A test specimen for compressive-shear fracture of metallic materials under high temperature and high strain and its test method

Abstract

This invention discloses a test specimen and method for testing the compressive-shear fracture of metallic materials under high temperature and high strain conditions. The specimen is a one-piece molded structure. The specimen substrate is a cylinder with symmetrically arranged inclined grooves on its circumferential surface, each with a cylindrical bottom, and a predetermined thickness is maintained between the two inclined grooves. At both ends of the inclined grooves are excised regions that penetrate the substrate and are centrally symmetrically distributed about the center point of the substrate. Each excised region consists of a main arc segment, lateral arc segments, and transition fillets. The center of the main arc segment is offset by a predetermined amount both parallel and perpendicular to the centerline of the inclined groove. This invention utilizes the cooperation between the inclined grooves and the end excised regions to form an interlaced central deformation zone in the middle of the substrate. Under axial compressive load, the induced central deformation zone is in a stable compressive-shear combined stress state. The stress state can be effectively controlled by adjusting structural parameters such as the inclined groove angle and the thickness of the deformation zone, thus providing a reliable basis for the study of the compressive-shear fracture behavior of metallic materials under high temperature and high strain conditions.

Description

Technical Field

[0001] This invention relates to the field of mechanical property testing and plastic forming technology for metallic materials. Specifically, it relates to a test specimen for compressive-shear fracture of metallic materials under high temperature and high strain conditions, and its testing method. Background Technology

[0002] In high-end equipment manufacturing fields such as aerospace, nuclear power, and petrochemicals, key components such as aero-engine casings, nuclear reactor shells, and high-neck flanges are typically formed using high-temperature volume forming processes such as hot forging and hot rolling. During the forming process, the metallic material often experiences large strains, and the deformation zone is subjected to extremely strong compressive stress. Under this state of large strain and strong compressive stress, the material is highly susceptible to ductile fracture, leading to component failure. Therefore, it is essential to construct high-precision ductile fracture criteria and accurately predict fracture tendency using finite element numerical simulation, thereby avoiding defects in the process design stage and providing reliable guidance for parameter optimization.

[0003] Constructing a high-precision ductile fracture criterion relies on obtaining fracture test data of materials under different stress states. However, current high-temperature fracture studies are mostly based on tensile-dominated stress states, which cannot truly characterize the compressive stress-dominated forming process. If conventional uniaxial compression tests are used, due to the increased plasticity of materials at high temperatures, the specimens only undergo upsetting deformation and are difficult to fracture, thus failing to obtain effective data. Therefore, shear stress must be introduced into the specimen to induce compressive-shear fracture. Existing compressive-shear fracture specimens are mostly designed for low-strain conditions at room temperature, which has fatal flaws when testing high-temperature, high-plasticity materials: on the one hand, because fracture requires a large reduction, the notches of existing specimens are prone to premature contact and closure before fracture, leading to direct test failure; on the other hand, during high-temperature, high-strain compression, the stress state of existing specimens changes drastically with strain, making it impossible to maintain a stable stress state.

[0004] Therefore, there is an urgent need for a test method for compressive-shear fracture specimens of metallic materials that can effectively prevent premature closure of the groove and maintain compressive stress dominance and a stable stress state under high temperature and high strain conditions. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the purpose of this invention is to provide a metal material compression-shear fracture specimen and its test method under high temperature and high strain conditions; the specimen of this invention can effectively avoid premature closure of the groove under high temperature and high strain conditions, and can maintain the dominance of compressive stress and the stability of the stress state.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A metal material compression-shear fracture specimen for high temperature and large strain includes a cylindrical matrix 1;

[0008] The circumferential surface of the substrate 1 is symmetrically provided with radially inward extending but not penetrating inclined grooves 2, the bottom of the inclined grooves 2 is cylindrical, and a metal layer of predetermined thickness is retained between the two inclined grooves 2.

[0009] End cut-off areas 3 penetrating the substrate 1 are provided at both ends of the inclined groove 2;

[0010] The outline of the end cut-off area 3 is composed of a main arc segment 31, an upper lateral arc segment 32, a lower lateral arc segment 33, and an upper transition fillet 34 and a lower transition fillet 35 located at their connection points, respectively.

[0011] The center of the main circular arc segment 31 is offset relative to the center of the base 1 in both directions parallel to and perpendicular to the center line of the inclined groove 2.

[0012] The two end excision areas 3 are centrally symmetrically distributed with the center point of the substrate 1.

[0013] Through the cooperation of the inclined groove 2 and the end cut-off area 3, an interlaced central deformation area 4 is formed in the middle of the substrate 1.

[0014] The shape and geometric parameters of the upper lateral arc segment 32 and the lower lateral arc segment 33 are determined by the starting point on the side of the base 1, the ending point on the main arc segment 31, and the preset radius.

[0015] The centerline of the inclined groove 2 forms a preset angle with the horizontal end face of the base 1; the preset offset of the center of the main arc segment 31 in the direction parallel and perpendicular to the centerline of the inclined groove 2 constitutes a reverse eccentric setting.

[0016] The geometric parameters of the substrate 1 are: height 4mm-150mm; diameter 4mm-50mm;

[0017] The height-to-diameter ratio is 1.0-3.0.

[0018] The geometric parameters of the inclined groove 2 are as follows: the angle between the center line of the inclined groove 2 and the horizontal end face of the base 1 is 15°-75°; the bottom radius of the inclined groove 2 is 0.5mm-50mm; and the width of the inclined groove 2 is 1mm-100mm.

[0019] The geometric parameters of the end cut-off area 3 are: the radius of the main circular arc segment 31 is 0.1mm-50mm;

[0020] The radii of the upper lateral arc segment 32 and the lower lateral arc segment 33 are both 1mm-80mm; the radii of the upper transition fillet 34 and the lower transition fillet 35 are both 0.1mm-50mm.

[0021] The preset distance between the centers of the two main circular arc segments 31 in the direction parallel to the center line of the inclined groove 2 is 0.5mm-50mm;

[0022] The preset distance between the centers of the two main circular arc segments 31 in the direction perpendicular to the center line of the inclined groove 2 is 0.1mm-100mm.

[0023] The geometric parameters of the central deformation zone 4 are as follows: the thickness of the central deformation zone 4 is 0.5mm-48mm, and the thickness is the minimum distance between the bottoms of the two inclined grooves 2.

[0024] The material of the sample is any one of cast iron, steel, titanium, titanium alloy, aluminum, aluminum alloy, copper, copper alloy, magnesium, or magnesium alloy.

[0025] The sample is a one-piece molded structure.

[0026] A method for conducting a hot compression fracture test on the above-mentioned metallic material compression-shear fracture specimen, the specific test steps of which are as follows:

[0027] S1. Place the sample between the two indenters in the vacuum or protective atmosphere chamber of the testing machine;

[0028] First, the sample is heated to 1250℃ at a heating rate of 5℃ / s and held for 5 minutes to allow the precipitated phase inside the material to fully dissolve, eliminate the initial microstructure segregation, and achieve microstructure homogenization. Then, the sample is cooled to the target deformation temperature of 1050℃~1200℃ set in Table 1 at a cooling rate of 10℃ / s and held at this temperature for 10 seconds to eliminate the temperature gradient in the central deformation zone 4.

[0029] S2. Under the condition of maintaining a constant test temperature, the indenter of the testing machine is controlled to apply an axial compressive load to the specimen, and the loading is strictly carried out at the loading speed of 6mm / s to 30mm / s as shown in Table 1; during the compression process with a large axial compression, the material in the central deformation zone 4 undergoes plastic deformation, and the groove wall does not contact and close in advance; the testing machine synchronously records the load-displacement data at high frequency; when the axial displacement of the indenter reaches the preset maximum compression, the system automatically stops loading immediately;

[0030] S3. After the testing machine stops loading, start the water spray quenching system to rapidly cool the fractured specimen to room temperature; this step preserves the macroscopic morphology and microstructure characteristics of the material at the moment of high-temperature high-strain fracture, so as to facilitate subsequent observation and research.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] 1. Preventing premature closure of the groove under large strain. To address the large compression required for high-temperature fracture testing, this invention increases the displacement margin of the specimen in the axial compression direction by coordinating the design of the groove inclination angle, groove width, and the height and diameter of the substrate. This prevents test failure caused by premature closure of the groove wall when the specimen experiences large strain, ensuring that the specimen can be compressed to fracture.

[0033] 2. Improved asymmetric flow and stable stress state. During the compression-shear process, to address the asymmetric flow and localized accumulation phenomena that easily occur in the upper and lower parts of the material, this invention employs a reverse eccentric setting of the main arc segment in the end-cutting area. This eccentric structure can geometrically compensate for the asymmetry of material flow on one side, ensuring that the concentrated area of ​​plastic deformation remains near the centerline of the inclined groove, preventing excessive concentration of compressive stress in localized areas due to material accumulation, thereby maintaining the stability of the stress state during sample deformation.

[0034] 3. Effective control of compressive and shear stress states. This invention can effectively adjust the distribution ratio of compressive and shear stresses within the central deformation zone by changing two structural parameters: the inclination angle of the inclined groove and the thickness of the staggered central deformation zone, thereby obtaining fracture data under different stress states. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the metallic material compression-shear fracture specimen of the present invention. Figure 1 ;

[0036] Figure 2 This is a schematic diagram of the structure of the metallic material compression-shear fracture specimen of the present invention. Figure 2 ;

[0037] Figure 3 This is a schematic diagram of the structure of the metallic material compression-shear fracture specimen of the present invention. Figure 3 ;

[0038] Figure 4 This is a load-displacement curve diagram during the test process of Embodiment 1 of the present invention;

[0039] Figure 5 The image shows the processed object of Embodiment 1 of the present invention and its macroscopic morphology after high-temperature compression shear fracture;

[0040] Figure 6 This is the equivalent plastic strain simulation cloud diagram of Embodiment 1 of the present invention;

[0041] Figure 7 This is a curve showing the evolution of stress state parameters in the central deformation zone of Embodiment 1 of the present invention;

[0042] Figure 8 This is the equivalent plastic strain simulation cloud diagram of Embodiment 2 of the present invention;

[0043] Figure 9 This is a graph showing the evolution of stress state parameters in the central deformation zone of Embodiment 2 of the present invention. Detailed Implementation

[0044] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0045] like Figure 1-3 As shown, this invention discloses a test specimen for compressive-shear fracture of metallic materials under high temperature and high strain, and its testing method. The specimen is a one-piece molded structure, including a cylindrical substrate 1. Symmetrical radially extending but not penetrating grooves 2 are provided on the circumferential surface of the substrate 1, with a predetermined thickness of metal layer remaining between the two grooves 2. End-cut regions 3 penetrating the substrate 1 are respectively provided at both ends of the grooves 2. The contour of the end-cut region 3 is composed of a main arc segment 31, an upper lateral arc segment 32, a lower lateral arc segment 33, an upper transition fillet 34, and a lower transition fillet 35. Through the cooperation of the grooves 2 and the end-cut regions 3, an interlaced central deformation zone 4 is formed in the middle of the substrate 1.

[0046] To ensure that reliable compressive-shear fracture data can be successfully obtained from the specimens under high temperature and high strain conditions, the key geometric parameters of this invention have been specifically set as follows:

[0047] 1. Geometric parameters of the substrate: The height H1+H2+H3+H4+H5 of substrate 1 is set to 4mm-150mm, the diameter D is set to 4mm-50mm, and the height-to-diameter ratio is set to 1.0-3.0. The appropriate matching of height and diameter aims to improve the specimen's resistance to instability during axial compression, preventing macroscopic bending instability under pressure. Simultaneously, this height range meets the processing requirements of large-angle inclined grooves and ensures sufficient axial deformation margin for the specimen before fracture, preventing premature interference at the groove wall.

[0048] 2. Geometric Parameter Limitations of the Inclined Groove: The angle α between the centerline of the inclined groove 2 and the horizontal end face of the substrate 1 is set to 15°-75°. This angle range is the core for controlling the distribution of compressive and shear stress weights. By changing the angle, the central deformation zone 4 can obtain different proportions of compressive and shear combined stress states. If the angle is less than 15°, the stress will tend to be close to a uniaxial compression state, and the material is prone to upsetting at high temperatures and is difficult to crack. If the angle is greater than 75°, the height dimension requirement of the substrate 1 is too large, and bending instability is easily caused by the imbalance of the height-to-diameter ratio during loading. The bottom surface of the inclined groove 2 is cylindrical, and its radius r is set to 0.5mm-50mm. Using a larger groove bottom radius can effectively avoid the initial stress concentration at the root of the groove bottom, delay the premature initiation of cracks, and ensure that the specimen can fully enter the large strain stage. Meanwhile, the groove width W of the inclined groove 2 is set to 1mm-100mm. The reasonable groove width, combined with the base size, increases the displacement margin of the sample in the axial compression direction, thereby avoiding premature closure of the groove wall under large deformation.

[0049] 3. Geometric parameter limitations for the end-cut region 3: The radius R2 of the upper lateral arc segment 32 is set to 1mm-80mm, the radius R3 of the lower lateral arc segment 33 is set to 1mm-80mm, the radius R4 of the upper transition fillet 34 is set to 0.1mm-50mm, and the radius R5 of the lower transition fillet 35 is set to 0.1mm-50mm. This combined design smooths the geometric contour of the end-cut region 3, eliminates stress concentration at the sharp angle of the cut, and prevents premature failure of the specimen outside the central deformation region 4. The radius R1 of the main arc segment 31 is set to 0.1mm-50mm, and the distance L between the centers of the two main arc segments 31 in the direction parallel to the center line of the inclined groove 2 is 0.5mm-50mm, and the distance e in the direction perpendicular to the center line of the inclined groove 2 is 0.1mm-100mm. The setting of the parallel spacing, together with the overall contour, determines the effective deformation range of the staggered central deformation zone 4, in order to adapt to the plastic rheological requirements of different materials; while the offset of the vertical spacing constitutes the reverse eccentric setting. This structure introduces a geometric pre-compensation amount to coordinate the asymmetrical flow and local accumulation of materials in the upper and lower parts during plastic deformation, so that the concentrated area of ​​plastic deformation is always kept on the center line of the inclined groove, preventing local areas from falling into an extreme strong compressive stress state due to excessive material accumulation, and maintaining the stability of the stress state.

[0050] 4. Geometric parameter limitations of the central deformation zone 4: The thickness t of the central deformation zone 4 is set to 0.5mm-48mm. This dimension directly determines the stress state and thermo-mechanical coupling response within the deformation zone: If the thickness is set too small, during high-temperature, high-strain compression, the extremely intense local plastic deformation work will be converted into a large amount of plastic deformation heat. The heat is difficult to conduct and dissipate rapidly to the matrix on both sides, which will lead to a significant local temperature rise and temperature gradient within the deformation zone. In severe cases, it will directly cause local melting of the material, resulting in data distortion. If the thickness is set too large, the shear-induced effect of the groove 2 on the material flow will be greatly weakened, and the compressive stress within the central deformation zone 4 will dominate, causing the sample to tend towards conventional upsetting and making it difficult to fracture.

[0051] The sample material of this invention can be any one of cast iron, steel, titanium or titanium alloy, aluminum or aluminum alloy, copper or copper alloy, or magnesium or magnesium alloy.

[0052] To further verify the reliability of the specimens under different high-temperature and high-strain conditions, two specific embodiments are provided. Both Embodiment 1 and Embodiment 2 use F44 super austenitic stainless steel as the specimen material, and their specific geometric parameters and corresponding hot compression test process parameters are shown in Table 1.

[0053]

[0054] The testing machine used in this invention is a thermal simulation testing machine, such as the Gleeble 3800, to conduct hot compression fracture tests on the samples from Examples 1 and 2 above. The specific test steps are as follows:

[0055] S1: Place the sample between the two indenters within the vacuum or protective atmosphere chamber of the testing machine. First, heat the sample to 1250℃ at a heating rate of 5℃ / s and hold for 5 minutes to allow the precipitated phases inside the material to fully dissolve, eliminate initial microstructure segregation, and achieve microstructure homogenization. Subsequently, cool the sample to the target deformation temperature set in Table 1 at a cooling rate of 10℃ / s and hold at this temperature for 10 seconds to eliminate the temperature gradient within the central deformation zone 4.

[0056] S3: Under the condition of maintaining a constant test temperature, the indenter of the testing machine is controlled to apply an axial compressive load to the specimen, and the loading is carried out strictly according to the loading speed shown in Table 1. During the compression process with a large axial downward pressure, thanks to the synergistic pre-compensation design of the inclined groove 2 and the end cut-off area 3, the material in the central deformation zone 4 can stably undergo plastic deformation, and the groove wall does not prematurely contact and close. The testing machine synchronously records the load-displacement data at high frequency. The load-displacement curve obtained in Example 1 is shown below. Figure 4 As shown, when the axial displacement of the pressure head reaches the preset maximum pressure, the system automatically stops loading immediately.

[0057] S3: After the testing machine stops loading, the water spray quenching system is activated to rapidly cool the fractured specimen to room temperature at an extremely high cooling rate. This step preserves the macroscopic morphology and microstructure characteristics of the material at the moment of high-temperature, high-strain fracture, allowing for subsequent observation and research on fracture morphology, precipitate distribution, etc. The actual specimen processed in Example 1 and its macroscopic morphology after fracture are shown below. Figure 5 As shown.

[0058] The present invention also verified the stress state stability of the above embodiments through finite element numerical simulation:

[0059] For Example 1, its equivalent plastic strain simulation contour plot is as follows: Figure 6 As shown, the stress state parameter evolution curve of the central deformation zone is as follows: Figure 7 As shown, the plastic strain of the specimen is highly concentrated in the central deformation region 4, and the specimen can maintain a stable stress state under high temperature and high strain.

[0060] For Example 2, its equivalent plastic strain simulation contour plot is as follows: Figure 8 As shown, the stress state parameter evolution curve of its central deformation zone is as follows: Figure 9 As shown.

[0061] By comparing the data from Example 1 and Example 2, it can be seen that the present invention can precisely control the stress state of the sample within a wide range by changing structural parameters such as the inclination angle of the inclined groove and the thickness of the central deformation zone, thereby satisfying the research on the compressive-shear fracture law of metallic materials under different conditions.

[0062] This invention utilizes the combination of inclined grooves and end-cut areas to form an interlaced central deformation zone in the middle of the matrix. Under axial compressive load, the induced central deformation zone is in a stable compressive-shear combined stress state, and the stress state can be effectively controlled by adjusting structural parameters such as the inclined groove angle and the thickness of the deformation zone. This provides a reliable basis for the study of compressive-shear fracture behavior of metallic materials under high temperature and high strain conditions.

[0063] As described above, the present invention can be well implemented.

[0064] As can be seen from the above experiments and finite element simulations, the specimen of the present invention can not only successfully complete high-temperature and high-strain loading on thermal simulation equipment such as Gleeble3800 without instability, but also flexibly obtain different stress states by changing the key structural parameters in Table 1.

[0065] The embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered as equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A metal material compression-shear fracture test specimen for high temperature large strain, characterized by, Includes a cylindrical base (1); The circumferential surface of the substrate (1) is symmetrically provided with radially inward extending but not penetrating inclined grooves (2), the bottom of the inclined grooves (2) is cylindrical, and a metal layer is retained between the two inclined grooves (2). End cut-off areas (3) penetrating the substrate (1) are provided at both ends of the inclined groove (2); The outline of the end cut-off area (3) is composed of a main arc segment (31), an upper lateral arc segment (32), a lower lateral arc segment (33), and an upper transition fillet (34) and a lower transition fillet (35) located at their connection points, respectively. The center of the main arc segment (31) is offset relative to the center of the base (1) in both directions parallel to and perpendicular to the center line of the inclined groove (2); The two end excision areas (3) are centrally symmetrically distributed with the center point of the matrix (1).

2. The metal material compression-shear fracture test piece for high temperature and large strain according to claim 1, wherein Through the cooperation of the inclined groove (2) and the end cut-off area (3), an interlaced central deformation area (4) is formed in the middle of the substrate (1).

3. The metal material compression-shear fracture specimen according to claim 1, characterized in that, The shape and geometric parameters of the upper lateral arc segment (32) and the lower lateral arc segment (33) are determined by the starting point on the side of the base (1), the ending point on the main arc segment (31), and the preset radius.

4. The metal material compression-shear fracture specimen according to claim 1, characterized in that, The centerline of the inclined groove (2) forms a preset angle with the horizontal end face of the base (1); the preset offset of the center of the main arc segment (31) in the direction parallel to and perpendicular to the centerline of the inclined groove (2) constitutes a reverse eccentric setting.

5. The metal material compression-shear fracture specimen according to claim 1, characterized in that, The geometric parameters of the substrate (1) are: Height ranges from 4mm to 150mm; Diameter ranges from 4mm to 50mm; The height-to-diameter ratio is 1.0-3.

0.

6. The metal material compression-shear fracture specimen according to claim 1, characterized in that, The geometric parameters of the inclined groove (2) are: The angle between the centerline of the inclined groove (2) and the horizontal end face of the substrate (1) is 15°-75°; The bottom radius of the inclined groove (2) is 0.5mm-50mm; The width of the inclined groove (2) is 1mm-100mm.

7. The metal material compression-shear fracture specimen according to claim 1, characterized in that, The geometric parameters of the end-cut region (3) are: The radius of the main circular arc segment (31) is 0.1mm-50mm; The radii of the upper lateral arc segment (32) and the lower lateral arc segment (33) are both 1mm-80mm; The radii of the upper transition fillet (34) and the lower transition fillet (35) are both 0.1mm-50mm; The preset distance between the centers of the two main arc segments (31) in the direction parallel to the center line of the inclined groove (2) is 0.5mm-50mm; The preset distance between the centers of the two main arc segments (31) in the direction perpendicular to the center line of the inclined groove (2) is 0.1mm-100mm.

8. The metal material compression-shear fracture specimen according to claim 1, characterized in that, The geometric parameters of the central deformation region (4) are: The thickness of the central deformation zone (4) is 0.5mm-48mm, which is the minimum distance between the bottoms of the two inclined grooves (2).

9. The metal material compression-shear fracture specimen according to claim 1, characterized in that, The material of the sample is any one of cast iron, steel, titanium, titanium alloy, aluminum, aluminum alloy, copper, copper alloy, magnesium, or magnesium alloy.

10. A method for conducting a hot compression fracture test on a metallic material specimen subjected to compression-shear fracture as described in claims 1-9, comprising the following specific test steps: S1. Place the sample between the two indenters in the vacuum or protective atmosphere chamber of the testing machine; First, the sample is heated to 1250℃ at a heating rate of 5℃ / s and held for 5 minutes to allow the precipitated phase inside the material to fully dissolve, eliminate the initial segregation of the structure, and achieve the homogenization of the structure; then, it is cooled to the target deformation temperature of 1050℃~1200℃ set in Table 1 at a cooling rate of 10℃ / s and held at this temperature for 10 seconds to eliminate the temperature gradient in the central deformation zone (4); S2. Under the condition of maintaining a constant test temperature, the indenter of the testing machine is controlled to apply an axial compressive load to the specimen, and the loading is carried out strictly according to the loading speed of 6mm / s~30mm / s shown in Table 1; during the compression process with a large axial downward pressure, the material in the central deformation zone (4) undergoes plastic deformation, and the groove wall does not contact and close in advance; the testing machine synchronously records the load-displacement data at high frequency; when the axial displacement of the indenter reaches the preset maximum pressure, the system automatically stops loading immediately; S3. After the testing machine stops loading, start the water spray quenching system to rapidly cool the fractured specimen to room temperature; this step preserves the macroscopic morphology and microstructure characteristics of the material at the moment of high-temperature high-strain fracture, so as to facilitate subsequent observation and research.

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