JPH0593681A - Measuring device of crack opening displacement - Google Patents

Abstract

PURPOSE:To detect precisely an initial stage of a crack opening. CONSTITUTION:In a measuring device of a crack opening displacement by a clip gage method, surface acoustic wave rosonators 11a and 11b are provided on leaf springs 4A and 4B of a clip gage and the amount of deflection of the leaf springs caused by the crack opening displacement is detected as the amount of change of a resonance frequency of the resonators. Leaf springs 4A, 4B, 15A and 15B are made of metal or constructed of a piezoelectric material, and the surface acoustic wave resonators 11A and 11B are stuck on the springs made of metal, while resonator electrodes 16A and 16B are formed directly on those constructed of the piezoelectric material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crack opening displacement measuring device using a clip gauge method.

[0002]

2. Description of the Related Art In a fracture mechanics test of materials such as metals, ceramics, and plastics, when the small-scale yield condition is sufficiently small that the plastic region at the crack end is sufficiently small, the linearity centered on the concept of stress intensity factor is used. Although the fracture mechanics is effective, the nonlinear (elasto-plastic) fracture mechanics that measures the crack opening displacement (COD) is effective when the small-scale yield is not satisfied and the plastic region covers a wide range. The formation of a plastic zone at the crack tip and the measurement of plane strain fracture toughness K _IC are carried out by the measurement.

FIG. 4 shows a crack opening displacement measuring device. A clip gauge 2 is attached to the notch sample 1 to which the pre-crack 1A has been added, with the pre-crack 1A interposed therebetween, and the load output ends 3A, 3B,
3C applies three-point bending stress from the lower side of the precrack 1A and both sides of the sample 1 in the direction of the arrow shown in the figure, and the opening displacement of the precrack 1A portion due to this bending stress is measured as the tip displacement of the clip gauge 2. ..

The clip gauge 2 is constructed as shown in FIG. One end of each of the two metal plate springs 4A and 4B is fixed by tightening a bolt 7 and a nut 8 via upper and lower round washers 5A and 5B and a spacer 6. Also, the leaf springs 4A, 4
Strain gauges 9A and 9B are attached to one surface of each of B by a polymer adhesive such as an epoxy resin, and a notch is provided at the tip, and the knife edge 10A attached to the sample 1 by this notch, 10B is locked.

Such a clip gauge 2 has a leaf spring 4
Due to the elasticity of A and 4B, the knife edge 10A of the sample 1
Sample 1 by the load output parts 3A to 3C locked to 10B
The amount of crack opening when a 3-point bending load is applied to the leaf spring 4
The deflection amounts of A and 4B are caused to act, and the deflection amounts are detected as the compression strain increase amounts of the strain gauges 9A and 9B. For the clip opening displacement Vg at this time, the crack tip opening displacement (CTOD) φ can be estimated from the following equation.

[0006]

[Equation 1]

However, the variables in the above equation have the relation shown in FIG. 6, where a is the crack length, r is the rotation coefficient, w is the sample plate thickness, and z is the sample plate thickness.
Is the knife edge plate thickness. Also, regarding the relationship between COD and CTOD, the opening at any position of the crack is called COD,
The opening at the crack tip position is called CTOD.

[0008]

In the conventional crack gauge displacement measuring device using the clip gauge method, the degree of plastic blunting of the crack tip is estimated from COD. In the configuration in which the deflection reduction is detected by the strain gauge, there is a problem in that the initial stage of crack opening cannot be accurately detected even in the case of a sample having a large plastic deformability such as metal due to the detection sensitivity.

For the same reason, it is difficult to measure the fracture toughness K _IC for a material such as ceramics or glass that is extremely small in deformation until it breaks because the conventional clip gauge method has poor measurement accuracy. ..

Further, in the method using the strain gauge, the variation of the measured value due to the temperature change during the measurement of the crack opening amount becomes large, and the surface of the metal leaf spring is coated with a polymer adhesive such as epoxy resin. The structure with a strain gauge attached has a problem that measurement cannot be performed at high temperatures.

An object of the present invention is to provide a crack opening displacement measuring device capable of accurately detecting the initial stage of crack opening, detecting less temperature fluctuation, and measuring in a high temperature state.

[0012]

According to the present invention, in order to solve the above-mentioned problems, a pair of leaf springs of a clip gauge are attached with a notch portion of a sample sandwiched between them so that crack opening displacement of the notch portion of the sample can be prevented. In the crack opening displacement measuring device by the clip gauge method obtained from the detected value of the deflection amount of the pair of leaf springs,
The pair of leaf springs are made of metal or a piezoelectric material, and electrodes are formed on the front surface or the back surface of the pair of leaf springs, respectively, or the piezoelectric material serves as a substrate, and the deflection amount of the leaf springs is used as the change amount of the resonance frequency. It is characterized by comprising a pair of surface acoustic wave resonators for detection.

[0013]

According to the above construction, the element for detecting the deflection amount of the leaf spring of the clip gauge is a surface acoustic wave resonator provided on the leaf spring, and the deflection amount of the leaf spring due to the displacement of the crack opening is used as the resonance frequency of the resonator. Is detected as the change amount of. As a result, the change within the bending angle of the leaf spring within 1 degree at the initial stage of the crack opening displacement has linearity and is detected as the change amount of the resonance frequency.

Further, by using a surface acoustic wave resonator in which the inflection point of the frequency-temperature characteristic meets the measured temperature condition such as room temperature, it is possible to suppress the fluctuation of the measured value due to the temperature fluctuation.

Further, the leaf spring is made of a piezoelectric material such as quartz, and the piezoelectric material is used as a substrate to form an electrode of the surface acoustic wave resonator on this surface, whereby the leaf spring and the surface acoustic wave resonator are separated from each other. In addition, the presence of the polymer adhesive is eliminated, and the measurement failure due to the thermoplasticity of the polymer adhesive at high temperature is eliminated.

[0016]

1 is a block diagram of a clip gauge showing an embodiment of the present invention. 5 is different from FIG. 5 in that the strain gauge is replaced by a pair of 1-port surface acoustic wave resonators 11.
The point is that A and 11B are provided. This resonator 11A, 11
In B, the interdigital transducer 13 and the reflectors 14A and 14B are separately formed as pattern electrode films on the surface of the piezoelectric substrate 12. The transducer 13
Mutual energy conversion between electricity and surface acoustic waves is performed, and the surface acoustic waves propagate to both sides on the piezoelectric substrate 12 and are reflected by the reflector 1.
4A and 14B, reflected by the reflectors 14A and 14B, and returned to the transducer 13 to be extracted as a resonated electric output.

The frequency of the surface acoustic wave is determined by the pair of interdigital electrodes 13A and 13A forming the transducer 13.
It is determined by the pitch where B intersects, and the pitch of the reflectors 14A and 14B is also formed according to the frequency.

As described above, the pair of surface acoustic wave resonators 1
The clip gauges 1A and 11B are attached to the surfaces of the leaf springs 4A and 4B with adhesives, respectively, and the clip gauges are attached to the sample 1 as shown in FIG. The amount of change (shift amount) of the resonance frequency of 11B is detected.

That is, the contraction deformation of the leaf springs 4A and 4B due to the progress of the crack opening displacement of the sample 1 causes the contraction deformation of the piezoelectric substrate 12, and this deformation causes the electrode 13 of the transducer 13 to be deformed.
It is detected as the amount of change in the resonance frequency due to the contraction of the distance between A and 13B (reduction of pitch). In this detection, the crack opening displacement (Vg in FIG. 6) is determined by the two leaf springs 4 facing each other.
Since it is the sum of the flexural displacement reduction amounts of A and 4B, it is obtained as the sum of the converted values of Vg corresponding to the resonance frequency change amounts of the surface acoustic wave resonators 11A and 11B.

In the present embodiment, when the lengths of the leaf springs 4A and 4B are set to 30 mm, if the variation width of the deflection angle of the leaf springs is within 1 degree, which is the initial stage of the crack opening displacement, the deflection angle and the resonance occur. The relationship with the amount of change in the resonance frequency of the daughters 11A and 11B is substantially linear, and a resonator with a resonance frequency of 200 MHz can secure measurement accuracy of about 0.02 degrees.

Further, the piezoelectric substrate 1 of the resonators 11A and 11B
As for 2, by using a quartz crystal piezoelectric substrate (for example, an ST cut plate) having an inflection point of the frequency-temperature characteristic near room temperature, there is a temperature change in the measurement at room temperature, but the amount of change in the measured value due to this It can be reduced compared to the conventional strain gauge measurement. At this time, the crystal substrate has a thickness of 0.1 mm or more.

FIG. 2 is a block diagram of a clip gauge showing another embodiment of the present invention. In this embodiment, crystal leaf springs 15A and 15B are used instead of the leaf springs 4A and 4B.
Surface acoustic wave resonator electrodes 16A and 16B are directly formed with the outer surfaces of 5A and 15B as substrate surfaces.

The crystal leaf springs 15A, 15B are formed of, for example, quartz ST cut plates, and the leaf spring portions 15A, 15B are formed.
Its one end is fastened and fixed by bolts 7 and nuts 8 via washers 5A, 5B, 5C, 5D and spacers 6, and a notch is formed at the tip on the opposite side.

The surface acoustic wave resonator electrodes 16A and 16B are
A 1-port type electrode structure similar to that of FIG. 1 is formed on the surfaces of the leaf spring portions 15A and 15B by vacuum deposition.

The clip gauge according to this embodiment is attached to the sample 1 as in the case of FIG. 1, and the crack opening displacement of the sample 1 is detected as the change amount (shift amount) of the resonance frequency of the resonators 16A and 16B. ..

Here, it should be noted that since the crystal leaf springs 15A and 15B are used as the substrate of the surface acoustic wave resonator and the electrodes 16A and 16B of the surface acoustic wave resonator are directly formed on the surface thereof, metal is used. The adhesive for sticking the leaf spring and the surface acoustic wave resonator does not intervene, and the leaf spring portions 15A and 15B and the electrodes 16A and 16B can be used for measurement in a high temperature state (for example, 150 degrees Celsius to 200 degrees Celsius or more). There is no plasticity between the cracks, and the crack opening displacement can be reliably acted as a change in the resonance frequency of the electrodes 16A and 16B.

The Curie point of quartz is about 500 degrees Celsius, and measurement is possible at temperatures below this temperature. At this time, by using a crystal having an inflection point matched to the measured temperature, it is possible to suppress a change in the measured value due to a temperature change.

In this embodiment, the leaf springs 15A and 15B are used.
Examples of the material include piezoelectric materials other than quartz, such as lithium niobate (LiNbO ₃ ) and lithium tantalate (Li).
TaO ₃ ) can also be used. Also, the leaf springs 15A and 15B
2 has a structure in which the base portion and the leaf spring portions 15A and 15B are integrally formed of a piezoelectric material such as quartz, instead of tightening and fixing via the spacer 6 as shown in FIG. Is also good.

In the above-described embodiments, the surface acoustic wave resonators 11A and 11B or the resonator electrodes 16A and 16A.
B can be a pair of two-port surface acoustic wave resonators or resonator electrodes shown in FIG. 3 to obtain the same effect. Further, the resonators 11A and 11B are attached to the leaf springs 4A and 4B, or the resonator electrodes 16 are attached to the leaf spring portions 15A and 15B.
In forming A and 16B, the back surface (inner side surface) of the leaf springs 4A and 4B or the leaf spring portions 15A and 15B may be used. In this case, the progress of the crack opening displacement is measured as the elongation deformation of the resonator.

[0030]

As described above, according to the present invention, a surface acoustic wave resonator in which a deflection amount of a leaf spring of a clip gauge is attached to the leaf spring or a leaf electrode portion of a piezoelectric material is used as a substrate to form a resonator electrode. Since it is configured to detect as the amount of change in the resonance frequency, it can be detected with linearity even in the initial stage of crack opening displacement, and it can be detected in the initial stage of crack opening regardless of the magnitude of plastic deformability. There is an effect that the displacement can be accurately detected and measured. In addition, the surface acoustic wave resonator can use a quartz crystal piezoelectric substrate as its piezoelectric substrate.Measurement due to temperature fluctuations can be made by using a piezoelectric substrate that has an inflection point of frequency-temperature characteristics near room temperature. The fluctuation of the value can be reduced.

Further, the leaf spring is made of a piezoelectric material, and the surface acoustic wave resonator electrode is formed by using this as a substrate, so that the leaf spring does not have to be attached with a polymer adhesive, and the leaf spring is kept in a high temperature state. Can be measured.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a clip gauge showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a clip gauge showing another embodiment of the present invention.

FIG. 3 is a configuration diagram of a resonator according to another embodiment of the present invention.

FIG. 4 is a configuration diagram of a crack opening displacement measuring device.

FIG. 5 is a conventional clip gauge configuration diagram.

FIG. 6 is a diagram showing how the crack tip opening is displaced.

[Explanation of symbols]

2 ... Clip gauge, 4A, 4B ... Leaf spring, 11A, 1
1B ... Surface acoustic wave resonator, 12 ... Piezoelectric substrate, 13 ... Transducer, 14A, 14B ... Reflector, 15A, 15
B ... Quartz leaf springs, 16A, 16B ... Surface acoustic wave resonator electrodes.

Claims (1)

[Claims] 1. A clip gauge method in which a pair of leaf springs of a clip gauge are attached to sandwich a notch portion of a sample, and a crack opening displacement of the notch portion of the sample is obtained from a detected value of a deflection amount of the pair of leaf springs. In the crack opening displacement measuring device by
The pair of leaf springs are made of metal or a piezoelectric material, and electrodes are formed on the front surface or the back surface of the pair of leaf springs, respectively, or by using the piezoelectric material as a substrate, and the deflection amount of the leaf springs is taken as the change amount of the resonance frequency. A crack opening displacement measuring device comprising a pair of surface acoustic wave resonators for detecting.