Физико-механические основы прочности и разрушения

Тема 1. Physical and mechanical fundamentals of strength and fracture of solids. History of knowledge development about the strength and fracture of deformable solids. Metals and nonmetals. Crystal structure of metals, imperfections of the crystal lattice, general properties of dislocations. Changes of structure at elastic macrostrain. Mechanisms of the development of brittle fracture during loading process on different structural-scale levels. Physical micromechanisms (slip and twinning) of viscous microcracks. Structural aspects of the strength of metals and non-metals (amorphous materials, polymers, composite materials, ceramic materials etc.), nanomaterials (thin filaments, films, graphene layers). General information about the physical fracture models such as structural, statistical, energy models. Statement of the main problems of the strength of materials and structural elements: 1 - analysis of external influences and determination of stress- strain
states, II - selection and justification of theories of strength, rigidity and stability, III - justification and purpose of safety margins, rigidity and stability, IV - a comprehensive definition of strength, stiffness and stability. Basic definitions and relationships Material Resistance.
Тема 2. Experimental mechanics of the destruction of solids. Durability of materials under cyclic loading under uniaxial stress and torsion conditions. Static strength tests of materials. Fragile destruction. Viscous fracture with the formation of a neck when tensile plastic materials. Durability of the material; wear, fatigue, corrosion, creep. Destruction under creep conditions (high-temperature creep, diffusion creep), staged creep process. Curves of long-term strength of materials. Basic concepts of material fatigue. Fatigue tests of materials, fatigue curves and durability of the final fracture of a material: low-cycle, limited, multi-cycle and gigacyclic fatigue, endurance, Wehler curve, symmetric and asymmetric loading and deformation cycles. The concept of the probability of failure, the normal distribution of durability, Weibull’s fatigue curves. Brittle fatigue. Four stages of the brittle fatigue. Lines of irreversible damage (French lines). Ductile fatigue. Low cycle fatigue, cyclic hardening and softening. Constitutive laws at low cyclic fatigue. The effect of variable temperature fields on the material fatigue. Dependence of fatigue on the frequency and asymmetry of a cycle under uniaxial cyclic loading. The concept of the dynamic strength of solids. Failure of solids under special conditions: cold brittleness, corrosion, hydrogen brittleness, rock failure processes in the problem of earthquakes.
Тема 3. Classical strength theories. Hypotheses of maximum normal stresses, maximum tangential stresses, maximum stress intensity, maximum principal strain, maximum shear strain. Hypothesis of Mor's Strength. Energy criterion of strength. Examples.
Тема 4. Fracture physical models (structural, statistical, energy models). Thermofluctuation theory of strength.
Тема 5. Hypotheses of damage accumulations. Damage tensor and A.A.Il’yshin’s theory of long-term strength. Damage operator. The hypothesis of linear and nonlinear damage summation for uniaxial loading processes. Kinetic concept of damage description by Yu. Rabotnov, V. Bolotin and L. Kachanov.
Тема 6. Fundamentals of the theory of failure loading processes at complex stress state. Generalization of classical strength theories.
Тема 7. The basis of fracture mechanics. Stress state of an elastic body with a crack. Stress intensity factor and methods of its calculation. Experimental definition of crack resistance. Brittle fracture criteria. A. Griffith’s energy criterion. Elasto-plastic failure. Plastic zone in the vicinity of mcrocrack top. Strain fracture criterion. On variational methods in the fracture mechanics of elastoplastic bodies. Rice-Cherepanov’s J-integral. Creep cracks. Crack Fatigue. Fatigue kinetic diagram. Paris equation of fatigue crack growth. On the fracture of nonmetallic with cracks (viscoelas-tic bodies, composites). On the fracture of glass and ice. About dynamic problems of fracture mechanics.
Тема 8. Strength of structural elements. Inhomogeneous stress state, stress concentration. Types of designs. Evaluation of the structure strength at the design stage. The concept of structural elements. Types of elements. Strength characteristics of structural elements. Strength evaluation at cyclic loading, resource (durability) at long-term loading, reliability of structural elements, survivability of structural elements. The influence of manufacturing techniques, structure and surface condition on the strength properties of structural elements. Geometric stress concentrators. Stress concentration factors. Corrosion damage. The concept of safety factor for durability of elements. Substantiation and purpose of safety margins, rigidity and stability. Different diagnostic methods for the appearance and growing of defects and cracks in structural elements, concepts of nonfracture testing methods, ultrasonic, magnetic, radiation, electronic flaw detection, acoustic emission method. Verification calculation of structural elements strength.
Problems of safety and risks.