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为了研究碳纤维不锈钢层板的冲击动态响应以及热载荷条件下的冲击性能,采用ABAQUS/Explicit,编写基于复合材料渐进损伤用户子程序VUMAT;引入Johnson-Cook模型,仿真计算了碳纤维增强环氧树脂基复合材料-SS304不锈钢层板热载条件下冲击动态响应过程;分析了其冲击动态响应及渐进损伤,着重讨论了热载荷条件对碳纤维金属层板的冲击能量吸收、接触力等抗冲击性能及失效模式的影响.结果显示,高速冲击载荷作用下,纤维层的脆性断裂、金属层的塑性变形以及纤维层与金属层之间的脱层是碳纤维不锈钢层板的主要失效形式.热载荷的存在直接影响了冲头的接触力,随环境温度升高,接触力总体上降低,子弹的速度衰减越慢,剩余速度增大.结果表明,热载荷降低了纤维金属板的冲击动能吸收特性,弱化了碳纤维金属板的抗冲击性能.无论是纤维金属层板的整体破坏,还是纤维失效、基体失效和脱层失效,热载荷都产生了重要影响. 相似文献
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发展了一种模拟固壁近旁轴对称Stokes流中粘性液滴的运动和变形及直接计算固壁上应力的边界积分方法.用此方法对不同的液滴-固壁初始相对间距、粘度比、表面张力和浮力联合参数以及环境流动参数情况进行了数值实验.数值结果显示,由于环境流动和浮力的作用,随着时间的推进,液滴在轴向压缩,在径向拉伸.当环境流动的作用弱于浮力作用时,随着时间的推移,液滴上升并向上弯,固壁上由液滴运动所引起的应力不断减小.当环境流动的作用强于浮力作用时,随着时间的推移,液滴变得越来越扁.在这种情形,当大初始间距时,壁面上的应力随液滴的演变而增大;当小初始间距时,由环境流动、浮力及壁面对流动的较强作用的联合影响,此应力随液滴的演变而减小.由于液滴运动所引起的壁面应力的有效作用仅限于对称轴附近的一个小范围内,且此范围随液滴与固壁的初始间距增大而增大.应力的大小随初始间距增大而大为减小.表面张力对液滴变形有阻止作用.液滴粘性会减小液滴的变形和位置迁移. 相似文献
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杂交应力元假设的高阶应力场可以用较疏的网格获得较高的计算精度.采用四叉树网格离散非均质计算域,四叉树杂交应力单元悬挂节点的位移协调条件自动满足,且得益于单元类型数量有限,单元刚度矩阵可以预计算,以便在实际计算时直接读取调用,大幅提高了计算效率.考虑夹杂的随机性对颗粒增强复合材料力学性能的影响,采用均匀化方法和Monte-Carlo方法,研究了随机夹杂的体积比、数量、长宽比对材料均质等效模量的影响,结果表明,复合材料的等效弹性模量随夹杂体积比、数量、长宽比的增大而增大,且对体积比最敏感. 相似文献
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湿热环境中复合材料层合圆柱薄壳的屈曲和后屈曲 总被引:5,自引:0,他引:5
在宏-细观力学模型框架下,讨论湿热环境对复合材料层合圆柱薄壳在轴向压缩作用下屈曲和后屈曲行为的影响.基于细观力学模型复合材料性能与湿度和温度变化有关.壳体控制方程基于经典层合壳理论,并包括湿热效应.壳体屈曲的边界层理论被推广用于湿热环境的情况,相应的奇异摄动法用于确定层合圆柱薄壳的屈曲荷载和后屈曲平衡路径.分析中同时计及壳体非线性前屈曲变形和初始几何缺陷的影响.数值算例给出完善和非完善正交铺设层合圆柱薄壳在不同湿热环境中的后屈曲行为.讨论了温度和湿度,纤维体积比率,壳体几何参数,铺层数,铺层方式和初始几何缺陷等各种参数变化的影响. 相似文献
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纤维悬浮槽流空间模式稳定性分析 总被引:1,自引:1,他引:0
采用扰动的空间发展模式而非通常的时间发展模式,对含有悬浮纤维的槽流进行了线性稳定性分析。建立了适用于纤维悬浮流的稳定性方程并针对较大范围的流动Re数及扰动波角频率进行了数值求解。计算结果表明,纤维轴向抗拉伸力与流体惯性力之比H可以反映纤维对流动稳定性的影响。H增大使临界Re数升高,对应的扰动波数减小,扰动空间衰减率增加,扰动速度幅值的峰值降低,不稳定扰动区域缩小,长波扰动所受影响相对较大。纤维的存在抑制了流场的失稳。 相似文献
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针对在Reynolds数Re=3000~50000、Stokes数S_(tk)=0.1~10、Dean数De=1400~2800的情况下,长径比β=2~12的圆柱状颗粒流经弯管湍流场时的取向与沉积特性进行了研究.圆柱状颗粒的运动采用细长体理论结合Newton第二定律进行描述,取向分布函数由Fokker-Planck方程给出,平均湍流场通过求解Reynolds平均运动方程结合Reynolds应力方程得到,作用在颗粒上的湍流脉动速度由动力学模拟扫掠模型描述.通过求解湍流场以及颗粒的运动方程和取向分布函数方程,得到并分析了沿流向不同截面和出口处颗粒的取向分布,讨论了各因素对颗粒沉积特性的影响.研究结果表明,随着S_(tk)和颗粒长径比β的增加、De和Re的减少,颗粒的主轴更趋向于流动方向.颗粒的沉积率随着De,Re,S_(tk)和颗粒长径比的增大而增加,所得结论对于工程实际应用具有参考价值. 相似文献
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本文提出预测复合材料中裂纹方向的比应变能密度准则,并将Tsai-Hill与Norris准则扩展来预测复合材料中的开裂方向.用这三个准则预测了具有各种不同纤维方向的单向纤维复合材料的裂纹扩展方向,预测结果与现有的比正应力准则和应变能密度准则进行了对比. 相似文献
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Fracture of fiber-reinforced materials 总被引:10,自引:0,他引:10
Yu-Chen Gao Yiu-Wing Mai Brian Cotterell 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1988,39(4):550-572
The fracture behaviour of fiber-reinforced materials is studied in this paper. Using a simple shear lag model, which includes friction at the debonded interface and the Poisson contraction of the fiber, the fiber-matrix debonding problem is solved. This gives the relationship between debonding load and debonded length. Interfacial friction is shown to have a significant effect on the debonding load. The fracture toughness of fiber-reinforced materials due to fiber debonding, frictional dissipation at fibre-matrix interface following debonding and other micro-fracture mechanisms is discussed with reference to strong and weak fibres. Finally, the strength and toughness of short fibre-reinforced materials are given.On leave from Harbin Shipbuilding Engineering Institute, Harbin, China 相似文献
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Yih-Cherng Chiang 《Mechanics of Composite Materials》2007,43(2):113-126
A model for a macroscopic crack transverse to bridging fibers is developed based upon the Coulomb friction law, instead of
the hypothesis of a constant frictional shear stress usually assumed in fiber/matrix debonding and matrix cracking analyses.
The Lamé formulation, together with the Coulomb friction law, is adopted to determine the elastic states of fiber/matrix stress
transfer through a frictionally constrained interface in the debonded region, and a modified shear lag model is used to evaluate
the elastic responses in the bonded region. By treating the debonding process as a particular problem of crack propagation
along the interface, the fracture mechanics approach is adopted to formulate a debonding criterion allowing one to determine
the debonding length. By using the energy balance approach, the critical stress for propagating a semi-infinite fiber-bridged
crack in a unidirectional fiber-reinforced composite is formulated in terms of friction coefficient and debonding toughness.
The critical stress for matrix cracking and the corresponding stress distributions calculated by the present Coulomb friction
model is compared with those predicted by the models of constant frictional shear stress. The effect of Poisson contraction
caused by the stress re distribution between the fiber and matrix on the matrix cracking mechanics is shown and discussed
in the present analysis.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 2, pp. 171–190, March–April, 2007. 相似文献
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Y. I. Kunets V. V. Matus V. V. Mykhas’kiv A. Boström Ch. Zhang 《Mechanics of Composite Materials》2008,44(2):165-172
The problem of interaction of a plane time-harmonic SH-wave with an elastic fiber of quasi-square or quasi-triangular cross
section, when an interface crack is present between an infinite elastic matrix and the fiber, is considered. The modified
null-field method taking into account the asymptotic behavior of the solution at crack tips is exploited for obtaining numerical
results. The effects of fiber shape, fiber/matrix material combination, debonding (crack size), and direction of wave incidence
on the scattering amplitude in the far zone are analyzed.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 2, pp. 245–254, March–April, 2008. 相似文献
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This paper investigates the elastic responses of fibrous nano-composites with imperfectly bonded interface under longitudinal shear. The proposed imperfect interface model is the shear lag (or the spring layer) model; the presented nano interfacial stress model is the Gurtin–Murdoch surface/interface model; and the three-phase confocal elliptical cylinder model is the geometry model accounting for the fiber section shape. By virtue of the complex variable method, a generalized self-consistent method is employed to derive the closed from solution of the effective antiplane shear modulus of the fibrous nano-composites with imperfect interface. Five existing solutions can be regarded as the limit form the present analytic expression. The influences of the interface elastic constant, the interfacial imperfection parameter, the size of the elliptic section fiber, the fiber section aspect ratio, the fiber volume fraction and the fiber elastic property on the effective antiplane shear modulus of the nano-composites are discussed. Particularly, numerical results demonstrate that the interfacial elastic imperfection will always cause a significant reduction in the effective antiplane shear modulus; and the fiber interface stress effect on the effective modulus of the fibrous nano-composites will weaken with the interfacial imperfection increases. 相似文献
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In this presentation, a review is given on the main effects of mineral particulate fillers (with an aspect ratio of about
unity) on the deformation and fracture of amorphous and semicrystalline thermoplastic and thermosetting polymers. Elastomeric
modifiers, polymer blends, and filled elastomers are not considered here. Fillers are generally used to reduce cost as well
as the thermal sensitivity of mechanical properties of the matrix material and to improve, if possible, the strength and toughness.
The addition of particulate fillers influences all stages of the fabrication and use of the resulting composites. We focus
on the effects of a stiff second phase on elastic moduli, matrix structure, and on deformation, creep, and failure mechanisms.
As the main mechanisms, particle-matrix debonding, void formation, and matrix microshear yielding are identified. Toughness
is less sensitive to the quality of adhesion since particle-matrix debonding and formation of voids can be tolerated. If well
controlled, debonding contributes to deformation (formation of voids should be well distributed in space and time). Reference
is also made to the surprising and positive effect of CaCO3 particles on the toughness and impact resistance of HDPE, which increases at small interparticle distances due to interfacial
effects on lamellar growth in the ligament area.
Submitted to the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000).
Published in Mekhanika Kompozitnykh Materialov, Vol. 36, No. 3, pp. 305–316, March–April, 2000. 相似文献
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Free vibration and static analysis of functionally graded material (FGM) plates are studied using higher order shear deformation theory with a special modification in the transverse displacement in conjunction with finite element models. The mechanical properties of the plate are assumed to vary continuously in the thickness direction by a simple power-law distribution in terms of the volume fractions of the constituents. The fundamental equations for FGM plates are derived using variational approach by considering traction free boundary conditions on the top and bottom faces of the plate. Results have been obtained by employing a continuous isoparametric Lagrangian finite element with 13 degrees of freedom per node. Convergence tests and comparison studies have been carried out to demonstrate the efficiency of the present model. Numerical results for different thickness ratios, aspect ratios and volume fraction index with different boundary conditions have been presented. It is observed that the natural frequency parameter increases for plate aspect ratio, lower volume fraction index n and smaller thickness ratios. It is also observed that the effect of thickness ratio on the frequency of a plate is independent of the volume fraction index. For a given thickness ratio non-dimensional deflection increases as the volume fraction index increases. It is concluded that the gradient in the material properties plays a vital role in determining the response of the FGM plates. 相似文献
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The full strain field near the interface of steel fiber/concrete in a half-mold specimen was measured using a combined method
of pullout test and digital image correlation. The strain localization mechanism of the interfacial failure is discussed.
The strain distributions near the interface at a straight fiber under different loads show that the interfacial shear failure
has a distinct characteristic of intervals in time and space directly related to the strain localization, which makes the
interfacial failure initiate, develop and transfer successively. In particular, the local strain distributions around pores
near the straight fiber interface demonstrate that the strain changes its sign at the irregular parts of the pore where the
initial debonding took place and the deformation path is affected by the pore. 相似文献
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A unilateral contact problem between elastic bodies at small strains glued by a brittle adhesive is addressed in the quasistatic rate-independent setting. The delamination process is modeled as governed by stresses rather than by energies. This leads to a specific scaling of an approximating elastic adhesive contact problem, discretized by a semi-implicit scheme and regularized by a BV-type gradient term. An analytical zero-dimensional example motivates the model and a specific local-solution concept. Two-dimensional numerical simulations performed on an engineering benchmark problem of debonding a fiber in an elastic matrix further illustrate the validity of the model, convergence, and algorithmical efficiency even for very rigid adhesives with high elastic moduli. 相似文献
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Junjie Ye Xuefeng Chen Zhi Zhai Bing Li Yugang Duan Zhengjia He 《Mechanics of Composite Materials》2010,46(4):405-416
This paper aims to investigate the effect of microstructure parameters (such as the cross-sectional shape of fibers and fiber
volume fraction) on the stress–strain behavior of unidirectional composites subjected to off-axis loadings. A micromechanical
model with a periodic microstructure is used to analyze a representative volume element. The fiber is linearly elastic, but
the matrix is nonlinear. The Bodner–Partom model is used to characterize the nonlinear response of the fiber-reinforced composites.
The analytical results obtained show that the flow stress of composites with square fibers is higher than with circular or
elliptic ones. The difference in the elastoplastic response, which is affected by the fiber shape, can be disregarded if the
fiber volume fraction is smaller than 0.15. Furthermore, the effect of fiber shape on the stress–strain behavior of the composite
can be ignored if the off-axis loading angle is smaller than 30°. 相似文献