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On the influence of high austenitizing temperatures and "overheating" on fracture and fatigue crack propagation in a low alloy s


This article presents the results of an experimental study of fracture and fatigue in a nanostructured (an average grain size of ～23 nm) bulk Ni18 wt pct Fe alloy that was produced using a pulsed electrodeposition technique.


Fatigue thresholds benefited similarly from more αMo phase, and the fracture and fatigue resistance was improved for all alloys tested at 1300 °C, the latter effects being attributed to improved ductility of the αMo phase at elevated temperatures.


Ambient to elevatedtemperature fracture and fatigue properties of MoSiB alloys: Role of microstructure


On the fracture and fatigue properties of MoMo3SiMo5SiB2 refractory intermetallic alloys at ambient to elevated temperatures (

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 In this paper, a brief review on the relationship between the mechanical properties and textures in titanium alloys was made. The types of textures and the influence of various factors on the textures in commercial titanium alloys were described. The effects of textures on the elastic modulus, yield and tensile strength, fracture and fatigue properties as well as some problems on the application of texture strengthening were discussed.  本文综述了钛合金织构与力学性能之关系诸方面研究。简要说明工业用钛合金中存在的一般织构形式及其影响因素;列举织构对钛合金弹性、屈服、拉伸强度、断裂及疲劳等各种性能的影响;讨论了有关钛合金织构强化实际应用的一些问题。  A difficult element of the classical plasticity theory is the concept of the yield surface which leads to experimental and numerical difficulties when attempting to describe and analyze the two or three dimensional response of a material, valanis circumvented this difficulty by developing the theory of endochronic plasticity which does not require the concept of yield for the description of plastic behavior of materials. Recently considerable attention has been paid to the validity, computational capability... A difficult element of the classical plasticity theory is the concept of the yield surface which leads to experimental and numerical difficulties when attempting to describe and analyze the two or three dimensional response of a material, valanis circumvented this difficulty by developing the theory of endochronic plasticity which does not require the concept of yield for the description of plastic behavior of materials. Recently considerable attention has been paid to the validity, computational capability .and predictive power of the endochronic plasticity, which is caused mainly by the fact that all applications of the theory have, so far, been limited to the homogeneous fields in quasistatic loading. To circumvented the mathematical difficulty for application of the endochronic constitutive equationwhere z is intrinsic time scale and p(z)a kernel function with weak singularity of the origin, an new endochronic elastoplastic constitutive equation has been develot ped. keeping in mind that the derivative of the heaviside step function H(z)is the Dirac delta function δ(z) andThen we can approximately take ρ(z) asThis form of ρ(z) is continuous and differentiable in (0,∞). we, therefore, can obtain the following new elastoplastic endochronic constitutive equationEq. (4) is a three dimensional constitutive equation, which can be specified and expressed as matrix form in. terms of {σ}, {ε} and {h} for particular case. Take plane problem as an example it can be reduced to eq. ( 5 ) by supposing the plastic incompressibility,where{D}is an adequate approximation to the elastic matrix{E}, {H}is a nonlinear part of eq. ( 5 ), which is history dependent and determined by z, ρ(z) and hardening function f(ζ). It was found that three terms in eq. ( 3 )suffice to describe the material response and ct, ai can be determined by the curve fitting in the following region from simple tensile test.over which ρ(z)decays very fast from singularity to a negligible value, while f(ζ)is a wellbehaved slowly varying function and can be determined outside the region .A numerical algorithm based on the finite element method of analysis of the boundary value problem in a continuum is presented, in the case where the elastoplastic response of the material is given by the new constitutive equation. It was found that this algorithm is more convenient for calculation than that of classical plasticity, in which the concept of yield surface has taken a very important role.By designing a special experiment and a finite element mesh(the smallest gague and element are equal in size and about 0.2 mm), the validity of the new elastoplastic constitutive eqation of the endochronic plasticity and the algorithm developed in this work are tested in the case of a complex boundary value problem nvolving a highly heterogeneous elastoplasiic strain field in a reclangi lar plate, with notches symmetrically placed with respect to longitudinal axis of symmetry. The plates were loaded cyclically in the direction of this axis .Excellent agreemen between experimental and calculated results is shown along two perpendicular direct i ,r.s in the notch tip for a cyclic history up to three reversals.The present results could have a wide scope of application in different branches of solid mechanics, for instance, elastoplastic structure analysis, fracture and fatigue. The examples of the applicaticn and some predicted and verified new phenomenon will be reported later.The work was finished under the guidance of Professor R. C. valanis, the author would like to express his deepst gratitute to him.  为了克服经典塑性理论发展中的困难,K.C.Valanis于1971年提出了内蕴时间塑性理论。并随之在金属、土壤等不同材料和不同力学问题(如单调及循环加载、蠕交、松驰等)的分析中获得了较为满意的结果。但是除波传播的情况有其特殊性外,其应用范围仅限于均匀应变场。本工作首先得到了新型的内蕴时间弹塑性本构方程,发展了相应的算法和材料函数确定方法,从而首次将内时理论应用于非均匀弹塑性应变场的分析。试验验证是对含对称分布的长边缘缺口板受对称循环载荷的条件下进行的,并使用了小至0.2毫米左右的应变片与有限元单元。结果表明:在沿缺口前缘两个垂直方向上的应变分布的理论计算值与试验结果在趋势上吻合很好。  This paper pre(?)ents a brief review on the viscoelastic properties of composite materials and makes an introduction to the research status in this respect. Emphasis is laid on the discussion of the nonlinear viscoelastic constitutive equations and on the predictions of the delayed strength. Some comments are given on the theories and models which relate creep to fracture and fatigue. Owing to the difficulties and complexities of the problems concerned and the lack of sufficient experimental verifications,... This paper pre(?)ents a brief review on the viscoelastic properties of composite materials and makes an introduction to the research status in this respect. Emphasis is laid on the discussion of the nonlinear viscoelastic constitutive equations and on the predictions of the delayed strength. Some comments are given on the theories and models which relate creep to fracture and fatigue. Owing to the difficulties and complexities of the problems concerned and the lack of sufficient experimental verifications, the present author is certain that the descriptions in this paper is quite superficial, and need to be deepened and perfected. In view of the importance of the research for the design of composite products and their reliable usage, a far more rapid development can be surely expected. To achieve a good understanding of this subject, we must pay more dividend.  本文对纤维增强聚合物基复合材料蠕变性能的研究槪况进行了综述,着重讨论非线性蠕变本构关系与蠕变延迟破坏理论,指出蠕变试验中应注意的几个问题,最后对材料蠕变与疲劳和断裂的相互关系提出几点粗浅看法。鉴于现有水平,本文只着重材料行为的宏观描述,避开对其微观物理机制的追究。   << 更多相关文摘 
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