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211.
探讨了一种能够揭示三维复合型断裂现象并能记录这些现象的三维复合型断裂研究的实验方法,用此方法完成了LC4-CS航空结构铝合金不同厚度紧凑拉伸试样的I+Ⅱ复合型断裂试验。结果表明:此方法能够简便地确定出复合型裂纹的起裂载荷、破坏载荷、裂尖张开位移、滑移位移和起裂角,基本解决三维复合型断裂研究所需实验数据问题。同时发现此种材料试样的承载能力和超裂方向的确具有明显的厚度效应。 相似文献
212.
反射型云纹法在岩石爆破机理研究中的应用 总被引:2,自引:0,他引:2
利用反射型动态云纹实验方法,对爆炸载荷作用下岩石平板试件中应力波传播及裂纹动态扩展进行研究,给出了高速转镜相机记录到的岩石平板爆炸加载实验时的动态云纹图。根据动态云纹图分析了炸药爆炸产生的应变场,并对裂纹的形成及其扩展速度的变化趋势进行了讨论。 相似文献
213.
本文通过试验研究了35CrMo 合金钢三点弯曲试样疲劳短裂纹的扩展特性;用电测法得到了裂尖处的载荷—应变标定关系。试验结果表明,短裂纹的扩展速率正比于局部应力幅的幂次和裂纹长度,即 da/dN=A(?),可以较好地描述疲劳短裂纹的扩展规律。 相似文献
214.
Using dislocation simulation approach, the basic equation for a finite crack perpendicular to and terminating at a bimaterial
interface is formulated. A novel expansion method is proposed for solving the problem. The complete solution to the problem,
including the explicit formulae for theT stresses ahead of the crack tip and the stress intensity factors are presented. The stress field characteristics are analysed
in detail. It is found that normal stresses {ie27-1} and {ie27-2} ahead of the crack tip, are characterised byQ fields if the crack is within a stiff material and the parameters |p
T
| and |q
T
| are very small, whereQ is a generalised stress intensity factor for a crack normal to and terminating at the interface. If the crack is within a
weak material, the normal stresses {ie27-3} and {ie27-4} are dominated by theQ field plusT stress.
This work was supported by the Swedish Research Council for Engineering Sciences. 相似文献
215.
A disk-shaped compact tension (DC(T)) test has been developed as a practical method for obtaining the fracture energy of asphalt
concrete. The main purpose of the development of this specimen geometry is the ability to test cylindrical cores obtained
from in-place asphalt concrete pavements or gyratory-compacted specimens fabricated during the mixture design process. A suitable
specimen geometry was developed using the ASTM E399 standard for compact tension testing of metals as a starting point. After
finalizing the specimen geometry, a typical asphalt concrete surface mixture was tested at various temperatures and loading
rates to evaluate the proposed DC(T) configuration. The variability of the fracture energy obtained from the DC(T) geometry
was found to be comparable with the variability associated with other fracture tests for asphalt concrete. The ability of
the test to detect changes in the fracture energy with the various testing conditions (temperature and loading rate) was the
benchmark for determining the potential of using the DC(T) geometry. The test has the capability to capture the transition
of asphalt concrete from a brittle material at low temperatures to a more ductile material at higher temperatures. Because
testing was conducted on ungrooved specimens, special care was taken to quantify deviations of the crack path from the pure
mode I crack path. An analysis of variance of test data revealed that the prototype DC(T) can detect statistical differences
in fracture energy resulting for tests conducted across a useful range of test temperatures and loading rates. This specific
analysis also indicated that fracture energy is not correlated to crack deviation angle. This paper also provides an overview
of ongoing work integrating experimental results and observations with numerical analysis by means of a cohesive zone model
tailored for asphalt concrete fracture behavior. 相似文献
216.
Effects of magnetic field on fracture toughness of soft ferromagnetic materials were studied using experimental techniques and theoretical models. The manganese–zinc ferrite with a single-edge-notch-beam (SENB) were chosen to be the specimen and the Vickers’ indentation specimen subjected to a magnetic field were chosen to be the specimens. Results indicate that there is no significant variations of the measured fracture toughness of the manganese–zinc ferrite ceramic in the presence of the magnetic field. The theoretical model involves an anti-plane shear crack with finite length in an infinite magnetostrictive body where an in-plane magnetic field prevails at infinity. Magnetoelasticity is used. The crack-tip elastic field is different from that of the classical mode III fracture problem. Furthermore, the magnetoelastic fracture of the soft ferromagnetic material was studied by solving the stress field for a soft ferromagnetic plane with a center-through elliptical crack. The stress field at the tip of a slender elliptical crack is obtained for which only external magnetic field normal to the major axis of the ellipse is applied at infinity. The results indicate that the near field stresses are governed by the magnetostriction and permeability of the soft ferromagnetic material. The induction magnetostrictive modulus is a key parameter for finding whether magnetostriction or magnetic-force-induced deformation is dominant near the front an elliptically-shaped crack. The influence of the magnetic field on the apparent toughness of a soft ferromagnetic material with a crack-like flaw can be regarded approximately in two ways: one possesses a large induction magnetostrictive modulus and the other has a small modulus. Finally, a small-scale magnetic-yielding model was developed on the basis of linear magnetization to interpret the experimental results related to the fracture of the manganese–zinc ferrite ceramics under magnetic field. Studied also is the fracture test of the soft ferromagnetic steel with compact tension specimens published in the existing literature. 相似文献
217.
X.-F. Li 《Archive of Applied Mechanics (Ingenieur Archiv)》2003,72(10):745-758
Summary The dynamic problem of an impermeable crack of constant length 2a propagating along a piezoelectric ceramic strip is considered under the action of uniform anti-plane shear stress and uniform
electric field. The integral transform technique is employed to reduce the mixed-boundary-value problem to a singular integral
equation. For the case of a crack moving in the mid-plane, explicit analytic expressions for the electroelastic field and
the field intensity factors are obtained, while for an eccentric crack moving along a piezoelectric strip, numerical results
are determined via the Lobatto–Chebyshev collocation method for solving a resulting singular integral equation. The results
reveal that the electric-displacement intensity factor is independent of the crack velocity, while other field intensity factors
depend on the crack velocity when referred to the moving coordinate system. If the crack velocity vanishes, the present results
reduce to those for a stationary crack in a piezoelectric strip. In contrast to the results for a stationary crack, applied
stress gives rise to a singular electric field and applied electric field results in a singular stress for a moving crack
in a piezoelectric strip.
Received 14 August 2001; accepted for publication 24 September 2002
The author is indebted to the AAM Reviewers for their helpful suggestions for improving this paper. The work was supported
by the National Natural Science Foundation of China under Grant 70272043. 相似文献
218.
This paper discusses an analytical and experimental investigations of the fatigue crack growth behavior in attachment lugs subjected to a randomized flight-by-flight spectrum. In the analysis, the stress intensity factors for through-the-thickness cracks initiating from lug holes were compared by weight function method, boundary element method (BEM), the interpolation of Brussat’s solution. The stress intensity factors of a corner crack at a transition region were obtained using two parameter weight function method and correction factors. Fatigue life under a load spectrum was predicted using stress intensity factors and Willenborg retardation model considering the effects of a tensile overload. Experiments were performed under a load spectrum and compared with the fatigue life prediction using the stress intensity factors by different methods. Changes of fatigue life and aspect ratio according to the clipping level of the spectrum were discussed through experiment and prediction. Effect of the spectrum clipping level on the fatigue life was experimentally evaluated by using beach marks of fractured surface. 相似文献
219.
建立并研究一类接触型界面裂纹模型对瞬态弹性波作用下的动态响应问题。文中利用积分变换和积分方程法推导了确定这类问题的奇异积分方程组。采用围道积分技术和切比雪夫多项式展开技术,得到了待定系数的非线性代数方程组。最后给出了裂纹尖端接触区大小和接触应力随时间变化的数值结果,揭示了这种接触裂纹的动力学特性及物理上的合理性。 相似文献
220.
A method for solving problems of fracture of an infinite solid with a circular cylindrical cavity and a coaxial cylindrical crack near the surface under an uniform axial compression is proposed using a non-classical criterial approach associated with a mechanism of a local stability loss near the defect. The theory of integral Fourier transforms and series expansions are used to reduce these problems to a system of paired integral equations and then to a system of linear algebraic equations with respect to the contraction parameter. 相似文献