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A B S T R A C T The model of a crack with a process zone is considered and generalized to orthotropic materials. It is assumed that a material in the process zone satisfies a strength condition of arbitrary form. Based on the crack model, the fracture of an orthotropic cracked plate under biaxial loading is studied. The crack is directed along one of the anisotropy axes with external loads being applied in parallel and perpendicularly to it. The influence of the biaxiality of external loading on the critical state of the cracked plate is analysed within the framework of the critical crack opening displacement and critical J-integral criteria. Numerical solution is obtained using the Mises-Hill and Gol'denblat-Kopnov strength criteria. Theoretical results are compared with experimental data obtained by testing specimens made of structural metals.Keywords biaxial loading; crack model; fracture; orthotropic plate; process zone. N O M E N C L A T U R E a ij= elastic constants d = process zone length E i = elastic moduli along the orhotropy axes F = function of a strength criterion G 12 = shear modulus J = J-integral J c = critical value of J-integral K I = stress intensity factor for the mode I crack l = half-crack length L = length of half-crack with a process zone p * , q * = ultimate loads p (0) * = ultimate load in uniaxial tension p (m) * = ultimate load for macrocrack S i = roots of a characteristic equation T 0 = function of elastic constants v = displacement of a cracked body β i = imaginary part of roots of a characteristic equation β = β 1 /β 2 δ = crack opening displacement δ c = critical value of crack opening displacement ν 12 = Poisson's ratio σ 0x , σ 0y = ultimate strengths in the x and y axis directions, respectively σ s 0x , σ s 0y = ultimate strengths in tension along the x-and y-axis σ p 0x , σ p 0y = ultimate strengths in compression along the x-and y-axis Correspondence: A. A. Kaminsky.

A modified Dugdale model is used to study the fracture of an orthotropic elastoplastic plate with a periodic system of rectilinear cracks. The material of the plate obeys a general yield criterion. The general form of solution is obtained in terms of Kolosov-Muskhelishvili potentials. The size of the plastic zone is expressed in terms of the external load and geometrical parameters. The equations for the determination of the stresses in the plastic zone and the crack opening displacement are derived. The effect of anisotropy on the formation of the plastic zones at the crack tip is examined Keywords: fracture, periodic system of cracks, orthotropic material, plastic zone, plane stress state 1063-7095/07/4305-0539