Strength of Materials, Vol. 39, No. 3, 2007 KINETICS OF SCATTERED FRACTURE IN STRUCTURAL METALS UNDER ELASTOPLASTIC DEFORMATION N. I. Bobyr’, A. P. Grabovskii, A. P. Khalimon, UDC 539.4 A. V. Timoshenko, and A. N. Maslo The paper presents a procedure whereby the damage accumulation kinetics in structural materials, such as steel 45, stainless steel 12Kh18N10T, aluminum alloy D16T, and titanium alloy VT22, under elastoplastic deformation is studied based on variation parameters of elastic modulus and resistivity. For complex stress conditions, a continuum model for damage accumulation is proposed which relates the damage parameter to the intensity of accumulated plastic strains. The data calculated by the proposed continuum model are compared to the experimental findings of the investigation of the damage accumulation kinetics for some structural metals. Keywords: damage accumulation, elastic modulus, resistivity, continuum model for damage accumulation. Introduction. In structural materials the nucleation of microvoids and microcracks, their subsequent growth and coalescence give rise to macrocracks which would ultimately result in failure of the materials. On the microstructural level, the initiation of microflaws affects the material’s physical-mechanical properties, such as elastic modulus, density, hardness, resistivity, etc. [1, 2]. This in turn impairs the structure’s ability to resist operational loads. The above-mentioned changes in physical-mechanical properties of a material are indicators of its degradation; this feature can be used to come up with a convenient experimental procedure for measuring the damage accumulation in a material’s structure. In doing so, the critical value of damage is considered as an important fracture parameter, which forms the basis for the development of a theoretical approach to predicting the fracture stage. The objective of the present wok has been to compare two experimental methods of determination of damage in structural materials: (I) by changes in resistivity and elastic modulus in a material under static deformation and (ii) based on a phenomenological model for damage accumulation, the parameters of which are determined by macroexperiments. Definition of Damage. According to the basic tenets of the continuum damage mechanics, a scalar parameter of damage D in a material under elastoplastic deformation is given by [1, 3] D S S D i = , (1) where S i is the current cross-sectional area and S D is the total area of microvoids and microcracks. The effective stress ~ σ corresponds to a damaged material’s cross-sectional area which effectively takes a load F [3], ~ , σ σ = - = - F S S D i D 1 (2) where σ is the actual stress in a deformed material. 0039–2316/07/3903–0237 © 2007 Springer Science + Business Media, Inc. 237 National Technical University of Ukraine “Kiev Polytechnic Institute,” Kiev, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 23 – 34, May – June, 2007. Original article submitted April 25, 2006.