A bond graph approach to the modeling of general multibody dynamic systems

A vector bond approach which effectively leads to a compact form of Hamiltonian bond graph structure and naturally to Hamilton’s equation of motion is proposed for the modeling of general multibody dynamic system. The methods for determining required bond graph elements are formulated in terms of kinematic influence coefficients. All moduli of transformers and their time rate of changes are found by pure vector (matrix) operations for the readiness for computer simulation of the resulting bond graph.     

Numerical modeling of dynamic recrystallization during nonisothermal hot compression by cellular automata and finite element analysis

In this study, dynamic recrystallization during nonisothermal hot compression was numerically simulated by cellular automata and finite element analysis. A modified cellular automata model was developed by introducing a new parameter for considering solute drag effect. The isothermal hot compression tests of pure copper were carried out to verify the modified cellular automata model by comparing material behavior and average grain size. The effect of solute drag was numerically considered and compared to the experimental data and the numerical data obtained by conventional cellular automata without solute drag effect. Then, the modified cellular automata model was applied to a nonisothermal hot compression by combining with a finite element analysis. The finite element analysis was conducted to acquire local parameters such as strain, strain rate, and temperature. These values were provided to the cellular automata model as input. The local changes of microstructure and average grain size were simulated by cellular automata and compared with nonisothermal hot compression results. The simulation results were in reasonably good agreement with experimentally determined microstructures by electron backscattering diffraction. The developed model was further applied to simulate a hot gear blank forging process to check its applicability. With the current approach, local microstructures can be determined for better understanding microstructural changes during the nonisothermal process.     

An experimental study on the behaviour under impact loading of metallic cellular materials

This paper presents an experimental study on the impact response of metallic cellular materials, i.e. aluminium honeycombs of various cell sizes and wall thicknesses, aluminium foams made from two different manufacturing processes (IFAM and Cymat), as well as hollow sphere agglomerates (nickel and iron). A 60 mm diameter nylon Hopkinson pressure bar is used to improve the signal/noise ratio and to host larger samples containing a sufficient number of cells. Quasi-static and classical Split Hopkinson Pressure Bar (SHPB) tests as well as direct impact Hopkinson bar tests (higher speeds up to 50 m/s) are performed. Significant rate sensitivities are observed for most of the cellular materials studied. Analyses of the potential causes of this macroscopic rate sensitivity show that the microinertia effect in the successive folding process could be an important factor.     

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.     

Simulation-based approach to modeling the chip formation energy of polishing process

Polishing is one typical material removal process, which is widely used for surface processing of porcelain tiles. Due to complex polishing head structure and kinematics features of polishing machine, polishing for porcelain tile is a high energy intensity process. To improve the energy efficiency by optimizing operation, it is essential to establish an energy consumption model for polishing process. This article divides the total energy of polishing process into constant energy and chip formation energy. Furthermore, this article focuses on modeling the chip formation energy for optimizing operation. Based on the energy conversion mechanism and energy flow characteristics, the chip formation energy of polishing process is further divided into three motion energies that govern the abrasive trajectory over the tile surface. A conceptual framework of simulation-based approach is then proposed for modeling chip formation energy of polishing process by integrating the above calculation algorithm of motion energy. Finally, a case study is implemented to illustrate the validation of the proposed approach, and the results show that it is a feasible tool to model the chip formation energy of polishing process and reveal the influence of different process operational parameters.     

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.     

A cellular finite element model for the cutting of softwood across the grain

In this paper, the mechanics of cutting wood across the grain are reexamined. A hybrid cellular/macroscopic finite element model of wood was developed to simulate the effects of cell collapse during the cutting process. Initially, the model was used to simulate the compression test across the grain. The linear elastic and cell collapse behaviours of the compression tests were sucessfully simulated. The model was then used to simulate two orthogonal cutting processes, wedge cutting and chip-forming cutting. The cellular/macroscopic model revealed that during the cutting process, the load compresses the wood until cell wall buckling occurs ahead of the tool. The collapse of the supporting cell wall results in a localized tensile stress in the longitudinal direction of the cell at the tip of the tool. It is postulated that this longitudinal tensile stress would lead to microfibrils being pulled out of the matrix and hence to failure of the cell wall. Therefore, the cellular/macroscopic model has been used to explain the mechanics of severing wood fibres during the process of cutting wood across the grain.     

Prediction of the effects on dynamic response due to distributed structural modification with additional degrees of freedom

The aim of this study is to investigate means of efficiently assessing the effects of distributed structural modification on the dynamic properties of a complex structure. The dynamic properties of the modified structure can be determined by experimental testing or numerical simulation, both of which are complex, expensive and time-consuming. Assuming that the original dynamic characteristics are already established and that the modification is a relatively simple attachment, the modified dynamic properties may be determined numerically without solving the equations of motion of the full-modified structure. The frequency response functions (FRFs) of the modified structure can be computed by coupling the original FRFs and a delta dynamic stiffness matrix for the modification introduced. The validity of this approach is investigated by applying it to a cantilever beam to which a smaller beam is attached as modification. The original FRFs were obtained experimentally as well as numerically. The delta dynamic stiffness matrix was determined numerically by modeling the attachment and part of the original structure including the attachment points. The FRFs of the modified beam were then computed. Good agreement is obtained by comparing the results to the FRFs of the modified beam determined experimentally as well as by numerical modeling of the complete modified structure.     

A simple approach to estimate failure surface of polymer and aluminum foams under multiaxial loads

From mechanical point of view, it is required to have a criterion for evaluating the failure of cellular solids (foams) under multiaxial loads. Well-documented experimental results in the literature show foams could fail by several mechanisms, e.g., elastic buckling, plastic yielding, brittle crushing or brittle fracture. In the previous years, both theoretical and phenomenological approaches have been applied to obtain the failure surface of various foams. The purpose of this paper is to present a simple approach to estimate the complete failure surface of “non-textured” foams. The predicted results of polymer and aluminum foams are compared with the experimental results reported in the literature. It is found that three selected tests will be sufficient to estimate the complete failure surface of a foam. The recommended testing stress states are σ₁=σ₂=σ₃>0, σ₁=σ₂=σ₃<0, and σ₁=−σ₂=−σ₃ (or σ₁=−σ₂, σ₃=0).     

A generalized self-consistent estimate for the effective elastic moduli of fiber-reinforced composite materials with multiple transversely isotropic inclusions

The effective elastic properties of a fiber-reinforced composite material with multiple transversely isotropic inclusions are estimated by the use of a generalized self-consistent method, which considers strong interactions between the inclusion and matrix as well as among inclusions. The accuracy of this method is established by comparing to the closed-form analytic solutions by Christensen when the matrix and inclusion are isotropic. Furthermore, current predictions from the generalized self-consistent method for a composite with multiple inclusions correspond well with the numerical results from finite element analysis. The generalized self-consistent method can be particularly useful in establishing micromechanics models of natural biological composite materials such as cortical bone to examine the dependence of the elastic properties of cortical bone on its porosity.     

A process-oriented approach to modeling the conceptual design of aircraft assembly lines

The need to develop methods and software applications to support the design of assembly lines is academically and industrially acknowledged. This paper focuses on the conceptual design of aeronautical assembly lines. A model is proposed to represent the process to design an aerostructure assembly line at the conceptual design phase and the knowledge requirements to support such process. The conceptual design process is documented in an Integrated Definition for Function Modeling model and the knowledge model is documented in Unified Modeling Language. The model provides a starting point in the formalization of the assembly line conceptual design. The objective is to use such model for the development of a knowledge-based application prototype in an industrially used software system.     

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.     

A new approach to modeling the surface topography in grinding considering ploughing action

The ground workpiece surface is generated simulating the trajectory of all the abrasive grains and trimming these trajectories by the appropriate method. A realistic simulation requires the trajectory to be correctly modeled. In the stage of trajectory modeling, most of the current approaches only consider the kinematics interaction between the grains and the workpiece, neglecting ploughing and rubbing. To overcome these problems, a new approach to modeling the surface topography in grinding is proposed in this paper. First, the depth of grain participated in the grinding is defined as a real-time cutting depth due to its changes with time, and the relationship between cross-sectional area of an un-deformed chip and real-time cutting depth is established. Second, the three-dimensional cutting trajectory of a grain is defined considering ploughing action is given assuming that the area of the remaining material on each side of the grain path is proportional to the un-deformed cutting area of the grain. With the 3D cutting trajectory, the surface topography is generated by simulating the trajectory of all the grain and removing the interfering material. Finally, this model has been validated by the experimental results for different cutting depth and feed rate.     

A dynamic surface topography model for the prediction of nano-surface generation in ultra-precision machining

Materials induced vibration has its origin in the variation of micro-cutting forces caused by the changing crystallographic orientation of the material being cut. It is a kind of self-excited vibration which is inherent in a cutting system for crystalline materials. The captioned vibration results in a local variation of surface roughness of a diamond turned surface. In this paper, a dynamic surface topography model is proposed to predict the materials induced vibration and its effect on the surface generation in ultra-precision machining. The model takes into account the effect of machining parameters, the tool geometry, the relative tool–work motion as well as the crystallographic orientation of the materials being cut. A series of cutting experiments was performed to verify the performance of the model and good correlation has been found between the experimental and simulation results.     

双光路法测量手性物质的旋光角

为排除光源波动引起的干扰,设计了一种双光路法测量手性物质旋光角实验装置,通过对手性物质灰黄霉素溶液在不同时间下的旋光角的多次测量、比较,显示该装置具有较高的精度,较好的重复性和方便性。     

A FEM study on the mechanical responses of pseudoelastic TiNi alloys to a particle normal loads

In this study, the models of four materials including three sorts of pseudoelastic TiNi alloys and a stainless steel (as a contradistinction) enduring a particle's normal loads were individually simulated based on bilinear strain hardening law by means of finite element method. Owing to the pseudoelasticity, TiNi alloys proved to have high elastic strain limit and low pseudo-Yong's modulus, with which the special mechanical response was created under normal loads. The results shown that pseudoelastic TiNi alloys occurred plastic deformation more difficult than the stainless steel, and the critical load of plastic deformation increased with the increasing elastic strain limit and the decreasing pseudo-Young's modulus. Plastic regions of three TiNi alloys with the elastic strain limit 0.02, 0.04 and 0.06 were 0.60, 0.32, 0.047 times of that of the stainless steel, respectively. When the pseudoelastic TiNi alloys endured a particle's normal loads, the phenomena of decreasing contact stress, von Mises stress and increasing the elastic strain were also observed in this FEM study. In terms of above results, the wear mechanism of pseudoelastic TiNi alloys was discussed finally.     

A layered approach to the non-linear static and dynamic analysis of rectangular reinforced concrete slabs

A simplified model for the static and dynamic behaviour of reinforced concrete slab has been developed, based on laminated theory. The proposed model considers the slab as a layered structure and leads to explicit relations, which account for the macroscopic linear and non-linear behaviour of slabs on lines of simple supports. The presented models aim to analyse and design slab to resist impact from rock falls. The results conform well with those of experimental and finite element methods, and indicate the anisotropy effects on natural frequencies and mode shapes of slabs which are highly reinforced in only one direction, such as rock shed slabs or slabs reinforced with FRP.     

A model for the friction of multiphase materials in abrasion

A model is presented for the sliding friction of multiphase materials in abrasion. The friction is described in terms of the load distribution between the phases. Different load distribution modes are used with Amontons' first law of friction to derive both the friction force and the coefficient of friction as functions of the area fractions of the phases, their individual coefficients of friction and their wear resistance. It is shown that the coefficient of friction of a multiphase material should depend on the load distribution mode and that the upper and lower limits for the coefficient of friction expected from composites or multiphase materials can be identified. For most pressure distribution modes, the friction depends on the wear resistance of the phases. The model is compared with results from abrasion tests on a silicon carbide reinforced aluminium alloy (AlSi7Mg) over a wide range of loads and with different fixed abrasive particles. The experimental results are described and interpreted in terms of the model.     

The influence of the finite initial strains on the axisymmetric wave dispersion in a circular cylinder embedded in a compressible elastic medium

The influence of the finite initial strains on the axisymmetric wave dispersion in a circular cylinder embedded in a compressible elastic medium is investigated within the scope of a piecewise homogeneous body model utilizing three-dimensional linearized theory of wave propagation in an initially stressed body. The material of the cylinder and the surrounding elastic medium are assumed to be compressible and the corresponding elasticity relations are described by the harmonic potential. The numerical results are presented and discussed. It is established that the dispersion curves are divided into four parts by the characteristic nondispersive wave velocities regarding the cylinder and the surrounding materials. As a result of the existence of the initial strains the lengths of these parts change and they move wholly up (down) under initial stretching (compressing) strain along the cylinder, i.e. along the wave propagation direction.     

Iterative control approach to high-speed force-distance curve measurement using AFM: time-dependent response of PDMS example

Force-distance curve measurements using atomic force microscope (AFM) has been widely used in a broad range of areas. However, currently force-curve measurements are hampered the its low speed of AFM. In this article, a novel inversion-based iterative control technique is proposed to dramatically increase the speed of force-curve measurements. Experimental results are presented to show that by using the proposed control technique, the speed of force-curve measurements can be increased by over 80 times--with no loss of spatial resolution--on a commercial AFM platform and with a standard cantilever. High-speed force curve measurements using this control technique are utilized to quantitatively study the time-dependent elastic modulus of poly(dimethylsiloxane) (PDMS). The force-curves employ a broad spectrum of push-in (load) rates, spanning two-order differences. The elastic modulus measured at low-speed compares well with the value obtained from dynamic mechanical analysis (DMA) test, and the value of the elastic modulus increases as the push-in rate increases, signifying that a faster external deformation rate transitions the viscoelastic response of PDMS from that of a rubbery material toward a glassy one.