JP4338823B2 - Damage control method for composite materials - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to composite materials and damage control methods for composite materials applied to next-generation aircraft structures, space equipment such as satellites and space stations, skyscrapers, public infrastructure, and high-speed vehicles.
[0002]
[Prior art]
Since the composite material applied to the structural material has a property that the inside of the material is easily damaged by an impact load, the design allowable value is set to about 1/4 of the original strength of the composite material. In order to raise this design tolerance, a material that suppresses damage is embedded in the composite material, and even when an impact load is applied to the composite material, safety is improved by detecting the load and damage at that time. Such composites are known.
[0003]
Japanese Patent Application Laid-Open No. Hei 6-2101818 describes a polymer-based composite functional material having a structure in which at least one shape memory alloy material having a reverse transformation end temperature or lower is arranged on the surface of the base material or in the base material. .
[0004]
Japanese Unexamined Patent Publication No. 7-48637 describes a metal matrix composite material having a structure in which at least one shape memory alloy material element that causes thermoelastic transformation is mixed or arranged in a base material.
[0005]
Japanese Patent Laid-Open No. 8-15208 discloses a change in current resistance of a thin line when a thin line of NiTi shape memory alloy is embedded in a composite material having a laminated structure and then a current is passed through the thin line to cause cracks or damage to the matrix material. A composite material damage detection system is described that detects.
[0006]
[Problems to be solved by the invention]
In the above-mentioned composite material, there is a possibility that a material having an effect of suppressing damage embedded in the composite material may become a foreign material of the composite material, and this may become a pseudo defect of the composite material and cause a decrease in strength of the composite material.
[0007]
In the above composite material damage detection system, it is premised that damage detection and damage suppression are performed with different materials, and shape memory alloy thin wires are used as materials, and shrinkage stress is uniformly generated on the shape memory alloy thin wires inserted into the composite material. This is intended to suppress transverse cracks, but this cannot cope with delamination that is likely to occur at the time of an impact load that reduces the design tolerance of the composite material.
[0008]
The present invention has been made in consideration of the above-described points. The composite material using the shape recovery function of the shape memory alloy foil as a damage suppressing function and the damaged portion of the composite material are accompanied by the shape change caused by heating the shape memory alloy foil. An object of the present invention is to provide a composite damage control method for repairing a damaged portion by applying a compressive force to the damaged portion of the composite material.
[0011]
[Means for Solving the Problems]
The damage control method for a composite material according to the present invention is a damage control method for a composite material for controlling damage to a damaged portion of the composite material, and the surface of at least two kinds of shape memory alloy foils having different strains at room temperature is provided on the surface. The shape memory alloy is roughened by treatment, and the at least two kinds of shape memory alloys roughened are alternately disposed between fiber reinforced resin layers to form a composite material, and the shape memory alloy corresponding to the damaged portion of the composite material Each of the foils is energized and heated, and the damage of the composite material is controlled by generating a compressive force or shear stress at the damaged portion of the composite material by a shape change caused by heating of the shape memory alloy foil. Features.
[0012]
In addition, a weak current can be passed through each shape memory alloy foil of the composite material to monitor the resistance change of the shape memory alloy foil, and the damaged portion of the composite material can be detected by the resistance change of the monitored shape memory alloy foil. .
[0013]
In the composite panel 1 of the present invention, the shape memory alloy foil 2 is disposed between the fiber reinforced resin layers 3 in a state where deformation is restrained at a temperature equal to or lower than the transformation point, and the shape memory alloy foil 2 is set to a temperature equal to or higher than the transformation point. By heating and changing the shape of the shape memory alloy foil 2, a shear stress is generated in each layer of the composite material to generate a stress that suppresses delamination.
[0014]
A composite panel 1 shown in FIG. 1 is formed from six fiber reinforced resin layers 3 and two types of shape memory alloy foils 2 having different strain magnitudes at room temperature. The fiber reinforced resin layer 3 located on the end side of the fiber is formed by laminating two carbon fiber reinforced resins 3a, and the fiber reinforced resin layer 3 located in the middle is laminated by three carbon fiber reinforced resins 3a. The two types of shape memory alloy foils 2 that are formed in the above and have different strain magnitudes at room temperature are alternately arranged between the fiber reinforced resin layers 3. The shape memory alloy foil 2 may have three or more types of room temperature at different strains, and each may be disposed between the fiber reinforced resin layers 3.
In addition, as for the said shape memory alloy foil 2, it is desirable to arrange | position in parallel so that the strip-shaped elongate piece may not mutually contact.
[0015]
Next, the manufacturing procedure of the composite material panel 1 will be described.
[0016]
First, both ends of each shape memory metal foil 2 are clamped by clip means 4 as shown in FIG. 3, and the clip means 4 and 4 are pulled in the direction of arrow A at room temperature, so that the shape memory alloy foil 2 has a temperature below the transformation point. Load distortion.
[0017]
Next, the shape memory alloy foil 2 loaded with strain is subjected to surface treatment to roughen the surface. As shown in FIG. 4, the surface treatment is performed by pickling treatment in which the shape memory alloy foil 2 is immersed in an acid treatment solution 6 such as nitric acid or hydrofluoric acid placed in a treatment layer 5 to form a rough surface 7. Done in This surface treatment can also be performed by a sputtering method or a sol-gel method in which a rough surface is formed by energy irradiation such as an electron beam. Since the shape memory alloy foil 2 has a transformation temperature of 60 to 70 ° C., it is necessary to take care that the shape memory alloy foil 2 does not exceed the transformation temperature when the surface treatment is performed.
[0018]
Next, the carbon fiber reinforced prepreg is pre-cut to a predetermined size, and the pre-cut prepreg 3a and the shape memory alloy foil 2 are laminated as shown in FIG. In this case, the shape memory alloy foil 2 loaded with strain is laminated such that the strain loaded state is maintained by strain holding means (not shown). In this case, high adhesive strength at the interface between the shape memory alloy foil 2 and the prepreg 3a can be obtained by chemically treating or physically roughing the shape memory alloy foil 2.
[0019]
The laminated structure of the prepreg 3a is arbitrary because it differs depending on the strength of the structure to be applied. However, the laminated structure of the prepreg shown in FIG. 5 is the shape memory alloy foil 2 for each 3PLY prepreg 3a centering on the shape memory alloy foil 2. A total of 16 PLYs are arranged and 2 PLY prepregs 3 a are arranged on both ends, and the shape memory alloy foil 2 is 5 PLYs in total.
[0020]
Specifically, if a laminate of a prepreg and a shape memory alloy foil has a crack growth allowable stress of 5 kgf / mm @ 2 on the structure, a shear stress that can suppress the stress is generated on the shape memory alloy foil. Be possible. In this case, a copper foil or the like capable of wiring to the shape memory alloy foil is also laminated and formed.
[0021]
Next, as shown in FIG. 6, the laminate of the prepreg and the shape memory alloy foil was cured for 90 minutes under the conditions of a temperature of 180 ° C., a vacuum pressure of 700 mmhg, and a pressure of 3.2 kgf / mm 2. The composite material panel 1 shown in FIG.
[0022]
Next, a damage control method for the composite material will be described.
[0023]
Since the shape memory alloy is a metal, the electric resistance value is arbitrarily determined by its cross-sectional area. For this reason, if a weak constant current is passed through the shape memory alloy in advance, for example, when a crack occurs inside the material, local distortion occurs in the shape memory alloy, and the electrical resistance of the shape memory alloy is caused by this distortion. Change. Therefore, if the output voltage is constantly monitored, damage inside the material can be detected by the change. By preliminarily examining and examining the change in voltage when damage occurs and storing the change in voltage in a computer, damage can be detected if there is an output equal to the damage.
[0024]
That is, the relationship between the strain and the electrical resistance of the shape memory alloy is as shown in FIG. 7, and the relationship between the electrical resistance and the damage of different types, positions and sizes such as transverse cracks and delamination generated in the composite material and the electrical resistance. By grasping the resistance distribution, it is possible to determine the type, position and size of damage occurring in the composite material.
[0025]
In addition, the type, position, and size of damage in the composite material can be observed as a 3D image.
[0026]
When delamination as shown in FIG. 8 occurs in the composite material panel 1, the stress applied to the fiber reinforced resin layer 3 or the stress balance due to stress concentration when the fiber reinforced resin layer 3 is damaged changes, A change in the stress balance is perceived as a distortion of the shape memory alloy foil 2 itself, and the change in the distortion becomes a change in electrical resistance due to a change in the shape of the shape memory alloy foil 2. Therefore, the damaged part of the composite panel 1 is detected by detecting which shape memory alloy foil of the plurality of shape memory alloy foils arranged in the composite material has changed.
[0027]
When the damaged part of the composite material panel 1 is detected, a current to the extent that the shape memory alloy foil 2 is heated is supplied to the shape memory alloy foil 2 corresponding to the damaged part of the composite material panel 1, and the shape memory alloy foil 2 Damage to the composite by suppressing the damage to the damaged part of the composite by applying compressive force or stress to the damaged part of the composite with the shape memory alloy foil whose temperature rises above the transformation temperature and changes shape by heating Control site damage.
[0028]
In the composite material panel shown in FIG. 8, the shape memory alloy foil 2 is arranged between the fiber reinforced resin layers 3 and 3, and these shape memory alloy foils 2 are given two kinds of strain. A relatively small strain is applied to the top shape memory alloy foil 2b, a relatively large strain is applied to the next shape memory alloy foil 2c, and a relatively small strain is applied to the lower shape memory alloy foil 2d. The lower shape memory alloy foil 2e is given a relatively large strain, and the lowermost shape memory alloy foil 2f is given a relatively small strain. When delamination occurs in the fiber reinforced resin layer 3e of this composite panel, the greatest change occurs in the electrical resistance values of the shape memory alloy foils 2e and 2d sandwiching the fiber reinforced resin layer 3e and other shape memory alloys. The electrical resistance value of the foil also changes. That is, depending on the degree of damage, the electrical resistance change between the shape memory alloy foils 2d and 2e becomes abrupt. At this time, in order to prevent the progress of delamination, the shape memory alloy foils 2d and 2e are energized. Since the shape memory alloy foil 2d is given a relatively small strain and a strain larger than that is given to the shape memory alloy foil 2e, the fiber reinforced resin 3e tends to be curved upwardly by the influence of the strain. Squeezed from the other layers that make up the panel. This action prevents delamination of the layers constituting the fiber reinforced resin layer 3e.
[0029]
【The invention's effect】
As described above, the composite material of the present invention uses the shape recovery function of the shape memory alloy foil as a damage suppression function by arranging the shape memory alloy foil that is distorted at room temperature between the fiber reinforced resin layers. By doing so, the damaged site can be repaired.
[0030]
The damage control method for a composite material according to the present invention monitors a change in resistance of a shape memory alloy foil provided with different strains at room temperature and disposed between the layers of the composite material. Detects the part, energizes the shape memory alloy foil corresponding to the detected damaged part of the composite material, and generates compressive force or shear stress by the shape memory alloy foil whose shape changes due to heating by applying current to the damaged part of the composite material The damage of the damaged part of the composite material can be controlled.
[Brief description of the drawings]
FIG. 1 is a perspective view of a composite material according to the present invention.
FIG. 2 is a diagram showing material characteristics of a shape memory alloy.
FIG. 3 is a view showing a stage of applying strain to the shape memory alloy foil at room temperature.
FIG. 4 is a view showing a surface treatment of a shape memory alloy foil.
FIG. 5 is a view showing a laminated structure of a fiber reinforced resin prepreg and a shape memory alloy.
6 is a diagram showing conditions for curing the laminate of FIG. 5;
FIG. 7 is a diagram showing the relationship between strain and electric resistance of a shape memory alloy foil.
FIG. 8 is a diagram illustrating a state in which delamination of the composite material is detected and controlled.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Composite material panel 2 Shape memory alloy foil 3 Fiber reinforced resin layer 3a Fiber reinforced resin prepreg

Claims (2)

A damage control method for a composite material for controlling damage of a damaged portion of the composite material,
Roughening the surface of at least two types of shape memory alloy foils with different strains at room temperature by surface treatment,
The at least two kinds of shape memory alloys roughened are alternately arranged between fiber reinforced resin layers to form a composite material,
Each of the shape memory alloy foils corresponding to the damaged portion of the composite material is heated by energization,
A damage control method for a composite material, comprising: controlling the damage of the damaged portion of the composite material by generating a compressive force or a shear stress in the damaged portion of the composite material by a shape change caused by heating of the shape memory alloy foil. By monitoring the resistance change of the shape memory alloy foil by passing a weak current through each shape memory alloy foil of the composite material,
The damage control method for a composite material according to claim 1 , wherein a damaged portion of the composite material is detected based on a resistance change of the monitored shape memory alloy foil.

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