J.P. Wang

Color-image processing for the evaluation of stream-lines in plane extrusion by fuzzy set theory

Abstract A color-imaging process with fuzzy set theory is proposed to find the distortion lines of a grid in the experimental mechanics of metal forming. In this procedure, four fuzzy sets are constructed to filter the image of specimen: the calibration of colors; the thinning of stream lines; the connection of breaking lines; and the deleting of blurs. After these four procedures, the stream lines can be obtained easily. Plane-strain extrusion through a cosine-curved die with 2:1 extrusion ratio is used to illustrate the procedure. The computed results are used to combine with the model of the finite flow-line regions method. Calculated results of the velocity and effective-strain fields are also presented, showing that this procedure gives reliable results.

An investigation into friction in dynamic plane upsetting

The evaluation of friction on the friction interface in plane-strain upsetting is developed. The distribution of friction shear stress is derived and found to be dependent on the ratio (called the F-coefficient) of the second derivative and the first derivative of the velocity in the x-direction. According to the value of the F-coefficient, friction conditions such as sticking, frictionless, and many kinds of function approximated to linear, exponential, and arc-tangent can be expressed easily. An optimal approach with velocity parameters is used to calculate the F-coefficient at various reductions in height in an experimental approach. It is shown that this method presents a good approach to evaluate friction in comparison with experimental data.

The dynamic analysis of visioplasticity for the plane upsetting process by the flow-function elemental techique

Abstract The flow-function elemental technique combined with visioplasticity is developed to analyze dynamic metal forming processes. In this technique, the minimization of the summation of the velocity differences between experimental and numerical points is evaluated with imposed constrained conditions, the plane upsetting process being used to illustrate the technique. Calculated velocity and stress fields are presented. The results show that the shear stress along the friction boundary increases rapidly, to reach sticking level almost at the end edge, and that the calculated normal pressure along the die surface has the same trend when compared with the values predicted using the slab method.

The finite flow-line regions approach to visioplasticity in plane-strain extrusion

Abstract A numerical approach is proposed to establish a new procedure for the visioplasticity method. In this procedure, finite flow-line regions are produced first, by the least-squares method, and then the velocity and strain-rate fields are obtained for each region. From the calculated strain-rate fields, the stress fields can be found from the integral equation in visioplasticity. A plane-strain extrusion through a cosine-curved die with a 2:1 extrusion ratio is used to illustrate the procedure. The computed solutions are compared with those of the flow-function elemental technique (FFET). The results of this latter method show good coincidence with the observed experimental phenomena.

The load analysis of the plane—strain forging processes using the upper-bound stream-function elemental technique

Abstract The upper-bound stream-function elemental technique (UBST) for the load analysis of the plane—strain forging processes is developed. This technique improves the ineffectiveness of UBET for solving forging problems that are geometrically complex or need a forming simulation for predicting the profile of the free boundary. This method combines the advantages of the stream function and the finite-element method (FEM); specifically, the curve-fitting property of the FEM and the fluid incompressibility of the stream-function. The formulated optimal design problems are solved by the flexible tolerance method. Two forming problems, strip upsetting and cosine-die extrusion, are used to illustrate the method, the reasonable results obtained showing that this technique can provide a powerful tool for industrial applications.

Neural network approach to recognize the grid patterns in experimental mechanics

Abstract In this paper, we develop a neural network system that applies to the work of experimental mechanics. Two procedures are presented: one is the color calibration that used to filter 256 colors into three colors by adaptive-competitive learning network (ACLN). The other is the pattern recognition that is used to recognize the grid patterns and search the intersection points of grids by back propagation neural network (BPNN). In this paper, plane extrusion through a cosine-curved die is adopted to illustrate as example. The results show that the correlative points between the calculation and experiment are shown quite well agreement.

The slip-line function model approach to plane dynamic analysis of visioplasticity

The flow-function elemental technique combined with visioplasticity is developed to analyze the plane upsetting process. In this technique, the minimization of the summation of the velocity differences between experimental and numerical points in flow-function elements is evaluated with imposed constrained conditions. A model called the slip-line function method is proposed to construct the slip-line field. Along the slip lines, the stress fields can be calculated easily from Henckys equations. The plane upsetting process has being used to illustrate this technique. The calculated velocity and stress fields are presented. The results show that the shear stress along the friction boundary increases rapidly, to reach sticking level almost at the end edge. The calculated normal pressure along the die surface has a more reasonable trend compared with the slab method.

Color-pattern image processing for the evaluation of stream-lines in plane-strain extrusion

Abstract A color-imaging process is proposed to find the stream-lines for the visioplasticity method; in this procedure models of various color-patterns are set up. The images from specimen scanning of the experimental data are compared and recognized with those models, the stream-lines then being obtained easily. Plane-strain extrusion through a cosine-curved die with a 2:1 extrusion ratio is used for the illustration of the procedure. The computed stream-lines are used to combine with the model of the finite flow-line-region method. The calculated results for the velocity and effective-strain fields are also presented, showing that this procedure gives reliable results for visioplasticity.

The UBST approach to the stress analysis of plane-strain upsetting with a newly constructed model of the slip-line field

Abstract This research presents a new model for constructing a slip-line field by combining the concepts of stream-lines. For the purpose of finding the strain-rate field of plane-strain upsetting, the upper-bound stream function elemental technique (UBST) method is used to find the optimal flow patterns with the technique of constraint. From the calculated strain-rate field and the above-mentioned model, the slip lines are drawn, along which slip lines the stress field can be found easily from Henckys equations. The results indicate that the slip-line field constructed by this method shows a good agreement with the shear boundary conditions, and that the trend of the normal pressure along the friction boundary is reasonable.

Fuzzy c-means approach to color-image processing for evaluating the grid lines in plane extrusion

Abstract The fuzzy c-means method is used to determine the distortion lines of grids in the experimental mechanics of metal forming. In this procedure, the fussy c-means (FCM) algorithm is first used to calibrate the colors of specimen, and then three fuzzy sets are constructed to filter the image of specimen, such as in the thinning of stream lines, the connection of broken lines and deletion of blurs. Plane-strain extrusion through a cosine-curved die with a 2:1 extrusion ratio is used to illustrate this procedure. The computed results are combined with the model of the finite flow-line region method. The calculated results of the velocity and effective-strain fields are also presented, which show that this procedure gives reliable results.