JP4206966B2 - Material testing machine - Google Patents

Description

  The present invention relates to a material testing machine, for example, a material testing machine suitable for conducting a material fatigue test.

  In a material testing machine, in general, a load mechanism is driven to apply a tensile or compressive load, or a repeated load on the test piece, and the test force acting on the test piece at that time, along with strain such as elongation of the test piece, etc. measure.

As the load mechanism, a mechanism using a hydraulic cylinder (for example, see Patent Document 1) and a mechanism for moving a crosshead by rotating a screw rod with a motor (for example, see Patent Document 2) are generally used.
JP 2003-28770 A Japanese Patent Laid-Open No. 2002-5801

  By the way, as described above, most of the load mechanism of the conventional material testing machine is a hydraulic drive type or a screw rod type, and those using air as a drive source have not been put into practical use. The reason is that because the air viscosity is small, the cushion is not effective at the stroke end of the cylinder, and because it is a compressible fluid, the response is greatly attenuated and the natural frequency is low. Yes.

  That is, in the hydraulic cylinder, as schematically shown in FIGS. 4A and 4B, the outer diameter of the piston 42 is provided between the cylinder end portion 411 of the cylinder 41 and the inflow / outlet port 412 of the hydraulic oil. When the cushion portion 413 having a slightly larger inner diameter is formed and the piston 42 moves from the other cylinder end portion 414 and enters the cushion portion 413, the hydraulic oil between the cylinder end portion 411 and the piston 42 It flows into the inflow / outflow port 412 through a slight gap between the outer peripheral surface of the piston 42 and the cushion portion 413, and the fluid pressure between the cylinder end portion 411 and the piston 42 increases due to the flow resistance at that time, and the cushioning effect. Is obtained.

  On the other hand, in a pneumatic cylinder, since the viscosity of air as a working fluid is low, it is difficult to obtain such a cushion effect. In order to obtain an effective cushioning effect, it is necessary to narrow the gap between the piston and the cushion part, but this not only increases the processing cost but also causes a failure.

Further, in the pneumatic cylinder, since the working fluid air is a compressible gas, the response is attenuated as shown below. That is, as schematically shown in FIG. 5, when the piston 52 is in the neutral position in the cylinder 51, the length in the longitudinal direction of the upper and lower gaps is L, the volume is V _C , and the pressure receiving area of the piston 52 is A when is _P, the apply force of F to the test piece by the piston 52, the pressure difference P _D of the upper and lower gaps in the cylinder 51 is required. When air flows into and out of the cylinder 51 via the servo valve, the pressure drop in the servo valve is negligible, so the pressure on the one side is actually atmospheric pressure P _A and the other side is P. _D. Since the air is compressed when the pressure increases from P _A to P _D , in order to obtain the pressure of P _{D in} the gap, V _C {(P _D / P _A ) −1 rather than the volume V _{C of} the gap. } (1)
Only an extra volume (volume under atmospheric pressure) of air needs to flow into the gap, and the response is attenuated accordingly.

Furthermore, the equivalent spring constant K of the fluid in the cylinder is K = (A _P k) / L (2)
In this formula (2), _AP is the pressure receiving area of the piston, L is the stroke on one side when the piston is in the neutral position, and k is the bulk modulus of air. Considering a model as shown in FIG. 6 and assuming that the mass of the piston is m, the resonance frequency f in the air cylinder is

It becomes. Since the bulk elastic modulus k of air is smaller than that of oil, the resonance frequency is lower than that of a hydraulic cylinder.

  From the above, the pneumatic cylinder is difficult to cushion, the response is greatly attenuated, and the resonance frequency is low. As described above, it is difficult to perform a test in which a load is repeatedly applied to a test piece, and a material testing machine using a pneumatic cylinder as an actuator for a load mechanism has not been put to practical use.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a material testing machine equipped with a pneumatic cylinder as an actuator for a load mechanism, overcoming various problems when the pneumatic cylinder is used as an actuator for a load mechanism of a material testing machine. is there.

In order to solve the above-described problems, a material testing machine according to the present invention includes a load mechanism that applies a load to a test piece, and the load mechanism uses a cylinder operated by a working fluid supplied through a servo valve as an actuator. In the material testing machine configured such that a load corresponding to the displacement of the piston is applied to the test piece, the cylinder is a pneumatic cylinder and the stroke end portions on both sides of the pneumatic cylinder or the pressure receiving surfaces on both sides of the piston In addition, the cushion material is attached so that the total thickness of the cushion material is a size that leaves a gap that gives the piston a stroke required for the test in the cylinder. and replaceably attached to the pressure receiving surface of the stroke end portion or the piston of the cylinder Characterized by Rukoto (claim 1).

Here, in the present invention, it is preferable to employ a configuration in which a protrusion or a notch is formed on the surface of the cushion material opposite to the cylinder stroke end portion or the mounting surface to the piston pressure receiving surface (Claim 2 ). .

The material for the cushioning material in the present invention can be employed rubber, a resin, or a soft metal than the material forming the cylinder and the piston (claim 3).

  In the present invention, a cushioning material is inserted into the stroke end of the pneumatic cylinder or the pressure receiving surface of the piston to provide a cushioning function with a simple structure, and at the same time, the damping of the response is reduced by the arrangement of the cushioning material. And, it is intended to achieve the intended purpose by increasing the resonance frequency.

  That is, according to the first aspect of the present invention, since the cushion material is provided between the piston and the cylinder end, the air pressure can be increased without providing a cushion portion utilizing the viscosity of the working fluid as in a conventional hydraulic cylinder. Cushion can be applied to the cylinder.

  In a fatigue test using a material testing machine, a piston in a cylinder is used so that both a test with a long stroke, such as when testing a soft material, and a test with a short stroke, such as when testing a metal material. A certain stroke is required. The cushion material plays a role of reducing the extra stroke, reduces the attenuation of the response, and increases the resonance frequency.

That is, by disposing the cushion material in the cylinder, as a result of voids in the cylinder is reduced, V _C decreases as shown in equation (1), the attenuation of the response decreases. In addition, as a result of the cushion material being disposed, the extra stroke in the cylinder is shortened, and as a result, the equivalent spring constant K of air shown in equation (2) is increased, and the resonance frequency f shown in equation (3) is increased.

In the invention according to claim 1 , the cushioning material can be replaced so that the stroke of the piston in the cylinder is filled with the cushioning material, leaving only the stroke required for the test. since the mounting to the pressure receiving surface of the piston laying even stroke end of the cylinder, it can be maximized effect of increasing the resonance frequency to reduce the attenuation of the response described above.

When the cushion material is attached to the stroke end of the cylinder or the pressure receiving surface of the piston, when the piston is located at the stroke end, the cushion material is in close contact with the mating member, and the air for operation is between them. Becomes difficult to invade. Therefore, as in the invention according to claim 2 , by providing a protrusion or a notch on the surface opposite to the cylinder stroke end or the piston pressure receiving surface of the cushion material, it is easy for air for operation to enter. The piston can be operated smoothly.

  And as a material of the cushion material in this invention, rubber | gum and resin can be used, Furthermore, a softer metal than the material which forms a cylinder and a piston can also be used.

  According to the present invention, while using a pneumatic cylinder as an actuator of a load mechanism of a material testing machine, it is possible to provide a cushion function at a low cost, reduce response attenuation, and increase a resonance frequency. Can be used for various fatigue tests.

Moreover, because it uses interchangeably provided a configuration the cushioning material to fill in the cushion material the remainder leaving only strokes required for the pressure receiving surface of the stroke end or the piston of the cylinder test, the response The attenuation reduction effect and the resonance frequency increase effect can be maximized.

Further, by forming protrusions or notches on the surface of the cushioning material as in the invention according to claim 2 , air can easily enter even in a state of close contact with the mating member at the stroke end, and the piston moves smoothly. Is obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a partial cross-sectional view showing a main configuration of the embodiment of the present invention.

  A table 2 is provided on the base 1, and a crosshead 4 is fixed on the table 2 via a plurality of columns 3. A cylinder body 5 a of the pneumatic cylinder 5 is fixed to the lower side of the table 2. The piston 5b of the pneumatic cylinder 5 is integrally provided with piston rods 5c and 5d on both sides in the axial direction. It is installed. The test piece W is used for the test in a state where both ends are held by the pair of upper and lower gripping tools 6a and 6b.

  A load cell 7 is provided between the upper gripping tool 6 b and the crosshead 4, and a load acting on the test piece W by the test is detected by the load cell 7 every moment. A stroke sensor 8 is attached to the lower piston rod 5d of the pneumatic cylinder 5, and the stroke sensor 8 detects the momentary displacement of the piston 5b.

  The pneumatic cylinder 5 is supplied with operating air supplied through the pipe 9 a or 9 b after being controlled by the servo valve 10. The air passing through the servo valve 10 is supplied to the upper or lower gap in the cylinder body 5a through a passage formed in the cylinder body 5a.

  Cushioning materials 11 made of an elastic material such as rubber are attached to the pressure receiving surfaces on both sides of the piston 5b. Each cushion material 11 is fixed to the pressure receiving surface of the piston 5b by a plurality of screws S, as shown in FIG. 2 (A) and a front view in FIG. 2 (B). In addition, a plurality of protrusions C are formed on the surface opposite to the mounting surface with respect to the pressure receiving surface. Ends on both sides of the cylinder body 5a are closed by lids 5e and 5f. By removing the lid 5e or 5f and taking out the piston 5b, the cushion members 11 can be arbitrarily replaced. Yes.

In the fatigue test to apply a repetitive load to the test piece is W, the total thickness of the cushion member 11, the gap only stroke required for the test in the cylinder body 5a is set to the remaining Ru dimensions.

  Now, according to the above embodiment, when the piston 5b is reciprocated, when the piston 5b reaches the upper and lower stroke ends, the lids 5e and 5f of the end portions of the piston 5b and the cylinder body 5a are connected. Since the cushion material 11 made of an elastic material is interposed therebetween, a good cushion function is exhibited. Further, since the projections C are formed on the surface of each cushion material 11, each cushion material 11 is in contact with the lids 5e and 5f of the stroke end portion of the cylinder body 5a only at the upper and lower stroke ends. When air is supplied between the two in order to move from one stroke end to the other, the air easily enters between the two, and the piston 5b can be moved smoothly.

Further, as schematically shown in FIG. 3, when the piston 5b is in a neutral position in the cylinder body 5a, the longitudinal dimension of the upper and lower gaps when the cushion material 11 is not provided is L, which is necessary for the test. When the stroke is set to Δ on one side, the thickness of each cushion member 11 is L−Δ in the above-described thickness setting method, but when the piston 5b is in the neutral position due to the attachment of the cushion member 11, the cylinder upper and lower gap volume V _C of the main body 5a ', when the pressure receiving area of the piston 5b and a _P,
V _C ′ = {L− (L−Δ)} A _P = ΔA _P (4)
It becomes. Table In this, as compared with the volume V _C of the voids in the case of not using the cushion member 11 by using the same pneumatic cylinder, (L-delta) means to become smaller by A _P, wherein the (1) The required amount of air flowing into the cylinder due to the compression of air can be reduced, and the attenuation of the response can be reduced accordingly.

  Further, by attaching a cushion material 11 having a thickness (L−Δ) to both sides of the piston 5b, the resonance frequency f ′ is

Therefore, it can be made higher than the resonance frequency f expressed by the expression (3) when the cushion material 11 is not provided.

In the embodiment of the following, although the example in which each cushion member 11 to the pressure receiving surface of the piston 5b, be attached to the cylinder body 5a and the lid 5e side is possible to obtain exactly the same effect as above it can. In this case, an air passage can be provided in each cushion member 11 so as to communicate with the air passage formed in the cylinder body 5a so that air can flow into the gap in the cylinder body 5a.

It is a fragmentary sectional view which shows the principal part structure of embodiment of this invention. It is the front view (A) of the cushioning material 11 in embodiment of this invention, and its BB sectional drawing (B). It is action explanatory drawing shown with the schematic diagram of the pneumatic cylinder 5 of embodiment of this invention. It is explanatory drawing of the cushion mechanism currently used in a hydraulic cylinder etc. It is explanatory drawing of the response attenuation | damping and resonance frequency which are shown with the schematic diagram of the conventional pneumatic cylinder. 6 is a vibration model of the pneumatic cylinder of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base 2 Table 3 Column 4 Cross head 5 Pneumatic cylinder 5a Cylinder body 5b Piston 5c, 5d Piston rod 5e, 5f Lid 6a, 6b Grasp 7 Load cell 8 Stroke sensor 9a, 9b Air piping 10 Servo valve 11 Cushion material C Protrusion S Screw W Specimen

Claims (3)

A load mechanism for applying a load to the test piece is provided. The load mechanism is configured such that a cylinder operated by a working fluid supplied through a servo valve is an actuator, and a load corresponding to the displacement of the piston of the cylinder is applied to the test piece. In the configured material testing machine,
The cylinder is a pneumatic cylinder, and a cushion material is attached to the stroke end part on both sides of the pneumatic cylinder or the pressure receiving surface on both sides of the piston, and the total thickness of the cushion material is tested in the cylinder. The cushion material is replaceably attached to the stroke end portion of the cylinder or the pressure receiving surface of the piston so as to have a size that leaves a gap for giving the stroke required for the piston to the piston. Material testing machine. The mounting surface and opposite surface to the cylinder stroke end portion or the piston pressure-receiving surface of the cushioning material, the material testing machine according to claim 1, characterized in that it is projecting or notches formed. The material testing machine according to claim 1 or 2 , wherein the cushion material is made of rubber, resin, or a metal softer than the material forming the cylinder and the piston.

Images