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1.
The strain energy density ratio criterion for predicting cracking direction incomposite materials is proposed.The Tsai-Hill criterion and Norris criterion ofcomposite materials are extended to predict the cracking direction in composites.Thethree criteria are used to analyse the crack propagation problem of the unidirectionalfibre composite sheet with various fibre directions.The predicted results are comparedwith those of the existing normal stress ratio criterion and strain energy densitycriterion.  相似文献   

2.
AN EQUIVALENT CONTINUUM METHOD OF LATTICE STRUCTURES   总被引:1,自引:0,他引:1  
An equivalent continuum method is developed to analyze the effective stiffness of three-dimensional stretching dominated lattice materials. The strength and three-dimensional plastic yield surfaces are calculated for the equivalent continuum. A yielding model is formulated and compared with the results of other models. The bedding-in effect is considered to include the compliance of the lattice joints. The predicted stiffness and strength are in good agreement with the experimental data, validating the present model in the prediction of the mechanical properties of stretching dominated lattice structures.  相似文献   

3.
The mechanical behaviors of shape memory alloy (SMA) wires reinforced smart structure with damage were analyzed through the variational principle, a governing equation for the structure was derived, mathematical expressions for the meso-displacement field, stress-strain field of typical element with damage were presented, and a failure criterion for interface failure between SMA wires and matrix was established under two kinds of actuation which are dead-load and temperature, where the temperature is included in effective free restoring strain. In addition, there are some other composing factors in the failure criterion such as the interface properties, dynamical properties of SMA, initial debonding length L-l etc. The results are significant to understand structural strength self-adapted control and failure mechanism of SMA wires reinforced smart structure with damage.  相似文献   

4.
The damage effects of water sorption on the mechanical properties of the hydroxya-patite particle reinforced Bis-GMA/TEGDMA copolymer (HA/Bis-GMA/TEGDMA) have been predicted using 3D finite cell models. The plasticizer effect on the polymer matrix was considered as a variation of its Young's modulus. Three different cell models were used to determine the influence of varying particle contents, interphase strength and moisture concentration on the debonding damage. The stress distribution pattern has been examined and the stress transfer mode clarified. The Young's modulus and fracture strength of the Bis-GMA/TEGDMA composite were also predicted using the model with and without consideration of the damage. The former results with consideration of the debonding damage are in good agreement with existing literature experimental data. The shielding effect of our proposed model and an alternative approach were discussed. The FCC cell model has also been extended to predict the critical load for the damaged and the undamaged composite subject to the 3-point flexural test.  相似文献   

5.
The plastic load-bearing capacity of ductile composites such as metal matrix composites is studied with an insight into the microstructures. The macroscopic strength of a composite is obtained by combining the homogenization theory with static limit analysis, where the temperature parameter method is used to construct the self-equilibrium stress field. An interface failure model is proposed to account for the effects of the interface on the failure of composites. The static limit analysis with the finite-element method is then formulated as a constrained nonlinear programming problem, which is solved by the Sequential Quadratic Programming (SQP) method. Finally, the macroscopic transverse strength of perforated materials, the macroscopic transverse and off-axis strength of fiber-reinforced composites are obtained through numerical calculation. The computational results are in good agreement with the experimental data.  相似文献   

6.
The investigation on fatigue lives of reinforced concrete (RC) structures strength- ened with fiber laminate under random loading is important for the repairing or the strengthening of bridges and the safety of the traffic. In this paper, two methods are developed for predicting the fatigue lives of RC structures strengthened with carbon fiber [aminate (CFL) under random loading based on a residual life and a residual strength model. To discuss the efficiency of the model, 12 RC beams strengthened with CFL are tested under random loading by the MTS810 testing system. The predicted residual strength approximately agrees with test results.  相似文献   

7.
Fiber reinforced lattice composites are lightweight attractive due to their high specific strength and specific stiffness.In the past 10 years,researchers developed three-dimensional(3D) lattice trusses and two-dimensional (2D) lattice grids by various methods including interlacing, weaving,interlocking,filament winding and molding hot- press.The lattice composites have been applied in the fields of radar cross-section reduction,explosive absorption and heat-resistance. In this paper,topologies of the lattice composites, their manufacturing routes,as well as their mechanical and multifunctional applications,were surveyed.  相似文献   

8.
This contribution attempts to model the alteration of the in-plane elastic properties in laminates caused by stitching,and to predict the in-plane effective tensile strength of the stitched composite laminates.The distortion of in-plane fibers is considered to be the main cause that affects the in-plane mechanical properties.A fiber distortion model is proposed to characterize the fiber misalignment and the fiber content concentration due to stitching.The undistorted region,the fiber distortion region,the resin-rich pocket and the through-thickness reinforcement section are taken into account.The fiber misalignment and inhomogeneous fiber content due to stitching have been formulated by introducing two parameters,the distortion width and maximum misalignment.It has been found that the ply stress concentration in stitched laminates is influenced by the two concurrent factors,the stitch hole and inhomogeneous fiber content.The stitch hole brings about the stress concentration whereas the higher fiber content at the local region induced by stitching restrains the local deformation of the composite.The model is used to predict the tensile strength of the [0/45/0/-45/90/45/0/-45]_(2s) T300/QY9512 composite laminate stitched by Kevlar 29 yarn with different stitching configurations,showing an acceptable agreement with experimental data.  相似文献   

9.
EFFECTIVE ELASTIC MODULUS OF BONE-LIKE HIERARCHICAL MATERIALS   总被引:1,自引:0,他引:1  
A shear-lag model is used to study the mechanical properties of bone-like hierarchical materials.The relationship between the overall effective modulus and the number of hierarchy level is obtained.The result is compared with that based on the tension-shear chain model and finite element simulation,respectively.It is shown that all three models can be used to describe the mechanical behavior of the hierarchical material when the number of hierarchy levels is small.By increasing the number of hierarchy level,the shear-lag result is consistent with the finite element result.However the tension-shear chain model leads to an opposite trend.The transition point position depends on the fraction of hard phase,aspect ratio and modulus ratio of hard phase to soft phase.Further discussion is performed on the flaw tolerance size and strength of hierarchical materials based on the shear-lag analysis.  相似文献   

10.
The modified equivalent inclusion theory by the authors and the internalvariable theory are employed to investigate the evolution of the microcracks in whiskertoughening ceramics and the influence of the microcracks on the mechanical propertiesof the material. The effect of residual thermostrain, whisker content and aspect ratio isconsidered. The modulus, initial nonlinear load, strength and nonlinear constitutiverelation are calculated and some important conclusions are given.  相似文献   

11.
李岩 《固体力学学报》2005,26(3):303-308
采用中间开孔试样对剑麻织物增强乙烯乙酯基复合材料的剩余强度进行了研究.两种化学处理剂硅烷和高锰酸钾分别被用来对纤维表面进行处理,并对处理前后该种复合材料的剩余强度的变化进行分析,同时,利用微观分析揭示了剑麻织物增强乙烯乙酯基复合材料的剩余强度与破坏形貌之间的关系.  相似文献   

12.
I. INTRODUCTION Sisal ?bre is a promising natural ?bre, which has a potential application as reinforcement in compositematerials[1 , 2]. It has relatively high strength, high modulus, low density, particularly low price andabundant availability[3??5]. Compared to glass ?bre, sisal ?bre has several advantages. It is environment-friendly, recyclable, and the price is almost one-ninth that of glass ?bre and one-?ve hundredth of carbon?bre[6]. Fundamental considerations of design and ap…  相似文献   

13.
Summary Notch-induced stress concentrations in anisotropic composite materials depend on their directional material properties, especially for uniaxially reinforced composites with high-modulus fibres. The design of notched high-performance composites requires therefore a special proof of their notched strength, which includes the structural parameters of the fibre/matrix combination, fibre orientation and layer arrangement. The assessment of the effects of the finite outer boundary is of practical importance when dimensioning critical notched regions. An anisotropic plate with finite dimensions and a hole in its center will be used here to model stress concentrations. The calculation is based on conformal mappings combined with complex-valued stress functions. The outer boundary is described using point-matching and the least-squares method. The solutions are conducive to the assessment of the essential influencing factors of material properties, geometry and loads. Notched finite plates made of fibre/matrix composites, mainly carbon-fibre reinforced polymers, will be presented as illustrations. Received 29 June 1998; accepted for publication 22 October 1998  相似文献   

14.
陈少华  彭志龙 《力学进展》2008,38(4):502-517
纺织结构作为聚合物复合材料的增强相在许多工业应用中变得非常重要, 例如在航海与航空 领域中, 由于其刚度及强度与其重量的高比值而倍受欢迎. 由于工业及工程应用的需求, 研 究纺织复合材料的弹性性质及失效行为变得非常重要. 这篇文章重点评论了关于二维编织复 合材料弹性、热、强度及失效分析的数值及解析模型, 给出了主要的建模技术及方法. 同时 也简单给出了编织复合材料从最初的一维模型到最近三维模型的发展. 本文的目的不是对所 论模型的数学方法进行详细分析, 而是告知研究者关于先前工作的主要思想. 这篇评论总共 引用了122篇文献.  相似文献   

15.
Cure residual stress and its effect on damage in unidirectional fibre-reinforced polymer–matrix composites under transverse loading were studied using a micromechanical unit cell model and the finite element method. The overall residual stress introduced from curing was determined by considering two contributions: volume shrinkage of matrix resin from the crosslink polymerization during isothermal curing and thermal contraction of both resin and fibre as a result of cooling from the curing temperature to room temperature. To examine the effect of residual stress on failure, a model based on the Maximum Principal Stress criterion and stiffness degradation technique was used for damage analysis of the unit cell subjected to mechanical loading after curing. Predicted damage initiation and evolution are clearly influenced by the inclusion of residual stress. Residual stress is always detrimental for transverse compressive loading and pure shear loading. For transverse tensile loading, residual stress is detrimental for relatively low resin strength and beneficial for relatively high resin strength. Failure envelopes were obtained for both biaxial normal loading and combined shear and normal loading and the results show that residual stress results in a shifting and contraction of the failure envelopes.  相似文献   

16.
王玮  杜星文 《力学进展》2007,37(2):205-213
织物复合材料具有高的抗损伤性, 各方向的性能优于层合复合材料, 因而引起人们的重视. 织物增强复合材料由于其高比强度、易于制造和充分发展的织物技术等优点使其已经广泛用 于航空、汽车和运动产品. 由于使用这些材料越来越普遍, 自动化生产替代了手工生产, 用 精确的方法模拟材料的变形是必不可少的. 为了精确的反映材料的行为, 那么就需要描述材 料力学性质的本构方程,而作为验证本构模型的试验是伴随着本构模型的发展而发展的. 本文首先综述了织物及织物复合材料的发展和现状, 接着重点介绍了织物及织物复合材料的本构理论的研究发展, 并对织物及织物复合材料的斜拉伸试验、像框试 验等内容进行了介绍. 最后根据织物复合材料的最新进展对其未来的发展趋势进行了展望.  相似文献   

17.
Moisture absorption in natural fiber reinforced composites causes remarkable degradation of mechanical properties. A nonlinear constitutive model is proposed to study the effect of the water uptake on the mechanical properties of unidirectional natural fiber reinforced composites. Accompanying the water absorption in the composites, there are several irreversible thermodynamic processes such as fiber degradation and interface damage. The energy dissipation induced by these processes is described by an internal variable, and two degradation parameters representing interface damage and fiber degradation are introduced to reflect the modulus reduction of the composite. Particularly, the model is used to derive the evolution of elastic moduli influenced by the moisture absorption. The predictions from the present model show a good agreement with experiment results of sisal fiber unidirectional reinforced composites.  相似文献   

18.
碳纳米管/碳纤维增强复合材料(carbon nanotube/carbon fibre reinforced plastic,CNT/CFRP)是一种多尺度复合材料,比传统CFRP有更好的综合性能和更广阔的应用前景。对CNT/CFRP在低速冲击下的响应和破坏进行了数值模拟研究。首先,基于先前的研究通过引入基体增韧因子、残余强度因子并改进损伤耦合方程,建立了新的FRP动态渐进损伤模型;然后,利用新建立的本构模型并结合黏结层损伤模型,对4种碳纳米管含量的增韧碳纤维增强树脂基复合材料层合板在5个能量下的冲击实验进行了数值模拟;最后,将模拟结果与文献中的相关实验结果进行了比较,并讨论了冲击速度的影响。结果表明:新建立的FRP本构模型能够预测CNT/CFRP层合板在低速冲击载荷作用下的响应、破坏过程和分层形貌,模拟得到的载荷-位移曲线和破坏形貌与实验吻合较好;冲击速度会影响CNT/CFRP层合板拉伸和压缩破坏的比例,相同的冲击能量下,更大的冲击速度会造成更多的拉伸破坏。  相似文献   

19.
《力学快报》2020,10(1):57-65
In this research, the tensile properties' performance of compression moulded discontinuous randomized zalacca fibre/high-density polyethylene under critical fibre length was analysed by means of experimental method and micromechanical models. These investigations were used to verify the tensile properties models toward the effect of fibre length and volume fraction on the composites. The experimental results showed that the tensile properties of composites had significantly increased due to the enhancement of fibre length. On the contrary, a decline in the tensile properties was observed with the increase of volume fraction. A comparison was made between the available experimental results and the performances of Tsai-Pagano, Christensen and Cox-Krechel models in their prediction of composites elastic modulus. The results showed that the consideration of fibre's elastic anisotropy in the Cox-Krenchel model had yielded a good prediction of the composites modulus, nevertheless the models could not accurately predict the composites modulus for fibre length study.  相似文献   

20.
戴瑛 《力学季刊》1998,19(2):118-124
本文利用轴对称边界元程序,对影响纤维同界面剪面应力分布的材料和几何参数;纤维与基体的弹性模量比,纤维体积分数,试件厚度和支撑孔尺寸进行了数值分析工作,找出了纤维压出实验中导致界面双向脱粘的主要影响参数,给出了关于性暮一经和纤维体积分数的两界面端初始剪切脱粘的发生区域。  相似文献   

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