JPS60209137A - Predicting method of fatigue damage - Google Patents

Abstract

PURPOSE:To predict the fatigue damage of a structure which has excellent precision and detection performance by fitting a prediction piece with a cut to the structure, and detecting its cracking. CONSTITUTION:The prediction piece 2 made of the same material with the structure 1 is fitted to a fatigue cracking dangerous position of the structure 1. Fatigue cracking starts at the position of the cut 3 earlier in the piece with the cut 3 than in the structure 1. The cracking starting at the cut 3 stops at a hole 4. The hole 4 has a smooth internal-diameter surface, so notch effect is small and the growth of the cracking to the structure body 1 is impeded. For the purpose, the generation of cracking in the piece 2 is detected to know the fatigue damage of the structure 1 before harmful cracking is generated in the structure 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for predicting the risk of fatigue damage in structures such as bridges before fatigue cracks or the like occur in the structure body. It is something.

Prior Art The following method can be considered as a conventional method for predicting the risk of fatigue damage that can be applied to structures such as bridges.

First, the first method is to apply stress measurement using a strain gauge. That is, this is a method in which a strain gauge is affixed to a region that is at risk of fatigue damage, the degree of stress is calculated from the output of the gauge, and the degree of damage is estimated from the magnitude.

However, with this method, it is difficult to affix strain gauges to existing elevated structures, the painted area must be treated before and after the strain gauge is affixed, and information can only be obtained from the area where the strain gauge is affixed. There were problems such as not being able to obtain

Further, as a second method, there is a method of measuring elastic waves using acoustic emission. This method takes advantage of the fact that in materials such as steel, sound or elastic waves are generated when plastic deformation or cracks occur or propagate.Acoustic emission wave receivers are installed in dangerous areas, and the risk of damage is determined from the signal. It is something to do.

However, this method relies on plastic deformation before crack initiation! The electromagnetic wave output is not large and difficult to detect, and the detection limit is generally considered to be a crack length of about 3 mm, which poses a problem in that it cannot be predicted.

Furthermore, a third method includes visual inspection and non-destructive inspection. This is a periodic inspection to detect whether or not fatigue cracks have occurred in dangerous areas by visual inspection and non-destructive inspection.

However, this method has the problem that the inspection environment for elevated structures such as bridges is generally poor, making it difficult to apply highly accurate non-destructive inspection methods, or requiring a large amount of man-hours to prepare scaffolding for inspection. . In addition, since the inspection results cannot be predicted if cracks have already occurred, there is a problem in that inspections must be carried out frequently from a very early stage.

Purpose of the Invention In order to solve the above-mentioned problems, the present invention is applicable to structures such as bridges where the inspection environment is poor, the installation work is not so difficult, and the accuracy and detectability are good. The purpose is to provide a fatigue damage prediction method.

Structure of the Invention A fatigue damage prediction method according to the first aspect of the present invention that meets this objective is to attach a prediction piece having a notch to a structure, generate a crack in the prediction piece before the structure, and then remove the prediction piece. It consists of a method of predicting the lifespan of a structure based on the occurrence of cracks.

Further, in the fatigue damage prediction method according to the second aspect of the present invention, a prediction piece having a notch and a hole in which a negative wave is sealed is attached to a structure, and the prediction piece is placed beyond the structure. This method consists of a method in which cracks are generated in the prediction piece, the negative waves seeped out onto the surface of the prediction piece are visually observed, the generation of cracks in the prediction piece is recognized, and the life of the structure is predicted from the occurrence of cracks in the prediction piece.

Functions and Effects of the Invention In the fatigue damage prediction method as described above, since a notch is provided in the prediction piece, fatigue cracks occur in the prediction piece before cracks occur in the structure body, and only the prediction piece can be viewed through the telescope. It is possible to predict the degree of fatigue damage in a structure by observing it and determining whether or not cracks have occurred. In this case, by appropriately selecting the notch shape of the prediction piece, it is possible to control at what stage the degree of fatigue damage of the structure body is predicted. Furthermore, if the prediction piece is made of the same material and has the same coating specifications as the structure itself, the influence of the environment on fatigue damage can be made the same.

In addition, if a negative wave is sealed in the sealed hole, when a crack occurs in the prediction piece, the crack will lead to the hole, and the sealed negative wave will leak to the surface of the prediction piece, preventing the occurrence of cracks in the prediction piece from a distance. It can be easily identified with the naked eye, improving convenience and identifiability.

EXAMPLES Below, preferred examples of the fatigue damage prediction method of the present invention will be described with reference to the drawings.

1 to 7 show the case of the first invention of the present invention.

Figure 1 shows a case where a bridge is used as an example of a structure. In the figure, 1 is the structure, which is supported on foundation supports. In such a structure 1, large tensile stress due to bending stress occurs at the lower edge of the structure 1, and moreover, vehicles passing through the bridge,
This occurs repeatedly due to the passage of railway vehicles, etc. Therefore, the lower edge portion of the structure 1 becomes a dangerous area where fatigue cracks may occur.

A prediction piece 2, which will be described below, is attached to a fatigue crack-prone area of the structure 1.

Attachment is by appropriate means such as welding, gluing, bolting, etc.

The prediction piece 2 is made of the same material as the main body of the structure 1, and is made of a plate member having a notch 3, as shown in FIGS. 2 and 3. The notch 3 is provided on the lower side where the maximum bending stress is applied when the prediction piece 2 is subjected to bending stress from the structure 1. A hole 4 having a smooth curved inner diameter surface is formed in the prediction piece 2 at a position facing the notch 3 and at a position away from the notch 3. When the prediction piece 2 is attached to the structure 1 by welding 5, the welding portion 5 is finished with a smooth curve so that no notch is formed.

As shown in FIGS. 4 and 5, the prediction piece 2 has an opening angle α of the notch 3, a curvature r2 of the tip of the notch 3, and
By appropriately selecting the curvature r1 provided on the left and right sides of the notch 3 of the prediction piece 2 so as to continue to the welded part 5, the distance d1 between the hole 4 and the hole 4 prevents cracks from forming from the notch 3. Ease is controlled.

In order to predict fatigue damage in the structure 1 using the prediction pieces 2, first, the prediction pieces 2 are attached to appropriate fatigue damage-prone parts of the structure. The attachment may be done in advance before construction of the structure 1, or may be attached to the existing structure 1.

The structure 1 is subjected to repeated loads, and the prediction piece 2 is also subjected to repeated stresses. Between the prediction piece 2 and the structure 1, fatigue cracks begin in the prediction piece 2 with the notch 3 first from the notch 3 portion.

Even if a crack 6 occurs from the notch 3, the crack 6 stops at the hole 4. -Hole 4 has a smooth inner diameter surface, so
The notch effect is small and prevents the crack 6 from propagating into the main body of the structure 1.

By detecting the occurrence of cracks 60 in the prediction piece 2, the degree of fatigue damage of the structure 1 can be known before harmful cracks occur in the structure 1. To detect the occurrence of crack 6,
For example, a conductive wire with a minute diameter may be pasted to the area between the notch 3 and the hole 4, and when the conductive wire is cut due to a crack, a lamp provided in an easily visible area may be lit. , or by other means.

FIG. 6 shows the relationship between the fatigue properties of the prediction piece 2 and the main body of the structure 1, particularly the occurrence of cracks at locations A, B, and C in FIG. 4. In the part A where the prediction piece 2 is not attached, cracks occur in the main body of the structure 1 according to the characteristic line A in FIG. If the prediction piece 2 and the main body of the structure 1 are finished at rl and the welded part 5 so that stress concentration does not occur as much as possible, the welded part 5 will follow the characteristic line B.
Accordingly, cracks occur. Although part B near the weld 5 may crack earlier than part A, it is finished to have the same lifespan as A as much as possible. At part 0, due to the degree of stress concentration determined by the opening angle α of notch 3 and the curvature r2 of the tip of the notch, cracks occur quite quickly (cracks occur). This is the characteristic line C'.The margin from when the crack penetrates to hole 4 until the crack occurs in the main body of structure 1 is E in Figure 6.
It depends on various dimensions and shapes such as rl, r2, α, d, and r3 of the prediction piece 2, and the margin can be freely adjusted.

FIG. 7 shows a different embodiment from FIG. 4, in which a notch 3' is also provided in the prediction piece 2 on the side opposite to the hole 4 of the notch 3. By doing this, it is ensured that cracks will not occur in the prediction piece 1. However, the notch 3- must be provided in a direction in which the crack does not propagate toward the structure 10 body.

FIGS. 8 and 9 show the case of the second invention of the present invention. In the second invention, the hole 4 is a sealed hole, and the liquid absorbent 7 is sealed therein. Since the rest is in accordance with the first invention, the same reference numerals as in FIGS. 1 to 7 are given to the corresponding parts, and the explanation thereof will be omitted.

In the case of the second invention, when the crack 6 generated from the notch 3 penetrates the hole 4, the liquid absorbent 7 in the hole 4 seeps onto the surface of the prediction piece 2, and it can be visually observed from a distance with a telescope etc. , the occurrence of cracks can be easily detected, and the structure '1
You can know the degree of damage. In other words, prediction piece 2
If there is a color change on the surface, it can be judged from the margin E to decide whether to conduct a complete inspection, and if there is no color change, it can be considered that there is a sufficient degree of safety against fatigue damage. Therefore, fatigue damage to the main body of the structure 1 can be easily predicted by observing only the color change.

In the above description, a bridge is taken as an example of the structure 1, but it may be any other structure, such as a steel tower or a crane.

As explained above, according to the present invention, the prediction piece 2 having the notch 3 is attached to the structure 1, and fatigue cracks are generated in the prediction piece 2 first. It does not generate cracks, can be applied to structures in poor inspection environments, is not difficult to install, and has the advantage of being able to determine the degree of fatigue damage of structures with good detectability.

[Brief explanation of the drawing]

FIG. 1 is an overall front view of a structure to which the first invention of the present invention is applied, FIG. 2 is a partial front view of the structure near the predictive piece attachment part, FIG. 3 is a side view of FIG. 2, and FIG. The figure is a partial front view of the part of the prediction piece in Figure 2, Figure 5 is a side view of the part in Figure 4, Figure 6 is a fatigue characteristic diagram, and Figure 7 is another example of the prediction piece of the first invention. FIG. 8 is a partial front view of the predictive piece portion of the second invention of the present invention; FIG. 9 is a side view of the portion shown in FIG. 8; FIG. 10 is a front view of the crack portion shown in FIG. 8. Figure. 1... Structure 2... Predicted piece 3... Notch 4... Hole 5... Welded part 6...・Crack 7・・・Color liquid Fig. 7 Fig. 9 1

Claims (2)

[Claims] (1) A prediction piece having a notch is attached to a structure, a crack is generated in the prediction piece before the structure, and the life of the structure is predicted from the occurrence of a crack in the prediction piece. Fatigue damage prediction method. (2) A prediction piece that has a notch and a hole filled with white liquid is attached to a structure, and cracks occur in the prediction piece before the structure and white seeps onto the surface of the prediction piece. 1. A fatigue damage prediction method characterized by recognizing the occurrence of cracks in a prediction piece by visually observing a liquid, and predicting the life of a structure based on the occurrence of cracks in the prediction piece.