JPS6336452B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a chuck device for a material testing machine, and in particular, the present invention relates to a chuck device for a material testing machine. The present invention relates to a chuck device for a materials testing machine for conducting high temperature cyclic fatigue tests, which applies an auxiliary force to the test piece that is compatible with the above.

(Prior Art) Generally, a chuck device in a material testing machine is designed to grip a test piece by mechanical or hydraulic action. The mechanical gripper uses a suitable manually adjustable spring device so that different clamping forces can be set for gripping the specimen.

In contrast, in the case of hydraulic gripping, the load ram is connected to an actuating cylinder or an actuating piston, which is supplied with pressure medium.

By controlling or adjusting the pressure in the working cylinder, the clamping force of the specimen can be adjusted via the loading ram.

In other chuck devices, the specimen is provided with a threaded end and tightened with a screw.

(Problems to be Solved by the Invention) The chuck device used in high-temperature fatigue tests is made of a heat-resistant material, but there is a gap in the chuck due to the difference in thermal expansion from the material of the test piece. It is necessary to apply an auxiliary force in the longitudinal direction of the test piece to eliminate play.

In the case of a mechanical chuck device, manual adjustment of the auxiliary force is complicated, and in the case of a hydraulic chuck device, a considerable amount of expense is required, and the auxiliary force cannot be automatically controlled by changes in the temperature of the chuck. Ta.

(Means for solving the problem) In the chuck device, the specimen must be gripped by the gripping member so that there is no play in the gripping part under all test conditions, and the auxiliary force applied to the specimen is It must be selected so that no play occurs during the test when repeated loads are applied to the specimen and when the test temperature is changed.

The object of the invention is to improve and simplify known chuck devices. According to the invention, each gripping end of the test specimen is pressed by a loading ram, which passes through the gripping member and acts on the end face of the test specimen in a longitudinal direction relative to the gripping member. Add a load to.

The test piece has, for example, a threaded end which is screwed into a pull rod chuck so that the auxiliary force acting on this end is automatically adjusted as a function of temperature. This auxiliary force depends on the strength of the gripping member at various temperatures,
It is intended to be adapted in particular to the reduction in strength at high temperatures, thereby eliminating manual adjustment or corresponding control and adjustment devices.

Furthermore, by using a spring that has a characteristic that the spring force changes from a proportional increase to a nearly constant value with respect to the spring stroke for a load ram made of a material with a coefficient of thermal expansion smaller than that of the material of the gripping member, the gripping part of the specimen can be The auxiliary force at can be automatically adjusted to the strength reduction of the chuck part, and the substantially constant part of the spring characteristics is determined so that the spring force varies as sharply as possible with respect to the spring stroke.

(Function) By matching the spring characteristics that apply an auxiliary force to the gripping member via the load ram with the expansion relationship between the load ram and the gripping member, the auxiliary force acting on the gripping part of the specimen can be reduced even at high temperatures. The stress can always be kept below the allowable stress value of the gripping member.

The load ram can be made of ceramic material,
Further, a disc spring is effective in easily generating the spring characteristics, and the maximum stroke of the spring can be adjusted by adjusting the threading of the end of the test piece, and the spring itself can be replaced.

(Example) The present invention will be described in detail below based on an example shown in the drawings.

FIG. 1 shows a chuck device according to the invention with a spring-loaded loading ram acting on the end of the specimen.

The chuck device 1, 1' is attached to the loading device 2 and to the upper fixture 2' of the testing machine, which are shown only schematically. The two chuck devices 1, 1' are of substantially identical construction, so that only one chuck device 1 is shown in detail in the drawing.

A test piece 3 is placed between both chuck devices 1, 1', and both ends of this test piece 3 are provided with threaded ends 3'.
are provided and connected at their ends 3' to the chuck devices 1, 1'.

In order to carry out the high temperature fatigue test, a heating furnace 4 surrounding the specimen 3 and the ends of the chuck device 1, 1' is used.
will be provided.

The chuck device 1 is composed of a main body 5 and a gripping member 6.

The main body 5 is formed in the shape of a U-link or a cylinder, and is attached to the loading device 2 of the testing machine at its open end.

The gripping member 6 is attached to the lid of the main body 5, for example, by screwing. The gripping member 6 is formed in the shape of a pull rod, and a female thread is provided at one end of the test piece for screwing the end 3' of the test piece 3.

Instead of screw clamping, it is also possible to provide the specimen with other types of chuck devices, such as clamping chuck devices.

The gripping member 6 is made of a heat-resistant material, while the main body 5 is made of a common material. This is because the body 5 is not actually heated during the test, but is instead cooled if necessary.

A load ram 7 made of pressure-resistant ceramic material is arranged in the gripping member 6. The material of the ram 7 is selected to have a coefficient of thermal expansion smaller than that of the material of the grip member 6, and has a compressive strength against the test specimen load in the test temperature range.

The load ram 7 is connected to a disk 8 which is biased by a disc spring 9. Disc spring 9 is supported against loading device 2 or, if body 5 is constructed accordingly, against body 5 .

An auxiliary force Fv is applied by the disk spring 9 to the end 3' of the specimen 3 through the disc 8 and the load ram 7, and this end 3' is forced against the gripping member 6 by the auxiliary force Fv. It is possible to eliminate play in the threaded part during repeated stress or repeated elongation tests. For these tests, the load on the specimen 3 was applied to the disc spring 9
Do not exceed the auxiliary force Fv.

In order to generate this auxiliary force Fv, instead of the disc spring 9, another spring or spring device with equivalent spring characteristics can be used. The main body 5 is formed in a square shape so that the disc spring 9 can be easily replaced and its maximum assisting force Fv can be adjusted at atmospheric temperature. That is, the maximum stroke of the disc spring 9 is adjusted by adjusting the screwing of the threaded end 3' of the test piece 3 to the gripping member 6 in the tightening or loosening direction, and the desired screwing position of the test piece 3 is adjusted. It provides auxiliary force Fv and eliminates play.

The strength of the gripping member 6 is greatly reduced at high temperatures, so that the auxiliary force, which is harmless at atmospheric temperature, can damage the gripping member 6 at high temperatures.

Conventionally, this problem has been prevented by manually adjusting the auxiliary force or hydraulically adjusting the auxiliary force for each high-temperature test condition.

By means of the device according to the invention, the auxiliary force Fv is automatically adapted to the temperature prevailing at the test piece 3 or the screwing point of the test piece and accordingly to the heat-resistant strength of the gripping element 6.

In the case of the disc spring 9 generating the auxiliary force Fv, the spring force initially increases approximately linearly at the beginning of the spring stroke.

As the spring stroke further increases, the spring force goes from increasing linearly to being approximately constant and decreasing. The qualitative curve of the spring force F with respect to the spring stroke S is shown in FIG. For the conditions of use described above, the disc spring 9 is designed such that the spring force F remains as constant as possible in the end region of the spring stroke S (between A and B in FIG. 2) and in the beginning region (between B and C). ) so that it increases almost uniformly.

The strength of the gripping member 6 remains approximately the same up to a certain temperature in the range of approximately 500°C to 600°C. Above that, this strength decreases approximately linearly with temperature. FIG. 3 shows typical changes in strength or permissible load δ _Z with respect to temperature t for the heat-resistant material constituting the gripping member 6.

Due to the different coefficients of thermal expansion of the gripping member 6 and the loading ram 7, the gripping member 6 and the loading ram 7 will expand differently as the temperature of the chuck device increases, in which case the gripping member 6 will expand more than the loading ram 7. The large coefficient of thermal expansion results in a large elongation. The difference in length change is determined by the length of both parts and the temperature difference. The difference in the length change of the load ram 7 relative to the gripping member 6 is related to determining the spring properties of the disk spring 9. The relationship between the spring stroke S and the spring force F of the disc spring 9, that is, the spring characteristics of the disc spring 9, is such that the auxiliary force Fv at the screwed part of the end 3' of the test piece 3 automatically responds to the temperature change of the gripping member 6. The thermal expansion ratio of the load ram 7 and the gripping member 6 with respect to temperature is adapted to suit the temperature.

For this purpose, the spring force of disk spring 9 at ambient temperature is selected in accordance with the desired auxiliary force Fv at the screwing point. In the case of this spring force, the disk spring 9 is compressed in the installed state and applies the desired auxiliary force Fv to the screwing point of the test piece 3 via the load ram 7.
This situation corresponds to point A in FIGS. 2 and 3.

When the gripping member 6 and the loading ram 7 are heated, the loading ram 7 is followed in the gripping member 6 due to its small length change. This is done by stretching the disc spring 9. The disc spring 9 initially operates within a certain range of spring characteristics. That is, a change in the spring stroke S causes the spring force F to change only slightly or not at all. This state is at point A in Figures 2 and 3.
This corresponds to the range between and point B.

Point B (Fig. 2) of the spring characteristics where the spring force F begins to decrease as the spring stroke S decreases is the point B (Fig. 2) of the strength change of the gripping member 6, where the strength of the gripping member 6 decreases as the temperature rises. Figure 3).

When the temperature t in the gripping member 6 exceeds point B and further increases in the direction of point C (FIG. 3). Due to its small thermal expansion, the load ram 7 is continuously followed into the gripping member 6 by the disk spring 9. The stretching of the disc spring 9, which is conditioned thereby, causes the spring force F to decrease approximately linearly with the spring stroke S, corresponding to the range from point B to C in FIG. In this way, the reduction in strength caused by the temperature rise of the gripping member 6 in the range from points B to C in FIG. There is a corresponding decrease in the spring force F.

The characteristics of the disc spring 9, the different length expansion relationships of the gripping member 6 and the loading ram 7, therefore mean that as the temperature increases and with the onset of a decrease in the strength of the gripping member 6, the spring force of the disc spring 9 also decreases. As such, they are mutually determined. This results in an automatic adaptation of the auxiliary force to the respective strength of the gripping element 6. In this case, the spring force of disc spring 9 is selected in such a way that the permissible stress of gripping member 6 is not exceeded over the entire temperature range of the device. With such a determination, a considerable correspondence between the strength properties of the gripping member 6 and the properties of the disc spring 9 is achieved.

If the temperature t decreases, the above-mentioned relationship is reversed, i.e. as the temperature decreases from point C towards B or A in Figure 3, the strength of the gripping member 6 increases again; and the length elongation of the loading ram 7 decreases with different magnitudes. As a result, the spring force F of the disk spring 9 increases again from the value C to the value B or A (FIG. 2).

〔Effect of the invention〕

As described above, the present invention uses a simple device to eliminate the play in the chuck part due to thermal expansion by automatically adjusting the auxiliary force that matches the strength of the chuck part in response to temperature changes. can do.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a chuck device according to the present invention, FIG. 2 is a characteristic diagram of a disc spring, and FIG. 3 is a diagram of changes in strength of a heat-resistant material. 1, 1'...Chuck device, 2...Loading device,
2'...Upper fixing stand, 3...Test piece, 3'...End of test piece, 6...Gripping member, 7...Loading ram, 9
……Disc spring.

Claims (1)

[Scope of Claims] 1 A load ram is applied to the end of the test piece to press this end against the chuck part to give an auxiliary force to the test piece, and the auxiliary force by the load ram increases the temperature of the test piece or the chuck part. In the chuck device of a materials testing machine for carrying out high temperature cyclic fatigue tests, the loading ram 7 is made of a material having a coefficient of thermal expansion smaller than that of the material of the gripping member 6 that grips the test piece 3. At the end of the loading ram 7 there is a spring 9 which has a characteristic that the spring force changes from a proportional increase to an almost constant rate with respect to the spring stroke. A chuck device for a material testing machine, characterized in that the characteristics of the spring 9 and the changes in strength of the load ram 7 and the gripping member 6 are mutually determined to adapt to a decrease in strength when the temperature rises. 2. A chuck device according to claim 1, characterized in that the load ram 7 is made of ceramic material. 3. A chuck device according to claim 1 or 2, characterized in that the spring 9 is formed as a disc spring. 4. Claims 1 to 3, characterized in that the maximum spring stroke of the spring 9 is adjustable.
chuck device according to any of paragraphs. 5. The chuck device according to any one of claims 1 to 4, wherein the spring 9 is replaceable.