JPS61196133A - Loading for sample material test - Google Patents

Abstract

PURPOSE:To enable a highly accurate testing, by arranging a conducting test object in a uniform normal magnetic field to run current to the test-sample crossing the flux of the magnetic field. CONSTITUTION:A conducting test sample 30 is arranged in a uniform normal magnetic field 10 and both ends of a discharge circuit 20 are connected to the test sample 30 to flow current in the direction crossing that of the flux of the magnetic field 10. Consequently, a magnetic force is generated in the test sample 30 according to the direction and the intensity of current to impart a uniform load thoroughly at a high accuracy without causing vibration and repulsion in the test sample 30. The load also is calculated from values of current and the magnetic field at a high accuracy. Moreover, this eliminates any load transmitting body which applies a load to the test sample 30 in contact therewith thereby facilitating the testing under a special condition.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a load application method for testing the strength characteristics of materials or structures.

(Prior Art) Conventionally, when testing the strength characteristics of a certain material, a test specimen 1 made of the material in a predetermined shape and size is placed on a predetermined table 2.3 as shown in FIG. , a load generated by a hydraulic power source (not shown) is transferred to the test body 1 via a load transmission body 4.
In addition, a method has been used to determine the strength characteristics by measuring the amount of displacement under the load and the load at the time of cracking or destruction. Further, at this time, the load was measured by the output value of a strain gauge attached to the load transmitting body 4.

(Problems to be Solved by the Invention) According to the above configuration, the load is applied through contact between the test specimen 1, the table 2.3, and the load transmitting body 4, but in this case, as shown in FIG. b) Test specimen 1 as shown in (c) and (e)
Due to vibrations, recoil, etc. that occur in It is not possible to accurately measure the applied load, and the fracture toughness (dynamic fracture toughness 'KId, J
Id) for a short period of time (e.g. 1 mS)
A large error occurred when applying a large load (dynamic load) to eC). Furthermore, when applying a load for such a short time, it is extremely difficult to control the load using a hydraulic power source or the like. Furthermore, the test specimen 1 and the load transmitting body 4
Therefore, when testing under special environmental conditions such as corrosion, high temperature, or low temperature, there were problems such as difficulty in isolating the test specimen 1 from the outside world.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention applies a conductive test specimen 30 or stress in a load loading method when testing the strength characteristics of materials or structures. A test body 50 with a conductive layer 151 provided on the surface thereof is placed in a uniform steady magnetic field 10, and a current is passed through the test body 30 or the conductive layer 51 in a direction that intersects the direction of the magnetic flux of the magnetic field 10. I did it like that.

(Function) According to the above configuration, as is well known, an electromagnetic force is generated in the test object 30 or the conductive layer 51 according to the direction and strength of the current. A uniform load can be applied to the entire part with high precision without causing jumps, and the load can be calculated easily and with high precision from the value representing the current value and the strength of the magnetic field.
Furthermore, the load can be easily controlled by controlling the current, and the load can be easily applied for a short time. Since this is not necessary, testing under special conditions becomes easier.

(Example) Figures 1 to 10 show a first example of the present invention, in which 10 is a magnetic field, 20 is a discharge circuit, and 30 is a test object.

The magnetic field 10 is a uniform steady magnetic field in which the magnetic flux with a magnetic flux density B is directed in the (-2) direction, and is formed between magnets 11 and 12 in which the south pole and the north pole are arranged to face each other.

The discharge circuit 20 includes a capacitor 21, a thyristor 22, a coil 23, and a resistor 24 connected in series, and both ends thereof are connected to a test object 30. In addition, capacitor 2
Since the circuit for charging the thyristor 1 and the circuit for making the thyristor 22 conductive are well known, their description will be omitted here.

The test specimen 30 is made of a conductive metal, such as A308 cl, 3 steel for nuclear reactor pressure vessels, formed into a rod shape with a rectangular cross section.
A crack 32 is previously provided approximately at the center of one narrow side surface 31. The test specimen 30 is placed on a pair of stands 40, 41 with one end 33 thereof in the magnetic field 10 so that its longitudinal direction is parallel to the and is supported near the other end 34. Both ends of the discharge circuit 20 are connected to one end 33 and the other end 34 of the test body 30, respectively. Furthermore, a well-known capacitor capacitance displacement meter (
(not shown) is attached, and furthermore, well-known potential difference detectors (not shown) are connected to both sides of the crack 32.

Figure 2 shows the specific shape of the test specimen 30, and the dimensions of each part are length 428HR, width 30am, and thickness 61m1!
Cable connection holes 33a and 34a with a diameter of 6M for connection with the discharge circuit 20 are provided at positions 7 am from one end 33 and the other end 34, respectively. The crack 32 consists of a groove 32a with a width of 2 mm and a length of 9 m+, and a fatigue crack 32b with a length of about 3 m continuous to the bottom of the groove 32a.

Cable connection holes 36, 37 with a diameter of 3 m are provided on both sides of the crack 32, respectively, for connection with the potential difference detector. Also, -14 from one end 33 and 34 of the side surface 31
It is supported by a stand 40.41 at the position of the shoes.

In such a configuration, if the capacitor 21 is charged with a sufficiently large voltage and the thyristor 22 is made conductive, the well-known LC
A pulse current I based on the discharge characteristics of the R series discharge circuit flows between one end 33 and the other end 34 of the test object 30 in the (-X) direction, and an impulsive electromagnetic force (IXB) in the (-y) direction is applied to the test. It is given to the body 3o.

For example, if the magnetic flux density B is 1.7 Tesla (2 Te5 la inside the test piece due to magnetic saturation), the discharge circuit 20
The value of each element is 22mF for capacitor 21.

The coil 23 is 11 μH, the resistor 24 is 45 mΩ (maximum charging energy 18 kJ), and when the thyristor 22 is made conductive with the charging voltage of the capacitor 21 of 1000 V, the time 0
．． A pulse current with a maximum current value of 18 kA flows through the test object 30 for 5 m5 ec, and an impactful electromagnetic force is applied to the test object 30.

In addition, test specimen 3 of magnetic material such as A308 cl, 3 steel
0, magnetic forces act in the (-Z) and (Z) directions in addition to the force acting in the (-y) direction. Although not shown, (
2) In order to suppress the deformation in the (-y) direction and to smoothly deform in the (-y) direction, and to disperse the frictional force generated at that time over the entire test specimen, Teflon was applied at 16 locations in the longitudinal direction of the test specimen 30 at equal intervals. A ring is attached, sandwiched between Teflon support plates, and supported from the sides.

In addition, the test is conducted by setting the temperature at several points between -196 and 115°C. Although the temperature setting method during the dynamic load test is not shown, in the case of high temperature, an asbestos plate is used to set the magnet 11. Build a furnace between 12 and heat it with two heaters, upper and lower.
In the case of low temperatures, an asbestos plate bottom is attached to the side support plate, and a refrigerant such as liquid nitrogen, alcohol, or dry ice is poured into this to completely immerse the test specimen 30 and cool it to a predetermined temperature.

Next, an analysis of the dynamic fracture toughness value when a dynamic load due to the electromagnetic force is applied will be described.

As is well known, electromagnetic force is a body force, and therefore is applied to the entire test specimen 30. To briefly explain the electromagnetic force analysis method, first, the current distribution inside the test object is calculated, and then a two-dimensional dynamic elastoplastic fracture analysis is performed using the electromagnetic force distribution obtained by multiplying this by the magnetic flux density as input data. Here, the destruction parameter is U Kishimoto (Kishimoto, two idiots, jam, 46-4
10. A (1977), 1049. ) by the body force (
The J integral (
J integral). The analysis conditions are magnetic flux density of 2T.
esla, the physical property values shown below were used, and plane stress was assumed.

Youna's modulus E-2,06x
10” HPaY 1eld strength 6
y = 441 HPa)1ardening
rate H' -1960HPaPois
son's ratio v-0,3Mass d
intensity ρ=8.03X10/(g/113
Figure 3 shows charging energy E. are the time histories of the current value (input value) and J integral (result) in the case of 7.0 kJ (indicated by the solid line in the figure) and 15.4 kJ (indicated by the broken line in the figure). Here, even though the current is only changed by a constant time constant and the time constant is constant, the time history of the J integral changes significantly, such as the peak time being delayed. This shows that the time history is a quantity that is extremely sensitive to changes in load conditions.

Although not shown, the support end reaction force included large vibrations whose vibration period almost matched the primary transverse vibration mode of the end of the test piece outside the support point. However, the value of the reaction force is always positive, and in the case of this test system, Kalthoff () <
althoff, Proc, I, Con
r.

AI) DliCatiOn Of FraCtll
re Mechanics t.

Materials and Structure
es, (1984).

107,), it is presumed that the test specimen does not recoil upon impact.

In this way, even in the electromagnetic force loading system, the influence of impact can be used to some extent, but the relationship between Jla and the displacement δ at the center of the test piece shown in FIG. 4 has a different tendency. In the same figure, the solid line is EC
=7. Dynamic load of OkJ, broken line is E. -15.4 kJ dynamic load, the dashed line shows the case of static load. Here, except that the maximum value of J changes depending on the size of the load, the loading speed is converted to 1.8 x 10 ~ 2.7 x 105 MN.
Despite the high speed of /m -8, there is little vibration, and the antinode history coincides with a difference of a few percent. Moreover, it also agrees with the static three-point bending results of the same-shaped specimen plotted for comparison.

This can be thought of as follows.

In other words, when electromagnetic force is applied to the entire test specimen as body force, no local high stress field is formed due to the impact except at the supporting end, and as a result, significant stress wave propagation from the load bearing area occurs. It doesn't happen. On the other hand, since the support end is far away from the crack, higher-order modes of the bending waves propagating from there are dispersed before reaching the crack. Therefore, the test specimen maintains a substantially quasi-static deformation mode even under high-speed deformation, and a stable J-δ relationship that is not easily affected by load changes as shown in FIG. 4 is obtained. Therefore, in the case of this test method, in addition to J-tlIl, J-δ is used for J value evaluation.
Although it is possible to use the relationship, the latter is used because it is stable against changes in loading conditions and the experimental value that directly represents the deformation behavior is the displacement δ at that time rather than the time of failure.

Here, as the dynamic fracture toughness value, KId is the potential difference method (E
P method) to determine the limit displacement δ. 1. Measured and corresponded from the J-δ relationship. LIC).

On the other hand, in the JId test, the maximum displacement δ1 is measured, the value J is determined from the J-δ relationship, and an R curve is created using this and Δa to determine JId.

FIG. 5 shows a static three-point bending test performed on the test specimen 30 (length: 300 feet, supporting position 70 feet from both ends 33, 34) using a well-known MTS tensile tester. The results of the analysis and experiment of the J-integral-load point displacement relationship for the cases of 7°C and 105°C are shown below. In the figure,
○ is the experimental value at 7℃, Δ is the experimental value at 105℃, and the broken line is 7℃.
The dashed line indicates the analytical value at 105°C. Here, the experimental values are calculated from Rice's simple equation based on the load-displacement relationship. The two agree well at both temperatures, confirming that this analytical method has sufficient accuracy.

FIG. 6 shows an example of the analysis and experimental results of the time history of the displacement δ at the center of the test body 30 obtained in the dynamic test at 7°C. In the figure, the broken line shows the analysis results, and the solid line shows the experimental results. The peak times etc. are not consistent, but overall the experimental values are a little low. The main reason for this is thought to be energy loss due to friction between the Teflon ring and Teflon plate (not shown) attached to the test specimen 30 as a countermeasure against magnetic force. However, it is estimated that the deformation mode will hardly change due to the frictional force that causes only a difference of this magnitude in the time history, and it is considered that the J-δ relationship, which is the basis of J value evaluation, can be used as is.

This test method, which uses electromagnetic force, is a complete load control test, so any displacement can be set by adjusting the electromagnetic energy. Therefore, it is easy to apply the R curve method in the upper 5heH region. However, when cleavage fracture occurs rapidly at low temperatures, it is necessary to consider another method because it is not possible to detect the occurrence from "load drop." Therefore, we decided to use the potentiometric method (EP method). did.

Figures 7 and 8 show the results when complete cleavage fracture occurred at -70°C. Here, Figure 7 shows the time history of the potential difference at the crack edge of the test piece α placed in the magnetic field and the dummy test piece β placed outside the magnetic field, and Figure 8 shows the current and the center of the test piece. This is the time history of part displacement. Looking at FIG. 7, after both of them followed the same hip history, only the potential difference of the test body α suddenly increased from time 1m5eC and continued to about 1.5m5eC. Cleavage failure occurs at 1 m5ec, and as the ligament decreases, the electrical resistance increases and 1.5m5
This is interpreted as a result of almost rupture at ec.

On the other hand, in the displacement curve of FIG. 8, there is no change at all near 1 m5 ec, but rather a small "step" is seen at the time of separation of the test specimen, 1.5 m5 ec.

Furthermore, it is difficult to evaluate the crack growth rate from the result of this potential difference in the case of high-speed crack growth such as brittle fracture because the calibration relationship between potential difference and crack length changes depending on the growth rate. However, ductile crack growth, which occurs at a relatively slow rate, can be achieved by comparing two potential differences.

Figure 9 shows a comparison of the static R-curve and dynamic R-curve obtained in the 7°C test. Here, as the blunting curve, J=46YΔa, which is recommended for this material by the TS subcommittee of the Japan Welding Society, was used. Note that δ is the yield stress obtained from the static tensile test. In this result, the dynamic result is clearly smaller at the initial stage of crack propagation, and the difference disappears as the crack progresses. Further, in the results at higher temperatures than this, FIG. 9 shows a similar tendency, although no difference was observed.

The relationship between the static and dynamic fracture toughness values obtained here and temperature is shown in FIG. All results were evaluated using J through numerical analysis and were converted into values using the following formula.

K=(EJ)” ・・・・・・(1)E
: The loading rate of Young's modulus dynamic test is Kz8×104 to 2×10 MN/m −
It is s.

In this test, the thickness of the specimen was thin due to the limited load capacity of the equipment, and most of the data did not satisfy the valid conditions regarding the thickness. However, since all tests were conducted on test specimens of the same shape, it is considered to be effective in examining dynamic effects. Therefore, looking at Figure 10, below the transition temperature region, KId changes to KIc, reflecting the difference in the fracture mode observed on the fracture surface.
It is 30-50% lower than that, and the transition temperature is 40-50℃.
The temperature has shifted to the high temperature side, showing good correspondence with the results of Iwadate et al. In addition, even in the uppershelf region, KId is 10 to 20% lower than KIc, but this is because crack propagation is similar to the decrease during unstable fracture where the shear fracture ratio decreases as the velocity increases. This is also considered to be the result of a decrease in the shear fracture ratio due to the strain rate effect. but,
This trend in the Upper 5 helf area is Kld crab work.

Said Iwadate et al. Logsdon (Log
sdon, W, A,, proc, of the W
inter Annual Meetino of
the ASM E.

MPC-8 (1978), 149. ) The results were completely different from those reported. The report by Iwadate et al.
It is stated that the increase in s is the cause of making Kld 15 to 20% larger than KIC, and it is believed that the KId value will certainly increase further if an analysis is performed in consideration of the strain rate effect in FIG. 10. However, considering that the value is proportional to the 172nd power of the load and that the high strain rate region is limited to the vicinity of the crack, even if the dynamic yield stress increases by about 20%, it will only increase by a few percent. It is estimated to be.

Therefore, if the above-mentioned strain rate effect on the amount of crack growth is also considered, it is considered that KId will not become larger than KIc.

From the above, the following conclusion can be drawn.

(1) In this test method, the load is electromagnetic force, which is a uniformly distributed force, so it is possible to avoid mixing higher-order mode vibrations into the toughness value, and the deformation mode is a constant mode that does not depend on the loading speed. Therefore, it has high reproducibility and is advantageous in determining toughness values.

(2>A308 cl, the dynamic fracture resistance value of 3 steel is not only below the transition temperature region, but also in the upper 5heil
It also decreases in the f range.

The explanation so far has been about the case of testing by applying a shocking dynamic load to the test specimen, but for example, if the current value is gradually increased and applied, it is possible to apply a static load. It is also possible to test fatigue strength, etc. by repeatedly applying a pulsed current that does not destroy the specimen at predetermined intervals, and various other tests can be performed by changing the way the current is applied. .

FIG. 11 shows a second embodiment of the present invention, in which a non-conductive test specimen is used. In the figure, 50
is a non-conductive test piece made of wood, synthetic resin, etc., and is formed in the same shape as the test piece 30 described above. Reference numeral 51 denotes a conductive layer formed on the upper surface of the test specimen 50, such as an aluminum tape, and is attached with an adhesive or the like.

Both ends of the aluminum tape 51 are connected to both ends of the discharge circuit 20. The conductive layer may be made of any material as long as it has conductivity, but as mentioned above, magnetic force acts in the (-2) direction and (Z) direction with iron-based metals, so non-magnetic materials may be used. Are suitable. Therefore, when a current (2) is applied to the aluminum tape 51 from the discharge circuit 20, an electromagnetic force (IXB) is applied to the aluminum tape 51 in the (-y) direction.
) is applied to the entire upper surface of the test specimen 50. Therefore, the same load as in the case of the first embodiment is applied to the test specimen 50, and the test can be conducted in the same manner. Note that the other configurations and operations are the same as those of the first embodiment.

(Effects of the Invention) As explained above, according to the present invention, in a load application method when testing the strength characteristics of a material or structure,
A conductive test piece or a test piece with a conductive N layer on the surface to which stress is to be applied is placed in a uniform steady magnetic field, and the test piece or conductive layer is placed in a direction that intersects the direction of the magnetic flux of the magnetic field. Since the current is passed towards the test object or conductive layer, an electromagnetic force is generated in the test object or the conductive layer according to the direction and strength of the current, which causes the test object or the conductive layer to take an image or recoil. It is possible to apply an even load to the entire area with high precision without generating any magnetic field, and the load can be calculated easily and with high precision from the value representing the current value and the strength of the magnetic field. can be easily controlled by controlling the above-mentioned current, it is easy to apply a short-time load, and furthermore, there is no need for a load transmitter to apply the load by contacting the test piece or the test piece. This has advantages such as ease of testing under special conditions.

[Brief explanation of drawings]

The drawings are provided to explain the present invention, and include Figures 1 to 11.
The figures show a first embodiment of the present invention, in which Fig. 1 is a perspective view showing the schematic configuration, Fig. 2 is a perspective view showing a specific example of the test specimen, and Fig. 3 is the time of Ti flow value and J integral. Figure 4 is a diagram showing a comparison between the dynamic J-δ relationship and static J-δ relationship. Figure 5 is a diagram showing a comparison between analysis and experiment of the static J-δ relationship. The figure shows a comparison between the analysis and experiment of the time history of displacement δ, Figure 7 shows the time history of potential difference, Figure 8 shows the time history of current and displacement, and Figure 9 shows the static R. A diagram showing a comparison between the curve and the dynamic R curve, FIG. 10 is a diagram showing the temperature dependence of static and dynamic fracture toughness values, and FIG. 11 is a schematic configuration diagram showing the second embodiment of the present invention. FIGS. 12(a) to 12(f) are diagrams showing how the test specimen vibrates in conventional tests. 10...Magnetic field, 20...Discharge circuit, 30.50...
- Test specimen, 40.41... stand, 51... conductive layer. Congee Otsu l Figure 3 Mochicho t (rnsec) Figure 4 Figure 5 Changed position, 6 (mm) Figure 6 Time ↑ (msec) To 9 Figure 8 Time ↑ (msec) Figure 9 Figure 10 Figure Temperature T (''C) Figure 11

Claims (2)

[Claims] (1) In the loading method when testing the strength characteristics of materials or structures, a conductive test specimen or a test specimen with a conductive layer on the surface to which stress is to be applied is placed in a uniform steady magnetic field. 1. A method for applying a load for a material test, characterized in that a current is passed through the test object or the conductive layer in a direction intersecting the direction of the magnetic flux of the magnetic field. (2) A load application method for material testing as set forth in claim 1, characterized in that a pulse current from an LCR series discharge circuit is passed as the current.