JPH0457214B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fatigue testing device for materials, and in particular, the present invention relates to a fatigue testing device for materials, and in particular, even if the material does not change significantly due to fatigue failure at the time of fatigue failure, the present invention relates to a fatigue testing device for materials. This relates to items that allow the breaking point to be clearly identified.

[Prior Art] Generally, fatigue testing of materials is performed by repeatedly applying a load to the material and determining the number of repetitions until the material breaks.

That is, for example, when two parts of a material are held down and a constant amplitude of repeated displacement is applied from one part, the amplitude of the load applied to the other part is measured, and if this load amplitude suddenly increases due to fatigue failure of the material, This measures the number of repetitions until the decrease occurs.

In this case, the fatigue failure point of the material is detected by detecting that the measured load amplitude falls within the range of two set levels A and B, as shown in FIG.
Alternatively, as shown in FIG. 5, this is done by detecting that the peak position of the load amplitude is out of the range of two set levels C and D.

[Problems to be Solved by the Invention] However, in such a conventional device, the support grid in the reactor fuel assembly whose front view is shown in FIG. 6A and the top view is shown in FIG. 6B, respectively. When performing a fatigue test on a plate-shaped body that is bent in a relatively complicated manner, such as a spring installed in a car, it is extremely difficult to determine the fatigue failure point.

Figure 7 is a diagram showing the transition of the measured load amplitude in this case, and although microscopic observation shows that fatigue fracture has already occurred at point K in the figure, the measured load amplitude hardly decreases. There was only an indiscernible change, and after this state continued for a certain period of time, it was not until point K' was reached that a sudden decrease in the measured load amplitude, ie, rupture, was observed.

The reason for this is that in a plate-shaped body with a relatively complex shape like the support grid mentioned above, even if one part of the plate-shaped body undergoes fatigue failure, other parts may not be completely destroyed, or even if the whole body fails, the plate-like body may not be completely destroyed. Although it is presumed that one part of the material gets caught on the other part and maintains its apparent strength for a certain period of time, there is no effective countermeasure against this.

An object of the present invention is to provide a material fatigue testing device that eliminates such drawbacks.

[Means and effects for solving the problem] The present invention includes a load application means that repeatedly applies a load to a material, and a method that measures changes in the load acting on the material when the load is applied by the load application means. In the fatigue testing apparatus, an alternating signal corresponding to a load change acting on the material sent from the material change detecting means is input, and the alternating signals are averaged. The present invention is characterized in that a signal processing means for converting into a substantially linear signal is provided, and a fatigue fracture point or a breaking point is displayed as an inflection point on the substantially linear change curve to make the point noticeable.

[Example] FIG. 1 is a block diagram showing a material fatigue testing apparatus according to an example of the present invention.

In FIG. 1, reference numeral 1 denotes a fatigue test apparatus main body constituting a load applying means, and this fatigue test apparatus main body 1 has a built-in vibration generator for applying arbitrary displacement to a material.

Further, a displacement transmission rod 2 connected to the vibration generator is erected at the upper part of the fatigue testing apparatus main body 1, and a test piece mounting rod on which a test piece 3 is placed is mounted on the upper part of this displacement transmission rod 2. A stand 4 is attached.

Further, two pillars 5, 5 are erected on the fatigue testing apparatus main body 1, a beam 6 is erected at the upper end of these pillars 5, 5, and a material is placed in the center of the lower part of the beam 6. A load cell 7 constituting change detection means is attached, and a detection rod 8 is attached to the load cell 7.

This detection rod 8 is provided so that its tip part faces the test piece mounting table 4, and is in contact with the test piece placed on the test piece mounting table 4, and is subjected to loads and other effects that are applied to the test piece. This is to transmit changes in the test piece to the load cell 7.

This load cell 7 converts the load and other mechanical changes transmitted by the detection rod 8 into electrical changes, and sends out the electrical signals from an output terminal.

Further, the output terminal of the load cell 7 is connected to the input terminal of the load amplifier 9.
An alternating current signal that constitutes a signal processing means that receives an alternating signal corresponding to changes in the load acting on the material, averages the alternating signal, converts it into a substantially linear signal, and outputs the output terminal. - connected to the input terminal of the DC converter 10, and the output terminal of the AC-DC converter 10 is connected to the input terminal of the recorder 11;

The load amplifier 9 amplifies the AC electric signal sent from the output terminal of the load cell 7 and applies the output to the AC-DC converter 10. It averages the alternating signals and converts them into substantially linear signals, which are then output.

Further, the recorder 11 records temporal changes in the signal sent from the AC-DC converter 10.

When performing a fatigue test on a material using the above-described fatigue testing apparatus, first, a test piece 3 of the material to be tested is placed on the test piece mounting table 4, and then the detection rod 8 is placed on the test piece. 3, and then a vibration generator built in the fatigue test apparatus main body 1 is activated to apply repeated displacement of a constant amplitude to the test piece 3.

As a result, a repeated load is applied to the test piece 3, and this repeated load is detected by the load cell 7 through the detection rod 8 and converted into an alternating electric signal.

This alternating electric signal is amplified by the load amplifier 9, converted into a substantially linear signal by the AC-DC converter 10, and then sent to the recorder 1.
Added to 1.

FIGS. 2 and 3 are charts showing the fatigue test results recorded by the recorder 11 in this manner.

In the figure, the vertical axis is load, and the horizontal axis is time or number of repetitions.

The test piece used was a spring formed in a support grid constituting the reactor fuel assembly shown in FIG. 6, and FIG. 2 shows that when the repeated displacement applied to the test piece 3 is relatively small, FIG. 3 shows the results when the size is larger than this.

As is clear from Figures 2 and 3, the fatigue failure points K ₁ and K ₂ are the inflection points P ₁ of the signal curve, respectively.
and P ₂ , and furthermore, the breaking point
K ₁ ′ and K ₂ ′ can be clearly identified as P ₁ ′ and P ₂ ′ in the signal curve.

As described above, according to this embodiment, even in a material such as the support grid in which the measured load does not change significantly at the time of fatigue failure, the fatigue failure point or rupture point can be clearly determined.

Further, the apparatus of this embodiment can be obtained extremely easily since it is sufficient to add a known AC-DC converter to a conventional general fatigue test apparatus.

In the above embodiment, the AC-DC converter 10 is used as the signal processing means, but the present invention is not limited thereto, and as the signal processing means, for example, a known method including a diode and a capacitor may be used. A rectifier circuit may also be used.

[Effects of the Invention] As described in detail above, in the present invention, an alternating signal obtained in response to a change in load acting on a material when a load is repeatedly applied to the material is input, and the alternating signal is By providing a signal processing means that averages the signal, converts it into a substantially linear signal, and sends it out, the fatigue fracture point or rupture point of the material at which the change in the material due to fatigue fracture does not appear significantly at the time of fatigue fracture. is made prominent as an inflection point of the linear signal, making it possible to clearly distinguish it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a material fatigue testing apparatus according to an embodiment of the present invention, and FIGS.
4 and 5 are diagrams for explaining the detection of fatigue fracture points by a conventional fatigue testing device.
The figure shows a spring formed in a support grid that constitutes a nuclear reactor fuel assembly, and Figure 7 shows the case where a fatigue test of the support grid shown in Figure 6 was conducted using a conventional fatigue testing device. FIG. 2 is a chart showing measurement results. 1, 2, 4...Fatigue test device main body, displacement transmission rod, and test piece mounting table constituting load application means, 7,
8... Load cell and detection rod constituting material change detection means, 10... AC-DC converter constituting signal processing means.

Claims (1)

[Claims] 1. A device comprising: a load applying means for repeatedly applying a load to a material; and a material change detecting means for measuring a change in the load acting on the material when the load is applied by the load applying means. In the fatigue test apparatus, an alternating signal corresponding to a load change acting on the material sent out from the material change detection means is input, and a signal that averages the alternating signal and converts it into a substantially linear signal. A material fatigue testing device characterized by being provided with a processing means.