CN102519791A - Mechanical fatigue tester for test piece, and its testing method - Google Patents

Abstract

The invention discloses a mechanical test piece fatigue testing machine and a testing method thereof. The testing machine includes a frame, a test piece and a stress monitoring device for monitoring the stress change of the test piece. One end of the test piece is fixed to the frame. , the other end is cantilevered, and the cantilever end of the specimen is connected to the frame through an eccentric vibrator; the eccentric vibrator includes a rotating mechanism, an eccentric block connected to the output shaft of the rotating mechanism through a connecting long handle, and an elastic connector. The rotating mechanism and the test piece are fixed, and the power supply circuit of the rotating mechanism is connected in series with a conductive element that feedbacks the fatigue crack limit of the test piece to stop the work of the eccentric exciter. The conductive element is installed on the test piece, and one end of the elastic connector is connected to the The test piece is connected, and the other end is connected to the frame. Therefore, the invention consumes less during the experiment, is easy to operate, has a wide loading range, high test accuracy, can perform stress dynamic monitoring, and has low processing requirements for samples.

Description

Mechanical specimen fatigue testing machine and its test method

technical field

The invention relates to a fatigue test device, which belongs to the fatigue test field of material structure performance test.

Background technique

In engineering practice, many materials or components are subjected to dynamic loads in practical applications. Unlike when subjected to static loads, these materials or components often undergo fatigue failure suddenly without significant deformation in advance, which affects the structure. Safety performance has a major impact. With the increasing research on the fatigue performance of materials, the types and functions of fatigue testing machines are increasing to meet the needs of fatigue testing of different materials. Fatigue testing machines mainly include hydraulic servo type, electromagnetic type and mechanical type. Among them, the hydraulic servo fatigue testing machine is a relatively advanced testing device, but the price is high, and the power consumption is high and the cost is high under low-frequency working conditions. The electromagnetic fatigue testing machine has a high frequency and is mainly used for fatigue performance testing of ferrous metals with good fatigue performance. The mechanical fatigue testing machine is suitable for fatigue tests that do not require high frequency, with low power and low cost. However, in the past mechanical fatigue testing machines, the judgment conditions for the end of the test are complicated, the response to the test termination command is slow, and the output load range is small, and the specimen cannot be prestressed to adjust the stress waveform.

Contents of the invention

Aiming at the deficiencies of the prior art, the invention provides a fatigue test method which can change the output load of the test machine, apply prestress to the test piece, independently determine the end condition of the test and automatically stop the test.

A mechanical test piece fatigue test method, comprising the following steps: (1) fixing one end of the test piece, setting the other end with a cantilever, and applying elastic prestress to the cantilever end of the test piece; (2) fixing the cantilever end of the test piece Apply an eccentric load, and connect the power supply circuit of the power device that outputs the eccentric load in series with the conductive element that feedbacks the fatigue crack limit of the test piece. In addition, the stress monitoring device installed on the test piece is used to monitor the stress change of the test piece under load .

Step (2) is to apply an eccentric load to the cantilever end through an eccentric exciter. The eccentric exciter includes a rotating mechanism and an eccentric block connected to the output shaft of the rotating mechanism through a long handle. The power supply circuit of the rotating mechanism and the conductive element in series.

Step (2) Before applying the eccentric load, preset the time threshold for a single application of the eccentric load.

A mechanical specimen fatigue testing machine based on the above specimen fatigue test method, comprising a frame, a specimen and a stress monitoring device for monitoring stress changes of the specimen, one end of the specimen is fixed to the frame, and the other end The cantilever is set, and the cantilever end of the specimen is connected to the frame through an eccentric vibrator; the eccentric vibrator includes a rotating mechanism, an eccentric block connected to the output shaft of the rotating mechanism through a connecting long handle, and an elastic connector. It is fixed with the test piece, and the power supply circuit of the rotating mechanism is connected in series with a conductive element that passes the fatigue crack limit of the test piece to stop the work of the eccentric exciter. The conductive element is installed on the test piece, and one end of the elastic connector is connected to the test piece. , and the other end is connected to the rack.

The conductive element is a sheet or linear body made of conductive material.

The stress monitoring device includes a strain gauge and a strain gauge connected with the strain gauge; the strain gauge is installed on the test piece.

The rotating mechanism is an electric motor, and the electric motor is fixed to the test piece through the base, and the connecting long handle is perpendicular to the machine shaft of the electric motor.

The motor is equipped with a timer that can preset the duration of a single startup of the motor.

The conductive element is tightened and fixed on the test piece at the position where the fatigue crack may occur by insulating colloid, and the conductive element is perpendicular to the development direction of the fatigue crack.

The elastic connecting piece is a spring, and the spring is sleeved on the periphery of the steel pipe, and the steel pipe is fixed on the frame.

According to the above technical scheme, the following beneficial effects can be achieved:

The fatigue testing machine of the present invention is simple in structure, has the characteristics of being able to change the output load of the testing machine, applying prestress to the test piece, and independently determining the end condition of the experiment and automatically stopping the test. Wide range, high test accuracy, dynamic monitoring of stress, low requirements for sample processing.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Figure 2 is a cross-sectional view of A-A in Figure 1 (the eccentric exciter is not marked);

Fig. 3 is the required cantilever sample processing schematic diagram of the present invention;

Among them: base 11; clamping platform 12; spring fixed arm 13; safety platform 14; test piece 2; clamping platform bolt connection reserved hole 21; motor connection bolt reserved hole 22; spring connection reserved hole 23; Eccentric block 31 ; connecting long handle 32 ; motor 33 ; conductive element 34 ; elastic connector 35 ; steel pipe 36 ; strain gauge 4 .

Detailed ways

The accompanying drawings disclose, without limitation, the structural schematic diagrams of the preferred embodiments involved in the present invention; the technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings.

The invention discloses a fatigue test method for a test piece, which comprises the following steps: (1) fixing one end of the test piece, setting the other end with a cantilever, and applying elastic prestress to the cantilever end of the test piece; (2) fixing the cantilever end of the test piece At the same time, through the conductive element installed on the test piece, the moment of the fatigue crack limit of the test piece is measured to control the load application time. In addition, the stress monitoring device installed on the test piece is used to monitor the test piece under load. time stress changes. Further, a fatigue test method for a mechanical specimen includes the following steps: (1) fixing one end of the specimen, setting the other end cantilevered, and applying elastic prestress to the cantilever end of the specimen; (2) The eccentric load is applied to the cantilever end of the test piece, and the power supply circuit of the power device that outputs the eccentric load is connected in series with the conductive element that feedbacks the fatigue crack limit of the test piece. stress changes. Step (2) is to apply an eccentric load to the cantilever end through an eccentric exciter. The eccentric exciter includes a rotating mechanism and an eccentric block connected to the output shaft of the rotating mechanism through a long handle. The power supply circuit of the rotating mechanism and the conductive element in series. And in step (2) before applying eccentric load, the time threshold for applying eccentric load once is preset.

Based on the above-mentioned specimen fatigue test method, the present invention discloses a mechanical type specimen fatigue testing machine as shown in Figures 1 to 3, comprising a frame, a specimen and a stress monitoring device for monitoring the stress variation of the specimen, and the frame consists of Base 11, clamping platform 12, spring fixed arm 13 and safety bearing platform 14; one end of the test piece is fixed to the clamping platform 12 of the frame, and the other end is cantilevered, and the cantilever end of the test piece is excited by eccentric The device is connected with the spring fixing arm 13 of the frame; the test piece 2 is a strip-shaped plate body, and there are reserved holes 21 for the clamping table bolt connection, 22 reserved holes for the motor connection bolt, and 23 reserved holes for the spring connection; The eccentric vibrator includes a rotating mechanism, an eccentric block connected to the output shaft of the rotating mechanism through a connecting long handle, and an elastic connector. The conductive element that produces fatigue crack limit to cut off the work of the eccentric exciter, the conductive element is installed on the test piece, and one end of the elastic connector is connected with the test piece, and the other end is connected with the frame. The conductive element is a sheet or linear body made of conductive material, and the conductive element used in the present invention is a thin copper wire. The stress monitoring device includes a strain gauge and a strain gauge connected with the strain gauge; the strain gauge is installed on the test piece. The rotating mechanism is an electric motor, and the electric motor is fixed to the test piece through the base, and the connecting long handle is perpendicular to the machine shaft of the electric motor. For some test pieces, the time to produce fatigue cracks is very long, and the single start-up time of the motor is too long, which is easy to be damaged. When the single operation time lasts for the preset motor single start time, the motor will automatically stop running, and the fatigue test will be carried out by starting the motor multiple times until the conductive element of the feedback fatigue crack limit breaks, causing the motor to lose power, and the fatigue test is completed . The conductive element is tightened and fixed on the test piece at the position where the fatigue crack may occur by insulating colloid, and the conductive element is perpendicular to the development direction of the fatigue crack. The elastic connecting piece is a spring, and the spring is sleeved on the periphery of the steel pipe, and the steel pipe is fixed on the frame.

According to the above technical scheme, it can be known that the fatigue testing machine of the present invention has the following characteristics:

Adjust the output load of the fatigue test: the long handle of the eccentric block passes through the hole in the vertical axis of the motor shaft, and the position is fixed with bolts to form an eccentric vibrator. By changing the connection position between the long handle of the eccentric mass and the crankshaft of the motor or replacing the eccentric mass of different mass, and changing the number of revolutions of the motor, the centrifugal force generated when the eccentric exciter rotates is changed, thereby changing the output load of the eccentric exciter. Before the experiment, it is necessary to determine the required output range of the experimental load, which can be applied from the small load to the required load of the specimen test.

Apply prestress to the specimen and adjust the amplitude: four large stiffness springs are arranged side by side along the cantilever end of the cantilever specimen, respectively connected to the top of the specimen from the upper and lower sides of the specimen, the spring runs through the steel pipe, and the steel pipe passes through the casing along the vertical direction It is directly fixed on the main body of the frame, and the upper and lower sections of the spring are respectively fixed on the steel pipe and the top of the cantilever end of the cantilever sample. When it is necessary to apply prestress or adjust the amplitude, the position of the upper end of the spring fixed on the steel pipe is changed up and down to apply prestress to the cantilever sample, thereby changing the stress waveform output by the fatigue test.

Stress monitoring: During the experiment, a strain gauge is attached to the required measurement position at the cantilever root of the cantilever sample, and the dynamic change of the stress is monitored through the regular reading of the strain gauge and the connection of points and lines.

Judgment of the end conditions of the test and the termination of the test: At the place where the fatigue cracks of the cantilever sample may develop, stick thin copper wires through insulating colloid, the thin copper wires are perpendicular to the direction of fatigue crack development, and the copper wires are connected in series in the motor circuit. , the thin copper wire is broken, the motor circuit is broken, the eccentric exciter is stopped, and the fatigue test is over. This is the termination sign of the fatigue test.

Motor operation criterion: set a single running time threshold for the motor. When the motor running time is within the single running time threshold and no destructive fatigue cracks appear on the test piece, the motor running time is calculated according to the single running time threshold, and the The running time of the motor is accumulated for each time; when the running time of the motor is within the threshold of a single running time, and destructive fatigue cracks appear on the test piece, the running time of the motor is recorded according to the time when the thin copper wire breaks, and compared with the previous times The corresponding number of fatigue tests of the specimen can be obtained by accumulating the running time of the motor.

Claims (10)

1. A mechanical test piece fatigue test method is characterized in that, comprising the following steps: (1) one end of the test piece is fixed, the other end cantilever is set, and elastic prestress is applied to the cantilever end of the test piece; (2) Apply an eccentric load to the cantilever end of the test piece, and connect the power supply circuit of the power device that outputs the eccentric load in series with the conductive element that feedbacks the fatigue crack limit of the test piece. In addition, the stress monitoring device installed on the test piece is used to monitor the test piece. Stress change under load. 2. The mechanical specimen fatigue test method according to claim 1, characterized in that step (2) is to apply an eccentric load to the cantilever end through an eccentric vibrator, and the eccentric vibrator includes a rotating mechanism and a connecting An eccentric block with a long handle connected to the output shaft of the rotary mechanism, and the power supply circuit of the rotary mechanism is connected in series with the conductive element. 3. The fatigue test method for mechanical specimens according to claim 1, characterized in that, before applying the eccentric load in step (2), the time threshold for applying the eccentric load once is preset. 4. A mechanical type test piece fatigue testing machine based on the described test piece fatigue test method of claim 2, comprising a frame, a test piece and a stress monitoring device for monitoring the stress variation of the test piece, characterized in that: the test piece One end of the piece is fixed to the frame, and the other end is cantilevered, and the cantilever end of the test piece is connected to the frame through an eccentric vibrator; the eccentric vibrator includes a rotating mechanism, an eccentric shaft connected to the output shaft of the rotating mechanism block and elastic connectors, the rotating mechanism is fixed to the test piece, and the power supply circuit of the rotating mechanism is connected in series with a conductive element that generates a fatigue crack limit by feeding back the test piece to cut off the work of the eccentric vibrator, and the conductive element is installed on the test piece , while one end of the elastic connector is connected to the specimen, and the other end is connected to the frame. 5. The mechanical specimen fatigue testing machine according to claim 4, characterized in that: the conductive element is a sheet or a linear body made of conductive material. 6 . The mechanical specimen fatigue testing machine according to claim 4 , wherein the stress monitoring device includes a strain gauge and a strain gauge connected with the strain gauge; and the strain gauge is installed on the specimen. 7 . 7. The mechanical specimen fatigue testing machine according to claim 4, characterized in that: the rotating mechanism is an electric motor, the electric motor is fixed to the specimen through the base, and the connecting long handle is perpendicular to the shaft of the electric motor. 8. The mechanical specimen fatigue testing machine according to claim 7, characterized in that: the motor is equipped with a timer that can preset the duration of a single startup of the motor. 9. The mechanical specimen fatigue testing machine according to claim 4, characterized in that: the conductive element is tightened and fixed on the specimen at the position where fatigue cracks may occur on the specimen through insulating colloid, and the development direction of the conductive element and the fatigue crack perpendicular to each other. 10. The mechanical specimen fatigue testing machine according to claim 4, characterized in that: the elastic connector is a spring, and the spring is sleeved on the periphery of the steel pipe, and the steel pipe is fixed on the frame.

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