Forming limit determining device based on proportional adjustment of connecting rod of biaxial stretching equipment
By introducing the link proportional adjustment and the design of rotating L-shaped support in the biaxial tensile test device, the problem of difficulty in controlling strain state under dynamic loading of existing systems is solved, and compact and low-cost biaxial stretching is achieved Testing ensures that the center of the sample remains unmoved and does not twist, improving the accuracy of the forming limit curve.
Patent Information
- Application Number
- CN202411124757.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-16
- Publication Date
- 2024-12-27
AI Technical Summary
The existing biaxial tensile testing system is difficult to achieve different strain states within the range of -0.5 to 1, which limits the accurate construction of forming limit diagrams, especially inadequate controllability under dynamic loading conditions.
A connecting rod proportional adjustment device based on a biaxial tensile test device is designed to achieve the tensile of different strain paths through the servo electric cylinder driving connecting rod and rotating L-shaped support. Combined with heating and optical measurement devices, the cross-shaped test is ensured. The sample is centered and does not twist during biaxial stretching, and the length of the connecting rod and rotating L-shaped support can be adjusted to achieve isobiaxial, flat and uniaxial stretching.
Achieve a more compact, easy to operate and low-cost biaxial tensile testing device, which can accurately obtain forming limit data under different strain paths, ensure that the center of the sample is still and does not twist, and improve the integrity and accuracy of the forming limit curve. sex.
Smart Images
Figure CN119198286A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a biaxial stretching test for studying the forming limit of a plate, and in particular to a forming limit determination device based on connecting rod ratio adjustment of a biaxial stretching device. Background Art
[0002] Formability refers to the ability of a metal sheet to form a specific shape without defects after plastic deformation. It is a very important indicator of the mechanical properties of the material. With the development of sheet metal forming technology at the end of the 19th century, the formability of metal sheets became a research focus, and a series of methods for evaluating the formability of metal sheets emerged. Among them, the forming limit diagram (FLD) is the most direct and effective method for quantitatively evaluating the formability of sheet metal. Its concept was first proposed by Keeler and later expanded and improved by Goodwin. The forming limit diagram represents the limit deformation capacity of the material before local necking or fracture occurs. It is composed of the limit major and minor strain points under the linear strain path from uniaxial tension, plane strain tension, to equal biaxial tension. If these limit strain points are connected by a curve, a forming limit curve (FLC) is formed. The area below the forming limit curve is the safe zone of plastic deformation, and the area above the forming limit curve is called the rupture zone. Due to its comprehensive, intuitive and concise characteristics, the forming limit diagram is widely used to judge whether the process design of complex-shaped stamping parts is reasonable, and to guide and improve the stamping production of automobile body covers, structural parts and other parts.
[0003] The experimental methods for obtaining the forming limit include the curved surface method, the plane method and the biaxial tensile test method. The curved surface method uses a hemispherical punch to punch the material until the specimen is necked or broken. By using specimens of different widths for experiments and changing the lubrication state between the specimen and the rigid hemispherical punch, different strain path states can be obtained. However, the curved surface method is easily affected by curvature, friction and thickness stress. The plane method is improved on the basis of the curved surface method by changing the hemispherical punch to a flat punch. However, the flat punch is in direct contact with the material for punching, which causes stress concentration in the material at the corner of the punch and causes fracture. In order to avoid the above problems, the cross-shaped biaxial tensile method is proposed to study the forming limit of sheet metal. The advantage of the cross-shaped specimen is that the sheet metal is always subjected to force in a plane state, which is convenient for theoretical analysis, and different strain states can be achieved in the center area by changing the load ratio in the two directions.
[0004] With the development of the cross-shaped biaxial tensile method, great efforts have been made to develop biaxial tensile test systems. According to the mechanism of achieving biaxial loading, the existing systems can be divided into three categories: (1) single-machine system; (2) connecting rod mechanism accessories; (3) others. The hydraulic biaxial testing machine developed by Mak i nde et al. in 1992 has two pairs of hydraulic drives in two vertical directions to perform biaxial loading on the cross-shaped specimen, and a force sensor and a displacement sensor are set in each direction. Kuwabara et al. developed a servo-hydraulic biaxial testing machine in 1998. Its composition structure is similar to that of the test machine developed by Mak i nde, but the difference is that the hydraulic drive has a pantograph mechanism, which improves the loading control accuracy. The first two testing machines can perform stress control under arbitrary proportions, but they are single-machine control systems and are only suitable for static loading, which puts forward higher requirements for dynamic loading controllability. Ferron et al. (1992) and Fraunhofer et al. (2005) designed an additional device of eight-link and four-link mechanism respectively, which converted the uniaxial drive in the vertical direction into biaxial drive in the horizontal direction, that is, when the pressure plate of the hydraulic universal testing machine moves downward, the motion is converted into two horizontal motions in different directions through eight and four links, so as to apply biaxial loading to the cross-shaped specimen. A difficulty in designing a biaxial tensile system is to realize different strain states in the specimen measurement area with strain β in the range of -0.5 to 1, such as uniaxial (β = -0.5) and equibiaxial (β = 1), which is necessary to complete FLCs. Summary of the invention
[0005] To solve the above problems, the present invention discloses a simple forming limit determination device based on connecting rod ratio adjustment of a biaxial tensile test device, which is combined with other heating and optical measuring devices to perform biaxial stretching on a cross-shaped specimen to obtain the forming limit of the alloy material.
[0006] The present invention provides a simple forming limit determination device based on the proportion adjustment of the connecting rod of a biaxial tensile test device, and the biaxial tensile test device includes a rectangular frame, a connecting rod 1, a rotating L-shaped support, a connecting rod rotating shaft, a connecting rod 2, an active connecting plate, a tensile movable circular rail, and a clamping end. The working principle of the biaxial tensile test device is that the servo electric cylinder drives the tensile movable circular rails on the left and right sides to move to the left and right sides, and drives the tensile movable circular rails on the upper and lower sides to move up and down through the accompanying rotation of a series of connecting rods, etc., thereby realizing biaxial stretching.
[0007] Furthermore, the rectangular frame mainly has a supporting and fixing function, and each of the four sides has an opening for the stretching movable circular rail to move, so as to achieve the stretching of the cross-shaped specimen, and keep the center of the cross-shaped specimen always in the same position during the stretching process, and the entire cross-shaped specimen is not twisted and always remains in one plane;
[0008] Furthermore, the stretching movable circular rail is connected to a servo electric cylinder, and the servo electric cylinder drives the stretching movable circular rails on the left and right sides to move to the left and right sides, driving the movable connecting plate in the horizontal direction to produce displacement, thereby realizing the horizontal stretching movement of the cross-shaped specimen;
[0009] Furthermore, one end of the connecting rod 1 and the connecting rod 2 are respectively connected to the movable connecting plates in the vertical direction and the horizontal direction through the connecting rod rotating shaft, and one end is connected to the rotating L-shaped support through the connecting rod rotating shaft. The movement of the movable connecting plate in the horizontal direction is transmitted to the rotating L-shaped support through the connecting rod 2. The rotating L-shaped support transmits the movement to the connecting rod 1 through rotation. The connecting rod 1 transmits the movement to the movable connecting plate in the vertical direction through rotation again, thereby pushing the movable connecting plate in the vertical direction to displace, realizing the vertical tensile movement of the cross-shaped specimen, and then realizing the biaxial stretching of the cross-shaped specimen.
[0010] Furthermore, the connecting rod 1, the connecting rod 2 and the rotating L-shaped support are the main parts for realizing different strain paths. By changing the lengths of the connecting rod 1 and the connecting rod 2, as well as the lengths of the two sides of the rotating L-shaped support, stretching under different strain paths can be realized. Taking equibiaxial stretching and plane stretching as examples, when the length ratio of the connecting rod 1 and the connecting rod 2 is 1:1, and the length ratio of the two sides of the rotating L-shaped support is 1:1, equibiaxial stretching can be realized. When the length ratio of the connecting rod 1 and the connecting rod 2 is 1:1.5, and the length of the two sides of the rotating L-shaped support is 1:1.5, plane stretching can be realized.
[0011] Compared with the prior art, the present invention
[0012] The advantages are: 1. Compared with the existing devices, the biaxial tensile test device has compact parts and small footprint, is easy to operate, easy to get started, simple in structure and low in cost;
[0013] 2. By changing the length ratio of the connecting rod and the rotating L-shaped support, the stretching of different strain paths can be achieved, and the disassembly is simple and easy to operate;
[0014] 3. The device converts the horizontal uniaxial force into biaxial force through the accompanying movement of the connecting rod linkage frame, thereby realizing biaxial stretching of the cross-shaped specimen, and can ensure that the center of the cross-shaped specimen remains stationary during the stretching process, and the specimen does not undergo torsional deformation and always remains in one plane. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Figure 1 It is a front view of a biaxial tension testing device for realizing planar tensioning according to a preferred embodiment of the present invention;
[0016] Figure 2 It is a front view of a rotating L-shaped support in a biaxial tensile testing device for realizing planar tensile in a preferred embodiment of the present invention;
[0017] Figure 3 It is a front view of a connecting rod 1 and a connecting rod 2 in a biaxial tension testing device for realizing planar tension according to a preferred embodiment of the present invention;
[0018] Figure 4 It is a front view of a rotating L-shaped support in a biaxial stretching test device for realizing equibiaxial stretching according to a preferred embodiment of the present invention;
[0019] Figure 5 It is a front view of a connecting rod 1 and a connecting rod 2 in a biaxial tension testing device for realizing equal biaxial tension according to a preferred embodiment of the present invention;
[0020] Figure 6 It is a forming limit diagram of an aluminum alloy sheet at different temperatures obtained by using a biaxial tensile testing device in a preferred embodiment of the present invention.
[0021] List of reference numerals: 1. rectangular frame; 2. connecting rod one; 3. rotating L-shaped support; 4. connecting rod shaft; 5. connecting rod two; 6. movable connecting plate; 7. stretching movable circular rail; 8. clamping end. DETAILED DESCRIPTION
[0022] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to directions in the accompanying drawings, and the words "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.
[0023] Embodiment 1:
[0024] like Figure 1 As shown, it is a front view of the main device of a forming limit determination method based on the proportion adjustment of the connecting rod of a biaxial stretching equipment. The main parts include a rectangular frame 1, a connecting rod 1 2, a rotating L-shaped bracket 3, a connecting rod shaft 4, a connecting rod 2 5, a movable connecting plate 6, a stretching movable circular rail 7, and a clamping end 8.
[0025] The rectangular frame 1 plays a fixed supporting role in the whole device, so that the whole device can be placed vertically on the experimental platform, making it easier to cooperate with the optical measuring device and the heating device during the test, and more intuitively observing the deformation of the cross-shaped sample during the stretching process. Before the test, the cross-shaped specimen is placed on the biaxial tensile test device and fixed with the clamping end 8. The four sides of the rectangular frame 1 are respectively passed by the stretching movable circular rails 7, and the servo electric cylinder is connected to the stretching movable circular rails 7 in the horizontal direction, driving the stretching movable circular rails 7 on the left and right sides to move left and right, driving the horizontal movable connecting plate 6 to produce displacement, thereby realizing the horizontal stretching movement of the cross-shaped specimen.
[0026] The horizontal stretching movable circular rail 7 moves and drives the horizontal movable connecting plate 6 connected thereto to move together. The horizontal movable connecting plate 6 is connected to the connecting rod 2 through the connecting rod rotating shaft 4, driving the connecting rod 2 5 to rotate. One end of the rotating L-shaped bracket 3 is connected to the connecting rod 2 5 by the connecting rod rotating shaft 4, and one end is connected to the connecting rod 1 2. The movement of the connecting rod 2 5 is transmitted to the connecting rod 1 2 via the rotating L-shaped bracket 3 to rotate. The movement of the connecting rod 1 2 drives the vertical movable connecting plate 6 to move, thereby realizing the biaxial stretching of the cross-shaped specimen. In the process of biaxial stretching of the specimen, due to the fixation of the rectangular frame 1 and the accompanying movement of the connecting rod, the center of the cross-shaped specimen remains stationary during the stretching process, and it always remains in one plane without twisting or bending.
[0027] In order to obtain the forming limit curve of the plate, it is only necessary to change the length and ratio of the connecting rod 1 2, the connecting rod 2 5, and the rotating L-shaped bracket. When equibiaxial stretching is performed, the length ratio of the connecting rod 1 2 and the connecting rod 2 5 is 1:1, and the length ratio of the two sides of the rotating L-shaped support is 1:1, so that the displacement ratio of the stretching circular rail 7 in the horizontal direction and the displacement ratio in the vertical direction can be 1:1, so that the strain ratio β of the cross-shaped specimen is 1:1, thereby realizing equibiaxial stretching; when plane stretching is performed, the length ratio of the connecting rod 1 2 and the connecting rod 2 5 is 1:1.5, and the length of the two sides of the rotating L-shaped support is 1:1.5, so that the displacement ratio of the stretching circular rail 7 in the horizontal direction and the vertical direction can be 1.5:1, and the strain ratio β of the cross-shaped specimen can be close to 0, realizing stretching close to the plane strain state; therefore, by changing the length and ratio of the connecting rod 1, the connecting rod 2 and the rotating L-shaped support, stretching under different strain states can be realized, and the data points constituting the forming limit curve can be obtained, making the forming limit curve more complete and accurate.
[0028] Embodiment 2:
[0029] On the basis of the above description, as a connecting rod ratio adjustment method in this embodiment, the plane strain state, the equibiaxial strain state and the uniaxial strain state are obtained by adjusting the connecting rod ratio.
[0030] Before the test begins, the cross-shaped specimen sprayed with speckles is installed in the biaxial tensile test device and fixed by the clamping end 8. The DIC optical measuring device is adjusted to align with the center of the cross-shaped specimen for strain data collection and analysis. The cross-shaped specimen is heated by a heating device. After heating to the required temperature and keeping the temperature for a period of time, the specimen is stretched and the DIC optical testing device is started. To achieve equal biaxial stretching, the lengths of the connecting rod 1 2 and the connecting rod 2 5 are both 65 cm, with a ratio of 1:1, and the lengths of the two sides of the rotating L-shaped support 3 are both 120 cm. Figure 2 and 3As shown, the displacement ratio of the horizontal tensile movable circular rail 7 to the vertical tensile rail 7 is 1:1, and the sample is in an equibiaxial tensile state. In order to achieve tensile deformation of different strain paths, the lengths of the connecting rod 1 2, the connecting rod 2 5, and the rotating L-shaped bracket 3 are adjusted. The length of the connecting rod 1 is 32 cm, the length of the connecting rod 2 5 is 48 cm, and the length ratio of the two connecting rods is 1:1.5. The lengths of the two sides of the rotating L-shaped bracket are 120 cm and 80 cm respectively, and the length ratio is 1.5:1. Figure 4 and 5 As shown, the displacement ratio of the horizontal stretching movable circular rail 7 to the vertical stretching is 1.5:1, and the 120cm long axis is connected to the connecting rod 2 5, so that the sample can be in a plane strain state; in order to obtain the forming limit curve of the plate, at least data under the uniaxial tensile strain state is required. In this set of equipment, only the two clamping ends 8 in the vertical direction need to be removed, and only the two clamping ends 8 in the horizontal direction are used to fix the sample, so that the uniaxial stretching of the cross-shaped sample can be achieved. The strain data under the three strain states are processed, and the data of the three limit strain points obtained are connected with a smooth curve to obtain the forming limit curve of the sample, as shown in FIG. Figure 6 shown.
[0031] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include technical schemes composed of any combination of the above technical features.
Claims
1. A forming limit determination device based on connecting rod ratio adjustment of biaxial stretching equipment, characterized in that: The invention comprises a rectangular frame (1), a connecting rod 1 (2), a rotating L-shaped support (3), a connecting rod rotating shaft (4), a connecting rod 2 (5), a movable connecting plate (6), a stretch movable circular rail (7) and a clamping end (8); the rectangular frame (1) is placed vertically on an experimental platform; each end of the rectangular frame (1) has a hole, wherein the stretch movable circular rail (7) passes through the hole and is connected to the movable connecting plate (6), and the other side of the movable connecting plate (6) is connected to the clamping end (8); the stretch movable circular rails (7) on the left and right sides are connected to a servo electric cylinder to drive the movable connecting plate (6) in a horizontal direction to generate displacement; wherein every two adjacent movable connecting plates (6) are connected by connecting rod 1 (2), connecting rod 2 (5) and the rotating L-shaped support (3).
2. The forming limit determination device based on connecting rod ratio adjustment of biaxial stretching equipment according to claim 1 is characterized in that: The connecting rod assembly comprises a connecting rod 1 (2), a connecting rod 2 (5), a rotating L-shaped support (3) and a connecting rod rotating shaft (4); wherein the connecting rod 1 (2) and the connecting rod 2 (5) are respectively rotatably connected to a movable connecting plate (6) arranged in a horizontal direction and a movable connecting plate (6) arranged in a vertical direction through the connecting rod rotating shaft (4); wherein one end of the rotating L-shaped support (3) is movably connected to the connecting rod 1 (2) and the other end is movably connected to the connecting rod 2 (5).
3. The forming limit determination device based on connecting rod ratio adjustment of biaxial stretching equipment according to claim 2, characterized in that: When stretching starts, the servo electric cylinder drives the stretching movable circular rails (7) on the left and right sides to move to the left and right sides, driving the movable connecting plate (6) in the horizontal direction to move, thereby realizing horizontal stretching of the cross-shaped specimen.
4. The forming limit determination device based on connecting rod ratio adjustment of biaxial stretching equipment according to claim 2, characterized in that: The movement of the movable connecting plate (6) in the horizontal direction is transmitted to the rotating L-shaped support (3) through the second connecting rod (5), and the rotating L-shaped support (3) transmits the movement to the first connecting rod (2) through rotation. The first connecting rod (2) drives the movable connecting plate (6) in the vertical direction to move, thereby pushing the movable connecting plate (6) in the vertical direction to move, thereby realizing the vertical tensile movement of the cross-shaped specimen, and further realizing the biaxial stretching of the cross-shaped specimen.
5. The forming limit determination device based on connecting rod ratio adjustment of biaxial stretching equipment according to claim 2, characterized in that: The connecting rod 1 (2), the connecting rod 2 (5) and the rotating L-shaped support (3) are main parts for realizing different strain paths. By changing the lengths of the connecting rod 1 (2) and the connecting rod 2 (5), as well as the lengths of the two sides of the rotating L-shaped support (3), stretching under different strain paths can be realized. Taking equibiaxial stretching and plane stretching as examples, when the length ratio of the connecting rod 1 (2) and the connecting rod 2 (5) is 1:1 and the lengths of the two sides of the rotating L-shaped support (3) are 1:1, equibiaxial stretching can be realized. When the length ratio of the connecting rod 1 (2) and the connecting rod 2 (5) is 1:1.5 and the lengths of the two sides of the rotating L-shaped support (3) are 1:1.5, plane stretching can be realized.