JPS6212898Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a high-strength bolt with high tensile strength.

As shown in the front view in Figure 1, in structures and equipment that require high-strength bolt joints A, delayed fractures, residual cracks, and decreases in axial force of high-strength bolts 1 can be quantitatively detected. It is necessary to avoid breakage, but conventionally it has been difficult to detect it in advance.Therefore, there has been a strong desire to develop a high-strength bolt that can easily predict such breakage.

This invention provides a high-strength bolt that meets the above-mentioned needs.By applying a prestress axial force equivalent to the load during use, the bolt head is subjected to a predetermined compression on the head bearing surface. It is characterized by having a light-reflecting foil placed on the surface and a transparent coating covering the light-reflecting foil and bonding only the periphery to the periphery of the bolt head.

Next, the high-strength bolt of this invention will be explained by way of example with reference to the drawings.

FIG. 2 shows a partially cutaway front view of a first embodiment of the high-strength bolt 1' of this invention.

The high-strength bolt 1' of this invention applies a prestress axial force a corresponding to the load during use, as shown in an enlarged plan view in Fig. 3 and an enlarged longitudinal sectional front view in Fig. 4. With the head 1'A under a predetermined compression b, the light reflecting foil 2 shown in FIG. The coating 3, its peripheral edge 3
This is a product in which only A is adhered and integrated around the periphery of the bolt head 1'A with adhesive 4, and after waiting for complete fixation, the load is removed.

As the light reflecting foil 2, an aluminum foil or the like is suitable, and as the transparent film 3, an epoxy resin or the like having a transmittance of 5% or more is suitable.

A high-strength bolt 1'' of a second embodiment shown in a partially cutaway front view in FIG. 5 and in a plan view in FIG.
This embodiment differs from the first embodiment only in that the transparent coating is a transparent coating 3' having a small hole 5 of the required diameter in the center.

The high-strength bolt 1″ of this invention constructed in this way
When used with a designed axial force corresponding to the prestress axial force a applied, initial tensile prestrain (see FIG. 7) occurs in the transparent coating 3' on the surface of the bolt head 1''A.

When this tensile prestrain is seen through a polarizing film, as shown in Figure 6, the distortion causes concentric circles with the same color stripes 6, indicating that the bolt axial force changes due to some reason during use. When this occurs, a change in the number of stripes is observed compared to the initial tightening, and the amount of decrease in the axial force can be determined from FIG. Therefore, it is easy to determine when it is necessary to replace the bolts. FIG. 8 is a diagram showing changes in bolt head stress and bolt axial stress.

Further, the bolt 1' of the first embodiment shown in FIG.
When the head 1'A of the head 1'A is viewed through a polarizing film, a dark field L having a brightness corresponding to the tensile strain is observed, as shown in FIG. If the bolt axial force changes for some reason during use, the brightness of the dark field L changes, so based on the calibration diagram shown in Figure 7, the axial force can be easily adjusted from the change. You can know the decrease.

As is clear from the above description, the high-strength bolt of this invention has the excellent advantage that changes in axial force can be observed extremely easily on site simply by using a polarizing plate.

[Brief explanation of the drawing]

Fig. 1 is a front view showing an example of the use of a high-strength bolt, Fig. 2 is a partially cutaway front view showing the first embodiment of the high-strength bolt of this invention, and Fig. 3 is an enlarged plan view when prestressed. Figure 4 is the same, vertical front view, Figure 5
The figure is a partially cutaway front view of the second embodiment of the high-strength bolt of this invention, Figure 6 is a plan view of the second embodiment in use, Figure 7 is a calibration diagram, and Figure 8 is the bolt head. FIG. 9, which is a diagram showing changes in stress and axial force, is a plan view of the first embodiment in use. In the drawings, 1'...high-strength bolt of the first embodiment of this invention,
1″...High-strength bolt of the second embodiment of this invention,
1'A, 1''A... Bolt head, 2... Light reflecting foil, 3, 3'... Transparent coating, 4... Adhesive, 5...
...small hole, 6...stripe, L...dark field.

Claims (1)

[Scope of utility model registration request] By applying a prestress axial force equivalent to the load during use, the light reflecting foil placed on the bolt head surface and this light reflecting foil are A high-strength bolt with a transparent coating that is bonded only to the peripheral edge of the cover and integrated with the periphery of the bolt head.