CN107957448B - Ultrasonic fatigue average stress loading device - Google Patents

Abstract

The invention relates to an ultrasonic fatigue average stress used in the field of ultrasonic fatigue testAnd (4) loading the device. The method solves the problem of average stress loading in an ultrasonic fatigue test. The technical scheme is as follows: the excircle of a positioning seat in the ultrasonic generating assembly penetrates through a through hole at the uppermost end of a vertical plate of the support, and the positioning seat and the vertical plate of the support are fastened by screws; a linear sliding sleeve a in the stress loading assembly is sleeved on the smooth straight rod in the middle of the sliding guide rod a, and a linear sliding sleeve b is sleeved on the smooth straight rod in the middle of the sliding guide rod b; a flange structure at the right end of a shell of the speed reducer in the power assembly is fastened with a vertical plate of the bracket by screws, and the left end of the ball screw is inserted into a flat key output hole of the speed reducer and can realize transmission after connection; the invention can provide +/-40 kN axial tension and pressure load application to a test piece in the ultrasonic fatigue test, can realize the 20kHz frequency fatigue test, effectively shortens the fatigue test time, and can efficiently finish 10¹⁰And (5) carrying out weekly fatigue test.

Description

An ultrasonic fatigue average stress loading device

technical field

The invention relates to an ultrasonic fatigue average stress loading device used in the field of ultrasonic fatigue test.

Background technique

Conventional fatigue tests can only complete the fatigue properties of materials in the range of 10 ⁶ to 10 ⁷ cycles. However, in many industrial sectors (such as high-speed trains, automobiles, airplanes, etc.), the actual service life of some structures and parts often needs to reach 10. ⁸ to 10 ¹⁰ cycles, for example, a high-speed aero-turbine engine running at 3000 r/min will experience 10 ¹⁰ stress cycles in a 20-year service period. Ultrasonic fatigue is an accelerated resonance fatigue test method, and its test frequency (20kHz) far exceeds the conventional fatigue test frequency (less than 200Hz). The essence of ultrasonic fatigue is the establishment of mechanical resonance waves on the loaded pattern.

Ultrasonic fatigue test research shows that many engineering materials will still experience fatigue fracture after 10 ¹⁰ cycles of stress cycles, so the fatigue strength design of 10 ⁷ cycles of fatigue test data cannot meet many practical engineering needs. However, using the conventional fatigue test method, the loading frequency is 100Hz, and it takes 115 days of continuous exercise to complete a fatigue test of 10 ⁹ cycles, which obviously wastes a lot of money and manpower, and the conventional fatigue testing machine cannot run continuously for such a long period; if ultrasonic waves are used With the fatigue test technology, the loading frequency is 20 kHz, and it only takes 14 hours to complete a fatigue test of 10 ⁹ cycles, and a SN curve of 10 ⁹ cycles can be successfully established.

Ultrasonic fatigue testing equipment is an indispensable core equipment for ultrasonic fatigue testing. At present, a large number of preliminary researches on ultrasonic fatigue testing methods and equipment have been carried out in the laboratory, and they have the ability to accurately test specimens with different material properties. According to the relevant technical requirements of fatigue testing, the ultrasonic fatigue test should carry out research on the average stress loading. However, the ultrasonic fatigue equipment currently used in the laboratory does not have the function of loading the average stress, which seriously affects the research process of related tests.

Based on the above technical background, the present invention provides an ultrasonic fatigue average stress loading device, which can perform ultrasonic fatigue average stress loading test and conduct more perfect ultrasonic fatigue test research.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an ultrasonic fatigue average stress loading device in order to solve the problem of average stress loading in the ultrasonic fatigue test.

In order to achieve the above purpose, the present invention adopts the following technical solutions: an ultrasonic fatigue average stress loading device, which is composed of an ultrasonic generating component, a stress loading assembly, a power assembly, a linear transmission assembly, a bracket vertical plate, a sliding guide rod a, a The locking nut, the positioning end plate, the sliding guide rod b and the test piece are composed. The ultrasonic generating component includes a piezoelectric transducer, a positioning seat and a displacement amplifier. The stress loading assembly includes a tension screw, a loading support, a loading slide, and a linear slide. Set a, linear sliding sleeve b, tray and rubber pad, powertrain includes servo motor and reducer, linear transmission assembly includes transmission key, spring clip, thrust bearing, roller screw, screw nut, sleeve, Linear sliding sleeve c, anti-rotation arm, anti-drop end cover, sensor base and load sensor; its structural features are: in the ultrasonic generating assembly, the piezoelectric transducer can convert the electrical signal output by the ultrasonic frequency generator into mechanical vibration Signal output; threaded holes are arranged at both ends of the positioning seat, a circle of raised steps is arranged in the middle of the outer circle of the positioning seat, and six step holes are evenly arranged in the circumferential direction of the raised steps; threaded holes are arranged at both ends of the displacement amplifier, and the cross-section of the left end of the displacement amplifier is arranged The diameter is larger than the diameter of the right end section, and the outer circular contour of the displacement amplifier transitions smoothly in the axial direction; the left end of the positioning seat and the output end of the piezoelectric transducer are fixed with studs, and the right end of the positioning seat and the left end of the displacement amplifier are fixed with studs; The upper, middle and lower parts of the loading slide plate are respectively provided with a through hole, four threaded holes are evenly arranged circumferentially at the outer right end of the upper through hole of the loading slide plate, and four threaded holes are evenly arranged circumferentially at the outer right end of the lower through hole of the loading slide plate. Eight threaded holes are evenly arranged at the outer left end of the through hole in the circumferential direction; the linear sliding sleeve a is embedded in the upper through hole of the loading sliding plate, the right side of the linear sliding sleeve a is raised and the outer edge of the loading sliding plate is fastened with screws; the linear sliding sleeve b is embedded in the loading sliding plate In the lower through hole, the convex outer edge on the right side of the linear sliding sleeve b and the loading slide plate are fastened with screws; the inner cavity of the loading support is set as a stepped hole, the right end of the tension screw is set as a step, and the tension screw is placed in the inner cavity of the loading support. In the hole, the right end of the loading support and the left side of the upper end of the loading slide are fastened with screws; the right end of the pallet and the loading slide are fastened with screws, the rubber pad is placed on the support surface of the pallet, and the pallet is installed on the lower side of the loading support; The output shaft of the servo motor and the input shaft of the reducer are connected, the casing of the servo motor and the casing of the reducer are fastened with screws, the output mode of the reducer is in the form of flat key hole output, and the right end of the casing of the reducer is a flange structure. The electrical signal outputs stable torque and speed; in the linear transmission assembly, a flat keyway is set on the left end of the ball screw, a ring groove is set on the right side of the flat keyway, the right part of the ball screw is set as a screw structure, and the right end of the ball screw is set A threaded hole is provided; the transmission key is installed in the flat key groove on the left end of the ball screw, the spring collar is installed in the groove of the ball screw clamp ring, and the thrust bearing is installed on the left end surface of the screw structure on the right part of the ball screw, preventing the end from falling off. The cover and the right end of the ball screw are screwed fixed; the screw nut is sleeved on the screw structure on the right part of the ball screw, there is a steel ball transmission between the screw nut and the ball screw, and the screw nut can rotate flexibly on the ball screw; The left end of the lead screw nut is provided with a raised outer edge. The raised outer edge of the left end of the rod nut and the left end of the sleeve are fastened with screws; the outer circle of the sensor seat is set as a stepped shaft, the steps on the left end of the sensor seat are evenly arranged with eight stepped holes in the circumferential direction, and the middle of the outer circle of the sensor seat is set as a male thread; the sensor seat The left end and the right end of the sleeve are fastened with screws, and the load sensor and the center of the outer circle of the sensor base are fixed with threads; the load sensor is a spoke structure, the inner hole of the load sensor is set as a female thread, and the outer side of the load sensor is evenly set with eight through holes; A through hole is arranged at the lower end of the rotating arm, and four threaded holes are evenly arranged on the outer side of the through hole; the linear sliding sleeve c is embedded in the through hole at the lower end of the anti-rotation arm, and the outer edge of the left end of the linear sliding sleeve c and the anti-rotation arm are fastened with screws to prevent rotation. The upper end of the arm and the outer circle of the sleeve are fastened with screws; four through holes are arranged from the top to the bottom of the bracket vertical plate, and six threaded holes are evenly arranged on the outer circumference of the through holes at the uppermost end of the bracket vertical plate; the upper and lower ends of the positioning end plate are located A through hole is provided respectively; the sliding guide rod a is set as a stepped shaft with a small diameter at both ends and a large middle diameter, the middle part of the sliding guide rod a is set as a smooth straight rod, and the two ends of the sliding guide rod a are set as male threads; the sliding guide rod b is set It is a stepped shaft with a small diameter at both ends and a large diameter in the middle. The middle part of the sliding guide rod b is set as a smooth straight rod, and the two ends of the sliding guide rod b are set as male threads; the left end of the sliding guide rod a passes through the bracket vertical plate and counts from top to bottom. In the second through hole, the right end of the sliding guide rod a passes through the upper through hole of the positioning end plate, and the two locking nuts are respectively fastened with the male threads at both ends of the sliding guide rod a; the left end of the sliding guide rod b passes through the lowermost end of the bracket vertical plate Through hole, the right end of the sliding guide rod b passes through the through hole at the lower end of the positioning end plate, and the two locking nuts are respectively fastened with the male threads at both ends of the sliding guide rod b; The frame is fixedly connected; the outer circle of the positioning seat in the ultrasonic generating assembly passes through the through hole at the uppermost end of the bracket vertical plate, and the positioning seat and the bracket vertical plate are fastened with screws; the linear sliding sleeve a in the stress loading assembly is sleeved on the sliding guide rod On the smooth straight rod in the middle of a, the linear sliding sleeve b is set on the smooth straight rod in the middle of the sliding guide rod b; the ball screw in the linear transmission assembly passes through the bracket vertical plate from the top to the third through hole, The spring clip is installed on the left end face of the bracket vertical plate, the thrust bearing is installed on the right end face of the bracket vertical plate, the right end of the outer circle of the sensor seat is inserted into the through hole in the middle of the loading slide plate, and the linear sliding sleeve c is sleeved on the smooth straight rod in the middle of the sliding guide rod b; The flange structure at the right end of the reducer shell in the powertrain and the vertical plate of the bracket are fastened with screws, and the left end of the ball screw is inserted into the flat key output hole of the reducer, and the transmission can be realized after connection; The middle of the test piece is set as a "thin neck" structure, the left end of the test piece is connected with the right end of the displacement amplifier in the ultrasonic generating assembly with a screw thread, and the right end of the test piece is connected with the tension screw in the stress loading assembly. In the case where the tension screw is not connected, the loading support directly applies axial pressure to the right end of the specimen.

In this ultrasonic fatigue average stress loading device, the natural frequencies of the positioning seat, the displacement amplifier, the test piece and the loading support are the same as the vibration frequency output by the piezoelectric transducer, and the axial lengths of the positioning seat, the displacement amplifier and the test piece are all the same. is half the wavelength of the resonant wave, and the axial length of the loading support is (2n+1)/4 wavelengths of the resonant wave, where n is a natural number; piezoelectric transducer, positioning seat, displacement amplifier, specimen and loading support The position of each connection surface is the position of the maximum amplitude of the resonance wave, and the stress at this position is zero; at the position of the connection surface of the positioning seat and the vertical plate of the support, the amplitude of the resonance wave is zero; the position of the connection surface of the loading support and the loading plate At , the amplitude of the resonant wave is zero; the amplitude of the resonant wave in the middle section of the specimen is zero, and the internal stress is the largest, which is the fatigue fracture surface.

The beneficial effects of the present invention are: (1) the present invention can realize the average stress loading in the ultrasonic fatigue test, make the ultrasonic fatigue test more complete, and further widen the test range of the ultrasonic fatigue test; As well as the natural frequency and length dimension design of the test piece and the loading support, the resonance requirements of the test piece are guaranteed, and the harm of resonance of other parts is effectively avoided; (3) The present invention adopts electrical signal control, compared with traditional electro-hydraulic servo drive The fatigue testing machine has low power consumption and high control precision; (4) the invention can realize 20kHz frequency fatigue test, effectively shorten the fatigue test time, and can efficiently complete 10 to ¹⁰ cycles of fatigue testing; (5) the invention can provide ±40kN axial tension and pressure, effectively complete the ultrasonic fatigue average stress loading test.

Description of drawings

1 is a schematic structural diagram of an ultrasonic fatigue average stress loading device of the present invention applying an average stress state;

2 is a schematic structural diagram of an ultrasonic fatigue average stress loading device of the present invention in a state where average stress is not applied;

Fig. 3 is a three-dimensional structural schematic diagram of an ultrasonic fatigue average stress loading device of the present invention;

In the picture: 01. Ultrasonic generator assembly, 011. Piezoelectric transducer, 012. Positioning seat, 013. Displacement amplifier, 02. Stress loading assembly, 021. Tension screw, 022. Loading support, 023. Loading slide plate, 024. Linear sliding sleeve a, 025. Linear sliding sleeve b, 026. Tray, 027. Rubber pad, 03. Powertrain, 031. Servo motor, 032. Reducer, 04. Linear transmission assembly, 041. Transmission key , 042. Spring collar, 043. Thrust bearing, 044. Ball screw, 045. Screw nut, 046. Sleeve, 047. Linear sleeve c, 048. Anti-rotation arm, 049. Anti-drop end cap, 0410 .Sensor seat, 0411. Load sensor, 05. Bracket vertical plate, 06. Sliding guide rod a, 07. Lock nut, 08. Positioning end plate, 09. Sliding guide rod b, 10. Specimen.

Detailed ways

As shown in Figure 1, Figure 2 and Figure 3, an ultrasonic fatigue average stress loading device of the present invention is composed of an ultrasonic generating assembly 01, a stress loading assembly 02, a power assembly 03, a linear transmission assembly 04, a bracket vertical plate 05. The sliding guide rod a06, the locking nut 07, the positioning end plate 08, the sliding guide rod b09 and the test piece 10 are composed. The ultrasonic generating assembly 01 includes a piezoelectric transducer 011, a positioning seat 012 and a displacement amplifier 013. The total stress loading is Cheng 02 includes tension screw 021, loading support 022, loading slide plate 023, linear sliding sleeve a024, linear sliding sleeve b025, tray 026 and rubber pad 027, power assembly 03 includes servo motor 031 and reducer 032, linear transmission assembly 04 includes transmission key 041, spring collar 042, thrust bearing 043, ball screw 044, screw nut 045, sleeve 046, linear sliding sleeve c047, anti-rotation arm 048, anti-drop end cover 049, sensor base 0410 and load Sensor 0411; its structural features are: in the ultrasonic generating assembly 01, the piezoelectric transducer 011 can convert the electrical signal output by the ultrasonic frequency generator into a mechanical vibration signal output; the two ends of the positioning seat 012 are provided with threaded holes, and the positioning seat A circle of raised steps is arranged in the middle of the outer circle of 012, and six step holes are evenly arranged on the upper circumference of the raised step; threaded holes are arranged at both ends of the displacement amplifier 013, and the cross-sectional diameter of the left end of the displacement amplifier 013 is larger than that of the right end, and the outer circle of the displacement amplifier 013 The contour transitions smoothly in the axial direction; the left end of the positioning seat 012 and the output end of the piezoelectric transducer 011 are fixed with studs, and the right end of the positioning seat 012 and the left end of the displacement amplifier 013 are fixed with studs; in the stress loading assembly 02, the loading slide The upper, middle and lower parts of 023 are respectively provided with a through hole, four threaded holes are evenly arranged circumferentially at the outer right end of the upper through hole of the loading slide 023, four threaded holes are evenly arranged circumferentially at the outer right end of the lower through hole of the loading slide 023, and the middle part of the loading slide 023 is evenly arranged Eight threaded holes are evenly arranged at the left end of the outer side of the hole; the linear sliding sleeve a024 is embedded in the upper through hole of the loading slide 023, the right convex outer edge of the linear sliding sleeve a024 and the loading slide 023 are fastened with screws; the linear sliding sleeve b025 is embedded in the loading In the lower through hole of the slide plate 023, the convex outer edge on the right side of the linear sliding sleeve b025 and the loading slide plate 023 are fastened with screws; the inner cavity of the loading support 022 is set as a stepped hole, the right end of the tension screw 021 is set as a step, and the tension screw 021 is placed in In the stepped hole in the inner cavity of the loading support 022, the right end of the loading support 022 and the left side of the upper end of the loading slide 023 are fastened with screws; the right end of the tray 026 and the loading slide 023 are fastened with screws, and the rubber pad 027 is placed on the supporting surface of the tray 026 , the tray 026 is installed on the lower side of the loading support 022; in the powertrain 03, the output shaft of the servo motor 031 and the input shaft of the reducer 032 are connected, the casing of the servo motor 031 and the casing of the reducer 032 are fastened with screws, and the output of the reducer 032 The mode is the flat key hole output form, the right end of the reducer 032 shell is a flange structure, the servo motor 0 31 can output stable torque and speed according to the electrical signal; in the linear transmission assembly 04, a flat keyway is set on the left end of the ball screw 044, a ring groove is set on the right side of the flat keyway, and the right part of the ball screw 044 is set as a lead screw Structure, the right end of the ball screw 044 is provided with a threaded hole; the transmission key 041 is installed in the flat keyway at the left end of the ball screw 044, the spring collar 042 is installed in the collar groove of the ball screw 044, and the thrust bearing 043 is installed in the ball screw 044 On the left end surface of the right screw structure, the anti-drop end cover 049 and the right end of the ball screw 044 are threaded and fixed; the screw nut 045 is sleeved on the screw structure on the right part of the ball screw 044, and the screw nut 045 and the ball screw There is a steel ball transmission between 044, and the screw nut 045 can be flexibly rotated on the ball screw 044; the left end of the screw nut 045 is provided with a raised outer edge, the left end of the screw nut 045 has a raised outer edge and the left end of the sleeve 046 is fixed with screws The outer circle of the sensor seat 0410 is set as a stepped shaft, the steps on the left end of the sensor seat 0410 are evenly arranged with eight stepped holes in the circumferential direction, and the middle of the outer circle of the sensor seat 0410 is set as a male thread; the left end of the sensor seat 0410 and the right end of the sleeve 046 are fastened with screws , the load sensor 0411 and the sensor seat 0410 are fixed with threads in the middle of the outer circle; the load sensor 0411 is a spoke structure, which can withstand the two-way load of tension and compression, the inner hole of the load sensor 0411 is set as a female thread, and the outer circumference of the load sensor 0411 is evenly arranged with eight A through hole is set at the lower end of the anti-rotation arm 048, and four threaded holes are evenly arranged on the outer side of the through hole; the linear sliding sleeve c047 is embedded in the through hole at the lower end of the anti-rotation arm 048, and the outer edge of the left end of the linear sliding sleeve c047 and the anti-rotation arm 048 are used. The screws are fastened, and the upper end of the anti-rotation arm 048 and the outer circle of the sleeve 046 are fastened with screws; the bracket vertical plate 05 is provided with four through holes in sequence from the top to the bottom, and the outer side of the through hole at the uppermost end of the bracket vertical plate 05 is evenly provided with Six threaded holes; the upper and lower ends of the positioning end plate 08 are respectively provided with a through hole; the sliding guide rod a06 is set as a stepped shaft with a small diameter at both ends and a large diameter in the middle, the middle of the sliding guide rod a06 is set as a smooth straight rod, and the sliding guide rod a06 is two The ends of the sliding guide rod b09 are set as male threads; the sliding guide rod b09 is set as a stepped shaft with a small diameter at both ends and a large diameter in the middle, the middle part of the sliding guide rod b09 is set as a smooth straight rod, and the two ends of the sliding guide rod b09 are set as male threads; sliding guide rod a06 The left end passes through the second through hole from the top to the bottom of the bracket vertical plate 05, the right end of the sliding guide rod a06 passes through the upper end through hole of the positioning end plate 08, and the two locking nuts 07 are respectively fixed with the male threads at both ends of the sliding guide rod a06. The left end of the sliding guide rod b09 passes through the lowermost through hole of the bracket vertical plate 05, and the right end of the sliding guide rod b09 passes through the lower end through hole of the positioning end plate 08. The lower end of the bracket vertical plate 05 is fixedly connected to the frame, and the lower end of the positioning end plate 08 is fixedly connected to the frame; Bracket vertical plate 05 is fastened with screws; stress loading assembly The linear sliding sleeve a024 in 02 is set on the smooth straight rod in the middle of the sliding guide rod a06, the linear sliding sleeve b025 is set on the smooth straight rod in the middle of the sliding guide rod b09; the ball screw 044 in the linear transmission assembly 04 passes through The bracket vertical plate 05 is the third through hole from top to bottom, the spring clip 042 is installed on the left end face of the bracket vertical plate 05, the thrust bearing 043 is installed on the right end face of the bracket vertical plate 05, and the outer circle right end of the sensor seat 0410 is inserted into the loading slide plate 023 The through hole in the middle, the outer side of the load sensor 0411 and the loading slide plate 023 are fastened with screws, the linear sliding sleeve c047 is sleeved on the smooth straight rod in the middle of the sliding guide rod b09; the right end flange structure and bracket of the reducer 032 in the powertrain 03 shell The vertical plate 05 is fastened with screws, the left end of the ball screw 044 is inserted into the flat key output hole of the reducer 032, and the transmission can be realized after connection; the two ends of the test piece 10 are provided with threaded holes, and the middle part of the test piece 10 is set as a "thin neck" structure , the left end of the specimen 10 and the right end of the displacement amplifier 013 in the ultrasonic generating assembly 01 are connected by studs, and the right end of the specimen 10 is threadedly connected with the tension screw 021 in the stress loading assembly 02; in the case of applying axial pressure to the specimen 10 Then, the tension screw 021 may not be connected, and the loading support 022 directly applies axial pressure to the right end of the specimen 10 .

In an ultrasonic fatigue average stress loading device of the present invention, the natural frequencies of the positioning seat 012, the displacement amplifier 013, the specimen 10 and the loading support 022 are the same as the vibration frequency output by the piezoelectric transducer 011, and the positioning seat 012, the displacement The axial length of the amplifier 013 and the specimen 10 is half the wavelength of the resonant wave, and the axial length of the loading support 022 is (2n+1)/4 wavelengths of the resonant wave, where n is a natural number; the piezoelectric transducer 011 , positioning seat 012, displacement amplifier 013, the position of each connection surface between the test piece 10 and the loading support 022 are all the positions of the maximum resonance wave amplitude, and the stress at this position is zero; the positioning seat 012 is connected with the support vertical plate 05 At the surface position, the resonance wave amplitude is zero; at the position of the connection surface of the loading support 022 and the loading slide 023, the resonance wave amplitude is zero; the resonance wave amplitude of the middle section of the specimen 10 is zero, and the internal stress is the largest, which is the fatigue fracture surface.

The working principle of the ultrasonic fatigue average stress loading device of the present invention is as follows: the ultrasonic frequency generator transmits electrical signals to the piezoelectric transducer 011 in the ultrasonic generating assembly 01, and the piezoelectric transducer 011 converts the electrical signals into mechanical The vibration signal output is transmitted to the positioner 012, and the amplitude is amplified by the displacement amplifier 013 and then transmitted to the specimen 10; the output torque of the servo motor 031 is controlled, and the output torque is amplified by the reducer 032 and then transmitted to the ball wire in the linear transmission assembly 04. The screw 044 is converted into the linear motion of the screw nut 045 by the transmission action of the ball screw nut pair, and is transmitted to the stress loading assembly 02 through the sleeve 046, the sensor seat 0410, and the load sensor 0411. At this time, the stress loading assembly 02 Axial average tensile and compressive loads can be applied to the test piece 10 .

Claims (6)

1. The utility model provides an ultrasonic fatigue average stress loading device, generate subassembly (01) by the supersound, stress loading assembly (02), power assembly (03), linear transmission assembly (04), support riser (05), slip guide arm a (06), lock nut (07), location end plate (08), slip guide arm b (09) and test piece (10) constitute, supersound generates subassembly (01) including piezoelectric transducer (011), positioning seat (012) and displacement amplifier (013), stress loading assembly (02) include tension screw (021), loading support (022), loading slide plate (023), linear sliding sleeve a (024), linear sliding sleeve b (025), tray (026) and rubber pad (027), power assembly (03) include servo motor (031) and reduction gear (032), linear transmission assembly (04) include transmission key (041), spring (042) rand, The device comprises a thrust bearing (043), a ball screw (044), a screw nut (045), a sleeve (046), a linear sliding sleeve c (047), an anti-rotation arm (048), an anti-falling end cover (049), a sensor seat (0410) and a load sensor (0411); the method is characterized in that: in the ultrasonic generating assembly (01), the piezoelectric transducer (011) can convert the electric signal output by the ultrasonic frequency generator into a mechanical vibration signal and output the mechanical vibration signal; threaded holes are formed in two ends of the positioning seat (012), a circle of raised steps are arranged in the middle of the excircle of the positioning seat (012), and six step holes are uniformly formed in the raised steps in the circumferential direction; threaded holes are formed in two ends of the displacement amplifier (013), the diameter of the section of the left end of the displacement amplifier (013) is larger than that of the section of the right end of the displacement amplifier, and the outline of the outer circle of the displacement amplifier (013) is in smooth transition in the axial direction; the left end of the positioning seat (012) is fixed with the output end of the piezoelectric transducer (011) by a stud, and the right end of the positioning seat (012) is fixed with the left end of the displacement amplifier (013) by a stud; in the stress loading assembly (02), a through hole is respectively arranged at the upper part, the middle part and the lower part of a loading sliding plate (023), four threaded holes are uniformly arranged at the right end of the outer side of the through hole at the upper part of the loading sliding plate (023) in the circumferential direction, four threaded holes are uniformly arranged at the right end of the outer side of the through hole at the lower part of the loading sliding plate (023) in the circumferential direction, and eight threaded holes are uniformly arranged at the left end of the outer side of the through hole; the linear sliding sleeve a (024) is embedded into a through hole at the upper part of the loading sliding plate (023), and the outer edge of the right bulge of the linear sliding sleeve a (024) is fastened with the loading sliding plate (023) by a screw; the linear sliding sleeve b (025) is embedded into a through hole at the lower part of the loading sliding plate (023), and the outer edge of the right side bulge of the linear sliding sleeve b (025) is fastened with the loading sliding plate (023) by screws; the inner cavity of the loading support (022) is provided with a step hole, the right end of the tension screw (021) is provided with a step, the tension screw (021) is placed in the step hole of the inner cavity of the loading support (022), and the right end of the loading support (022) and the left side of the upper end of the loading sliding plate (023) are fastened by screws; the right end of a tray (026) is fastened with a loading sliding plate (023) by screws, a rubber pad (027) is placed on the bearing surface of the tray (026), and the tray (026) is installed at the lower side of a loading bearing (022); in the power assembly (03), an output shaft of a servo motor (031) is connected with an input shaft of a speed reducer (032); in the linear transmission assembly (04), a flat key groove is formed in the left end of a ball screw (044), a circle of clamping ring groove is formed in the right side of the flat key groove, the right portion of the ball screw (044) is of a screw structure, and a threaded hole is formed in the right end of the ball screw (044); the transmission key (041) is arranged in a flat key groove at the left end of the ball screw (044), the spring collar (042) is arranged in a collar groove of the ball screw (044), the thrust bearing (043) is arranged on the left end surface of a right screw structure of the ball screw (044), and the anti-drop end cover (049) and the right end of the ball screw (044) are fixed by threads; the screw nut (045) is sleeved on a screw structure at the right part of the ball screw (044), steel balls are arranged between the screw nut (045) and the ball screw (044) for transmission, and the screw nut (045) can flexibly rotate on the ball screw (044); the left end of the screw nut (045) is provided with a convex outer edge, and the convex outer edge of the left end of the screw nut (045) and the left end of the sleeve (046) are fastened by a screw; the excircle of the sensor seat (0410) is provided with a step shaft, the step at the left end of the sensor seat (0410) is uniformly provided with eight step holes along the circumferential direction, and the middle part of the excircle of the sensor seat (0410) is provided with male threads; the left end of the sensor seat (0410) and the right end of the sleeve (046) are fastened by screws, and the load sensor (0411) and the middle part of the excircle of the sensor seat (0410) are fixed by threads; the lower end of the anti-rotation arm (048) is provided with a through hole, and four threaded holes are uniformly formed in the circumferential direction of the outer side of the through hole; the linear sliding sleeve c (047) is embedded into a through hole at the lower end of the anti-rotation arm (048), the outer edge of the left end of the linear sliding sleeve c (047) is fastened with the anti-rotation arm (048) by a screw, and the upper end of the anti-rotation arm (048) is fastened with the excircle of the sleeve (046) by a screw; four through holes are sequentially arranged on the vertical support plate (05) from top to bottom, and six threaded holes are uniformly formed in the circumferential direction of the outer side of the through hole at the uppermost end of the vertical support plate (05); the upper end and the lower end of the positioning end plate (08) are respectively provided with a through hole; the sliding guide rod a (06) is provided with a step shaft with small diameters at two ends and large diameter in the middle, the middle part of the sliding guide rod a (06) is provided with a smooth straight rod, and two ends of the sliding guide rod a (06) are provided with male threads; the sliding guide rod b (09) is provided with a step shaft with small diameters at two ends and large diameter in the middle, the middle part of the sliding guide rod b (09) is provided with a smooth straight rod, and two ends of the sliding guide rod b (09) are provided with male threads; the left end of the sliding guide rod a (06) penetrates through a second through hole of the support vertical plate (05) from top to bottom, the right end of the sliding guide rod a (06) penetrates through a through hole in the upper end of the positioning end plate (08), and two locking nuts (07) are respectively fastened with male threads at two ends of the sliding guide rod a (06); the left end of a sliding guide rod b (09) penetrates through a through hole at the lowest end of a support vertical plate (05), the right end of the sliding guide rod b (09) penetrates through a through hole at the lower end of a positioning end plate (08), and two locking nuts (07) are respectively fastened with male threads at two ends of the sliding guide rod b (09); the lower end of the support vertical plate (05) is fixedly connected with the rack, and the lower end of the positioning end plate (08) is fixedly connected with the rack; the excircle of a positioning seat (012) in the ultrasonic generating assembly (01) penetrates through a through hole at the uppermost end of a support vertical plate (05), and the positioning seat (012) and the support vertical plate (05) are fastened by screws; a linear sliding sleeve a (024) in the stress loading assembly (02) is sleeved on the smooth straight rod in the middle of the sliding guide rod a (06), and a linear sliding sleeve b (025) is sleeved on the smooth straight rod in the middle of the sliding guide rod b (09); a ball screw (044) in the linear transmission assembly (04) penetrates through a third through hole from top to bottom of a support vertical plate (05), a spring collar (042) is installed on the left end face of the support vertical plate (05), a thrust bearing (043) is installed on the right end face of the support vertical plate (05), the right end of the excircle of a sensor seat (0410) is inserted into a through hole in the middle of a loading sliding plate (023), the outer side of a load sensor (0411) is fastened with the loading sliding plate (023) through a screw, and a linear sliding sleeve c (047) is sleeved on a smooth straight rod in the middle of a sliding guide rod b (09); a flange structure at the right end of a shell of a speed reducer (032) in a power assembly (03) is fastened with a vertical plate (05) of a bracket by screws, and the left end of a ball screw (044) is inserted into a flat key output hole of the speed reducer (032) and can realize transmission after connection; threaded holes are formed in two ends of a test piece (10), the middle of the test piece (10) is of a thin neck structure, the left end of the test piece (10) is connected with the right end of a displacement amplifier (013) in the ultrasonic generation assembly (01) through a stud, and the right end of the test piece (10) is connected with a tension screw (021) in the stress loading assembly (02) in a threaded mode.

2. The ultrasonic fatigue mean stress loading device of claim 1, wherein: the natural frequency of the positioning seat (012), the displacement amplifier (013), the test piece (10) and the loading support (022) is the same as the vibration frequency output by the piezoelectric transducer (011), the axial lengths of the positioning seat (012), the displacement amplifier (013) and the test piece (10) are all half resonant wave wavelength, the axial length of the loading support (022) is (2n +1)/4 resonant wave wavelengths, and n is a natural number.

3. The ultrasonic fatigue mean stress loading device of claim 1, wherein: the positions of the connecting surfaces among the piezoelectric transducer (011), the positioning seat (012), the displacement amplifier (013), the test piece (10) and the loading support (022) are positions with the maximum amplitude of the resonant wave, and the stress at the positions is zero; the amplitude of the resonance wave is zero at the position of the connecting surface of the positioning seat (012) and the vertical plate (05) of the bracket; the amplitude of the resonant wave is zero at the position of the connecting surface of the loading support (022) and the loading sliding plate (023); the amplitude of the resonance wave of the middle section of the test piece (10) is zero, the internal stress is maximum, and the test piece is a fatigue fracture surface.

4. The ultrasonic fatigue mean stress loading device of claim 1, wherein: the load sensor (0411) is of a spoke type structure and can bear tension and compression bidirectional loads, an inner hole of the load sensor (0411) is provided with female threads, and eight through holes are uniformly formed in the circumferential direction of the outer side of the load sensor (0411).

5. The ultrasonic fatigue mean stress loading device of claim 1, wherein: under the condition that the test piece (10) only bears the axial pressure load, the tension screw (021) is not connected, and the loading support (022) directly applies the axial pressure to the right end of the test piece (10).

6. The ultrasonic fatigue mean stress loading device of claim 1, wherein: servo motor (031) shell and reduction gear (032) for the shell screw fasten, reduction gear (032) output mode is flat keyhole output form, reduction gear (032) shell right-hand member is the flange structure, servo motor (031) can be according to stable moment of torsion and the rotational speed of signal of telecommunication output.

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