JPS6223810B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a material testing jig. More specifically, the present invention relates to a jig for fatigue testing of brittle materials.

Fatigue test jigs conventionally used in tensile-compression fatigue testing machines are often used for ductile materials such as metals, and the jigs used there are often brittle due to the high strength and ductility of metal test pieces. It does not consider strict homogeneous tightening and stress concentration for the material. Currently, the jigs used in fatigue testing machines for brittle materials are the same as those for metal fatigue testing, as shown in Figure 1. Due to its low strength and brittleness, it has often suffered breakage due to bending forces resulting from non-uniform tightening, or crack failure due to stress concentration at the shoulders or threads of the gripping portion of conventional test specimens.

An object of the present invention is to enable a prescribed fatigue test to be performed on material specimens having low strength and brittleness without causing damage due to non-uniform clamping, stress concentration, etc.

In other words, there are two typical types of conventional fatigue test jigs: a shouldered test piece type and a threaded test piece type, as shown in Figure 1 a and b, respectively. Insert the shouldered test piece into the hole of the mounting flange as shown in Figure 1a, press the stepped part of the shoulder of the grip with a two-split push tool, and press the push tool while turning the cap nut. Fix the specimen through the The disadvantage of this type is that when a brittle material specimen is attached, stress concentration due to the step at the shoulder of the grip can cause cracking and failure. In other words, the degree of stress concentration, when described using the symbols shown in FIG. 1, increases as D/d increases and r/d decreases. That is, once D/d is determined, the stress concentration becomes smaller as r becomes larger. However, in that case, the contact area between the pusher and the test piece becomes smaller and the surface pressure increases. In order to solve these drawbacks, it is necessary to increase d to reduce the stress generated at the stress concentration portion, and to increase the contact area of the shoulder portion to obtain an appropriate surface pressure. However, such a test piece has a much larger grip part,
Another drawback is that the jig becomes larger. In addition, due to machining errors in the shoulder of the test piece or the pushing tool, the tightening surface pressure may not be uniform over the entire pressure-receiving area of the shoulder of the test piece, resulting in uneven tightening. This phenomenon causes bending stress on the test piece. This may cause breakage during testing. The above are the drawbacks of the shouldered test piece type. Next, the disadvantages of the screw-in test piece type are as follows. Since this test piece has a threaded portion, stress concentration occurs in the root diameter portion of the thread. In particular, when a lock nut is tightened, the tightening stress of the lock nut is added to the threaded part in addition to the stress during the test, so the stress generated in the threaded part becomes quite large, causing cracking and failure during the test. To solve this problem, the threaded portion should be made larger than the effective diameter of the test piece in order to reduce the stress generated in the threaded portion. However, these test pieces have a disadvantage in that the screw portion is quite large, making it uneconomical in terms of material removal when preparing the test piece.

The object of the present invention is to provide a material testing jig that does not have these drawbacks. As shown in FIG. 2, the structure of the material testing jig of the present invention is as follows: First, a pushing tool 2, which is divided into two or more parts, is attached to the tapered part of a material test piece 1. Then,
The outer periphery of the pusher 2 and the hole of the holding box 3 fit together, and when the holding box 3 is attached to the base plate 7 of the testing machine using the bolts 4 and disc spring washers 5, the test piece 1 is attached to the bolts. 4, it is fixed in close contact with the tapered part of the base plate and the pusher 2. Also the third
The figure is a cross-sectional view when FIG. 2 is viewed in the direction A to A, and FIG. 4 is a detailed view of the pusher 2. Moreover, FIG. 5 shows a material test piece.

Such a structure has the following effects. First of all, since the gripping part of the test piece is tapered, the contact area with the push tool 2 is large, and the shape is difficult to cause stress concentration, so the test piece is prevented from cracking and breaking.
Next, when the test piece 1 is attached, the contact pressure between the test piece 1 and the base and the contact pressure between the test piece 1 and the pusher 2 are determined by the amount of displacement of the disc spring washer 5.
By tightening the bolt 4 so that the amount of displacement is maintained between A and B in FIG. 6, the compressive load can be kept approximately constant. That is, both of the above contact pressures are maintained at pressures between A and B.
Now, when a tensile load is applied in the vertical direction to apply a tensile stress to the test piece 1, the disc spring washer 5 is deformed through the pusher 2, the holding box 3, and the bolt 4. If the pusher 2 is made of a material with a high Young's modulus that is hard and difficult to deform, when a tensile load is applied to the test piece 1, only a small amount of deformation will be transmitted to the disc spring washer 5. In the case of a material with a small modulus, when a tensile load is applied to the test piece 1, the pusher 2
is greatly deformed, and it is possible to maintain uniform contact with the entire surface of the tapered portion of the test piece 1. Considering the amount of deformation transmitted from the test piece 1 to the bolt 4, it is better to use the push tool 2 made of a material with a small Young's modulus than with the push tool 2 made of a material with a large Young's modulus. You can see that it's big. Although this large amount of deformation cannot be absorbed by a normal spring washer, it can be sufficiently absorbed by using one disc spring washer 5 or a combination of several disc spring washers 5. If the relationship between load and deformation of the disc spring washer 5 as a whole is between A and B in FIG. 6 even at the load of the above-mentioned tensile test, there is still some compressive load between the base plate and the test piece 1. Even if a compressive load is applied and then a compressive load is applied, the test can be carried out smoothly without creating an unnecessary gap between the base plate and the test piece 1. When a compressive load is applied to the test piece 1, the test piece 1 is pressed against the base plate, and the contact pressure between the two increases, but on the other hand, the test piece 1 and the pusher 2
The contact pressure between the two appears to be decreasing. However, the deformation of the tapered part of the test piece 1 can be absorbed by the disc spring washer 5 through the pushing tool 2, restraint box 3, and bolt 4. If the washer 5 is used, the contact pressure between the test piece 1 and the pusher 2 actually hardly changes, as can be seen from FIG. Next, when a tensile load and a compressive load are repeatedly applied to the test piece 1 and a fatigue test is performed on the test piece 1, the advantages of this jig are more clearly exhibited. That is, tensile −
As the number of repetitions of the compressive load increases, the tapered part of the test specimen 1 and the contact part with the base plate deform, and the push tool 2
deformation, and deformation of other connected objects up to the disc spring washer 5 will increase. Among these deformations, the deformation of the pusher 2 makes the contact with the test piece 1 uniform, and during the tensile test, it is difficult to apply an eccentric load such as a bending load to the test piece 1, which has the advantage of preventing bending and breakage. . However, if a spring washer or the like is used in place of the disc spring washer 5, the spring washer will not be able to absorb the above-mentioned overall deformation, and a gap will be created between the base plate and the test piece 1 at the time of maximum tensile load. This advantage will disappear.

In this way, by using the pusher 2 made of a ductile material on the brittle material test piece 1, uniform contact can be obtained between the test piece 1 and the pusher 2, and the resulting deformation can be prevented by the disc spring washer 5. The contact pressure between the test piece 1 and the base plate is not zero and the contact pressure between the test piece 1 and the pusher 2 is almost constant during a repeated fatigue test of tensile and compressive loads. The fatigue test can be carried out smoothly because the temperature is maintained at a constant value and there is almost no change. Finally, adjustment plate 6
Since the gap between the holding box 3 and the base plate is distorted due to processing errors of the test piece 1, an appropriate gap is maintained by combining several adjustment plates 6 of different thicknesses. This gap is necessary when tightening the restraint box 3 with the bolt 4.

This fatigue test jig can be applied not only to test pieces of brittle materials but also to test pieces of metal materials. Further, the pusher 2 may be divided into any number of parts, and the material may be metal, synthetic resin, hard rubber, etc. depending on the test piece and test conditions. Further, several disc spring washers may be used in the same direction or in combination back to back to obtain the desired tightening force.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional material testing jig.
101 is the shouldered test piece; 102 is the mounting flange; 103 is the grip; 104 is the split pusher; 105 is the bag Nut; 106 is a screwed test piece; 107 is a lock nut; 108 is a mounting flange; 109 is a base plate. FIG. 2 is an assembled cross-sectional view of the entire material testing jig of the present invention; FIG. 3 is a cross-sectional view of FIG. 2 when viewed from A to A; FIG. 4 is a pusher 2 FIG. 5 shows a detailed view of a material specimen.
FIG. 6 is a graph showing the load and displacement of the disc spring in the material testing jig of the present invention, where the vertical axis shows the compressive load and the horizontal axis shows the displacement. Here, 1 is a material test piece, 2 is a push tool, 3 is a holding box, 4 is a bolt, 5 is a disc spring washer, and 6 is an adjustment plate.

Claims (1)

[Claims] 1 As shown in the drawing, a pushing tool 2 split into two or more parts is attached to the tapered part of the material test piece, and a holding box is attached to the base plate 7 with bolts 4 and disc spring washers 5. It consists of 3,
The outer periphery of the pusher 2 and the hole of the holding box 3 are fitted into each other, and the grip is a fixture for fatigue testing of brittle materials for fixing a material test piece 1 having a tapered shape. Ingredients.