SU1640586A1 - Method for determination of material damage under creep - Google Patents

Abstract

The invention hasas fatigue testing of materials and structural elements. The aim of the invention is to improve the accuracy of determination of material damage during creep by taking into account the effect of damage kinetics. During testing, a batch of samples is loaded with a constant load, sustained until failure, the fracture time is measured for several fixed stress levels. long-term damage to the material is judged under stress conditions. After this, an additional sample, identical to the samples of the lot, is subjected to instantaneous stretching, the instantaneous strain and strain corresponding to the ultimate strength are measured, the integral parameter is determined, taking into account the instantaneous damage to the material, and the dependence of the damage kinetics on stresses, until the moment of destruction. The total damage to the material is determined taking into account the long-term and instantaneous damage 4 or

Description

The invention relates to tests for creep and long-term strength of materials and structural elements.

The aim of the invention is to improve the accuracy of creep damage determination by taking into account the effect of stresses on the damage kinetics.

FIG. 1 is a diagram of instantaneous stretching; FIG. 2 - kinetic dependence of damage; in fig. 3 - dependence of damage accumulation, in FIG. 4 - results of comparison with experiment calculations of durability under two-stage loading.

The proposed method is as follows.

A batch of samples from the test material is alternately secured in the grippers of the testing machine, heated, loaded with a constant time load, o. held until failure, and the failure time TRI (t,) is measured for several fixed stress levels (i 1, n). The results of long-term durability tests are approximated straight in the logarithmic coordinate system, and the parameter m, the angle of inclination of this straight to the IgtR axis, is determined and, using the value of t, the value of long-term damage is found. In addition, a sample of the material is subjected to instantaneous stretching, an instantaneous strain Ј0, corresponding to a stress a, is measured, a strain, t B, corresponding to the tensile strength, is measured and, depending on

AI s4gs- v 81 + 82

ABOUT

1 o ate

00

about

tnte

/ p (e) de-f p (e)

° Јв

KB

j (e) de

determine the value of A (a) instantaneous work done by the stress a on deformation Јv. Here, Si and S2 are the areas of the areas under the instantaneous stretching diagram (Fig. 1).

From instantaneous and temporary damaged balance conditions ™

()) + A) 1 (2) (Fig. 2), taking into account the equation

,) 1 i + m + W ((7)

(3)

damage accumulation determines the value of the integral parameter Q (0), which takes into account the amount of instantaneous damage to the material from the applied load

but"

From relations (3) and (4), we find the magnitude of the damage accumulated in the material during time t under the action of voltage a. When switching from a lower voltage to a larger total durability will be less than one (Fig. 3), when switching from a higher voltage to a smaller total durability becomes greater than one, which indicates the dependence of damage accumulation on the prehistory of loading.

When implementing the method, the tests were carried out at a temperature of 750 ° C on samples made of alloy EI437B. Two programs of stepwise change of loads (Fig. 4) were implemented: with additional loading (300-400 MPa) and partial unloading (400 -300 MPa).

Using the proposed method

allows to increase the accuracy of damage assessment under creep conditions under both stationary and non-stationary loading conditions. and on this basis calculate the creep strain given

the third stage, when there is an intense accumulation of damage and a change in voltage.

Claims (1)

Claim Method for Determining Damage material during creep, which consists in loading alternately a batch of specimens to destruction, varying from specimen to specimen, but with constant loads, measured for each the stress of the sample at the time of destruction and the time from the beginning of loading to its destruction and by the ratio of the temporal characteristics of the stress state is judged on the long-term damage to the material, which is characterized by the fact that. in order to increase accuracy by taking into account the effect of stresses on the kinetics of damage, an additional sample identical to a batch sample is subjected to an instantaneous tensile strain, the instantaneous strain corresponding to the instantaneous tensile stress is measured, and the strain corresponding to the tensile strength is determined by the instantaneous damage, which is the amount of instantaneous work performed by the instantaneous tensile strain on the strain corresponding to the tensile strength, and, compared the magnitude of the instantaneous and long-term damage, judged on the damage to the material. Fig- / qi L BUT / about Fig 2 1 t About 0.2 Oft- 06 06 1.0 12 Figz tl t, ODI