柔性立管内衬层的非线性力学行为分析

由于聚合物材料的黏弹性,柔性立管内衬层易发生蠕变而"嵌入"至骨架层沟槽中,这一现象可能造成立管结构完整性缺失和骨架层撕裂等安全隐患,但现有的分析理论及有限元模型中,对材料的性质均是做了简单的线性假设,并未考虑聚合物材料的非线性黏弹性特性。基于PA11的试验测试结果,分别采用时间硬化非线性本构模型和考虑时温影响的多重积分非线性本构模型来表征材料性质,并对比两种模型与试验数据拟合情况。根据内衬层与骨架层的真实结构建立二维有限元数值模型,采用两种理论模型进行结构的非线性蠕变行为分析及对比。结果表明：非线性蠕变本构模型能够在在非稳态阶段和存在温度梯度的条件下,更加准确地预测的结构关键部位应变和应力,可为柔性立管内衬层的设计及评估提供借鉴和参考。     

Internal stresses during rolling friction and their evaluation

The estimation of wear of materials intended for practical use demands a detailed knowledge of applied forces and internal stresses in materials. For a dry friction rolling-body model the relationship between the internal stresses and the normal force, slip and rolling length was determined. The evaluation of the internal stresses was carried out on the basis of a practical (wheel/rail) frictional system. X-ray determination of forces proved to be an efficient method of measuring forces in the surface of metallic rolling bodies. The purpose of internal stress measurements is to follow plastic deformation at frictional surfaces and consequently to establish new criteria for the deformation and resistance of materials and their application to frictional systems.     

Investigation of the viscous and thermal effects on ductile fracture in sheet metal blanking process

In this paper, a methodology is proposed to predict the ductile damage in the sheet metal blanking process using a coupled thermomechanical finite-element method. A constitutive material model combined with the ductile fracture criteria was used. The effect of material softening due to the heat generated during plastic work in a specimen was considered in blanking simulations. To verify the validity of the proposed model, several blanking simulations are performed and the results compared with those obtained from an experimental study. The interaction of fracture initiation and temperature distribution in the sheet metal during the process was studied. The effect of velocity and the clearance on the product shape were examined. It was seen that at high punch speeds the viscous and thermal effects have significant effects on product quality.     

矿车与柔性车挡碰撞过程仿真分析

多盘摩擦吸能器与柔性车挡联动,可以有效地将矿车的动能转化为摩擦热。钢丝绳是多盘吸能器的重要组成部分,其受力是多盘吸能器设计的重要参数。为了准确分析钢丝绳受力的变化规律,建立了相应的非线性仿真模型,从而分析了矿车与柔性车挡之间的碰撞规律。     

Thermostressed state of a pad–disk tribosystem during single braking

The temperature and stress distributions in a disk under single braking have been studied. The finite-element method (FEM) has been used to obtain a numerical solution to the heat-conduction boundary problem for a steadily decelerated rotating disk heated in a local area of the working surface by a frictional heat flow. Given the temperature field, the finite-element method has been used to solve the corresponding quasistatic thermoelasticity boundary problem. The elastostatic boundary problem has been numerically solved separately for a disk loaded with distributed normal and shear stresses in the contact area. The complete field of stresses in the disk has been determined by adding up elastic and thermoelastic components. Numerical analysis has been performed for a cerametallic (FMC-11) pad—cast-iron (ChNMKh) disk friction couple.     

Thermomechanical analysis of ultra-high molecular weight polyethylene-metal hip prostheses

In order to predict the frictional heating and the contact stresses between the polyethylene cup and the metallic ball-head forming the articulation of a hip prosthesis a three-dimensional finite element model was developed and calculated. The non-linear model includes a fully coupled thermomechanical formulation of the mechanical properties of the ultra-high-molecular-weight polyethylene, and a large-sliding Coulomb frictional contact between the two components. The model predicts the temperature of the polyethylene with an accuracy that was tested by comparing the model predictions with the temperature measurements. The temperature measurements were taken by thermocouples placed on the cup surface, the head surface and the inside of the thermostatic bath, during a complete test within a hip joint wear simulator. The model was found to be very accurate, predicting the measured temperatures with an accuracy better than 2 per cent. The temperature peak (51 degrees C) was predicted at the contact surface. The model results indicate that frictional heat is mostly dissipated through the metallic ball-head. The full coupling between the thermal and the mechanical conditions used in this study appears to be necessary if accurate predictions of the polyethylene deformation are required.     

Temperature and stress analysis and simulation in fractal scanning-based laser sintering

A model for calculating the evolution of temperature and thermal stresses within a single metallic layer formed on the powder bed using different scanning patterns in selective laser sintering (SLS) was proposed. The model allows for the non-linear behavior of thermal conductivity, specific heat, and elastic modulus due to temperature changes and plastic deformation capabilities with a bilinear isotropic hardening behavior. The effect of laser scanning patterns on temperature, residual thermal stresses and distortion were investigated. It was shown that the distortion and transient stresses of a layer processed by a moving laser beam is decreased with fractal scanning pattern.     

Static and dynamic stresses of practical thermowells

A flexible beam model is proposed for calculating the flow induced stresses and application limits of common thermowell designs. It is intended to replace traditional selection methods with one which emphasizes mechanical integrity and process containment.     

Friction compensation and evaluation for a force control application

The presence of non-linear friction poses a significant problem for controller design in many motion control applications. Since most currently available compensation schemes for non-linear friction require a well-established friction model, the controller design problem becomes more difficult in applications where the frictional forces cannot be modeled accurately. In this paper, friction compensation is considered for an actuator used in a force control application involving very low motion amplitudes. The non-linear frictional effects are particularly significant and are, furthermore, difficult to model accurately. An existing control scheme, originally proposed for sensitivity reduction in systems with plant model uncertainty, is used here for friction compensation. Experimental and simulation results are used to demonstrate the effectiveness of the friction compensation that is achieved using this method, as compared to other methods of friction compensation. Furthermore, the effectiveness of such compensation is quantitatively analysed using two methods: an analysis based on the describing function approach, and a performance robustness analysis based on structured singular values.     

Model updating of locally non-linear systems based on multi-harmonic extended constitutive relation error

Improving the fidelity of numerical simulations using available test data is an important activity in the overall process of model verification and validation. While model updating or calibration of linear elastodynamic behaviors has been extensively studied for both academic and industrial applications over the past three decades, methodologies capable of treating non-linear dynamics remain relatively immature. The authors propose a novel strategy for updating an important subclass of non-linear models characterized by globally linear stiffness and damping behaviors in the presence of local non-linear effects. The approach combines two well-known methods for structural dynamic analysis. The first is the multi-harmonic balance (MHB) method for solving the non-linear equations of motion of a mechanical system under periodic excitation. This approach has the advantage of being much faster than time domain integration procedures while allowing a wide range of non-linear effects to be taken into account. The second method is the extended constitutive relation error (ECRE) that has been used in the past for error localization and updating of linear elastodynamic models. The proposed updating strategy will be illustrated using academic examples.     

Non-linear bending of thin, ideally elastic rods

A number of methods are available for the solution of elastica problems including the analytical elliptic-integral approach, various predictor-corrector methods and discrete analyses based on non-linear finite-element theory. In this paper an alternative discrete approach is proposed based on obtaining, by Dynamic Relaxation, finite difference solutions to the governing differential equations.Results from the method are presented for the large deflection behaviour of a cantilever beam and a circular ring and satisfactory correlation is demonstrated with the results of previously published exact analyses.     

Finite element analysis of plane-strain sheet bending

Sheet bending between the die and the punch is analyzed as a bulk deformation process under the plane-strain condition by the finite-element method. The two finite-element formulations used for the analysis are the rigid-plastic analysis using the incremental theory and the elastoplastic analysis with large-stain formulation. The two solutions are compared in terms of detailed mechanics during bending. Spring-back and residual stresses upon unloading are obtained by rigid-plastic loading and elastoplastic unloading calculations as well as by the elastoplastic calculations for loading and unloading. The solutions agree with each other very well with minor differences.     

Die compaction of copper powder designed for material parameter identification

This article presents uniaxial compaction experiments of a fine copper powder in a cylindrical die. The compaction process consists of monotonic loading and of loading paths with inserted unloading and reloading cycles. An experimental setup that has been developed for determining the axial and radial stresses during the compaction is described and the calibration of the new device using highly accurate p-finite element simulations of the dies response to internal pressure is shown. The experimental results were subsequently used for the identification of the material parameters of a constitutive model for granular materials recently proposed by Bier and Hartmann [A finite strain constitutive model for metal powder compaction using a unique and convex single surface yield function. accepted for publication by European Journal of Mechanics, Series A/Solids 2006.]. The identification of the elasticity parameters was treated with special attention.     

Simulation research on the anisotropic cutting mechanism of KDP crystal using a new constitutive model

Potassium dihydrogen phosphate (KDP) exhibits anisotropic and hydrostatic pressure-dependent mechanical characteristics during processing. However, none of the existed material models is capable of describing the mechanical properties of the crystal. Thus, a new constitutive model, which combines the anisotropic elastic and pressure-dependent plastic model has been proposed in this paper. In addition, the tensile stress failure criterion is adopted as the fracture criterion of KDP crystal. Subroutine of the new material model is programmed and integrated into the commercial finite element software LS-DYNA. On the basis of that, the unknown material parameters of KDP are successfully identified with the aid of the nanoindentation/scratch technique and finite-element simulation. Finally, 2-D and 3-D cutting simulations applying the new model are performed to investigate the influence of cutting parameters on the brittle ductile transition depth and cutting force. The simulation results show good agreement with the KDP cutting experiment results, which confirm the validity and capability of the proposed constitutive model.     

The Application of Chip Removal and Frictional Contact Analysis for Workpiece–Fixture Layout Verification

In this paper, a workpiece–fixture layout verification approach with the application of frictional contact and chip removal effects using a finite-element technique, is presented. The objective of the proposed system is to overcome the deficiencies of existing fixture design approaches. Workpiece–fixture layout verification analysis is carried out for time varying machining forces to ensure that the workpiece will be held against the cutting and clamping forces. The chip removal effect and frictional contact between the workpiece and the fixture elements are taken into account using a material removal approach based on element death technique and nonlinear finite-element analysis. A case study illustrates the application of the proposed approach. ID="A1"Correspondance and offprint requests to: Professor F. ?ztürk, Department of Mechanical Engineering, Mühendislik-Mimarlik Fakültesi, G?r¨kle Kampusu, Bursa 16059, Turkey. E-mail: ferruh@uladag.edu.tr     

Characteristics of the Friction Between Aluminium and Steel at Elevated Temperatures During Ball-on-Disc Tests

Appropriate specification of the frictional boundary condition for the finite-element (FE) simulation of metal-forming processes is of great importance to the trustworthiness of the results. The research reported in this communication aimed at understanding the interfacial contact between aluminium and steel at elevated temperatures and determining friction coefficients at this material mating. A series of high-temperature ball-on-disc tests were carried out with the AA7475 aluminium alloy as the material of disc and the hardened H11 steel as the material of ball. A mathematical model developed in the preceding research was employed to account for the evolution of the contact interface during ball-on-disc tests. Friction coefficients at different temperatures and over a number of laps were determined. The shear friction stresses and mean contact pressures along with the progress of the tests at 350–500 °C were calculated. It was found that the friction coefficients obtained from ball-on-disc tests alone were insufficient to represent the frictional interaction between deforming aluminium and steel at elevated temperatures. The evolution of the contact interface with increasing sliding distance must be taken into consideration and the friction behaviour can be reasonably characterized by using friction stress.     

悬臂梁非线性振动的压电分阶最优控制

提出非线性的分阶最优控制策略,并将其应用于悬臂梁非线性振动的压电减振控制.建立悬臂梁非线性压电减振系统动力学模型,导出减振系统的非线性动力学运动微分方程.将梁振动挠度和压电驱动器的控制电压同时展开为小参数形式,利用摄动法实现非线性压电控制微分方程的线性化.通过空间解耦,得到状态空间方程.设计非线性分阶控制器,对该减振系统进行分阶最优控制.     

FEM Comparison of Ball and Roller Bullgears

A structural finite element model has been developed for calculating the forces transmitted through the rolling elements (load distribution) in a bullgear assembly. The elastic structural model consists of 3-D beam elements used to approximate the global race deflection and non-linear springs that approximate the combined rolling element/raceway contact deflections. For rollers, an upperbound on the contact stress (assuming linear variation of force along the length of the roller) is estimated by modeling the rollers as pairs of nonlinear springs. The finite element approach iteratively solves the contact forces at each, rolling element. Contact stresses are then calculated from the contact, forces using Hertz contact theory. This approach is applied to analyze two proposed designs of ball and crossed roller bearing, bullgear assemblies used for rotating the radar antenna on top of a ship's mast. The loads analyzed include those arising from wind loading and from out-of-flatness of the inner race of the bearings due to deflection of the mast. The distribution of the load and the maximum contact stresses for the proposed bullgear assemblies are estimated and compared. It is found that the maximum contact stress in the crossed roller bearing is less than that in the ball bearing for both types of loads. Furthermore, the analysis shows that the out-of-flatness loading produces significantly higher stresses than wind loading.