Study of the Effects of Thermomechanical Coupling Near Stress Concentrators in Viscoelastoplastic Bodies

A model is developed to investigate thermal effects in elastoviscoplastic bodies. It allows us to obtain some quantitative and qualitative information on the stress–strain state of a body and to carry out a nondestructive diagnostics of internal defects, which are stress and strain concentrators. The problem on the plane stress state of a rectangle with a hole is considered as an example. The plate is made of steel and aluminum alloy. The variation in the temperature on the external contour of the body under monotonous and cyclic tension in the elastic and plastic domains is studied     

Nonlinear Single-Frequency Vibrations and Dissipative Heating of Inelastic Piezoelectric Bodies

A generalization is made of the results obtained at the S. P. Timoshenko Institute of Mechanics of the National Academy of Sciences of Ukraine in developing models of single-frequency vibrations and dissipative heating of inelastic piezoelectric solids and methods for solving the associated nonlinear boundary-value problems. The solutions of specific problems and new effects due to the interaction of electromechanical and thermal fields are considered.     

Thermomechanical Model of Growing Cylindrical Bodies Made of Physically Nonlinear Materials

The finite-element method is used together with the theory of growing bodies to model the residual stress-strain state of cylindrical bodies with built-up layers. The case of two built-up layers is analyzed. Numerical and experimental results are compared __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 9, pp. 118–126, September 2005.     

Thermomechanical Behavior and Durability of Shear-Compliant Inelastic Shells of Revolutionwith Piezo-Electric Pads During Axisymmetric Resonant Vibrations

International Applied Mechanics - A refined statement and methodology for solving the problem of electrothermomechanical behavior and predicting the durability of inelastic shells of revolution...     

Stress Concentration Near an Elliptic Crack in the Interface Between Elastic Bodies under Steady-State Vibrations

The paper addresses the three-dimensional problem on steady-state vibrations of an elastic body consisting of two perfectly joined dissimilar half-spaces with an elliptic mode I crack located in one of the half-spaces normally to the interface. The problem is reduced to a boundary integral equation for the crack opening function. The integration domain of the equation is bounded by the crack domain, and the interaction between the crack and the interface is described by a regular kernel. The equation is solved using the mapping method. Numerical results are obtained for the case where the surfaces of the elliptic crack are subjected to harmonic loading with constant amplitude. The dependences of the stress intensity factors on the wave number are presented for various relationships among the mechanical constants that ensure the absence of near-surface waves     

Drag of Bodies of Revolution in Supersonic Flow with Heat and Mass Addition to the Near Wake

It is shown experimentally that the base drag of bodies of revolution in Mach 1.15 to 3.0 flow can be completely eliminated using special techniques for injecting hydrogen and the products of incomplete combustion of pyrotechnic compounds into the near wake. The experimental data obtained are generalized.     

Thermomechanical Multiscale Constitutive Modeling: Accounting for Microstructural Thermal Effects

In this work we present a thermomechanical multiscale constitutive model for materials with microstructure. In these materials thermal effects at microscale have an impact on the effective macroscopic stress. As a result, it turns out that the homogenized stress depends upon the macroscopic temperature and its gradient. In order to allow this interplay to be thermodynamically valid, we resort to a macroscopic extended thermodynamics whose elements are derived from the microscopic behavior using homogenization concepts. Hence, the thermodynamics implications of this new class of multiscale models are discussed. A variational approach based on the Hill–Mandel Principle of Macro-homogeneity, and which makes use of the volume averaging concept over a local representative volume element (RVE), is employed to derive the thermal and mechanical equilibrium problems at the RVE level and the corresponding homogenization expressions for the effective heat flux and stress. The material behavior at the RVE level is described through standard phenomenological constitutive models. To sum up, the novel contribution of the model presented here is that it allows to include the microscopic temperature fluctuation field, obtained from the multiscale thermal analysis, in the micro-mechanical problem at the RVE level while keeping thermodynamic consistency.     

On the Energy Theory of the Electromechanical Coupling Coefficient for Vibrations of Piezoelectric Bodies

International Applied Mechanics - The electromechanical coupling coefficient (EMCC) for the vibrations of inelastic piezoelectric bodies is defined. The effect of energy dissipation is taken into...     

Thermomechanical transitions in doubly-clamped micro-oscillators

The small size and low damping of MEMS oscillators give rise to phenomena that are not observed routinely at the macroscopic scale. In this work we document and explain an experimentally observed transition in the response of a doubly clamped micromechanical oscillator with pretension. The transition from softening to hardening is repeatedly observed upon increasing the power of an incident sensing laser beam, a procedure routinely used to improve signal strength during optical detection of resonant motion of microstructures. At intermediate laser power, a novel resonant response that displays characteristics of both softening and hardening in the same sweep, is observed experimentally. Increased laser heating of a structure in tension may be expected to increase softening behavior. Using tools from non-linear dynamics and continuum mechanics, we show that the observed counter-intuitive behavior can be explained by a competition between the opposing responses of linear and non-linear stiffnesses to a change in temperature.     

Thermomechanical assessment of damage in composites

This paper examines, experimentally and numerically, the use of thermal emission measurements to determine the surface stresses for fibre composite materials. Particular attention is paid to the use of this method for problems associated with damage assessment and repair. In contrast to most traditional methods, the thermal emission profile reflects the interaction of load, geometry, material and damage in a non-destructive fashion. It represents a possible method for the scaling of test data obtained from coupon tests to tests on full scale structures.     

层合结构压电器件的机电耦合效应

压电传感器和致动器都可以看成是一种复合材料层合板结构，由压电材料层和非压电(弹性)材料层交替铺设而成。对于这类任意铺设的层合板悬臂梁结构，我们推导出了表示力学变形与外加电场之间耦合效应的解析表达式。进而，又推导出了两类(一类为单层压电-弹性层，另一类为双层压电-弹性层)层合型悬臂梁结构机电耦合性能的解析公式。在该机电耦合模型中，包括了两个压电常数d211和d222。此外，还建立了含压电材料的有限元算式，进行了实验测量。最后，通过比较解析解(包括考虑了d222参数的理论值和没有考虑d222参数的理论值)，实验值以及有限元计算结果，发现它们吻合得很好，而且考虑d222是十分必要的。     

刚－弹惯性耦合下变形体动力学响应分析

本文以绕定轴转动弹性梁为对象对其在刚－弹惯性耦合下的动力学响应进行数值分析，并与传统的准静态分析方法，线弹性动力学分析方法在理论与数值上进行比较。对所研究的对象用Ｊｏｕｒｄａｉｎ变分原理建立动力学方程，用一致质量有限单元法对弹性梁进行离散；用正则振动模态降低弹性自由度数目。通过数值计算比较说明传统分析方法的局限性。     

基于动柔度法的门杆耦合

本文基于动柔度法法计算了闸门与启闭杆耦合的结构动态特性,比较了门杆开启的两种运行方式,初步探讨了抗振中门杆的相互关系     

Inelastic deformation of conductive bodies in electromagnetic fields

Inelastic deformation of conductive bodies under the action of electromagnetic fields is analyzed. Governing equations for non-stationary electromagnetic field propagation and elastic–plastic deformation are presented. The variational principle of minimum of the total energy is applied to formulate the numerical solution procedure by the finite element method. With the proposed method, distributions of vector characteristics of the electromagnetic field and tensor characteristics of the deformation process are illustrated for the inductor–workpiece system within a realistic electromagnetic forming process.     

Inelastic deformation and localization in polycarbonate under tension

It is demonstrated that uniaxial tension deformation in polycarbonate and other polymers that exhibit large inelastic deformation is unstable beyond a certain stretch. The instability first appears as a shear banding phenomenon at a characteristic angle and is then followed by a stabilized neck generation and propagation. The intrinsic material law for polycarbonate is used in a numerical implementation to reproduce completely the deformation behavior observed in uniaxial tension. In particular, it is demonstrated through numerical simulations, that intrinsic material softening is not necessary for the formation of a shear band and continued growth of a stable neck and further that the interpretation of the tensile response in terms of the constitutive behavior of the material poses significant problems.     

Floating Bodies in Neutral Equilibrium

In his paper preceding in this issue, Finn proved that if the contact angle γ of a convex body B{\mathcal{B}} with a given liquid is π/2, and if B{\mathcal{B}} can be made to float in “neutral equilibrium” in the liquid in any orientation, then B{\mathcal{B}} is a metric ball. The present work extends that result, with an independent proof, to any contact angle in the range 0 < γ < π. Our result is equivalent to the general geometric theorem that if for every orientation of a plane, it can be translated to meet a given strictly convex body B{\mathcal{B}} in a fixed angle γ within the above range, then B{\mathcal{B}} is a metric ball.     

全制动工况下轮轨热-机耦合效应的分析

采用有限元法从摩擦热效应角度探寻轮轨表面破坏的原因,建立了轮轨热-机械载荷耦合接触模型,分析纯滑动接触过程中轮轨的温升以及热应力,模型中考虑了轮轨间非稳态热传导、与环境的热对流和热辐射以及轮轨间的接触计算,分析了滑动接触过程中应力场的分布特点以及速度的影响.结果表明:所采用的接触算法能够求解二维轮轨全制动工况下的热接触问题;轮轨摩擦热效应只存在于表层,其影响随着深度增加而减小;轮轨的相对滑动速度越高,其热效应越明显.     

Dynamic Effects Accompanying the Flow Past Oscillating Bodies Mounted with a Narrow Clearance in Pipes

The unsteady and steady flow past a sphere mounted with a very narrow clearance in a cylindrical pipe is experimentally investigated. The unsteady flow is studied for the case of regular transverse self-oscillations of the sphere accompanied by its impact interaction with the pipe wall. In the steady flow regime the center of the sphere is fixed on the pipe axis. The dependence of the local resistance due to the presence of the sphere and of the body drag coefficient on the relevant dimensionless parameters is determined. The dynamic characteristics for the steady and unsteady regimes are compared.     

Some Comments on the Coupling Effects of Angle-Ply Laminates

ABSTRACT

It is shown that by making a judicious choice of thicknesses of the laminae of angle-ply laminates, the degrading effect of coupling between bending and extension can be eliminated altogether for alternating laminates, and partially reduced for other types. This results in optimal use of materials for given conditions.