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1.
Based on the mechanics of anisotropic materials, the dynamic propagation problem of a mode Ⅲ crack in an infinite anisotropic body is investigated. Stress, strain and displacement around the crack tip are expressed as an analytical complex function, which can be represented in power series. Constant coefficients of series are determined by boundary conditions. Expressions of dynamic stress intensity factors for a mode Ⅲ crack are obtained. Components of dynamic stress, dynamic strain and dynamic displacement around the crack tip are derived. Crack propagation characteristics are represented by the mechanical properties of the anisotropic materials, i.e., crack propagation velocity M and the parameter ~. The faster the crack velocity is, the greater the maximums of stress components and dynamic displacement components around the crack tip are. In particular, the parameter α affects stress and dynamic displacement around the crack tip. 相似文献
2.
Bao-Lin Wang Naotake Noda Jie-Cai Han Shan-Yi Du 《European Journal of Mechanics - A/Solids》2001,20(6):377
In this paper, we develop a model to treat penny-shaped crack configuration in a piezoelectric layer of finite thickness. The piezoelectric layer is subjected to axially symmetric mechanical and electrical loads. Hankel transform technique is used to reduce the problem to the solution of a system of integral equations. A numerical solution for the crack tip fields is obtained for different crack radius and crack position. 相似文献
3.
Conventional measurements of energy release rates,G
I andG
II, for delaminations in composite materials, generally utilize loads, crack lengths and simple standard specimen geometries. In this work, a more widely applicable measurement method, using phase shifting moiré and the J integral, is presented. The experimental technique described requires only fringe-pattern information and the elastic constants for the measurements—thus it can be used when the standard methods are inapplicable. Using conventional double-cantilever beam and end-notched flexure specimens, the energy release rate has been measured simultaneously by the moiré method and the standard methods, with good agreement found between the two. This development will for the first time permit the experimental validation of new finite-element routines as they are developed.Paper was presented at the 1993 SEM Spring Conference on Experimental Mechanics held in Dearborn, MI on June 7–9. 相似文献
4.
Liu Cheng 《Acta Mechanica Sinica》1989,5(3):244-252
In this paper, the dynamic propagation problem of a mixed-mode crack was studied by means of the experimental method of caustics.
The initial curve and caustic equations were derived under the mixed-mode dynamic condition. A multi-point measurement method
for determining the dynamic stress intensity factors,K
I
d
, andK
II
d
, and the position of the crack tip was developed. Several other methods were adopted to check this method, and showed that
it has a good precision. Finally, the dynamic propagating process of a mixed-mode crack in the three-point bending beam specimen
was investigated with our method. 相似文献
5.
In-plane unidirectional shear properties of carbon/epoxy and glass/epoxy materials were measured using unidirectional and
cross-ply specimens utilizing the Wyomingmodified two-rail shear test fixture. Simple test specimens of trapezoidal and rectangular
geometries, and specimens with tabs were tested. Various specimen sspect ratios were also considered. Untabbed unidirectional
specimens exhibited premature shear failures but cross-ply specimens produced reasonably reliable results with acceptable
failure modes. Both bonded tab and integral tab 0° specimens were found to give comparable results. Unidirectional and cross-ply
PEEK specimens, and angle-ply and quasi-isotropic AS4/3501-6 specimens, were also tested. 相似文献
6.
The originally developed reflection method of caustics is presented for application to cracks in mechanically anisotropic materials such as fiber-reinforced composites. The derived solutions for the combination of crack-opening modes I and II show that the size of the dark spot depends on the load intensity, whereas its shape depends strongly on the mechanical properties of the material, the orientation of the crack tip and the mixed-mode mixture. The evaluation of optical effects is possible using the diameter-measuring method or the advanced multipoint overdeterministic data reduction method. To find the exact position of caustics, the experimental images are analyzed by the simple boundary value method and a more sophisticated differential method, which is accomplished by shifting the real image onto the gradient image. The standard experimental testing procedure is performed for cracks oriented 0 deg, 45 deg and 90 deg to the material axes in carbon-fiber-reinforced polymer composites. 相似文献
7.
Some dynamic problems for elastic materials with functional inhomogeneities: anti-plane deformations
The paper considers two dynamical problems for an isotropic elastic media with spatially varying functional inhomogeneity, the propagation of surface anti-plane shear SH waves, and the stress deformation state of an anti-plane vibrating medium with a semi-infinite crack. These problems are considered for five different types of inhomogeneity. It is shown that the propagation of surface anti-plane shear waves is possible in all these cases. The existence conditions and the speed of propagation of surface waves have been found. In the section devoted to the investigation of the stress deformation state of a vibrating medium with a semi-infinite crack, Fourier transforms along with the Wiener Hopf technique are employed to solve the equations of motion. The asymptotic expression for the stress near the crack tip is analyzed, which leads to a closed form solution of the dynamic stress intensity factor (DSIF). Here also the problem is considered for five different functional inhomogeneities. From the formulae for DSIF thus obtained one can see that the inhomogeneity can have both a quantitative and qualitative impact on the character of the stress distribution near the crack.Received: 25 July 2002, Accepted: 3 April 2003, Published online: 27 June 2003PACS:
83.20.Lr, 83.50.Tq, 83.50.Vr, 46.30.Nz 相似文献
8.
IntroductionWiththedevelopmentofinformationindustryandtheapearanceofsmartmaterialsandsmartstructures,itbecomesmoreandmoreimpo... 相似文献
9.
Two systems of non-homogeneous linear equations with 8 unknowns are obtained.This is done by introducing two stress functions containing 16 undetermined coefficients and two real stress singularity exponents with the help of boundary conditions.By solving the above systems of non-homogeneous linear equations,the two real stress singularity exponents can be determined when the double material parameters meet certain conditions.The expression of the stress function and all coefficients are obtained based on the uniqueness theorem of limit.By substituting these parameters into the corresponding mechanics equations,theoretical solutions to the stress intensity factor,the stress field and the displacement field near the crack tip of each material can be obtained when both discriminants of the characteristic equations are less than zero.Stress and displacement near the crack tip show mixed crack characteristics without stress oscillation and crack surface overlapping.As an example,when the two orthotropic materials are the same,the stress singularity exponent,the stress intensity factor,and expressions for the stress and the displacement fields of the orthotropic single materials can be derived. 相似文献
10.
周承倜 《应用数学和力学(英文版)》1991,12(2):113-120
In this paper,the general equations of dynamic stability for composite laminatedplates are derived by Hamilton principle.These general equations can be used to considerthose different factors that affect the dynamic stability of laminated plates.The factors aretransverse shear deformation,initial imperfections,longitudinal and rotational inertia,andply-angle of the fiber,etc.The solutions of the fundamental equations show that someimportant characteristics of the dynamic instability can only be got by the considerationand analysis of those factors 相似文献
11.
The fracture problems near the similar orthotropic composite materials are interface crack tip for mode Ⅱ of double disstudied. The mechanical models of interface crack for mode Ⅱ are given. By translating the governing equations into the generalized hi-harmonic equations, the stress functions containing two stress singularity exponents are derived with the help of a complex function method. Based on the boundary conditions, a system of non-homogeneous linear equations is found. Two real stress singularity exponents are determined be solving this system under appropriate conditions about bimaterial engineering parameters. According to the uniqueness theorem of limit, both the formulae of stress intensity factors and theoretical solutions of stress field near the interface crack tip are derived. When the two orthotropic materials are the same, the stress singularity exponents, stress intensity factors and stresses for mode II crack of the orthotropic single material are obtained. 相似文献
12.
This paper provides a method for studying the penny-shaped cracks configuration in functionally graded material(FGM) structures
subjected to dynamic or steady loading. It is assumed that the FGMs are transversely isotropic and all the material properties
only depend on the axial coordinatez. In the analysis, the elastic region is treated as a number of layers. The material properties are taken to be constants
for each layer. By utilizing the Laplace transform and Hankel transform technique, the general solutions for the layers are
derived. The dual integral equations are then obtained by introducing the mechanical boundary and layer interface conditions
via the flexibility/stiffness matrix approach. The stress intensity factors are computed by solving dual integral equations
numerically in Laplace transform domain. The solution in time domain is obtained by utilizing numerical Laplace inverse. The
main advantage of the present model is its ability for treating multiple crack configurations in FGMs with arbitrarily distributed
and continuously varied material properties by dividing the FGMs into a number of layers with the properties of each layer
slightly different from one another.
This work was supported by Failure Mechanics Laboratory of State Education Commission and the Post-doctor Research Fund of
China. 相似文献
13.
14.
三点弯曲试样动态应力强度因子计算研究 总被引:2,自引:0,他引:2
利用Hopkinson压杆对三点弯曲试样进行冲击加载,采集了垂直裂纹面距裂尖2mm和与裂纹面成60°距裂尖5mm处的应变信号。根据裂尖附近测试的应变信号计算试样的动态应力强度因子,并与有限元计算结果进行比较,结果表明由于裂尖有一段疲劳裂纹区,通过裂尖附近应变信号来计算动态应力强度因子时,如果裂尖位置确定不准及粘贴应变片位置不够准确对计算结果将带来很大影响。因此利用应变片法计算动态应力强度因子时,为了获得更准确的计算结果,在实验后应对试件裂纹面进行分析测量,重新确定裂尖位置,必要时需对应变片至裂尖距离进行修正后再计算动态应力强度因子值。 相似文献
15.
The problem considered here is the response of a non-homogeneous composite material containing some cracks subjected to dynamic
loading. It is assumed that the composite material is orthotropic and all the material properties depend only on the coordinatey (along the thickness direction). In the analysis, the elastic region is divided into a number of plies of infinite length.
The material properties are taken to be constants for each ply. By utilizing the Laplace transform and Fourier transform technique,
the general solutions for plies are derived. The singular integral equations of the entire elastic region are obtained and
solved by the virtual displacement principle. Attention is focused on the time-dependent full field solutions of stress intensity
factor(SIF) and strain energy release rate. As a numerical illustration, the dynamic stress intensity factor of a substrate/functionally
graded film structure with two cracks under suddenly applied forces on cracks face are presented for various material non-homogeneity
parameters. 相似文献
16.
17.
We present a procedure for measuring the dynamic fracture-initiation toughness of materials. The method is based on three-point
bending tests at high loading rates, performed in an experimental device which is a modification of the classical split Hopkinson
pressure bar. Coupled with the loading device, a high-speed photography system was used to measure the crack mouth opening
displacement (CMOD) directly on the specimen. The stress intensity factor was calculated by three different simplified methods
and the time to fracture was obtained from an appropriate specimen instrumentation. To evaluate the results derived from the
simplified methods, a two-dimensional full-numerical analysis of the dynamic bending fracture test was made. The model includes
the specimen, the input bar, the impacting projectile and the supporting device and takes into account the possible loss of
contact during the experiment between the input bar and the specimen and between the specimen and its supports. From the tests
and numerical results, it can be concluded that the CMOD procedure, together with the knowledge of the time to fracture determined
using crack gages, seems to be the best method for measuring dynamic fracture-initiation toughness. 相似文献
18.
H. Miyagawa C. Sato K. Ikegami 《Archive of Applied Mechanics (Ingenieur Archiv)》2001,71(4-5):283-295
Summary Strain distribution near the crack tip of Raman-inactive Carbon Fiber Reinforced Plastics (CFRP) was measured by Raman spectroscopy.
A PbO thin film was deposited on the measured surface of the specimen by physical vapor deposition (PVD). The results agree
well with those obtained by conventional experimental methods and FEM analysis. The proposed method allows to investigate
fracture toughness of Raman-inactive materials.
Received 8 December 1999; accepted for publication 28 March 2000 相似文献
19.
You-Wen Liu 《Acta Mechanica Solida Sinica》1990,3(4):417-432
This paper deals with the problems of circular-arc crack between bonded dissimilar materials under antiplane concentrated forces. By applying the analytic continuation technique and the analyzing method of the Singularity in complex functions, we obtain universal solutions for the problems. For several typical cases the closed form solutions are obtained and the stress intensity factors are devived From these solutions, we provide a series of particular results, some of which coincide with those in Ref.(7). 相似文献