Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
1996-08-29
2001-06-05
McCall, Eric S. (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
C073S775000
Reexamination Certificate
active
06240786
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a two-layer structure composite material, comprising a piezoelectric material and a structural material, for detecting cracks in a structural material with the purpose of predicting destruction.
2. Description of Prior Art
Structural ceramic materials are fragile, and some treatment is needed when high reliability is required. In this respect, there are strong demands on a new type of ceramics, in which functional ceramics is combined with structural ceramics which generates a signal when cracks occur and contributes to the prediction of the possible destruction of the material before it actually occurs. Such the prediction of destruction is needed not only for structural ceramics but also for general structural materials, in which cracks may occur.
To detect cracks in structural materials, an acoustic emission method is normally used. In this case, it is necessary to set a large sensor on a structural material. However, in case sufficient space is not available to set the sensor, or in case a structural material is rotating at high speed, it is not possible to identify the occurrence of cracks and hense it is necessary for the prediction of possible destruction to disassemble and inspect a material at regular interval.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a two-layer structure composite material, by which it is possible to detect crack and to predict possible destruction before it actually occurs, and which can be used for a structural material with complicated shape, for a structural material with no additional space for providing a sensor or for a structural material in which the sensor cannot be mounted because it is rotating at high speed.
To attain the above object, a two-layer structure composite material comprises a structural material and a voltage generating material, which contains ferroelectric material, pyroelectric material or piezoelectric material. The voltage generating material is provided with an electrode to take out the generated voltage.
As the voltage generating materials, perovskite type, wurtzite type, ZnO type etc. are used. It is convenient to produce a two-layer structure of the structural material and piezoelectric material, it is advantageous because it can be used as an electrode for detecting cracks.
The above structural materials are combined with a ferroelectric material, a pyroelectric material or piezoelectric material, which generates voltage when impact force is applied. As such materials for generating voltage, perovskite type, wurtzite type or ZnO type materials are suited. As a perovskite type material, ABO
3
type ferroelectric materials can be used. As a wurtzite type material, AlN, GaN, InN, NbN or TaN may be used. As a ZnO structural material, ZnO and others may be used. Further, perovskite type materials may be mixed with resin or rubber and used. The ferroelectric materials must be used under Curie temperature.
To produce the two-layer structure composite material of the present invention, a structural material and a ferroelectric material or a piezoelectric material may be bonded together using an adhesive. Or, ferroelectric film or piezoelectric film may be generated on the structural materials using sol-gel method, CVD method, PVD method, etc.
The electrodes connected with the ferroelectric film or the piezoelectric film may be provided on both sides of the ferroelectric material or the pyroelectric material, or a comb type electrode may be provided on one side. As a result, the voltage generated owing to the occurrence of cracks can be easily detected. As described above, in case a conductive material is used as a structural material, it can be utilized as an electrode.
The two-layer structure composite material for detecting cracks thus obtained is used under such condition that a device for measuring and recording the generated voltage is connected with the electrode. When impact force is transmitted to the structural material, the force is propagated to the voltage generating material bonded to the structural material. Then, the occurrence of the cracks can be easily found by detecting the voltage using the measuring and recording device. Thus it is possible to predict the description of the structural material before it actually occurs.
REFERENCES:
patent: 3603142 (1971-09-01), Saylak et al.
patent: 4255974 (1981-03-01), Dufrane et al.
patent: 4503710 (1985-03-01), Oertle et al.
patent: 4924708 (1990-05-01), Solomon et al.
patent: 5209126 (1993-05-01), Grahn
patent: 5349869 (1994-09-01), Diaz et al.
Akiyama Morito
Nonaka Kazuhiro
Watanabe Tadahiko
Agency of Industrial Science and Technology
McCall Eric S.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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