焊接接头裂端塑性区发展与应力三轴性

采用有限元计算方法分析了平面应变条件下中心裂纹和三点弯曲不同强度匹配和裂纹深度试样中的裂端场．结果发现，焊接接头裂端应力三轴性随加载方式、裂纹长度及焊缝和母材匹配性质不同而变化，并从焊缝和母材塑性区发展及应变硬化方面进行了解释．同时指出。

Crack propagation mechanism of compression-shear rock under static-dynamic loading and seepage water pressure

To reveal the water inrush mechanics of underground deep rock mass subjected to dynamic disturbance such as blasting, compression-shear rock crack initiation rule and the evolution of crack tip stress intensity factor are analyzed under static-dynamic loading and seepage water pressure on the basis of theoretical deduction and experimental research. It is shown that the major influence factors of the crack tip stress intensity factor are seepage pressure, dynamic load, static stress and crack angle. The existence of seepage water pressure aggravates propagation of branch cracks. With the seepage pressure increasing, the branch crack experiences unstable extension from stable propagation. The dynamic load in the direction of maximum main stress increases type I crack tip stress intensity factor and its influence on type II crack intensity factor is related with crack angle and material property. Crack initiation angle changes with the dynamic load. The initial crack initiation angle of type I dynamic crack fracture is 70.5°. The compression-shear crack initial strength is related to seepage pressure, confining pressure, and dynamic load. Experimental results verify that the initial crack strength increases with the confining pressure increasing, and decreases with the seepage pressure increasing.

Stability analysis of the temperature cracks in Xiaowan arch dam

In the Xiaowan arch dam there are massive temperature cracks nearly parallel to the dam axis. Obviously, whether the cracks may spread or not during the water storage process is one of the crucial factors for the safety of a dam. In this paper, a new type of crack element, in which the contact component is implicitly included into the concrete component, is proposed to simulate the effects of the existing cracks. The crack element is proved by numerical example to share the merits of both conventional contact elements and joint elements. With a finite element model of the cracked arch dam together with its rock foundation established, the transient displacement and stress fields of the dam are obtained. The complicated rock foundation, the construction process of the arch dam, the massive cracks, the transient temperature field, as well as the water storage process have been taken into consideration in the simulation. In addition to the global model, several sub-models for typical crack tips are also generated with finer elements placed around the tips. Thus, more accurate displacement and stress distribution are obtained by simultaneous sub-model simulation. Based on the calculation of stress intensity factor for crack tips by extension method, the temperature cracks in the Xiaowan arch dam are finally proved to be stable.

Determination of T-stress using finite element analysis

A method that uses finite element analysis to determine the non-singular stress （T-stress） at a crack tip is proposed in this study. T-stress includes two components： the Tx-stress parallel to the tangent of the crack at its tip and the Ty-stress perpendicular to this tangent. The effects of contact and friction on both the Tx- and Ty-stresses on the crack flanks are considered in the method. Because the method uses a single standard elastic finite element analysis derived directly from the equation of the stress fields around the crack tip and does not require any assumptions or simplification, it can be used to determine the T-stress for any given geometry and loading condition. Theoretical results are used to calibrate the results, which exhibited good agreement and to discuss the T-stress computational methodology. Furthermore, the Tx- and Ty-stresses in center-cracked Brazilian disc （CCBD） specimens subjected to diametrical or partially distributed compression were numerically computed, and the effects of contact and friction on the Tx- and Ty-stresses are discussed.

Fracture mechanics associated with non-classical heat conduction in thermoelastic media

This paper studies the thermoelastic fracture in a solid under non-classical Fourier heat conduction.The temperature field and the associated thermal stresses are solved by the dual integral equation technique.Both thermally insulated crack and heated crack are considered.It is found that the crack tip thermal stress is singular and can be expressed in terms of the thermal stress intensity factor in a closed-form.Numerical results show that the crack considerably amplifies the local thermal stresses,confirming the significance of the effect of non-classical heat conduction on the thermoelastic fracture mechanics of materials.

Electromechanical cracking in ferroelectrics driven by large scale domain switching

Experimental results indicate three regimes for cracking in a ferroelectric double cantilever beam (DCB) under combined electromechanical loading. In the loading, the maximum amplitude of the applied electric field reaches almost twice the coercive field of ferroelectrics. Thus, the model of small scale domain switching is not applicable any more, which is dictated only by the singular term of the crack tip field. In the DCB test, a large or global scale domain switching takes place instead, which is driven jointly by both the singular and non-singular terms of the crack-tip electric field. Combining a full field solution with an energy based switching criterion, we obtain the switching zone by the large scale model around the tip of a stationary impermeable crack. It is observed that the switching zone by the large scale model is significantly different from that by the small scale model. According to the large scale switching zone, the switch-induced stress intensity factor (SIF) and the transverse stress (T-stress) are evaluated numerically. Via the SIF and T-stress induced by the combined loading and corresponding criteria, we address the crack initiation and crack growth stability simultaneously. The two theoretical predictions roughly coincide with the experimental observations.

Transient near tip fields in crack dynamics

Transient effects of stress-strain fields in the vicinity of a stationary crack tip under high rate loads are discussed.Exact analytical solutions to near tip stresses are compared to fields prescribed by leading terms(one or several) of Williams asymptotic expansion.Influence of load application mode,time(or,which is the same,distance from a crack tip) and Poisson's ratio on this discrepancy is extensively examined.Some effects connected with crack tip propagation speed are also discussed.Significant inconsistencies between real(or received in numerical solutions of state equations-e.g.finite element computations) crack tip fields and stress intensity factor(SIF) singular field observed by numerous researchers are explained.The scope of problems where SIF field can be used for correct prediction of dynamic stress-strain fields in the crack tip region is established.Possibility to correctly approximate fields that are not SIF dominated,accounting additional terms of Williams expansion,is studied.