Materials Science Forum Vols. 575-578

Abstract: The paper simulated and researched the straightening process of heavy rail by finite element software of ANSYS/LS-DYNA. The residual stress of the rail head, rail base, rail loin in the 7th deformation zone meets the real straightening condition in the straightening simulation. The calculation indicates: The residual stress of the rail head, rail base, rail loin in various deformation zones varies significantly like the variation of tensile-compression-tensile. Compared with the on-site rule, the residual stress of rail base decreased155 Mpa, this is in agreement with the values of practice.

Abstract: At the early stage of product design, the information about mould, blank and boundary condition are not definite. It is difficult to calculate with incremental method. For solving this problem, one-step finite element method(FEM) was put forward in recent years. It starts from product shape, takes it as the middle plane of formed part, disperses it and determines the location of nodes in initial blank at certain boundary conditions with finite element method. Then the corresponding blank shape can be obtained by one-step FEM. In this paper it is discussed that the basic theory of one-step FEM and the research of the key technology. And it is simulated the pressing of auto panel with one-step FEM. It is put forward that the final part should consider the effect of the technology. Through comparing one-step FEM with incremental method, it is showed that one-step FEM could calculate rapidly and had some credibility. It was suitable to evaluate the formability at the early stage of product design.

Abstract: Behavior of the transversal crack and the longitudinal crack on slab surface during V-H rolling was simulated by the FEM. The contact pressure on crack surfaces and the crack-tip stress change rules during rolling were analyzed. Results show that the contact pressure on crack surfaces decreases and the tensile stress appears at crack tip in the zone of slippage on the delivery side, which may make the cracks propagation. For the phenomenon, the stress distribution along rolling direction and along width direction in rolling are analyzed, and the influence of forward slip on the closure and growth of the surface transversal crack and the surface longitudinal crack are discussed. Results support some significant information for researching the behavior of the slab surface defects in rolling process.

Abstract: We present a method for computing the stress intensity factors in bimaterials based on the goal oriented finite element error estimate. The goal oriented analysis focuses on computing the bounds on the local quantities of interest, e.g. local stresses, local displacements, stress intensity factors etc, of a structure, and with the bounds obtained on the coarse finite element mesh we can obtain the quantities of interest with nearly the same accuracy as that obtained on the fine finite element mesh. In this paper the stress intensity factors in bimaterials are first formulated as explicit computable linear function of the displacements by means of the two-points extrapolation method. Then the goal oriented finite element method is used to compute the lower and upper bounds on the stress intensity factors, and the average of the bounds is considered as a prediction of the stress intensity factor. At last, the stress intensity factors, 0 K and r K , in bimaterials are computed with the proposed method to show its efficiency.

Abstract: Two-wedge Cross Wedge Rolling (TCWR) is a metal processing technology in which a heated cylindrical billet is plastically deformed into an axial part by the action of two wedges dies moving tangentially relative to the work piece. The metal deformation process is more complicated in TCWR than in single-wedge CWR. In this paper, a new and innovative numerical model of TCWR was developed, using advanced explicit dynamic finite element method (FEM). The whole TCWR process was simulated successfully, the three-dimensional nonlinear deformation process including stress and strain variation among the whole stages was analyzed at length, and 4 different principal stresses, including the first, second, third and von Mises equivalent stresses, at different billet centers are presented serving as a TCWR design guideline. Experimental result proves that the finite element simulation in TCWR process is true and this fundamental investigation provides a multi-wedge guideline in selecting CWR tool parameters and tool manufacturing.

Abstract: Based on the dynamic analysis method and central difference explicit algorithm, a dynamic explicit finite element code is developed for modeling the hammering deformation processes, in which hammer velocity is calculated by the energy balance principle. The dynamic upsetting processes of copper block under different hammer velocities are simulated using the developed code, and the deformed configuration, the displacement and the equivalent plastic strain distribution are investigated. Then, the calculated results are compared with that obtained by the static implicit program, and the comparison shows that the results obtained by the developed code are nearly identical to that obtained by the static implicit program under a low hammer velocity, and that there is a great difference between them under a high hammer velocity, which can be explained from the viewpoint of inertial effect and stress wave propagation effect. The research results indicate that the developed code adequately considers the dynamic characteristic under drop hammer impact, and can be used to analyze the effect of hammer velocity on the deformation during the hammering deformation process.

Abstract: Hot simulation tests at different deformation technology parameters were carried out for a microalloyed high strength steel produced by CSP hot rolling and the stress-strain curves during deformation were measured. Based on the experimental results and the discussions of present flow stress models, a new flow stress model incorporating interactional effect of deformation temperature, strain and strain rate on flow stress was developed in the paper. Excellent agreement between measured and predicted flow stress values is obtained for new flow stress model of a microalloyed high strength steel rolled by CSP. In addition, the comparisons of flow stress prediction errors between several models and one given in the paper reveal that the prediction accuracy of new flow stress model presented in the paper is higher than other models.

Abstract: A thermal-mechanical analysis of metal forming based on meshfree method is performed. During the coupled analysis, two independent sub-systems, i.e. the velocity field and temperature field are considered. The effect of deformation on temperature field is added into the temperature solution by the vector of heat flux generated by internal energy, and the effect of temperature on plastic deformation is considered by the flow stress at that temperature. The unknown function of temperature distribution is constructed using reproducing kernel approximation. Contours of the temperature field of a metal ring under compression are obtained. Using the thermal-mechanical coupling method, the results are compared with those obtained by FEM and experiment to verify the accuracy of the proposed method.

Abstract: The induction heating process of slab steel had been discussed by finite element method. The results obtained were in good agreement to the measured value. In addition, the low-frequency induction heating process of slab steel was investigated and analyzed in detail according to the practice requirements of a steel mill. During the heating process of slab steel by low-frequency induction, the temperature increasing speed of surface is faster than that of center in initial time. With the increment of heating time, the temperature increasing speed of surface becomes lower because of the heat loss of boundary. A 90 percent of the slab steel temperature had risen from 1100°C to 1400°C with 110Hz and 6.2×106A/m2 after 30min, which could be satisfied with heating requirements.

Abstract: Fast Finite Element (FFE) method had advantage of high precision and fast computing velocity. The online application of FFE method was significance both in theory and practice. In this paper the fast calculation of rigid plastic finite element method (RPFEM) in hot strip rolling was developed in this paper. The results of rolling force were good agreement to the measured results. The influence of element on calculating time and accuracy was discussed. The running time of one-dimension search was reduced greatly by combining Newton method with Brent method. Improved Newton method with trust region method and forced positive definite Hessian matrix method were used to reduce the convergence time. The better initial value could be obtained by improved mid-point integral Newton method. In addition, the influence of operating system, hardware and software on the calculating time was also discussed. The project of temperature FFE online calculation application in a plate mill was put forward.