JPS6317852Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial field of application This invention relates to fasteners for tightening materials such as bolts, nuts, screws, or clips, and is particularly applicable to fasteners that are applied with an external force exceeding the elastic limit after tightening. However, it is designed to return to its original tightened state after the external force is removed.

Prior Art Conventionally, when ordinary steel bolts 2 and nuts 3 are assembled and fastened to two fastening plates 1A and 1B as shown in Fig. 1, after fastening, as shown in Fig. 1A, the plates 1B When external force F is applied, it is a force that forces the bolt 2 to deform more than its elastic limit,
The bolt 2 is plastically deformed as shown in FIG. 1B, and after the external force is removed, permanent deformation remains in the bolt 2, and a gap δ is created between the plates 1A and 1B, which reduces the fastening ability of the bolt 2 and nut 3. In addition, the durability of the bolt 2 also decreases.

Purpose of the invention This invention aims to solve the above-mentioned problem. Even if an external force is applied after tightening that forces the amount of deformation to exceed the elastic limit, the original tightened state will be restored after the external force is removed. The purpose of this is to improve the tightening ability, ensure the safety associated with this, and improve the durability of the bolt.

Structure and operation of the invention In order to achieve the above-mentioned object, this invention has the following objectives: In a fastener consisting of a bolt and nut, the bolt or the nut, or both the bolt and the nut, or
Fasteners such as screws and clips are made of a shape memory alloy that has a very large amount of spring back, that is, pseudo-elastic force, and after tightening the material to be fastened, an external force exceeding the elastic limit of the fastener or With an external force above the pseudoelastic limit,
In addition, even if a gap is created between the bolts to be tightened due to the application of an external force that forces plastic deformation exceeding the elastic limit, the bolts should be tightened so that the plastic deformation is limited to a range that can be recovered by pseudo-elastic force. A portion is provided to restrict the movement of the attachment material, and after the external force is relieved, the attachment returns to its original tightened state due to pseudo-elastic force. Specifically, the fastener is formed from a shape memory alloy whose pseudo-elastic temperature range is set to include the temperature of the atmosphere in which the fastener is used, and after tightening, an external force is applied to exceed the yield point. The present invention provides a fastener characterized in that it is configured to return to the original tightened state after unloading when deformation strain is applied.

Embodiments Hereinafter, this invention will be explained in detail with reference to embodiments shown in the drawings.

As is well known, in shape memory alloys, up to a certain temperature above the transformation temperature, even if stress is applied to the parent phase (austenite phase) to a region outside of its elastic range, the stress generated at the time of application is simply removed. It has a property of recovering all the apparent deformation strain caused by stress-induced martensitic transformation, that is, it has a pseudoelastic property.

The present invention utilizes the above-mentioned characteristics of pseudoelasticity, and for example, the transformation temperature is set to below room temperature (approximately -10° to 20°C) so that the pseudoelastic temperature range includes the operating atmosphere temperature.
1, which was set so that the operating atmosphere temperature at room temperature (5°C to 35°C) falls within the pseudoelastic range (-10°C to 50°C).
A fastener is formed of a directional shape memory alloy or a bidirectional shape memory alloy, and in the embodiment shown in FIG. 2, a bolt 5 is formed.

As the shape memory alloy, a nickel-titanium type shape memory alloy or a copper type shape memory alloy is used, which has a long fatigue life, a large recovery stress, and good corrosion resistance.

In Figure 2, 6 is a nut made of normal material, 7,
8 is a plate to be tightened, and 7a and 8a are bolt mounting holes, respectively.

Using the bolt 5 made of a shape memory alloy whose transformation temperature is below room temperature and whose austenite phase (mother phase) is at room temperature, as shown in FIG. 8a to the bolt 5
Insert the bolt 5 that protrudes from the lower plate 7.
Screw the nut 6 onto the shaft portion 5a of the bolt head 5b.
The plates 7 and 8 to be tightened are tightened between the nut 6 and the nut 6.

A clamped plate 7 fastened by a clamping body (bolt 5) and a clamping body (nut 6) constituting a clamping tool,
When an external force is applied to the plate 8 to lower the plate 8, and the lower end of the stop portion formed by bending the plate 8 downward comes into contact with the base 9, as shown in FIG. 2B, the bolt 5 The extended shaft portion 5b
is deformed to become long and thin in diameter, and a gap δ is created between the plates 7 and 8. When the external force F described above is an external force that forces a deformation amount that exceeds the elastic limit, when the temperature at the time of loading the external force is above the transformation temperature and within the pseudoelastic range, the bolt 5
Following elastic deformation, deformation exceeding the yield point (elastic limit), that is, stress-induced martensitic transformation occurs, and the material deforms plastically into the shape B above. At this time, the engagement portions at the tips of the base 9 and the plate 8 to be tightened are positioned so that the amount of deformation strain ε does not exceed the limit that can be recovered by the pseudoelastic force of the bolt 5. When the amount of deformation strain ε is up to about 8% for nickel-titanium alloys and about 2% for copper-based alloys, permanent deformation due to slipping does not occur, and therefore, when the external force F is removed, the stress-induced marten・The deformation (strain) caused by the site transformation has completely recovered, and the bolt 5 returns to the shape shown in C, which is the same as in Figure 2 A. The gap δ between the plates 7 and 8 disappears, and the bolt 5 and nut 6 plates 7, 8
is concluded.

Incidentally, if the strain induced in the bolt 5 by the external force F is within the limit of recovery due to pseudoelasticity, it is not necessarily necessary to provide the stop portion or the base 9 on the plate 8.

Comparing the relationship between stress σ and strain ε in the above-mentioned shape memory alloy bolt and ordinary steel bolt, as shown in the diagram in Figure 3, the amount of strain ε is approximately 0.3.
% is the yield point, and the steel bolt shown by the solid line does not recover to its original shape when the strain ε exceeds approximately 0.3%, and breaks when the strain ε reaches approximately 30%, which is indicated by the x mark in the figure. On the other hand, with shape memory alloy bolts, permanent deformation does not occur until the yield point is exceeded and the strain amount ε reaches approximately 8%, and the shape is completely recovered when the load is removed, as shown by the dashed line in the figure. in this way,
Bolts made of shape memory alloys far exceed the elastic limit of normal steel bolts, and even if the amount of deformation occurs is approximately 20 to 25 times as much for Ni-Ti type bolts and approximately 7 times as much for Cu type bolts, the shape is completely maintained after unloading. The bolt does not lose its fastening ability, and the durability of the bolt is also improved.

In the above embodiment, the bolt is made of a shape memory alloy, but both the bolt and the nut may be made of a shape memory alloy. Furthermore, it is also applied to fasteners such as screws and clips that expand and absorb the load when an external force is applied. It may also be formed from a memory alloy.

Effects As is clear from the above explanation, the fastener according to this invention uses a shape memory alloy to form the fastener, sets the operating atmosphere temperature to be within the pseudoelastic range, and When the fastener is used to fasten the fastened material, if an external force is applied to the fastened material and the fastener is deformed, the fastener is deformed within the limit that can be recovered by pseudo-elastic force. Since the movement of the material to be fastened is regulated, the fastener returns to its original shape due to pseudo-elastic force after the external force is removed, and the fastening ability is completely maintained. Moreover, since the fastener itself completely recovers its shape, it has the effect of improving durability.

[Brief explanation of the drawing]

Figures 1A and B are sectional views showing a state of fastening using a conventional fastener, and Figures 2A, B, and C are sectional views of the fastener according to this invention. Cross-sectional view C when external force is applied is a cross-sectional view when external force is unloaded, and Figure 3 shows the stress of the conventional bolt and the bolt of this invention.
FIG. 3 is a diagram showing strain relationships. 5... Bolt, 6... Nut, 7, 8... Plate to be tightened.

Claims (1)

[Scope of Claim for Utility Model Registration] A fastener that is used by being inserted into a mounting hole drilled in a plate to be fastened, in which the bolt 5 constituting the fastener is made of a one-way or two-way shape memory alloy, and , insert the bolt 5 into the mounting hole of the plate to be tightened and tighten the nut 6.
In order to stop the deformation of the bolt 5 caused by an external force after the bolt 5 is screwed into the plate and fastened, the movement of the plate to be tightened is stopped so that it does not exceed the range that can be recovered by pseudoelasticity. A fastener characterized in that the bolt 5 returns to its original tightened state due to the pseudoelasticity of the bolt 5 after the load is removed.