SU1656397A1 - Method of determination of endurance limit of sheet material - Google Patents

Abstract

The invention relates to a testing technique and makes it possible to determine the fatigue limits of materials. The purpose of the invention is to approximate test conditions to operational ones and to increase informativity. According to the proposed method, the blanks are bent in the form of a channel, several blanks are stretched along the channel axis to different levels of deformations of each of the blanks under the conditions of limiting the transverse movement of its shelves, cutting of the samples is carried out from the region of uniform elongation of the blanks and tested for breaking, by mechanical characteristics the magnitudes of the energy absorption of the material are determined, the remaining blanks are stretched to the level of deformation at which the energy absorption is maximum, and the samples cut from them load cyclically and determine the fatigue limit of the deformed material. 3 il. (Ls

Description

The invention relates to a testing technique, and specifically to methods for determining the endurance limits of materials.

The purpose of the invention is to approximate test conditions to operational ones and to increase informativity.

1 shows a diagram of the device for implementing the method; figure 2 is a view of And figure 1; on fig.Z - view B in figure 1.

The device contains clamps 1, made in the form of a clamp with threaded coaxial holes in its shelves and designed to accommodate a channel-like workpiece 2. stops 3. designed to be placed between the shelves of a channel-like workpiece 2

clamps, and screws 4, placed in the corresponding openings of the shelves of clamps 1 and intended to clamp the shelves of the channel-like workpiece 2 to the ends of the respective stops 3.

The method is carried out as follows.

The billet 1 of sheet material is bent in the form of a channel. Several channel-shaped blanks 1 are stretched along the axis by forces P to varying levels of deformations of each of them under conditions of limiting the lateral movement of its shelves by stops 3, which are fixed between the shelves of the blanks 1 by screws 4. Release the channel-like blanks 1 from the devices and cut the samples from

he ate oh soi xi

areas of uniform elongation. The obtained samples are ruptured and the mechanical characteristics of the samples with different values of material deformation are determined, i.e. define temporary

g n p

resistance 7B, -,, limit current - L mm J

and uniform relativity Cfj

. L

LMM J

elongation Јv%. Determine the energy margin of the material

2 From

8B.

The remaining channel-like blanks 1 are stretched to the level of deformation, at which the energy absorption of the material is maximum. The cutting of samples from them is carried out from the area of uniform elongation. The samples are loaded cyclically until signs of their destruction appear, and the endurance limit of the pre-deformed material with the maximum energy absorption in the stress-deformed state that arises in the product when it is stamped from sheet material.

Example. Sheet workpieces made of cold-rolled two-phase ferritic-martensitic steel of the OZHGYU size of 1.5 x 70 x 300 mm were cold-pressed on the press to give the shape of a channel, the ratio of whose working length to the width of its wall was more than 4 mm. working zone of channel-like blanks. At the gripping points, the height of the shelves of the workpieces was increased by 3-5 mm in comparison with their size in the working part, in order to avoid the destruction of the blanks at the places of their gripping in the testing machine.

A part of the obtained channel-like blanks 1 with a flange width of 50 mm and a working length of 190 mm was stretched on a TT-DM-L Instron testing machine to a uniform elongation of 2, 5, 7, and 10 material. Then these blanks were subjected to aging at 180 ° C with an exposure of 1 h, which corresponds, for example, to the mode of painting and drying the car body,

After aging, samples of size 1.5 x 12.5 x 200 mm were cut from the blanks, which, in accordance with GOST 11701-84, were subjected to tensile testing with the determination of mechanical characteristics. The formula determined the energy absorption margin / 30 of the material and found that its maximum value is 5.60 with a deformation of 7%.

The remaining channel-shaped blanks 1 in the amount of 10 pieces were deformed to 7% and subjected to artificial aging in the above mode. Cut out of these blanks and fabricate samples of 20 mm width working part with a radius

100 mm. Samples were tested for fatigue in accordance with GOST 25,502-79 with asymmetric tensile stress cycles with a cycle asymmetry factor of 0.2. The endurance limit was determined by building a fatigue curve. It was 404 N / mm2 and exceeded by 15% the endurance limit of the original sheet material, which is equal to 355 N / mm2.

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Claims (1)

Invention Formula The method for determining the endurance of the sheet material, which consists in that the blank material subjected to deformation by stretching, cutting a sample out of it, cyclically loading it until the signs of destruction appear, and determine the endurance limit of the material, characterized in that. in order to approximate the test conditions to operational and increase the information content, the main and additional blanks are bent in the form of a channel; several blanks are stretched along the axis channel to different levels of deformation of each of the blanks under the conditions of limiting the transverse movement of its shelves, cutting samples carried out from the area of uniform elongation of the blanks and test them to break, according to the mechanical characteristics determine the energy absorption of the material, the remaining blanks where the energy absorption of the material is maximum, and the fatigue limit is determined on samples cut from the last blanks. II h r JJ.L JLljJ. ak / / 2 Type B 3 L