PSI - Issue 13

V. Moskvichev / Procedia Structural Integrity 13 (2018) 2114–2119 V. Moskvichev / Structural Integrity Procedia 00 (2018) 000 – 000

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4

The general algorithm of calculations based on fracture mechanics and safety criteria includes the following stages: 1. Selection of the calculation scheme and cases to be analyzed.

2. Building up the database of calculation characteristics. 3. Determination of nominal and local stress-strain states. 4. Analysis of the conditions for the onset of the limit state. 5. Choice of the failure criterion. 6. Analysis of the strength, crack resistance, resource and safety conditions.

7. Determination of a system of safety factors for loads, stresses, deformations; for fracture toughness characteristics; for the defect size; for the durability and residual lifetime; for the brittleness temperature.

4. Examples of applied problems

Based on the fracture mechanics methods and criteria, reliability theory and risk analysis using equations (1-4) and the above algorithm, a number of applied problems has been solved. 1. Design of welded structures (Fig. 2). To solve problems of the service life design of welded joints, a method of statistical testing has been developed. The method is based on application the defect kinetic equations coupled with numerical calculations of stress-strain state and probabilistic models of defects, loading and the fracture toughness. This allows to obtain: - reliability functions of welded joints in the presence of different types of weld defects; - probabilistic diagrams of the residual life linking the number of loading cycles, loading level and the probability of safe life; - probabilistic diagrams of the service life allowing to estimate the influence of loading level, defect size, component thickness and operational temperature. Results of deterministic and probabilistic modeling of the crack growth kinetics have led to the development of a method to evaluate the safe residual life of CTS structures in the form of the equation (4) [4, 5]. Evolution of the probabilistic fracture mechanics approaches and the reliability theory have given a tool for the probabilistic risk analysis of structures including estimation of the risk function (3) [2]. The algorithm includes - analysis of stress-strain state of a structure; - modeling of a potential fracture zone considering a possible limit state; - calculation of the fracture probability.

Fig. 2. Design of welded structures

In solving problems of the risk analysis, an important role belongs to mathematical and numerical experiment. Methods and techniques mentioned above have been implemented evaluating parameters of reliability and risk of fracture for components of VVER-1000 reactor (Fig. 3, 4)