Hvozdiuk M. Development of the method for assessing fracture resistance of composite materials

Thesis covers the problem of assessing the limiting-equilibrium state and fracture resistance of anisotropic materials, weakened by cracks. The energy criterion for evaluation of the limiting equilibrium of thin-walled composites with a notch based on the balance of energies of elasto-plastic deformations and fracture of material was formulated. The equations for evaluation of the critical value of loading and the equations for finding the direction of the initial crack start form the criterion basis. The methods and technical means for evaluation of the technical characteristics of fracture toughness of different types of composites under static loading are developed. A new approach to determination of the elasto-plastic displacements at the notch tip using the method of speckl images digital correlation of the deformed surface of a plane composite specimen under tension is proposed. The investigation method and technical means for determining the crack growth resistance characteristics of thin-walled composites with surface defects that propagate along the material thickness are developed. The optimal thickness and the volume content of the reinforcement of structural layers of a three-layered plastic glass pipeline was established. The strength and crack growth resistance of boron aluminium were investigated. The optimal annealing temperature of Al-B composite that leads to its higher strength and fracture toughness was evaluated. The influence of corrosive environment on the crack growth resistance of boron aluminium is shown. The method of the cracked composite beams strengthening used for reinforcement of iron-concrete beams of flights with high-strength carbon plastic strips during bridge passage reconstruction is proposed.