划伤对复合材料层合板承载能力的影响

为了研究划伤对复合材料层合板承载能力的影响,通过对含划伤试件和未损伤试件进行拉伸试验的方法研究了层合板划伤处的损伤类型以及损伤演化过程;同时通过粘贴电阻应变片来分析划伤附近的应变变化规律。结果表明:划伤试件在加载初期主要以基体损伤为主,后期主要以纤维拉伸断裂为主;划伤的存在使得试件的形心与加载中心不重合,使试件在加载后期发生了弯曲变形。可见,划伤明显地降低了试件的承载能力。

多工况飞机货舱门开启功能的可靠性优化设计

在多工况下的复杂系统可靠性优化设计中,可靠性设计人员需要在考虑专家意见对假设型工况的具体影响后,才能完成相应的可靠性优化设计。因此,在已知相关权重信息后,结合直觉模糊集和人因可靠性理论,在直觉型TOPSIS方法和蒙特卡洛方法的基础上完成针对飞机货舱门开启功能的可靠性优化设计方案,不但可以分析单一假设型工况下专家意见对可靠性优化设计的影响,而且可以兼顾不同专家意见对多假设型工况下非劣解集决策的影响,为其他多工况下复杂系统的可靠性优化设计提供一个可行的案例。

Limit Load Analysis of Pipes with Local Wall-thinning

The loss of metal in a pipe due to corrosion usually results in localized thinned areas with various depths and an irregular shape on its surface. In this paper, a number of numerical models of pipes with different size defects are established. The limit loads of these pipes are researched using the nonlinear finite element method. The effect of defect parameters of the local wall-thinning pipes on the limit load is discussed. The results show that limit loads decrease obviously when the depths and lengths of the defect increase. However, when the defect length reaches a certain value, the effect of defect length on limit loads is not significant. These results are compared with the results of the method of API 579. When the defect length is adequately small, the results of FEM are in good agreement with the ones of APl 579, but when the defect depth and length is adequately large, the API 579 is not suitable.

THE ANALYSES OF THE THREE-DIMENSIONAL STRESS STRUCTURE NEAR THE CRACK TIP OF MODE Ⅰ CT SPECIMENS IN ELASTICPLASTIC STATE(Ⅱ)--THE ANALYSES OF THE STRESS STRUCTURE

Based on[1],the stress structures of the smooth region and shear lip of the specimens have been investigated in the paper.The characteristics of the stress structure in the smooth region have been found that the variable z can separated out;the stresses in the midsection can be obtained by the plane strain FEM results or HRR structure modified by the stress triaxiality.The effects of load level and thickness on the stress structure can be reflected by the distribution of CTOD along the thickness direction.The obtained expressions of the stresses are very simple and visualized.The analyses of the stress structure in the shear lip show that the stresses can be obtained by different methods of interpolation to a certain precise degree.A new degree parameter of the plane strain state has been put forward and studied.The parameter can reflect relatively well the variation of the kind and thickness of the specimen as well as the load level.The fracture parameter has also been investigated to be sure that it can be obtained by modified CTOD with the stress triaxiality.

THE ANALYSES OF THE THREE-DIMENSIONAL STRESS STRUCTURE NEAR THE CRACK TIP OF MODE I CT SPECIMENS IN ELASTICPLASTIC STATE(Ⅰ)--THE ANALYSES OF CONSTRAINT PARAMETERS AND FRACTURE PARAMETERS

In the present paper,three dimensional analyses of some general constraint parameters and fracture parameters near the crack tip of Mode I CT specimens in two different thicknesses are carried out by employing ADINA program.The results reveal that the constraints along the thickness direction are obviously separated into two parts:the keeping similar high constraint field(Z_(1))and rapid reducing constraints one(Z_(2)).The two fields are experimentally confiremed to correspond to the smooth region and the shear lip on the fracture face respectively.So the three dimensional stress structure of Mode I specimens can be derived through discussing the two fields respectively.The distribution of the Crack Tip Opening Displacement(CTOD)along the thickness direction and the three dimensional distribution of the void growth ratio(V_(g))near the crack tip are also obtained.The two fracture parameters are in similar trends along the thickness direction,and both of them can reflect the effect of thickness and that of the loading level to a certain degree.

Vibration Analysis of a Pipe Conveying Fluid Under Harmonic Excitation

In this paper, using Hamilton principle, the control equation of fluid-structure interaction vibration of a pipe conveying fluid under simple harmonic excitation was established and a novel method, Galerkin-Modality＇ s method was proposed to solve this equation. The influence of the damp, the flow velocity, the pressure and the length of the pipe supported by simple supports on the piping＇ s first two natural frequencies was discussed. The criti- cal pressure and the critical length of the pipe were obtained. The influence of the flow velocity and pressure on the piping＇s maximal relative displacements were analyzed.