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1.
混凝土断裂过程区的虚拟裂纹粘聚力奇异性 总被引:4,自引:0,他引:4
混凝土断裂过程区视为具有粘聚阻力作用的虚拟裂纹,其非线性断裂和尺寸效应特性是与该虚拟裂纹粘聚力分布规律密切相关的。通过得到的粘聚应力分布函数解析结果,对该粘聚力分布特征的分析得知,在基于断裂过程区之外用线弹性场的力学模型上,该粘聚力随距离虚拟裂纹尖点的靠近,仍具有平方根奇异性。从而本文提出一个能够反映裂纹发展状态的粘聚应力奇异性强度参数,它是无粘聚力的线弹性裂纹应力强度因子和表征裂纹张开位移分布多项式参数的函数;因此,该参数可以作为混凝土非线性断裂的一个参量。文中就已有断裂试验测试结果进行了算例分析和相应的讨论。 相似文献
2.
双材料中平片裂纹问题的超奇异积分方程解法 总被引:1,自引:0,他引:1
利用三维断裂力学的超奇异积分方程方法,对双材料空间中重直于界面的平片裂纹Ⅰ型问题进行了研究。首先根据双材料空间的弹性力学基本解,使用边界积分方程方法,在有限部积分的意义下导出了以裂纹面位罗间断为未知函数的超奇异积分方程,并为其建立了数值法。在此基础上,讨论了用裂纹面位移问题计算应力强度因子的方法。最后用此计算了几个典型的Ⅰ型下片裂纹问题的应力强度因子,其数值结果令人满意。 相似文献
3.
Direct Extraction of Cohesive Fracture Properties from Digital Image Correlation: A Hybrid Inverse Technique 总被引:2,自引:0,他引:2
The accuracy of an adopted cohesive zone model (CZM) can affect the simulated fracture response significantly. The CZM has
been usually obtained using global experimental response, e.g., load versus either crack opening displacement or load-line
displacement. Apparently, deduction of a local material property from a global response does not provide full confidence of
the adopted model. The difficulties are: (1) fundamentally, stress cannot be measured directly and the cohesive stress distribution
is non-uniform; (2) accurate measurement of the full crack profile (crack opening displacement at every point) is experimentally
difficult to obtain. An attractive feature of digital image correlation (DIC) is that it allows relatively accurate measurement
of the whole displacement field on a flat surface. It has been utilized to measure the mode I traction-separation relation.
A hybrid inverse method based on combined use of DIC and finite element method is used in this study to compute the cohesive
properties of a ductile adhesive, Devcon Plastic Welder II, and a quasi-brittle plastic, G-10/FR4 Garolite. Fracture tests
were conducted on single edge-notched beam specimens (SENB) under four-point bending. A full-field DIC algorithm was employed
to compute the smooth and continuous displacement field, which is then used as input to a finite element model for inverse
analysis through an optimization procedure. The unknown CZM is constructed using a flexible B-spline without any “a priori”
assumption on the shape. The inversely computed CZMs for both materials yield consistent results. Finally, the computed CZMs
are verified through fracture simulation, which shows good experimental agreement. 相似文献
4.
本文采用奇异积分方程法分析了横观各向同性体中的埋藏裂纹。建立了张开型埋藏裂纹的Cauchy型奇异积分方程。当裂纹面和弹性对称轴垂直时,得到的裂纹张开位移方程的求解与各向同性情况类似。当裂纹面和弹性对称轴平行时,根据加权余量法,建立了弱解方程。给出两个算例,计算了圆形裂纹和椭圆形裂纹上的张开位移分布。数值结果表明:本文的方法是有效的。横观各向同性体中,埋藏裂纹方位任意时的裂纹张开位移方程,根据本文的方法易于得到。 相似文献
5.
相对于有限元法,边界单元法在求解断裂问题上有着独特的优势,现有的边界单元法中主要有子区域法和双边界积分方程法.采用一种改进的双边界积分方程法求解二维、三维断裂问题的应力强度因子,对非裂纹边界采用传统的位移边界积分方程,只需对裂纹面中的一面采用面力边界积分方程,并以裂纹间断位移为未知量直接用于计算应力强度因子.采用一种高阶奇异积分的直接法计算面力边界积分方程中的超强奇异积分;对于裂纹尖端单元,提供了三种不同形式的间断位移插值函数,采用两点公式计算应力强度因子.给出了多个具体的算例,与现存的精确解或参考解对比,可得到高精度的计算结果. 相似文献
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7.
采用修正的剪滞理论建立了岩石、混凝土等准脆性材料的I-II复合型裂缝在单向拉伸荷载作用下的计算模型,得到了与实验相吻合且优于传统S判据的断裂角。通过对远场应力、斜裂缝区应力以及子层位移的合理简化,得到了求解剪滞分析模型的边界条件,进而得到了含斜裂缝的各子层位移分布函数。引入最大应力集中因子,对I-II复合型裂缝前缘应力场进行简化;基于斜裂缝沿最大应力集中因子方向扩展,得到裂缝的断裂角。根据斜裂缝的应力分布,设置不同的子层分区,得到了更为细化的位移分布模式。通过对计算数据的分析,针对单向拉伸荷载作用下的I-II复合型裂缝,建立了按应力场分区设置子层的分层剪滞模型,得到更为精确的斜裂缝断裂角。 相似文献
8.
The scattering of general SH plane wave by an interface crack between two dissimilar viscoelastic bodies is studied and the
dynamic stress intensity factor at the crack-tip is computed. The scattering problem can be decomposed into two problems:
one is the reflection and refraction problem of general SH plane waves at perfect interface (with no crack); another is the
scattering problem due to the existence of crack. For the first problem, the viscoelastic wave equation, displacement and
stress continuity conditions across the interface are used to obtain the shear stress distribution at the interface. For the
second problem, the integral transformation method is used to reduce the scattering problem into dual integral equations.
Then, the dual integral equations are transformed into the Cauchy singular integral equation of first kind by introduction
of the crack dislocation density function. Finally, the singular integral equation is solved by Kurtz's piecewise continuous
function method. As a consequence, the crack opening displacement and dynamic stress intensity factor are obtained. At the
end of the paper, a numerical example is given. The effects of incident angle, incident frequency and viscoelastic material
parameters are analyzed. It is found that there is a frequency region for viscoelastic material within which the viscoelastic
effects cannot be ignored.
This work was supported by the National Natural Science Foundation of China (No.19772064) and by the project of CAS KJ 951-1-20 相似文献
9.
I.IntroductionCrazingdamageisacommonphenon1enonoffractureofpolymericmaterials.Theformationofcrazezoneisamid-stateinthefractureprocessofthematerialsfromperfectstatetofaiIurc.Microscopically,inthisregionthereexistssomefibrilslinkingthetwocracksurfacesandres… 相似文献
10.
本文利用三维断裂力学的超奇异积分方程求解理论,对三维无限体中两平行平片裂纹在任意载荷作用下的相互干扰问题作了研究。首先导出了以裂纹面移间断(位借)为未知函数的超奇异积分方程组,然后为其建立了有限积分边界元法;在此基础上,讨论用了裂纹面位移间断计算应力强度因子的方法,最后用此计算了两平行平片裂纹的相对位置对裂前沿应力强度因子的影响,其数值结果令人满意。 相似文献
11.
《International Journal of Solids and Structures》2006,43(5):1159-1188
Solution of Cauchy-type singular integral equations permits the evaluation of the fracture parameters at the crack tips very accurately. However, it does not permit the determination of the crack opening and sliding displacements while ensuring no crack surface interpenetration unless the location of the contact zone is known a priori. In order to circumvent this shortcoming, this study presents a solution method based on the Hadamard-type singular integral equations to obtain the crack opening and sliding displacements directly while enforcing the appropriate conditions to prevent interpenetration. Furthermore, the crack opening displacements are physically more meaningful and readily validated against the finite element analysis predictions. The numerical solutions of the hypersingular integral equations provide not only crack opening and sliding displacements directly but also the stress intensity factors and energy release rates. Also, the behavior of the energy release rate is examined as the cohesive crack located parallel to the interface approaches the interface from either the soft or the stiff side of the interface. The limiting value of the energy release rate is established by considering an interface crack. As the cohesive crack approaches the interface from either side of the interface, the energy release rate approaches to that of the interface crack. However, the length of contact zone between the cohesive crack surfaces under uniform shear loading does not approach to that of the interface crack. 相似文献
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IntroductionTheclassicalconhnuummechanicshasbeenusedtosolvemanyproblemsinmacrofracturemechanics,butencountersdifficulheswhentheeffectofITilcrocharacteristicdimensionshouldbetakenintoaccount.Thestressfieldverynearthecracktipisstillnotclear.Somephenomenaofshortcrackscannotbeexplained["']andsomemechanismoffracturehasnotbeensolvedyet.Thenon-localelashcitytheoryseemsattractivetotheseproblems.Thetheoryofnon-localelasticity,establishedanddevelopedbyEringenetal[3),connectstheclassicalcontinuummechan… 相似文献
14.
On anti-plane shear behavior of a Griffith permeable crack in piezoelectric materials by use of the non-local theory 总被引:3,自引:0,他引:3
In this paper, the non-local theory of elasticity is applied to obtain the behavior of a Griffith crack in the piezoelectric
materials under anti-plane shear loading for permeable crack surface conditions. By means of the Fourier transform the problem
can be solved with the help of a pair of dual integral equations with the unknown variable being the jump of the displacement
across the crack surfaces. These equations are solved by the Schmidt method. Numerical examples are provided. Unlike the classical
elasticity solutions, it is found that no stress and electric displacement singularity is present at the crack tip. The non-local
elastic solutions yield a finite hoop stress at the crack tip, thus allowing for a fracture criterion based on the maximum
stress hypothesis. The finite hoop stress at the crack tip depends on the crack length and the lattice parameter of the materials,
respectively.
The project supported by the National Natural Science Foundation of China (50232030 and 10172030) 相似文献
15.
Qin Taiyan Nanjing University of Aeronautics Astronautics Nanjing P. R. ChinaYue Jinchao Tang Renji Dept. of Engineering Mechanics Shanghai Jiaotong University Shanghai P. R. China 《Acta Mechanica Solida Sinica》1995,8(1):64-74
By using the analytic theory of hypersingular integral equations in three-dimensional fracture mechanics, the interactions between two parallel planar cracksunder arbitrary loads are investigated. According to the concepts and method of finite-part integrals, a set of hypersingular integral equations is derived, in which theunknown functions are the displacement discontinuities of the crack surfaces. Then itsnumerical method is proposed by combining the finite-part integral method with theboundary element method. Based on the above results, the method for calculating thestress intensity factors with the displacement discontinuities of the crack surfaces ispresented. Finally, several typical examples are calculated and the numerical resultsare satisfactory. 相似文献
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17.
A general case of proportional loading with a complex stress state of the material in the pre-fracture zone, which is typical
for polycrystalline solids with plastic deformation, is considered. A sufficient criterion of fracture is proposed for the
case of a complex stress state with non-proportional deformation of the material in the pre-fracture zone. Critical parameters
of fracture (pre-fracture zone length and load) for cracks propagating in quasi-brittle materials are obtained with the use
of a modified Leonov-Panasyuk-Dugdale model. The pre-fracture zone width is determined by solving the problem of the plasticity
theory in the vicinity of the crack tip. The proposed modification of the Leonov-Panasyuk-Dugdale model makes it possible
to estimate the critical opening of the crack and the critical displacement of the crack flanks. Inequalities that describe
different mechanisms of material fracture under proportional loading (predominantly shear fracture mechanism and fracture
mechanism through cleavage) are derived. 相似文献
18.
利用双材料位移基本解和Somigliana公式,将三维体内含垂直于双材料界面混合型裂纹问题归结为求解一组超奇异积分方程。使用主部分析法,通过对裂纹前沿应力奇性的分析,得到用裂纹面位移间断表示的应力强度因子的计算公式,进而利用超奇异积分方程未知解的理论分析结果和有限部积分理论,给出了超奇异积分方程的数值求解方法。最后,对典型算例的应力强度因子做了计算,并讨论了应力强度因子数值结果的收敛性及其随各参数变化的规律。 相似文献
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20.
采用Somigiliana公式给出了三维横观各向同性压电材料中的非渗漏裂纹问题的一般解和超奇异积分方程,其中未知函数为裂纹面上的位移间断和电势间断.在此基础上,使用有限部积分和边界元结合的方法,建立了超奇异积分方程的数值求解方法,并给出了一些典型数值算例的应力强度因子和电位移强度因子的数值结果,结果令人满意. 相似文献