance than filler shape in the wear-reducing action of PTFE-based composites, and whisker-like filler is better than particle-like filler. 相似文献
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Hong Gun Kim 《Journal of Mechanical Science and Technology》1998,12(2):257-266
In discontinuous composites, the fiber end effects can be neglected when the length of fiber is much greater compared to the
diameter. Thus, conventional shear lag theory is very useful for predicting composite properties deduced from each constituent.
However, in the case of short fiber or whisker reinforced composites, the end effects cannot be neglected, and the composite
properties are functions of material and geometrical parameters since the fiber end effects significantly influence the behavior
of composites. For a good understanding of the behavior of short fiber or whisker reinforced composites, it is necessary to
first understand the mechanism of stress transfer and it has well been modified before. However, the modification was limited
to the basic elastic stress calculation of the fiber and matrix in a micromechanical model. Accordingly, the former modification
of the shear lag model has been extended to predict the overall elastic composite behavior and elastic-plastic behavior of
which result can predict the stress concentration in the matrix as well as the onset of matrix yielding. The extended modification
results showed that it gives a good agreement with finite element analysis as well as with experimental data. It was also
found that the local matrix yielding is initiated in the vincinity of the fiber ends which produces local plasticity and an
elastic-elastic transition before the composite stress reaches matrix yield stress. 相似文献
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本文对SiC晶须增韧Al2O3陶瓷刀具材料的摩擦磨损特征和耐磨性能进行了试验及理论研究。用有限元法分析了SiC晶须在磨损过程中的力学特点,解释了晶须定向对不同表面的耐磨性能的影响。通过对x射线衍射极点密度的测试计算,发现基体Al2O3的晶体有择优取向的趋势,从而由晶体学角度分析并提出该现象对试件不同表面耐磨性能的差异也有一定影响。切削试验进一步验证了以上结论。本文提出应选用平行于热压轴方向的表面作为承受磨损的面。 相似文献
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碳纳米管和复合材料基体间的界面力学行为是影响复合材料宏观力学性能的重要因素,为此本文利用有限单元法对单壁碳纳米管增强聚合物复合材料的界面脱黏、切应力分布及拔出载荷进行了数值模拟。建立了一个轴对称三圆柱壳模型,引入ABAQUS中的Cohesive单元模拟了单壁碳纳米管和聚合物基体之间的界面层,分析了单壁碳纳米管的长细比、界面强度以及热残余应力等因素对碳纳米管与聚合物基体间的界面切应力以及拔出载荷的影响。模拟结果表明:当单壁碳纳米管的长度变化为50~100 nm、与基体之间的界面强度为50~100 MPa、环境温度变化为100℃ 时,碳纳米管的长细比、界面强度以及由于热失配所引起的残余应力对单壁碳纳米管与聚合物基体间的界面切应力以及拔出载荷有着显著的影响。 相似文献
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单层涂层最佳厚度的有限元分析 总被引:9,自引:0,他引:9
采用有限元数值计算的方法对TiN、TiC、Si3 N4及SiC四种材料的硬涂层体系表面下的应力分布进行了模拟分析。结果表明 ,对于TiN材料 ,当涂层厚度与接触半宽之比t/a <0 .3时 ,表面下的最大剪应力分布对提高轴承疲劳寿命较为有利 ;t/a =0 .5时 ,涂层系统的摩擦力学性能最差。涂层厚度较薄时 ,位于赫兹接触中心附近的涂层表层上的最大剪应力要远大于基体内的最大静态剪应力 ;当t/a >0 .1时 ,涂层表面上的最大剪应力对提高轴承疲劳寿命较为有利 ;涂层材料与基体材料的弹性模量之比小于 2 .0时 ,有利于提高涂层系统的疲劳寿命 相似文献
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Small iron spheres were made to impinge normally on iron plates at several different temperatures in gases with various oxygen activities. The spheres welded permanently to the plate when the impact occurred under purified hydrogen and at low impact velocities but rebounded at impact velocities larger than a characteristic value which increased with an increase in either the temperature or the surface cleanliness of the sphere and plate. Permanent adhesion can be prevented, even at low impact velocities, by coating the iron with very thin films of wüstite or with thinner films of Al2O3. The linear increase in impact area with impact velocity can be understood from the theory of the hardness indenter, using the appropriate high strain rate flow stress. It is inferred that a bond always forms between colliding bodies but that permanent adhesion occurs only when the elastic energy stored during impact is less than the energy required to break the bond by crack propagation. The stored elastic energy increases with impingement velocity by more than does the energy required for the propagation of a crack to separate the bodies completely. Consequently, there exists a critical velocity beyond which permanent adhesion does not occur. 相似文献