RU2416086C1 - Method for determination of fatigue point of material - Google Patents

Abstract

FIELD: machine building. ^ SUBSTANCE: method for determination of fatigue point of material for symmetrical cycle of loading consists in loading sample of analysed material by extension with continuous rate of straining upon preliminary single unloading from value of load equal to (âm+âB)/2 to zero value, in measuring time of repeated loading to stress (âm+âB)/2 and time until physical fracture of a sample. On base of ratio â-1=te/tfâe there is evaluated the fatigue point. In ratio â-1 is fatigue point of material for symmetrical cycle of loading, te is time of development of elastic strain, tf is time to physical fracture of the sample, âe is stress of elastic strain development equal to (âm+âB)/2. ^ EFFECT: upgraded accuracy of tests and increased efficiency at determination of fatigue point â-1 for symmetrical cycle of loading of elastic-ductile material. ^ 1 tbl

Description

The invention relates to a testing technique, and in particular to methods for determining the endurance limit of a material.

A known method for determining the fatigue limit of a material [1], which consists in testing standard samples in tension with a constant strain rate. By recording chart pt (load - time of loading) was measured time t _y of elastic deformation and time t _a before the destruction of the sample, determine the limit of his strength σ _in the material, but the endurance limit σ _-1 is judged by the relation

σ _-1 = t _y / t _in σ _in

The disadvantage of this method is the need to obtain a strain diagram at the time of the test, as well as the difficulty of determining the plot of the diagram of elastic work of the material.

The technical task of the present invention is to increase the accuracy of tests and increase productivity in determining the endurance limit σ _-1 for a symmetric loading cycle of elastic plastic materials.

This object is achieved by loading a sample of the material by stretching at a constant strain rate after preliminary flash unloading a load value equal to half the sum (σ _r + σ _a) / 2, the material yield point (σ _m) and tensile strength of the material (σ _c) to zero values measured prior to loading the re-voltage (σ _r + σ _a) / 2 and the time until the physical destruction of the sample, but the endurance limit ratio judged by

σ _-1 = t _y / t _p σ _y

where σ _-1 is the material endurance limit for a symmetric loading cycle, t _y is the time of development of elastic deformation during repeated loading, t _p is the time to physical destruction of the sample during repeated loading, σ _y is the stress of development of elastic deformation during repeated loading, equal to (σ _t + σ _c ) / 2. The method is as follows.

3-6 standard samples are made from the test material. Loading samples of the test material is carried out by stretching on a machine of type P-20 with a constant strain rate. Initially loading the sample to produce a load equal to half the sum (σ _r + σ _a) / 2, the yield stress of the material (σ _r) and yield strength of the material (σ _c), whereupon its complete discharge to zero. Then the measured time t _y reloading of elastic deformation to the voltage _at σ = (σ _r + σ _a) / 2 and t _p the time until the physical destruction of the sample, but the endurance limit ratio judged by

σ _-1 = t _y / t _p σ _y

Example

Standard samples of various materials were tested. The samples were tested for rupture with a loading speed of 1.7 mm / min on a P-20 machine. The endurance limit was determined by symmetric bending on a machine such as MUI 6000. The results of the test of materials are shown in the table.

According to the test results, we can conclude that it is advisable to use this method, because there are few discrepancies between the experimental and reference data [2], and the time spent on determining the endurance limit is significantly reduced.

Material grade σ _t , MPa σ _in , MPa t _y / t _p σ _y , MPa σ _-1 Base of tests, cycles Proposed Standard Aluminum bronzes Bro.AJ9-4 340 510 0.43 425 182.8 185 10 ⁶ Bld.A5 490 810 0.21 650 136.5 134 2 × 10 ⁷ Deformable aluminum alloys AMg2M 90 180 0.89 135 120,2 120 5 × 10 ⁸ AK4-1 265 445 0.36 355 127.8 130 2 × 10 ⁷ Carbon steel Art 3 215-240 375-470 0.58 295-355 171.1-205.9 170-220 10 ⁷ 30g 315-320 555-700 0.57 435-510 248-290.7 220-320 10 ⁷ 30HGSA 843-1489 1107-1711 0.48 975-1600 468-768 480-700 10 ⁷

Literature

1. A.S. USSR No. SU 1665278 A1, G01N 3/32, publ. 07/23/91.

2. Reference on the resistance of materials / Pisarenko G.S., Yakovlev A.P., Matveev V.V .; Repl. ed. Pisarenko G.S. - 2nd ed., Revised. and add. - Kiev: Science. Dumka, 1988 .-- 736 p.

Claims (1)

A method for determining the material endurance limit for a symmetric loading cycle, namely, that the loading of a sample of the material under study is carried out by stretching with a constant strain rate and the time of development of elastic deformation and the time to physical destruction of the sample are measured, and the tensile strength of the sample is determined, and the endurance limit is judged taking into account the maximum load, characterized in that the loading of the sample of the investigated material is carried out by stretching after preliminary about dnokratnogo unloading a load value equal to half the sum (σ _r + σ _a) / 2, the yield stress of the material (σ _r) and yield strength of the material (σ _c) to zero, measured during repeated loading to the voltage (σ _r + σ _a) / 2 and the time to physical destruction of the sample, and the endurance limit is judged by the relation σ _-1 = t _y / t _p σ _y , where σ _-1 is the endurance limit of the material for a symmetric loading cycle, t _y is the time of development of elastic deformation, t _p - time to physical destruction of the sample under repeated loading, σ _y - voltage of elastically deformation under repeated loading equal to (σ _r + σ _a) / 2.