JPS6251414B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a material fatigue testing machine, and particularly to a material fatigue testing machine suitable for low-speed, long-term fatigue testing. Conventionally, many methods are known for investigating the fatigue characteristics of materials under repeated loads or strains. Some material fatigue tests, such as high temperature fatigue,
In the case of creep-fatigue tests where creep and fatigue overlap, or corrosion-fatigue tests in corrosive environments, there are cases where extremely long continuous tests, such as several months at low speed, are required. Conventional drive systems for material fatigue testing machines include those that use hydraulic cylinders and pistons;
Common examples include those that use an electric motor and a cam or screw mechanism, and those that utilize electromagnetic force or resonance due to other factors. These fatigue testing machines basically have mechanical moving parts, and their long-term low-speed operation tends to cause problems in terms of maintenance management and operating costs, as well as problems in terms of noise and safety during operation. There are many. In particular, those with many mechanical moving parts had many problems, such as the testing machine being large and complex, expensive to manufacture, and a high failure rate over the long term. The present invention was made to solve the above-mentioned problems, and its purpose is to eliminate mechanically moving parts,
The object of the present invention is to provide a material fatigue testing machine that is simple and suitable for long-term, low-speed operation. The gist of the present invention is to use a heat actuator that uses thermal expansion and contraction as a driving source by heating and cooling a metal rod or metal tube. A fatigue testing machine for materials is characterized in that a desired strain or load is repeatedly applied to a test piece by controlling heating and cooling of an insulated heat actuator. The testing machine of the present invention will be explained based on the drawings.
FIG. 1 is a side view showing an outline of the testing machine of the present invention. In the figure, 1 is a test piece, which is attached via chucks 3a and 3b in the usual manner. Reference numeral 2 denotes a heat actuator in which a heating wire 5 is provided on the surface of a metal rod, preferably a thin metal tube that has a small heat capacity and is strong against buckling, to heat and cool the metal rod. In order to prevent heat from being transferred to the parts 4a and 4b, they are provided with a reduced cross-sectional area, provided with heat dissipation fins, or forcedly cooled by water cooling, air cooling, or the like. The upper end 4a and lower chuck 3b of the heat actuator 2 are held by a frame 7 by a leaf spring 6 to prevent bending loads from acting on the test piece 1. The leaf spring also functions to prevent heat transfer from the heat actuator 2 due to convection. When operating this testing machine, the strain control test is performed by opening and closing the current passed through the heating wire 5 according to the signals from the extensometer 8 attached to the test piece 1, and the load control is performed by opening and closing the electric current passed through the heating wire 5 according to the signals from the load cell 9 connected to the chuck 3a. You may conduct a test. In the case where the test piece 1 and the heat actuator 2 are arranged in series as shown in Fig. 1, when the heat actuator 2 is heated, a tensile load is generated on the test piece 1 due to compression and cooling, but the rate of change is It can be selected from a wide range depending on the amount of heat generated by the hot wire 5 and the cooling method of the heat actuator 2. When changing the temperature of heat actuator 2 between T ₁ and T ₂ , in principle, approximately produces a relative strain of However, α is the coefficient of thermal expansion of the metal rod, l ₁ and A ₁ are the effective length and cross-sectional area of the test piece,
l ₂ and A ₂ represent the effective length and cross-sectional area of the metal rod. The rigidity of the frame is said to be sufficiently high. Both l ₁ /l ₂ and A ₁ /A ₂ can be easily reduced to 1/20 or less, and if stainless steel is used as the material for the metal rod, α = 1.8 × 10 ^-5 /℃, so _T2
If −T ₁ =200°C, then ε0.036. Since the repeated strain width in a general strain control fatigue test is in the range of about 0.001 to 0.02, it can be seen that a sufficiently effective fatigue test is possible. FIG. 2 shows an example of the structure of the testing machine of the present invention. The figure shows the changed parts of the structure, and the other parts are omitted with the structure shown in FIG. 1. 2A is the same as that shown in FIG. 1, in which the test piece 1 and the heat actuator 2 are connected in series. This is because compression acts on the test piece 1 when the heat actuator 2 heats it. In Figure 2B, two heat actuators 2a and 2b are arranged in parallel to a test piece 1, and when both heat actuators 2a and 2b are heated simultaneously, tension is applied to the test piece 1. , there is an advantage that it is easy to isolate heat between the heat actuator and the test piece. In Figure 2 C, the heat actuator 2 has a tube structure, and a shaft that passes through the inside and connects to the other end applies force to the test piece 1, so it is formally the same parallel type as in Figure 2 B. When the heat actuator is heated, tension is applied to the test piece. Figure 2D shows three heat actuators 2a,
2b, 2c, series heat actuator 2a and parallel heat actuator 2.
Excellent performance can be obtained by independently controlling b and 2c. For example, when the series heat actuator is in the cooling process, the parallel heat actuator is simultaneously heated, or conversely, one is heated and the other is cooled at the same time.
In addition to doubling the width and speed of tension and compression, it is also possible to perform programmed load tests that independently control the amplitude and average value by using one to control the load amplitude applied to the specimen and the other to control the average load. It can be carried out. 2(e) is a series-parallel double type with a coaxial double structure of a series heat actuator 2a and a parallel heat actuator 2b, and can be used in the same way as FIG. 2(d). Note that the above A, C, and H allow the support of adjacent frames to be shared when multiple devices are installed side by side, which is advantageous for increasing the number of testing machines that is essential for low-speed, long-term testing. . Furthermore, by using the heat actuator in combination with appropriate fulcrums and levers, it can be applied to various fatigue test formats such as twisting formats, bending formats, and combinations thereof. Fig. 3 shows a bending type, and Fig. 4 shows a twisting type. Each number in the figure is the same as above. Example

【table】

【table】

[Table] When the test piece strain ε is calculated from equation (1) under the above conditions, it is 0.013. However, if the stiffness of the chuck of the testing machine is taken into consideration, the strain applied to the effective length of the test piece will be approximately 1/2 of the calculated value, and the strain detected by the actual extensometer and the strain that is controlled to be constant will be approximately 1/2 of the calculated value.
It was 0.006. Figures 5 and 6 respectively show the temperature T and test piece strain εα temporal t changes of the series type heat actuator. Since the strain on the test piece is caused by the temperature change of the heat actuator, it changes in a curve similar to the temperature change curve of the heat actuator, as shown in Figure 6, and the time per cycle is also 20 Although it took about 10 minutes, we were able to achieve the intended purpose of repeatedly deforming the test piece with a constant strain width of 0.006. In the figure, 10 is the test piece extensometer attached, 11 is the test start, 12 is air cooling, 13 is heating, 14 is tension, 1
5 indicates compression. As described above, the material fatigue testing machine of the present invention has the following features. 1. Since it has no mechanical moving parts, it can operate noise-free, pollution-free, and maintenance-free for long periods of time. 2. Because it is structurally simple, it can be small and lightweight, and a large number of testing machines can be accommodated in a limited installation space. 3. Both the manufacturing and operating costs of the testing machine can be significantly reduced. 4. The test piece temperature can be controlled independently of the heat actuator temperature. 5 As in creep fatigue test, one cycle maximum
Long-term tests such as 10 hours and a total test time of 10,000 hours can be performed economically. 6 Tests under corrosive environments such as stress corrosion cracking can also be conducted.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the testing machine of the present invention, Figure 2 A,
B, C, D, and H are structural diagrams of the testing machine of the present invention;
Figures 3 and 4 are diagrams with the bending type and torsion type added, respectively. Figure 5 is a diagram of the temporal temperature change of the heat actuator during the test. Figure 6 is the diagram of the specimen strain during the test. A temporal change diagram is shown. 1: Test piece, 2, 2a, 2b, 2c: Heat actuator, 3a, 3b: Chuck, 4a, 4
b: heat actuator end, 5: heating wire,
6: Leaf spring, 7: Frame, 8: Extensometer, 9: Load cell, 10: When installing test piece extensometer, 11:
Test start, 12: air cooling, 13: heating, 14: tension, 15: compression.

Claims (1)

[Claims] 1 A heat actuator whose driving source is thermal expansion and contraction caused by heating and cooling of a metal rod or metal tube is used. 1. A material fatigue testing machine characterized in that a desired strain or load is repeatedly applied to a test piece by controlling heating and cooling of an eta.