CN105675412A - Bending fretting fatigue experimental equipment and experimental method - Google Patents

Abstract

The invention discloses a bending fretting fatigue experiment device, which comprises a sample, a sample clamping and fixing part, a normal contact load applying part, a bending fatigue load applying part and a data acquisition control system. One end of the sample is fixed on the sample The fixed part is clamped, and the other end is provided with a bending fatigue load applying part, which is pressed by the normal contact load applying part. Both the sample clamping fixed part and the bending fatigue load applying part are electrically connected to the data acquisition and control system. The invention also discloses a bending fretting fatigue test method, the method is as follows: assemble the device, install the sample, apply a normal contact load to the round bar sample, and when the load is applied to the set condition, control the electric The hydraulic servo fatigue testing machine enables the round bar sample to be tested according to the set parameters. The experimental device and method are simple to operate, truly simulate the bending fretting fatigue damage of components under alternating loads, have high control and test precision, good reproducibility of experimental data, and accurate and reliable experimental results.

Description

A bending fretting fatigue experimental device and experimental method

technical field

The invention belongs to the technical research field of fretting fatigue, and in particular relates to a bending fretting fatigue experimental device and an experimental method.

Background technique

Fretting refers to the relative motion of extremely small amplitude (micron level) between two contact surfaces (such as tight fitting surfaces) under the action of alternating loads such as mechanical vibration, fatigue load, electromagnetic vibration or thermal cycle. The contacting surfaces are usually nominally stationary, i.e. fretting occurs in mechanical parts that are "tightly" fitted.

Fretting fatigue refers to the phenomenon that the contact interface undergoes slight relative motion (usually at the micron level) due to the different deformations of the contact body due to the external alternating fatigue stress, which promotes the early initiation and accelerated growth of fatigue cracks, resulting in premature failure of the component. Phenomenon, it is a fatigue strength and fatigue life problem accompanied by fretting wear. Studies have shown that fretting fatigue can reduce the fatigue life of components by 20% to 80%, or even lower.

Fretting fatigue damage generally exists in tight fitting parts in machinery, railways, automobiles, ships, aerospace, bridge engineering, nuclear reactors, power industry and other fields. With the increasing requirements for high precision, long life and high reliability in the engineering field The hazards of fretting fatigue damage are becoming more and more prominent in the increasingly complex and harsh working conditions. Fretting will accelerate the initiation and growth of fatigue cracks in parts, which will significantly reduce the service life of parts. According to the survey, fretting fatigue has become one of the main reasons for the failure of some key components, and it is called "cancer" in the industry.

Bending fretting fatigue damage generally exists in rotating parts, which greatly reduces the service life of these parts. The bending fretting fatigue test and analysis are carried out to clarify its bending fretting fatigue characteristics and damage mechanism, which can provide accurate and reliable test basis for the design, manufacture and maintenance of related parts, and help reduce the initiation and damage of fatigue cracks. It is of great significance to extend and improve the service life of components. At present, there are no experimental equipment and experimental methods specially designed for bending fretting fatigue experiments.

Contents of the invention

The object of the present invention is to provide a bending fretting fatigue experiment device and experimental method. The device has a simple structure and is easy to operate, and can perform bending fretting fatigue experiments on various working conditions and specifications of material samples, and has high control and testing accuracy. , the experimental data is more accurate, reliable and reproducible.

To achieve the above object, the present invention adopts the following technical solutions:

The invention provides a bending fretting fatigue experimental device, comprising a sample (2), a sample clamping and fixing part, a normal contact load applying part, a bending fatigue load applying part and a data acquisition control system, the sample ( 2) One end is fixed on the sample clamping and fixing part, the other end is provided with the bending fatigue load applying part and is pressed vertically up and down by the normal contact load applying part, and the sample clamping and fixing part A force sensor (12) is provided, and both the force sensor (12) and the bending fatigue load application part are electrically connected to the data acquisition control system, and the data acquisition control system controls the experimental conditions and collects experimental data.

The sample clamping and fixing part includes a base (1) fixed on the base of the fatigue test bench, a long groove arranged in the middle of the base (1), a square hole arranged on the base (1), The clamping block (3) and fixing screw one (4) arranged in the square hole, the left end of the sample (2) passes through the clamping block (3) in the square hole of the base (1) And the fixing screw one (4) is fixed on the base (1).

The normal contact load applying part includes a bearing platform (7), an upper fretting pad clamping seat (11), a loading plate (15), and a linear guide rail (17), and the linear guide rail (17) passes through the upper The micro-movement pad clamping seat (11), the bottom end is fixed on the bearing platform (7), and the top is fixed on the loading plate (15), and the bearing platform (7) is fixed by fixing screws two (5) and The fixed plate (6) is fixed in the long groove in the middle of the base (1), and its position can be adjusted within a certain distance according to the experimental requirements. The lower fretting pad (8) is arranged in the middle of the bearing platform (7). The upper fretting pad holder (11) is provided with an upper fretting pad (10), and the sample (2) is arranged between the upper fretting pad (10) and the lower fretting pad (8). ), the upper part of the upper fretting pad clamping seat (11) is provided with a groove, and a force sensor (12) is arranged in the groove to measure the normal contact load loaded in real time. The loading plate (15) A loading screw (16) is arranged on the top, and a steel ball (14) is set between the loading screw (16) and the upper fretting pad clamping seat (11), and the loading screw (16) and the steel ball (14) A normal contact load is applied to the upper fretting pad clamping seat (11).

The bending fatigue load applying part is an electro-hydraulic servo fatigue testing machine (9).

Further, the upper fretting pad clamping seat (11) is installed on the linear guide rail (17) through two linear bearings (18), and the upper and lower sides of the force sensor (12) are respectively provided with a piece for protecting the The gasket (13) of the force sensor (12) body, the linear bearings (18) are installed on both sides of the upper fretting pad clamping seat (11), so that the frictional force of its movement on the linear guide rail (17) is almost zero.

The present invention also provides a bending fretting fatigue test method, the method comprising the following steps:

a. Fix the base (1) at a suitable position on the fatigue test bench, and then fix the bearing platform (7) with the lower fretting pad (8) and the linear guide rail (17) in the middle of the base (1) Its position in the long groove is determined according to the needs of the experimental conditions, and then the left end of the sample (2) is fixed in the left square hole of the base (1), and the right end is placed on the lower fretting pad ( 8), then the upper fretting pad holder (11) with the upper fretting pad (10) is vertically slid down through the linear guide rail (17), so that the upper fretting pad (10) and the sample ( 2) Vertical and orthogonal to achieve good point contact;

b. Turn the loading screw (16), the applied normal contact load will be displayed on the computer connected to the data acquisition control system through the measurement of the force sensor (12), when the normal contact load is applied to the set experimental conditions , stop screwing the loading screw (16), and then control the electro-hydraulic servo fatigue testing machine (9) through the data acquisition control system, so that the sample (2) performs bending micro-motion according to the set parameters (amplitude, frequency, etc.) Fatigue experiment. During this process, various experimental data will be fed back to the data acquisition and control system for analysis through sensors, and the change curves of various parameters will be drawn.

Beneficial effects of the present invention:

First, the round bar sample and the cylindrical upper fretting pad form an orthogonal point contact mode, and the bending fretting fatigue load is applied by the electro-hydraulic servo fatigue testing machine, and the electro-hydraulic servo fatigue testing machine has a small vibration amplitude and a high frequency , high precision, accurately realized the bending fretting fatigue experiment of the round bar sample, and truly and effectively tested and analyzed the bending fretting fatigue;

Second, the combination of linear bearings and linear guide rails is used to make the friction force between the upper fretting pad clamping seat and the guide rail almost zero when sliding up and down, and to make the normal contact load measured by the force sensor and the actual applied to the The load deviation on the sample is almost zero, which greatly guarantees the accuracy of the experimental data and the credibility of the experimental results;

Third, the force sensor, electro-hydraulic servo fatigue testing machine is combined with the data acquisition and control system to accurately set and output various experimental parameters (normal contact load, bending fatigue load, experimental frequency, etc.), and accurately collect various experimental result data , which can realize bending fretting fatigue experiments under various complex working conditions.

In a word, by adopting the experimental device and experimental method of the present invention, it is possible to conveniently and accurately carry out bending fretting fatigue experiments of various working conditions and specifications of materials according to the set conditions, and more realistically simulate the components under alternating loads. The bending fretting fatigue damage has high control and test precision, more accurate and reliable experimental results, and good reproducibility of experimental data, which overcomes the shortcomings of existing experimental methods such as poor precision, single results, and poor data reproducibility.

Description of drawings

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

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

Fig. 2 is a schematic diagram of the front view structure of an embodiment of the present invention;

Fig. 3 is a left view structural schematic diagram of an embodiment of the present invention;

Fig. 4 is the bending fretting fatigue S-N curve of the 7075 aluminum alloy of the embodiment of the present invention, where ▲ is the bending fretting fatigue normal stress = 368.4MPa, For bending fretting fatigue fracture life more than 10 ⁶ times;

Fig. 5 is the impact diagram of the contact load on the SN curve of the embodiment of the present invention, wherein, Bending fretting fatigue normal load 250N, is the case where the corresponding bending fretting fatigue fracture life exceeds 10 ⁶ times; ▲ is the bending fretting fatigue normal load of 500N, is the case where the corresponding bending fretting fatigue fracture life exceeds 10 ⁶ times; ■ is the bending fretting fatigue normal load of 750N, It is the case where the corresponding bending fretting fatigue fracture life exceeds 10 ⁶ times;

Fig. 6 is a graph showing the influence of contact load on bending fretting fatigue life according to an embodiment of the present invention, where W=6.0kN, σ _a,max =305.6MPa.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

In this example, the extruded 7075 aluminum alloy bar was used as the test material, and its bending fretting fatigue damage behavior was systematically studied. 7075-T651 aluminum alloy is a high-strength aluminum alloy with general corrosion resistance and good mechanical properties, and can be anodized. It is widely used in key structural parts such as aerospace. Because fretting damage is common in its application fields, the research on this alloy not only has the scientific significance of deepening the basic theory of fretting fatigue, but also has practical significance in guiding the anti-fretting fatigue damage in the field of engineering applications.

As shown in Figures 1 to 3, it is an embodiment of the present invention, including a sample clamping and fixing part, a normal contact load applying part, a bending fatigue load applying part and a data acquisition control system part, wherein the sample is clamped and fixed Part of the composition is: the base 1 is installed and fixed on the base of the fatigue test bench, and the left end of the sample 2 is fixed to the base through the upper and lower clamping blocks 3 in the square hole on the left side of the base 1 and the fixing screw 4 on it. 1 above. The composition of the normal contact load application part is: the bearing platform 7 is fixed in the long groove in the middle of the base 1 through the fixing screw 2 5 and the fixing plate 6, and its position can be adjusted within a certain distance according to the experimental requirements. The lower micro-movement pad 8 is installed in the middle of the bearing platform 7, and two linear guide rails 17 are installed on both sides. The sample 2 is sandwiched between the upper fretting pad 10 and the lower fretting pad 8 on the moving pad clamping seat 11 . The loading plate 15 is fixed on the top of the linear guide rail 17, and the normal contact load is applied through the loading screw 16 and the steel ball 14. The force sensor 12 is placed in the upper hole of the upper fretting pad holder 11 to measure the normal contact load applied in real time. The composition of the bending fatigue load application part is: the bending fatigue load is applied by the Nissan Shimadzu EHF-UM100k2-040-0A electro-hydraulic servo fatigue testing machine 9 . Both the electro-hydraulic servo fatigue testing machine 9 and the force sensor 12 are connected with the data acquisition control system, which controls the experimental conditions and collects the experimental data.

The use method and working process of this device are:

Fix the base 1 at a suitable position on the fatigue test bench, and then fix the bearing platform 7 with the lower fretting pad 8 and the linear guide rail 17 in the long groove in the middle of the base 1, and its position in the long groove Determined according to the needs of the experimental conditions, then fix the left end of the sample 2 in the left square hole of the base 1, place the right end on the lower fretting pad 8, and then place the upper fretting pad 10 on the The pad clamping seat 11 slides down vertically through the linear guide rail 17, so that the upper fretting pad 10 is perpendicular to the sample 2 and achieves good point contact.

Turn the loading screw 16, the applied normal contact load will be displayed on the computer connected to the data acquisition control system through the measurement of the force sensor 12, when the normal contact load is applied to the set experimental conditions, stop the twisting and loading Screw 16, and then control the electro-hydraulic servo fatigue testing machine 9 through the data acquisition control system, so that the sample 2 can be subjected to bending fretting fatigue test according to the set parameters such as amplitude and frequency. During this process, various experimental data will be fed back to the data acquisition and control system for analysis through sensors, and the change curves of various parameters will be drawn.

Bending fretting fatigue S-N curve

Due to the local contact stress of bending fretting fatigue, the fatigue strength of the sample shows a sharp decrease trend. If no normal load is applied to the fretting pad position of the sample, the sample passes through 1.0×106 times when the bending stress is 611.21MPa None of the cycles failed, but when a normal load of 500N (contact stress of 368.4MPa) was applied at the fretting pad location, the bending fatigue strength decreased sharply to about 240MPa. It can be clearly seen from Figure 4 that the S-N curves all present the characteristics of a "C" curve. Under the action of high bending fatigue stress, as the fatigue stress decreases, the fracture life of the sample decreases significantly. Under the action of , the bending fretting fatigue life is reduced to the lowest value, which can be called the "nose" of the "C" curve. If the bending stress continues to decrease to a lower value, the bending fretting fatigue life shows a trend of rapid increase again.

In general, in the study of fretting wear, it is found that there are three different regions in the fretting operation under different test conditions, namely the partial slip region (Partialslipregime, PSR), the mixed region (Mixedfrettingregime, MFR) and the slip region ( Slipregime, SR). According to previous research work on fretting fatigue, a general change law is found, that is, with the increase of normal pressure and displacement amplitude, a concave area appears in the change curve of fretting fatigue life. In fact, the concave area is directly related to the mixed area, which is the most intense area of local contact fatigue. Based on this, it can be inferred that the bending fretting fatigue S-N curve presents a "C"-shaped curve characteristic because the fretting runs in different regions, and usually the mixed region is the most dangerous region, where microscopic cracks are most likely to initiate and Extended, therefore, the "nose" of the "C"-shaped curve can be considered the result of fretting operating in the mixed region. This consistency with the fretting wear phenomenon reflects the interaction between local wear and local fatigue, as well as local fatigue and overall fatigue from different angles. When the bending fatigue stress is higher than the "nose" of the "C" curve, it enters the slip zone due to the relatively large relative displacement of the contact area; when the bending fatigue stress is lower than the "nose", the fretting correspondingly operates in the partial sliding Move area. In the slip zone, the wear rate is higher than the crack initiation rate, resulting in cracks being eliminated due to material wear during the nucleation stage, so that the fretting fatigue life tends to be longer. In the partial slip area, the contact area usually shows slight damage, while the central adhesion area has almost no damage, and the microscopic cracks are suppressed and are not easy to initiate and expand, so that the fretting fatigue life is greatly increased.

In summary, it can be concluded that the bending fretting fatigue life is closely related to the fretting operation area of the contact zone. When the contact interface operates in the partial slip zone and the slip zone, the fretting fatigue life of the sample is relatively higher than that in the mixed zone, but above the nose region, although the fretting fatigue life increases, the overall fatigue life decreases The tendency of is also increased, in other words, when the test parameters are controlled below the "C" curve, the sample runs in a safe area, which is a range suitable for engineering applications.

Influence of Contact Load on S-N Curve

Figure 5 shows the corresponding changes in the bending fretting fatigue S-N curve of 7075 aluminum alloy when the normal load (contact stress) on the fretting pad is changed. When the normal load on the fretting pad is 250N, the bending fretting fatigue strength of 7075 aluminum alloy is about 320MPa, and its fretting fatigue life decreases firstly with the increase of fatigue stress, and then increases instead. The fatigue S-N curve presents the characteristic of "C" type curve. When the normal load increases to 500N, the fatigue strength decreases sharply to about 240MPa, and the fretting fatigue S-N curve also presents a "C"-shaped curve feature. Under the action of low bending fatigue stress, with the increase of fatigue stress, the test The fracture life of the samples decreased significantly. Under the bending stress of 331.0MPa, the fretting fatigue life decreased to the lowest value, which is the "nose" of the "C" curve. With the further increase of the fatigue stress, the fatigue life shows an increasing trend, and if the bending stress continues to increase to a higher value, the fretting fatigue life shows a decreasing trend. When the normal load is 750N, the bending fretting fatigue strength of 7075 aluminum alloy is about 280MPa, which is significantly increased compared with 500N, and the bending fretting fatigue life also decreases first and then increases with the increase of fatigue stress , and finally decreased, the fretting fatigue S-N curve also presents the characteristic of "C" type curve. Therefore, under the above three loads, there are "C" curve characteristics. As explained above, the concave area of the fretting fatigue life change curve is related to the existence of the mixed area. Under the same bending fatigue load, as the normal load increases, the relative displacement between the fretting pad and the sample shows a decreasing trend, and the fretting operation area is from the slip zone to the mixed zone and partial slip zone change of direction.

Effect of Contact Load on Bending Fretting Fatigue Life

As shown in Figure 6, when the maximum bending fatigue load is 6.0kN, as the contact load increases, the fretting fatigue life presents a trend of first decreasing and then increasing. This result further indicates the existence of the fretting mixed zone, that is, as the contact load increases, the fretting operation area shifts from the slip zone to the mixed zone and the partial slip zone, so that according to the damage characteristics of the fretting damage zone: complete slip The wear in the slip zone is relatively serious, and almost no cracks can be found; the microscopic cracks in the mixed zone are the main damage characteristics, and the wear is relatively slight; in the partial slip zone, the wear is the slightest, and generally no microscopic cracks are seen. At the same time, with the increase of the contact load of the fretting pad, the local contact damage is an increasing trend. Based on the above analysis, it can be seen that although there is wear in the complete slip area, the contact stress is small and the service life is the longest; the microscopic cracks in the mixed area lead to the shortest fretting fatigue life; although the partial slip area has small fretting displacement, the contact stress is the longest. The stress is larger so that the fretting fatigue life is relatively larger than that in the mixed region and smaller than that in the partial slip region.

The experimental device and experimental method of the present invention can conveniently and accurately carry out bending fretting fatigue experiments of various working conditions and specifications of materials according to the set conditions, and more realistically simulate the bending fretting fatigue of components under alternating loads. Dynamic fatigue damage, high control and testing precision, more accurate and reliable experimental results, and good reproducibility of experimental data.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (6)

1. A bending fretting fatigue experimental device, characterized in that: comprise a sample (2), a sample clamping and fixing part, a normal contact load applying part, a bending fatigue load applying part and a data acquisition control system, the test One end of the sample (2) is fixed on the clamping and fixing part of the sample, and the other end is provided with the bending fatigue load application part and vertically pressed up and down by the normal contact load application part, and the sample is clamped and fixed. A force sensor (12) is arranged on the part, and the force sensor (12) and the bending fatigue load applying part are both electrically connected to the data acquisition control system. 2. A bending fretting fatigue test device according to claim 1, characterized in that: the sample clamping and fixing part comprises a base (1) and a long slot arranged in the middle of the base (1) , the square hole on the base (1), the clamping block (3) and the fixing screw one (4) arranged in the square hole are arranged, and the left end of the sample (2) passes through the base ( 1) The clamping block (3) in the square hole and the fixing screw one (4) are fixed on the base (1). 3. A bending fretting fatigue test device according to claim 1, characterized in that: the normal contact load application part comprises a bearing platform (7), an upper fretting pad clamping seat (11), a loading plate (15), a linear guide rail (17), the linear guide rail (17) passes through the upper fretting pad clamping seat (11), the bottom end is fixed on the bearing platform (7), and the top end is fixed on the described On the loading plate (15), the bearing platform (7) is fixed on the base (1) through the fixing screw two (5) and the fixing plate (6), and the lower microstructure is arranged in the middle of the bearing platform (7). An upper fretting pad (10) is arranged on the upper fretting pad holder (11), and the sample (2) is arranged on the upper fretting pad (10) and the upper fretting pad (10). Between the lower fretting pads (8), the upper part of the upper fretting pad clamping seat (11) is provided with a groove, and a force sensor (12) is arranged in the groove, and a loading plate (15) is provided with a loading plate (15). screw (16), a steel ball (14) is set between the loading screw (16) and the upper fretting pad clamping seat (11), through the loading screw (16) and the steel ball (14) The fretting pad holder (11) exerts a normal contact load. 4. A bending fretting fatigue test device according to claim 3, characterized in that: the upper fretting pad clamping seat (11) is installed on the linear guide rail (17) through two linear bearings (18) ), the upper and lower sides of the force sensor (12) are respectively provided with a gasket (13) for protecting the body of the force sensor (12). 5. A bending fretting fatigue test device according to claim 1, characterized in that: the bending fatigue load applying part is an electro-hydraulic servo fatigue testing machine (9). 6. A bending fretting fatigue test method, characterized in that: comprising the steps of: a. Fix the base (1) at a suitable position on the fatigue test bench, and then fix the bearing platform (7) with the lower fretting pad (8) and the linear guide rail (17) in the middle of the base (1) Its position in the long groove is determined according to the needs of the experimental conditions, and then the left end of the sample (2) is fixed in the left square hole of the base (1), and the right end is placed on the lower fretting pad ( 8), then the upper fretting pad holder (11) with the upper fretting pad (10) is vertically slid down through the linear guide rail (17), so that the upper fretting pad (10) and the sample ( 2) Vertical and orthogonal to achieve good point contact; b. Turn the loading screw (16), the applied normal contact load will be displayed on the computer connected to the data acquisition control system through the measurement of the force sensor (12), when the normal contact load is applied to the set experimental conditions , stop screwing the loading screw (16), and then control the electro-hydraulic servo fatigue testing machine (9) through the data acquisition control system, so that the sample (2) is subjected to the bending fretting fatigue test according to the set parameters. In the process, various experimental data will be fed back to the data acquisition control system for analysis through sensors, and the change curves of various parameters will be drawn.