首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 156 毫秒
1.
考虑过渡区界面影响的混凝土宏观力学性质研究   总被引:1,自引:0,他引:1  
杜修力  金浏 《工程力学》2012,(12):72-79
混凝土材料的宏观力学特性及破坏机理由其细观组分来决定,界面过渡区是影响混凝土断裂破坏路径及宏观力学特性的重要因素。认为界面过渡区是区别于远处砂浆基质的一层含较高孔隙率的近场砂浆材料,采用"两步等效法"得到了混凝土细观单元的等效本构关系模型。最后基于细观单元等效化方法分析了在单轴拉伸、单轴压缩及弯拉载荷条件下混凝土试件的破坏过程及宏观力学性质,探讨了界面过渡区对混凝土力学特性的影响,并与随机骨料模型分析结果进行了对比。结果表明:界面相的存在对混凝土的弹性模量、强度及残余强度等力学性质有很大影响,在对混凝土宏观力学特性及细观断裂破坏过程进行研究时不可忽略其影响。  相似文献   

2.
考虑孔隙及微裂纹影响的混凝土宏观力学特性研究   总被引:1,自引:0,他引:1  
杜修力  金浏 《工程力学》2012,(8):101-107
混凝土是一种典型的多孔介质材料,孔隙分布错综复杂,孔径尺寸跨越微观尺度和宏观尺度,对混凝土弹性模量及强度等力学参数产生巨大影响。认为混凝土是由骨料、孔隙及砂浆基质组成的三相复合材料,采用Monte Carlo法将孔隙、微裂纹及微缺陷与骨料颗粒随机投放在砂浆基质中。根据三相球模型及中空圆柱形杆件模型得到含孔材料的有效力学性质,并推导得到含孔材料的等效本构模型。建立含孔隙混凝土试件的细观单元等效化力学模型,对二级配含孔隙混凝土试件在单轴拉伸及压缩条件下的反应进行了非线性分析。结果表明:孔隙、微裂纹的存在对混凝土宏观弹性模量、强度及残余强度等力学性质都有很大影响,在对混凝土宏观力学特性分析及研究混凝土损伤断裂时不应忽略其影响。  相似文献   

3.
饱和岩土类多孔材料内固、液相不同属性产生的各向异性和多孔微结构的不均匀性使得材料的细观力学特性计算变得十分复杂。为准确预测岩土类材料的有效弹性性能和细观应力-应变场,基于Biot多孔弹性介质理论,建立可描述岩土类多孔材料固液相运动的能量泛函和相应的多孔弹性本构关系;利用细、宏观尺度比作为小参数将能量变分泛函渐近扩展为系列近似泛函;以场变量波动函数为未知量,通过解决近似泛函的最小化问题(驻值问题)得到波动函数的解析解,从而建立逼近物理和工程真实性的细观力学模型,并通过有限元技术得以数值实现。多孔介质材料细观力学特性算例表明:与经典均匀化理论(将液体类比为具有较高泊松比的固体材料)相比,基于变分渐近均匀化细观模型预测的多孔介质材料细观力学特性更精确,尤其是能准确重构多孔微结构内局部应力-应变场分布,为损伤破坏、局部断裂分析奠定了坚实基础。  相似文献   

4.
混凝土材料具有明显的应变率效应,对其力学性质增强机理的认识还不统一。在细观随机骨料模型基础上,采用特征单元尺度划分试件网格,推导了考虑材料拉/压强度应变率效应的细观单元等效本构关系,建立了非均质混凝土材料的细观单元等效化数值模型。基于二维模型对Dilger等混凝土动态压缩试验进行了数值模拟,获得的数值结果与试验数据及随机骨料模型结果吻合良好,证明了细观单元等效化方法的准确性;进而对三维混凝土试件动态单轴拉伸和压缩破坏模式及宏观力学性质的加载速率效应进行了研究。数值结果表明:随着加载速率的增加,混凝土裂纹(损伤)数量增大,混凝土破坏将耗散更多的能量,是混凝土动态强度提高的主要原因。  相似文献   

5.
模拟水泥基复合材料细观断裂过程的随机弹簧元   总被引:2,自引:0,他引:2       下载免费PDF全文
叙述了水泥基复合材料从微观裂缝发生到断裂形成的一个计算机模拟系统。该系统主要是通过把骨料和水泥基分别看成具有不同性质的构造单元考虑水泥基复合材料的非均质性;用弹簧元法的单元形状任意性与变位不连续性模拟其构造上的随机性及其断裂形成过程。并以数值模拟混凝土试件的拉伸断裂和压缩断裂为例,探讨材料的裂缝细观进展机理及其和宏观力学特性的关系。  相似文献   

6.
正自2004石墨烯被发现以来,凭借其独特的性质引起了全世界科学研究者的广泛关注。最初发现的石墨烯是由诺贝尔物理学奖获得者Novoselov和Geim两位科学家采用胶带反复剥离石墨制备得到的~([1])。石墨烯是由碳原子以sp2杂化排列排列形成的具有蜂窝状结构的二维晶体材料,是构成石墨材料的基本单元,理论厚度约为0.35nm,是目前世界上发  相似文献   

7.
关于多孔材料的新模型   总被引:5,自引:1,他引:4  
指出了多孔材料的经典性模型-Gibson-Ashby模型的不足,如孔隙单元非密积、棱柱状态不等价等,提出了一个能弥补Gibson-Ashby模型这些不足的新模型.应用这个新模型,可获得与实验结果符合良好的三维网状泡沫材料电阻率关系和力学关系的表征.实验结果证明,应用于多孔材料时,由新模型所得的有关数理关系明显优于Gibson-Ashby模型。  相似文献   

8.
采用粒子沥滤结合气体发泡的方法制备聚乳酸(PLA)多孔支架,探讨浓度、发泡剂、温度等条件对支架宏观形貌和微观性质的影响,研究各个因素之间的相互关系,研究其表面形貌与微观结构之间的关系。研究发现对于不同尺寸制孔剂制备的支架,通过调节浓度、温度等条件,可以得到相似的薄层多孔的表面形貌,其对应的微观结构和性能(力学、孔隙率、贯通性)较好。  相似文献   

9.
纸张材料弹性模量与剪切模量的关系   总被引:1,自引:1,他引:0  
谢一环 《包装工程》2012,33(21):37-40
研究了正交各向异性的纸张的各个材料参数之间的关系,以减少描述纸张材料性能所需的独立参数,并在纸制结构分析中,合理匹配了材料参数。通过对材料单元在纯剪切载荷作用时与纯主应力载荷作用时的两种变形进行力学比较分析,获得了纸张的弹性模量、剪切模量和泊松系数之间的关系,并导出了简单数学公式。该公式在纸制结构设计、振动分析以及有限元计算等方面有实用的意义。  相似文献   

10.
采用第一性原理计算研究了超硬材料z-BC2N的弹性各向异性性质、应力-应变关系、硬度及最小热导率性质。计算得到的晶体力学行为判据B/G为0.87,泊松比为0.084,普适弹性各向异性指数为0.09992。[100]晶向上最大拉伸强度达到180 GPa,(100)[010]应变方向上最大剪切强度达到160 GPa,维氏硬度值为77.07 GPa。基于Cahill模型得到的最小热导率为6.811 W/(m·K)。结果表明:z-BC2N是脆性材料且力学稳定性良好,有非常高的拉伸强度、剪切强度,体弹模量为各向同性,杨氏模量各向异性程度不大。z-BC2N的最小热导率低于金刚石的最小热导率。  相似文献   

11.
《Composites Part B》2013,45(1):714-721
Statistical continuum theory is a powerful tool for predicting the effective properties of heterogeneous materials, where the shape of the fillers is random over the representative volume element (RVE). Due to this geometrical complexity of the shape of fillers, the heterogeneous material might present some anisotropy, which can be difficult to measure experimentally. In these cases the statistical continuum theory can be used as a tool to predict the degree of anisotropy. The aim of the present work is to present an implementation method based on analytical probability functions that can be easily integrated numerically to predict the effective properties of heterogeneous materials. In this regard, the strong-contrast version of the statistical continuum theory is used to predict the effective mechanical properties of heterogeneous materials. For validation, the effective mechanical properties of porous P-311 glass are predicted using the strong-contrast approach, and compared to experimental results and to ones calculated using a differential scheme (DS) model, which is based on Eshelby’s theory of inclusion embedded in an equivalent continuum matrix. Further, to demonstrate the effectiveness of the strong-contrast approach in dealing with anisotropic materials, the effective mechanical properties of a macroscopically anisotropic heterogeneous material are predicted and compared to ones calculated using the DS model. Finally, remarks on the implementation of the strong-contrast approach are highlighted through calculations using fillers with different sizes.  相似文献   

12.
The fundamental macroscopic material property needed to quantify the flow in a fibrous medium viewed as a porous medium is the permeability. Composite processing models require the permeability as input data to predict flow patterns and pressure fields. As permeability reflects both the magnitude and anisotropy of the fluid/fiber resistance, efficient numerical techniques are needed to solve linear and nonlinear homogenization problems online during the flow simulation. In a previous work the expressions of macroscopic permeability were derived in a double-scale porosity medium for both Newtonian and rheo-thinning resins. In the linear case only a microscopic calculation on a representative volume is required, implying as many microscopic calculations as representative microscopic volumes exist in the whole fibrous structure. In the non-linear case, and even when the porous microstructure can be described by a unique representative volume, microscopic calculation must be carried out many times because the microscale resin viscosity depends on the macroscopic velocity, which in turn depends on the permeability that results from a microscopic calculation. Thus, a nonlinear multi-scale problem results. In this paper an original and efficient offline-online procedure is proposed for the efficient solution of nonlinear flow problems in porous media.  相似文献   

13.
材料现代分析方法与新材料技术的发展   总被引:3,自引:3,他引:0  
着重从宏观的角度论述材料现代分析方法与新材料技术发展的关系。从材料科学研究的实质出发,其目的在于解释材料的宏观性能与微观组织结构的关系,指出材料现代分析方法是进行材料科学研究以及材料工程应用及失效分析必不可少的研究方法,是对材料的组元、成分、结构特征以及组织形貌或缺陷等进行观察和分析的重要手段,列举了主要材料现代分析的方法和技术的进展。阐述了在新材料的研究及产品的应用中,材料检测评价技术所起的重要地位和作用。  相似文献   

14.
High-quality magnesium foams were fabricated by an infiltration technology using tailor-made salt–flour mixture space holders. The pore structures and mechanical properties of space holder particles as well as the resultant foam production with spherical pores were characterized in the present study. The particles after high-temperature sintering dissolved rapidly in water due to their porous structures, guaranteeing the weak corrosion and high-purity of magnesium foams. The spherical pores foams exhibited usual stress–strain behaviors and nearly isotropic properties. The yield strengths of the foams increased with the decrease of sample porosity, and the relative mechanical properties of foams were mostly dependent on their relative densities, which obeyed a power law relation. Moreover, porous magnesium materials with tunable pore structures could be fabricated owing to the flexible forming features of salt–flour mixture, showing great application prospects in bone implant material field.  相似文献   

15.
The theoretical need to recognize the link between the basic microstructure of nonlinear porous materials and their macroscopic mechanical behavior is continuously rising owing to the existing engineering applications. In this regard, a semi-analytical homogenization model is proposed to establish an overall, continuum-level constitutive law for nonlinear elastic materials containing prolate/oblate spheroidal voids undergoing finite axisymmetric deformations. The microgeometry of the porous materials is taken to be voided spheroid assemblage consisting of confocally voided spheroids of all sizes having the same orientation. Following a kinematically admissible deformation field for a confocally voided spheroid, which is the basic constituent of the microstructure, we make use of an energy-averaging procedure to obtain a constitutive relation between the macroscopic nominal stress and deformation gradient. In this work, both prolate and oblate voids are considered. As a numerical example, we study macroscopic nominal stress components for a hyperelastic porous material consisting of a neo-Hookean matrix and prolate/oblate voids subjected to 3-D and plane strain dilatational loadings. In this numerical study, the relation between the relevant microstructural variables (i.e., initial porosity and void aspect ratio) for a rather large range of applied stretch is put into evidence for two types of loading. Finally, a finite element (FE) simulation is presented, and the homogenization model is assessed through comparison of its predictions with the corresponding FE results. The illustrated agreement between the results demonstrates a good accuracy of the model up to rather large deformations.  相似文献   

16.
Herein, it is concerned with the use of profilometry-based indentation plastometry (PIP) to obtain mechanical property information for particulate metal matrix composites (MMCs). This type of test, together with conventional uniaxial testing, has been applied to four different MMCs (produced with various particulate contents and processing conditions). It is shown that reliable stress–strain curves can be obtained using PIP, although the possibility of premature (prenecking) fracture should be noted. Close attention is paid to scale effects. As a consequence of variations in local spatial distributions of particulate, the “representative volume” of these materials can be relatively large. This can lead to a certain amount of scatter in PIP profiles and it is advisable to carry out a number of repeat PIP tests in order to obtain macroscopic properties. Nevertheless, it is shown that PIP testing can reliably detect the relatively minor (macroscopic) anisotropy exhibited by forged materials of this type.  相似文献   

17.
One of the most common materials utilized by material extrusion 3D printing is acrylonitrile butadiene styrene (ABS). The work presented in this research explored the effect of the addition of reinforcing materials on the mechanical properties of ABS in an effort to create materials with enhanced physical properties. A comparison was made between pure ABS, two ABS matrix composites, and one ABS/elastomer blend with the purpose of characterizing the effect of additives on the mechanical properties. Tensile test results of specimens built in different orientations showed that ABS reinforced with 5% by weight TiO2 exhibited the highest ultimate tensile strength for specimens built in both horizontal and vertical directions with 32.2 and 18.4 MPa, respectively. The compounding of an elastomeric material with ABS improved the surface finish of parts as they were visibly smoother compared to those printed from the ABS baseline material, though there was an observable decrease in the ductility of tensile specimens. Analysis was performed on the fracture surface of the tensile specimens through the use of scanning electron microscopy. Fractography revealed different modes of failure related to the different additives. The effects of additives on the anisotropy associated with the mechanical properties of 3D-printed parts were also analyzed.  相似文献   

18.
含孔隙混凝土复合材料有效力学性能研究   总被引:3,自引:1,他引:2  
混凝土、岩石等工程材料是典型的多孔介质材料,孔隙或微裂纹的存在对材料的弹性模量及强度等力学参数产生很大影响。该文基于三相球模型确定了含孔隙复合材料的有效体积模量,提出采用空心圆柱形杆模型推导得到了含孔隙复合材料有效剪切模量的理论公式,并在各向同性材料的假设条件下确定了材料的有效弹性模量及泊松比;推导并得到了含孔隙材料的有效抗拉、抗压强度及有效抗剪强度与孔隙率之间的定量关系公式,并进一步得到了含孔基质在达到有效强度时的临界应变与孔隙率之间的定量关系。结果表明该文方法能较好的预测含孔混凝土材料的有效力学性能,且公式简单,易于应用。  相似文献   

19.
A porous CuAlMn shape memory alloy with adjustable pore characteristics and mechanical properties has been successfully fabricated via the sintering–dissolution process for the first time. Micro amount of fluoride was added to accelerate the sintering of CuAlMn powders covered with the oxide film. The resultant material exhibits uniformly distributed and interconnected macroscopic pores. In order to eliminate possible adverse effects of the microstructures resulted from slow cooling on the properties of the resultant materials, appropriate solution and quench treatments were carried out. The microstructures and quasi-static compressive deformation behaviors of the resultant materials were also examined before and after treatments.  相似文献   

20.
《Thin solid films》2006,494(1-2):223-227
Yttria stabilized zirconia (YSZ)/Al2O3 composite coatings were prepared by an electrophoretic deposition (EPD) method. The mechanical properties of the coatings were determined by nanoindentation and residual stresses were measured by Cr3+ fluorescence spectroscopy. It was found that the nanoindentation was sensitive to the presence of sub-micrometer pores. In order to determine the macroscopic mechanical properties, a penetration depth of > 1000 nm was required due to the porous and inhomogeneous nature of the materials. Both microstress and mechanical properties exhibited a gradient across the coating thickness, which can be attributed to the density gradient caused by constrained sintering of the coatings. It has been confirmed that the mechanical properties determined by nanoindentation are not affected by the external applied stress. AFM examination confirmed there was no impression pile-up during indentation.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号