JPH0736007U - Knife edge for measuring opening displacement of shallow cracks - Google Patents

Abstract

(57) [Summary] [Purpose] The objective is to easily and accurately determine the opening displacement of a shallow crack or notch, which is difficult to measure with conventional crack opening displacement measurement technology that uses a knife edge and a clip gauge. [Structure] A knife edge that is fixed to the upper part of the crack opening of a sample to measure the crack opening displacement, has an elongated portion with a width smaller than the crack depth at both ends of the knife edge, and a central portion has a clip. A knife edge for shallow crack opening displacement measurement, characterized by having a gap and an inclination for attaching a gauge. [Effect] By making the knife edge of the present invention with a material having high rigidity and strength, the opening displacement of a crack having the same depth as the lower limit of measurement of the clip gauge can be measured.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a knife edge shape to be measured using a crack opening displacement clip gauge on a surface of a material having a notch or a defect having a depth of about several millimeters.

[0002]

[Prior art]

 Figure 3 shows the conventional measurement method for opening displacement of cracks and notches using knife edges and clip gauges. Hereinafter, a method of measuring the opening displacement of the crack 4 or the defect of the material 2 using the conventional knife edge 1 and the clip gauge 3 will be described step by step.

The knife edges 1 are usually used in pairs, and are symmetrically placed on both sides of the crack 4 or the defect, and fixed to the material 2 having the crack or the defect by pasting or screwing. Attach the clip gauge 3 between the two knife edges 1. The clip gauge is connected to a dynamic strain amplifier via a bridge box that forms a Wheatstone bridge circuit, and the voltage output is connected to an XY recorder or the like. Tension or bending is applied to a material with a crack or defect attached with a knife edge and a clip gauge, and the opening displacement of the crack or defect of the material is recorded on an XY recorder or the like.

FIG. 4 shows the high strain region distribution region of the material during measurement of crack or notch opening displacement when the crack or defect is deep. On the other hand, Fig. 5 shows the high strain region distribution of the material when the cracks and defects are shallow. In FIGS. 4 and 5, 1 is a knife edge, 2 is a material having a crack or notch, and a hatched portion is a high strain region.

When the crack or defect is deep as shown in FIG. 4, the high strain region of the material is distributed outside by about 45 degrees from the crack tip as shown in FIG. 4, so that the strain at the knife edge mounting portion is very large. It is small, and the opening displacement at the tip of the knife edge is a measure of the opening displacement on the surface of the measurement target. However, when the crack or defect is shallow, the amount of displacement at the knife edge tip does not correspond to the opening displacement of the material surface crack or notch. This phenomenon is caused by the fact that the strain in the high edge region of the material is distributed as shown in FIG. Therefore, when measuring the opening displacement with the knife edge, the knife edge must be installed within 45 degrees from the crack tip in order to eliminate the effect of the high strain range.

With a conventional knife edge, when the depth of cracks or defects is about 4 mm or less, a knife edge having a width X of the knife edge shown in FIG. 3 of less than about 3 mm is required, which makes attachment of the knife edge difficult. It was Also, in the case of artificial defects, the edge shape as shown in Fig. 6 may be processed in advance near the surface, but it is difficult to process when there are cracks or shallow defects or surface cracks of wide plates. Met.

[0007]

[Problems to be solved by the device]

 An object of the present invention is to provide a knife edge for easily and accurately determining the opening displacement of a shallow crack or notch, which is difficult to measure with the conventional crack edge displacement measurement technology using the above knife edge and clip gauge. is there.

[0008]

[Means for Solving the Problems]

 The present invention solders the knife edge to a material having a crack or a notch so that the width X of the knife edge, which is related to the size of a high strain region related to the depth of a crack or a defect, is small, and is screwed to the material. The position of the margin for fixing by spot welding is devised. More specifically, in order to measure the crack opening displacement, the knife edge is fixed at the top of the crack opening of the sample. The portion is a knife edge for measuring shallow crack opening displacement, which is characterized by having a gap and an inclination for attaching a clip gauge.

[0009]

[Action and Example]

 The present invention will be described with reference to the embodiments shown below. FIG. 1 shows the shape of a knife edge according to the present invention. The rectangular parallelepiped portions A at both ends of the knife edge are the margins for sticking to the object to be measured with solder, and the width X thereof is smaller than the crack depth. The elongated portion sandwiched between the attachment margins A, that is, the central portion B is a portion to which a clip gauge for measuring the crack opening displacement is attached, and has a gap and an inclination necessary for attachment. FIG. 7 shows a method for measuring the opening displacement of a material crack or defect using the knife edge and clip gauge of the present invention.

Hereinafter, a method of measuring the opening displacement of a material crack or defect using the knife edge and clip gauge of the present invention will be described step by step. Knife edges are usually used in pairs, placed symmetrically on both sides of the crack or defect, and the attachment portion of FIG. 1A is attached to the material having the crack or defect. Install a clip gauge between the two knife edges. Connect the clip gauge to a dynamic strain amplifier via a bridge box that forms a Wheatstone bridge circuit, and connect the voltage output to an XY recorder. Tension or bending is applied to a material with a crack or defect attached with a knife edge and a clip gauge, and the opening displacement of the crack or defect of the material is recorded on an XY recorder or the like.

Using the measuring method according to the above procedure, a notch having a plate width of 3 mm and a depth of 3 mm is machined in the plate width direction on the surface of a flat plate (plate thickness 22 to 80 mm, plate width 250 to 300 mm), and a tensile test is performed. The opening displacement was measured when the measurement was performed. It is clear from the stress-strain distribution near the crack calculated by the finite element method that the measurement accuracy is more accurate than the conventional measurement method using a knife edge. By improving the rigidity and strength of the knife edge, the opening displacement of a crack can be measured at the same depth as the lower limit of the clip gauge measurement.

Further, as shown in FIG. 8, a protrusion 5 is attached to a portion to be attached to a material having a crack or a defect, and only that portion is attached with solder or the like to measure the opening displacement of a shallow crack or notch. Is also possible.

[0013]

[Effect of device]

 By making the knife edge of the present invention with a material having high rigidity and strength, the opening displacement of a crack having the same depth as the lower limit of measurement of the clip gauge can be measured.

[Brief description of drawings]

FIG. 1 is a knife edge of the present invention.

[Figure 2] Clip gauge

FIG. 3 is a measurement procedure of opening displacement of a crack or a notch using a conventional knife edge and a clip gauge.

FIG. 4 is a high strain region and a knife edge of a material when a crack or a defect is deep.

FIG. 5 is a high strain region and a knife edge of a material when a crack or a defect is shallow.

FIG. 6 is a view in which a knife edge and a notch portion are integrated.

FIG. 7 is a procedure for measuring the opening displacement of a crack or notch using the knife edge and the clip gauge of the present invention.

FIG. 8 is a knife edge in consideration of measurement of opening displacement of a shallower notch.

[Explanation of symbols]

 1 Knife edge 2 Material with crack 3 Clip gauge 4 Crack

Claims (1)

[Scope of utility model registration request] 1. A knife edge fixed to an upper portion of a crack opening of a sample for measuring a crack opening displacement, having an elongated portion having a width smaller than a crack depth at both ends of the knife edge, and a central portion. Is a knife edge for shallow crack opening displacement measurement, which has a gap and an inclination for attaching a clip gauge.