Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
2001-03-30
2003-02-18
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
Reexamination Certificate
active
06520024
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crack-type fatigue detecting sensor, a method for fabricating the crack-type fatigue detecting sensor, and a method for estimating fatigue damage using the crack-type fatigue detecting sensor, which are suitably practiced for measuring damage due to fatigue of various members of a structural component such as a bridge, a machine, a vehicle, an air plane, and the like.
2. Description of the Related Art
A typical prior art is disclosed in Japanese Laid-Open Patent Publication No. Sho. 62-265558. This prior art discloses a crack-type fatigue detecting sensor in which a fracture piece having a slit causing fatigue damage is fixed to a surface of a plate-shaped substrate, a method for fabricating a crack-type fatigue detecting sensor in which opposite end portions (in a longitudinal direction) of a fracture piece having a slit are bonded to a surface of a substrate by bond for fixation, and a method for estimating damage using a crack-type fatigue detecting sensor in which two crack-type fatigue detecting sensors having different crack propagation characteristics are fixed to a member to be tested, lengths of respective cracks propagating during the same period are measured, and damages occurring in the period, due to fatigue of the member to be tested, which are associated with these lengths of crack propagation, are estimated.
Another prior art is disclosed in Japanese laid-Open Patent Publication No. Hei. 9-304240. In this prior art, a thin-plate shaped fracture piece made of a material identical to a material of a structural component for which fatigue damage is predicted and having a slit in a central portion in a longitudinal direction thereof is sandwiched between two synthetic resin thin plates and these are bonded in a region except the central portion of the fracture piece that includes the slit. This test piece is made of the material identical to that of the member to be tested. The crack-type fatigue detecting sensor is fabricated in such a manner that a member having a circular hole in the central portion in the longitudinal direction thereof and the slit extending from the circular hole toward both ends in a width direction thereof is sliced into pieces having a thickness equal to a thickness of the fracture piece, and so formed fracture piece is sandwiched between the two synthetic resin thin plates and the opposite end portions of the fracture piece in the longitudinal direction thereof are bonded to the thin plates. This prior art also discloses a method for estimating damage using the crack-type fatigue detecting sensor, in which the crack-type fatigue detecting sensor is fixed at a position apart from a portion at which stress concentrates, which is so-called a hot spot such as a weld toe, and life of the member to be tested is estimated based on an S−N (=stress−number of repeated load cycles) diagram for the member to be tested created in advance.
Still another prior art is disclosed in Japanese Laid-Open Patent Publication No. Hei. 10-185854. In this prior art, a crack-type fatigue detecting sensor having a plurality of strain gauges spaced apart from one another and placed either in parallel or in series in a direction perpendicular to a direction of a crack of fatigue damage occurring on the member to be tested is attached to the member to be tested, a value of a length of crack propagation occurring on the fracture piece is electrically measured, and damage due to fatigue of the member to be tested is estimated based on this measured value.
A further prior art is disclosed in Japanese Patent No. 2952594. In this prior art, a fracture piece having a slit is provided with strain gauges or crack gauges obtained by placing a plurality of electric resistance wires in parallel with one another in a direction orthogonal to a direction in which a crack initiating from a tip end portion of the slit propagates, for facilitating measurement of a length of crack propagation occurring on the fracture piece, and based on the measured length, damage due to fatigue is estimated.
In the prior art disclosed in the Japanese Laid-Open Patent Publication No. Sho. 62-265558, since the fracture piece, on which no tensile stress remains, is fixed to the substrate, strain occurring on the member to be tested is transmitted to the fracture piece through the substrate, causing the crack to occur at the tip end portion of the slit of the fracture piece, and from the length of the crack, damage due to fatigue of the member to be tested is measured. Therefore, the fracture piece requires tensile stress large enough to cause the crack at the tip end portion of the slit, and strain of the member to be tested that is too small to cause any crack cannot be detected. As a result, sensitivity is low.
In the prior art disclosed in the Japanese laid-Open Paten Publication No. Sho. 9-304240, the fracture piece is sandwiched between two synthetic resin thin plates such that the opposite end portions of the fracture piece in the longitudinal direction are joined to these plates, and one of the thin plates is fixed to the member to be tested. Therefore, the strain occurring on the member to be tested is transmitted to the fracture piece through the thin plate. The strain occurring on the member to be tested is not reliably transmitted to the fracture piece because a part of the strain is absorbed in the thin plate. As a result, sensitivity is low. The crack-type fatigue detecting sensor of this prior art has a large outer shape (70 mm long, 20 mm wide, and 1.5 mm thick). For this reason, this sensor cannot be attached to the member to be tested in proximity to a peripheral end of, for example, a welded bead of this member. Therefore, a position at which damage is measured is limited. Under the circumstance, it is highly probable that the aim cannot be achieved.
In the prior art disclosed in the Japanese laid-Open Patent Publication No. Hei. 10-185854, without an element corresponding to a substrate of the present invention, the fracture piece is directly attached to the member to be tested and the length of crack propagation occurring on the fracture piece is electrically measured by an electric means such as the strain gauge or the electric resistance wire and monitored. The fracture piece has a fixed thickness and a large outer shape (170 mm long, 50 mm wide, and 0.5 mm thick) and the position at which the fatigue damage of the member to be tested is measured is extremely limited.
In the prior art disclosed in the Japanese Patent No. 2952594, although the following two respects are devised to improve the strain sensitivity of the crack initiating from the slit of the sensor attached to the member to be tested, problems associated with its cost and practical use arise. i) Because the crack is difficult to occur in a condition in which only grooves are formed, load is repeatedly subjected to cause the fatigue crack to occur and its tip end portion is made sharp. Still, the crack is difficult to occur under the influence of the compressive stress remaining at the tip end portion of the crack. So, heat treatment (residual stress relief annealing) is carried out to reduce the residual stress. This results in enormous labor and high cost in fabrication. ii) When directly attaching the sensor to the member to be tested, tensile residual stress is given to the sensor. This is sometimes impossible in practice and its management is extremely difficult.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a crack-type fatigue detecting sensor which has a compact configuration and is capable of measurement at a position selected with improved degree of freedom and with high sensitivity, high precision, and high reliability, a method for fabricating the crack-type fatigue detecting sensor, and a method for estimating damage using the crack-type fatigue detecting sensor.
To achieve the above-described problem, there is provided a crack-type fatigue detecting sensor comprising: a foi
Dake Yoshinori
Kobayashi Tomohei
Koe Shigeki
Murakami Akio
Nihei Kanta
Kawasaki Jukogyo Kabushiki Kaisha
Marshall Gerstein & Borun
Noori Max
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