CN103076246B - Double-shaft high-low cycle complex fatigue tester - Google Patents

Abstract

A double-shaft high-low cycle complex fatigue tester comprises a hydraulic fatigue tester, an upper clamping head, a lower clamping head, an electromagnetic vibration exciter, a sample, a fixture, and a locating connecting device. The electromagnetic vibration exciter is connected with a middle clamping block 2 in the fixture via a cylindrical connector, a connecting rod and a U-shaped connector in a positioning connecting device; the middle clamping block 2 and a middle clamping block 1 are used for clamping a square mass boss at the middle part of the sample via a connecting piece, and the two ends of the sample are connected with a plywood in the fixture via the connecting piece; the plywood is connected with the connector in the fixture via bolts in the connecting piece; and the vertical ends of the connector are placed in the grooves of the upper clamping head and the lower clamping head of the hydraulic fatigue tester, contacted with the hydraulic fatigue tester, and clamped tightly via the hydraulic pressure of the tester. The tester is simple in structure and convenient to operate, solves the problems of load interference and load coordination in the vertical direction and the horizontal direction during bidirectional loading aiming at the plate-shaped sample, and can be used for simulating fatigue load borne by the blades of the rotor of a gas turbine engine.

Description

A biaxial high-low cycle composite fatigue test device

technical field

The invention relates to a biaxial high-low cycle compound fatigue test device, which belongs to the field of material and structure fatigue performance test.

Background technique

The design of modern gas turbine engines needs to achieve a comprehensive balance between high performance, high reliability, and good economy. Rotor blades of gas turbine engines, such as fans, compressors, and turbine blades, are subjected to large low-frequency centrifugal force loads due to rotation during operation, and are also subjected to high-frequency loads of forced vibration of airflow, which makes high and low in the engine rotor blades. Cyclic composite fatigue failure mode. This means that in order to design a well-performing and reliable engine, it is necessary to improve the fatigue resistance of the components.

Improving the fatigue resistance of components is mainly achieved through the improvement of material properties and structural fatigue performance of components. Among them, the research on the fatigue performance of materials requires various fatigue test data.

During the working process of the gas turbine engine, due to the high-speed rotation of the rotor, the fan, compressor and turbine blades all bear high centrifugal force. At the same time, in each stage of the compressor and turbine, there are stator blades and rotor blades. The stator blades guide the airflow to flow through the rotor blades, and the pressure and velocity of the airflow will change periodically when passing through each stator blade, which is reflected as a periodic excitation force on the rotor blades. When certain conditions are met, the rotor blades need to withstand high-frequency forced vibration loads, resulting in high-cycle fatigue; at the same time, the blades also bear low-cycle fatigue mainly due to centrifugal stress during the start-stop process. When the fatigue performance of the rotor blade is insufficient, composite fatigue damage will occur.

The purpose of the invention is to simulate well the damage caused by the high-low cycle composite fatigue load occurring in the operation of the rotor blade, and mainly conduct the high-low cycle composite fatigue test on the plate-shaped sample.

Contents of the invention

1. Purpose of the invention

The purpose of the present invention is to provide a biaxial high-low cycle composite fatigue test device to solve the problem of bidirectional simultaneous loading of plate samples.

2. Technical solution

The present invention is a dual-axis high-low cycle composite fatigue test device, as shown in Figure 1, the device includes a hydraulic fatigue test machine, upper and lower chucks, an electromagnetic exciter (18), a sample (7) and fixtures and positioning connections device. The positional connection relationship between them is: the electromagnetic exciter (18) is positioned through the cylindrical connector (16), the connecting rod (15), the U-shaped connector (14) and the middle clamp block in the fixture 2 (11) connection; the middle clamp block 2 (11) and the middle clamp block 1 (10) clamp the square mass block boss in the middle of the sample (7) through the connector, and the two ends of the sample (7) are connected to the The splint (3) in the fixture is connected; the splint (3) and the connector (2) in the fixture are connected by bolts; the vertical end of the connector (2) is placed in the groove of the upper and lower chucks of the hydraulic fatigue testing machine and connected with the hydraulic fatigue The testing machine is contacted and clamped by the hydraulic pressure of the testing machine.

The hydraulic fatigue testing machine is a Shimadzu EHF-EM100K hydraulic fatigue testing machine, which can provide a dynamic force of 100KN and a static force of 150KN. Its upper and lower chucks are accessories of this machine.

The electromagnetic exciter is a JZQ-80 type exciter, which can provide a frequency of 1-1.5KHz and a maximum excitation force of 800N, and it is fixed on a large-mass workbench through a connecting piece. At the same time, the electromagnetic exciter is equipped with corresponding power amplifier and signal source.

The sample, as shown in Figure 5, adopts a symmetrical design, with a square mass boss in the middle, and a strip at both ends that is square and with through holes; its function is: (a) it can pass through the designed mass boss geometric dimensions to adjust its mass, and then change the natural frequency and mode of the sample to better simulate the natural frequency and mode of the real blade; (b) the transition area between the mass block boss and the flat plate smooth section can make The bending stress caused by the high cyclic fatigue load is effectively concentrated in the examination part; (c) the side plane in the center of the mass block boss provides a horizontally excited loading surface to avoid surface damage caused by direct loading on other parts of the sample. The sample adopts a symmetrical design, so that when a high cyclic excitation load is loaded on the side plane of the middle boss, the stress caused by the upper and lower parts of the sample is the same, and it can also ensure that the sample can still be applied when both ends of the sample are fixed. High cyclic fatigue loading in the horizontal direction. Both ends of the sample are thickened and have pin holes, which can be connected by pins to achieve reliable positioning and transmit low cyclic fatigue loads, while avoiding additional bending moments caused by low cyclic fatigue loads.

The fixture includes a splint (3), a connecting head (2), an intermediate clamping block 1 (10) and an intermediate clamping block 2 (11); the former two are connected by bolts; the latter two clamp the sample (7) by bolts The boss of the square mass block in the middle; the splint (3) is designed in half, and its shape is an L-shaped structural member, and its elevation and plane are provided with connection holes; the splint (3) is in plane contact with the sample. A certain pressure is generated under the action of the connecting bolts, which can effectively improve the contact rigidity. The transition fit between the splint (3) and the pin hole on the sample and the pin (6) is convenient for loading and unloading without causing excessive gaps to affect the loading accuracy. At the same time, the transition fit can make the pin (6) a load-bearing component , effectively avoiding the damage of bolts due to shear force. The connector (2) is a T-shaped structural part, and its horizontal surface is provided with a connecting hole; its vertical end is placed in the upper and lower chuck grooves of the hydraulic fatigue testing machine to contact the hydraulic fatigue testing machine. The dispersed bolt position design can effectively improve the rigidity, and at the same time, the sample can be centered by fine-tuning the relative position of the connection. The intermediate clamping block 1 (10) is a rectangular piece with a groove in the middle and connecting holes at both ends; the shape of the intermediate clamping block 2 (11) is a T-shaped structural member, and the shape and size of the horizontal plane are similar to those of the intermediate clamping block. Corresponding to block 1 (10), its vertical end is provided with a connecting hole, and is connected with a U-shaped connector (14) through a small pin (13).

The positioning connection device includes a U-shaped connector (14), a connecting rod (15) and a cylindrical connector (16), the threaded end of the connecting rod (15) is screwed to the thread on the U-shaped connector (14), The spherical end of the connecting rod (15) is connected with a cylindrical joint (16) with a spherical hinge. The U-shaped connector (14) is a rectangular piece with a U-shaped groove, the U-shaped groove is provided with a connecting hole, and the lower end of the U-shaped groove is provided with a threaded connecting hole. This connecting rod (15) is a round rod, one end of the round rod is threaded, and the other end is set to a spherical hinge. The cylindrical connector (16) is in the shape of a shaft sleeve, and the outer circumference is provided with three threaded fixing holes uniformly distributed, and one end of the inner hole is processed into a ball hinge and is hinged with the ball hinge end of the connecting rod (15). The other end of the hole is connected with the excitation head of the electromagnetic exciter (18), and is clamped by three screws evenly distributed in the circumferential direction.

In the test, install the fixture, the sample and the positioning connection device, load the low cycle fatigue load, and then adjust the height of the vibrator to keep the same height as the excitation point in the middle of the sample, then the horizontal high cycle fatigue load can be loaded. The horizontal load range to be loaded should be less than the maximum lateral load that the fatigue testing machine can bear in the vertical direction.

3. Advantages and effects

(1) Effectively solve the interference problem of loading in vertical and horizontal directions. Exciting the middle part of the sample can realize high-cycle fatigue load loading under the condition that the two ends of the sample are fixed; the pin and ball connection between the exciter and the sample fixture can effectively avoid the vertical load due to small The displacement caused by the change produces a bending moment.

(2) Fewer parts and simple structure. The two ends of the sample are clamped with relatively simple fixtures, and the vibration is excited in the middle, which avoids the need for specially designed complex fixtures due to simultaneous loading of vertical loads and horizontal loads. At the same time, the program can be completed only on the ordinary fatigue testing machine equipped with a certain power exciter.

(3) The sample design is more representative. The design of the sample with a boss in the middle can well simulate the natural frequency and mode shape of the real blade, and the stress state of the bidirectional loading is closer to the stress state of the rotor blade in operation. At the same time, when the frequency of the horizontal excitation force is equal to the first-order resonance frequency of the sample, the force state of the blade in the resonance state can be better simulated.

Description of drawings

Figure 1: General structure diagram of the double-axis high-low cycle composite fatigue test device of the present invention

Figure 2: Three-dimensional view of the connector

Figure 3: Three-dimensional view of the splint

Figure 4: Three-dimensional stereogram of the sample

Figure 5: Three-dimensional perspective view of the middle clamp block 1

Figure 6: Three-dimensional perspective view of the middle clamp block 2

Figure 7: Three-dimensional view of the U-shaped connector

Figure 8: Three-dimensional perspective view of cylindrical connector

Figure 9: Three-dimensional view of connecting rod

Figure 10: Sectional view of the ball joint

Figure 11: Schematic diagram of sample loading for finite element analysis

Figure 12: Schematic diagram of the finite element analysis results of the stress distribution of the sample under the action of tensile force

Figure 13: Schematic diagram of the finite element analysis results of the first-order mode shape of the sample under the action of tensile prestress

Figure 14: Schematic diagram of the finite element analysis results of the mode response of the sample loaded with transverse harmonic excitation

Figure 15: Schematic diagram of finite element analysis results of bending stress distribution of specimen loaded with transverse harmonic excitation

The symbols in the figure are explained as follows:

1 Shimadzu E-100K fatigue testing machine lower chuck 2 connector 3 splint

4 hexagon socket bolts 1 5 hex socket bolts 2 6 large pins

7 Sample 8 Hexagon socket bolt 3 9 External hexagon nut 1

10 Intermediate clip 1 11 Intermediate clip 2 12 Shimadzu E-100K fatigue testing machine upper chuck

13 small pins 14 U-shaped connectors 15 connecting rods

16 Cylindrical connector 17 Fastening screw 18 Electromagnetic exciter

19 T-bolts 20 Outer hex nuts 2 21 Gaskets

22 large quality workbenches

Detailed ways

See Fig. 1 - Fig. 10, the present invention is a biaxial high-low cycle composite fatigue test device, the device mainly includes a hydraulic fatigue test machine and upper and lower chucks (1), (12), electromagnetic exciter (18 ), sample (7) and fixture and positioning connection device. The positional connection relationship between them is: the electromagnetic exciter (18) is positioned through the cylindrical connector (16), the connecting rod (15), the U-shaped connector (14) and the middle clamp block in the fixture 2 (11) connection; the middle clamp block 2 (11), the middle clamp block 1 (10) clamp the square mass block convex in the middle of the sample (7) through the inner hexagonal bolt 3 (8) and the outer hexagonal nut 1 (9). platform, the two ends of the sample (7) are connected to the splint (3) in the fixture through the hexagon socket bolt 2 (5) and the large pin (6); the splint (3) is screwed to the flat end of the connector (2) in the fixture ; The vertical end of the connector (2) is placed in the upper and lower chucks (1) and (12) grooves of the hydraulic fatigue testing machine to contact the hydraulic fatigue testing machine, and clamped under the hydraulic pressure of the testing machine.

The hydraulic fatigue testing machine is a Shimadzu EHF-EM100K hydraulic fatigue testing machine, which can provide a dynamic force of 100KN and a static force of 150KN.

The electromagnetic exciter is a JZQ-80 type exciter, which can provide a frequency of 1-1.5KHz and a maximum excitation force of 800N. It passes T-shaped bolts (19), outer hex nuts 2 (20), gaskets (21) is affixed on the large mass workbench (22). At the same time, the electromagnetic exciter is equipped with corresponding power amplifier and signal source.

The sample (7), as shown in Figure 5, adopts a symmetrical design, with a square mass block boss in the middle, and a strip-shaped piece with square holes at both ends; its function is: (a) the mass block can be designed to The geometric dimensions of the boss are used to adjust its mass, thereby changing the natural frequency and mode of the sample to better simulate the natural frequency and mode of the real blade; (b) the transition between the boss of the mass block and the smooth section of the flat plate The area can effectively concentrate the bending stress caused by the high cyclic fatigue load on the examination part; (c) the side plane in the center of the mass block boss provides a horizontally excited loading surface to avoid surface damage caused by direct loading on other parts of the sample . The sample (7) adopts a symmetrical design, so that when a high cyclic excitation load is loaded on the side plane of the middle boss, the stress caused by the upper and lower parts of the sample (7) is the same, and it can also ensure that the two ends of the sample (7) In the case of fixed supports, high cyclic fatigue loads in the horizontal direction can still be applied. Both ends of the sample are thickened and have pin holes, which can be connected by pins to achieve reliable positioning and transmit low cyclic fatigue loads, while avoiding additional bending moments caused by low cyclic fatigue loads.

The clamp includes a splint (3), a connecting head (2), an intermediate clamping block 1 (10) and an intermediate clamping block 2 (11); the former two are connected by a hexagon socket bolt 1 (4); the latter two are connected by an internal hexagon The bolt 3 (8) clamps the square mass block boss in the middle of the sample (7); the splint (3) is designed in half, and its shape is an L-shaped structural part, and its elevation and plane are provided with connection holes; the splint (3) Planar contact with the sample generates a certain pressure under the action of the connecting bolts, which can effectively improve the contact rigidity. The transition fit is adopted between the splint (3) and the pin holes on the sample (7) and the large pin (6), which is convenient for loading and unloading without causing excessive gaps to affect the loading accuracy. At the same time, the transition fit can make the pin (6) Become a load-bearing component, effectively avoiding the damage of bolts due to shearing. The connector (2) is a T-shaped structural part, and its horizontal surface is provided with a connecting hole; its vertical end is placed in the upper and lower chuck grooves of the hydraulic fatigue testing machine to contact the hydraulic fatigue testing machine. The dispersed bolt position design can effectively improve the rigidity, and at the same time, the sample can be centered by fine-tuning the relative position of the connection. The intermediate clamping block 1 (10) is a rectangular piece with a groove in the middle and connecting holes at both ends; the shape of the intermediate clamping block 2 (11) is a T-shaped structural member, and the shape and size of the horizontal plane are similar to those of the intermediate clamping block. Corresponding to block 1 (10), its vertical end is provided with a connecting hole, and is connected with a U-shaped connector (14) through a small pin (13).

The positioning connection device includes a U-shaped connector (14), a connecting rod (15) and a cylindrical connector (16), the threaded end of the connecting rod (15) is screwed to the thread on the U-shaped connector (14), The spherical end of the connecting rod (15) is connected with a cylindrical joint (16) with a spherical hinge. The U-shaped connector (14) is a rectangular piece with a U-shaped groove, the U-shaped groove is provided with a connecting hole, and the lower end of the U-shaped groove is provided with a threaded connecting hole. The connecting rod (15) is a round rod, one end of the round rod is threaded, and the other end is set as a spherical hinge. The cylindrical connector (16) is in the shape of a shaft sleeve, and the outer circumference is provided with three threaded fixing holes uniformly distributed, and one end of the inner hole is processed into a ball hinge and is hinged with the ball hinge end of the connecting rod (15). The other end of the hole is connected with the excitation head of the electromagnetic exciter (18), and is clamped by three fastening screws (17) evenly distributed in the circumferential direction.

1. Carry out finite element analysis on the sample (7) to determine the excitation frequency of low cycle fatigue load and high cycle fatigue load. Figure 11 is a schematic diagram of loading in finite element analysis. Figure 12-Figure 15 is the analysis result of ABAQUS software for a certain titanium alloy sample: Figure 12 shows that when the maximum value of the low cyclic load _F1 is 64KN, the maximum stress of the stress concentration part of the sample is 844MPa, and its stress distribution ; Figure 13 is the first-order mode based on the stress distribution shown in Figure 12, and the first-order natural frequency of the sample is 1410Hz; Figure 14 and Figure 15 are the mode shapes of the sample when F ₂ =625Sin8860t N is loaded, and Stress distribution in the Z direction. From these analysis, it can be determined that the maximum force of the low-cycle test is 64KN, the force amplitude in the high-cycle horizontal direction is 625N, and the frequency is 1410Hz, which is the resonance frequency of the sample. The estimated high-cycle stress ratio is R=0.43. In the test, the loading of the design stress level and stress ratio is realized by adjusting the above parameters.

2. Connect the sample (7) to the fixture, and connect it to the fatigue testing machine in the vertical direction, and make the sample (7) center by fine-tuning the position of the connecting bolt.

3. Clamp the middle clamping block to the middle of the sample (7) with bolts, and then load the low cycle fatigue load to the maximum value in the vertical direction. The displacement control method is adopted when loading low cyclic fatigue loads to ensure stable loading of low cyclic loads.

4. At this time, adjust the height of the electromagnetic exciter (18) so that the excitation head and the excitation point of the sample are kept at the same height, and use the connecting rod (15), small pins (13) and bolts to connect the electromagnetic exciter ( 18) Connected. Adjust the tightness of the connection so that it can transmit the exciting force well.

5. Set the position of the vibrometer to accurately measure the vibration displacement. The monitoring point of the vibrometer is the stress concentration point shown in Figure 11, or its symmetrical position.

6. Set high-cycle excitation load spectrum and low-cycle load spectrum, and carry out biaxial high-low cycle fatigue test.

7. According to the measured displacement after the test, use the finite element analysis to obtain the real stress state of the assessment point, and analyze it to draw a conclusion.

Claims (1)

1. the twin shaft height composite fatigue test unit that circulates, is characterized in that: this device comprises hydraulic fatigue machine and upper and lower chuck, electromagnetic exciter (18), sample (7) and fixture and locating connector; Electromagnetic exciter (18) is connected by cylindricality connector (16), connecting link (15), U-shaped connector (14) and the middle fixture block 2 (11) in fixture in locating connector; Middle fixture block 2 (11), middle fixture block 1 (10) are clamped the square mass boss at sample (7) middle part by web member, sample (7) two ends are connected with the clamping plate (3) in fixture by web member; Clamping plate (3) are connected by bolt with connector in fixture (2); The vertical end of connector (2) is placed in the upper and lower chuck groove of hydraulic fatigue machine and contacts with hydraulic fatigue machine, relies on this testing machine hydraulic coupling to clamp;

Described hydraulic fatigue machine, provides dynamic 100KN, the power of static 150KN; Its upper and lower chuck is this machine annex;

Described electromagnetic exciter, it is 1-1.5KHz that frequency is provided, the exciting force of maximum 800N, it is fixed on large quality work platform by web member; This electromagnetic exciter is equipped with corresponding power amplifier and signal source simultaneously;

Described sample, is to adopt symmetric design, middle with square mass boss, and two is square and bars with through hole;

Described fixture comprises clamping plate (3), connector (2), middle fixture block 1 (10) and middle fixture block 2 (11); The former two is bolted; The latter two clamp the square mass boss at sample (7) middle part by bolt; These clamping plate (3) are to adopt point half design, and profile is L-type structural member, and its facade and plane are all provided with connecting hole; Plane contact between clamping plate (3) and sample produces predetermined pressure under coupling bolt effect, effectively improves contact rigidity; Between pin-and-hole on clamping plate (3) and sample and pin (6), adopt transition fit, not only be convenient to handling but also be unlikely to produce excessive gap affects loading accuracy, transition fit makes pin (6) become load parts simultaneously, has effectively avoided bolt owing to being subject to shearing to produce destruction; This connector (2) profile is T-shaped structural member, and its surface level is provided with connecting hole; Its vertical end is placed in the upper and lower chuck groove of hydraulic fatigue machine and contacts with hydraulic fatigue machine; The bolt position design disperseing improves rigidity effectively, makes sample centering by the fine setting that connects relative position simultaneously; This centre fixture block 1 (10) is the rectangular-shaped piece that middle part has groove, two ends and be provided with connecting hole; The profile of this centre fixture block 2 (11) is T-shaped structural member, the profile of its surface level and size are corresponding with middle fixture block 1 (10), it is vertically held and is provided with connecting hole, is connected with U-shaped connector (14) by little pin (13);

Described locating connector comprises U-shaped connector (14), connecting link (15) and cylindricality connector (16), screw thread on the thread end of connecting link (15) and U-shaped connector (14) is spirally connected, and the spheric end of connecting link (15) is connected with cylindricality connector (16) ball pivot; This U-shaped connector (14) is to have rectangular-shaped of U-lag, and U-lag is provided with connecting hole, and U-lag lower end is provided with threaded connection hole; This connecting link (15) is round bar part, and one end of round bar is screw thread, and the other end is set to ball pivot shape; The profile of this cylindricality connector (16) is sleeve-like part, excircle is provided with three uniform screw thread fixed orifices, it is hinged that the ball pivot end of ball pivot shape and connecting link (15) is processed in endoporus one end, the endoporus other end is connected with the excitation head of electromagnetic exciter (18), adopts three uniform screws of circumferencial direction to clamp.