Cyclic stress-strain data analysis under biaxial tensile stress state

A new device was developed to assess fatigue life under biaxial tensile loading at elevated temperatures. It makes use of an annular disk specimen and can be easily mounted onto a standard push-pull machine so that the axial force is converted into radial forces extending across the disk specimen. Therefore, a positive ratio of the tangential to the radial stress can be imposed at the reduced section of the disk specimen; this ratio depends on the specimen configuration and may be fixed to a value ranging from 0.5 to 0.9 by varying the inner diameter of the disk. The proposed device has performed successfully and was used to study the cyclic behavior of Type-304 stainless steel subjected to various biaxial tensile stress states at room temperature and at 200°C. The data obtained from this experimental procedure have been analyzed to evaluate the effectiveness of some correlations already available for treating the biaxial cyclic stress-strain response in terms of the uniaxial behavior. This analysis shows that a successful correlation should account for all the stress components. The authors discuss the concept used in the modeling of the material cyclic behavior and the formulation of a biaxial fatigue damage parameter necessary for an effective analytical life prediction methodology.     

Delayed fracture of an isotropic viscoelastic material with a crack under cyclic loading

The delayed fracture of an isotropic viscoelastic plate is examined as a process involving the subcritical propagation of a straight normal-rupture crack during fatigue loading. Calculations are based on the modified {ie165-1} of fracture, it being assumed that the size of the prefracture zone ahead of the moving crack remains constant. This zone is also assumed to be small compared to the size of the crack itself. Solutions for a time-dependent crack length are given both for media which undergo quasi-viscous flow (an integral operator with an Abelian kernel is used) and for media whose creep curves have a horizontal asymptote (an integral operator with a kernel in the form of the fractional-exponential function of Yu. N. Rabotnov is used). S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 35, No. 2, pp. 60–64, February, 1999.     

Delayed fracture of a transversally isotropic viscoelastic material with a crack under a cyclic load

The delayed fracture of a transversally isotropic viscoelastic material due to slow subcritical growth of a flat circular macrocrack of normal separation under a cyclic load is investigated. The analysis is based on the modified δC of fracture and the hypothesis of the constancy of the prefracture zone. The study is made within the framework of the Boltzmann-Volterra theory for bounded resolvent operators of difference type, which describe the transversal isotropy of the strain properties of the material. To determine the analytic form of the kernel for the irrational function of a linear combination of the above-mentioned integral operators, the method of continued fractions is used. Analytical and numerical calculations are carried out for the bounded resolvent operators of difference type with the kernel in the form of Rabotnov's fractional exponential function. S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 36, No. 1, pp. 123–129, January, 2000.     

On the precession of a standing wave in a string with fixed ends

Nonlinear differential equations of motion of a string are derived. In the single-mode approximation, the evolution of a transverse standing wave is studied. The dependence of the precession velocity and the correction to the vibration frequency on the semiaxes of the ellipse along which the string midpoint moves is determined.     

Forced axisymmetric vibrations of a thick circular rigidly fixed piezoceramic plate

A new closed-form solution of the axisymmetric nonstationary problem of elasticity is constructed for a circular thick piezoceramic plate whose outer cylindrical surface is rigidly fixed. The use of mixed boundary conditions for a curvilinear plane allows one to obtain sufficiently simple computational relations. The closed-form solution is constructed by the method of expansion in the vector eigenfunctions in the form of a structure algorithm of finite transformations. The obtained solutions are used to determine the natural vibration frequency, the stress-strain state of the considered element, and all characteristics of the induced electric field.     

The stress-strain state of a plate with a multilayer inclusion

A modified boundary-element method is proposed to analyze the stress-strain state of a plate with a multilayer inclusion of arbitrary shape. The two-dimensional approximation of displacements on each boundary element makes it possible to determine all the stress/strain components at the interface between the inclusion and each layer. The stress state of a plate with an elliptical and a rectangular multilayer inclusion under unidirectional tension (a load uniformly distributed along the edges) is analyzed as numerical examples. The numerical examples demonstrate high accuracy and computational efficiency of the method __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 3, pp. 104–110, March 2007. For the centenary of the birth of G. N. Savin.     

Determination of the stress-strain state of shells of revolution under localized effects

S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 31, No. 3, pp. 50–55, March, 1995.     

On the stress-strain state of a transversally isotropic body with a paraboloidal inclusion

A closed solution is presented for the three-dimensional problem of the stress-strain state of an unbounded elastic body with a soldered-in transversally isotropic inclusion in the form of a paraboloid of revolution. Here, it is assumed that the body is under axisymmetric tension (compression). A solution of the corresponding problem for a paraboloidal recess is obtained as a special case. Podil’chuk [2, 3] has investigated similar problems for isotropic bodies with an inclusion assuming the form of a paraboloid of revolution or an elliptical paraboloid. Translated from Prikladnaya Mekhanika, Vol. 34, No. 11, pp. 16–22, November, 1998.