CN109724873B - CT sample crack propagation test fixture suitable for tension and compression loads - Google Patents

Abstract

The invention discloses a CT sample crack propagation test fixture suitable for tension and compression loads, which can apply stable tension and compression alternating loads to a CT sample. The chuck is connected with a special CT sample through a pin; the inclined surface of the wedge-shaped block is attached to the inclined groove of the chuck, and the upper surface of the wedge-shaped block is attached to the bottom surface of the pressing block; the arc-shaped bulge of the pressing block clamps a notch of a specially-made CT sample; the hoop is sleeved on the chuck, and the fastening screw is connected with the hoop through threads and props against the side face of the wedge-shaped block; the upper end of the metal rod is connected with the fatigue machine clamp through a screw hole in the center of the fastening disc; the fastening nut is attached to the bottom surface of the chuck; a circle of screws are arranged on the fastening disc; the screw withstands the fatigue machine clamp. The invention can ensure that no clearance is generated between the clamp and the sample when the tension-compression alternating load is loaded, and the loading axis is kept unchanged. Meanwhile, the invention is suitable for CT samples with different sizes and is convenient to install.

Description

A CT Specimen Crack Propagation Test Fixture Adapted to Tensile and Compressive Loads

technical field

The invention relates to metal material fatigue performance test equipment, in particular to the field of design and manufacture of uniaxial tensile/compression fatigue test fixtures for metal materials, in particular to a CT specimen crack propagation test fixture adapted to tensile and compressive loads.

Background technique

Aero-engine rotor components are subject to huge fatigue loads, and most of them are in a high temperature and corrosive environment, which is prone to cracks. Cracks on compressor blades, compressor discs, turbine blades, turbine discs and other components will seriously affect the safety of aero-engines. Therefore, it is necessary to study the crack growth rate of rotating parts under fatigue load. Studies have shown that the crack growth rate is closely related to the characteristic parameters such as the stress ratio of the fatigue load, and the crack growth rate under tension-tensile fatigue load and tension-compression fatigue load is quite different. Therefore, it is necessary to design crack growth tests under fatigue loads with different stress ratios, which requires the test fixture to be able to adapt to fatigue loads with different stress ratios such as tension-compression and tension-tension.

The standard compact tensile specimen (CT specimen for short) recommended in GB-T6398 can be used for experimental research on the growth rate of a class of cracks. The axial fatigue load is applied through the pin hole, and the stress concentration is generated at the position of the prefabricated crack, causing the initiation and propagation of the crack. However, when applying tensile-compressive fatigue loads, the test fixture has a significant problem: in the process of changing the load between tension and compression, it will inevitably pass through the state of zero load. If the specimen is installed with the pin clearance fit, there will be a period of idling when the load is zero, which is not conducive to the loading of the fatigue machine, and does not match the actual fatigue load. .

Chinese invention patent CN 105004607A discloses a tension-compression integrated experimental fixture for a universal testing machine, but the main problem it solves is the buckling of the plate under compression, and it cannot directly solve the free-running problem when the tension-compression load of the CT specimen changes .

Chinese invention patent CN 106885729A discloses a high-temperature tensile-compression fatigue test fixture for a flat plate specimen, which can solve the problem of loosening of the wedge-shaped friction chuck when reversely loaded. However, the CT specimen was originally connected to the fixture through pins. If the friction connection is used instead, the loading axis will change and the experimental results will be affected. Therefore, the problem in the tensile and compression test of the CT specimen cannot be solved.

Chinese invention patent CN 104792612A discloses a high-temperature tensile-compression fatigue test fixture for a hollow round bar test piece, which solves the problem of thread gaps in the process of pulling and pressing the hollow round bar test piece. However, the fixture is only suitable for round bar standard samples and cannot be used for CT samples.

Chinese utility model CN 205898563U discloses a hydraulic clamping device for a high-frequency fatigue test of a thin-walled plate specimen. However, this clamping method is not suitable for the test of CT specimens, especially it cannot guarantee that the loading axis is the direction of the test design.

To sum up, the design of the existing test fixture cannot be used for the realization of the tensile and compressive load during the crack propagation test of the CT specimen, and another fixture needs to be designed to accommodate the tensile and compressive fatigue load.

SUMMARY OF THE INVENTION

The technical problem solved by the present invention is: to overcome the problems in the prior art, to provide a CT sample crack propagation test fixture suitable for tensile and compressive loads, to meet the requirements of clamping CT samples under tensile and compressive fatigue loads, and the specific requirements include: (1) Solve the idle travel of the fixture during the change of tensile and compressive fatigue loads; (2) Ensure that the loading axis remains unchanged regardless of whether it is tension or pressure; (3) For CT specimens of different sizes, the fixture is easy to replace; (4) Easy to assemble.

The solution of the present invention is: a CT specimen crack propagation test fixture suitable for tensile and compressive loads, comprising: a chuck, a wedge block, a pressing block, a ferrule, a fastening screw, a pin, a special CT specimen, a metal rod , Fastening nuts, fastening discs and screws; overhead nail holes on the chuck, which are connected to the special CT sample by pins; the inclined surface of the wedge-shaped block is in contact with the inclined surface of the inner side of the chuck; the lower surface of the pressure block and the upper surface of the wedge-shaped block Contact, the upper surface of the pressure block has an arc-shaped protrusion, which clamps the notch on the lower surface of the special CT specimen; the ferrule covers the chuck; the tightening screw is connected to the threaded hole on the ferrule, and is tightened against the wedge-shaped The side of the block; the upper end of the metal rod passes through the tightening nut and is connected with the threaded hole on the lower surface of the collet; the tightening nut is tightened to bear against the lower surface of the collet; the lower end of the metal rod passes through the tightening disk, and the thread and fatigue The machine fixture is connected; a circle of screws is installed on the tightening plate, and the screws are tightened to withstand the fatigue machine fixture.

When the load applied by the fatigue machine is tensile force, the tensile force is transmitted to the metal rod by the fatigue machine fixture through the thread; the metal rod is connected with the chuck through the upper end thread, and the tensile force is transmitted to the chuck; the chuck transmits the tensile force to the special CT through the pin. on the sample.

When the load applied by the fatigue machine is pressure, the pressure is transmitted by the fatigue machine fixture to the tightening plate through the tightened screw, and then to the metal rod through the thread; the metal rod transmits the pressure to the tightening nut through the upper end thread, and the tightening nut will The pressure is transmitted to the collet; the collet transmits the pressure to the wedge block through the inclined surface, and then transmits the pressure to the pressure block in contact with the wedge block; the pressure block transmits the pressure to the special CT sample through the arc-shaped protrusion.

Compared with the existing CT specimen crack propagation test fixture scheme, the advantages of the present invention are:

(1) The present invention can adapt to the tensile and compressive fatigue load, and the clamp has no idle path during the change of the tensile and compressive load;

(2) The present invention can ensure that the loading axis remains unchanged for the applied tensile and compressive loads;

(3) The present invention facilitates the replacement of fixtures for samples of different sizes. For CT samples of different sizes, it is only necessary to replace the wedge blocks and pressing blocks of different sizes to meet the test requirements;

(4) The present invention is easy to assemble.

Description of drawings

Fig. 1 is the fixture assembly drawing of the present invention (only the lower half of the whole set of fixtures is drawn, and the upper half is exactly the same as the upper half), wherein Fig. 1(a) is an external view; Fig. 1(b) is a split Figure 1(c) is the enlarged appearance after dissection.

Fig. 2 is a schematic view of the chuck 1 of the fixture of the present invention, wherein Fig. 2(a) is an external view; Fig. 2(b) is a dissected external view.

3 is an external view of the wedge-shaped block 2 of the fixture of the present invention;

Fig. 4 is the appearance view of the pressing block 3 of the fixture of the present invention;

Fig. 5 is the external view of the ferrule 4 of the clamp of the present invention;

6 is an external view of the fastening screw 5 of the fixture of the present invention;

Fig. 7 is the external view of the pin 6 of the fixture of the present invention;

FIG. 8 is an external view of a specially made CT sample 7;

9 is an external view of the metal rod 8 of the clamp of the present invention;

Figure 10 is an external view of the fastening nut 9 of the fixture of the present invention;

FIG. 11 is a front view of the fastening disc 10 of the clamp of the present invention;

Detailed ways

The invention designs a CT specimen crack propagation test fixture suitable for tensile and compressive loads.

In the actual test process, the whole set of fixtures includes two fixtures of the present invention, which are divided into an upper fixture and a lower fixture, which are respectively connected to the two pin holes of the specially made CT sample 7 .

When using the fixture of the present invention, the concrete method is as follows:

(1) Assemble the upper clamp and the lower clamp respectively, and connect with the specially made CT sample 7. The specific method is:

1. First, insert the wedge block 2, the pressure block 3 and the special CT sample 7 into the chute of the chuck 1 to ensure that the inclined surface of the wedge block 2 is in contact with the chute of the chuck 1, and the lower surface of the pressure block 3 is in line with the wedge shape. The upper surface of the block 2 is attached, and the notch of the CT sample 7 is attached to the arc-shaped protrusion of the pressing block 3. Align the special CT specimen 7 with the pin hole of the collet 1, and insert the pin 6.

2. Put a ferrule 4 on the jacket of the collet 1 so that the threaded hole of the ferrule 4 is aligned with the longer side of the wedge block 2 . Fastening screws 5 are screwed into the threaded holes of the ferrule 4 against the side of the wedge-shaped block 2 .

3. Screw the tightening nut 9 into the thread on the upper end of the metal rod 8, and connect the thread on the upper end of the metal rod 8 with the collet 1.

4. Screw the tightening disc 10 into the thread at the lower end of the metal rod 8, and screw the screw 11 into the threaded hole around the tightening disc 10.

(2) Clear the tensile force of the fatigue machine to zero, and then connect the threads of the metal rods 8 of the upper clamp and the lower clamp to the upper and lower general clamps with threaded holes of the fatigue machine, respectively.

(3) Apply tension to the whole set of fixtures and the sample through the fatigue machine, so that the whole set of fixtures are subjected to tension, and the gap between the thread and the threaded hole, the pin and the pin hole is eliminated. The required tensile force is not greater than the maximum load in the test and does not affect the test results.

(4) Tighten the following three screws and nuts when the clamp is under tension:

1. Tighten the fastening screw 5 to hold the side of the wedge block 2;

2. Tighten the tightening nut 9 against the lower surface of the chuck 1;

3. Tighten the screw 11 against the surface of the fatigue machine fixture.

(5) The tensile force of the fatigue machine is unloaded to zero. The test fixture is installed.

Claims (4)

1. A CT sample crack propagation test fixture adapted to tensile and compressive loads, characterized in that it comprises: a chuck (1), a wedge-shaped block (2), a pressing block (3), a ferrule (4), a fastening screw (5), pin (6), special CT specimen (7), metal rod (8), fastening nut (9), fastening disc (10) and screw (11); pin for collet (1) The hole is connected with the special CT sample (7) by the pin (6); the inclined surface of the wedge-shaped block (2) is fitted with the inclined groove of the chuck (1), and the upper surface of the wedge-shaped block (2) is connected with the pressing block (3) The bottom surface of the clamping block (3) is protruded and stuck to the notch of the specially made CT sample (7); the ferrule (4) covers the chuck (1); the fastening screw (5) and the sleeve The hoop (4) is connected by threads and bears against the side of the wedge block (2); the thread on the upper end of the metal rod (8) passes through the tightening nut (9) and is connected with the threaded hole at the bottom of the collet (1). 8) The thread at the lower end passes through the threaded hole in the center of the tightening disc (10), and is connected with the fatigue machine fixture; the tightening nut (9) is fitted with the bottom surface of the chuck (1); a circle is installed on the tightening disc (10). The screw (11); the screw (11) withstands the fixture of the fatigue machine. 2. The CT specimen crack propagation test fixture according to claim 1, characterized in that: the tightening screw (5) is tightened to stand against the side of the wedge-shaped block (2), which can eliminate the pressure block (3) and the special Gap between CT specimens (7). 3. CT sample crack propagation test fixture according to claim 1, is characterized in that: described tightening nut (9) is tightened, withstood the bottom surface of collet (1), can eliminate collet (1) and metal Clearance between the threads on the upper end of the rod (8). 4. The CT sample crack propagation test fixture according to claim 1, characterized in that: the screw (11) is tightened to withstand the fatigue machine fixture, which can eliminate the gap between the lower end thread of the metal rod (8) and the fatigue machine fixture Clearance.

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