RU2490613C2 - Sample to test diffusion connection of sheet billets for shifting, method of manufacturing and testing - Google Patents

Abstract

FIELD: testing equipment.

SUBSTANCE: sample comprises two overlapping plates that form a diffusion connection and having pads matched with them, arranged at the sides opposite to the connection. The sum of thicknesses of the first plate and the coupled first pad is equal to the sum of thicknesses of the second plate and the coupled second pad. The length of the working part of the sample is equal to the overlapping length, making at least a quarter of the sample height. The length of the process part of the sample makes a half of the difference between the total length of the sample and the overlapping length, and the thickness of the process part of the sample does not exceed the difference between the half of the sample height and the radius of transition between the end of overlapping and adjacent surface of the appropriate process part of the sample. The sample width is equal to at least half of overlapping length. When the sample is made, two plates are laid one onto the other. Pads are installed onto plate surfaces that are opposite to the connection. The produced pack is welded by diffusion welding, applying a welding force to surfaces of pads perpendicularly to the diffusion connection. Samples are cut after welding from the pack. A block is cut from the welded pack, at least from three samples connected to each other with a link, the length of which is established as at least the width of the block, afterwards the working and process parts of samples are made, and the link is removed. In process of sample testing, loading forces are applied to ends adjacent to the tested diffusion connection.

EFFECT: increased accuracy, reduced spread of experiment results, higher validity of produced results of mechanical tests.

5 cl, 8 dwg

Description

The invention relates to testing equipment, in particular, allows you to test the strength of the shear method inseparable joints, obtained mainly by diffusion welding, when performing standard mechanical tests, and can be used in aircraft, engine and other engineering industries to monitor the modes of operation of diffusion welding in the process manufacturing of aircraft parts, as well as units and assemblies of modern aircraft engines.

A known model for performing mechanical tests (in accordance with RD26-11-08-86 "Guiding document. Welded joints, mechanical tests"), designed to assess the strength of a welded joint, as well as a method for testing samples (GOST 6996-66 "Welded joints. Methods for determination of mechanical properties ”, approved by the USSR State Standard 03.03.1966). Currently, it is the main governing document governing the implementation of destructive testing of permanent joints obtained by welding in the liquid as well as in the solid phase.

The disadvantages of the known sample and method of testing are as follows. Upon receipt of a solid-phase joint, for example, by diffusion welding, with a joint strength close to the strength of the base material, a certain number of welded joint defects remain in the joint zone, the shape of which is close to spherical or equilibrium. The size of defects in this case usually does not exceed the value of 0.1 ... 1.0 microns.

When performing mechanical tests of such a welded joint for peeling under conditions of deformation of samples by uniaxial tension, the strength of the joint is higher than the strength of the base material. In this case, the results of mechanical tests of the welded joint do not reflect the real situation from the point of view of the defectiveness of the welded joint, and they cannot be considered reliable.

A known model for testing a welded joint in shear (USSR author's certificate No. 1188574, IPC G01N 3/24, publ. 30.10.85).

In accordance with this technical solution, the shear joint test specimen consists of overlapping two plates and four reinforcing plates. The plates are made of one material, and the lining of another. The pads are placed on both sides of the plates in such a way that there is a gap between the common end of each plate and the plate adjacent to its surface and the end of the plate adjacent to the surface of the other plate facing the same side.

According to the method of manufacturing this test specimen for shear joint testing, two plates are initially placed so that an overlap is formed, then two plates are welded, and the overlays are connected to the plates by the diffusion method at a temperature of at least 50 ° C below the temperature of the plate joints.

The known design of the samples, consisting of 2 main plates made of one material and 4 technological overlays made of another material, does not provide the ability to obtain an accurate test result of the strength of the diffusion connection, since the test result with this design of the sample depends on the number plates and linings. In this case, it is difficult to take into account the deviations in the sizes of the plates, the necessary accuracy of their mutual positioning, as well as the mechanical characteristics of the material of the plates and technological overlays when assembling the plates and pads into a package.

The disadvantage of this technical solution is the fact that the diffusion joint under study is formed during welding of overlapped plates. Experiments show that during the formation of an lap joint during welding from the edges of the diffusion joint adjacent to the ends of the plates, stress concentrators are formed in the form of undercuts. The angle at the top of the cuts will depend on many factors:

- from the accuracy of the positioning of the plates forming the overlap, and from the accuracy of the positioning of the reinforcing pads;

- from the size of the chamfer when deburring from the edge adjacent to the edge of the connection;

- on the thickness of the welded plates;

- on the magnitude of the applied welding pressure.

Obviously, these undercuts will influence the test result, which is also difficult to take into account.

Another disadvantage of the considered technical solution is the fact that the process of obtaining samples is divided into 2 stages. At the first stage, the test compound is formed by making an overlap, and then reinforcement plates are welded. Such a 2-stage sample fabrication scheme will inevitably affect the properties of the reheat diffusion compound under study. This effect is especially noticeable in the case of welding materials that undergo phase transformations during heating, for example, when welding titanium alloys, which will lead to an ambiguous interpretation of the welding conditions on the experimental results.

In accordance with the known technical solution, a sample having an overlap joint obtained by diffusion welding and manufactured in accordance with a 2-stage welding scheme is then subjected to mechanical tests by deformation by uniaxial tension. The claimed design of the sample allows you to perform mechanical tests of the joint in shear by installing them in the wedge grips of the machine due to the application of tensile forces to their surfaces located behind the overlap, forming the investigated diffusion joint, either perpendicularly or parallel to it.

Such a loading scheme leads to the formation in the connection zone of a complex stress state scheme with a prevailing tensile component, which makes it impossible to carry out a comparative analysis of the shear test results with the results of tests of the base material or weld joint according to the relevant GOST.

In addition, the performance of tests using wedge grippers is associated with a risk of sample skew when installed in grips and the plane of the test compound does not coincide with the axis of application of force (axis of the testing machine), which will also affect the form of the stress state formed in the joint zone and, as a result, - the reliability of the test results. The effect of misalignment on the reliability of the test result is enhanced with a decrease in the length of the sample, which usually has a limited size when forming a diffusion compound.

Closest to the proposed technical solution is a sample for testing a metal compound in shear and a method for its manufacture and testing (USSR author's certificate No. 1619112, IPC ⁵ G01N 3/24, publ. 07.01.91).

In this technical solution, a sample for testing a metal joint in shear comprises two identical plates overlapping and two pairs of identical overlays connected to their opposite surfaces, installed so that the overlays of each pair are separated by a gap located at the end of the corresponding plate, and the overlap length is set from ratios: C = bσ / 4τ, where b is the sum of the plate and plate thicknesses of the sample, σ and τ are the tensile yield strength and the shear strength of the main material, respectively Ala welded plates.

The design of the sample in accordance with the considered technical solution allows to increase the accuracy of the test results by taking into account plastic deformation at the beginning of the fracture of the connection. However, it does not exclude the appearance of a scatter in the test results due to the lack of a regulation on the length of the gap and the difficulty in ensuring the necessary accuracy of manufacturing its length in the samples, which is also responsible for the formation of an equally reproducible deformed state in the joint zone. In addition, the claimed design does not take into account the thickness of the plates forming the investigated diffusion compound, the thickness of the pads and the width of the samples, which also affects the formation of a particular type of stress state in the joint zone. The design of the sample makes it possible to test samples only by uniaxial tension, which complicates the assessment of the resistance of the welded joint of sheet materials to dynamic stresses.

In addition, the claimed design of the sample does not take into account the relationship between the type of loading and the type of stress state formed in the zone of the diffusion joint, which makes it difficult to carry out a comparative analysis of the results of tests of diffusion joints for shear with the results of tests of the base material and welded joints for peeling made by uniaxial tension of the samples in accordance with GOST. This information is extremely important in connection with the development of work on the creation of a hollow broad-chordal working blade of the first stage of a fifth-generation engine compressor.

The objective of the invention is to increase the accuracy, reliability of the test results of the diffusion connection of sheet blanks and the possibility of an unambiguous comparison of the test results with the results of mechanical tensile testing of the base material, as well as providing the ability to conduct tests under dynamic loading.

The problem is solved by a sample for testing the diffusion connection of sheet blanks in shear, consisting of working and technological parts, containing two overlapped plates forming a diffusion connection and having overlays aligned with them located on the sides opposite from the connection. Unlike the prototype, the sum of the thicknesses of the first plate and the first lining combined with it is equal to the sum of the thicknesses of the second plate and the second lining combined with it, and the length of the working part of the sample is equal to the overlap length of at least a quarter of the height of the sample, the length of the technological part of the sample is half the difference between the total length of the sample and the length of the overlap, and the thickness of the technological part of the sample does not exceed the difference between half the height of the sample and the radius of the transition between the end face of the overlap and the adjacent surface sponds to the technological part of the sample, the sample width is equal to at least half the length of the overlap.

The problem is also solved by the method of manufacturing a sample for testing the diffusion connection of sheet blanks in shear, namely, that two plates are superimposed on one another with the formation of a diffusion connection, overlays are installed on the surfaces opposite to the connection of the plates, the formed package is welded by diffusion welding, applying a welding force to the surfaces lining perpendicular to the diffusion connection, after welding, samples are cut from the bag. Unlike the prototype, a block is cut out of the welded bag from at least three samples connected by a jumper, the length of which is set at least the width of the block, after which the working and technological parts of the samples are made, and the jumper is removed.

According to the invention, the bag is welded by applying a welding force to all free surfaces.

The problem is also solved by the method of testing a diffusion compound by deformation by a uniaxial loaded specimen described above. Unlike the prototype, loading forces are applied to the ends of the sample adjacent to the test diffusion compound. According to the invention, the samples are deformed by uniaxial tension or compression.

The technical result of the invention is achieved due to the following.

The proposed design of the sample ensures the alignment of the axis of the sample, which lies in the plane of the test diffusion connection, with the axis of the applied load, taking into account the dimensions of the plates and overlays. When this condition is met, the accuracy of the test results is improved by eliminating the bending of the sample during the test.

The length of the working part of the sample, equal to the overlap length, which is at least a quarter of the height of the sample, eliminates the influence of the plastic component when a load is applied to the corresponding ends of the sample on the initial diagram of mechanical tests. Those. This condition makes it possible to eliminate the appearance of plastic deformation of the ends when the specimen is destroyed by a diffusion joint when exposed to a force from a deforming tool.

The length of the technological part of the sample, which is half the difference between the total length of the sample and the overlap length, provides symmetry of the sample relative to the middle of the working part of the sample and also helps to reduce the occurrence of bending deformation during deformation of the sample.

The choice of the thickness of the technological part of the sample, not exceeding the difference between half the height of the sample and the radius of the transition between the end face of the overlap formed and the adjacent surface of the corresponding technological part of the sample, is aimed at improving the accuracy and reliability of the experimental results due to the fact that in this design the diffusion line and the end surface perpendicular.

The condition that the width of the specimen exceeds the overlap length allows conditions to be formed in the diffusion joint zone during testing that are close to the conditions of a plane-deformed state, which allows more accurate comparison of the results of the diffusion joint shear test with the properties of the base material obtained in testing cylindrical specimens in accordance with GOST.

The proposed method for manufacturing a sample for testing the diffusion connection of sheet blanks in shear, when a block consisting of three or more samples connected by a jumper is cut from a welded bag, after which the working and technological parts of the samples are made, and the jumper is removed, it allows to produce samples in one installation, providing high precision manufacturing of the working area (overlap), which allows to reduce the spread in the test results caused by manufacturing inaccuracies.

Performing diffusion welding of the bag, applying welding forces to all free surfaces of the bag, the conditions for obtaining a diffusion joint in the manufacture of multilayer cellular structures, for example, hollow wide-chord fan blades of a fifth-generation gas turbine engine, are modeled. In this case, when during diffusion welding of the package, the stress state coincides with the stress state in the manufacture of the hollow blade preform, the reliability of assessing the quality of the diffusion connection of the package increases.

When performing uniaxial loaded mechanical tests in which the test diffusion joint is present, by applying a loading force to the ends of the specimen of the claimed design adjacent to the test diffusion joint, conditions are created for the formation of a stress state in the joint zone close to a simple shear. This circumstance makes it possible to bring the results to the test results of the base material using standard cylindrical samples and testing them in accordance with GOST.

In addition, an increase in the reliability of the test results is ensured by the creation, when performing tests in the working zone of the sample, of a stress state close to a simple shear. This gives the basis with a sufficient degree of reliability to accept shear stresses equal to shear stresses, i.e.

$${\tau }_{\mathrm{from}R}=P/S\sim .\tau =\widetilde{\mathrm{one}}/\surd 3({\tilde{\sigma }}_{\mathrm{one}}).$$

In the presented formula, P is the loading force, S is the overlap or diffusion joint area, equal to the product of the overlap length 1 by the sample width h, S = 1 × h, σ ₁ are the main stresses arising in the working part of the cylindrical sample under uniaxial tension .

Obviously, the possibility of creating a stress state close to a simple shear during testing in the sample working zone appears when the load is applied to a pair of sample ends adjacent to the input and output edges of the overlap, which forms the diffusion joint under study.

When loading samples by uniaxial compression, the possibility of dynamic loading appears (testing samples for impact on the pile drivers with a vertically falling load), which expands the range of test methods for the diffusion connection of sheet materials, adding to them a dynamic loading method. It is known that dynamic tests are more objective methods for assessing the bearing capacity of a diffusion compound and give more reliable test results.

The claimed technical solution is illustrated by the following drawings.

Figure 1. Sample for testing a diffusion compound in shear.

Figure 2. The scheme of combining plates and pads forming a package.

Figure 3. Scheme for cutting out a block of samples for testing diffusion compounds from a package of plates and overlays.

Figure 4. A block of samples for testing diffusion compounds after removal of the technological part.

Figure 5. A specimen mounted in grips for performing uniaxial tensile mechanical tests.

6. A specimen mounted in grippers to perform mechanical tests with uniaxial compression.

7. The diffusion zone of the sheet blanks of VT6S titanium alloy. a - magnification × 2000. b - magnification × 3000.

Fig. 8. Diffusion surface of sheet blanks of VT6S titanium alloy after shear tests. and - magnification × 33. b - magnification × 1000.

The sample (Fig. 1) consists of two lap welded plates 1, 2 and reinforcing plates 3, 4. The letter A indicates the total length of the sample, B is the height of the sample, C is the width of the sample, D is the length of the technological part, F is the working part of the sample or overlap, E is the height of the technological part, r is the radius of the transition between the end face of the overlap and the adjacent surface of the technological part of the sample. Plates 1 and 2 form the test diffusion compound. The plates may have different thicknesses, in which case the thickness of the reinforcing pads will also be different. The ratio of the thicknesses of the plates and overlays is aimed at ensuring the location of the welded joint in the middle of the height of the sample B. The choice of the overlap F equal to 1/4 of the height of the specimen B in combination with the regulated width of the specimen C equal to at least half the length of the overlap F determines the formation during testing in the zone welded joint stress state, close to a simple shear.

The height of the technological part E is chosen in such a way as to ensure the formation of a predetermined shear strain in the joint zone.

The sample is made from a package of sheet blanks, overlapped and welded by diffusion welding, the length or width of the plates to be welded 1, 2 and the plates 3, 4 assembled into a bag (Figure 2), chosen from the condition of equality to the sum of the length of the sample A and technological allowance Δ ( Figure 3). The length of the allowance Δ is set equal to at least the width of the sample C (Figure 1).

From the package welded by diffusion welding, a block assembly is cut out (Figure 3), consisting of at least three plates of width C (Figure 1), connected to each other by technological allowance Δ. In this case, the cut planes are perpendicular to the plane of the diffusion connection, the cut length is set equal to the length of sample A. Production of the working (overlap) and technological parts is performed simultaneously in the entire assembly of samples (Figure 4), by partially removing the technological part of the sample with a thickness of G = B / 2 + r and length D and D + Δ. respectively. Jumper Δ. cut off after manufacturing the working and technological parts.

The obtained samples are tested by deformation, applying forces to the ends of the welded plates adjacent to the overlap forming the test compound, as shown in Fig. 5, which shows a sample 5 mounted in grips 6 and 7, which are connected through holes to the rods of the testing machine to prevent occurrence distortions under tension.

The specimens installed in the grips are deformed by uniaxial tension, which initiates shear deformation in the diffusion joint zone.

Having installed the samples in the grips of a different shape (Fig.6), it is possible to carry out tests with uniaxial compression. It is more rational to carry out mechanical tests of samples by uniaxial compression during dynamic shear tests of diffusion joints on instrumented rams with a vertically falling load.

When testing samples of this design in the connection zone, a stress state is formed, which is close to a simple shear.

To confirm this statement, the claimed technical solution was tested. For these purposes, we used modern methods of mathematical analysis, which fully confirmed this statement.

The claimed technical solution was tested on the example of testing the diffusion connection of sheet blanks from 2-phase (α + β) VT6 titanium alloy.

An example illustrates a sample, a manufacturing method and a test method for a diffusion joint of two plates of the same thickness.

Two plates of 100.0 mm × 50.0 mm × 1.0 mm were cut from the sheet. The plates were degreased by rubbing with calico soaked in technically pure acetone. Then, the oxide film was removed from the surfaces of the plates to be welded, scraping them with a metal brush. After removal of the oxide film from the surface of the plate, the plates were degreased by ultrasonic treatment successively in technical acetone and alcohol.

At the end of the degreasing operation, the plates 1 and 2 were superimposed on top of one another so that the edges of the plates coincided (Figure 2). In this position, the plates were fixed, grabbing them with argon-arc welding along the edges.

On the free surfaces of the plates (oppositely aligned for diffusion welding) two overlays 3 and 4 were applied (FIG. 2), 100.0 mm × 50.0 mm × 5.0 mm in size. Pre-workpieces were also subjected to stripping and degreasing operations.

The pads were fixed relative to two plates by tapping with argon-arc welding.

After that, the resulting package, consisting of 2 plates and 2 overlays, was installed in a special tool, which ensured that a uniform compression force was applied to the package of plates and overlays, and diffusion welding was performed. The diffusion welding mode was chosen as follows: the environment is vacuum, a depth of 10 ^-3 Pa; welding temperature - 925 × 1.0 ° C; welding working pressure - 3.0 MPa; welding time - 3.0 hours.

At the end of the diffusion welding process, a block consisting of 3 pieces fastened together by a jumper of samples 3.0 mm thick each (Figure 3) was cut out of the bag. Cutting the bag into samples was performed by EDM cutting with a wire with a diameter of 0.3 mm. The cut length was chosen equal to 40.0 mm, and the length of the jumper was 10.0 mm, respectively. Then made the technological part (Figure 4) with a length of 19.0 mm and a height of 5.85 ± 0.01 mm In the manufacture of the technological part, the working part was formed - an overlap of 2.0 mm in length. After the operation of manufacturing the technological and working parts, the jumper was cut off, thus obtaining 3 samples for mechanical testing in one of the welding modes.

Samples were tested on an Instron universal dynamometer (model 5095). Samples were installed in the grips, a diagram of which is shown in Fig.5. The grips were fixed with pins on the rods of the testing machine. Further, mechanical tests of the samples were carried out, deforming them with uniaxial tension with a moving beam moving speed of 1.0 mm / min.

The table summarizes the experimental values of the mechanical tests of three samples. From the test results it follows that the strength of the diffusion compound is approximately equal to 91% of the strength of the base material.

The destroyed samples were subjected to metallographic and fractographic studies. To carry out the studies, a JSM 840 scanning electron microscope was used.

On figa, b and figa, b shows photographs of the zone of the diffusion connection, as well as the fracture surface at various magnifications.

The results of metallographic and fractographic studies have confirmed that the strength of the diffusion joint, equal to ~ 91% of the strength of the base material, is due to the presence of defects in the diffusion joint zone in the form of pores 1 ... 2 μm in size.

Table. Values of maximum force and shear stresses. Sample No. Maximum force P, H Maximum shear stress τ, MPa The value of the reduced force, √3τ, MPa Stress σ _in , MPa one 3462.34 461.77 798.48 890.5 2 3538.97 472.27 817.53 892.1 3 3532.21 475.46 822.72 889.3 Average 3511.18 469.83 812.33 890.6

The obtained experimental results showed that the proposed technical solution improves accuracy, reduces the spread of experimental results, and also increases the reliability of the obtained results of mechanical tests.

Claims (5)

1. A test sample for the diffusion connection of sheet blanks in shear, consisting of working and technological parts, containing two lapped plates forming a diffusion joint and having overlays aligned with them located on the sides opposite from the joint, characterized in that the sum of the thicknesses of the first plate and the first lining combined with it is equal to the sum of the thicknesses of the second plate and the second lining combined with it, and the length of the working part of the sample is equal to the overlap length of at least four vertically, the length of the technological part of the sample is half the difference between the total length of the sample and the length of the overlap, and the thickness of the technological part of the sample does not exceed the difference between half the height of the sample and the radius of the transition between the end face of the overlap and the adjacent surface of the corresponding technological part of the sample, and the width of the sample is not less than half the length of the overlap. 2. A method of manufacturing a sample for testing the diffusion connection of sheet blanks in shear, namely, that two plates are superimposed on one another with the formation of a diffusion connection, overlays are installed on the surfaces opposite to the connection of the plates, the formed packet is welded by diffusion welding, applying a welding force to the surfaces of the overlays perpendicular to the diffusion joint, after welding, samples are cut from the bag, characterized in that at least the block is cut from the welded bag of the three samples connected by a jumper, the length of which is set at least the width of the block, after which the working and technological parts of the samples are made, and the jumper is removed. 3. The method according to claim 2, characterized in that the package is welded by applying a welding force to all free surfaces. 4. A method for testing a diffusion compound by deforming the sample by uniaxial loading according to claim 1, characterized in that the loading forces are applied to the ends of the sample adjacent to the test diffusion compound. 5. The test method according to claim 4, characterized in that the samples are deformed by uniaxial tension or compression.

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