JPH0557532A - Crack develop restraining method - Google Patents

Abstract

PURPOSE:To prolong the life of a structure member by injecting fine powder into a tip part of a crack happening in the structure member to blind the crack in cranes, etc. CONSTITUTION:A drilling hole 3 is drilled in the surface middle part of a crack 2 of a structure member 1, and also masking is made with a mask material 4 such as a vinyl tape except the middle part and end parts of the crack 2. Then a mixture of fine powder 5 having a particle diameter of l micron or less, e.g. SiO2 fine powder having a powder diameter of 0.5 micron degree, and penetrant such as an ink liquid is injected with a pressure charger 6 like injectors from the drilling hole 3. This can lessen opening part displacement at a crack tip part to load variation, enabling the restraint of crack spread.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crack growth inhibiting method suitable as a measure for extending the life of cranes, construction machines, bridges, and other machines and structures that are prone to fatigue cracks under repeated loads.

[0002]

2. Description of the Related Art Conventionally, the following method is often used as a life extension measure when a crack such as a fatigue crack is found in a structural member of a machine such as a crane, a construction machine, a bridge, or a structure. .. (1) Welding repair method: A method of removing cracks and re-welding. (2) Stop hole method: As shown in the plan view of FIG. 5, a circular through hole, that is, a stop hole 10 communicating with the front and back of the member is opened at both end portions of the crack 2 generated in the component member 1, and How to relieve high stress concentrations. (3) High strength bolt friction welding method: Fig. 6 (A) plan view, (B)
As shown in the side view, an attachment plate 11 that covers the crack 2 is applied to both front and back surfaces of the component member 1 and tightened by high-strength bolts 12 to perform frictional joining. Often used together.

However, such a method has the following drawbacks. (1) Since the welding repair method is a large-scale construction work, there is a problem that it is difficult to perform it in service. Furthermore, since a high tensile residual stress is introduced by welding, the life may be relatively short and cracks may recur or propagate. (2) The stophole method is the easiest to construct when the crack shape is simple in the plate thickness direction (for example, a through-crack with the same length on the front and back sides). There is a problem that it cannot be applied in the case of complexly modified surface cracks.
Furthermore, cracks may recurrence or propagate at the ends of the stophole with a relatively short life due to stress concentration in the stophole. (3) The high-strength bolt friction welding method is limited to relatively large cracks in flat structures. Also, as in (1), it will be a large-scale construction work.

[0004]

SUMMARY OF THE INVENTION The present invention has been proposed in view of such circumstances, and even if a part of a crack is present on the outer surface, it can be changed in a complicated manner in the plate thickness direction. However, it is possible to properly suppress the growth of cracks in the structural members of machines and structures with a very simple construction content, and to achieve a stable life extension effect in accordance with the conventional method. The purpose is to provide a method for suppressing crack growth.

[0005]

To this end, the present invention is characterized in that fine powder is injected into the tip portion of a crack generated in a structural member of a machine or a structure, and this is clogged with the tip portion of the crack. To do.

[0006]

[Operation] When a variable load is applied to the crack portion, the crack tip opening displacement is considered to be 1 micron or more when the crack propagates, and therefore, for example, at the crack tip portion By clogging fine powder of 1 micron or less (wedge effect), it is possible to reduce the displacement of the crack opening / closing port due to the action of external force.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the crack growth inhibiting method of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the method of the present invention, FIG. 1 (A) is a plan view and FIG. 1 (B) is a side view. 2 is a diagram showing a relationship between a load and a crack tip opening displacement amount for explaining the operation of the method of the present invention, and FIG. 3 is an explanatory diagram of an aperture displacement state at each point on the diagram of FIG. FIG. 4 is an explanatory view of a concrete experimental example of the method of the present invention.

In FIG. 1, a component 1 of a machine or structure
A crack 2 is generated by the load S acting on the crack tip, and the crack tip shows an opening amount of δ _s . Therefore, in the crack growth suppressing method of the present invention, first, a drill hole 3 is formed in the central portion of the surface of the crack 2, and the crack 2 is masked with a mask material 4 such as vinyl tape except for the central portion and the end portion. .. Then, a mixture of fine powder 5 having a particle size of 1 micron or less, for example, SiO ₂ fine powder having a particle size of about 0.05 micron and a penetrant such as an ink liquid is injected from a drill hole 3 with a pressure load device 6 such as a syringe. Push the fine powder 5 into the crack tip.

Here, the operation of the method of the present invention will be described with reference to FIG. 2: a diagram showing the relationship between the load and the opening displacement of the crack tip, and FIG. 3: an explanation of the state of aperture displacement at each point on the diagram of FIG. It will be described with reference to the drawings. First, letting δ ₀₁ be the opening displacement when there is no load S at point (I) in the lower left of the diagram in FIG. 2, the opening displacement state is as shown in FIG. 3 (I), and the load S is applied to this. At the point of aperture displacement δ _s in the upper right (IIa) of Fig. 2,
The crack tip is open and looks like Figure 3 (IIa). Next, in this state, if the fine powder 5 is injected into the crack tip (IIb), the fine powder 5 accumulates at the crack tip as shown in FIG. Even at the point of opening displacement δ _{02 in} III), the opening displacement state of the crack tip is shown in Fig. 3 (II).
As shown in I), the closing of the crack 2 is hindered by the fine powder 5 accumulated at the crack tip. Therefore, as shown in FIG. 2, the change Δδ ₂ of the opening / closing opening displacement Δδ with respect to the fluctuating load ΔS is before the fine powder injection. Becomes smaller with respect to the change Δδ ₁ .

However, the crack initiation and propagation depend on the fluctuating load Δ
Since the opening / closing opening displacement Δδ of the crack tip with respect to S is determined, it is necessary to reduce the opening / closing displacement Δδ of the crack tip with respect to the fluctuating load ΔS by injecting the fine powder 5 into the crack tip in this manner. Thereby, the growth of the crack 2 can be suppressed.

Next, a specific experimental example in which a fatigue test using a one-sided notch test piece was conducted in order to investigate the effect of the method of the present invention will be described with reference to FIG. 86 mm long and 2 horizontal for the specimen
A steel plate having a thickness of 0 mm and a thickness of 4 mm was machined with a discharge notch having a depth of 3 mm on only one side in the longitudinal center portion, and two test pieces were prepared in which a fatigue crack was introduced up to a position of 5 mm from the surface. When a variable load was applied to these test pieces, both two test pieces exhibited similar crack growth behavior up to 6.1 mm as indicated by ○ and ●.

[0012] Therefore, one of them continued the test as it is (○
Mark), another one was temporarily interrupted the test, the surface of the crack of the test piece was masked with vinyl tape excluding the central part and the end part, and then the particle diameter was 0.05 μm from the central part of the crack. _{2 A} mixture of fine powder and ink liquid was put into a syringe and pressed into the crack by applying pressure until the liquid came out at the end of the crack. After that, when the same variable load as before the interruption was applied,
As shown by the mark ●, the crack growth rate was reduced to 1/10 or less compared to that without fine powder injection (marked ○), confirming the effect of the method of the present invention.

[0013]

In summary, according to the present invention, a fine powder is injected into the tip of a crack generated in a component of a machine or a structure and the fine tip is clogged at the tip of the crack, whereby the crack Even if a part is exposed on the outer surface, even if it changes in a complicated manner in the plate thickness direction, it is possible to accurately suppress the development of cracks that have occurred in the components of machines and structures with a very simple construction content. Therefore, the present invention is extremely useful industrially because it provides a method for suppressing crack growth that can achieve the stable life extension effect according to the conventional method.

[Brief description of drawings]

FIG. 1 is a plan view and FIG. 1B is a side view showing an implementation point in an embodiment of a crack growth inhibiting method of the present invention.

FIG. 2 is a diagram showing a relationship between a load and a crack tip opening displacement amount for explaining the operation of the method of the present invention.

FIG. 3 is an explanatory diagram of an aperture displacement state at each point on the diagram of FIG.

FIG. 4 is an explanatory diagram of a specific experimental example of the method of the present invention.

FIG. 5 is a plan view showing a conventional stophole method.

6A and 6B show a conventional high-strength bolt friction welding method. FIG. 6A is a plan view and FIG. 6B is a side view.

[Explanation of symbols]

 1 Components 2 Cracks 3 Drill holes 4 Mask material 5 Fine powder 6 Pressure application equipment

Claims (1)

[Claims] 1. A method for suppressing crack growth, which comprises injecting fine powder into a tip portion of a crack generated in a structural member of a machine or a structure to clog the fine powder with the tip portion of the crack.