Device and method for testing forming limit of sheet material in three-dimensional stress state

Abstract

The invention provides a device and a method for testing a forming limit of a sheet material in a three-dimensional stress state, relating to the device and the method which are used for testing the forming limit of the sheet material. Aiming to the problems that the forming limit of the sheet material in the three-dimensional stress state is difficult to test and an influence of normal pressure to the forming limit is difficult to estimate, the device comprises an upper die and a lower die. In a test, a fluid medium is injected into the lower die, a test sample of the sheet material is placed, mold clamping force is applied, the fluid medium is injected into the upper die, and pressurized deformation is carried out by controlling pressure in the upper die and the lower die in sequence. Braking strains of the test sample of the metal sheet material can be calculated according to measured data before and after circular or square mesh deformation, namely epsilon 1=Ln[d1-d/d] and epsilon 2=Ln[d-d2/d]; a plurality of groups of different limit strain data points can be obtained by changing a ratio of a long shaft to a short shaft of an oval cross section of a cavity; and the obtained data points can be connected or fitted by respectively using the epsilon 1 and the epsilon 2 as a transverse coordinate and a vertical coordinate, so as to obtain the sheet material forming limit curve at the three-dimensional stress state at a certain normal pressure condition to estimate the influence of the normal strain to the forming limit in the three-dimensional stress state.

Description

technical field [0001] The invention relates to a device and method for testing the forming limit of a plate under a three-dimensional stress state. Background technique [0002] The forming limit is an important performance index and process parameter in the field of sheet metal forming, reflecting the maximum deformation degree of the sheet before plastic instability. In order to determine the forming limit of sheet tensile instability, many research and evaluation methods have been proposed from the aspects of theory and experiment. Among them, the Nakazima test method is a commonly used method at present, and its essence is a hemispherical rigid punch bulge test. Print a circular grid on the surface of the sample by screen printing, change the width of the sample and the lubrication between the test piece and the punch to carry out the hemispherical rigid punch bulge experiment, after the sample breaks, the grid changes from a circle to a Ellipse, measure the size of t...

AI Technical Summary

Problems solved by technology

[0004] In view of the fact that the current Nakazima test method for measuring the forming limit cannot meet the actual situation of blank deformation under the three-dimensional stress state, the present invention provides a test device and method for the forming limit of the sheet metal under the three-dimensional stress state. The forming limit under the state, to meet the practical application

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