JPH0469745B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a crack growth monitoring device for a complex structure that directly determines the stress intensity factor, which is a parameter governing the crack growth rate. (Prior Art) Bridges and other complex structures receive varying loads due to the passing of vehicles and other heavy objects, which can result in damage due to fatigue and cracks. These cracks will have to be repaired eventually, but
It must be safe and must not be destroyed, at least until repaired. To this end, a monitoring device is required that not only monitors the current crack growth rate but also collects data for estimating the future growth amount and direction of growth. Conventionally, devices have been used to measure the actual stress of structures, but there has been no device that can determine the stress intensity factor that governs the crack growth rate in complex structures. (Problems to be Solved by the Invention) Therefore, the problem is to develop an automatic monitoring device consisting of a specially shaped strain gauge and an arithmetic device to determine the stress intensity factor. (Means for Solving the Problem) As shown in FIG. 1, a thin film base 3a having a slit 6a in the center is provided with slits 6a arranged at equal intervals (or irregular intervals) on a circumference centered at one end of the slit 6a. good)
Multiple 3-axis rosette gauges distributed in
paste). 1 to 13 are three-axis rosette gauges, and one crack gauge 15 is pasted on the opposite side of the slit 6a. These are led to the arithmetic unit 7a via the connector 16. Arithmetic device 7
a is made compact and placed near the structure. The arithmetic unit 7a is composed of a dynamic strain meter, an extreme value detection circuit, and its arithmetic circuit for calculating, storing, and recording stress intensity coefficients, a timer, and a storage device for stress intensity coefficients and crack gauge outputs, and is used to calculate and record the stress intensity coefficients and crack gauge outputs. The stress intensity factor is calculated from the gauge data, and the configuration of this monitoring device serves as a means to solve the problem. (Function) To determine the stress near the tip of the 3-axis rosette gauge with one end of the slit as the center, proceed as follows. Now in Figure 3 or 4, in the X direction (
Let the output of the p-th three-axis rosette gauge in the Y direction (direction), the Y direction (direction), and their bisector direction (direction) be ε〓ε〓ε〓, and the tension at any p point among the measurement points is The equation holds true if the stresses are σ _x and σ _y and the shear stress is τ _xy . σ _x = (E/1−υ ² )・(ε _I +υε〓)……(A) σ _y = (E/1−υ ² )・(ε〓+υε〓)……(B) τ _xy =− 1/2 (σ ₁ −σ ₂ ) sin2θ ...(C) Here, σ ₁ = {E/(1−υ ² )}(ε ₁ +υε ₂ ) σ ₂ = {E/(1−υ ² ) }(ε ₂ +υε ₁ ) ε ₁ = (ε〓+ε〓)/2 +√{(〓+〓)2-〓} ² +{(〓-〓
)2} ² ε ₂ = (ε〓+ε〓)/2 −√{(〓+〓)2-〓} ² +{(〓-〓
)2} ² θ＝0.5tan ^-1 {(ε〓＋ε〓−2ε〓)／(ε〓−ε
〓)} Here υ is Poitson's ratio. The process of calculating the stress intensity factor from the reading of the strain gauge 3a1 will be described below. (See Document 1) 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-point rosette gauge on the circumference S will be explained with reference to FIG. 5b. Γ is the boundary of a circle with radius R, and n three-axis rosette gauges 1, 2, 3, ... p, p+1 ... n are arranged on the circumference of the circle.
Arrange as shown in the figure. From the pth among them, p+1
The angle that the th measurement point makes with the origin O, and p
Let γ γ ₀ be the angle that measurement points from th to p+2th measurement points make with the origin O, and let _x and _y be the x and y components of the surface force acting on the boundary, then the surface force at measurement point p is is {} _p = { _x / _y } _p = l _x σ _x + l _y τ _xy l _x τ _xy + l _y σ _y p (1) However, (l _x , l _y ) are directed outward on the boundary Γ of S. It is the direction cosine of the drawn normal. 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 0 a ₄ a ₂ 0 0 a ₅ a ₃ 0 0 a ₆ ......(3) {Q} ^T = [T _xp T _yp T _{x p+1} T _{y p+1} T _{x p+2} T _{y p+2} ] ...(4) a=(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 τ _xy at each measurement point p are determined from the strain gauge 3a1 using the equations (A), (B), and (C). Next, the stress in the crack is the stress intensity factor K, K
(Let the mode be K and the mode be K.): K K=√2[Hα] {Q} ... (5) Since it can be found from (5), the stress in the crack can also be found.
Here, [Hα] is a constant constant specific to the shape expressed as a matrix, and is a strain gauge placed on the 12 equally divided points on the circumference, and a 3-axis rosette gauge is placed on the 12 equally divided points on the circumference. The case is as follows.

[Table] ・・・・・・・・・・・・(6)
[Q] ^T = [T _x1 T _y1 ...T _xp T _yp ...T _x13 T _y13 ]...(7) However, [Hα ^T ] indicates the transposed matrix of [Hα].
If the measured values of the triaxial rosette gauge divided into 12 equal parts are given to [Q], K and K are determined by equation (5), and the stress intensity factor of the cracked portion is determined. (Refer to Document 1) In addition, as the crack grows, the grid of the crack gauge 15 is sequentially cut and a signal is output. In FIG. The amount of growth of the crack and its time are stored in the storage device 12a.
If you memorize this, the crack growth can be automatically recorded. The above two records (time series data of the stress intensity factor and the amount and time of crack growth) can be taken back to the factory and printed on a storage medium such as a cassette tape or diskette and used for subsequent analysis. (Example) FIG. 1b shows a device for monitoring growth cracks in a structure according to the present invention. The configuration of the strain gauge 3a1 will be explained. The thin film base 3a is located at the center point 5a of the strain gauge.
It is a circular thin film with the center at , and a slit 6a is cut outward in the radial direction from the center. Appropriate radius R
3-axis rosette gauges 1 to 13 are arranged on the circumference. Figure 1 shows the case where it is divided into 12 equal parts, of which 1 and 13 are placed directly above and below the slit. In this embodiment, the equal number of the rosette gauge is 12, but any number other than 12 that can be arranged may be used as the equal number. 15 is the center point 5a of the crack gauge
It is arranged on the opposite side of the slit 6a in contact with the slit 6a. To set the individual three-axis rosette gauges at once, it is highly productive to use the photoresist method. The strain gauge 3a1 is set in a structure as follows. That is, as shown in FIG. 3, the tip of the crack that has occurred in the object to be tested and the strain gauge 3a
While aligning one end of the center point 5a of the strain gauge 3a1 with one end of the center point 5a of the strain gauge 1, the other end of the crack in the target object and the opening side of the slit 6a of the strain gauge 3a1 face the same direction, and glue the strain gauge 3a1 and the target object using instant adhesive or the like. do. FIG. 1a shows a strain gauge 3a1 (a rosette gauge and a crack gauge) of the present invention attached to an object. In this embodiment, K and K were determined as follows. The strain gauge 3a1 has three outputs from one rosette gauge, and since there are 13 rosette gauges, there are a total of 39 outputs. Upon receiving these inputs, the dynamic strain meter 9a calculates 39 stresses [〓 _x 〓 _y 〓 _xy ] _p p = 1 to 13, and sends these to the next extreme value search and storage circuit 1.
Enter in 0a. That is, the dynamic strain meter 9a is expressed by formulas (A) and (B)
Calculation (C) is performed and the result is output to the next extreme value search and storage circuit 10a. FIG. 4 shows temporal changes in stress values σ _x , σ _y , and τ _xy obtained from the strain gauge 3a1. In the figure, from the left to the extreme values i = 1 , 2 , 3 ...
It is numbered. Find the stress value [〓 _x 〓 _y 〓 _xy ] _p p = 1 to 13 for each extreme value i, use equation (5) to find (K, K) _i for each i, and from this calculate the time Get a change. FIG. 2 is a block diagram showing the above arithmetic device. The extreme value search and storage circuit 10a calculates K and K using equation (5) from each stress and shear stress, and inputs the temporal change to the next storage device 12. (Effects of the invention) (1) While aligning the tip of a crack that has occurred in the structure with one end of the strain gauge, the crack in the structure and the slit in the strain gauge can be glued together with instant adhesive, etc., facing the same direction. Work has become significantly easier. (2) Stress intensity factor K (mode) and K (mode) that act on a crack when various stresses act on a crack that occurs in a structure with unclear boundary conditions
Since the temporal changes in can be measured separately, K
Data for predicting the amount of future crack growth can be obtained from K/K, and data for predicting the direction of crack growth can be obtained from K/K. (3) Since there is a crack gauge, the crack growth process can be monitored unattended.

[Brief explanation of drawings]

Figure 1a is an overall view of the automatic crack growth monitoring device, b
2 is a block diagram of a calculation device, FIG. 3 is a numbered diagram of measurement points by a 3-axis rosette gauge, FIG. 4 is an illustration of fluctuating stress generated in each rosette gauge, and FIG. The figure is an explanatory diagram of the numbers and symbols of the rosette gauge positions on the crack panel. 1a...Structure, 2a...Crack, 3a...Thin film base, 3a1...Strain gauge, 6a...Slit, 7a...Arithmetic device, 9a...Dynamic strain (39 channels), 10a...Extreme value search and memory circuit,
11a...K, K arithmetic circuit, 12a...memory circuit, 13a...dynamic strain (1 channel).

Claims (1)

[Claims] 1. A thin film base having a slit opened from the periphery toward the center, and a plurality of triaxial rosette gauges distributed and pasted on the circumference of the thin film base centered on the end of the slit, and the opposite side of the slit. The stress component is calculated from the output of the strain gauge consisting of a crack gauge attached to the side and the three-axis rosette gauge, the extreme value of the stress component and its time are calculated, the stress intensity factor at the extreme value is calculated, and the time series is calculated. 1. A crack growth monitoring device for a structure, comprising a storage device for storing the crack gauge output and its time.