JPH0431530Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Industrial Application Field) This relates to strain gauges for crack monitoring that monitor the progress of cracks in complex structures and provide materials for taking countermeasures in advance. (Prior art) As a method for experimentally finding the stress of a crack that occurs in a complex structure with unknown boundary conditions, the fourth
As shown in the figure, a method has already been published in which the stress is determined experimentally by attaching a large number of 3-axis rosette gauges with high accuracy on the circumference centered on the tip of the crack, and this value is used as a boundary condition to determine the stress within the boundary. (See Reference 1). Figure 4a shows the external shape of the inclined internal crack piece,
FIG. 4b shows the arrangement of three-axis rosette gauges arranged on the circumference around one end of the crack (see Document 2). (Problem to be solved by the invention) As is clear from the above method as shown in Figure 4,
Since a large number of 3-axis rosette gauges must be accurately pasted on the circumference around the tip of the crack, it takes a lot of time and effort, and is inefficient. (Means for solving the problem) Therefore, on a thin film base having a slit in the center, a plurality of sheets are distributed at equal intervals (irregular intervals are also acceptable) on the circumference centered at one end of the slit. Attach the 3-axis rosette gauge. In addition, on the same thin film substrate, in contact with the center and on the opposite side of the slit, there is a
By pasting two crack gauges together, the method of installing strain gauges was improved. (Example) FIG. 1 illustrates the structure of a strain gauge for crack monitoring according to the present invention. The thin film base 1 is a circular thin film centered on the strain gauge center point 4, and has a slit 5.
is cut radially outward from the center. 3-axis rosette gauge 2a to 2m on the circumference of a suitable radius R
is located. Although FIG. 1 shows an example in which the gauge is divided into 12 equal parts, the number of 3-axis rosette gauges may be arbitrary. 3 is a crack gauge, which is placed in contact with the center point 4 and on the opposite side of the slit 5. It is even more effective to use a photoresist method to set the individual three-axis rosette gauges at once. This strain gauge can be set in a structure as follows. That is, as shown in Figure 3, while aligning the tip of the crack that has occurred in the object to be tested with the center point 4 of the strain gauge, align the other end of the crack in the object and the opening side of the slit of the strain gauge. The strain gauge and the object are adhered with instant adhesive or the like in the direction of the strain gauge. Figure 2 shows where the strain gauges (rosette gauge and crack gauge) of the present invention are attached to an object. (Function) The stress near the slit portion can be determined from the stress determined by arranging a 3-axis rosette gauge on the circumference of a circle centered on one end of the slit as follows. In Fig. 5a, it is assumed that forces Pi and Ui are applied to the object and a crack occurs as shown in the figure. One end of the crack is surrounded by a circle or square like S, and a 3-axis rosette gauge is placed around the circumference. The arrangement of the three-axis rosette gauge on the circumference S will be explained with reference to FIG. 5b. r is the boundary of a circle with radius R, and n three-axis rosette gauges are arranged on the circumference. p+ among them
The angle that the first measurement point makes with the origin O, and the angles that the pth to p+2th measurement points make with the origin O are γ, γ ₀ , and _x and _y act on the boundary. If _the x _{and y} components _{of the} surface _{force are} is the direction cosine of the normal drawn outward on the boundary Γ of . The surface force T at any point between n measurement points on Γ is approximated by a quadratic formula: { _i }={}={ _x / _y }=[M] {Q}...(
2) becomes. Here, [M] = a ₁ 0 a ₂ 0 a ₃ 0 0 a ₄ 0 a ₅ 0 a ₆ (3) {Q} ^T = [Txp ^T _yp ^T _{x p+1} ^T _{y p+1} ^t _{x p+ 2}
^T _{y p+2} ] (4) a ₁ = (1-γ/γ) ₀ (1-2γ/γ) ₀ a ₂ =4 (γ/γ ₀ ) (1-γ/γ ₀ ) a ₃ = ( γ/γ ₀ ) (2γ/γ ₀ −1) a ₄ = (1−γ/γ ₀ )(1−2γ/γ ₀ ) a ₅ =4(γ/γ ₀ )(1−γ/γ ₀ ) a ₆ =(γ/γ ₀ )(2γ/γ ₀ −1) The subscript T of {Q} ^T in equation (4) indicates a transposed matrix. The stress components σ _x , σ _y , and σ _xy at each measurement point p described above are measured by strain gauges. Next, the stress in the crack part can be found from the stress intensity factor K (where the mode is K and the mode is K) as K K√2[Hα] {Q} ...(5), so the stress in the crack part can also be found. .
Here, [Hα] is a constant constant specific to the shape expressed as a matrix, and when strain gauges are placed on 12 equally divided points on the circumference, it becomes as follows.

[Table] [Q] ^T = [T _x1 T _y1 ...T _xp T _yp ...T _x13 T _y13 ]
...(7) However, [Hα] ^T indicates the transposed matrix of [Hα]12
If the measured values of the equally divided strain gauges are given to [Q], K and K are determined by equation (5), and the stress intensity factor of the cracked portion is determined. Further, since the crack gauge 3 outputs a signal by sequentially cutting the grids as the crack grows, by measuring this, it is possible to measure cracks over time. 3. Effects of the invention (1) Individual 3-axis rosette gauges can be easily and accurately placed in the same position by simply aligning the center of the strain gauge with the tip of the crack in the object, aligning the opening direction, and gluing. It is. The growth of cracks can be monitored by wiring the crack gauge output to a monitoring station. In addition, the calculated values can be confirmed by comparing the predicted crack growth obtained from the rosette gauge with the actual crack growth obtained from the crack gauge. (2) If rosette gauges and crack gauges are formed on a substrate using a photoresist method, more effective productivity can be obtained, and an excellent strain gauge that can easily follow strain can be obtained. (3) Three-axis rosette gauges were installed directly above and below the opening crack. Triaxial stress can be measured even if the opening crack of the strain gauge and the crack of the object do not completely match, and the gauge of the opening crack of the strain gauge is set at a position shifted from the uniaxial stress part of the object. can.

[Brief explanation of the drawing]

Figure 1 is a diagram of the strain gauge of the present invention, Figure 2 is a diagram of the strain gauge of the present invention (rosette gate and crack gauge) attached to an object, and Figure 3 is a diagram of the strain gauge of the present invention (rosette gauge only) attached to an object. The installed view, Figure 4 is a layout diagram of conventional test pieces and strain gauges, and Figure 5 is an explanatory diagram of crack panels and symbols. Explanation of symbols, 1...Thin film base, 2a, 2b,
2c...2m,...3-axis rosette gauge, 3...
Crack gauge, 4... Gauge center point, 5... Slit. (1) Hideo Kitagawa, Haruo Ishikawa: Transactions of the Japan Society of Mechanical Engineers Vol. 44, No. 383, p. 2209, (2) Toshio Hattori: Industrial Measuring Instruments, p. 420.

Claims (1)

[Scope of utility model registration request] A thin film disk with a slit end in the center, and a plurality of triaxial rosette gauges distributed and attached on the circumference of the thin film disk with the end of the slit as the center, in contact with the center and on the opposite side of the slit. A strain gauge for crack monitoring characterized by being composed of an installed crack gauge.