Non-contact crack opening displacement measuring device and method for bending fracture test

Abstract

The invention belongs to the field of material performance test, and especially relates to a non-contact crack opening displacement measuring device and method for a bending fracture test. The non-contact crack opening displacement measuring device comprises a mechanical experimental machine; a bending test tooling including an upper pressing head and two lower pressing heads, and a sample is clamped between the upper pressing head and the lower pressing heads; a digital image acquisition system including an industrial camera, an imaging lens, an annular LED illuminating light source arrangedat the front end of the imaging lens, a camera support system and a reflecting mirror, wherein the reflecting mirror is arranged at the lower part of the sample at an inclined angle of 45 degrees; thereflecting mirror reflects light generated by the light source to a fracture surface of the sample, and meanwhile, a surface image of the fractured sample is reflected into the imaging lens; and a control system for displaying an image of the industrial camera in real time, and calculating the real-time crack opening displacement. According to the non-contact crack opening displacement measuringdevice for the bending fracture test provided by the invention, an optical imaging system is used for collecting images around a crack opening of the sample, and a digital image correlation algorithmis used for calculating the real-time crack opening displacement, so that non-contact measurement can be realized, and the measurement device does not have any influence on the sample.

Description

technical field [0001] The invention belongs to the field of material performance testing, in particular to a non-contact crack opening displacement measuring device and method for bending fracture testing. Background technique [0002] Single-sided notched specimen bending fracture testing, such as three-point bending or four-point bending, is a common method for evaluating the fracture toughness of materials. For brittle materials, when the sample meets the conditions of linear elastic fracture mechanics, the three-point bending test generally refers to the national standard GB / T 4161-2007 or the American ASTM E399-17 standard to directly obtain the critical stress intensity factor KIC for material fracture. For tough materials, the national standard GB / T 21143-2014 or the American ASTM E1820-15 standard is generally referred to, and the critical J integral or critical crack tip opening displacement based on elastic-plastic fracture mechanics is adopted. [0003] Regardle...

AI Technical Summary

Problems solved by technology

However, there are many deficiencies in the clip-type extensometer: (1) the gauge length is fixed, the measuring range is limited, and it is difficult to measure a wide range of opening displacement; (2) it is in direct contact with the sample and exerts a large It is used for particularly brittle or soft materials; (3) before and after the sample test, the extensometer needs to be installed and removed, which is complicated to operate; (4) when the material breaks suddenly, the extensometer is easy to drop and mechanically damaged; (5) limited Applicable temperature range, not compatible with high temperature test

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