M. Salimi

Modified slab analysis of asymmetrical plate rolling

In this paper the general case of asymmetrical plane strain rolling due to unequal roll diameter, unequal surface speed of the rolls and different contact friction is considered. An analytical model based on the slab method of analysis was used and further developed to obtain the characteristics of asymmetrical sheet rolling and to predict strip curvature. This method describes an enhancement to the rolling theory where friction becomes an integral part of deformation mechanics in the roll gap. To verify the validity of the proposed analytical model, the analytical rolling force, torque and curvature were compared with experimental and analytical results of other investigators. Very good agreements are found. Capability as well as the simplicity of the proposed model in predicting more accurate theoretical results for the rolling force, torque and curvature makes it suitable for the online control application.

Guide roll simulation in FE analysis of ring rolling

Abstract A new method (thermal spokes) has been proposed to simulate the guide roll effect in FE analysis of the ring rolling process. The method is simple to use with existing FE formulations, does not introduce further nonlinearities, and results in more stable and faster solution to ring rolling simulations. The method has been successfully employed in a 2D FE simulation of rolling flat rings. A special feature of the method is its ability to take into account the stiffness of the adjustment mechanism of the guide rolls. On the other hand, a simple modification has been introduced on the lever arm principle, which might be used to estimate guide roll forces in elementary analysis. Incorporating the thermal spokes method in the ring rolling simulation showed important effects of the guide rolls on the ring–tool contact region, roll force and drive torque. Finite element results are in good agreement with experimental results and confirm the validity of the thermal spokes approach as well as the proposed modified lever arm principle.

Determination of internal mechanical characteristics of woven fabrics using the force-balance analysis of yarn pullout test

Abstract Pullout test is a conventional and suitable method to investigate the effects of yarn properties and the structural characteristics of weave on fabric mechanical behaviour. Frictional specifications of the fabric yarns influence the fabric strength and efficiency and its ability to absorb energy. This paper is concerned with formulating an analytical model on yarn pullout force in plain-woven fabrics. The model can predict variations in the internal mechanical parameters of woven fabrics based on a force-balance analysis. These parameters are yarn-to-yarn friction coefficient, normal load at crossovers, lateral forces, lateral strain, weave angle variations, and pullout force. These parameters were predicted using fabric deformation data, which were measured by image processing method during a yarn pullout test and the information of weave angle of fabric, its modulus and density, which were obtained experimentally. Yarn pullout force was calculated through Amontons friction law to evaluate the efficiency of the presented model. This study demonstrates that the force-balance model is correlated quantitatively with the experimental yarn pullout results.

Modeling of Shape Memory Alloys Based on Microplane Theory

A three-dimensional microplane constitutive model utilizing statically constrained formulation with volumetric—deviatoric split is presented for shape memory alloys (SMAs). Shear stress within each microplane is described by resultant shear component on the plane. One-dimensional stress—strain laws are used for normal and shear stresses on microplanes by considering suitable adjustments between the macroscopic and the microscopic quantities. The behavior of SMAs under simple and complicated loadings is studied. The model represents interaction between the stress components and the deviation from normality in the case of nonproportional loadings. The results are in good agreement with the existing theoretical and experimental findings.

Modeling of the cyclic thermomechanical response of SMA wires at different strain rates

A one-dimensional coupled thermomechanical model is presented for shape memory alloys (SMAs) under non quasi-static loading by defining a Helmholtz free-energy function consisting of strain energy, thermal energy, and the energy of phase transformation. The first law of thermodynamics is used to address the thermomechanical coupling due to the influence of strain rate on the SMA temperature. The convective heat transfer coefficient of an SMA wire is calculated by using temperature-dependent empirical relations, and it is shown that no single empirical formula for the heat transfer coefficient can be applied to obtain experimentally consistent results under different loading conditions. The martensite fraction is decomposed into stress-induced and temperature-induced fractions so that the model is capable of predicting both the shape memory effect and the pseudoelasticity. Cyclic loading, the effect of wire diameter and the variation of dissipated energy with strain rate are studied, and the general features of the responses are found to be in agreement with the experimental observations.

Microplane modelling of shape memory alloys

A three-dimensional (3D) constitutive model based on a statically constrained microplane theory with volumetric–deviatoric split is proposed for polycrystalline shape memory alloys (SMAs) under multiaxial loading paths. Microplane governing equations are 1D stress–strain relations for normal and shear stresses on each microplane, in which suitable relationships between the microscopic and macroscopic quantities are considered so that switching between elastic and inelastic local responses automatically occurs according to the macroscopic response of SMA without additional constraint. Shear stress on each microplane is expressed by the resultant shear component within the plane to overcome directional bias and to prevent the appearance of shear strain in a pure axial loading or axial strain in a pure shear loading while microplane formulations based on two shear directions may predict such impractical results. The behaviour of SMA under simple and complicated loadings has been studied. In nonproportional loading paths, the model shows interaction between stress components, as well as deviation from normality. Predicted results from the model are in good agreement with those of the existing theoretical and experimental investigations.

A new calibration method for ductile fracture models as chip separation criteria in machining

Abstract Several leading commercial FEM codes offer a number of fracture options without giving any guidance to the users in determining the fracture parameters for different materials. A modification is implemented to Johnson and Cook’s calibration method to provide simultaneous consideration of both active failure mechanisms in actual domain of the field variables. Application of FE simulation of machining to accumulate damage is the key point to solve problems of available calibration method. As a result, a new set of fracture constants is presented for AISI 1045 steel. It is demonstrated that due to different failure mechanism a unique fracture model cannot be the representative of crack generation in all machining zone. Then the classical Lagrangian simulation is modified based on this concept.

Evaluation of chip formation simulation models for material separation in the presence of damage models

Abstract This paper appraises two major chip formation techniques in finite element (FE) simulation of machining. The first one considers chip formation as a wedge indentation process, while the second one considers chip separation due to ductile fracture. The first technique has been implemented in an Arbitrary Lagrangian–Eulerian (ALE) simulation of machining and the chip formation is assumed to be due to plastic flow. Therefore, the chip is formed by continuous remeshing of the workpiece. In the updated Lagrangian (UL) simulation as an implementation of the second technique, the Johnson–Cook (J–C) damage criterion is used where elements in the sacrificial layer are deleted, as the accumulated damage in such elements exceeds the predefined critical value. The experimental data of the Assessment of Machining Models (AMM) effort for orthogonal cutting is used as a source to verify the models. It is found that predictions of the first technique for strains and temperatures within the deformation zones are not satisfactory and the predicted resistance of workpiece material to cutting is unrealistically high. Instead, the results obtained by second technique are shown to be more reasonable with less computational cost and less possibility of software crash. However, in the case of calculating the field variables the major differences are located in the material separation affected zones; the two thin boundary layers on the cut surface and underside of the chip.

Finite Element Simulation of a Yarn Pullout Test for Plain Woven Fabrics

In this study, a three-dimensional (3D) model of a yarn pullout test for plain woven fabrics is introduced. The main focus of the study is on the realization of a 3D fabric geometrical model, the incorporation of anisotropic material properties and the validation of yarn and fabric finite element meso-models using experimental results. The material properties of yarn and fabric were assumed to be linear orthotropic. The required engineering constants were obtained from experimentally-measured tensile, compression and shear diagrams. The accuracy of the applied engineering constants was investigated by finite element (FE) modeling of yarn pure bending. The yarn pullout test was modeled with the Abaqus FE package. The fabric sample was modeled with solid elements for the weft and warp yarns in the interlacing points, which are directly involved in the yarn pullout, plus shell elements for the parts of the fabric that undergo only shear deformation. The effects of the geometrical model and material anisotropy were investigated and the predicted force—displacement profiles of the yarn pullout test were compared with experimental measurements.

Determination of bending actuators set points to control crown and flatness in hot rolling of strip

Abstract In this paper a new numerical method is presented in which the slit beam model is employed and further developed to include the surface elastic deformation of rolls due to the rolling load/roll separating force in a four high mill. Mathematical analysis and finite element method in calculating surface coefficients were used. Then the surface coefficients were employed in the slit beam model. In this manner detecting any discontinuity in roll separating force is easily possible and hence set points are calculated more accurately.