RU2318198C1 - Machine for elongation testing of samples - Google Patents

Abstract

FIELD: measuring equipment, namely machines for elongation testing of samples.

SUBSTANCE: the machine contains a force frame, made in form of a base, upper immobile traverse beam, guiding columns, drive screws. Drive screws are connected to mobile traverse beam through nuts, mounted immovably in the traverse beam. On the base a force indicator is mounted, to which an immobile holder is connected through a traction. Mobile holder through a traction is connected to mobile traverse beam. Into the traction of one of holders (for example, into the upper traction) a joint bearing is integrated, rotation axis of which coincides with longitudinal axis of the sample, allowing free rotation of the holder around its axis during testing. The joint may be integrated directly into the holder. Presence of a joint in "holders-sample" chain makes it possible to prevent possible occurrence of unaccounted contact tensions caused by convolution in the sample. Drive screws are made with opposite direction of thread and kinematically interconnected in such a way, that opposite direction of rotation is ensured.

EFFECT: increased trustworthiness of measurement results due to prevention of unaccounted tensions in the sample and reduced weight and size characteristics of the machine.

2 cl, 3 dwg

Description

The invention relates to testing equipment, and in particular to machines for tensile testing of samples.

Known test machines that provide tensile testing of specimens with rigid fixation of the test specimen (see Golubkov BC, Pirogov KM, Smushkovich BL Test machines in textile materials science. - M .: Legprombytizdat, 1988, p.205, p. .22-23).

The disadvantage of these machines is the increased sensitivity to distortion of the sample when installed in the grips and the associated possibility of the occurrence of eccentric application of the load, and accordingly unaccounted for additional normal stresses in the sample.

Closest to the technical nature of the claimed machine is the explosive machine IR 5143-200 selected as a prototype, containing a power frame made in the form of a base, columns fixed to it connected to a fixed beam, a movable beam with its movement mechanism made in the form of running gears the screws installed in the frame, the drive for their rotation and the nuts fixedly mounted on the movable traverse, captures for fixing the sample, one of which is connected to the movable traverse, and the other to the power frame, comb m the connection of one of the grips is carried out through a double hinge so that self-alignment of the gripper in a vertical plane is ensured (see Explosive Machines IR 5143-200-10 and IR 5143-200-11. Prospect OAO Tochpribor, Ivanovo, 2001. Brown E.D., Gorbunov V.N., Smushkovich B.L. Methods and equipment for predicting the friction-wear characteristics of friction units of heavy engineering products // Heavy Engineering (Journal), 2001, No. 4, p. 18).

Due to the self-locking of the capture in a known machine eliminates the possibility of unaccounted for normal stresses. But its disadvantage is the fundamental possibility of unaccounted tangential stresses in the cross section of the sample, which can also lead to distortion of test results.

The objective of the invention is to increase the reliability of the test results by eliminating unaccounted stresses in the sample and reducing the mass-dimensional characteristics of the machine.

This goal is achieved by the fact that the machine for testing tensile specimens, containing a power frame made in the form of a base, columns fixed to it, connected to a fixed beam, a movable beam with its movement mechanism made in the form of spindles installed in the frame, drive their rotation and running nuts fixedly mounted on the movable traverse, grippers for securing the sample, one of which is connected to the movable traverse, and the other to the power frame, while one of the grippers is installed with the possibility during rotation during the test around the axis coinciding with the longitudinal axis of the sample, and the spindles are made with the opposite direction of cutting and the opposite direction of rotation from the drive.

Comparative analysis with the prototype shows that the inventive machine is characterized in that one of the grips is mounted with the possibility of rotation during the test around an axis that coincides with the longitudinal axis of the sample, and the spindles are made with the opposite direction of cutting and the opposite direction of rotation from the drive.

Figure 1 shows a diagram of the proposed machine; figure 2 (aa) is a diagram of the action of the moments; figure 3 (a, b, c) - embodiments of the hinge assembly in the proposed machine.

The machine (Fig. 1) contains a power frame made in the form of a base 1, an upper fixed crosshead 2, guide columns 3, lead screws 4. The lead screws are connected to the movable crosshead 5 through nuts 6 installed in it. A force sensor 7 is installed on the base 1 , with which through the rod 8 is connected a stationary grip 9. The movable grip 10 through the rod 11 is connected with a movable traverse 5. In the grippers 9 and 10, the test sample 12 is fixed.

The movable crosshead 5 (FIG. 2) in a horizontal section is affected by a torque M _t equal to the algebraic sum of the friction moments in the nuts 6 of the spindles 4, i.e. M _t = M ₁ + M ₂ with the same direction of rotation of the screws and M _t = M ₁ -M ₂ with the opposite direction of rotation of the screws.

In Fig.2, the directions of the moments M _t and M _p are shown conditionally for the case M ₂ > M ₁ .

This torque is perceived by the power frame of the tensile testing machine (base 1, fixed crosshead 2, columns 3, spindles 4) and the chain “grips 9 and 10 - sample 12”.

If the torsional stiffness (the ratio of torque to angular deformation) of the power frame is c _p and the chain is c _о , then from the condition of compatibility of torsion deformation we find

Torsion moment on the sample

Torsion moment on the frame

Depending on the ratio c _p / c _о, we have

0≤M _about ≤M _t and 0≤M _p ≤M _t , and M _about + M _p = M _t

Thus, in the general case, the friction moment in the screw pairs loads not only the power frame, but also the test specimen, creating unaccounted tangential stresses in it and distorting the uniaxial stress state.

As can be seen from the formula, the moment on the sample M _about can be reduced in three ways:

1. To reduce the magnitude of the moment on the movable traverse M _t Since the direction of the moment of friction on the screw nut coincides with the direction of its rotation n, then in the case of the opposite direction of rotation of the screws M _t = M ₁ -M ₂ (the direction of the thread on the screws should also be opposite).

2. Increase rigidity c _{p of the} power frame. But this entails an increase in the mass-dimensional characteristics of the machine.

3. Reduce stiffness c _{о of the} chain “captures-sample”. This can be achieved by introducing into the chain a hinge, the axis of rotation of which coincides with the longitudinal axis of the sample, around which it can freely rotate during the test.

In the thrust of one of the grips (for example, the upper 11), a hinge assembly 13 is integrated, which can be made in various versions.

Option 1 - a friction hinge (figa).

Link 11 consists of two half-links, upper and lower. The lower half-rod is connected to the upper half-rod through the support bearing 14 and the cup 15, which is a guide and does not limit the relative movement of the half-links. A spring 16 is installed in the cup 15. The thrust bearing 14 may be rolling or sliding.

Option 2 - an elastic hinge (figb, c).

Rod 11 also consists of two semi-links, which are connected by a plate torsion 17 made with low torsional and high axial stiffness. The sleeve 18 serves as a guide for the half-rods 11.

The swivel angle may be limited.

There are other possible versions of the hinge assembly that meet the requirement not to limit the possibility of rotation of the gripper during the test around an axis that coincides with the longitudinal axis of the sample, including The hinge can be integrated directly into the grip.

The spindles 4 (FIG. 1) are made with the opposite direction of cutting and are kinematically connected in this way (for example, through worm gears or a crossing belt drive, not shown in FIG. 1) to provide the opposite direction of rotation. A possible option is also an individual drive of each screw from its electric motor.

The machine operates as follows.

Sample 12 is installed in the grips 9 and 10 of the machine (figure 1). Moreover, the presence of the hinge 13 allows you to compensate for some propeller flat samples, since the axis of rotation of the hinge coincides with the longitudinal axis of the sample, around which it can freely rotate. This eliminates the possibility of unaccounted tangential stresses from twisting in the sample. If necessary, the hinge can be arrested (turned off) while fixing the sample in the grippers.

When moving the beam 5 (speed v _o ), the sample 12 is stretched. Since the spindles 4 rotate in the opposite direction, the total moment on the traverse is minimal and equal to M _t = M ₁ -M ₂ .

The presence of the hinge 13 reduces the torsional rigidity from _{o of} the gripper-sample chain to a value tending to zero or substantially lower rigidity c _{p of the} power frame, due to which the torque is practically not transmitted to the sample and does not create unaccounted tangential stresses in it.

Claims (2)

1. A machine for testing tensile specimens, comprising a power frame made in the form of a base, columns fixed thereon, connected to a fixed beam, a movable beam with a mechanism for its movement, made in the form of spindles mounted in the frame, their rotation drive and running nuts fixedly mounted on the movable yoke, a force sensor mounted on a base with which a fixed jaw is connected through the thrust and a movable yoke connected through the thrust with the movable yoke, characterized in that one of the jaws a rotatably mounted during testing around an axis coinciding with the longitudinal axis of the specimen. 2. The machine according to claim 1, characterized in that the spindles are made with the opposite direction of cutting and the opposite direction of rotation from the drive.

Images