JPS62144044A - Tensile testing of ceramics - Google Patents

Abstract

PURPOSE:To enable accurate measurement of tensile strength or creep strength, by a method wherein a groove is provided in the perimeter of a support of a round-bar test piece, a plurality of pins each with a curved tip are engaged with the groove to transmit a tension force through a pin. CONSTITUTION:A round-bar test piece is made up of an evaluating part 1a and a support part 1b formed in a large diameter at both ends thereof. The support 1b is provided with a hemispherical groove 1d in the perimeter and the groove 1d is engaged by a pin 2 made of ceramics. The pin 2 is fitted into a hole 3b of a cylinder 3a of a pull rod 3 formed to cover the test piece support part 1b and the end thereof is supported with a ring 5 retained by a stopper 4 from outside. When a tension force is transmitted to the pull rod 3, uniform shear force and bending moment act on each pin 2. This allows an axial force alone to work on the test piece 1 thereby prevent rupture of the support part 1b before the evaluating part 1a is done.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for tensile testing ceramics.

[Conventional technology]

Ceramics have advantages such as high strength and high corrosion resistance in high-temperature regions, light weight, and low coefficient of linear expansion and thermal conductivity, and have recently been used in various fields where these characteristics are required. For example, it is effective and has great potential for application as a structural material that is exposed to high stress in high temperature and corrosive environments such as in gas turbines.

On the other hand, when ceramics are used under harsh conditions such as high temperatures, corrosive atmospheres, long-term constant stress, and repeated stress,
Its material properties change and it can fracture at relatively low stresses. Phenomena such as leap and fatigue are important factors in structural design and life prediction, and therefore, when using ceramics as a structural material, it is necessary to fully understand its characteristics.

However, it is only recently that ceramics have attracted attention as structural materials, and it cannot be said that methods for evaluating their characteristics have been established. Furthermore, conventional methods for evaluating the characteristics of metal materials cannot be applied directly to ceramics because they are brittle materials.

Mechanical testing methods for ceramics include tensile-compression tests using round bar test pieces, cantilever bending tests using plate-shaped test pieces, and bioscillatory tests of 3-point bending and 4-point bending.
Although it is carried out at high temperatures up to around 0°C, bending tests are often carried out, and the reality is that tension and compression tests using round bar test pieces are almost never carried out. .

In general, the strength of ceramics is controlled by surface and internal defects, so it is difficult to accurately understand the behavior of internal defects in conventional bending tests, and the strength of ceramics is dependent on volume. From the viewpoint of performance, it is more desirable to perform a tension compression test, which is a test in a state closer to that of a practical member, than the above-mentioned bending test.

[Problem that the invention seeks to solve]

The biggest difference between ceramic materials and metal materials is
Its ductility is extremely poor.

Therefore, when performing a tensile test on ceramic materials, even if the center axis of the load shifts slightly, shearing force or bending stress is generated, resulting in fracture at low stress levels, or stress concentration at the specimen holding part. There is a problem that the material breaks at a certain point, and the true strength cannot be measured in many cases.

In order to solve such problems, for example,
No. 13935, a test method has been proposed in which the shoulder of a test piece is engaged with a rod-shaped body to apply a load. However, this method is ineffective unless the shape of the test piece shoulders is made strictly symmetrical, and it is difficult to obtain such a test piece using current ceramic processing technology. .

An object of the present invention is to obtain a tensile test method for ceramics that allows easy and accurate determination of tensile strength or creep strength.

[Means for solving problems]

The present invention provides a groove in the supporting part of a round rod-shaped test piece, engages a plurality of pins with curved tips in the groove, and transmits tensile force through these pins. This is a test method.

[Effect]

As described above, the present invention applies tensile force by engaging a plurality of pins in the grooves of the test specimen support, so the stress is reduced compared to the method described above in which the shoulder of the test specimen is supported by a rod-shaped body. Since the voltage is distributed to each pin and applied to the support part, the test piece is difficult to break, and the groove provided around the support part of the test piece does not require the precision required for the shoulder part of the test piece mentioned above. It has the advantage of being easy to process. Furthermore, according to the present invention, the shape of the shoulder of the test piece, which has conventionally been a part prone to breakage, can be optimized regardless of the supporting part, so the breakage can be reliably caused in the test piece evaluation section and accurately. Tensile strength or creep strength can be determined.

[Example] Fig. 1 shows an embodiment of the present invention, in which a round bar-shaped test piece 1 consists of an evaluation section 1a and support sections 1b formed with a large diameter at both ends of the evaluation section 1a. and the support portion 1b are smoothly connected to form a shoulder portion 1c. The support part 1
A groove 1d having a hemispherical cross section is provided around b, and a pin 2 made of ceramic is engaged with this groove 1d.

The pin 2 is fitted into a hole 3b of a cylindrical portion 3a of a pull rod 3 formed to cover the test piece support portion 1b, and its end is fitted into a ring 5 which is fitted into the pull rod 3 and locked by a stopper 4. Supported from the outside. Further, the pull rod 3 is connected to a drive device (not shown) via a universal joint 6, so that the tensile force from the drive device is transmitted to the test piece 1 via the universal joint 6, the pull rod 3, and the pin 2. .

FIG. 2 shows an axial cross section of the test piece support part 1b.
(a) pin 2 at 120° intervals, (b) pin 2 at 9
The pins 2 are arranged radially at equal intervals about the central axis of the test piece 1, and the shape of the tip of the pin 2 is close to a spherical surface. is formed.

If a tensile test is carried out with such a configuration, the groove 1d is the same as the test piece 1.
As long as the pins 2 are formed in a uniform shape and symmetrical about the central axis of That will happen.

Furthermore, even if there are errors or irregularities in the groove d that are unavoidable during processing, the shape of the specimen supporting portion 1b is such that it can sufficiently withstand the bending stress and shearing force generated due to these errors. Therefore, even in such a case, the support part 1b will not break before the evaluation part 1a breaks. Moreover, since the test piece shoulder 1c does not take any part in supporting the test piece 1 itself in the present invention, its shape can be optimized against bending stress, etc. Even if such a problem occurs, it is possible to prevent the shoulder IC, which is the connecting part between the support part 1b and the evaluation part 1a, from breaking immediately.

Furthermore, by making the tip of the pin 2 spherical or curved, the engagement between the pin 2 and the groove 1d is stabilized in a more optimal state.

Fig. 3 shows a groove 1e with an elliptical cross section provided around the supporting portion 1b of the test piece 1. The cross-sectional shape of the groove provided around the supporting portion can be adjusted as appropriate depending on the test piece material and test conditions. You can choose.

〔Effect of the invention〕

As described above, the present invention is a test method in which a groove is provided around the supporting portion of a round bar-shaped test piece and a plurality of pins are engaged with the groove. Stresses such as torsion are less likely to occur, and as a result, it is possible to prevent the test piece from breaking due to low stress due to force other than axial force acting on the evaluation section.

Therefore, tensile tests and creep tests can be performed with higher accuracy.

[Brief explanation of drawings]

1 to 3 are diagrams showing embodiments of the present invention,
Fig. 1 is a partially cutaway cross-sectional view showing how the test piece is attached, Fig. 2 is a cross-sectional view showing how the pins are arranged, and Fig. 3 is a cross-sectional view showing how the test piece is attached according to another embodiment. FIG. 1... Test piece 1a... Evaluation part 1b...
・Support part 1c...Shoulder part ld, Is...
Groove 2...Pin 3...Pull rod
3a... Cylinder part 3b... Hole 4.
...Stopper 5...Ring 6...Universal joint agent Patent attorney Nori Chika Ken Yudo Hirofumi Mitsumata Fig. 1 (α) Fig. 2 Fig. 3 (b) Fig.

Claims (1)

[Claims] A tensile test method for ceramics in which a groove is provided around the support of a round rod-shaped test piece, a plurality of pins each having a curved tip are engaged with the groove, and tensile force is transmitted through these pins.