JP5716616B2 - Material testing machine - Google Patents

Description

  The present invention relates to a material testing machine including a crosshead that can be moved up and down with respect to a support.

  Conventionally, a tensile test is performed by extending and lowering the crosshead along a support column erected on the base by expanding and contracting the lifting cylinder, and applying a test force to the test body installed between the base and the crosshead. A material testing machine for performing a compression test, a fatigue test, and the like is known (see, for example, Patent Document 1 and Patent Document 2). In such a material testing machine, a clamping means such as a hydraulic clamp for fixing the crosshead at a predetermined height position is disposed on the crosshead. During the test, a hydraulic source is connected to the hydraulic clamp. By supplying and pressurizing pressure oil, the crosshead is fixed to the column and when adjusting the height position of the crosshead according to the size of the specimen, the pressure oil in the hydraulic clamp is removed to release the pressure. In addition, the crosshead can be moved up and down along the column by expansion and contraction of the lifting cylinder.

Japanese Patent Laid-Open No. 9-210887 Utility Model Registration No. 3134723

  By the way, in a material testing machine having such a clamping means, when the fixing and releasing of the crosshead to and from the support column are repeated, stress is repeatedly applied to the components of the clamping means, resulting in fatigue failure of the components. There is.

  For example, as described in Patent Document 1, in the hydraulic clamp, the clamp rod of the hydraulic clamp is disposed in the through hole of the cross head, and the nut is fastened to the screw portion formed at the end of the clamp rod. It is attached to the crosshead. For this reason, the clamp rod is pulled in the axial direction of the clamp rod by the flow of pressure oil into the clamp cylinder of the hydraulic clamp when the cross head is fixed to the support column. If the crosshead is fixed and released repeatedly, stress is repeatedly applied to the bolt-nut fastening body formed at the end of the clamp rod, and the load on the clamp rod is within the elastic limit. Even in such a case, fatigue failure may occur at the threaded portion of the clamp rod.

  In order to prevent such accidents due to fatigue failure, it is conceivable to periodically replace the relevant parts. However, in this type of material testing machine, the usage frequency, test conditions, etc. are not used between users. There is a big difference in the situation. Actual fatigue failure is a phenomenon that depends on the actual usage of each material testing machine, and if the part replacement time is determined using the years of use as an index based on the design conditions set by the design side, for users with low usage frequency, Even parts that can still withstand sufficient use will be scrapped early and will be uneconomical.

  In addition, if an excessively high safety factor that places importance on safety is set and the apparatus is designed, problems of enlarging the apparatus and making it redundant also arise. In some cases, the operability of the apparatus is impaired due to the enlargement of the apparatus.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a material testing machine capable of presenting a more appropriate part replacement time to the user.

The invention according to claim 1 is a cross head that moves up and down along a column erected on a base, and a load actuator that applies a test force to a test body installed between the base and the cross head An elevating cylinder for elevating the crosshead, a fixing means disposed on the crosshead and fixing the crosshead to the support column at an arbitrary height position, and fixing the crosshead by the fixing means / Counting means for measuring the number of repetitions of the unlocking operation, and the fixing means is a hydraulic clamp that is actuated by pressure oil from a hydraulic source, and the hydraulic clamp is capable of fixing / unfixing the crosshead. A clamp rod is provided as a component that repeatedly receives stress when repeatedly executed, and the counting means connects the hydraulic source and the hydraulic clamp. The pressure fluctuation detecting frequency of the pressure switch disposed conduit, wherein a number of iterations of the fixed / unlocking operation of the crosshead measures the number of times that the clamp rod is subjected to stress and displaying .

The invention according to claim 2 warns that, in the invention according to claim 1, the number of repetitions measured by the counting means has reached the upper limit of use determined based on the fatigue life of the clamp rod. Warning means is provided.

According to a third aspect of the present invention, in the invention of the second aspect, the fatigue life is calculated based on an SN diagram prepared in advance from a result of a fatigue test performed on the clamp rod , and the crosshead. It is estimated from the stress amplitude obtained from the fluctuation of stress generated in the clamp rod during the fixing / unfixing operation.

According to the first aspect of the present invention, since the counting means for measuring and displaying the number of repetitions of the fixing / unfixing operation of the crosshead by the hydraulic cylinder is provided, the user can repeat the operation by confirming the number of measurements by the counting means. It is possible to grasp the replacement timing of the clamp rod from the frequency of use of the clamp rod , which is a component of the hydraulic cylinder that receives stress.

According to the second aspect of the invention, there is provided warning means for warning that the number of repetitions measured by the counting means has reached the upper limit number of use determined based on the fatigue life of the clamp rod of the hydraulic cylinder. From this, it is possible to prevent sudden stoppage of the apparatus.

According to the third aspect of the present invention, the fatigue life is determined based on the SN diagram prepared in advance from the result of the fatigue test performed on the clamp rod of the hydraulic cylinder and the fixing / unlocking operation of the crosshead. Since it is estimated from the stress amplitude obtained from the stress fluctuation generated in the clamp rod, it is possible to prevent fatigue failure of the clamp rod and to design the device without setting an excessive safety factor And the redundancy of the apparatus can be reduced.

It is a front view of the material testing machine which concerns on this invention. It is a side view of the material testing machine which concerns on this invention. 2 is a schematic cross-sectional view of a hydraulic clamp 50 disposed on a cross head 24. FIG. 3 is a schematic diagram of a hydraulic circuit of a hydraulic clamp 50. FIG. 5 is a SN diagram of a clamp rod 53. FIG.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a front view of a material testing machine according to the present invention, and FIG. 2 is a side view thereof.

The material testing machine includes a pair of posts 22 provided upright on a base 21, a cross head 24 which moves up and down along the column 22, a pair of lifting for raising and lowering the cross head 24 depending on the size of the test specimen And a cylinder 23 for use. The cross head 24 includes an optional load actuator 25 for applying a test force to the test body disposed between the base 21 and the cross head 24, a pressure plate 28 for pressing the test body from above, and an optional cross head 24. a hydraulic clamp 50 as a fixing means for fixing the support 2 2 at the level is disposed of.

  The load actuator 25 disposed on the upper portion of the cross head 24 is a hydraulic cylinder that is driven by pressure oil from a hydraulic source (not shown), and the piston rod of the hydraulic cylinder penetrates the cross head 24 and the platen 28. It is connected to. When the compression test is performed, the upper and lower ends of the test body installed on the base 21 are pressed by the platen 28 and the base 21 by driving the load actuator 25. When the upper grip is connected to the piston rod and the lower grip is disposed on the base 21, the upper and lower ends of the upper grip and the lower grip are gripped by the drive of the load actuator 25. It is also possible to conduct a tensile test in which a tensile load is applied to the test specimen. Note that the load actuator 25 is not limited to a hydraulic cylinder, and may be a pneumatic cylinder, an electromagnetic load actuator, or the like.

  The lifting cylinder 23 is erected on the outer side of the support column 22 and expands when pressurized oil is supplied into the lifting cylinder 23, and contracts when the pressurized oil is discharged from the lifting cylinder 23. Single acting cylinder. The cross head 24 is connected to a pair of lifting cylinders 23 and is moved up and down along the columns 22 by the expansion and contraction of the lifting cylinders 23.

  FIG. 3 is a schematic cross-sectional view of the hydraulic clamp 50 disposed on the crosshead 24.

Hydraulic clamp 50 comprises a clamp cylinder 51 the ram 52 and the clamp rod 53, as shown in FIGS. 1 and 2, is connected to a portion connected to the strut 22 in the crosshead 24 on lifting cylinders 23 A total of 8 pieces are arranged with 4 pieces between each part.

The clamp cylinder 51 and the ram 52 are connected by a clamp rod 53 inserted into the through hole of the cross head 24. The clamp rod 53 is a so-called implanted bolt having male screw grooves cut at both ends, and a nut 55 is fastened with a washer 54 sandwiched between a screw portion 58 having a male screw groove cut therein, whereby the hydraulic clamp 50 is connected to the crosshead 24. It is arranged. The nut 55 fastened to the threaded portion 58 of the clamp rod 53 employs a grooved nut that inserts a split pin into the groove to prevent loosening.

  The clamp cylinder 51 is formed with a flow path 56 for supplying pressure oil into the clamp cylinder 51. As shown by a broken line in FIG. 3, a sealing portion for sealing pressure oil is formed between the clamp cylinder 51 and the ram 52.

  FIG. 4 is a schematic diagram of a hydraulic circuit of the hydraulic clamp 50.

  The hydraulic circuit of the hydraulic clamp 50 includes a hydraulic source unit 38 dedicated to the hydraulic clamp 50, and a pressure switch 46 that detects pressure fluctuations in a pipe 45 that supplies oil (hydraulic oil) from the hydraulic source unit 38 to the hydraulic clamp 50. With. A control device 35 for controlling the operation of the entire material testing machine is connected to the hydraulic power source unit 38, and the operator operates a clamp switch 39 connected via the control device 35, whereby the hydraulic clamp 50. The clamp-unclamp state can be switched.

Also connected to the control device 35 is a personal computer 60 having a display unit 61 for displaying a test state and the like and an input unit 62 for inputting a command such as test execution by an operator.

  The hydraulic power source unit 38 includes an oil tank 44 that stores oil, and a pump 41 that supplies oil stored in the oil tank 44 to the hydraulic clamp 50 by driving a motor (not shown). The hydraulic clamp 50 receives supply of pressure oil pumped by the pump 41 via the pipe line 45 connected to the flow path 56 described above.

  A counter 47 with a display is connected to the pressure switch 46 disposed in the pipe 45, and this counter 47 integrates and displays the number of pressure fluctuations detected by the pressure switch 46. The counter 47 functions as the counting means in this invention.

  In such a material testing machine, during the test, the hydraulic clamp 50 is in a clamped state, and the crosshead 24 is fixed to the column 22. On the other hand, when the cross head 24 is moved according to the size of the test body before or after the test, the hydraulic clamp 50 is unclamped to release the fixing of the cross head 24 to the column 22 and the lifting cylinder 23. The cross head 24 is made movable by expanding and contracting.

  First, when the crosshead 24 is fixed to the column 22, the operator operates the clamp switch 39 so that the hydraulic clamp 50 is in a clamped state. When the clamp switch 39 is operated, a control signal is sent to the hydraulic power source unit 38 via the control device 35, and the oil stored in the oil tank 44 by the operation of the pump 41 is supplied to the hydraulic clamp 50 via the pipe 45. To be pumped. At this time, if the pressure switch 46 detects that there has been a pressure fluctuation corresponding to the supply of pressure oil necessary for putting the hydraulic clamp 50 in the clamped state in the pipe line 45, that is, a pressure exceeding the set pressure value. The detection signal is sent to the counter 47, and the count number of the counter 47 is increased by one. The pressure oil flows from the flow path 56 of the clamp cylinder 51 into the sealed portion (see the broken line portion in FIG. 3) between the clamp cylinder 51 and the ram 52, whereby the clamp cylinder 51 is pressed toward the cross head 24 side. The The hydraulic clamp 50 fixes the crosshead 24 to the column 22 by the action of the tightening force caused by such pressure.

  Next, when the cross head 24 is moved, the operator operates the clamp switch 39 so that the hydraulic clamp 50 is in an unclamped state. When the clamp switch 39 is operated, a control signal is sent to the hydraulic power source unit 38 via the control device 35, and the pressure oil sealed between the clamp cylinder 51 and the ram 52 of the hydraulic clamp 50 flows into the flow path 56. And is discharged to the oil tank 44 through the pipe 45. If it does so, the pressing force to the cross head 24 side by the clamp cylinder 51 will be cancelled | released, and fixation to the support | pillar 22 of the cross head 24 will be cancelled | released. At this time, the pressure in the pipe 45 is lowered to the tank pressure in the oil tank 44. As a result, the operator can move the cross head 24 to a desired height position by moving the lifting cylinder 23 up and down.

Thus, in the operation of repeatedly fixing and releasing the cross head 24 to the support column 22, a stress (mainly an axial tensile load) is repeatedly applied to the clamp rod 53 of the hydraulic clamp 50. Stress concentration at the fastening portion between the portion 58 and the nut 55 causes fatigue failure. In order to use the material testing machine safely, it is required to replace the clamp rod 53 before the clamp rod 53 undergoes fatigue fracture. In the material testing machine of this embodiment, the clamp rod 53 is repeatedly stressed. The number of times is accumulated by the counter 47 by detecting the pressure fluctuation at the time of clamping by the hydraulic clamp 50. For this reason, the operator can easily know when the replacement time of the clamp rod 53 has arrived by confirming whether or not the cumulative number of the counter 47 exceeds the predetermined upper limit number of use of the clamp rod 53.

FIG. 5 is an SN diagram of the clamp rod 53.

  In this embodiment, since the hydraulic clamp 50 is employed as a fixing means for fixing the crosshead 24 to the support column 22, among the components of the hydraulic clamp 50, repeated stress is applied by the fixing / unfixing operation of the crosshead 24. The fatigue life of the clamp rod 53 to be received is estimated from the SN diagram, and the use limit number of the clamp rod 53 is determined based on the fatigue life.

  The SN diagram is created from test results obtained by conducting a fatigue test in advance using a bolt-nut fastening body in which the nut 55 is fastened to the clamp rod 53 as a test body. Note that the SN diagram shown in FIG. 5 is different in the processing method of the threaded portion 58 of the clamp rod 53 where the stress is concentrated and the pitch of the thread groove from the viewpoint of usability in selecting the components of the hydraulic clamp 50. And the results obtained by repeatedly applying a predetermined stress to these test bodies are plotted on a graph. In the SN diagram, black diamonds and black squares have the same pitch and different processing methods. Black squares and black triangles have the same processing method and different screw pitches.

  The fatigue life of the clamp rod 53 is determined in advance by measuring the stress fluctuation generated in the clamp rod 53 during the fixing / unlocking operation of the cross head 24 with a stress meter or the like, and preparing the stress amplitude obtained from the stress fluctuation in advance. Estimated by fitting to SN diagram. For example, if the stress amplitude of the actual clamp rod 53 is 250 MPa, the number of repetitions corresponding to this in the SN diagram of FIG. 5 is approximately 6000 times. Then, the number of times that the clamp rod 53 fatigues and breaks, that is, the fatigue life of the clamp rod 53 when the fixing / unfixing operation of the crosshead 24 is repeated with this material testing machine is estimated 6000 times. When there is a large difference in fatigue life depending on the processing method and pitch, the respective fatigue lives are estimated.

  The upper limit number of times the clamp rod 53 is used also indicates the replacement time of the clamp rod 53 before the clamp rod 53 undergoes fatigue fracture. Must. For this reason, in the case of the estimated fatigue life of 6000 times, for example, 3000 times is determined as the use limit number with a sufficient margin. In addition, when the difference of the fatigue life by a processing method or a pitch arises, the estimated fatigue life according to the processing method and pitch of a product is employ | adopted.

  In addition, when other clamping mechanisms, such as a pneumatic type, are adopted as a fixing means for the cross head 24, a fatigue test is performed on the component parts of the clamp mechanism, and an SN diagram is created. The fatigue life is estimated, the number of times of use is determined, and the part replacement time is set.

  In the above-described embodiment, when the operator views the display on the counter 47, the number of times of fixing / unfixing the crosshead 24, that is, the number of times of use of the clamp rod 53 does not exceed the number of times of use (for example, 3000 times). The operator confirms whether or not, by connecting the pressure switch 46 or the counter 47 to the control device 35, the count number of the counter 47 is displayed on the display unit 61 of the personal computer 60, and May display a warning on the display unit 61 to warn that the usage limit has been exceeded. As warning means for warning the operator that the use limit has been exceeded, not only warning display on the display unit 61 but also other warning means such as a warning sound can be adopted.

  Further, the counter 47 may be disposed between the clamp switch 39 and the control device 35 so that the number of operations of the clamp switch 39 is integrated. In this case, the number of clamp-unclamp switching operations of the clamp switch 39 corresponds to the number of times stress is repeatedly applied to the clamp rod 53. The object counted by the counter 47 is not limited to the pressure fluctuation signal detected by the pressure switch 46, and the arrangement position of the counter 47 is based on some fluctuation generated from the clamp switch 39 to the hydraulic clamp 50. Any position where the signal can be detected may be used.

21 Table 22 Strut 23 Lifting Cylinder 24 Crosshead 25 Load Actuator 28 Pressure Plate 35 Control Device 38 Hydraulic Source 39 Clamp Switch 41 Pump 42 Servo Motor 44 Tank 45 Pipeline 47 Counter 50 Hydraulic Clamp 51 Clamp Cylinder 52 Ram 53 Clamp Rod 54 Washer 55 Nut 56 Flow path 58 Screw part 60 Personal computer 61 Display part 62 Input part

Claims (3)

A crosshead that moves up and down along a support post erected on the base;
A load actuator for applying a test force to a test body installed between the base and the crosshead;
An elevating cylinder for elevating the crosshead;
A fixing means disposed on the cross head and fixing the cross head to the support column at an arbitrary height position;
Counting means for measuring the number of repetitions of the fixing / unfixing operation of the crosshead by the fixing means;
Equipped with a,
The fixing means is a hydraulic clamp that is operated by pressure oil from a hydraulic source,
The hydraulic clamp has a clamp rod as a component that repeatedly receives stress when the fixing / unlocking operation of the crosshead is repeatedly executed,
The counting means is the number of pressure fluctuation detections of a pressure switch disposed in a pipe line connecting the hydraulic source and the hydraulic clamp, and is the number of repetitions of the fixing / unfixing operation of the crosshead. A material testing machine that measures and displays the number of times stress is received . The material testing machine according to claim 1,
A material testing machine comprising warning means for warning that the number of repetitions measured by the counting means has reached the upper limit of use determined based on the fatigue life of the clamp rod . The material testing machine according to claim 2,
The fatigue life is obtained in advance from the creation and S-N line had been view, the stress variation occurring in the clamp rod at the time of fixing / unlocking operation of the crosshead from the fatigue tests performed on the clamp rod results stress A material testing machine estimated from the amplitude.

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