JP2003335876A - Composite material having shape-memory alloy embedded therein - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease the number of materials by making a distortion censer serve also as an actuator. <P>SOLUTION: A previously distorted shape-memory alloy (SMA) wire embedded in a matrix material of a composite material detects deformation or distortion of the composite material, and restrains and restores damages of the composite material by its contracting and restoring power (actuator functions). A processor detects an electric resistance of the SMA wire by a resistance detecting circuit, calculates the changes in the resistance caused by distortion by a processor (CPU), and generates restoring power for the SMA wire to self-restrain and self-restore the composite material. The SMA wire embedded in the composite material is utilized not only as the actuator for restraining and restoring damages but also as a censor for detecting distortion, deformation and damages. Thus, the number of materials used for the composite material can be decreased. The temperature compensation of the resistance of the SMA wire can be made by providing another SMA wire in an unloaded state to measure the resistance of the SMA wire. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to deformation of a composite material,
Smart materials (smart materials, intelligent materials) that have self-sensing and self-repairing functions by self-detecting strain and damage
In particular, the present invention relates to an intelligent material that uses a shape memory alloy that has self-detection, self-suppression, and self-repairing functions as the material itself that constitutes the composite material.

[0002]

2. Description of the Related Art Optical fibers are widely used to detect deformation, strain, and damage (sensor function) inside structural materials and structures (Akiyoshi Shimada et al.,
"Optical fiber sensor hull damage detection system", The Institute of Electronics, Information and Communication Engineers, Volume 7-10, (November 1999);
Attack, "Fatigue crack monitoring of super hybrid materials by embedded optical fiber", Materials, Vol. 48, No. 4, 403
~ 409 (1999); Shintaro Kitade et al., "Impact damage detection test of FRP laminated plate using optical fiber", Material, 44th
Volume 504, pp. 1196-1200 (1995)).

However, the cost of assembling the optical fiber and the cost of the sensing system are high. Further, the optical fiber itself is easily damaged, and the optical fiber may be damaged inside the material. In this case, the deformation, strain,
Damage detection becomes impossible. Further, a strain gauge may be attached to the surface of the structure to detect strain, and thus deformation, strain, or damage may be detected. However, with this method, only the local state near the strain gauge can be detected, and strain cannot be detected over the entire material. Further, the strain gauge has a problem in its durability.
Furthermore, these were only damage detection functions (sensor functions).

On the other hand, a shape memory alloy (SMA, Shape Memory Alloy) embedded in a material is used as a means for suppressing and repairing the deformation, strain, and damage in the structural material and structure.
Is used. This utilizes the restoring force function (actuator function) to the memory shape due to the phase transformation of the shape memory alloy, and suppresses and repairs the material damage.

The material of the above-mentioned sensor and actuator is 2
Deformation, strain, etc. in materials such as structures that combine two or more
An intelligent material is manufactured by embedding a sensor such as an optical fiber having a damage detection function and an SMA wire having a material deformation, strain, damage suppression, and repair function.

[0006]

However, it is not preferable to add a large number of different materials to the composite material, since this leads to deterioration of the constituent materials and the overall structure. Therefore, it is necessary to reduce the number of composite materials as much as possible.

[0007]

In order to solve the above problems, the present invention provides a shape memory alloy wire embedded in a base material of a composite material, which has a function of detecting deformation, strain, and damage, and suppressing the deformation.
Provided is a smart composite material (intelligent composite material) including a member having two functions of restoration at the same time.

The present inventors have found that S due to additional stress and load.
It was found that the strain of MA has a predetermined relationship with its electric resistance value. The deformation and strain of the composite material are detected by detecting the change in the electrical resistance value of the SMA embedded in the composite material. Further, since the deformation and strain of the composite material are related to the degree of damage, By detecting the change in electrical resistance, the damage state can be detected.

According to the present invention, the resistance detecting circuit detects the electric resistance value of the pre-strained SMA wire embedded in the base material of the composite material, and the processor calculates the change in the resistance value due to the strain. Provided is a composite material which is capable of detecting strain and further suppressing and repairing damage of the composite material by the contraction restoring force (actuator function) of the SMA wire whose energization and heating are controlled by a processor.

Further, according to the present invention, a second shape memory alloy wire for temperature compensation is provided in the vicinity of the shape memory alloy wire in an unloaded state against stress, and the shape memory alloy wire and the second shape memory alloy wire are provided. Provided is a shape memory alloy-embedded composite material capable of temperature-compensating and detecting the resistance value of a shape memory alloy wire by connecting and to a resistance detection circuit.

In the present invention, SMA embedded in a composite material
Not only is it used as an actuator to control and repair damage to wires, but it is also used as a sensor to detect strain, deformation, and damage. Thereby, the number of materials used for the composite material can be reduced. Further, a processor can be provided to realize a composite material having self-sensing, self-suppressing, and self-repairing functions.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention can be applied to various types of composite materials / structures that require reliability. Here, carbon fiber reinforcement (CFRP, Carbon Fiber Reinforced Plas), which is widely expected to be put to practical use in various fields including the space and aviation fields as a base material for composite materials and structures
stics) will be described as an example.

FIG. 1 shows an embodiment of a composite material having self-sensing, self-suppressing and self-repairing functions according to the present invention. In the figure, 1 is an SMA wire embedded CFRP composite material piece, 2 is a CFRP material layer of a composite material base material, 3 is an SMA wire, 4 is a lead wire, 5 is a current control circuit, 6 is a DC power supply, and 7 is a resistance detection circuit. , 8 are CPUs that calculate resistance value changes and control the output current of the current control circuit 5, and 9 is a control circuit. Control circuit 9
May be integrally formed with the CFRP composite material.

The example of FIG. 1 shows Ti-N in CFRP composite material pieces.
An example of an SMA-embedded CFRP composite material piece in which an i-based SMA wire is embedded to provide damage suppression and damage repair functions is shown. Diameter of Ti-Ni system (50.5% atomic Ni) for SMA wire
A 0.4 mm wire with a width of 50 mm and a thickness of 0.2 mm as the base material CFR
P prepreg was used. Prior to embedding the SMA wire 3 in the CFRP composite material, the SMA wire is subjected to a tensile load in a tensile tester to provide a prestrain of about 3% (sometimes 0.5-7%). 6 layers of CFRP prepreg (The laminated structure is [0 _{1
/ 90 4/0 1])} 1mm the SMA wire 3 to the middle part of (1 to 4 mm
The molded laminate is molded and laminated by sandwiching the gap (may be a space). The CFRP molded laminate in which the SMA wire is embedded is heated and pressed under the conditions of 180 ° C., 0.3 MPa and 2 hours by a hot press machine so that the SMA wire embedded CFR is obtained.
A P-composite material was manufactured and cut into pieces of composite material with a width of 10 mm.

The SMA wire 3 in the composite material piece is heated by applying a current of 0.5 to 5 A controlled by the current control circuit 5 from the DC power source 6 to the SMA wire 3 (S
MA energization heating) A contraction restoring force is generated and the composite material contracts. FIG. 2 shows that after the tensile stress is applied to the composite material to give the damage defect and the residual strain generated inside the laminated plate, S of FIG.
The SMA wire 3 of the CFRP composite material 1 in which the MA wire is embedded, is heated in the composite material by heating with an electric current.
An example of evaluation of recovery force by MA wire is shown. The vertical axis represents the strain ΔL / L of the composite material, and the horizontal axis represents the temperature of the composite material. Here, L represents the original length of the composite material, and ΔL represents its displacement.

In FIG. 2, 0%, 1%, 3% and 5% represent the prestrain applied to the SMA wire. In a composite material piece (0% prestrain) which was not prestrained, the strain generated by electric heating showed a tendency of expansion. It is considered that this is because there is no pre-strain, so that the SMA does not generate shrinkage restoring force, and it is due to the thermal expansion of the resin.

On the other hand, in the case of the prestrained composite material piece, the compression strain increases as the temperature rises, and this tendency becomes more remarkable as the prestrain increases. From this, it is understood that by applying the pre-strain, the function as the actuator works, and the contracting force for suppressing and repairing the damage of the base material is obtained.

FIG. 3 shows the relationship between the rate of change in electrical resistance of the SMA wire and the strain of the composite material when a strain is applied to the composite material (CFRP layer + SMA wire) while applying a tensile load. In the figure, the vertical axis represents the electrical resistance change rate ΔR / R of the SMA wire, and the horizontal axis represents the strain. Where R is before deformation of the composite material (when there is no strain in the composite base material)
The electric resistance value of the SMA wire, ΔR, represents the amount of change in the electric resistance value of the SMA wire when strain or deformation occurs.

As shown in FIG. 3, it can be seen that the electric resistance value of the SMA wire tends to increase with the strain of the composite material. On the other hand, as the strain of the base metal increases,
Transverse cracks that occur inside the material
se crack, the number of cracks in the composite material piece without fiber breakage) increases. From these, embedded
It is considered that the increase in the electrical resistance of the SMA wire corresponds to the increase in the number of transverse cracks generated inside the material, that is, the increase in damage. Therefore, the embedded S
Deformation, strain and damage can be detected by detecting changes in the electrical resistance of the MA wire.
Wires can be used as sensors.

FIG. 4 shows the relationship between the damage degree of CFRP (the number of transverse cracks generated in the composite material piece) and the strain. At this time, the number of transverse cracks was measured using an optical microscope. Generally, as shown in FIG. 4, the damage degree of CFRP is related to strain, and the number of transverse cracks is rapidly increased above a certain strain, which leads to the destruction (fatal failure) of the entire composite material. .

In order to prevent a fatal material failure, it is necessary to detect the CFRP before it develops throughout the composite material and to detect CFRP.
It is necessary to suppress the strain of the material below a certain value (threshold value). Explaining with the characteristic example of FIG. 4, for example, the strain is
When it becomes 1.5% or more, that is, when the electric resistance change of the SMA wire of FIG. 3 becomes about 7% or more, the SMA wire is electrically heated to give a contraction restoring force to the SMA wire.
Provides shrinkage force to the CFRP composite. This gives C
The effect of suppressing and repairing damage of the FRP composite material is exhibited.

Therefore, in order to suppress the destruction of the entire composite material, the electrical resistance change of the embedded SMA wire is measured, and when it becomes a certain threshold value or more (about 7% or more in this case), the SMA current heating is performed. Material damage can be suppressed. Further, the processor can calculate the change in electric resistance value of the SMA wire and diagnose the deformation / strain / damage state of the composite material.

The embodiment of FIG. 1 of the present invention is a piece of composite material containing a device using the above principles. When a tensile load in the direction of the arrow in the figure is applied to the composite material piece 1, S
The MA wire 3 is also strained and deformed. The resistance detection circuit 7 includes a multimeter, a bridge circuit having one branch of an SMA wire, and a measurement power supply, and S
The resistance R of the MA wire 3 is measured.

The processor (CPU) 8 takes in the measured resistance value from the resistance detection circuit 7 at every predetermined sampling time, and the resistance value greatly changes compared to before the breakage of the composite material (in the examples of FIGS. 3 and 4, about 7% change), the resistance detection circuit 7 is disconnected from the lead wire 4, and the current control circuit 5 causes the SM
A predetermined current is applied to the A wire 3 to heat the SMA wire 3. The SMA wire heated by electric current generates a contracting force in the direction of the arrow in the figure, contracts the strain and deformation of the composite material, and suppresses and restores the strain and deformation of the composite material.

When the heating time for obtaining a sufficient contracting force has elapsed, the heating current supplied from the current control circuit 5 is cut off. At the same time, the resistance detection circuit 7 is again connected to the lead wire 4,
The resistance detection of the SMA wire is restarted, the next strain detection,
Prepare for repair control. In this way, the contraction force of the SMA wire is controlled so that the tensile strain on the composite material becomes equal to or less than the predetermined value. Although the resistance value of the SMA wire fluctuates due to the prestrain and the temperature rise of the base material due to the heating by energization, since the strain state is detected by the resistance value change rate in the present invention, this resistance value fluctuation is small enough to be ignored. Become. If it cannot be ignored, it may be calibrated by the resistance value change rate calculation of the processor (CPU).

In the case of CFRP composite material, damage is considered to be microscopic (transverse crack) or macroscopic. FIG. 5 shows the result of the transverse crack generated inside the composite material piece due to the tensile load being repaired by the damage repairing function of the present invention. At this time, the pre-strain of the embedded SMA wire is 3%. Figure 5
(A) shows a state in which a transverse crack has occurred due to a tensile load in the direction of the arrow. A temperature above the reverse transformation temperature (A _f = 52.3 ° C) by self-detecting the damage state and heating the SMA wire embedded in the composite material by applying electricity.
Heated to 80 ° C. At this time, the prestrained SMA wire undergoes a phase transformation from the martensite phase to the austenite phase, and a shrinkage restoring force is generated in the SMA wire. Figure 5 (b)
Shows the state of the repaired composite material piece due to shrinkage of the entire composite material piece in the direction of closing the transverse crack.

FIG. 6 shows a damage repair result of a composite material piece when a large damage occurs due to a tensile load or the like. Figure 6
From this, it was confirmed that the SMA wire-embedded composite material of the present invention can repair damage to the composite material larger than the transverse crack. From this, CFRP
It can be seen that the transverse cracks and large cracks that have occurred can be repaired by using the SMA wire embedded in the substrate as an actuator.

From these results, it has been confirmed that deformation, strain,
The embedded SMA wire that has been used as an actuator for damage suppression and repair functions can now be used as a sensor for deformation, strain, and damage detection. As a result, only one type of material (SMA wire) is embedded in the base material to detect and suppress deformation, strain and damage.
We have realized the production of composite materials with a restoration function at the same time. In addition, the processor (CPU) realizes an intelligent composite material that can diagnose deformation, strain, and damage of the composite material based on the change in the electric resistance value of the SMA wire, and suppress and repair the deformation, strain, and damage according to the result. . (See Figure 6).

FIG. 7 is another embodiment of the present invention, which is different from the embodiment of FIG. 1 in that the strain state can be detected and the damage can be suppressed and repaired with respect to the strain applied in two directions of the composite material. The difference is that it is a composite material piece. A large surface composite material can be manufactured by combining and bonding a plurality of composite materials. The principle of suppressing and repairing damage generated in the composite material is the same as that of the embodiment shown in FIG.

7, 11A is a composite material piece corresponding to the composite material piece of FIG. 1 for detecting strain in the lateral direction, suppressing damage, and repairing damage, and 11B is for the vertical strain of FIG.
It represents a composite material piece capable of detecting strain, suppressing damage, and repairing them, and one composite material piece 11 is constituted by both. 3A1 and 3B1 are SMA wires, 4A1 and 4B1
Is a conducting wire for supplying a current for electrically heating the SMA wire, and 51A and 51B are constant current control circuits.

Further, in the figure, 12A and 13A, 12
B and 13B, 12 and 13, 42A and 43
A, 42B and 43B, 52A and 53A, 52B
And 53B, the composite material piece 11A or 11B, the composite material piece 11 composed of both, and the conductive wire 4 respectively.
1A or 41B, current control circuit 51A or 51
The same as B.

71 is SMA wire 31A, 31B, 32
A resistance detection circuit that measures resistances of A, 32B, 33A, and 33B, and 81 represents a processor (CPU). The resistance detection circuit 71 includes a multimeter and a bridge circuit having one branch of an SMA wire and a power source for measurement, and the lead wires 41A, 41B, 42A, 42B, 43A, 4 are provided at each measurement sample time.
4B is switched at the measurement sample time, and the resistance values R1A, R1B, ... R3A, R3BR of each SMA wire are measured.

When the resistance detection circuit 71 detects an SMA wire whose rate of change in the resistance value of the SMA wire becomes a predetermined value, the SMA wire is electrically heated. Electrically heated SMA
The wire generates a contracting force, contracts the strain and deformation of the composite material piece, and suppresses and repairs the strain and deformation of the composite material.

However, the resistance value of the SMA wire changes not only with the strain but also with the temperature as in the case of general metals, so it is necessary to eliminate the influence of the temperature. Further, since the SMA wire has a phase transformation, the resistance change with temperature is complicated. FIG. 8 shows an example of measuring the temperature dependence of the electrical resistance value of the SMA wire. In the differential scanning calorimetric curve (arbitrary unit) in the lower part of the figure, the SMA wire undergoes a phase transformation at a rapidly changing temperature around 30 ° C and 60 ° C (phase transformation temperature). Is shown. It can be seen that at the phase transformation temperature, the electric resistance value of the upper portion changes abruptly. In other temperature zones, it is a simple increase as in general metals. So SM
In order to detect only the resistance change due to strain / deformation of the A wire, it is necessary to remove the change in resistance value with respect to the temperature change of the SMA wire.

Therefore, the temperature dependence is removed by using another SMA wire (reference wire) which is not affected by strain. When there is no temperature compensation, the electric resistance change (ΔR / R) is calculated by the following equation (1).
In the formula (1), Rs is an electric resistance value of the SMA wire and depends on strain, and Rs0 is an initial resistance value and represents a constant for normalization.

[0036]

[Equation 1]

In order to remove the temperature dependence in this,
Normalize by the electric resistance value Rr of the reference wire.
That is, it is calculated by the following equation (2). Where Rr0
Represents the initial resistance of the reference wire. This can eliminate the temperature dependence.

[0038]

[Equation 2]

FIG. 9 shows another embodiment of the shape memory alloy-embedded composite material of FIG. The configuration different from the embodiment of FIG. 1 is that the reference wire 3 installed in an unloaded state
The point is that conductors 4A and 4B connected to the resistance detection circuit 7 for measuring the resistance values of R and the reference wire are newly provided. Two reference wires 3R, 3R
Are connected at the hidden end by the CFRP layer in the figure.
The reference wire 3R is installed near the SMA wire 3 in such a position as to be in an unloaded state, and is brought into a temperature state corresponding to the temperature of the SMA wire 3.

When the reference wire 3R is installed in the peripheral portion or the corner portion of the composite material block, the influence of the stress applied to the reference wire 3R when measuring the resistance is small, and the influence is ignored in the actual energization control. Yes, it works as if a substantially unloaded condition was maintained. Further, by providing a through hole in the composite material block and installing the reference wire 3R therein, the reference wire 3R can be put into a substantially unloaded state.

SMA wire 3, reference wire 3
The resistance value of R is measured by the multimeter of the resistance detection circuit 7 together with the initial resistance values Rs0 and Rr0, and the value is recorded in the memory in the processor (CPU) 8. The processor (CPU) 8 calculates the temperature-compensated electric resistance value change ΔR / R by the equation (2). The strain ΔL / L of the SMA wire is accurately obtained based on this electric resistance change ΔR / R, and detection and control are performed by the same method as in the embodiment of FIG. Of course, it can be applied to the embodiment of FIG.

FIG. 10 shows the results of temperature compensation using the reference wire 3R in two environments of 26 ° C. and 3 ° C. In the figure, the lower two lines are examples of measurement of the change in electrical resistance ΔR / R and the strain ΔL / L of the SMA wire when temperature compensation is not performed and when the upper two lines are temperature compensated. By performing temperature compensation, it is possible to suppress the temperature dependence (parallel movement to the vertical axis). In the example of the figure, the temperature compensation is not perfect, but the error is about 0.004% / ° C., which is sufficient for practical use.

[0043]

By embedding only one type of shape memory alloy wire in a structure and using it as a sensor and an actuator, a composite material having deformation, strain, damage detection, suppression, and repair functions at the same time becomes possible. . This has made it possible to simplify the structure using smart composite materials and reduce costs. In addition, reliability and safety of various structures can be improved and life of the structures can be extended. Furthermore, by providing a shape memory alloy wire in the unloaded state in the immediate vicinity of the shape memory alloy wire and measuring the resistance value, temperature compensation of the resistance value of the SMA wire is performed, and detection, suppression of deformation, strain, damage is performed. ， The repair function can be performed accurately.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a composite material having self-detection, self-suppression, and self-repairing functions of strain, deformation, and damage of the present invention.

FIG. 2 is a diagram showing an example of evaluation of recovery force by an SMA wire generated by heating a composite SMA wire by applying electricity.

[Fig. 3] Composite material (CFRP layer +
It is a figure which shows the relationship between the strain of an SMA wire and the strain of a composite material at the time of giving strain to a SMA wire.

FIG. 4 is a diagram showing a relationship between a damage degree of a CFRP composite material piece (the number of transverse cracks generated in the composite material piece) and strain.

5A and 5B are diagrams showing repair of a transversal crack that has occurred according to the present invention, wherein FIG. 5A is a diagram showing a transversal crack occurring in a composite material, and FIG. 5B is a diagram showing a result of transversal crack healing. .

6A and 6B are diagrams showing repair of a larger damage caused by the present invention, wherein FIG. 6A shows the occurrence of larger damage and FIG. 6B shows the result of repairing the damage.

FIG. 7 is a diagram showing another embodiment of the present invention.

FIG. 8 is an example showing the temperature dependence of the electrical resistance value of an SMA wire.

FIG. 9 is a diagram showing another embodiment of the present invention.

10 is a diagram illustrating an example of temperature compensation of the embodiment of FIG.

[Explanation of symbols]

1,11A, 11B, 11 Composite material pieces 2 CFRP layer 3,31A, 31B SMA wire 3R reference wire 4,41A, 41B Conductor 5,51A, 51B Current control circuit 6 DC power supply 7,71 Resistance detection circuit 8,81 Processor (CPU)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideki Nagai             1-1-1 Higashi 1-1-1 Tsukuba City, Ibaraki Prefecture             Inside the Tsukuba center (72) Inventor Teruo Kishi             1-1-1 East, Tsukuba City, Ibaraki Prefecture             AIST Tsukuba Center F term (reference) 2F063 AA25 BA17 CA29 DA05 DA22                       DC08 EC05 FA12 LA27                 4F072 AA01 AA06 AB10 AG03 AG17                       AK05 AK14 AL02 AL09

Claims (4)

[Claims] 1. A base material, a shape memory alloy wire embedded in the base material, a resistance detection circuit for detecting a change in electric resistance value of the shape memory alloy wire, and a shape when the change in electric resistance value of the shape memory alloy wire reaches a predetermined value. A composite material having a current control circuit for passing a predetermined current through a memory alloy wire, which detects strain, deformation amount, and damage of the composite material by a change in electric resistance of the shape memory alloy wire, and by the restoring force of the shape memory alloy wire. A shape memory alloy-embedded composite material characterized by being suppressed and repaired by the composite material itself. 2. The base material of the composite material is a reinforcing material such as fiber, and self-suppresses and repairs cracks and macroscopic damage that occur in the composite material without breaking the reinforcing material such as fiber. The shape memory alloy embedded composite material according to claim 1. 3. A resistance detection circuit for detecting the electric resistance value of the shape memory alloy wire and a change in the resistance value based on the measured resistance value of the resistance detection circuit, and controlling the restoring force of the shape memory alloy wire. The deformation of the composite material,
The shape memory alloy-embedded composite material according to claim 1 or 2, further comprising a processor that self-controls strain and damage and repairs itself. 4. A second shape memory alloy wire for temperature compensation is provided in the vicinity of the shape memory alloy wire in an unloaded state against stress, and the shape memory alloy wire and the second shape memory alloy wire are subjected to resistance detection. The shape memory alloy embedded composite material according to any one of claims 1 to 3, wherein the resistance value of the shape memory alloy wire can be detected by temperature compensation by being connected to a circuit.