Application of the ultrasound control to evaluation of the crack-resistance of low-carbon martensite steel 07Kh3GNMYuA

2021 ◽  
Vol 87 (1) ◽  
pp. 45-51
Author(s):  
R. A. Vorob’ev ◽  
V. N. Litovchenko
Keyword(s):  
Heat Treatment ◽  
Stress Intensity ◽  
Crack Resistance ◽  
Critical Stress ◽  
Mechanical Characteristics ◽  
Intensity Coefficient ◽  
Acoustic Characteristics ◽  
Stress Intensity Coefficient ◽  
The Impact

The goal of the study is to reveal the impact of change in the structural state of steel 07Kh3GNMYuA after heat treatment on the values of the critical stress intensity coefficient (K1c) obtained at a temperature of 50°C and on the velocity of ultrasound wave propagation, as well as to determine a correlation between them for rapid assessment of the crack resistance using acoustic characteristics. The mechanical characteristics of the material and the critical stress intensity coefficient K1c were obtained on the test machine «Inspekt 100 Table». The tangent method is used for determination of K1c. Three samples per K1c value were used in the experiment for a three-point bending scheme at the operating temperature T = –50°C. Acoustic parameters were measured using the echo-pulse method. The results of ultrasonic scanning of heat-strengthened samples made of steel 07Kh3GNMYuA demonstrated the possibility of non-destructive quantitative evaluation of the critical stress intensity coefficient. New data on the mechanical properties of steel 07Kh3GNMYuA and on the correlation between the velocity of longitudinal elastic waves and the values of the critical stress intensity coefficient of structures were obtained. Deviation of the calculated values of K1c obtained using acoustic measurements from the experimental values does not exceed 10%. The proposed model, which explains change in the acoustic characteristics of steel 07Kh3GNMYuA on the basis of phase changes occurring in the steel structure upon tempering, provides conducting of similar studies for other modes of heat treatment and other steel grades. The method is a low labor- and time-consuming procedure for determination of the mechanical characteristics of the products made of steel 07Kh3GNMYuA, since it does not require the manufacturing of samples and their testing. The developed procedure can be proposed for manufacturing application, as the main or additional method for evaluation of the mechanical parameters of materials after various modes of heat treatment.

scholarly journals A PROBABLISTIC APPROACH TO EVALUATION OF THE ULTIMATE LOAD ON FLEXURAL RC ELEMENT ON CRACK LENGTH

2020 ◽  
Vol 16 (1) ◽  
pp. 98-105
Author(s):  
Sergey Solovyev
Keyword(s):  
Reinforced Concrete ◽  
Stress Intensity ◽  
Crack Length ◽  
Reliability Analysis ◽  
Critical Stress ◽  
Probabilistic Approach ◽  
Structural Elements ◽  
Intensity Coefficient ◽  
Stress Intensity Coefficient ◽  
Concrete Elements

The fracture mechanics of concrete and reinforced concrete is a promising direction in the development of methods for reinforced concrete structural elements design and inspection. At the same time, probabilistic methods of design and behavior analysis of structural elements are of particular interest. The article describes a probabilistic approach to load-bearing capacity and reliability analysis of flexural reinforced concrete elements based on the crack length criterion. The functional relationship between the critical stress intensity coefficient of concrete and the design compressive strength of concrete is given. The article presents a method for the reliability analysis of flexural reinforced concrete elements at the operational stage with limited statistical data about the critical stress intensity coefficient of concrete. The ultimate value of the failure probability (or reliability index) should be set for each object individually based on the value of the acceptable risk.

RELIABILITY ANALYSIS OF REINFORCED CONCRETE FLEXURAL ELEMENT ON CRACKING BASED ON FRACTURE MECHANICS

2020 ◽  
pp. 40-44
Author(s):  
S. A. Solov’ev ◽  
O. V. Yarygina
Keyword(s):  
Compressive Strength ◽  
Reinforced Concrete ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Reliability Analysis ◽  
Critical Stress ◽  
Intensity Coefficient ◽  
Concrete Compressive Strength ◽  
Concrete Element ◽  
Stress Intensity Coefficient

The article describes a probabilistic approach to the reliability analysis of a flexural reinforced concrete element by the cracking criterion using the provisions of fracture mechanics. Two mathematical models of limit state are proposed for reliability analysis: with the evaluation of the critical stress intensity coefficient directly and through the design concrete compressive strength. On the basis of regression analysis, the relationship between the critical stress intensity coefficient and the design concrete compressive strength is established which can be used in the inspection of reinforced concrete structural elements. The influence of the design concrete compressive strength on the failure (cracking) probability of the flexural reinforced concrete element is analyzed. The numerical example of reliability analysis is given for the reinforced concrete beam by the criterion of cracking. It is noted that the required level of reliability should be set for each structural object individually based on the acceptable risk value using economic and non-economic losses.

Crack Resistance Increase of Bushings while Assembling Joints with Tension

2021 ◽  
Vol 313 ◽  
pp. 22-30
Author(s):  
S.D. Popov ◽  
G.V. Redreev ◽  
A.N. Sorokin ◽  
A.V. Shimokhin ◽  
V.M. Pomogaev
Keyword(s):  
Stress Intensity ◽  
Crack Resistance ◽  
Outer Diameter ◽  
Intensity Coefficient ◽  
Repair Work ◽  
Stress Intensity Coefficient ◽  
Force Criterion ◽  
Urgent Task ◽  
The Press ◽  
Full Scale Tests

In order to restore worn parts during repair work, it is often used to press the repair bushings. While assembling joints, cracks may form in the spanning part (bushing), as it may have surface and structure defects. Therefore, an urgent task is to increase the crack resistance of joints with tension during its assembly. The paper examines the influence of the geometry of the spanning part on the process of cracking. To assess the effect of defects on the crack formation, the method of modeling defects with a surface crack of a semi elliptical shape was used. The crack resistance is estimated using the force criterion of fracture mechanics – the stress intensity coefficient. As a result, it was found that the ratio between the wall thickness of the enclosing sleeve and its outer diameter has a significant effect on the crack resistance of the joint with tension, which allows reducing the origin probability and crack development during its pressing by varying these parameters. While assembling joints, the following methods are often used: mechanical-using a press and thermal with heating of the covering part. When the method of joint with cooling of the covered part, the greatest strength of the joint is achieved, but the probability of cracking increases. This is because when the temperature of the enclosing sleeve decreases in contact with the cooled shaft, the critical stress intensity coefficient (fracture toughness), which is a mechanical characteristic of crack resistance, decreases. To reduce the effect of cooling the sleeve, you can use a combined method of assembling the joint, in which the covered part is cooled and the covering part is heated. It is shown that to assess the fracture resistance at low temperatures, it is optimal to conduct full-scale tests, where the cooling and heating temperatures of the press joint parts are the experimental factors.

Critical Stress Intensity Coefficient at Transverse Shear for Nanofibrobeton

2021 ◽  
pp. 41-47
Author(s):  
E.A. SADOVSKAYA ◽  
E.N. POLONINA ◽  
S.N. LEONOVICH ◽  
S.A. ZHDANOK ◽  
V.V. POTAPOV
Keyword(s):  
Stress Intensity ◽  
Transverse Shear ◽  
Critical Stress ◽  
Intensity Coefficient ◽  
Stress Intensity Coefficient

Study on the Effects of Heat Treatments on the Physical and Mechanical Characteristics of 1.4301 Stainless Steel

2021 ◽  
Vol 42 ◽  
pp. 57-62
Author(s):  
Maria Stoicănescu
Keyword(s):  
Heat Treatment ◽  
Stainless Steel ◽  
Stainless Steels ◽  
Mechanical Characteristics ◽  
Austenitic Stainless Steels ◽  
Heat Treatments ◽  
Hot Plastic Deformation ◽  
Improved Characteristics ◽  
Physical And Mechanical Characteristics

The 1.4301 stainless steel is part of the category of austenitic stainless steels, steels which do no undergo heat treatments in general, as they are intended for hot plastic deformation in particular. The aim of the research presented in this paper was to obtain significantly improved characteristics of the resistance properties in relation to the values obtained under classical conditions, by applying heat treatments. Samples taken from the delivery state material underwent annealing, quenching and ageing heat treatments. Subsequently, the samples thus treated were subjected to tests enabling the determination of the correlations between the heat treatment parameters, the structure and the properties.

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