Evaluation of self-etching primer on bond strength in feldspathic ceramic

The aim of the study was to evaluate the effect of self-etching silane primer on long-term bonding strength on feldspathic ceramic. Ceramic blocks (IPS Empress CAD, Ivoclar Vivadent) were cut with a low-speed diamond disk (Isomet 1000, Buehler) into 40 blocks of 12x7x6mm, under water cooling, and randomly divided into two groups (n=20), according to the surface conditioning: hydrofluoric acid (HF) (Condac, FGM) or self-etching silane primer (MEP) (Monobond Etch and Prime, Ivoclar Vivadent). After the blocks were bonded to composite resin blocks (12 x 7 x 3mm) (Liss, FGM) with a light cured cement (Variolink Esthetic LC, Ivoclar Vivadent) and LED photoactivation (Radii Cal, SDI) for 40 s on each luting interface line. The sets were cut in sticks with 1-mm2 cross-section composed of ceramic/cement/composite and tested after 24h (baseline) and 90 days aging by stored in distilled water at 37ºC. Microtensile bond strength testing (mTBS) was performed using a universal machine (DL-1000, EMIC) submitted to traction with speed of 0.5mm/ min until rupture of adhesion. Fracture of specimens were examined under stereomicroscopy to determine the failure pattern. Bond strength (MPa) was calculated, and the failure pattern and interface topography were assessed using scanning electron microscopy (SEM). No significant different mTBS was observed between groups HF and MEP (p>0.05). Storage time of the samples did not affect the mTBS from the groups. Surface etching pattern with HF produced higher surface alterations than a self-etching primer. Application of MEP may be considered an alternative for silanization for feldspathic ceramic.

Stressed state of two-layer strip when interacting with rigid base

Relevance. In the calculation of multilayer bases, when the material of one or several layers has a pronounced anisotropy, the nature of the distribution of displacements and stresses depends on the direction of the anisotropy axes in each layer. Therefore, it is necessary to have an evaluation of the influence of this factor in the design and analysis of the operation of multilayer media. The aim of the work - to research the stress state in a strip composed of two anisotropic plane-parallel layers with different physical characteristics, lying without friction on a rigid base. Methods. The integration of the equations of the plane problem of the theory of elasticity of an anisotropic body is carried out by the symbolic method in combination with the method of initial functions. The initial functions on the contact line of the strip and the base are determined from the conditions of tight adhesion between the layers, the conditions of tight contact and the absence of friction between the strip and the base, the nature of the load applied to the upper plane of the strip. After transformations, the functions of displacements and stresses in each layer are written through the normal surface load in the form of improper integrals. Results. Plots of changes in stresses in the strip from the values of the characteristics of anisotropic materials, layer thicknesses are given. The maximum stresses on the interface line of the layers and on the line of contact with the base, depending on the direction of the anisotropy axes in each layer, are presented in the tables and shown in graphs. The effect of the elastic modules of materials on the nature of the stress distribution in a strip composed of two isotropic materials is estimated.

On the Interaction of Cracks and Stringers with a Heterogeneous Wedge-Shaped Body, Manufactured from Different Materials at an Antiplane Deformation

The problem of stress state of an elastic piecewise-homogeneous wedge-shaped body at an antiplane deformation, consisting of heterogeneous wedges with different shear modules and opening of apex angles is considered, when a system of arbitrary finite number of collinear cracks is located on the interface line of the heterogeneous materials and the boundary faces of the compound wedge are reinforced with stringers of finite lengths. The solution of the problem is reduced to solving a system of three singular integral equations (SIE) using the Mellin integral transform, which based on quadrature formulas Gauss for calculating SIE with Cauchy kernel and ordinary integrals reduces to a system of systems of linear algebraic equations (SLAE). As a result, the characteristics of the problem are expressed by explicit simple structures algebraic formulas.

A Cattaneo-Mindlin problem for a rigid punch with tangential load applied above the interface line

We study the contact between a rigid flat punch and an elastic half-space using Coulomb friction for a normal load followed by a tangential load applied at a certain height above the interface line. The study is inspired by recent experiments by the group of Jay Fineberg in Israel. Three regimes are found in the evolution of slip at the interface depending on a dimensionless parameter [Formula: see text] , the ratio between the halfwidth of the contact and the product of twice friction coefficient and height of the loading point. Normal pressure and shear tractions are plotted for each case. It is shown that the effect of height does not collapse the data, contrary to the experimental data of Fineberg’s setup. However, this is not surprising given the many deviations from the ideal configuration we have studied, namely the finite thickness of the bottom block, the presence of vertical surfaces on the upper block (both not permitting the assumption of halfspace elasticity) and finally local effects due to concentrated tangential load which give rise to local and not only global induced moment.

Microstructures and Properties of Ni25 and Fe304 Repairing Layers Prepared by Plasma Surfacing

Microstructures and properties of plasma surfaced Ni25 and Fe304 layers prepared on nodular cast iron substrate were investigated. The study showed that the interface boundary existed between the layers and substrate. Compared with typical microstructures of welded joint, the similar columnar grains in the layers perpendicular to the interface line were observed, which were hardly seen in the plasma sprayed coating. The conclusion could be drawn that the bonding between the Ni25 and Fe304 layers and nodular cast iron substrate belonged to the metallurgical cohesion. The XRD analysis showed that the metal compounds such as Ni4B3，Cr7BC4，γ-(Fe, Ni) and Cr7C3were found in the layers. The study demonstrated that the layers had proper strength and hardness to repair the surface defects of the nodular cast iron.

MICROSTRUCTURAL EFFECTS IN THE STEEL HWS 1.2379 APPLYING THE PROCESS OF PLASMA TRANSFERRED ARC PTA.

ABSTRACTAt present, the industrial sector requires the recovery of tool steel components subjected to severe wear which are built with steel HWS these have the same properties in all tribology directions and have great success in building tooling. In this paper, we recover the previously HWS steel machining with a fillet of 2mm caused by the metallurgical recovery of the component, applying the process of plasma transferred arc PTA which has very good fats dilution properties in comparison to other conventional processes currently applied for the recovery of tooling, such as GTAW, SMAW, SAW. The experiment was conducted with input D2 and M2 with one and two welding seams, making the assessment metallography, hardness and wear tests pin-on-disk. Finding a decrease in the hardness of the interface line, according to the evaluation of wear pin-on-disk, had a higher wear rate of the filler metal in the M2 D2.

Microstructures and Properties of Plasma Surfaced NiCrBSi+WC/Co Layers

Microstructures and properties of plasma surfaced NiCrBSi+20%WC/12Co layer prepared on the die steel (H13) substrate were investigated. The study showed that the interface boundary existed between the layer and substrate. Compared with the typical microstructures of welded joint, the similar columnar grains in the layer perpendicular to the interface line were observed, which were never seen in the plasma sprayed coating. The conclusion could be drawn that the bonding between the NiCrBSi+20%WC/12Co layer and H13 substrate belonged to the metallurgical cohesion. The XRD analysis showed that the main phases in the layer included γ-(Fe, Ni), Cr7BC4, Ni4B3, Cr7C3 and Co7W6, which brought higher strength and higher hardness to the surfaced layer than the H13 substrate.