Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N3/20—Investigating strength properties of solid materials by application of mechanical stress by applying steady bending forces
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M13/00—Testing of machine parts
  • G01M13/02—Gearings; Transmission mechanisms
  • G01M13/025—Test-benches with rotational drive means and loading means; Load or drive simulation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
  • G01M5/0033—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by determining damage, crack or wear
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M99/00—Subject matter not provided for in other groups of this subclass
  • G01M99/007—Subject matter not provided for in other groups of this subclass by applying a load, e.g. for resistance or wear testing
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N2203/0058—Kind of property studied
  • G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N2203/02—Details not specific for a particular testing method
  • G01N2203/026—Specifications of the specimen
  • G01N2203/0262—Shape of the specimen
  • G01N2203/0278—Thin specimens
  • G01N2203/028—One dimensional, e.g. filaments, wires, ropes or cables

Definitions

• the invention relates to a method of performing rotating bending fatigue test for test specimens of circular cross-section, during which the test specimen, in particular wires, is repeatedly loaded, thereby the behaviour of the test material in normal use in a given time interval is simulated.
• the purpose of testing is to obtain information about the mechanical properties of the material during loading, thanks to which it is possible to evaluate the service life of the tested material in machine parts.
• the material fatigue happens if the number of load cycles reaches hundreds of thousands, millions or more.
• the stress during cyclic loading of the specimen is less than the yield strength of the material, because material fatigue occurs in components that are subjected in service to repeated loads less than the yield strength of the material but higher than the fatigue limit.
• a crack may form which spreads out with increasing number of load cycles until the fatigue fracture of the component occurs.
• This fracture is characterized by the fact that it is not preceded by plastic deformation. Cracks typically occur in places of stress concentration, i.e. in places of notches, for example in places where there is a hole, thread, high surface roughness, weld, crack, material defect, therefore often fatigue tests are performed on notched test specimens.
• a device adapted to perform a rotating bending fatigue test typically consists of a motor, a drive spindle and a support bearing. The specimen is placed between the drive spindle to which it is clamped and the support bearing. The specimen is typically provided with a notch, hole, etc., which serve as stress concentrators.
• these devices are only adapted to examine straight specimen (specimen with a straight longitudinal axis). In the case of testing, for example, a wire, which is typically produced in coils with a certain radius of curvature of the longitudinal axis of the wire, it is necessary to straighten the wire before clamping.
• a device for performing bending fatigue testing which comprises, among other things, a guide sleeve for fixing the test specimen, which is housed in a cage and in a guide sleeve there is housed a fixing sleeve for clamping the test specimen.
• a horizontal and vertical clamp is connected to the cage, which serves to monitor the course of the load in both load axes of movement with the device frame.
• a solution is known from utility model application 2014-30046 "Jaw for clamping miniature round specimens in fatigue life testing machines", which is adapted for clamping miniature round specimens, which comprises a fixed specimen holder provided with two holes and a clamping stone which is provided with a recess in the shape of a cylindrical surface with serrations.
• the jaw further comprises a movable specimen holder, which is also provided with two holes and a clamping stone.
• the connection of the fixed and movable specimen holder is made by means of pins which are inserted into the respective holes and connected by a pressure element.
• the present document also relates to a field other than the present invention.
• the friction in the support bearing generates a torque causing an additional torsional load along the entire length of the test specimen.
• the ratio between the bending stress (desired, defined) and the torsional stress (undesired, undefined) decreases. Therefore, when loading thin specimens (e.g. wires), the resistance of the non-driven jaw (e.g. support bearing) significantly distorts the measurement result.
• the force sensor is used to record data on the load and a fracture is detected by the fracture detection sensor.
• the mutual angle of the jaw axis vectors is 30-180°, and it is also preferred that the jaw axes together with the clamped test specimen face downwards, thereby eliminating the affecting of the test results obtained by undesired lateral bending of the specimen weight.
• Figure no. 1 schematically shows a device for performing rotating bending fatigue test under rotation.
• Figure 2 shows the clamping jaws, where the tangent to the longitudinal axis of the specimen at the clamping point is perpendicular to the face of the clamping jaw, and
• Figure 3 schematically shows the specimen with a clamping angle of, for example, 90°.
• Figure 4 shows the geometry of the wire, the clamping jaws being at an angle of 90°, the thick black solid line shows the clamped loaded test specimen, the solid grey line indicates the unloaded specimen, the dashed line indicates the collet axes, and the dashed line indicates the arc guides.
• Figure 5 shows a graph representing the stress according to the rotation of the specimen, where on the horizontal axis the angle of rotation of the specimen is plotted, on the vertical axis the tensile stress on the specimen surface is plotted and on the vertical axis on the right of the graph the magnitude of the force, where the thick black line indicates the stress on the inside of the specimen, the thick black dashed line indicates the stress on the outside of the specimen, the grey solid and dashed line shows the stresses on the sides and the grey dotted the line shows the magnitude of force on the sensor.
• Figure 6 shows a graph showing the values of stresses, forces and distances on the vertical axis, the size of the test radius on the horizontal axis, where the thick black line indicates the maximum stress, the thick black dashed line indicates the maximum force between the collets, the thin solid black line indicates the test length of the specimen, a thin dashed line indicates the pitch of the collets, and the dotted line indicates the curvature of the test length of the specimen.
• Figure 7 schematically shows a specimen with a clamping angle of, for example, 120° and in Figure 8 with a clamping angle of 180°, in Figure 9 with a clamping angle of 270°.
• Figure 10 shows the geometry of the wire, with the clamping jaws at an angle of 120°, the thick black solid line showing the clamped loaded test specimen, the solid grey line indicating the unloaded specimen, the dashed line the collet axes and the dashed line the arc guides.
• Figure 11 shows a graph representing the stress according to the rotation of the specimen, where on the horizontal axis the angle of rotation of the specimen is plotted, on the vertical axis the tensile stress on the surface of the specimen, and on the vertical axis on the right in the graph, the magnitude of the force between the jaws is plotted, where a thick black line indicates stress on the inside of the specimen, thick black dashed line indicates stress on the outside of the specimen, grey solid and dashed line shows stress on the sides and the grey dotted line shows the amount of force on the sensor.
• the method of performing rotating bending fatigue test based on the principle of computer-controlled cyclic loading consists in that into the jaws 2, 22, which are on the frame 1, a test specimen 3 is clamped to having an exemplary circular cross-section, in particular these are test specimens made of wires. Tangent of the longitudinal axis of the test specimen 3 at the clamping point it is coaxial with the axis of the clamping jaw 2, 2' and perpendicular to its face. The mutual angle of the vectors of the jaws 2, 2.' is 0-270°.
• the electric motors 4, 4' of the jaws are started, the rotation of which is synchronized with each other to minimize the torsional stress of the test specimen 3.
• the local values of this voltage then change according to the sine cycle with each revolution.
• test specimen 3 is stressed on the surface from the maximum tension to maximum pressure and is thus caused by cycles in the order of 10 3 to 10 9 .
• Data is recorded using a force sensor 5 which is connected to a computer on the actual values of the stresses on the surface of the test specimen 3.
• the refractive detection sensor 6 which is connected to the computer, the moment of destructive failure of the test specimen 3 is recorded and the electric motors 4, 4' providing the rotation drive are automatically stopped.
• the jaws 2, 2' are actively braked by means of the braking mechanism of the electric motor in order to prevent their rotation due to inertia.
• the method of performing a rotating bending fatigue test according to the invention is performed on a test specimen 3, which is defined by its cross-sectional diameter (wire diameter), production radius of the longitudinal axis (wire curvature) and modulus of elasticity, for example on a test specimen which is wire with a diameter of 0,55 mm, with a production radius of 200 mm and with a modulus of elasticity of 210 GPa.
• the production radius of the wire is the radius of the wire in the free unloaded state.
• test radius is calculated and then the appropriate angle of the jaws 2, 2' is determined according to the required test length and then the exact test length of the specimen 3 and the distance of the jaws 2, 2' are calculated to ensure even distribution of bending stress throughout test length of the specimen 3.
• the specified bending stress o for wire testing is 790,9 MPa.
• the amount of stress is chosen depending on the expected fatigue life.
• clamping geometries For the bending stress of 790,9 MPa selected above (corresponding to the test radius 115 mm), the following clamping geometries can be selected, for example, to achieve different test lengths:
• Table 1 shows the test parameters for a clamping angle of 90°, a jaw distance of 162,6 mm, a test length of 180,6 mm.
• Table 1 Example 2
• a test voltage of 636,1 MPa corresponding to a test radius of 150 mm is selected for a wire with a diameter of 0,55 mm, with a modulus of elasticity of 210 GPa and a production radius of 230 mm.
• a jaw angle of 120° is selected and a test length of 314,2 mm and a jaw distance of 259,8 mm are calculated, as shown in Figures 10, 11.
• Method of performing rotating bending fatigue test based on the principle of a computer-controlled cyclic loading and software evaluation of measured values, can be used in test laboratories and scientific institutions conducting destructive testing to obtain information about the mechanical properties of materials.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• General Health & Medical Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
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• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Engineering & Computer Science (AREA)
• Aviation & Aerospace Engineering (AREA)
• Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)

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• 2021
  • 2021-08-19 CZ CZ2023-320A patent/CZ2023320A3/cs unknown
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  • 2021-08-19 WO PCT/CZ2021/000041 patent/WO2022161555A1/en not_active Ceased
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