NDTnet 1998 Aug, Vol.3 No.8

Abstract

To the analysis of a material deformed condition and estimation of sheet materials punchability the diagram of limiting deformations ( DLD) is applied. The diagram is plotted in coordinates of main critical deformations ₁ and ₂. Measurement of deformations is carried out by a method of coordinate grids, plotted on a surface of sheet half-finished product. However, measurement of deformations by this method and the punchability determination is long and not efficient process.
In the report the developed DLD and nondestructive testing technique of sheet materials punchability with use of a probe e.m.f. higher harmonics is informed about. As a result of experimental researches it is established, that the correlation between the size of main plastic deformations ₁ and ₂ and the amplitude of the third harmonic of a probe, which measures the tangential component of a secondary magnetic field, exists. With ₁ and ₂ increase the third harmonic decreases. It allows to measure ₁and ₂ by the higher harmonics method.
The testing of punchability is carried out as follows. The third harmonics amplitudes U^t₃₁ and U^t₃₂, proportional ₁ and ₂, are previously measured on samples with various factors of a stressed-deformed condition m. where

m= (2₂2+₁) / (2₁+₂)

DLD are plotted in coordinates U^t₃₁ and U^t₃₂- The U^t₃₂ and U^t₃₁ are measured in two mutual-perpendicular directions on a half-finished product. These measured meanings are plotted on the DLD and by its position respecting limiting deformation curve we can determine reserves of plasticity and punchability of sheet materials.
In the report it is informed on developed devices for U^t₃₁ and U^t₃₂ measurement, and also about the results of DLD use for the punchability control of automobile body details on a factory of AutoVAZ ( Russia ). With the help of DLD the punchability process and deformations' distribution at the dangerous points of the complex form details have been studied.
The developed technique of the nondesttructive testing of sheet materials punchability with use of the limiting deformations diagram by the higher harmonics method allows to replace a technique of punchability estimation at measurement of deformations by a method of coordinate grids. It can be used for determination of a plasticity reserves and loading character, revealing of dangerous sites with the maximum deformations, punchability estimation at the entrance control.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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