A uniaxial tensile test fixture

Abstract

The present application belongs to the technical field of material mechanical property testing, and particularly relates to a uniaxial tensile test fixture, wherein a main loading mechanism and a secondary loading mechanism are cooperated with each other to convert the uniaxial tensile stress applied on the main loading mechanism into three mutually orthogonal tensile stresses, thereby overcoming the complex structure of the multi-axial tensile test equipment which needs to set an independent multi-axial tensile system; the stress is applied on the sample through the main tensile rods and the secondary tensile rods arranged in three directions, and based on the synchronous action of the three stresses, the three concentrated stresses on the sample are realized; the positioning ring surrounding the secondary loading mechanism is arranged to keep the three stresses mutually orthogonal during the test; the structure is simple, easy to operate and low in cost, and according to the positional relationship of the main tensile rods and the secondary tensile rods, the three mutually orthogonal concentrated stresses on the sample are generated, and the mechanical test of rigid materials such as structural metals and alloys, building concrete, rock and soil is applicable.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material mechanical property testing, and particularly relates to a uniaxial tensile test fixture capable of realizing a three-way stress concentration state. BACKGROUND

[0002] For structural engineering materials and load-bearing structural components, the reliability of mechanical properties is an important indicator to determine their service safety and life. Under actual service conditions, materials and structural components will be subjected to complex tensile stress states such as biaxial or triaxial tensile stress in addition to simple uniaxial tension. For example, when there are micro defects or micro cracks in the local position of the material or structural component, three-way stress concentration will occur at these local positions, which will limit the plastic deformation of the material, increase the brittleness, and ultimately lead to early failure. This local three-way stress concentration state is also one of the important inducing factors for the load capacity decline and rapid fracture of the structural component. Therefore, it is necessary to test and study the mechanical properties such as elasticity, plasticity and strength of the structural material unit under the condition of three-way stress concentration. The current test analysis methods under the action of triaxial tensile stress mainly include theoretical analysis, simulation calculation and direct test. The accuracy of theoretical analysis and simulation calculation depends on the perfection of the theory and the accuracy of the input parameters, and needs to be verified by test data. Direct test mainly uses special multi-axial tensile test equipment. For example, Liu Junxin et al. used Xi'an Li Chuang SDT-100 type microcomputer controlled electro-hydraulic servo soil dynamic triaxial test machine to study the triaxial tensile strength of cohesive soil. A kind of in-situ triaxial tensile fatigue test device under multi-field coupling disclosed in Chinese patent 201520521378 includes a triaxial tensile, fatigue loading and measuring subsystem, a thermal field loading subsystem, a cantilever indentation loading and measuring subsystem. The triaxial tensile, fatigue loading and measuring subsystem includes a main platform, a triaxial tensile motor drive unit, an axial movement unit, a fatigue and clamp unit, an adjustable shock absorbing foot cup, a connecting platform, a tension sensor, the main platform is supported by six adjustable shock absorbing foot cups and placed on a shock isolation platform; the triaxial tensile motor drive unit is connected with the axial movement unit through the connecting platform; the fatigue and clamp unit is fixed on the axial movement unit by three internal hexagonal screws a, the test piece and the pressure plate are fixed on the fatigue and clamp unit by two internal hexagonal screws b, one end of the tension sensor is fixed on the baffle by a nut a, and the other end is bolted on the fatigue and clamp unit; the thermal field loading subsystem includes a heating table and a silicon nitride ceramic heating sheet, the heating table is connected with the main platform by an internal hexagonal screw c, and the silicon nitride ceramic heating sheet is inserted into the slot of the heating table; the cantilever indentation loading and measuring subsystem includes a flexible hinge and a piezoelectric ceramic unit, a cantilever beam support, a cantilever beam, a cover, a pressure head, a pin shaft, an adjustable support table, an adjusting screw, a compression spring, a butterfly nut and a weighing sensor, the support is connected with the main platform by a butterfly nut; the flexible hinge and the piezoelectric ceramic unit are connected with the cantilever beam support by four internal hexagonal screws e; the cantilever beam is connected to the cantilever beam support by a pin shaft; the weighing sensor and the pressure head are installed in the cantilever beam, the upper end of the weighing sensor is connected with the cover by a nut b;The adjustable support table adjusts the height of the cantilever beam in the free state, the height of the adjustable support table is adjusted by adjusting the adjusting bolt, and the elastic support force between the adjustable support table and the cantilever beam support is provided by the compression spring; the three-axis tensile loading is realized by driving the stretching platform through a two-stage worm gear reducer of a motor, a screw nut pair mechanism; a thin film three-axis tensile testing machine disclosed in Chinese patent 201410120435 includes a horizontal double-axis testing device and a Z-axis tensile testing device; wherein the horizontal double-axis testing device includes four oil cylinders, four first tension sensors, four first clamps, a guide rail, a water platform, four first columns and a plurality of angle steels; the water platform is a right-angled cross, each end of the right-angled cross is fixedly connected with the four first columns; the four oil cylinders are fixed at each end of the right-angled cross, and each oil cylinder is connected with the corresponding first tension sensor and first clamp in sequence through a connecting rod; the guide rail is arranged on the surface of the right-angled cross, the first clamp is arranged on the guide rail and can move along the guide rail; two of the first columns are fixedly connected with the angle steels; the Z-axis tensile testing device is constructed on the horizontal double-axis testing device and includes four second columns, two frame members, a first fixed guide rail beam, a second fixed guide rail beam, a movable guide rail beam, a Z-axis platform, a first fixed plate, a movable rod, an electric cylinder, a second tension sensor and a second clamp; the bottom end of each second column is fixed on the corresponding angle steel; the two frame members and the second fixed guide rail beam are welded into a I-shaped whole and are fixedly connected with the top end of the second column, the first fixed guide rail beam is parallel to the second fixed guide rail and is fixedly connected with the top end of the second column and the frame member; the two ends of the movable guide rail beam are connected with the first fixed guide rail beam and the second fixed guide rail beam and can move along the guide rails on the first fixed guide rail beam and the second fixed guide rail beam; the Z-axis platform is arranged on the movable guide rail beam and can move along the movable guide rail beam; the first fixed plates are arranged on the two sides of the movable guide rail beam, the first fixed plates are connected with the Z-axis platform through a pin; the trunnion of the electric cylinder is arranged in the bearing of the Z-axis platform, the electric cylinder is connected with the Z-axis platform through the movable rod, the piston rod of the electric cylinder penetrates the Z-axis platform and the movable guide rail beam along the Z-axis downward and is connected with the second tension sensor and the second clamp in sequence; the oil cylinder and the motor cylinder are retracted and the three-dimensional connected test piece to be measured is stretched to realize three-axis tensile loading through the three-axis control system.

[0003] However, the above patent products and the test devices and test equipment in the prior art often have complex system, cumbersome operation, high cost, and cannot meet the needs of conventional laboratory testing. Therefore, a uniaxial tensile test fixture for realizing three-way stress concentration state is developed and designed, which is directly matched with a commercially available conventional uniaxial tensile testing machine, converts the uniaxial tensile stress generated by the tensile testing machine into three-way tensile stress orthogonal to each other, so that the sample is in a three-way stress concentration state, and the mechanical property response characteristics of the structural material unit are further evaluated. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art, and develop a uniaxial tensile test fixture capable of realizing three-way stress concentration state, which is matched with a commercially available conventional uniaxial tensile testing machine, and performs three-way concentrated stress loading on the sample.

[0005] In order to achieve the above-mentioned purpose, the main body structure of the uniaxial tensile test fixture according to the present application comprises a main loading mechanism and a secondary loading mechanism connected to each other, and a positioning ring for positioning the main loading mechanism and the secondary loading mechanism; the main loading mechanism loads the sample through a main pull rod, and the secondary loading mechanism loads the sample through a secondary pull rod.

[0006] The main body structure of the main loading mechanism 1 according to the present application comprises two units arranged opposite to each other in the vertical direction, each unit comprising a main loading end 11, a loading screw 12 arranged on the top surface of the main loading end 11, a slide rail 13 arranged on the side surface, and a loading screw hole 14 arranged on the bottom surface; a track groove 15 is arranged on the slide rail 13; the main body structure of the secondary loading mechanism 2 comprises four units arranged opposite to each other around the central axis of the main loading mechanism 1, each unit comprising a secondary loading end 21, a loading through hole 22 arranged at the center, and a slide sleeve 23 arranged at the left and right ends; the slide sleeve 23 with an inner hollow structure is provided with a rolling groove 25 for installing a ball 26; the positioning ring 3 is sleeved on the secondary pull rod 6, arranged around the secondary loading mechanism 2, and the main body structure thereof comprises four units, each unit comprising an arc-shaped plate 32, a through groove 33 arranged at the center, and a support plate 34 arranged on the inner side; a connecting screw hole 51 is arranged at the center of each side surface of the sample 5.

[0007] One end of the main pull rod 4 is connected with the loading screw hole 14, and the other end is connected with the connecting screw hole 51 on the top surface or the bottom surface of the sample 5; one end of the secondary pull rod 6 is connected with the connecting screw hole 51 on the side surface of the sample 5, and the other end passes through the loading through hole 22, is sleeved with a nut 61, and then passes through the through groove 33, so that the nut 61 is screwed and fixed outside the secondary loading end 21.

[0008] The uniaxial tensile test fixture is used for testing, when the main loading mechanism moves up or down relative to the tension, the main tension rod generates the tensile stress in the vertical direction on the sample; at the same time, the slide rail pushes the sliding sleeve, the sliding sleeve slides along the slide rail and expands outward, drives the secondary tension rod connected with the secondary loading mechanism to move outward along the rod axis, generates the tensile stress in the horizontal direction on the sample, and realizes the mutual orthogonal three-way stress concentration state of the sample.

[0009] Compared with the prior art, the main loading mechanism and the secondary loading mechanism are matched with each other, the uniaxial tensile stress applied on the main loading mechanism is converted into the mutual orthogonal three-way tensile stress, the complex structure form of the independent multi-axial tensile system of the multi-axial tensile test equipment is overcome; the stress is applied on the sample through the main tension rod and the secondary tension rod arranged in three directions, the three-way concentrated stress loading on the sample is realized based on the synchronous action of the three-way stress; the positioning ring surrounding the secondary loading mechanism is arranged, the mutual orthogonal three-way stress in the test process is maintained; the structure is simple, easy to operate and low in cost, the mutual orthogonal three-way concentrated stress on the sample is generated according to the position relationship of the main tension rod and the secondary tension rod, the secondary tension rod always maintains coplanar and perpendicular to the main tension rod in the test process through the limiting and supporting action of the through slot and the supporting plate, the mutual orthogonal three-way stress concentration state of the sample is maintained, and the mechanical test of rigid materials such as structural metals and alloys, building concrete, rock soil and the like is suitable. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 It is the schematic diagram of the main structure principle of the application.

[0011] Figure 2 It is the schematic diagram of the structure principle of the main loading mechanism.

[0012] Figure 3 It is the schematic diagram of the structure principle of the secondary loading mechanism.

[0013] Figure 4 It is the schematic diagram of the structure principle of the main tension rod, the secondary tension rod, the positioning ring and the sample. CONCRETE IMPLEMENTATION METHOD

[0014] The application will be further described below in combination with the drawings and the concrete implementation method.

[0015] Example 1:

[0016] The main body structure of the single-axis tensile test fixture involved in the embodiment comprises a main loading mechanism 1, a secondary loading mechanism 2, a positioning ring 3, a main pull rod 4, a sample 5 and a secondary pull rod 6; the main loading mechanism 1 is connected with the secondary loading mechanism 2, the positioning ring 3 positions the main loading mechanism 1 and the secondary loading mechanism 2, the main loading mechanism 1 loads the sample 5 through the main pull rod 4, and the secondary loading mechanism 2 loads the sample 5 through the secondary pull rod 6.

[0017] The main body structure of the main loading mechanism 1 involved in the embodiment comprises two units oppositely arranged in the vertical direction, each unit is composed of a main loading end 11, a loading screw rod 12, a slide rail 13, a loading screw hole 14 and a track groove 15; the top surface of the cuboid structure of the main loading end 11 is connected with the loading screw rod 12, the four side surfaces are respectively connected with the slide rail 13 of the arc structure, the bottom surface is provided with the loading screw hole 14 in the center, the four slide rails 13 are in a 90° rotational symmetry relationship along the central axis of the main loading mechanism 1, the inner and outer side surfaces of the slide rail 13 are respectively provided with the track groove 15, and the slide rails 13 of the two opposite main loading mechanisms 1 are arranged in a staggered manner.

[0018] The main body structure of the secondary loading mechanism 2 involved in the embodiment comprises four units arranged at equal intervals, which are arranged in pairs opposite to each other around the central axis of the main loading mechanism 1 and matched with the positions of the slide rails 13, and each unit is composed of a secondary loading end 21, a loading through hole 22, a sliding sleeve 23, a sliding cavity 24, a rolling groove 25 and a ball 26; the center of the cuboid structure of the secondary loading end 21 is provided with a transverse loading through hole 22, the right end is provided with an upwardly extending sliding sleeve 23 of the arc structure, the left end is provided with a downwardly extending sliding sleeve 23, the center of the sliding sleeve 23 is provided with a sliding cavity 24 of the arc structure, the upper and lower inner walls are respectively provided with a rolling groove 25, and a plurality of balls 26 are arranged in the rolling groove 25; the sliding cavity 24 is matched with the upper and lower two slide rails 13 at the same position, the balls 26 are matched with the track grooves 15, so that the slide rails 13 penetrate into the sliding cavity 24, and the sliding sleeve 23 slides relative to the slide rail 13.

[0019] The main body structure of the positioning ring 3 involved in the embodiment comprises four foldable units connected through hinges 31, each unit is composed of an arc-shaped plate 32, a through groove 33 and a support plate 34; the center of the arc-shaped plate 32 is provided with the through groove 33, the inner side (below the through groove 33) is provided with the support plate 34, the support plate 34 supports the secondary pull rod 6 and limits the displacement of the secondary pull rod 6 in the vertical direction, but does not affect the displacement of the secondary pull rod 6 in the axial direction; the head and tail ends of the positioning ring 3 are provided with fixing lugs 35, the fixing lugs 35 are provided with fixing screw holes 36, and the fixing screws 37 penetrate through the two fixing screw holes 36 to connect the head and tail ends of the positioning ring 3, forming a ring structure.

[0020] The sample 5 involved in the embodiment is of a cubic structure, and the center of each side surface is provided with a connecting screw hole 51.

[0021] The one end of the main pull rod 4 is connected with the loading screw hole 14, and the other end is connected with the connecting screw hole 51 on the top surface or bottom surface of the sample 5. The one end of the auxiliary pull rod 6 is connected with the connecting screw hole 51 on the side surface of the sample 5, and the other end is sleeved with the nut 61 after passing through the loading through hole 22 and then is out of the through slot 33.

[0022] Example 2:

[0023] When the single-axis tensile test fixture is installed before the test, the installation of the main loading mechanism 1 and the auxiliary loading mechanism 2 is as follows:

[0024] Firstly, the slide rail 13 is inserted into the sliding cavity 24, so that the two main loading mechanisms 1 and the four auxiliary loading mechanisms 2 are matched and connected;

[0025] Then, one end of the main pull rod 4 is screwed into the loading screw hole 14, and the other end is screwed into the connecting screw hole 51 on the top surface and bottom surface of the sample 5. The position of the sample 5 is adjusted so that it is in the center of the axis of the two main loading mechanisms 1, and the connection between the sample 5 and the main loading mechanism 1 is completed.

[0026] Secondly, one end of the auxiliary pull rod 6 is screwed into the connecting screw hole 51 on the side surface of the sample 5, and the other end is screwed and fixed on the outside of the auxiliary loading end 21 after passing through the loading through hole 22 and sleeving with the nut 61, and the connection between the sample 5 and the auxiliary loading mechanism 2 is completed.

[0027] Thirdly, the positioning ring 3 is wrapped around the outside of the auxiliary loading mechanism 2, and is sleeved on the four auxiliary pull rods 6 through the through slot 33. The fixing bolt 37 is screwed into the fixing screw hole 36, and the screwing and fixing of the positioning ring 3 are completed.

[0028] Finally, the loading screw rod 12 is screwed into or clamped in the chuck of the tensile testing machine, and the installation of the single-axis tensile test fixture is completed.

[0029] Example 3:

[0030] The single-axis tensile test fixture involved in the embodiment generates mutually orthogonal three-way concentrated stresses on the test sample 5 according to the mutually orthogonal positional relationship of the two main pull rods 4 and the four auxiliary pull rods 6 during the test. The limiting and supporting effect of the through slot 33 and the supporting plate 34 on the auxiliary pull rods 6 enables the four auxiliary pull rods 6 to always remain coplanar and perpendicular to the two main pull rods 4 during the test, thereby maintaining the mutually orthogonal three-way stress concentration state of the test sample 5. Specifically, the main loading mechanism 1 is subjected to a tensile stress in the vertical direction according to the preset program of the tensile testing machine, and the main pull rods 4 conduct the stress to the test sample 5 to generate a tensile stress in the vertical direction on the test sample 5. With the relative upward and downward movement of the main loading mechanism 1, the slide rail 13 pushes the sliding sleeve 23, and the sliding sleeve 23 expands outward along the slide rail 13 through the cooperation of the ball 26 and the track groove 15, thereby driving the auxiliary pull rods 6 connected with the auxiliary loading mechanism 2 to move outward along the rod axis, and generating a tensile stress in the horizontal direction on the test sample 5.

Claims

1. A uniaxial tensile test fixture, the main body structure comprising a main loading mechanism and a sub-loading mechanism connected to each other, and a positioning ring for positioning the main loading mechanism and the sub-loading mechanism; characterized in that, The main loading mechanism loads the sample through the main pull rod, and the auxiliary loading mechanism loads the sample through the auxiliary pull rod; The main body structure of the main loading mechanism includes two units arranged opposite in the vertical direction, each unit includes a main loading end in the cuboid structure, a loading screw arranged on the top surface of the main loading end, four slide rails in the arc structure arranged on the four side surfaces of the main loading end, and a loading screw hole arranged on the bottom surface of the main loading end; the slide rail is provided with a rail groove; The main body structure of the auxiliary loading mechanism includes four units arranged opposite around the central axis of the main loading mechanism, each unit includes an auxiliary loading end in the cuboid structure, a horizontal loading through hole arranged in the center of the auxiliary loading end, an arc-shaped slide sleeve extending upward arranged on the right end of the auxiliary loading end, and an arc-shaped slide sleeve extending downward arranged on the left end of the auxiliary loading end; the slide sleeve in the hollow structure is provided with a rolling groove for installing a ball; The positioning ring is sleeved on the auxiliary pull rod and arranged around the auxiliary loading mechanism, and the main body structure of the positioning ring includes four units, each unit is composed of an arc-shaped plate, a through groove arranged in the center of the arc-shaped plate, and a support plate arranged on the inner side of the arc-shaped plate; The sample is in the cuboid structure, and a connecting screw hole is arranged in the center of each side surface; The four slide rails are in a 90° rotational symmetry relationship along the central axis of the main loading mechanism, and the slide rails of the two opposite main loading mechanisms are arranged staggered; The center of the slide sleeve is provided with a sliding cavity in the arc structure, the sliding cavity is matched with the upper and lower slide rails at the same position, the ball is matched with the rail groove, the slide rail penetrates into the sliding cavity, and the slide sleeve slides relative to the slide rail; One end of the main pull rod is connected with the loading screw hole, the other end is connected with the connecting screw hole on the top surface or the bottom surface of the sample, one end of the auxiliary pull rod is connected with the connecting screw hole on the side surface of the sample, and the other end is sleeved with a nut after penetrating through the loading through hole and then penetrates out through the through groove; The main loading mechanism and the auxiliary loading mechanism cooperate with each other to convert the uniaxial tensile stress applied on the main loading mechanism into three-directional tensile stress.

2. The uniaxial tensile test fixture of claim 1, wherein, The four units of the positioning ring can be folded, connected through hinges, the support plates support the auxiliary pull rod and limit the displacement of the auxiliary pull rod in the vertical direction; the head and tail ends of the positioning ring are provided with fixing ears, the fixing ears are provided with fixing screw holes, the fixing screws penetrate through the two fixing screw holes to connect the head and tail ends of the positioning ring, and a ring structure is formed.

3. The uniaxial tensile test fixture of claim 1 or 2, wherein, During the test, when the main loading mechanism moves upward or downward under tension, the main pull rod generates tensile stress in the vertical direction on the sample; at the same time, the slide rail pushes the slide sleeve, the slide sleeve slides along the slide rail and expands outward, driving the auxiliary pull rod connected with the auxiliary loading mechanism to move outward along the rod axis, generating tensile stress in the horizontal direction on the sample, and the sample is in a three-directional stress concentration state.

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