RU226200U1 - Installation for contact fatigue testing - Google Patents

Abstract

The utility model relates to equipment for conducting research work in materials science. The purpose of the proposed device is to study contact fatigue phenomena in metal under pulsating loading. The installation includes: electric motor; coupling; shaft; ball bearing supports; eccentric; pusher; sliding supports; force-setting glass; indenter; test sample; frame; dynamometer; rods; nut; spring; load cycle counter.

Description

The utility model is intended for carrying out research work on the study of contact fatigue phenomena.

The variety of operating conditions for machine parts that transmit forces to other parts through direct contact of surfaces is very large. The strength and wear resistance of which often affect the strength and reliability of the unit or machine as a whole.

The need for an experimental study of strength under pulsating contact, in addition to its practical importance for a number of parts, is due to the convenient combination of cyclic loading conditions with a certain spatial distribution of stress and deformation.

There is a known installation for studying the process of material fatigue in the rolling contact zone (Makhutov N.A. Structural strength, resource and technogenic safety: In 2 hours / N.A. Makhutov. - Novosibirsk: Nauka, 2005. - Part 1: Strength criteria and resource - 494 pp.).

In it, rolling friction occurs against the background of cyclic deformation of the contacting bodies, ensuring the operation of the system under conditions of contact-mechanical fatigue. However, this method of conducting an experiment is characterized by the complexity of studying the process of material fatigue near the contact zone.

An installation for testing material samples with repeated impacts is also known (patent RU 2374624). An installation for testing material samples by repeated blows contains a housing, a pendulum mounted on it in the form of a two-armed lever with a load on one of its arms, a device for swinging the pendulum, a passive sample grip mounted on the other arm of the lever, an active sample grip, adjustable stops placed at different positions. sides from the swing axis of the pendulum and intended for periodic interaction with the active grip. The disadvantage of this installation is noise, which makes it difficult to use, and low productivity, since the double-arm levers, with an increase in the frequency of impacts, begin to elastically deform and the load transfer becomes uneven.

The purpose of the useful model is to identify the influence of the steel structure after hardening on the development of damage accumulation processes in the contact zone and to draw up a diagram of contact-fatigue failure during pulsating contact.

For this purpose, a device has been developed that allows testing on flat samples with dimensions of 100x18x2.5 mm.

The device diagram is shown in Fig. 1, general view - in Fig. 2.

The device is made on a base to which an electric motor, two shaft supports with rolling bearing units, two sliding bearing housings, a guide frame for attaching the sample, a calibrated dynamometer and a cycle counting device are attached using screw connections. To transmit torque from the electric motor to the shaft, a coupling is installed. The shaft that sets the movement of the eccentric is installed in rolling bearings, the adjustable eccentric is mounted on a splined connection between the shaft supports. A pusher mounted on a rod, which is installed in plain bearings, rests against the eccentric. The rod ends with a thread with a screwed-on glass that sets the force. The force is created by a loading spring located inside the glass, connected to a rod, which ends with a ball indenter resting on the test sample. The sample is fixed in a frame, which is fixed in the guides. A calibrated dynamometer is installed behind the guides. The cycle counting device is installed on the base and interacts with the end of the shaft opposite the coupling.

The device works as follows. From electric motor 1 (Fig. 1) with a speed of n=3000 rpm, torque is transmitted through coupling 2 to shaft 3 mounted in two supports 4 with rolling bearings. An adjustable eccentric 5 is fixed to the shaft 3, the translational movement of which through the pusher 6 with a frequency of 50 Hz is transmitted to the rod 16, installed in the sliding bearing 7 and ending with a thread onto which the glass 8, which sets the force Pm, is screwed. A loading spring 15 is installed on the rod 13, compression which is adjusted by a glass 8 and a nut 14. The force from the spring through the indenter 9 is transmitted to the sample 10, fixed in the frame 11. The frame is fixed in the guides in six different positions. This allows each sample to be tested at six voltage levels. The indenter is a ball made of steel ШХ15 with a diameter of 3; 5 or 10 mm. The spring force was controlled by a calibrated dynamometer 12. The number of loading cycles was recorded by a counting device 17.

The device implements the test circuit shown in Fig. 3, where a - loading diagram: 7 - sliding support; 9 - indenter; 10 - sample; 11 - frame for fastening the sample, Pm - average normal load; Ra is the amplitude of the normal load of the cycle; 6 - stress cycle: σ - stress; Tc - cycle period.

The maximum normal stress σ _zmax was selected for the design stress in the contact zone:

where P is load (Pm, Ra);

E - elastic modulus (for steel E=21.08⋅10 ⁴ MPa);

R is the indenter radius.

The formation of pittings (chipping pits) along the contour of the contact patch was taken as a criterion for assessing contact fatigue failure.

To more accurately determine the number of cycles at which chipping pits are formed, during testing of the sample at each stress level, a dependence was constructed

D _n =ƒN _c

where N _c is the number of loading cycles;

D _n is the diameter of the contact patch, measured on an optical microscope (for example, MIM-7).

At the moment of pitting formation, a sharp increase in the contact patch occurs. This phenomenon is taken as a criterion for failure at a given level of cycle stress. After determining the number of loading cycles during which contact fatigue failure occurs at various stress levels, contact fatigue graphs are constructed in coordinates

σ _zmax =ƒN _c

Tests are carried out on three samples for each treatment. Before testing, the working surface of the samples is polished.

The technical result of the utility model is its use in research work in materials science. Due to shockless loading, the operation of the device is accompanied by a low noise level.

Sources of information taken into account during the examination:

1. Makhutov N.A. Structural strength, resource and technogenic safety: In 2 hours / N.A. Makhutov. - Novosibirsk: Nauka, 2005. - Part 1: Criteria for strength and service life. - 494 p.

2. Patent RU 2374624.

Claims (1)

The device for carrying out research work on the study of contact fatigue phenomena is assembled on a single base, to which an electric motor with a speed of n=3000 rpm, two shaft supports with rolling bearing units, sliding bearing housings, and a guide frame for fastening are attached using screw connections sample, calibrated dynamometer, cycle counting device; the electric motor is configured to transmit torque through a coupling to a shaft mounted in rolling bearings; an adjustable eccentric is mounted on the shaft, configured to transmit translational motion to a pusher, which is configured to transmit it to a rod mounted in plain bearings and ending with a thread onto which a force-setting glass is screwed on, a loading spring is installed on the rod, the compression of which is regulated by the glass and a nut, the force from the spring is transmitted through the indenter to the sample fixed in the frame, the number of loading cycles is determined using a cycle counting device.