Wedging of an edge crack in the elastic wedge

We study the problem of wedging of an elastic wedge realized along the edge crack with the help of a hard wedge. The analytic solution of the problem is obtained by the Wiener–Hopf method. We determine the stress intensity factors, the distributions of stresses on the continuation of the crack and in the contact zone, and the circular displacements of the crack lips.     

The influence of porosity on the fatigue crack growth behavior of Ti–6Al–4V laser welds

The effect of porosity––a common welding defect––on the fatigue crack growth rate (FCGR) in Ti–6Al–4V laser welds was investigated. The experimental results reveal that porosity was present in partial penetration welds over a narrow fusion zone (FZ) with martensite structure. The FCGR of the FZ was lower than that of the base plate. The fracture surface morphology of weld metal was much rougher as compared to that of the base plate. Randomly oriented martensite in the FZ led to local cleavage fracture along a preferred plane, thus, altering the crack growth direction significantly out of the primary crack plane. The zigzag crack path in the FZ resulted in a reduced FCGR at a given ΔK compared to the base plate. Besides, the porous weld showed a serration on the crack growth curve, and behaved the similar crack growth characteristics as the defect free one. SEM fractography revealed that the deflection of crack path around porosity together with local notch blunting as the crack tip pierced into porosity, balanced the increased FCGR for the occurrence of instant crack advance as the crack front reached the porosity at a low stress ratio. In contrast, the serration and drop in FCGR occurred sparingly at a high stress ratio as the crack front met the porosity.     

Bending of a plate containing a periodic system of collinear cracks with regard for the contact of crack lips

We study the process of bending of a plate weakened by a periodic system of collinear cracks with regard for the contact of crack lips. The stress-strain state of the plate is found by the method of solution of the problems of linear conjugation from the theory of functions of complex variable. It is shown that if the crack lips are in contact over a part of the thickness of the plate, then the intensity factors of forces decrease and the intensity factors of moments increase as compared with the case of contact of the crack lips along the line of intersection with the surface. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 2, pp. 46–52, March–April, 2008.     

Prediction of the temperature dependence of fracture toughness of 12Cr–2Ni–Mo refractory steel

We study the influence of temperature and the size of the specimens on the characteristics of static crack resistance of 12Cr–2Ni–Mo refractory steel. It is shown that, in the temperature range 20–450°C, the increase in the thickness of specimens leads to an insignificant increase in fracture toughness obtained along a 5% secant line according to the standards of evaluation of the characteristics of crack resistance. The evaluation of the characteristics of crack resistance of 12Cr–2Ni–Mo steel with regard for the scale effect according to an earlier developed numerical-experimental model reveals the existence of satisfactory agreement with the experimental data in the entire investigated temperature range. Translated from Problemy Prochnosti, No. 4, pp. 78–88, July–August, 2009.     

Shear stress intensity factor near semi-infinite cylindrical crack edges under their shock loading

The discontinuous solution of the torsional vibration equation for an elastic medium with a flaw in the form of a semi-infinite cylindrical crack is constructed. The method of solving the integro-differential equation describing the distribution of shear stresses along the edges of a cylindrical crack is presented. The evaluation procedure for a stress intensity factor and its numerical calculation for the case of short times under the shock loading of cylindrical crack edges are given. It is established that the magnitude of a dynamic stress intensity factor can be used to determine the condition of shock wave interactions with structural heterogeneities at the high-rate deformation of treated surfaces containing flaws in the form of cylindrical cracks. Translated from Problemy Prochnosti, No. 3, pp 63–72, May–June, 1999.     

Correlation of a plastic zone length near the tip of a mode I crack in an orthotropic material with anisotropy parameters

We derived equations that relate the length of a plastic zone near a mode I crack tip in a plate made of an orthotropic material with yield strength levels in the direction of the anisotropy axes. The case of crack orientation along one of the anisotropy axes is examined, with the latter being determined by the strain hardening of a material at the stage preceding the crack nucleation. The growth of yield strength along the axes lying in the plane of the plate is shown to result in smaller sizes of the plastic zone. An increase in yield strength in the direction of the normal to the above plane leads to an increase in its length. Ukrainian Regional Research and Design Institute of Civil Engineering, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 32–37, July–August, 1999.     

Investigation of the initiation of corrosion cracks in the cladding layer of a bimetal

We describe a specially-designed installation for the corrosion testing of bimetals, study the effect of the state of the surface of the cladding layer of a bimetal on the initiation of corrosion cracks, investigate the influence of the disclocation structure on the processes of pitting and crack initiation, analyze distinctive features of the process of propagation of corrosion cracks in the cladding layer along the interface of the metals, and suggest a method for the protection of two-layer structures against corrosion cracking by polishing and etching with aqua regia. NIIKHIMMASH, Severodonetsk. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 1, pp. 107–110, January–February, 1997.     

On the static equilibrium of an elastic orthotropic medium with an arbitrarily oriented elliptical crack

We analyze the problem of the stress distribution in an elastic orthotropic medium with an arbitrarily oriented elliptical crack. To construct the problem solution, the Willis approach is used which is based on the triple Fourier transformation of spatial variables and Fourier-image of Green’s function for an infinite anisotropic space. The investigation results in special cases are compared with the data of other authors. The effect of the elliptical crack orientation in an orthotropic space on the distribution of the stress intensity factors along its contour is studied. __________ Translated from Problemy Prochnosti, No. 4, pp. 146–159, July–August, 2007.     

Contact Interaction of Crack Lips in Shallow Shells in Bending with Tension

In the two-dimensional statement, we consider a problem of bending and tension of a shallow cracked shell. The effect of crack closure caused by bending is described within the framework of the classical theory of shells according to the model of contact of crack lips along a line in the face surface. We study the influence of contact interaction of crack lips and surface curvature on the stressed state and limiting equilibrium of cylindrical and spherical shells. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 4, pp. 45–52, July–August, 2005.     

Assessment of the crack resistance of multiple-seated lock joints of gas turbine blades

We present results of assessing the crack resistance of three-seat lock joint of gas turbine blade under low-cycle fatigue and creep conditions of material in the presence of a hypothetical crack. The stress intensity factor is calculated by the finite element method. __________ Translated from Problemy Prochnosti, No. 5, pp. 89–95, September–October, 2008.     

Closure of a Longitudinal Crack in a Shallow Cylindrical Shell in Bending

We study the two-dimensional problem of contact interaction of the lips of a longitudinal crack in a cylindrical shell subjected to bending under the assumption of contact along a line. The influence of the surface curvature and crack closure on the stressed state and limiting equilibrium of the shell is analyzed. The numerical results are compared with the asymptotic solution of the problem. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 2, pp. 45–48, March–April, 2005.     

Plastic zone near the crack tip in a material with strain anisotropy caused by loading along spatial rectilinear trajectories

The equation of the boundary of the plastic zone near the tip of a mode I crack is deduced for the case of a plate made of a material with strain anisotropy. It is assumed that the anisotropy is caused by hardening in the process of plastic deformation performed prior to the appearance of the crack under loading along arbitrary rectilinear trajectories in the space of the stress tensor. An analysis of this equation demonstrates that the main factors affecting the shape and size of the plastic zone are the level of plastic strains accumulated in the process of preloading, their sign, and the orientation of the crack relative to the axes of anisotropy. Translated from Problemy Prochnosti, No. 6, pp. 21–27, November–December, 1997.     

Analysis of the electromagnetic field perturbed by a subsurface crack in a half space

The rigorous method of integral equations is used to study the field of a longitudinal crack located in a conducting half space. The results of evaluation of the electric and magnetic components of the perturbed field are presented for different locations of the crack. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 69–74, September–October, 2006.     

‘Pressurized’ Mode III Crack in an Elastic Perfectly Plastic Solid

This paper presents the solution for the elastic plastic boundary of a fully ‘pressurized’ mode III crack in an elastic perfectly plastic solid. By fully ‘pressurized’ (in analogy to an internally pressurized mode I crack) is meant that the crack faces are subjected to an externally applied (shear) stress equal to the (shear) yield stress. The dislocations in stress space method is used to find the solution. At the crack plane a plastic zone for the fully pressurized crack extends out a distance 0.273 a from a crack tip, where a is the half width of the crack. (The comparable distance found from a Bilby–Cottrell–Swinden crack is 0.414 a.) The plastic zones originating at the two crack tips merge, in a point, at the center of the crack. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Meshless Cohesive Segments Method for Crack Initiation and Propagation in Composites

A modeling method aimed at eliminating the need of explicit crack representation in bi-dimensional structures is presented for the simulation of the initiation and subsequent propagation within composite materials. This is achieved by combining a meshless method with a physical stress–displacement based criterion known as Cohesive Model. This model consents to apply a penalty-based approach to delamination modeling where a variable penalty factor along the crack segment allows to loosen or tight the two parts according to their relative displacements. Results are showed for classical single mode loading benchmark cases and compared to experimental results taken from the literature.     

Fracture analysis in 2D magneto–electro–elastic media by the boundary element method

An integral formulation for 2D cracked infinite anisotropic magneto–electro–elastic media is presented. Based on the method proposed by Garcia-Sanchez et al. (Comput Struct 83: 804–820, 2005), the hypersingular kernels are analytically transformed into weakly singular and regular integrals with known analytical solution. Special quadratic discontinuous crack tip elements are employed to model the singular characteristics of the stresses, electric displacements and magnetic inductions. The extended stress intensity factors at the crack tips are calculated using the extended discontinuous displacements at crack tip elements based on one point extended displacement formulation. Some results for curved cracks in magneto–electro–elastic media are also presented.     

Transformation toughening in the γ-TiAl–β-Ti–Vsystem: Part II A molecular dynamics study

Molecular dynamics simulations of the evolution of materials in a region surrounding a crack tip were carried out for the case of a crack in a γ-TiAl phase impinging at a right angle onto the interface between a γ-TiAl phase and a metastable Ti–15V (at %) phase. The corresponding linear anisotropic solutions for the singular stress and displacement fields were used to both generate the crack in the original crystal and to prescribe the boundary conditions applied to the computational crystal during the molecular dynamics simulation runs. The atomic interactions were accounted for using appropriated embedded atom method (EAM) type interatomic potentials. The crack-tip behaviour for the two-phase γ–β material was ultimately compared with the one in the corresponding single-phase material, i.e. to the one in pure γ and the one in pure β crystals. The simulation results showed that under the same applied level of external stress, the crack tip became blunt and the crack stopped propagating in the γ-TiAl–β-Ti–15V bicrystal and in the single β-phase crystal while the crack extended by brittle cleavage in the single-phase γ crystal. The blunting process was found to be controlled by the martensitic transformation that took place in the β-phase ahead of the crack tip. Depending on the local stress conditions the crystal structure of martensite was found to be either hexagonal close packed (h.c.p.), body centred orthorhombic (b.c.o.) and/or face centred orthorhombic (f.c.o.). Finally the implications of crack tip martensitic transformation on the toughness of the materials are analysed in quantitative terms using the concept of Eshelby's conservation integral, i.e. the energy release rate. This revised version was published online in November 2006 with corrections to the Cover Date.     

To the theory of cutting quasibrittle materials

We analyze the relationship between cutting forces and fracture toughness of a brittle material under several simplifying assumptions. A numerical method was used to evaluate the influence of the length of a crack in front of the cutter on the cutting force under the condition of stable growth of the crack. It is shown that the model of cutting proposed by Cherepanov gives satisfactory results in estimating the maximum cutting force. Translated from Problemy Prochnosti, No. 5, pp. 30–34, September–October, 1997.     

Influence of the modes of operation and structural factors on the crack propagation in 12Cr–2Ni–Mo steel

We study the influence of temperature, specimen sizes, loading frequency, and the time of holding under long-term static loading on the crack growth rate in 12Cr–2Ni–Mo steel. It is shown that the influence of these factors on the crack growth rate is insignificant. A numerical-experimental model is proposed for the evaluation of the time of subcritical crack growth with regard for the duration and cyclic character of loading. Translated from Problemy Prochnosti, No. 3, pp. 66–77, May–June, 2009.