共查询到20条相似文献,搜索用时 15 毫秒
1.
A series of six frozen stress photoelastic tests was conducted to investigate the distribution of stress-intensity factor (SIF) along a crack which occurred at the juncture of a pipe (nozzle) with a cylindrical pressure vessel. Typical photoelastic-fringe patterns are shown for slices which were taken mutually orthogonal to the flaw border and the flaw surface. A typical plot of normalized apparent SIF vs. square root of normalized distance from the crack tip is presented. The variation in SIF along the flaw border is given for all six different crack geometries and, also, the variation of SIF with varyinga/T is presented. 相似文献
2.
A new photoelastic model for studying fatigue crack closure 总被引:1,自引:0,他引:1
The photoelastic analysis of crack tip stress intensity factors has been historically developed for use on sharp notches in
brittle materials that idealize the cracked structure. This approach, while useful, is not applicable to cases where residual
effects of fatigue crack development (e.g., plasticity, surface roughness) affect the applied stress intensity range. A photoelastic
model of these fatigue processes has been developed using polycarbonate, which is sufficiently ductile to allow the growth
of a fatigue crack. The resultant stress field has been modeled mathematically using the stress potential function approach
of Muskhelishvili to predict the stresses near a loaded but closed crack in an elastic body. The model was fitted to full-field
photoelastic data using a combination of a generic algorithm and the downhill simplex method. The technique offers a significant
advance in the ability to characterize the behavior of fatigue cracks with plasticity-induced closure, and hence to gain new
insights into the associated mechanisms. 相似文献
3.
L. V. Voitovich M. P. Malezhik I. S. Chernyshenko 《International Applied Mechanics》2010,46(6):677-682
The well-known equations of photoelasticity of linear viscoelastic bodies are used to describe the photoelastic behavior of
a viscoelastic orthotropic plate with a crack. Expressions for the stress intensity factors (SIFs) at the crack tip are obtained
using photoelastic measurements. The time dependence of the SIFs is analyzed and shown to be determined by the angles between
directions of the crack and tension 相似文献
4.
Shape-memory TiNi fiber-reinforced/epoxy matrix composites have been fabricated, and the suppression of crack-tip stress intensity
and the change in fracture toughness have been systematically investigated. Stress-strain data for these composite specimens
with notches at various angles and different crack lengths in the transverse direction have been measured in tensile tests.
The stress intensity factor at the crack tip is experimentally determined from photoelastic fringe patterns. The decreases
inK values are attributed to the compressive stress field in the matrix induced when the pre-strains of the TiNi fiber contract
to their initial length upon heating above the austenitic final temperature. We present the influences of the pre-strain of
TiNi fibers and the compressive domain size between a crack tip and fiber on theK value. 相似文献
5.
6.
An interacting micro-crack damage model for failure of brittle materials under compression 总被引:3,自引:0,他引:3
B. Paliwal 《Journal of the mechanics and physics of solids》2008,56(3):896-923
A model is developed for brittle failure under compressive loading with an explicit accounting of micro-crack interactions. The model incorporates a pre-existing flaw distribution in the material. The macroscopic inelastic deformation is assumed to be due to the nucleation and growth of tensile “wing” micro-cracks associated with frictional sliding on these flaws. Interactions among the cracks are modeled by means of a crack-matrix-effective-medium approach in which each crack experiences a stress field different from that acting on isolated cracks. This yields an effective stress intensity factor at the crack tips which is utilized in the formulation of the crack growth dynamics. Load-induced damage in the material is defined in terms of a scalar crack density parameter, the evolution of which is a function of the existing flaw distribution and the crack growth dynamics. This methodology is applied for the case of uniaxial compression under constant strain rate loading. The model provides a natural prediction of a peak stress (defined as the compressive strength of the material) and also of a transition strain rate, beyond which the compressive strength increases dramatically with the imposed strain rate. The influences of the crack growth dynamics, the initial flaw distribution, and the imposed strain rate on the constitutive response and the damage evolution are studied. It is shown that different characteristics of the flaw distribution are dominant at different imposed strain rates: at low rates the spread of the distribution is critical, while at high strain rates the total flaw density is critical. 相似文献
7.
C. William Smith 《Experimental Mechanics》1980,20(11):390-396
8.
工程结构裂纹尖端应力强度因子(SIF)由于形状、荷载的复杂性及边界条件的不确定性,难以用解析法得到,数值计算也有困难,而光弹性法弥补了上述方法的不足。本文用环氧树脂制作圆轴模型,采用机加工的方法制作圆轴模型裂纹,然后将加载模型进行应力冻结,通过光弹性实验研究分析了圆轴裂纹尖端应力分布。由于带环形裂纹的圆轴在弯扭组合变形时,离中性轴最远的裂纹尖端处于复合裂纹状态,而三维光弹性应力冻结法是测定复杂三维问题复合裂纹的有效方法。本文用双参数法测定I型应力强度因子,用切片逐次削去法测定Ⅲ型应力强度因子,实验误差较小。 相似文献
9.
10.
本文用光弹性法分析了双层复合材料结构的裂纹问题,研究了两种不同材料的存在对应力强度因子的影响,以及讨论了由于裂纹不断加深,应力强度因子的变化规律,并与计算的结果作了比较,在裂纹不接近界面情况下,两者结果吻合的较好。 相似文献
11.
12.
The variation of stress field around an oscillating crack tip in a quenched thin glass plate is observed using instantaneous
phase-stepping photoelasticity. The successive images around the propagating crack are recorded by a CCD camera that is equipped
with a pixelated micro-retarder array. Then, the phase maps of the principal stress difference and the principal direction
are easily obtained even though the photoelastic fringes cannot be visualized. The path of the crack growth as well as the
stress intensity factors and the crack tip constraint are obtained from these phase distributions. Results show that the mode
I stress intensity factor and the crack tip constraint vary remarkably with the crack growth. In addition, the results show
that the mode-II stress intensity factor exists even though the crack propagates smoothly. 相似文献
13.
In this paper, the theoretical solution developed by Vaughan and Wu for the stress analysis of a circular disk with a radial
edge crack extending to its center is validated by photoelasticity. The photoelastic results include the fullfield isochromatics
as well as measurements of the maximum shear stress at a number of test points. Additionally, the experimental stress intensity
factor is extracted from the photoelastic data by Irwin's two-parameter method. Good agreement is observed when the theoretical
stress field and stress intensity factor are compared with the experimental results. It is concluded that the Vaughan-Wu solution
can be confidently applied in fracture mechanics analyses. The application of such a solution to the stress analysis of two-dimensional
bodies with complex geometries subjected to complex loading is also noted. 相似文献
14.
《International Journal of Solids and Structures》1999,36(27):4089-4109
Engineering materials are rarely free of flaws. Mode I cracking from pre-existing flaws is the major cause of the brittle fracture in compression of materials such as concrete and rock. A 3-D ellipsoidal flaw model is used to show the significant influence of flaw geometry on crack initiation in uniform uniaxial, biaxial and triaxial compression. The model shows that the governing criterion for crack initiation may change from energy to stress with increasing crack size, and that for voids of similar size a spherical void is the most critical shape for crack initiation. The model thus provides a basis for a better understanding of both the phenomenon and the mechanism of brittle fracture in compression. 相似文献
15.
Failure of rock mass that is subjected to compres-sive loads occurs from initiation, propagation, and linkage of new cracks from preexisting fissures. Our research inves-tigates the cracking behaviour and coalescence process in a brittle material with two non-parallel overlapping flaws using a high-speed camera. The coalescence tensile crack and tensile wing cracks were the first cracks to occur from the pre-existing flaws. The initiation stresses of the primary cracks at the two tips of each flaw were simultaneous and decreased with reduced flaw inclination angle. The following types of coalescence cracks were identified between the flaws: pri-mary tensile coalescence crack, tensile crack linkage, shear crack linkage, mixed tensile-shear crack, and indirect crack coalescence. Coalescence through tensile linkage occurred mostly at pre-peak stress. In contrast, coalescence through shear or mixed tensile-shear cracks occurred at higher stress. Overall, this study indicates that the geometry of preexisting flaws affect crack initiation and coalescence behaviour. 相似文献
16.
The scattered-light photoelastic technique was utilized to determine Mode I stress-intensity factors associated with a semi-elliptical
surface flaw in a plate subjected to cylindrical bending. Stress-intensity factors were experimentally determined for the
point of maximum flaw penetration and the point of intersection of the flaw border with the free surface of the plate. Experimental
results compare favorably with those obtained in a three-dimensional finite-element analysis. 相似文献
17.
本文用热光弹性法对金属构件因热疲劳裂纹扩展而引起的残余应力场进行分析,并针对具体实验采用实验中途调节参数的方法满足了相似准则,使结果具有良好的精度. 相似文献
18.
Flaw tolerance refers to a state in which a pre-existing crack-like flaw does not propagate even as the material is stretched to failure near its theoretical strength. Such an optimal scenario can be achieved when the characteristic length scale is reduced to below a critical value. So far, the critical conditions to achieve flaw tolerance have been discussed mostly for homogeneous materials or for two dissimilar materials in frictionless or perfectly bonded adhesion. In this paper, we consider the role of friction in flaw tolerant adhesion between two dissimilar elastic solids. We adopt a frictional contact model in which slip is allowed wherever the shear stress along the interface reaches a threshold value defined as the friction strength. The critical length scale for flaw tolerance is derived analytically for a penny-shaped crack and for an external circular crack. Compared to the cases of frictionless contact, we find that interfacial friction can reduce the critical length scales for flaw tolerance by up to 12.5%. 相似文献
19.
Stress concentrations in thin-plate configurations commonly used in fatigue bending tests were determined by photoelastic means. The test configurations were rectangular and tapered plates with a centrally located hole. These configurations were machined from plates constructed by cementing together two sheets of similar photoelastic material. A reflective-type cement was used. In this manner, photoelastic measurements for the bending case were indicative of the average between maximum fiber stress and the stress at the reflective surface. The maximum fiber stress was then computed assuming that plane sections remain plane. Although bending was of primary concern, tension tests were also performed. The measured stress concentrations are compared with available analytical solutions. In the case of bending, the results are compared with infinite-plate solutions since the perforated finite-width plate bending problem has not been solved. 相似文献
20.
In this paper, a circumferential external surface flaw in a metallic round pipe under cyclic bending loading is considered.
Because of very rapid changes in the geometrical parameters around the crack front region, the mesh generation of this region
must be done with great care. This may lead to an increase in the run time which makes it difficult to reach valid results
and conclusions. Because of the advantages of the sub-modeling technique in problems which need very high mesh density, this
method is used. Stress intensity factors in mode I condition are determined using three-dimensional finite element modeling
with 20 node iso-parametric brick elements in the ANSYS 9.0 standard code and the singular form of these finite elements at
the crack front. In order to estimate the analysis error, the structural parameter error in energy norm criterion was used.
Because of the advantages of non-dimensional analysis, this method is employed, and the stress intensity factors are normalized.
For the analysis of the fatigue crack growth, the Paris law is used. The propagation path of the surface flaw is obtained
from the diagram of aspect ratio versus relative crack depth. The fatigue crack growth analysis (the relative crack depth
against loading cycles diagram) of different initial crack aspect ratio under cyclic loading is also considered. Fatigue shape
development of initially semi-elliptical external surface defects is illustrated. The effect of the Paris exponent (material
constant) on fatigue crack propagation is shown as well. Moreover, the fatigue crack growth of several specimens is assessed
experimentally using a manually-constructed experimental set up. Finally, the experimental results obtained by cyclic bending
loading tests are compared with the numerical results. The experimental results show good conformity with the finite element
results. 相似文献