Three-dimensional Plastic Deformation Research Articles

Study on the influence of relative vibration between tool and workpiece on plastic side flow

The mutual vibration between the tool and the workpiece not only affects the surface roughness value, but also the vibration energy has a very important influence on the mechanical properties and plastic deformation of the material. Based on the interaction mechanism between the tool and the workpiece surface, the three-dimensional plastic deformation in the third deformation zone is studied. The analytical relationship among vibration and plastic side flow is explored, and the method of restraining plastic side flow is put forward. The change mechanism of flow velocity of materials under the influence of vibration is analyzed. Through analysis, vibration makes the material soften, which leads to more obvious plastic side flow phenomenon. Reducing vibration can effectively inhibit plastic side flow phenomenon. Finally, the influence of relative vibration between tool and workpiece on the formation process of surface cracks of workpiece is studied, and the number of cracks per unit area can be well reduced by reducing the vibration. The research content of this paper can provide theoretical basis for improving the surface quality of ultra-precision turning of spherical/aspherical surfaces, and is of great significance to the processing of high-quality spherical/aspherical mirrors.

Numerical modeling of TRIP steel in axial crashworthiness

With their high strain rate hardening capacity and good combination of strength and ductility, transformation induced plasticity (TRIP) steels offer lightweight solutions for reinforcement components undergoing crash events. The TRIP effect correlates with stress-stimulated martensitic transformation from austenite, which depends on a myriad of kinematic ingredients, including three-dimensional plastic deformation, temperature change, strain-rate, and stress state. The complex interdependency of these kinematic ingredients requires stepwise and time iterative numerical analyses, especially when boundary-value problems are imposed. Typically engineering desired boundary value problems involve simulations designed to control energy absorption under complex crash scenarios. In this paper, we demonstrate a new phenomenological framework for thermo-mechanical modeling of multi-phase TRIP steel that captures the evolution of phase transformation. The model was implemented into the user-defined subroutine of the explicit dynamic version of the commercial finite element software LS-DYNA. Simulations were performed on a top-hat crush tube made of an industrial multiphase TRIP 800 steel. The results were utilized within an optimization simulation framework to pinpoint composition windows, which maximize the energy absorption capacity. When not concerned about peak crush force, larger compositions of austenite (typically ∼70%) will outperform all other compositions. However, lowering the austenite volume fraction with higher volume fractions of bainite (∼80%) with balanced ferrite could produce a top-hat crush rail with a superior crush force and efficiency compared to TRIP 800 steel without increasing the peak crush force.

A Rapid Online Calculation Method of Three-dimensional Plastic Deformation in Strip Rolling

Three-dimensional strip plastic deformation model is a key part of shape setup model in hot rolling. The numerical efficiency, accuracy and stability of the method are the main factors that may restrict its online application. Considering the theoretical limitations of existing models, basic equations include equilibrium equations with the effect of shear stress, constitutive equations based on incremental theory, and lubricated friction with the respective coefficients of friction at longitudinal and transverse direction. After normalization of parameters and the asymptotic analysis, the strip plastic deformation model is established, and solved by finite volume method and BICGSTAB algorithm to get the transverse distribution of rolling force of each stand. Compared to the finite element model established by ANSYS software, the new model has reliable results and a short computation time of 31 milliseconds, which show its feasibility of online application.

The Analysis of Influence on the Edge Drop of Tandem Cold Rolling Mill

Edge-drop control enlarges the shape control theories and technologies. But compared to the profile and flatness control technology, the edge drop control is a developing topic. This paper analyze the influence of strip thickness, strip width, reduction ratio, friction coefficient and deformation resistance on the edge drop based on the elastic deformation of rolls and the three-dimensional plastic deformation of strip for UCMW cold rolling mill. The results will support the further research on the edge drop control for cold rolling mill.

입자법을 이용한 토사의 대변형 해석법 개발

본 연구에서는 토사 유동과 같은 대변형 해석을 위해 기존 유한요소법이나 유한차분법과 달리 격자를 사용하지 않는 입자법을 사용하였으며, 입자법은 구배, 발산, 라플라시안과 같은 미분연산자에 대응하는 입자간 상호작용모델을 이용하여 연속체의 지배방정식을 이산화하였다. 외부 하중이나 함수비 증가에 따라 고체에서 유체 상태로 변하는 흙의 3차원 대변형 거동을 해석하기 위해 기존 입자법에 흙의 파괴상태를 고려할 수 있는 Mohr-Coulomb 파괴기준을 도입하였으며, 흙의 파괴 이전의 항복이나 경화현상으로 인한 대변형은 흙을 점성 유체로 가정하여 해석하였다. 개발된 입자법은 먼저 구속압이 작용하지 않고 강도가 0인 모래기둥 붕괴실험 결과를 이용하여 검증한 다음, 점착력을 가지고 자립이 가능한 점토기둥 붕괴실험을 실시하여 흙의 항복이나 파괴로 인한 대변형을 시뮬레이션하였다. 개발된 입자법은 모래와 점토의 3차원 대변형 거동을 유사하게 잘 예측하였으며, 파괴 이전에 발생하는 흙의 항복으로 인한 소성변형에 따른 흙기둥 내의 수직 및 전단응력 변화도 계산할 수 있었다. In this study, a particle method without using grid was applied for analysing large deformation problems in soil flows instead of using ordinary finite element or finite difference methods. In the particle method, a continuum equation was discretized by various particle interaction models corresponding to differential operators such as gradient, divergence, and Laplacian. Soil behavior changes from solid to liquid state with increasing water content or external load. The Mohr-Coulomb failure criterion was incorporated into the particle method to analyze such three-dimensional soil behavior. The yielding and hardening behavior of soil before failure was analyzed by treating soil as a viscous liquid. First of all, a sand column test without confining pressure and strength was carried out and then a self-standing clay column test with cohesion was carried out. Large deformation from such column tests due to soil yielding or failure was used for verifying the developed particle method. The developed particle method was able to simulate the three-dimensional plastic deformation of soils due to yielding before failure and calculate the variation of normal and shear stresses both in sand and clay columns.

Evaluation of the measurement of metal flow and strain distribution in bulk metal forming

A measuring method, using rings of screw threads is proposed in order to solve the difficulties associated with measuring the strain and flow distributions during die forging processes. This method does not use a substitute material to measure the magnitude of the three-dimensional plastic deformation and it can therefore be used in quantitative analysis. Using the proposed method, the strain and four flow lines of typical sections were measured and analysed during the deformation of a coupled model. A distribution rule for the stress—strain relationship is presented. The proposed method is shown to be able to measure and analyse the metal flow during die forging. It can be used to study material flow and to predict strain distribution in general bulk metal forming processes such as extrusion.

Three-dimensional Numerical Analysis of Microstructural Evolution in and after Bar and Shape Rolling Processes.

An integrated numerical model predicting microstructural evolution, three-dimensional plastic deformation and temperature changes has been applied to industrial hot bar rolling and H-beam rolling. This model enables us to predict three-dimensional metal flow and temperature changes as well as transient in grain size change and dislocation density distribution in and after hot rolling. To demonstrate the successfulness of the proposed model, it was applied to the analysis of two different industrial bar rolling schedules, in which total number of passes and caliber systems were different with each other. It was also applied to the analysis of the H-beam rolling sequences with different heat treatment conditions. Microstructural evolution starting from deformed austenite to ferrite/pearlite/bainite after phase transformation was successfully simulated. Microstructural evolution in and after hot rolling as well as metal flow and temperature can be easily obtained through the proposed model using rolling condition and alloy composition as the functional variables. This model is a very useful tool for designing and optimizing rolling conditions so that products with the best internal quality and dimensional accuracy can be obtained.

Development of a three-dimensional finite-element program for metal forming and its application to precision coining

Process design is one of the most important fields in metal forming, where the finite element method has appeared to be a useful method for industrial applications. In this study, a program using the rigid–plastic finite-element method has been developed for process design in three-dimensional plastic deformation. The dies in the computation consist of four-node patches, and an area-comparison scheme is adopted to decide the contact condition between the die and the workpiece. Surface integration for the calculation of the friction between the die and the workpiece has been implemented with care in the numerical treatment. The developed program is applied to a precision-coining process to determine the amount of piercing.

Extension of the Backward Tracing Scheme of the Rigid-Plastic FEM in Three-Dimensional Deformation

Preform design is one of the critical fields in metal forming. The finite element method (FEM) has been effective in designing preforms and process sequence, for which the backward tracing scheme of the rigid-plastic FEM has been explored. In this work a program using the backward tracing scheme of the rigid-plastic FEM is developed for three-dimensional plastic deformation, which is an extension of the scheme from two-dimensional cases. The calculation of friction between workpiece and die, and handling of boundary conditions during backward tracing require sophisticated treatment. The developed program is applied to upsetting of a rectangular block and to side pressing of a cylindrical workpiece. The results of the two applications show feasibility of the program on three-dimensional plastic deformation.

Finite Element Simulation of Three-Dimensional Plastic Deformation in Shape Rolling. 3rd Report. Simulation of Non-Steady-State Deformation around Front and Rear Ends.

Non-steady-state three-dimensional deformation around the front and the rear ends in shape rolling with grooved rolls is simulated by the rigid-plastic finite element method using the isoparametric hexahedral elements with eight nodes. To simulate complex non-steady-state deformation in shape rolling, a non-steady-state scheme using a remeshing technique is proposed. The workpiece is remeshed at each step of deformation to locate nodal points at the boundary of the interface between the roll and the workpiece. The present method can calculate not only the non-steady state deformation around the front and the rear ends but also steady-state-deformation. As examples of non-steady state simulation, rolling processes of bars and beams with grooved rolls are chosen. The deforming shape and the distributions of stress and strain for the workpiece in non-steady and steady states are computed.

Finite element simulation of three-dimensional plastic deformation in shape rolling. 2nd Report, Simplified three-dimensional simulation by generalized plane-strain deformation.

An efficient simulation method for predicting the width-spread in caliber rolling by the rigid-plastic finite element method is proposed. In this method, the three-dimensional deformation of the workpiece between the caliber rolls is simplified to the generalized plane-strain deformation where the strain rate is assumed to be uniform in the rolling direction over a cross section. Rolling by shaped rolls is treated as equivalent to compression with shaped dies, and the axial stress due to friction is taken into account. The deformed shape of a rectangular bar after caliber rolling is predicted and the calculated results of the width-spread are shown to agree with the experimental results. The deformed shape, the distribution of equivalent strain in the workpiece and the computing time are compared with those of the full three-dimesional simulation. The proposed simplified simulation method is found to provide sufficiently accurate results in terms of width-spread with a very short computing time.

Finite element simulation of three-dimensional plastic deformation in shape rolling. 1st report. Fully three-dimensional simulation of steady-state deformation.

Three-dimensional steady-state deformation in shape rolling with grooved rolls is simulated by the rigid-plastic finite element method using the isoparametric hexahedral elements with eight nodes. To simulate complex steady-state deformation in shape rolling, a method featuring both the steady-state and the nonsteady-state schemes is proposed. For the three-dimensional element mesh, the boundary conditions of metal flow along the curved roll surface and of friction between the roll and the workpiece are dealt with at each node over the interface. Contact of the nodal points with the roll surface and detachment from the surface are judged at each step of calculation. As examples of three-dimensional simulation, rolling processes of bars and beams with grooved rolls are chosen. The deforming shape and the distributions of stress and strain in the workpiece are computed.

Experimental investigation of the strain state in the ring-forging process

A method for calculating the strain state during three-dimensional plastic deformation is presented. The method is based on the measurement of the co-ordinates of net nodes marked on the surface to be investigated: in the present case the method is applied to the ring-forging process. Specimens were forged between the mandrel and a flat die and also between the mandrel and a die of inverted V-shape with included angle ϕ=135°. The results obtained in the tests allow an assessment of the influence of the relative width of the specimen, α (α=original width of the ring divided by its origianal outer diameter), and the relative diameter of the mandrel, δ (δ=diameter of the mandrel divided by the I.D. of the ring), on the strain state in the deformation zone. A flat die and a relative diameter of the mandrel of δ⩾0.8 afford less inhomogenity of strain and less irregularity of the cross-section in comparison with the results of using the inverted V-shaped die.

Some observations on the effect of specimen size upon the plastic deformation around deep notches

The purpose of this work was to investigate the effect of specimen thickness on the three-dimensional plastic deformation of notches. Notched bend specimens, made of lead as a model material, were tested. Transverse and longitudinal deformations at the notch root were measured using simple experimental techniques. The results provide a picture of the transition from the plane stress to the plane strain deformation of a notch root, which is discussed and interpreted. The shape which is assumed by the notch under the condition of plane plastic flow is shown to be a consequence of the plastic incompressibility of the material. Further, the formation of cracks at the notch root is discussed.