JP3197925B2 - Prior Fatigue Failure Detection Method for FRP Members - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber reinforced plastic (FRP) member capable of detecting fatigue fracture of a fiber reinforced plastic (FRP) member in advance and a method for detecting the same.

[0002]

2. Description of the Related Art FRP
Is widely used in various fields because it is lightweight, has high strength, and can be easily formed into various shapes. However, if the FRP product is used for a long time,
Fatigue of the RP causes micro-cracks in the FRP, separation of the matrix and the reinforcing fiber, and the like, which eventually leads to fatigue failure.

[0003] Therefore, in order to know the durable limit of FRP,
FRP that can detect fatigue fracture of FRP in advance
Various studies have been made on a method for detecting fatigue fracture of a member.

[0004] For example, a light transmission method, an X-ray method, an ultrasonic method, an acoustic emission method (AE method), etc.
Methods for determining the degree of fatigue degradation of RP are being developed. However, the methods based on the light transmission method, the X-ray method, and the ultrasonic method are limited to relatively large defects of the FRP. On the other hand, according to the AE method, relatively small defects can be found, but a complicated operation such as applying a load to the FRP product at the time of measurement is required, and there is a problem in accuracy.

As another method, Japanese Unexamined Patent Publication No. Sho 60-114741 discloses a method in which a carbon long fiber is disposed integrally with an FRP member, an electric current is applied to the long fiber, and the presence or absence of a disconnection is inspected. This discloses a method of detecting fatigue failure of the FRP member in advance. However, this method requires a complicated operation such as manufacturing the FRP member and the long fiber separately for inspection and bonding the long fiber to the surface of the FRP member. Further, since it is necessary to bond long linear fibers, this method cannot be applied to an FRP member having a complicated shape. In addition, by applying electricity during inspection, F
There is also a possibility that the characteristics of the RP may be deteriorated.

[0006] Therefore, the above problems have been solved, and FR
To enable you to detect fatigue failure of P in advance, fatigue failure detection method of the FRP member has been desired.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems and to detect in advance the fatigue fracture of FRP easily and non-invasively for FRP members, and to be applied to FRP members having complicated shapes. It is an object of the present invention to provide a detection method capable of detecting fatigue fracture of an FRP member in advance.

[0008]

In view of the above objects, as a result of intensive studies, the present inventors have found that if a magnetic material having stress-magnetic properties is blended to produce an FRP member, the FRP member can be disposed within the FRP member. The present inventors have found that by detecting a change in the magnetic permeability of the magnetic material, the fatigue fracture of the FRP member can be detected in advance, and the present invention has been completed.

[0009]

[0010] In other words, the fatigue fracture thing of the FRP member of the present invention
The pre- detection method hardens the FRP composed of the reinforcing fiber, the resin matrix, and the magnetic material having the stress-magnetic property ,
The FRP member is manufactured such that a compressive stress is applied to the reinforcing fiber, and the change in the magnetic permeability of the magnetic material disposed in the FRP member is measured, whereby the reinforcing fiber is hung on the reinforcing fiber.
The method is characterized in that the degree of release of the compressive stress is detected and the fatigue fracture is detected in advance.

Hereinafter, the present invention will be described in detail.

In general, a compressive stress of about several kg / mm ² is applied to the reinforcing fibers from the periphery thereof by the hardening of the matrix resin composed of the reinforcing fibers and the resin matrix. When the FRP becomes fatigued, microcracks are generated and propagated in the matrix, and peeling between the reinforcing fibers and the matrix occurs. Therefore, the compressive stress applied to the reinforcing fibers is gradually released. As such fatigue progresses, the FRP member eventually breaks down.

Therefore, in order to detect the fatigue fracture of the FRP member in advance, it is sufficient to detect the degree of release of the compressive stress applied to the reinforcing fibers. To do this,
A magnetic material having a property (hereinafter referred to as stress-magnetic property) in which the magnetic (permeability) property greatly changes due to stress is compounded before curing, and the change in the magnetic permeability is detected, and the magnetic permeability becomes a certain level. , It is possible to know that there is a great risk of fatigue failure.

[0013] In the present invention, the stress-
Examples of the type of the magnetic material having magnetic characteristics include an Fe-based amorphous alloy and an Fe-rare earth-based giant magnetostrictive material. In particular, as the Fe-based amorphous alloy, an Fe-Si-B-based amorphous alloy is preferable, and particularly preferably, Fe 65
~ 67 atomic%, Si 8 ~ 9 atomic%, B11 ~ 13 atomic%, Co10 ~
It is an amorphous alloy having a composition of 12 atomic% and Cr 1 to 3 atomic%. When the content of each chemical component is set as described above, the stress-magnetic characteristics of the amorphous alloy can be further improved, and the corrosion resistance can be improved. This improvement in corrosion resistance is also effective in extending the life of an amorphous alloy because FRP has considerable hygroscopicity.

The shape of the magnetic material having the above-mentioned stress-magnetic characteristics includes long fibers, short fibers, ribbons, flakes, and the like.
It may be in any form of powder, but it is preferable to use a long fiber (wire) for the purpose of increasing the detection sensitivity.

When the magnetic material is a wire, the diameter of the wire is preferably 10 to 200 μm, particularly preferably 100 to 150 μm. When the diameter of the wire is less than 10 μm, it is difficult to form the wire, whereas when the diameter exceeds 200 μm, it becomes difficult to make the wire amorphous.

The mixing ratio of the above magnetic substance to the FRP member is 0.5 to 50% by volume (hereinafter referred to as V / f), particularly 1 to 50%.
It is preferably set to 10%. If V / f is less than 0.5%, it is difficult to measure the change in permeability, while V / f is 50%.
%, It becomes difficult to form the FRP member,
The advantage of high specific strength is lost.

Hereinafter, the present invention will be described by taking an amorphous wire as an example of a magnetic material having stress-magnetic characteristics.

As a method of blending the amorphous wire with the resin matrix, a method of blending the amorphous wire or a woven fabric (net-like material) made therefrom with the matrix separately from the reinforcing fibers can be adopted.
From the viewpoint of uniform dispersion, a method of forming a mixed fiber or a mixed woven fabric made of an amorphous wire and a reinforcing fiber and then blending the mixed fiber with a matrix is preferable. In addition, this mixed woven fabric may be made of mixed fibers. For example, it may be made of amorphous alloy fibers as warp yarns and reinforcing fibers as weft yarns.

The location of the above-mentioned amorphous wire (including one processed into a mixed fiber or woven fabric) is FR
Although it may be uniformly disposed in the P member, it is disposed so as to be concentrated at a specific location (for example, a surface layer) in the FRP member in order to increase sensitivity according to a method for measuring magnetic permeability described later. May be. The orientation of each fiber axis of the amorphous wire is preferably parallel to the main stress direction. This is because strength is advantageous.

Examples of the resin matrix in which the above amorphous wire is blended include epoxy resin, unsaturated polyester, phenol resin, polyamide, polyetheretherketone, etc., but are not limited thereto.
A thermosetting resin and a thermoplastic resin conventionally used as a matrix of the FRP member can be used.

The reinforcing fibers include, but are not limited to, glass fibers and aromatic polyamide fibers, and those conventionally used as reinforcing fibers can be used. The compounding ratio of the reinforcing fiber to the FRP member is
V / f is preferably 20 to 70%, particularly preferably 55 to 65%.

As a molding method for manufacturing the FRP member, first, a mixed fiber (yarn) containing a reinforcing fiber and an amorphous wire at a predetermined ratio is produced, woven, and then woven with an epoxy resin or the like. A method of impregnating with a resin and then heat-curing or radiation-curing can be used. The amorphous wires may not be woven in advance, but may be dispersed together in the FRP member during the impregnation of the resin.

The measurement of the magnetic permeability of the amorphous wire disposed in the FRP member as described above can be performed using a magnetic sensor.

As a magnetic sensor, the magnetic permeability of an amorphous wire disposed in an FRP member can be measured.
Any type of RP can be used as long as it has a sensitivity enough to detect the degree of fatigue of the RP.

As a magnetic sensor, for example, as shown in FIG. 1, a sensing coil 2 is installed in contact with both surface layers of the FRP member 1 or in a non-contact state, and a magnetic field formed at the time of measuring the magnetic permeability is closed. A magnetic sensor of the form:

In FIG. 1, U-shaped first and second ferrite cores 3a and 3b are fixed in cover members 6a and 6b, respectively. The first excitation coil 4a and the first detection coil 5a are separately wound around the first ferrite core 3a,
The second exciting coil 4b and the second detecting coil 5b are separately wound around the second ferrite core 3b. The first and second excitation coils 4a and 4b are connected to a high-frequency current power supply 7,
The first and second detection coils 5a and 5b are connected to a detector 8. When a high-frequency current is supplied from the high-frequency current power supply 7 to the first and second excitation coils 4a and 4b, magnetic lines of force indicated by dotted lines A penetrate the FRP member to form a closed magnetic path. As a result, the induced electromotive force is transmitted to the second detection coils 5a and 5a.
b, and this is measured by the detector 8 as mutual inductance (hereinafter referred to as inductance).

The inductance varies depending on the magnitude of the compressive stress of the amorphous wire disposed in the FRP member, and hence the magnitude of the magnetic permeability. Therefore, by measuring the inductance, the compressive stress of the amorphous wire disposed in the FRP member can be indirectly measured.

In terms of detection sensitivity, it is preferable to perform measurement using a closed-type sensor as shown in FIG. 1 rather than a pickup-type sensor described later.

As another magnetic sensor, for example, a commercially available pickup type sensor as shown in FIG. 2 can be used. This pickup type sensor has a planar excitation coil (not shown) and a planar detection coil (not shown).
And a lead wire 10.

When the sensing coil 9 is placed in contact with the surface layer of the FRP member or in a non-contact state, and a high-frequency current is supplied to the exciting coil, the sensing coil 9 passes through the FRP member as shown by the dotted line B in FIG. A magnetic field is formed, and the inductance is detected as in the case of the closed-type magnetic sensor described above.

Using this pickup type sensor,
Magnetic permeability can be easily measured even for an FRP member having a complicated shape.

As another magnetic sensor, as shown in FIG. 3, a sensor having a sensing coil 11 wound around the entire circumference of the FRP member may be used. This magnetic sensor has a sensing coil 11 composed of an excitation coil (not shown) and a detection coil (not shown) and a lead wire 12. Even if the sensing coil 11 is brought into contact with the entire circumference of the FRP member, it does not come into contact. May be installed.

When a high-frequency current is supplied to the exciting coil, F
A magnetic field is formed as shown by a magnetic field line indicated by a dotted line C in FIG. 3 that passes through the RP member, and the inductance is detected as in the case of the above two types of magnetic sensors.

When the magnetic permeability of the amorphous wire disposed in the FRP member is measured as described above, as the FRP member becomes fatigued, the compressive stress is gradually released, and the magnetic permeability changes. This can be detected, for example, as a change in the inductance of the amorphous wire as shown in FIG. Here, FIG. 6 is a graph showing an example of a change in inductance when a tensile stress is repeatedly applied to the FRP member. Depending on the type of reinforcing fiber, the direction in which the wires are arranged, and the location, the residual stress may remain as a tensile stress, which may be gradually released.

For example, if the FRP member breaks at the point E in FIG. 6, the inductance changes slowly in the initial stage of mild fatigue, but changes abruptly immediately before the breakage. Therefore, a level changed by, for example, 10% from the initial magnetic permeability is determined as a criterion for fatigue, and FR is determined.
The fatigue limit of the P member can be known in advance.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on specific embodiments. Example 1 From a glass fiber (diameter 8 μm) and a wire (diameter 30 μm) of an Fe-based amorphous alloy having a composition of 66.5 atomic% of Fe, 8.5 atomic% of Si, 12 atomic% of B, 11 atomic% of Co, and 2 atomic% of Cr, Mixed fibers were prepared so that the ratio (glass fiber / amorphous wire) became 14/1, and a mixed woven fabric (size 25 mm × 250 mm) was prepared from the obtained mixed fibers.

The obtained mixed woven fabric was impregnated with an epoxy resin. A plurality of the obtained prepreg woven fabrics are stacked and put in a mold. The prepreg woven fabric and the epoxy resin are arranged in the mold so as to have a volume ratio of 6: 4, and are molded and heated at 120 ° C. for 2 hours. And cured, FRP specimen (25mm × 250mm × 3mm)
I got

The above-mentioned mixed woven fabric was disposed near the surface layer in the FRP test piece, and the orientation of the fiber axis of each mixed fiber was the main stress direction. In this FRP test piece, the volume fraction (V / f) of the glass filament was 56%, and the V /
The f was 4% and the V / f of the epoxy resin was 40%.

As shown in FIG. 4, the obtained test piece 13 is set on a tensile tester 14 (5 ton hydraulic fatigue tester, manufactured by Sam Electronics Co., Ltd.), and the sensing coil 15 is set around the entire circumference of the test piece 13. Without gaps. As shown by D and D 'in FIG. 4, in the direction perpendicular to the test piece 13, a constant amplitude tensile stress (2) which changes in a sinusoidal shape (frequency: 20 Hz) as shown in FIG.
^{kg / mm 2 ~20kg / mm 2} ) was repeatedly applied and allowed to fatigue the FRP specimen 13. Then, the inductance was measured by the magnetic sensor having the sensing coil 15 and the detector 16 under the following measurement conditions. The measurement was performed every 10 ^N (N = 1, 2, 3,...) Times of stress cycle repetition. FIG. 6 shows the measurement results. Incidentally, the test piece was broken at a stress cycle repeated several 10 ⁷ times.

Measurement conditions Sensing coil 15: 200 turns around the circumference Basic inductance: 10 mH (millihenry)

As can be seen from FIG. 6, the inductance gradually increases as the number of stress cycle repetitions increases, but increases rapidly immediately before the breakage.

[0042]

As described above, according to the method of the present invention, F
By detecting a change in the magnetic permeability of the magnetic material disposed in the RP member with a magnetic sensor or the like, the fatigue failure of the FRP member can be easily known in advance. Further, according to the method of the present invention, since the FRP member is non-invasive, the quality of the FRP member does not deteriorate even if the detection is repeated. Further, since the measurement of the magnetic permeability can be performed without contacting the FRP member, the method of the present invention can be applied to an FRP member having a complicated shape.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a method for measuring magnetic permeability.

FIG. 2 is a schematic view showing another method of measuring magnetic permeability.

FIG. 3 is a schematic view showing still another method of measuring magnetic permeability.

FIG. 4 is a schematic view showing a method for measuring a magnetic permeability by applying a tensile stress to a test piece in Example 1.

FIG. 5 is a graph showing tensile stress conditions (magnitude and time) applied to a test piece in Example 1.

FIG. 6 is a graph showing the relationship between the number of stress cycle repetitions and the inductance in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... FRP member 2, 9, 11, 15 ... Sensing coil A, B, C ... Magnetic field line 3a, 3b ... Ferrite core 4a, 4b ... Exciting coil 5a, 5b ... Detection Coil 6a, 6b Cover member 7 High-frequency current power supply 8, 16 Detector 10, 12 Lead wire 13 FRP test piece 14 Tensile tester

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01N 3/00-3/62 G01N 17/00 G01N 27/72 JICST file (JOIS)

Claims (4)

(57) [Claims] 1. A fiber-reinforced plastic comprising a reinforcing fiber, a resin matrix, and a magnetic material having stress-magnetic characteristics.
(Hereinafter referred to as FRP) , and compresses the reinforcing fibers.
The FRP member is manufactured so that a force is applied, and by measuring the change in the magnetic permeability of the magnetic body disposed in the FRP member, the release of the compressive stress applied to the reinforcing fiber is measured .
A method for detecting fatigue fracture of an FRP member, wherein the degree is detected in advance and fatigue fracture is detected in advance. 2. Fatigue fracture inspection of an FRP member according to claim 1.
The change of the magnetic permeability of the magnetic body by applying a stress.
Fatigue fracture detection of FRP members characterized by constant measurement
How to get out. 3. The fatigue of the FRP member according to claim 1 or 2.
In the fracture detection method, a sharp change in the magnetic permeability of the magnetic material is performed.
Is defined as the fatigue limit of the FRP member.
A method for detecting fatigue fracture of an FRP member. 4. The method for detecting fatigue fracture of an FRP member according to claim 1, wherein the magnetic material is an amorphous wire.