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
  • G01N3/32—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
  • G01N2203/0014—Type of force applied
  • G01N2203/0016—Tensile or compressive

Definitions

• the present invention relates to a method of determining the fatigue threshold value of a material, whereby a test specimen of the material which has a crack notch is subjected to a time dependent alternating load causing crack propagation which by a gradually decreasing load mean value is retarded and whereby it is ensured that the distance between two points, one on each side of the crack notch, alternates between two values.
• the invention also relates to a device for carrying out this method.
• a disadvantage of the method described in the essay is that the ratio between the minimum, P min , and the maximum, P max , values of the cyclic load variesduring the reduction, of the load, cf Fig 1a, which means that the measured threshold value will depend on said alternating ratio.
• the object of the present invention is to remove the above men tioned disadvantage when determining the fatigue threshold value of a material. This is carried out by the method and the device accounted for in the characteristic part of the appended claims.
• Fig 1a shows the course of a time dependent alternating load according to the initially mentioned essay.
• Fig 1b shows the output signal from a positioning gauge by which is detected the variation of the distance between two points one on each side of a crack notch (CGD) in a fatigue test specimen.
• Fig 1c depicts a time dependent alternating load according to the present invention.
• Fig 2 shows one embodiment of a conventional test specimen used in fatigue testing.
• Fig 3 shows schematically an arrangement for fatigue testing of a test specimen according to Fig 2.
• a test specimen according to Fig 2 is subjected to a time dependent alternating load P.
• the test specimen has a crack notch 1 which propagates on condition that the alternating load is of sufficient magnitude.
• the load P will decrease as shown in Fig 1a.
• the ratio P min /P max in the following designated as the R-value, alternates during the test as a conse ⁇ uence of the constant value of P min . This means that the threshold value will be determined for a final value of R which can not be predicted at the start of the fatigue test.
• the numeral 4 is a loading device by which a test specimen 5, of the same kind as the one shown in Fig 2, clamped in the loading device, is subjected to a time dependent alternating load P.
• the loading device 4 contains a load frame 7 and two jaws 8, 9 for clamping of the test specimen 5.
• the upper jaw 8 is via a load transducer 10 connected to a spindle 11 threaded into the load frame.
• the spindle 11 has a hand wheel 12 by which the distance between the jaws can be adjusted.
• the lower jaw 9 is connected to item 13 which is slidably mounted in the load frame 7 and operatively connected 'to a hydraulic cylinder unit 14, shown dashed in the figure where as well the piston-rod 15 of the unit is shown.
• the control system 6 contains two calculation loops, one of which has the task of producing a signal corresponding to the instantaneous P min -value of the load.
• the other is arranged to produce a control signal for controlling the hydraulic cylinder unit 14 with regard to the instantaneous P max - and P min -values of the load.
• the first mentioned calculation loop consists of a calculation unit 16 connected to a manually adjustable set point unit 17 for setting a predetermined R-value, and the previously mentioned load transducer 10.
• the other calculation loop consists of a control unit 18 connected to the hydraulic cylinder unit 14.
• To the control unit are connected the computation unit 16, a set point unit 19 for manual adjustment of P max and a positioning gauge 20 arranged to the test specimen.
• the positioning gauge 20 may be optical or mechanical and serves to produce a signal corresponding to the change in the distance (CGD) between the points 2, 3 in Fig 2.
• the set point units 16 and 19 are manually preset to given values of E and P max respectively.
• the signals from the load transducer are manually preset to given values of E and P max respectively.
• the control unit 18 produces a signal which causes the hydraulic cylinder unit 14 to subject the test specimen to a load which changes according to the control signal .
• the ratio between the minimum and maximum value of the load will thus be kept constant and equal to the preset R-value.
• the maximum and minimum values of the load are made to assume such values that the distance (CGD) between the points 2, 3 is kept constant in spite of the crack propagation.

Landscapes

• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
• Metal Rolling (AREA)
• Burglar Alarm Systems (AREA)

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• 1978
  • 1978-08-30 SE SE7809119A patent/SE413438B/sv not_active IP Right Cessation
• 1979
  • 1979-08-28 WO PCT/SE1979/000176 patent/WO1980000493A1/en unknown
  • 1979-08-28 DE DE792953044T patent/DE2953044T1/de active Granted
  • 1979-08-28 GB GB8027584A patent/GB2050630B/en not_active Expired
  • 1979-08-29 NO NO792806A patent/NO144940C/no unknown
• 1980
  • 1980-03-25 EP EP79901048A patent/EP0016205A1/en not_active Withdrawn

Non-Patent Citations (1)

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