A constitutive model for transversely isotropic foams, and its application to the indentation of balsa wood

An elastic-plastic constitutive model for transversely isotropic compressible solids (foams) has been developed. A quadratic yield surface with four parameters and one hardening function is proposed. Associated plastic flow is assumed and the yield surface evolves in a self-similar manner calibrated by the uniaxial compressive (or tensile) response of the cellular solid in the axial direction. All material constants in the model (elastic and plastic) can be determined from a combination of a total of four uniaxial and shear tests. The model is used to predict the indentation response of balsa wood to a conical indenter. For the three cone angles considered in this study, very good agreement is found between the experimental measurements and the finite element (FE) predictions of the transversely isotropic cellular solid model. On the other hand, an isotropic foam model is shown to be inadequate to capture the indentation response.     

Hybrid experimental/numerical technique for determination of the complex dynamic moduli of elastic porous materials

Polyurethane (PU) and other plastic foams are widely used as passive acoustic absorbers. For optimal design, it is often necessary to know the viscoelastic properties of these materials in the frequency range relevant to their application. An experimental/numerical technique has been implemented to determine the Young and shear dynamic moduli and loss factor of poroelastic materials under low-frequency 40–520Hz random excitation. The method consists of measuring the dynamic response of the sample at its surface, and matching the response with the predictions from a finite element model in which the two complex elastic moduli are the adjustable parameters. Results are presented for measurements made in air, under standard pressure and temperature conditions, and compared with predictions based on Okuno’s model. The dependence of elastic moduli on the dimension of the sample and its boundary conditions is also studied. This paper was recommended for publication in revised form by Associate Editor Hong Hee Yoo Professor Yeon June Kang received his B.S. and M.S. degrees in Mechanical Design and Production Engineering from Seoul National University in 1988 and 1990, respectively. He then went on to receive a Ph.D. degree in Acoustics and Vibra-tion from School of Mechanical Engineering, Purdue University in 1994. After his Ph.D., he continued to work as a Postdoctoral Research Associate at Ray W. Herrick Laboratories, Purdue University until 1996. Since 1997, Dr. Kang is working at the Department of Mechanical and Aerospace Engineering, Seoul National University. Dr. Kang’s research interests are in the area of acoustical materials, noise and vibration in automotive engineering, and Korean Bells.     

Stability loss analyses of the elastic and viscoelastic composite rotating thick circular plate in the framework of the three-dimensional linearized theory of stability

In the present paper, in the framework of the three-dimensional linearized theory of stability the rotationally symmetric stability loss problems of the elastic and viscoelastic composite rotating thick circular and annular discs are investigated. The method for solution to these problems is developed by employing Laplace transform and finite element method. It is supposed that the disc and annular disc have an insignificant rotationally symmetric initial imperfection and as a stability loss criterion, the case where this imperfection starts to increase and grows indefinitely, is taken. Numerical results related to the critical angular velocity for elastic problems and to the critical time for viscoelastic problems are presented.     

A mesomodel for the numerical simulation of the multiphasic behavior of materials under anisothermal loading (application to two low-carbon steels)

The determination of residual stresses induced by welding or heat treatment operations requires the use of complex models taking into account thermal, metallurgical and mechanical phenomena. In this paper, we propose a mechanical model in which each phase can follow its own constitutive law. This model also takes into account phase transformation plasticity, which is treated independently of the behavior of each phase. This model has been implemented into the French FEM code Castem 2000. The interest of the proposed method is that it allows one to mix any type of nonlinear behavior using Taylor homogenization hypothesis. There is no need to develop a theory to get the equations of the homogenized material law. Two numerical examples demonstrate the efficiency and the flexibility of this approach. The results obtained are compared to experimental values for a typical welding situation and a high-temperature response. This comparison seems to indicate that viscous effects in the materials have a significative influence on the residual stresses produced by welding.     

具有区间参数的不确定结构静力区间分析的一种算法

将结构系统中的不确定性参数用区间数来表示,用有限元法建立静力区间线性方程组。对该方程组的求解提出了一种区间逐步离散的方法。此方法通过令独立的不确定性参数取区间内的离散值,将区间线性方程组的求解转化为相应的确定性问题,再搜索各方程解中的最大最小值得到每个区间分量的边界。先用数学算例对该算法的正确性和有效性进行了验证,然后应用于静力区间分析的工程算例,并与其它算法进行了比较。计算结果表明该算法的计算效率和准确性较高。     

A theoretical and experimental investigation of surface generation in diamond turning of an Al6061/SiCp metal matrix composite

In this paper, the surface generation in ultra-precision diamond turning of Al6061/15SiC_p metal-matrix composites was investigated based on different analytical approaches which include parametric analysis, cutting mechanic analysis, finite element method (FEM) analysis and power spectrum analysis. Parametric analysis was performed to explore the in situ inter-relationships between the process parameters and the surface roughness. The surface properties of the diamond turned surface were extracted and analyzed by the power spectrum analysis of the surface roughness profiles. Different surface generation mechanisms were deduced based on the cutting mechanics and FEM analysis. The results of the theoretical analyses were verified through a series of cutting tests conducted under various cutting conditions and a good correlation between the theoretical and experimental results was obtained.     

滑块式万向联轴器和轧辊的装配体有限元分析

滑块式万向接轴因其能在倾角较大情况下传递较大的扭矩而被广泛应用,但是延用至今的强度计算方法,或因假设条件多,使计算误差大,或因经验公式范围有限而不能满足进一步研究的需要。利用有限元技术,对轧机滑块式万向联轴器和轧辊的装配体进行强度计算,计算出关键零件的危险位置。因假设条件少,更符合实际情况,因此计算结果更为准确、可靠。     

某四缸汽油机气缸盖气缸体组合结构有限元分析

建立了某四缸汽油机气缸盖、缸体、主轴承盖等零件的三维有限元组合模型。使用有限元分析软件Abaqus,在考虑各组件非线性接触关系的基础上,计算了该组合体在标定工况下的振动响应。对该发动机进行了表面振动测量,通过振动测点处实验数据与该点处计算数据的对比验证了有限元模型建立的合理性。分析了爆发工况下缸体、缸盖火力面及缸孔的振动变形。结果表明:缸体裙部刚度较弱容易产生变形;缸盖火力面鼻梁区变形较大,缸盖火力面与气缸盖连接处容易产生较大的应力;缸孔的变形量较小在工程允许的范围之内。