柔度法研究镍铬合金焊材的高温疲劳裂纹扩展行为

金属材料的高温疲劳裂纹扩展速率试验,关键问题在于高温环境下精确测量试样的裂纹长度.基于柔度测试技术,通过改进现有高温应变引伸计实现了FFCT试样的高温疲劳裂纹扩展速率测试.利用有限元方法对具有分层构形CT试样的柔度方法进行了研究,获得了分层结构CT试样的等效弹性模量表达式,通过迭代方法对实时裂纹长度进行修正,获得了良好的预测精度.完成了镍铬合金焊带、焊条和焊丝三种焊材常温和350 ℃下的疲劳裂纹扩展速率试验,获得了相应的疲劳裂纹扩展规律.     

物理老化对玻璃态高聚物非线性蠕变行为的影响

在不同应力水平下对经历不同老化时间的有机玻璃(PMMA)进行常温蠕变测试,分析物理老化和应力对材料蠕变柔量函数的影响.分析表明,老化时间对PMMA蠕变行为的影响满足流变简单性规律,即不同老化时间的蠕变柔量曲线可以沿对数时间轴平移而叠加到参考曲线上.取最长的老化时间为参考状态,依时间-老化时间等效原理,得到了各应力水平下的蠕变柔量主曲线.老化移位因子与老化时间在双对数坐标图上呈现线性关系,其负斜率就是老化移位率.结果表明,老化移位率随应力的增高而减小.     

Calculating the Linear Creep Strains of Viscoelastic Fibers under Tension

The linearity domain for the viscoelastic properties of high-molecular organic fibers is determined. The linearity criteria are coincidence of experimental compliance curves and linearity of isochronic creep curves. Statistical criteria are used to establish linearity. The influence function in the constitutive equation of linear viscoelasticity is an Abel-type power kernel. The calculated and experimental creep strains are in good agreement both at the initial stage of deformation and after long-term loading__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 5, pp. 97–106, May 2005.     

一种工程实用的分数指数黏弹性固体模型

从热力学对模型的限制出发,提出了一种工程实用的、新固体流变模型-分数指数模型,它可与实验结果很好吻合,具有简单实用、计算速度快、自相谐调的优点,克服了目前固体模型收敛速度太慢、计算量太大的严重缺点,可以广泛应用于线性或非线性黏弹性被子示问题的计算之中。     

可塌陷气管的p—V关系和极限流量

通过对正常大鼠气管在不同轴向伸长比条件下作液体灌注实验,并对所得压力-容积数据进行最小二乘拟合,得到包含在拟合函数关系式中的大鼠气管材料常数,文章详细分析这些材料常数的力学含义,并对可塌陷气管的顺应性和极限流量进行讨论,文章结果为分析气管在特定力学环境中的适应性生长和塌陷特性提供重要的信息。     

Determination of optimized blending fractions for particle size distributions or molecular weight distributions involving various physical properties

It has been shown in this study that the effects of particle size distribution or molecular weight distribution on selected physical properties can be related by a generalized blending approach that involves similar equations. The blending equations developed involve different z-fractions where z = 3 for volume blending of spherical particles, or z = 2 for surface blending of spherical particles, or z = 1 for the weight blending of molecular weights. This new analysis approach addresses the magnitude of the ratios of particle size averages, D_x/D_y, or ratios of molecular weight averages, M_x/M_y, as well as the location of this maximum, the level of distribution information available for the starting materials, and the type of z-fraction blending. To illustrate this approach suspension viscosity/concentration data was used to show how the D_x/D_y ratio could be introduced successfully to analyze latex volume blending where z = 3. In addition, the maximum steady-state elastic compliance, J_e, as a function of weighted blends (z = 1) of two different molecular weights of polyisobutylene was shown to fit the simple equation J_e = 1.187 (M₃/M₂) (M₄/M₁) reasonably well. © 1995 John Wiley & Sons, Inc.     

Nonlinear Creep of Viscoelastic Organic Fibers under Tension

The nonlinearity of the creep of nylon fibers is justified based on the similarity of a set of isochronous creep curves, which also includes the instantaneous deformation curve. Nonlinear hereditary constitutive equations of creep are derived. The real values of the influence function are determined as the basic rheological characteristic of the material. The applicability of Boltzmann's, Abel's, Rzhanitsyn's, and Rabotnov's kernels is estimated quantitatively. The choice of an Abel-type kernel is justified. The calculated and experimental data are in satisfactory agreement for a loading duration of up to 1,000 hours and an order of magnitude change in the stresses __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 7, pp. 102–115, July 2005.     

Fluctuations and viscoelasticity

Viscoelasticity is exhibited by polymers, metals undergoing diffusion creep, etc. The strain is a linear functional of the stress, but there is no unique equilibrium relationship between them. Under a constant stress, the strain does not saturate to an equilibrium value. This divergence is the main difficulty facing a first-principles theory of viscoelasticity, in contrast to anelasticity which has already been understood as a relaxation process in terms of response theory, fluctuations and related concepts. We now present such a theory, based on the recognition that viscoelasticity occurs whenever the spontaneous fluctuations of the strainrate, butnot of the strain, form a stationary random process. We give fundamental formulas for the creep function and the complex compliance, in terms of the spontaneous fluctuations of the strain rate, that apply to both viscoelasticity and anelasticity. A detailed stochastic analysis of the basic viscoelastic network equation corroborates and complements these results. The unphysical instantaneous response of the network is eliminated, and the network parameters are related to internal fluctuations. A certain functional form of the creep function is derived that is common to several physical situations, a few of which are mentioned. Detailed applications will be taken up elsewhere.     

INVESTIGATION ON COMPLIANCE ROTATION CORRECTION FOR COMPACT TENSILE SPECIMEN IN UNLOADING COMPLIANCE METHOD

The rotation correction method of unloading compliance for a compact tensile (CT) specimen in the current Jintegral resistance curves or critical Jintegral test standards was under suspicion by tracing to its source, and a new rotation correction method was proposed. The rotation center of the specimen is close to the crack tip, and the material constitutive relationship has little effect on the rotational radius R. If the formula for rotation correction recommended in current standards is used to measure the crack length of CT specimen, it will lead to larger error. A new formula with better accuracy for the crack length measurement of the CT specimen was presented.     

A mixed variational formulation of a contact problem with adhesion

A mathematical model describing the contact between a viscoplastic body and a deformable foundation is analyzed under small deformation hypotheses. The process is quasistatic and in normal direction the contact is with adhesion, normal compliance, memory effects and unilateral constraint. We derive a mixed-variational formulation of the problem using Lagrange multipliers. Finally, we prove the unique weak solvability of the contact problem.