Page 8 - dyser_Stankevych

8

the stages and mechanisms of fracture and estimation of degradation degree of structural

materials under the influence of the various physical factors.

At the base of the developed in the dissertation methodology of the solids fracture

diagnostics and their state estimation by the energy parameters of the AE signals are the

following scientific results.

A general analytical solution of the problem of elastic waves propagation initiated

by the displacement of the opposite surfaces of the penny-shaped cracks relative to their

center in a three-layer composite structure is constructed using the boundary integral

equations method.

The problem for three typical partial cases of multilayered composites (“la-

yer+halfspace with crack”, “layer+layer with crack”, “layer+layer+halfspace with

crack”) was solved numerically. It assisted to study the dynamics of wave processes on

the composite surface and to create the preconditions for efficient use of the elastic

wave’s parameters during the TD of products and elements of structures.

The displacement fields on the surface of multilayered composites depend on the

elastic characteristics and geometric dimensions of their components, the frequency of

displacement of the crack surfaces, the distance from the observation point to the fractu-

re epicenter and the depth of the crack in the composite. Taking into account of these

dependencies makes it possible to determine the features of fracture in the composite

and to create new methods of AE-diagnostics of products and structural elements.

A new method of local features estimation of AE signals is developed, which is

based on the determination of the energy parameters of the local maximums of the

signals continuous WT. It has been found out that the AE signal energy parameter, its

frequency and duration of radiation of are enough informative characteristics to identify
types and mechanisms of the signal generation.

A new energy criterion for quantitative estimation of the materials macrofracture
types based on the energy parameter of WT of AE signals has been constructed. So, the

AE signals with energy parameter E WT  , 0 01 correspond to the ductile fracture, with

energy parameter ,0 01 E WT  1 , 0 – to the ductile-brittle (microcracking) and with