JP2014178192A - Plane bending fatigue testing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plane bending fatigue testing machine capable of easily performing the adjustment of testing conditions without stopping the testing machine while allowing the same load as that of the conventionally known testing machine to be applied to a testing piece.SOLUTION: A plane bending fatigue testing machine includes: first holding parts (5A, 50A, 50A') for holding one end of a plate-like testing piece (TP); a second holding part (8A) for holding the other end of the test piece; a rotation servo motor (20) for generating a drive force to displace the first holding part so as to apply a bending moment to the test piece; a motor controller (100) for controlling the rotation servo motor so that the rotation servo motor performs a rotation rocking motion which alternately normally rotates and reversely rotates; and transmission members (3, 4, 5; 50; 50B) transmitting the rotation rocking motion generated by the rotation servo motor to the first holding parts and allowing the first holding parts to perform the rocking motion with the center of the test piece located at a neutral position as a center.

Description

  The present invention relates to a plane bending fatigue testing machine for performing a fatigue test of a material by repeatedly applying a plane bending moment to a plate-like test piece.

  Fig. 1 shows the configuration of a plane bending fatigue tester (based on JIS Z2275), which is generally called a Schenck type plane bending fatigue tester and has been widely used by material researchers. FIG. 1 is created based on the principle of operation described on the web page referred to as Non-Patent Document 1 in this specification.

  As shown in FIG. 1, the plane bending fatigue testing machine has an electric motor 2 attached to the side surface of the machine base 1, and the eccentric amount of the rotating shaft 2 a of the electric motor 2 can be manually adjusted. An eccentric cam (eccentric device) 3 is attached. A first end of a connecting rod 4 is pivotally attached to the eccentric cam 3. The second end of the connecting rod 4 is pivotally attached to the tip of the drive arm 5. The base end of the drive arm 5 is pivotably pivotable on a swing shaft 6 rotatably supported by a bearing (bearing) (not shown) attached to a bearing base (not shown) firmly fixed to the upper surface of the machine base 1. It is worn. A first holding portion 5 </ b> A for fixing the first end of the test piece TP is provided at an intermediate portion of the drive arm 5.

  The lower end portion of the support spring plate 7 is fixed to the upper surface of the machine base 1. The support spring plate 7 extends in the vertical direction, and the center line of the support spring plate 7 passes through the center axis of the swing shaft 6. The supporting spring plate 7 supports the load in the vertical direction acting on the test piece TP, so that only the load acts on the load cell 10 without applying a bending moment. The upper end portion of the support spring plate 7 is attached to the proximal end of the measurement swing arm 8. The tip of the measurement swing arm 8 is attached to the load cell 10 via a torsion bar 9. A second holding portion 8 </ b> A for fixing the first end of the test piece TP is provided at an intermediate portion of the measurement swing arm 8. The second holding portion 8A may be regarded as a substantially fixed member that has only a negligible displacement as compared with the first holding portion 5A. When the test piece TP is in the neutral position (the position where no load is received) shown in FIG. 1, the central axis of the swing shaft 6 passes through the center point C of the test piece TP. Accordingly, it can be said that the first holding portion 5A is a member that swings around the center point C of the test piece TP in the neutral position in a side view. The center point C of the test piece TP is the thickness of the test piece at the center in the length direction of the constricted part (test part), that is, the minimum cross-sectional position in a plane-bending test piece having a known shape (see also FIGS. 2 and 3). It means the center point in the width direction and the width direction.

  By changing the eccentric amount of the eccentric cam 3 (that is, the distance between the rotating shaft 2a of the electric motor 2 and the pivot of the first end of the connecting rod 4), the swing angle range of the drive arm 5 is changed. Thus, the bending moment applied to the test piece TP can be changed. The bending moment actually generated can be calculated based on the detected value of the load cell 10. Further, the electric motor 2 can be moved vertically along the side surface of the machine base 1 and fixed at an arbitrary position, thereby changing the average bending moment applied to the test piece TP. Can do.

  In this plane bending fatigue testing machine, the eccentric amount of the eccentric cam 3 is adjusted as follows. First, the test machine is stopped, and the test piece TP is firmly fixed to the first and second holding portions 5A and 8A with screws. Loosen the screw fixing the eccentric cam 3, adjust the position of the eccentric cam 3 so that the pivot of the first end of the connecting rod 4 is located at a position where a desired bending moment can be obtained, and again The eccentric cam 3 is fixed by tightening the screw. In this state, the eccentric cam 3 is manually forcibly rotated once and the detection value detected by the load cell 10 is confirmed. The fine adjustment of the position of the eccentric cam 3 is repeatedly performed until the detected value becomes a desired value. This work requires skill and is very troublesome. Furthermore, in some old-fashioned testing machines, there are those in which the measurement swing arm 8 is supported on the upper surface of the machine base 1 via a spring instead of the load cell 10. In this type of apparatus, the displacement amount of the measurement swing arm 8 is measured by a dial gauge, and is used instead of load detection by the load cell 10. In this case, a series of adjustment operations becomes even more troublesome. Hereinafter, in this specification, the plane bending fatigue tester having the configuration shown in FIG. 1 is also referred to as a “conventional tester”.

  When the bending stiffness changes due to fatigue damage to the test piece TP itself, the generated bending moment may also change. In this case, if the operation of the testing machine is stopped during the test and the eccentric amount of the eccentric force m 3 is not readjusted, the “bending moment constant test” cannot be performed over the entire fatigue life. It turns out that. However, in the case of a smooth test piece that does not have a stress concentration part in the test part (neck part), the bending stiffness changes only to a negligible level in most of the fatigue life, so the influence on the fatigue life evaluation can be ignored. In many cases, the examination is conducted. Strictly speaking, however, the bending stiffness changes greatly in the process of fatigue cracks occurring and progressing, and therefore the bending moment changes greatly. Therefore, a constant load control test is conducted over the entire fatigue life. It doesn't matter.

  Further, in the case of a notch specimen having a stress concentration portion in the test portion, fatigue damage such as a crack occurs in the stress concentration portion from the beginning of the fatigue life and progresses, so the bending rigidity of the test piece changes. For this reason, if the test is continued with the eccentricity of the eccentric force 3 kept constant, the bending moment applied to the test piece changes (generally decreases), and a correct fatigue life cannot be evaluated.

[Http://www.tksnet.co.jp/products/materials05_01.html]Takes Group website / product guide / material testing machine / plane bending fatigue testing machine page

  One object of the present invention is to adjust the test conditions (for example, the amount of displacement of the test piece, the load applied to the test piece, etc.) while allowing the test piece to be given the same load as a conventional testing machine. An object of the present invention is to provide a plane bending fatigue testing machine that can be easily performed without stopping the testing machine.

  The present invention provides a plane bending fatigue testing machine for performing a fatigue test by repeatedly applying a plane bending moment to a plate-like test piece, a first holding portion for holding one end of the plate-like test piece, and the plate-like test piece A second holding part that holds the other end of the test piece, a rotary servo motor that generates a driving force for displacing the first holding part to give a bending moment to the plate-like test piece, and a forward rotation alternately. And a motor controller for controlling the rotary servo motor so that the rotary servo motor performs a reverse rotational swing motion, and the rotational swing motion generated by the rotary servo motor is transmitted to the first holding unit, There is provided a plane bending fatigue testing machine comprising: a transmission member that causes the first holding portion to perform a swinging motion around the center of the plate-shaped test piece in a neutral position.

  According to the present invention, it is possible to easily apply a load similar to that of a conventional testing machine to a test piece, and easily adjust test conditions (for example, a displacement amount of the test piece, a load applied to the test piece). It can be carried out. Furthermore, the test conditions can be changed without stopping the testing machine.

It is a schematic side view for demonstrating the structure and operating principle of the conventional plane bending fatigue testing machine. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view for explaining the configuration and operating principle of a first embodiment of a plane bending fatigue testing machine according to the present invention. It is a schematic perspective view which shows the modification of 1st Embodiment. It is a schematic perspective view which shows the structure of 2nd Embodiment of the plane bending fatigue testing machine by this invention. It is a figure for demonstrating the bending rigidity change during a fatigue test. It is a graph explaining the test result performed using the testing machine by 1st Embodiment.

  Next, embodiments of the invention will be described with reference to the accompanying drawings.

  FIG. 2 is a schematic side view showing the configuration of the plane bending tester according to the first embodiment of the present invention. In FIG. 2, the same members as those shown in FIG. 1 are denoted by the same reference numerals, and a duplicate description of these members is omitted.

  In the first embodiment shown in FIG. 2, a servo motor 20 that can rotate forward and backward and can control the rotation shaft (drive shaft) to an arbitrary rotation phase (rotation swing angle) is used as the electric motor. It is done. The operation of the servo motor 20 is controlled by a controller 100 described in detail later. A disk member 50 concentric with the rotation shaft is attached to the rotation shaft of the servo motor 20, and is located at a position away from the center of the disk member 50B by a predetermined distance in the radial direction from the rotation shaft of the servo motor 20. A first holding part 50A for fixing the first end of the test piece TP is provided. In a side view, the rotation axis O of the rotation shaft of the servomotor 20 coincides with the center of the disk member 50 and the center C of the test piece TP.

  As is clear from the above configuration, the first holding portion 50A of the embodiment shown in FIG. 2 is completely the same as the swing axis of the first holding portion 5A of the conventional testing machine in FIG. 1 (as a relative position with respect to the test piece TP). It can be swung around the swing axis at the same position. The structure of the testing machine (support spring plate 7, measurement swing arm 8, second holding part 8A, torsion bar 9, load cell 10, etc.) involved in holding the second end of the test piece TP is completely the same as that of the conventional testing machine. Are the same. That is, it is structurally possible to make the load form on the test piece TP exactly the same as that of the conventional test machine.

  FIG. 3 is a perspective view showing a modification of the first embodiment shown in FIG. In FIG. 3, a part of the measurement swing arm 8 and the support spring plate 7 are not shown in order to prevent the drawing from becoming complicated. Also in this modification, the structure of the tester involved in holding the second end of the test piece TP (support spring plate 7, measurement swing arm 8, second holding portion 8A, torsion bar 9, load cell 10, etc.) has been conventionally used. It is exactly the same as the testing machine. In the modification shown in FIG. 3, a bearing base 51 that holds a bearing 52 such as a ball bearing is firmly fixed on the machine base 1. The bearing 52 supports the swing shafts 53 at both ends of the U-shaped drive arm 50B. Therefore, the drive arm 50 </ b> B can swing around the central axis of the swing shaft 53. The swing shaft 53 on the side close to the servo motor 20 is directly coupled to the rotary shaft 21 of the servo motor 20 so as not to be relatively rotatable. The first holding portion 50 </ b> A ′ is attached to the drive arm 50 </ b> B at a position separated from the swing shaft 53 by a predetermined distance in the radial direction. Therefore, also in this modification, by rotating and swinging the rotating shaft 21 of the servo motor 20 (as a relative position with respect to the test piece TP), the swing axis of the first holding unit 5A of the conventional testing machine in FIG. The first holding portion 50A ′ can be swung around the swing axis at the same position. The modification shown in FIG. 3 is the same as the embodiment shown in FIG. 2 except for the above points.

  In the modification shown in FIG. 3, the rotating shaft 21 of the servo motor 20 is directly connected to the swing shaft 53 of the drive arm 50B, but the present invention is not limited to this. For example, the rotation shaft (drive shaft) 21 of the servo motor 20 may be provided separately from the rotation shaft (driven shaft), and both the rotation shafts may be connected to each other so as to be able to transmit a driving force by a transmission mechanism such as a timing belt or a gear. In this case, the other rotation shaft (driven shaft) is disposed coaxially with the swing shaft 53 of the drive arm 50B and is directly connected to the swing shaft 53 of the drive arm 50B.

  FIG. 4 is a schematic perspective view showing the configuration of a plane bending tester according to the second embodiment of the present invention. Also in FIG. 4, part of the measurement swing arm 8 and the display of the support spring plate 7 are omitted in order to prevent the drawing from becoming complicated. In the embodiment shown in FIG. 4, a servo motor 20 that can rotate forward and reverse and can control the rotation shaft (drive shaft) to an arbitrary rotation phase (rotation angle) is used as the electric motor. 1 except that the mechanism for adjusting the amount of eccentricity of the eccentric cam 3 is omitted, and the function for adjusting the vertical position of the electric motor (in this case, the servo motor 20) is omitted. It is the same as the conventional testing machine shown. However, regarding the eccentricity adjustment mechanism of the eccentric cam 3 and the vertical position adjustment function of the electric motor, the bending moment range that can be realized by the testing machine and the control resolution at the time of large amplitude and small amplitude For example, it may be left without being omitted. 4 corresponds to the bearing base and bearing (bearing) not shown in FIG. 1, and the swing shaft 53 corresponds to the swing shaft 6 in FIG.

  Also in the second embodiment shown in FIG. 4, the load mode on the test piece TP can be made exactly the same as that of the conventional test machine. The second embodiment shown in FIG. 4 has an advantage that the conventional testing machine can be modified to the testing machine according to the present invention with a slight improvement. That is, the test machine according to the present invention can be modified by simply changing the motor of the conventional test machine to a servo motor and providing an appropriate controller for controlling the servo motor. On the other hand, in the embodiment shown in FIG. 2 and FIG. 3, the configuration of the driving mechanism of the test machine is simplified, and between the first support portion 50A that supports the first end of the test piece and the rotation shaft of the motor. Since the number of links intervening in the space decreases, it can be expected that the controllability of the operation of the first support portion 50A is improved.

  Next, the controller 100 will be described. The controller 100 can perform the following basic control.

[Constant load control (closed loop feedback control)]
When performing a constant load control test, the tester operator designates (inputs) a load waveform using a user interface (not shown) of the controller 100, and further designates load peak values (peak side peak value and valley side peak value) ( input. The “load” specified here may be the load itself detected by the load cell 10 or the bending stress generated in the test piece TP that can be calculated from the load detected by the load cell 10. It may be a bending moment or the like. During the test, the load applied to the test piece TP in real time is detected by the load cell 10 and sent to the controller 100. The controller 100 rotates and swings the servo motor so that the detected value matches the target value according to the difference between the detected value of the load cell 10 and the target value (target load at each time point defined by the load waveform). To control. Since the load waveform of the conventional testing machine is a sine wave, it is preferable to select a sine wave as the load waveform in order to match the load conditions with the conventional testing machine. Instead of detecting the load on the test piece TP with the load cell 10 as described above, the load may be detected with a strain gauge attached to the test piece TP.

[Constant displacement control (closed loop feedback control)]
In this case, for example, based on a detected value of a rotary encoder (not shown) that can measure the rotational swing angle of the rotary shaft (21) of the servo motor 20, the controller 100 performs the rotational swing operation of the servo motor 20. To control. The test machine operator designates (inputs) a displacement amount waveform using a user interface (not shown) of the controller 100, and further designates (inputs) displacement amount peak values (peak side peak value and valley side peak value). The “displacement amount” referred to here may be the rotational swing angle of the rotating shaft of the servo motor 20 and corresponds to an appropriate parameter that can be expressed as a function of the rotational swing angle, for example, the rotational swing angle. The displacement amount of the first end of the test piece TP or the first holding portion 5A may be used. During the test, the rotary swing angle of the rotary shaft of the servo motor 20 is detected in real time by the rotary encoder and sent to the controller 100. The controller 100 controls the rotation of the servo motor so that the detected value matches the target value according to the difference between the detected value of the rotary encoder and the target value (target displacement amount at each time point defined by the displacement amount waveform). Control dynamic motion. Since the displacement amount waveform of the conventional testing machine is also a sine wave, it is preferable to select the sine wave as the displacement amount waveform in order to match the load conditions with the conventional testing machine. When performing this constant displacement control, instead of using the detection value of the rotary encoder, a displacement meter (not shown) that can directly measure the displacement amount of the first end of the test piece TP or the first holding portion 5A. The detected value can also be used.

[Open loop control]
Instead of performing closed loop control as described above, reverse loop operation is performed using the target load peak value or displacement peak value as a limit value, and open loop control is performed in which the operating speed of the servo motor 20 is constant. You can also. In this case, for example, the testing machine operator inputs a peak value (limit value) of the target displacement amount to the controller 100. The controller 100 controls the servo motor 20 in a speed control mode with a constant rotation speed, and when a detection value of a rotary encoder (not shown) that measures the rotation swing angle of the rotation shaft of the servo motor 20 reaches a limit value. In addition, the rotational swing direction of the servo motor 20 is reversed. As the limit value, for example, a load detected by the load cell 10 can be used.

  According to the above embodiment, the following advantageous effects can be obtained.

  (1) Control mode while allowing the same load to be applied to the test piece as in the conventional testing machine (which means the plane bending fatigue testing machine of the type shown in FIG. 1 as described above, the same applies hereinafter). Regardless of (load control, displacement control, closed loop control, open loop control), the labor required for adjusting test conditions (for example, the displacement of the test piece, the load applied to the test piece, etc.) Compared with this, it can be greatly reduced. In addition, the test conditions can be changed without stopping the testing machine. In the plane bending fatigue testing machine according to the above embodiment, it is structurally possible to make the load form on the test piece TP exactly the same as the conventional testing machine. For this reason, with the change of the configuration of the testing machine, matching with past data collected by the conventional machine is not lost.

  (2) Since the peak value (peak side peak value and valley side peak value) of the load or displacement can be individually set, it has been provided in the conventional testing machine to adjust the average load (target bending moment). The position adjustment mechanism of the electric motor can be omitted. Of course, in order to ensure the flexibility of load condition adjustment, the position adjustment mechanism of the electric motor may be left.

  (3) A constant load control test, which was impossible with a conventional testing machine, can be performed. With conventional testing machines, only a constant displacement control test was possible. When a constant displacement test is performed, the bending moment slightly changes due to changes in bending rigidity (hardening / softening phenomenon of the material) due to fatigue damage of the specimen before fatigue cracking, even with a smooth specimen. (See FIG. 5 (a)). Also, when fatigue cracks occur early in the fatigue life, such as when using notched specimens, and the majority of the fatigue life is spent on the development of fatigue cracks, the bending stiffness changes greatly during the test period, Therefore, the bending moment changes greatly (see FIG. 5B). This cannot be a constant load control test used to measure a fatigue characteristic test, and more strictly speaking cannot be a constant displacement control test. However, according to the above embodiment, a closed loop load control test corresponding to an arbitrary target waveform can be performed regardless of the change in the bending rigidity of the test piece. A more accurate displacement control test can also be performed.

(4) Since the load can be freely changed during operation of the testing machine, the stress intensity factor gradual reduction test can be performed fully automatically. The stress intensity factor gradual decrease test is a known test, which will be briefly described. -After conducting a fatigue test with a stress intensity factor K ₁ (load (load stress σ ₁ )) at which the crack progresses, the crack length a ₁ is measured, and if the crack has progressed, the crack length a ₁ reduces the stress intensity factor than K ₁ in consideration of the (usually 10% reduction) is allowed stress intensity factor K ₂ become as shown in target load (load stress sigma ₂₎₎ by setting the fatigue test continue. Finally, the stress intensity factor when the crack does not substantially progress (usually, it is considered that the crack does not progress with da / dn <10 ⁻¹⁰ m / cycle) is determined as the lower limit stress intensity factor. -When performing this stress intensity factor gradual reduction test, the crack growth is monitored in real time using a crack length measuring device of the test piece (for example, a measuring device by the proximity terminal DC potential difference method). Based on the measurement result of the crack length measuring device, the reduced load stress is automatically determined by the calculation program, and the operation of the servo motor 20 is controlled so that the determined load stress is realized. This operation will automatically reduce the load stress until the cracks are almost undeveloped. Thereby, the stress intensity factor gradual reduction test can be performed fully automatically. In order to perform this stress intensity factor gradual reduction test with a conventional testing machine, a great amount of labor is required. However, according to this embodiment, the labor can be dramatically reduced.

  Next, the advantages of the plane bending fatigue testing machine that enables load control will be specifically described taking a crack growth test for measuring fatigue crack growth characteristics as an example.

Austenitic stainless steel SUS316L with or without cavitation peening (CP) or non-NP (NP) is prepared, and fatigue crack propagation is controlled by load control using the plane bending fatigue testing machine according to the first embodiment shown in FIG. The characteristics were investigated. The length of the fatigue crack was measured by the proximity terminal DC potential difference method. The result of the fatigue test with constant load amplitude by load control is shown by the crack growth rate curve of NP plotted with white diamonds and the crack growth rate curve of CP plotted with black diamonds in the graph of FIG. In the graph of FIG. 6, the vertical axis represents “crack growth rate da / dN (m / cycle)” and the horizontal axis represents “stress intensity factor ΔK (MPam ^1/2 )”. This result can be judged to indicate a correct characteristic that conforms to the Paris law.

  As a comparative example, a fatigue test by displacement control was performed. Here, fatigue crack propagation characteristics were investigated by displacement control using the plane bending fatigue testing machine according to the first embodiment shown in FIG. That is, in this comparative example, in the conventional plane bending fatigue tester shown in FIG. 1, the eccentric amount of the eccentric cam 3 is once measured after the initial load is adjusted by adjusting the eccentric amount of the eccentric cam 3. This corresponds to the case where the fatigue test is continued without adjustment. In the NP crack growth rate curve plotted with white circles in the graph of FIG. 6, there is a region where the crack growth rate is constant as surrounded by an ellipse. This is because in the case of displacement control, the stress decreases as the crack progresses. That is, this result is not appropriate as a fatigue crack growth characteristic.

  As can be seen from the above, the plane bending fatigue testing machine according to the present embodiment allows a load to be applied to the test piece in the same manner as the conventional testing machine, while the crack propagation process has much fatigue life. In the fatigue evaluation test that occupies and the fatigue crack growth test for measuring the crack growth characteristics, there is an advantageous effect that appropriate data can be obtained.

  As is well known, in a conventional testing machine, a torsion test of a round bar test piece is performed with a plane bending fatigue tester by attaching an attachment for a torsion test to the first holding part and the second holding part. However, it goes without saying that the same use is possible also in the plane bending fatigue testing machine according to the present embodiment.

2 Servo motor 5A, 50A, 50A '1st holding part 8A 2nd holding part 100 Motor controller 3, 4, 5; 50; 50B Transmission member 10 Sensor

Claims (6)

In a plane bending fatigue testing machine for performing fatigue tests by repeatedly applying a plane bending moment to a plate-shaped specimen,
A first holding part for holding one end of the plate-shaped test piece;
A second holding part for holding the other end of the plate-shaped test piece;
A rotary servo motor that generates a driving force for displacing the first holding portion in order to give a bending moment to the plate-shaped test piece;
A motor controller that controls the rotary servo motor so that the rotary servo motor performs a rotational swing motion that alternately forwards and reverses alternately;
Transmission that causes the first holding portion to perform the swinging motion about the center of the plate-like test piece in the neutral position by transmitting the rotational swinging motion generated by the rotary servo motor to the first holding portion. Members,
A plane bending fatigue testing machine equipped with A sensor that detects an actual value of a parameter that changes in accordance with a displacement amount of the first holding portion or a change in a bending moment generated in the test piece;
A motor controller for controlling the rotational swing motion of the rotary servomotor based on the detection value of the sensor so that the actual value of the parameter becomes a target value;
The plane bending fatigue testing machine according to claim 1, further comprising:   The load cell as the sensor is connected to the second holding unit, and the motor controller controls the rotational swing motion of the rotary servo motor so that the detected value of the load cell becomes a target value. The plane bending fatigue tester described.   A rotary encoder that detects the swing angle of the rotary servo motor is provided as the sensor, and the motor controller controls the rotational swing motion of the rotary servo motor so that the detected value of the rotary encoder becomes a target value. The plane bending fatigue testing machine according to claim 2.   The transmission member is directly connected to a rotating shaft that rotates by receiving a driving force from the rotating shaft of the rotating servo motor or the rotating shaft of the rotating servo motor, and swings around a swing shaft that is coaxial with the rotating shaft. The plane bending fatigue test according to any one of claims 1 to 3, wherein the first holding portion is provided at a position that is made of a moving member and is radially separated from the swing shaft of the swing member. Machine.   The transmission member is provided with an eccentric cam attached to a rotation shaft of the rotary servo motor, a connecting rod pivotally attached to the eccentric cam, and pivotally attached to the connecting rod and provided with the first holding portion. The plane bending fatigue testing machine according to any one of claims 1 to 3, further comprising a driven arm.

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