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 10 毫秒
1.
《Composites Part B》2001,32(2):131-138
In this work, the effect of surface cracks on strength has been investigated theoretically and experimentally for glass/epoxy filament wound pipes, which are mainly used for bazooka launchers. The pipes with surface crack which have several notch-aspect ratios a/c and notch-to-thickness ratios a/t in the axial direction were exposed to open-ended internal pressure. Critical stress intensity factors were determined experimentally for several winding angles by tensile tests with center notched ring specimens. The strength values of pipes with surface cracks are compared with internal pressure test results and theoretical results.  相似文献   

2.
The stress intensity factor is derived for both single and multiple longitudinal, elliptical cracks in the wall of a pressurized thick cylinder of given geometry. For this purpose, it is found necessary to combine known solutions to the stress intensity factor for a straight longitudinal crack with the effects of a curved crack front and multiple cracking. The analysis is appraised from a number of fatigue tests reported for % Ni-Cr-Mo cylinders with diameter ratios of between 2 and 3 under repeated and fluctuating pressure cycles. When cylinders with poorly finished bores are assumed to be initially flawed, it is found that their fatigue lives under high ranges of pressure may be predicted reliably for the single crack propagation failures observed. This analysis employs published WOL or SEN fatigue crack growth data for the alloy. The enhancement in fatigue life that results from an improved surface finish has enabled that proportion of life expended during the initiation phase to be determined. It is further shown that the observed effect of mean stress and surface finish on the fatigue limit may be quantified with a change to the threshold of stress intensity for crack growth. A number of tests were conducted with two-step changes to the amplitude of the pressure cycle. In this instance, nonlinear, stress dependent, cumulative damage rules are shown to offer no advantage over Miner's rule in the prediction of fatigue life.  相似文献   

3.
4.
《Composites Part A》2007,38(4):1192-1199
The aim of this study is to examine the corrosion fatigue behavior of filament wound composite pipes with a surface crack under alternating internal pressure. The filament wound pipes are composed of multi-layered E-glass/epoxy composites with a [±75°]3 lay-up. The surface notches were formed on the outer surface of the pipe along the pipe axis. Dilute (0.6 M) HCl acid was applied to the surface crack region by a corrosion cell mounted on the outer surface of the pipe. The results of an experimental investigation into the corrosion fatigue tests are conducted to observe the oil leakage failure and the crack propagation of the composite pipe subjected internal pressure loading with an open ended condition in which the pipe can be deformed freely in the axial direction. The internal pressure was generated by conventional hydraulic oil for fatigue loading. The fatigue tests are performed at 0.42 Hz frequency and a stress ratio of R = 0.05 in accordance with ASTM D-2992 standard. The oil leakage from the crack tip was observed after the crack propagation reached to the critical stress intensity level. The fatigue crack propagation behavior with the environment exposure was strongly dependent on the crack parameters such as crack-depth ratio and crack-aspect ratio. The micro structure of the fracture surface with the effect of environment and the fatigue loading were also observed.  相似文献   

5.
A methodology for fatigue analysis of damaged steel pipelines under cyclic internal pressure is proposed. This methodology employs stress concentration factors, which are commonly used to modify standard S–N curves of metallic structures under high cycle fatigue loadings. Experiments are accomplished to evaluate the strain behavior of small-scale steel pipes during denting and cyclic internal pressure. A nonlinear finite element model is developed to obtain stress concentration factors induced by plain dents on steel pipes under internal pressure. Afterwards, analytical expressions are developed to estimate stress concentration factors as function of the damaged pipe geometric parameters. Finally, fatigue tests are conducted to evaluate the finite life behavior of small-scale damaged pipes under cyclic internal pressure and to validate the proposed methodology of fatigue analysis.  相似文献   

6.
内外压作用下纤维缠绕厚壁柱形容器的强度   总被引:2,自引:1,他引:2  
研究各向同性材料内胆外对称均衡缠绕纤维的厚壁圆柱形容器在内外压力作用下的应力和强度特性。采用正交各向异性本构关系和轴对称厚壁筒理论, 获得纤维层和内胆的应力, 以及纤维方向三向应力的解析公式。利用Hoffman和Tsai-Wu失效准则研究薄壁筒理论和三维应力对应的强度随壁厚和缠绕角的分布规律。计算比较了有、 无内胆的纤维缠绕容器的强度随缠绕角的变化情况。利用ANSYS软件的层合单元SOLID191建立的模型给出的纤维向应力和强度比与本文理论结果吻合很好。研究发现: 基于层合板理论的二维纤维向应力公式给出了不准确的纤维向应力, 不准确的横向应力造成容器纤维层的强度值偏低; 不同的纤维类型和缠绕角, 厚度-半径比对强度比的影响不同; 基于二维应力分析的薄壁筒理论给出的纤维层强度比小于三维分析的结果; 缠绕角对无内胆的缠绕容器强度比的影响比有内胆的更敏感。   相似文献   

7.
8.
In this paper, the fatigue life, surface crack extension direction and crack growth rate in an elastic bar with a circular cross section are determined through experiments under cyclic torsion with axial static and cyclic tension/compression loading. The effects of the loading type, loading value and stress ratio on the crack growth behaviour are discussed. The results show that, under pure fatigue torsion loading, the crack extension direction is almost the same whatever the value of torsion loading. Under fatigue torsion with cyclic tension loading, it is found that the crack extension direction is mainly determined by the alternating parts of the stresses and is almost independent of the average parts of the stresses, whereas the fatigue life is obviously dependent on the average stress.  相似文献   

9.
10.
The stress analysis and fatigue crack growth behaviour of a part‐through‐cracked double‐curvature thin‐walled shell is examined. An external surface crack is assumed to lie in one of the principal curvature planes of the shell, and to present a semi‐elliptical shape. The stress intensity factors (SIFs) along the crack front for different elementary opening stresses acting on the crack faces are determined through a three‐dimensional finite element analysis. Then approximate values of SIF in the case of a cracked pressure vessel are computed by employing the above results together with the superposition principle and the power series expansion of the actual opening stress. Finally, a numerical simulation procedure is carried out to predict the crack growth under cyclic internal pressure. Some results are compared with those of other authors.  相似文献   

11.
Structures used at elevated temperature subject to severe cyclic thermal stress. Therefore, accurate prediction procedures for thermal fatigue crack growth should be applied to rationalise component flaw assessment. Fatigue crack propagation tests under thermal stress were carried out using an modified type 316 stainless steel (316FR), which is a candidate material for the fast reactor in Japan. Thermal stress of the tests was generated by cyclically changed temperature distribution through thickness in a plate by induction heating and air-cooling. Numerical analysis was also carried out to examine the applicability of the J integral under cyclic thermal stress. The J integral under elasto-plastic condition under thermal stress is close to the elastically calculated J integral. Prediction by J integral tends to be conservative for deeper cracks, and modification of the J integral value using crack opening ratio gives good agreement with the experimental crack growth.  相似文献   

12.
In this work, the buckling phenomenon of slender pressurized pipes under concentrically applied indirect axial force is experimentally and theoretically investigated. The axial force is applied via a frictionless piston. The deformation trend of a polyvinylchloride pipe sample under this compressive axial force is monitored by means of a number of strain gauges. The strain readings are processed by a computer equipped with strain processing software. The buckling modes as well as the buckling load of the system are thus experimentally determined. To describe the stability behaviour of the pipe analytically, several theoretical models are employed and the buckling phenomenon in such a pressurized pipe is analytically ascertained. Numerical values for the critical buckling loads are also obtained. The experimental and theoretical buckling studies are correlated. Through these correlations, the buckling of pressurized pipes under indirect axial pressure is substantiated and an appropriate theoretical model to describe the phenomenon is established.  相似文献   

13.
14.
This research aims to establish an optimal design method of filament wound structures under internal pressure. So far, most design and manufacturing of filament wound structures have been based on manufacturing experiences, and there is no established design rule. In this research, the semi-geodesic path algorithm was used to calculate possible winding patterns taking into account the windability and slippage between the fiber and the mandrel surface. In addition, finite element analyses using commercial code, ABAQUS, were performed to predict the behavior of filament wound structures. On the basis of the semi-geodesic path algorithm and the finite element analysis method, a filament wound structure was designed using the genetic algorithm.  相似文献   

15.
16.
17.
18.
The crack propagation under Gaussian stationary stochastic loading in presence of crack growth retardation effects is considered. The Wheeler retardation model is applied. The crack growth process is modeled by Markovian diffusion process. Some properties of envelope and clustering effect of the load process are taken into account in calculation of parameters of the Kolmogorov diffusion equation. The mean time to failure when the crack reaches its critical length is determined. The analysis of the mean lifetime equation and results of an example show that the stochastic fluctuations of the stationary load process alone do not affect significantly random variations of the lifetime. A quasi-deterministic relation between the features of the fatigue fracture and some material and load parameters is proposed. It gives a potential to consider effectively the fatigue crack propagation with retardation effects as an additional failure mode in reliability analysis.  相似文献   

19.
A computational model for contact fatigue damage analysis of gear teeth flanks is presented in this paper. The model considers the conditions required for the surface fatigue crack initiation and then allows for proper simulation of the fatigue crack propagation that leads to the appearance of small pits on the contact surface. The fatigue process leading to pitting is divided into crack initiation and a crack propagation period.The model for prediction of identification of critical material areas and the number of loading cycles, required for the initial fatigue crack to appear, is based on Coffin-Manson relations between deformations and loading cycles, and comprises characteristic material fatigue parameters. The computational approach is based on continuum mechanics, where a homogenous and elastic material model is assumed and results of cyclic loading conditions are obtained using the finite element method analysis.The short crack theory together with the finite element method is then used for simulation of the fatigue crack growth. The virtual crack extension (VCE) method, implemented in the finite element method, is used for simulating the fatigue crack growth from the initial crack up to the formation of the surface pit. The relationship between the stress intensity factor K and crack length a, which is needed for determination of the required number of loading cycles Np for a crack propagation from the initial to the critical length, is shown.  相似文献   

20.
Composite pipes in this study are composed of multi-layered filament-wound (FW) structures. Each layer of the pipes is assumed to be anisotropy. Based on the three-dimensional (3-D) anisotropic elasticity, an exact elastic solution for stresses and deformations of the pipes under internal pressure is presented. Moreover, detailed stress and strain distributions for three given angle-ply pipe designs are investigated by using the present theory. The shear extension coupling is also considered because the lay-up angles with +φ and −φ layers cannot exist in the same radius. For cylindrical-pressure vessels with different angle-ply pipe, the ratio of applied hoop-to-axial stress in each layer is different. Even if quite a thin-walled pipe, the ratio of hoop-to-axial stress is no longer a constant of 2:1.  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