Mehmet Rusen Gecit

Fracture of a surface layer bonded to a half space

Abstract The plane problem of a cracked elastic surface layer bonded to an elastic half space is considered. The surface layer is assumed to contain a transverse crack whose surface is subjected to uniform compression. The problem is formulated in terms of a singular integral equation, the derivative of the crack surface displacement being the density function. By using appropriate quadrature formulas, the integral equation reduces to a system of linear algebraic equations. This system is solved; the stress intensity factors and the crack surface displacement for various crack geometries, namely for internal crack, edge crack, crack touching the interface, and completely broken layer cases, are obtained.

Axisymmetric contact problem for a semiinfinite cylinder and a half space

Abstract This paper is concerned with the elastostatic contact problem of a semi-infinite cylinder compressed against a half space. It is assumed that the contact between the cylinder and the half space is frictionless and that only compressive normal tractions can be transmitted through the interface. The problem is reduced to a system of singular integral equations of the second kind using the transform technique. The order of stress singularity at the corner is determined and the integral equations are solved numerically. Numerical results for contact pressure, stress intensity factor and interface slope are given in graphical form for various material pairs.

Axisymmetric contact problem for an elastic layer and an elastic foundation

Abstract This paper is concerned with the axisymmetric problem of an elastic layer lying on a semi-infinite foundation. The layer is pressed against the foundation by a uniform clamping pressure applied over its entire surface and a uniform vertical body force due to the effect of gravity. In addition, an axisymmetric vertical line load is applied to the layer. It is assumed that the contact between the layer and the foundation is frictionless and that only compresive normal tractions can be transmitted through the interface. The contact along the interface will be continuous if the value of the line load is less than a critical value. However, interface separation takes place if it exceeds this critical value. The problem is formulated and solved for the cases of tensile and compressive line loads. Numerical results for contact stress distributions are given for different material combinations.

The axisymmetric double contact problem for a frictionless elastic layer indented by an elastic cylinder

Abstract This paper is concerned with the smooth receding contact between an elastic layer and a half space when the layer is compressed by a frictionless semi-infinite elastic cylinder. Upon loading, the contact along the layer-subspace interface shrinks to a circular area, radius of which is unknown. The analysis leads to a system of singular integral equations of the second kind. The integral equations are solved numerically and the contact pressures, extent of contact and the stress intensity factor round the edge of the cylinder are calculated for various material combinations.

Biomechanical and histological outcome of combined raloxifene–estrogen therapy on skeletal and reproductive tissues

Estrogen replacement is a potent therapy for postmenopausal osteoporosis. However, its carcinogenic effects on breasts and the uterus limit its utilization. Raloxifene has estrogen-like effects on bones without the carcinogenic symptoms on breast or uterine tissue. Their individual effects are well characterized, but the results of their interaction remains elusive. In this work, we investigate the consequences of a combined raloxifene/estrogen therapy on bone and uterus with experimental osteoporosis. 40 Wistar rats began treatment 3 months post-ovariectomy. Estrogen and raloxifene were administered 0.03 mg/kg/day and 1.5mg/kg/day separately and together for 5 times per week for 12 weeks. Biomechanical tests and bone mineral density measurements, histology of uterus, and blood markers were analyzed. The co-administration group had higher toughness and ultimate strength than the ovariectomized controls (P<0.01). E+R had better biomechanical properties than the single treatments; yet the differences were not significant. Uterus histology signified high degeneration in the estrogen group. The raloxifene group had less degeneration but higher vascularization. Less immune reaction and vascularization were observed in the group with combined dosage than in those with individual treatments. Hence, the uterus of the combined treatment had fewer side effects than the ones that were individually treated. Mutual antagonization might be possible between raloxifene and estrogen, and that might have caused a decrease in the adverse effects. Overall, combined therapy might be useful to minimize the individual side effects of raloxifene and estrogen on the uterus and still provide bone strength and toughness.

Extension of a finite strip bonded to a rigid support

This paper considers the elastostatic plane problem of a finite strip. One end of the strip is perfectly bonded to a rigid support while the other is under the action of a uniform tensile load. Solution for the finite strip is obtained by considering an infinite strip containing a transverse rigid inclusion at the middle and two symmetrically located transverse cracks. The distance between the two cracks is equal to twice the length of the finite strip. In the limiting case when the rigid inclusion and the cracks approach the sides of the infinite strip, the region between one crack and the rigid inclusion becomes equivalent to the finite strip. Formulation of the problem is reduced to a system of three singular integral equations using the Fourier transforms. Numerical results for stresses and stress intensity factors are given in graphical form.

Prospective evaluation of Vitamin K2, Raloxifene and their co-administration in osteoporotic rats

In this study, therapeutic effects of Vitamin K2, Raloxifene and their co-administration on bone, uterus, blood and weight profiles were investigated with an ovariectomized rat model. Forty Wistar rats were divided into five groups (n=8): Raloxifene (R), Vitamin K2 (K), Raloxifene+Vitamin K2 (R+K), ovariectomized controls (OVX) and Sham-operated controls (Sham). Treatment began 3 months after ovariectomy. Vitamin K2 and Raloxifene were administered 30 and 1.5 mg/kg/day separately and in combination five times per week for 12 weeks. All treatment groups had significantly higher ultimate strength and energy absorption capacity (P<0.05) than ovariectomized controls in both femur and tibia. Histological results showed that treatment groups had healthy lumen structure, whereas OVX had degeneration. Adverse effects which were seen in individual treatments (myometrium weakening in K, endometrium weakening in R, and ALP increase in group R) were not observed in the R+K group implying a synergistic effect of these two agents when they are co-administered. According to blood analysis, ALP values were significantly high in Raloxifene-only group (P<0.0001). This effect is suppressed in the co-administered group. In summary, the groups R, K and R+K had significantly higher ultimate strength and less susceptibility to fracture than ovariectomized controls. In summation, Vitamin K2 treated groups (either in single or combined with Raloxifene) had considerable biomechanical performance and reproductive tissue profile indicating that this agent is prospectively effective in osteoporosis management.

Axisymmetric pull-off test for a cracked adhesive layer

This paper is concerned with the elastostatic axisymmetric problem for an elastic incompressible adhesive layer bonded to a rigid substrate along its lower surface. An upward tensile force is applied to the upper surface of the adhesive layer through a rigid cylinder. The adhesive layer contains a penny-shaped crack parallel to its lateral surfaces. Solution of the governing equations of linear elasticity is obtained through the use of Hankel transforms. Due to the presence of the crack, the adhesive layer is treated as being composed of two sublayers for which the solutions are matched at the plane of the crack. The mixed boundary conditions of the problem lead the analysis to a system of four singular integral equations for cylinder-layer interface stresses and crack surface displacement derivatives. These integral equestions are solved numerically and the interface stress distributions, stress intensity factors at the crack tip and around the edge of the cylinder, probable cleavage angle, and the strai...

Pull-off test for a cracked layer bonded to a rigid foundation

Abstract This paper is concerned with the plane strain problem of an elastic incompressible layer bonded to a rigid foundation. An upward tensile force is applied to the top surface of the layer through a rigid strip of finite thickness. The layer contains either a finite central crack or two semi-infinite external cracks. The analysis leads to a system of singular integral equations. These integral equations are solved numerically and the interface stress distributions, stress intensity factors at the crack tips and at the corners of the rigid strip, probable cleavage angle for the finite crack and strain energy release rate are calculated for various geometries.

Bending of a semi-infinite elastic strip bonded to an infinite strip

Abstract This paper considers the elastostatic plane problem of a semi-infinite strip bonded to an infinite strip along its short end and subjected to a bending moment at its far end. The infinite strip is bonded to a rigid substrate along its entire lower side. Solution for the semi-infinite strip is obtained by the superposition of a simple bending solution due to the load at infinity and a residual solution. The residual solution is obtained by a further superposition of Fourier transform solutions for an infinite strip and an antisymmetric half plane. Formulation of the problem is reduced to a system of three singular integral equations of the second kind. These integral equations are solved numerically and the interface stress distributions and the stress intensity factors at the corners are calculated for various geometries and material combinations. Numerical results are presented in graphical form.