Critical Shear Stress of Bimodal Sediment in Sand-Gravel Rivers

A new model for the critical shear stress and the transport of graded sediment is presented. The model is based on the size distribution of the bed surface and can be used to compute sediment transport rates in numerical simulations with an active layer model. This model makes a distinction between unimodal and bimodal sediments. It is assumed that all size fractions of unimodal sediments have the same critical shear stress while there is selective transport for the gravel fractions of bimodal sediments. A recently published laboratory transport data set is used to calibrate our model.     

基于压水试验数据的渗透系数应力敏感性研究

岩体渗透率与应力关系是进行岩体渗流应力耦合分析的基础。基于龙滩水电站边坡岩体渗流压水试验结果和边坡岩体岩性及物理力学性质，对岩体渗透系数和地应力进行了分析计算，给出了边坡岩体渗透率随应力变化的关系式，为进行边坡岩体渗流一应力耦合分析提供了可靠数据。     

Characterization of EBPVD micro-layer composites and simulation of its internal stress state

Based on the basic operating principal and the technology characteristic of electron beam physical vapor deposition(EBPVD) technique, EBPVD was used to prepare the micro-layer composites. The effect on the substrate preheating temperature was taken into accounts and the finite element analysis package ANSYS was used to simulate the internal stress field and the potential displacement changing tendency. The results show that one of the most important quality factors on the judgment of micro-layer composites is the adhesion between the substrate and the deposition layers as well as among the different deposition layers. Besides the existance of temperature gradient through the thickness of layers, the main reason for the internal stress in micro-layer composites is the mismatch of various properties of the layer and the substrate of different thermal expansions and crystal lattice types. With the increase of substrate preheating temperature, the inter-laminar shear stress also takes on a tendency of increase but the axial residual stress decrease.     

裂隙岩体边坡稳定性的渗流与应力耦合分析

用裂隙岩体渗流与应力耦合分析的四自由度全耦合法对岩质边坡进行耦合分析,通过强度折减有限元法求解岩体边坡的稳定安全系数。四自由度全耦合法建立了同时以渗流水压和位移为未知量的耦合方程组,使得渗流场与应力场的求解能够一次性完成,与两场交叉迭代分析方法相比达到了彻底的完全耦合。通过强度折减,整个系统达到不稳定状态,有限元计算将不收敛,此时的折减系数就是安全系数。算例表明由此求得的边坡稳定安全系数和滑动面都与传统方法十分接近。     

Residual stresses and transformation toughening in MoSi2 composites reinforced with partially stabilized zirconia

The results of study of the effects of yttria stabilization (0–6 mol.%) on the room-temperature fracture behavior and toughening mechanisms in zirconia-reinforced MoSi₂ are presented in this paper. Transformation toughening is shown to occur only in composites reinforced with zirconia particles stabilized with 2 mol.% yttria. However, the fracture toughness levels are comparable in the other composites with yttria levels between 0 and 6 mol.%. Toughening in the other composites is attributed to the combined effects of residual stress, microcrack shielding/anti-shielding and/or crack deflection. A rigorous micromechanics-based model is presented for the estimation of residual stress levels in brittle materials reinforced with phases that can transform during cooling or under stress. The model is applied successfully to the rationalization of the observed fracture and toughening phenomena.     

A CONSTITUTIVE MODEL FOR ELASTIC-PLASTIC DEFORMATION UNDER CYCLIC MULTIAXIAL STRAINING

Abstract— The yield criterion is interpreted as defining the metric of the stress space. Hydrostatic stresses correspond to null geodesies. The plastic strain increment represents a normal projection of the increment undergone by a certain scalar function (hardening function) which depends only on the distance between stress points. This establishes a flow rule formally equivalent to the Prandtl-Reuss equations. Consideration of un-loading processes leads to the analysis of equivalent paths and to the definition of a generalized length or separation which provides a new representation of kinematic hardening.     

二滩拱坝混凝土设计及试验研究

二滩水电站混凝土双曲拱坝，坝高２４０ｍ，是我国已建和在建的第一高坝。根据拱坝应力状况，仿真试验试件尺寸，二向、三向轴受力状况混凝土的力学变形特性，建立了相应的方程式。二滩拱坝混凝土强度设计龄期为１８０ｄ，抗渗标号不小于Ｓ１２，抗冻标号选用Ｄ２００，胶材用量不超过２００ｋｇ／ｍ３，也不少于１７０ｋｇ／ｍ３，粉煤灰掺量控制在３０％以内，Ａ、Ｂ、Ｃ三区混凝土强度分别采用３５、３０、２５ＭＰａ。经试验和复核，大坝混凝土强度的安全系数是完全足够的。     

Prediction of High-Temperature Long-Term Strength for Damaged Structures

A method is proposed for analytical estimation of the high-temperature long-term strength of structures with material discontinuities, which are stress raisers. We consider the processes involving the formation of diffusion pores. Diffusion processes in metals are strongly enhanced with increasing temperature and stresses.     

An eight‐node hybrid‐stress solid‐shell element for geometric non‐linear analysis of elastic shells

This paper presents eight‐node solid‐shell elements for geometric non‐linear analysis of elastic shells. To subdue shear, trapezoidal and thickness locking, the assumed natural strain method and an ad hoc modified generalized laminate stiffness matrix are employed. A selectively reduced integrated element is formulated with its membrane and bending shear strain components taken to be constant and equal to the ones evaluated at the element centroid. With the generalized stresses arising from the modified generalized laminate stiffness matrix assumed to be independent from the ones obtained from the displacement, an extended Hellinger–Reissner functional can be derived. By choosing the assumed generalized stresses similar to the assumed stresses of a previous solid element, a hybrid‐stress solid‐shell element is formulated. Commonly employed geometric non‐linear homogeneous and laminated shell problems are attempted and our results are close to those of other state‐of‐the‐art elements. Moreover, the hybrid‐stress element converges more readily than the selectively reduced integrated element in all benchmark problems. Copyright © 2002 John Wiley & Sons, Ltd.     

正交异性材料在R.Hill屈服准则下平面应力问题的特征场(h>2)

大多数金属材料在承载时产生了各向异性强化的特点,因此,对这一类材料特性的深入研究显得十分必要,正确建立及分析理论模型将对在实际工程中的应用提供很好的理论依据。本文在R.Hill屈服准则下提出了无量纲化的解析应力解,讨论了屈服参数2>h时,正交异性材料平面应力问题的应力场及应力特征场,利用应力微分平衡方程得到了决定特征曲线特征的参数。结果说明特征线一般互不正交。特别地分析了平头冲压边界附近的情况,得到了各应力状态不同区域的应力特征场,应用数值分析的方法对过渡区进行了计算。