Search results for "Shear"
showing 10 items of 804 documents
Shear bond strength of one-step self-etch adhesives to dentin: Evaluation of NaOCl pretreatment
2018
Background The aim of this study was to evaluate the influence of dentin pretreatment with NaOCl on shear bond strength of four one-step self-etch adhesives with different pH values. Material and methods Bovine permanent incisors were used. Four one-step self-etch adhesives were tested: Adper™ Easy Bond, Futurabond NR, G-aenial Bond, Clearfil S3 Bond. One two-step self-etch adhesive (Clearfil SE Bond) was used as control. Group 1- no pretreatment; group 2- pretratment with 5,25 % NaOCl; group 3- pretreatment with 37 % H3PO4 etching and 5,25 % NaOCl. A hybrid composite resin was inserted into the dentin surface. The specimens were tested in a universal testing machine. The examiners evaluate…
Microleakage and shear bond strength of orthodontc brackets bonded to hypomineralized enamel following different surface preparations
2014
Objectives: This study investigated the effects of several conditioning methods on shear bond strength (SBS) and microleakage of orthodontic brackets bonded to demineralized enamel. Study Design: One hundred premolars were selected and immersed in a cariogenic solution for 12 weeks. The teeth were randomly assigned into 5 groups. In groups 1 and 2, the teeth underwent acid etching for 30 and 120 seconds, respectively. In group 3, a combination of laser and acid etching was employed. A self-etch primer (SEP) was applied in group 4 and in group 5, the teeth were exposed to acidulated phosphate fluoride (APF) for 4 minutes before etching. After bracket bonding, the teeth were immersed in methy…
Fatigue fracture plane under Multiaxial Random Loadings - prediction by variance of equivalent stress based on the maximum shear and normal stresses
1992
It is assumed that the plane in which the maximum variance of the equivalent stress appears is critical for a material and the fatigue fracture should be expected in this plane. The equivalent stress is calculated according to the fatigue criterion of maximum shear and normal stresses in the fracture plane. It was demonstrated that for each stationary random stress state there is one or more critical planes where the fatigue fracture plane can be expected. The variance method together with the discussed fatigue criterion give good results for three analysed types of carbon steels under multiaxial cyclic loadings.
ESTIMATED AND EXPERIMENTAL FATIGUE LIVES OF 30CrNiMo8 STEEL UNDER IN-AND OUT-OF-PHASE COMBINED BENDING AND TORSION WITH VARIABLE AMPLITUDES
2007
Abstract— Calculated fatigue lives, based on three criteria for multiaxial random fatigue, were compared with lives obtained from tests on cylindrical specimens of 30CrNiMo8 steel subjected to in- and out-of-phase bending and torsion at variable amplitudes. In the chosen fatigue criteria the expected position of the fracture plane, determined from a variance method for the equivalent stress, were taken into account. The equivalent stress history was related to the rain flow method and fatigue damage was evaluated from the Palmgren–Miner hypothesis. It has been shown that the expected fatigue fracture planes agree with those determined by experiments. The most realistic estimations of fatigu…
Fatigue life estimation for 30CrNiMo8 steel under in- and out-of-phase combined bending and torsion with variable amplitudes
1996
Fatigue life successively calculated according to three criteria of multiaxial fatigue for randomly varying loading is compared with fatigue life obtained by Sanetra and Zenner in testing cylindrical specimens of 30CrNiMo8 steel by in- and out-of-phase bending and torsion with variable amplitudes. The position of the plane of fatigue fracture is determined using the variance method. The histories of equivalent stresses are schematically represented by the Monte Carlo method. Fatigue damage was computed using the Palmgren-Miner hypothesis. The most realistic estimates of fatigue life in the scatter band of the results with a factor of 3 are obtained on the basis of the criterion of maximum t…
Viscoelastic properties of concentrated dispersions in water of soy lecithin
2003
Abstract Viscoelastic properties of soy lecithin dispersions at 60, 120, 180 and 240 g l−1 in water have been studied as a function of ionic strength (NaCl concentrations in the range 10−5–10−2 mol l−1) and of preparation method (sonication, freezing–unfreezing). Viscosity measurements of sonicated dispersions in a rotatory viscometer show Newtonian and plastic (Bingham) behavior, whereas the frozen–unfrozen dispersions show a spectacular change in their viscoelastic properties, that is, a non-Newtonian behavior with pseudoplastic characteristics and rheopexy. These properties have been related to electrokinetic characteristics of the segregated vesicles in each case. A decrease in ζ-potent…
Shear Strength of a Compacted Scaly Clay from Suction-Controlled Triaxial Tests
2012
The paper presents the results of an experimental research aimed at investigating the shear strength characteristics of an unsaturated compacted scaly clay. Shear strength was investigated by suction-controlled triaxial compression tests on dynamically compacted samples. Collected results point out that suction effects on stiffness and shear strength can be very different for suction values applied lower or greater than air entry value (AEV), corresponding to the material void ratio.
Influence of delay between dental bleaching with 35% hydrogen peroxide and orthodontic brackets on the bond strength at the enamel/adhesive interface
2019
Background The aim of this study was to evaluate the influence of waiting time between the bleaching with 35% hydrogen peroxide and orthodontic brackets bonding on shear bond strength (SBS) in enamel. Material and Methods Eighty bovine teeth were randomly divided into four groups (G): G1(negative control) and G2, G3 and G4 (experimental groups). The experimental groups were submitted to bleaching. Prior to orthodontic brackets bonding to enamel the procedure was adopted different waiting times, as follows: G2 (1 day); G3 (7 days) and G4 (14 days). It was performed enamel etching (30s), washing water (30s), application of adhesive system followed by photoactivation (20s). A thin layer of com…
Symplectic analysis of thin-walled curved box girders with torsion, distortion and shear lag warping effects
2022
Shear lag effect and torsional and distortional warping can significantly affect the performance of thin-walled curved box girders used in modern bridge engineering. The structural behaviour of these bridges exhibits complexity due to coupled bending and torsion together with warping effects of non-uniform torsion, distortion and shear lag. A practical method of analysis, based on the symplectic approach, with the same perspective as the Higher Order Beam Theories, is presented for overcoming the difficulties of numerical approaches via the Finite Element Method. In this paper, the Hamiltonian Structural Analysis method implements the analysis of the shear lag effect together with non-unifo…
Numerical and experimental investigation of a cross-flow water turbine
2016
ABSTRACTA numerical and experimental study was carried out for validation of a previously proposed design criterion for a cross-flow turbine and a new semi-empirical formula linking inlet velocity to inlet pressure. An experimental test stand was designed to conduct a series of experiments and to measure the efficiency of the turbine designed based on the proposed criterion. The experimental efficiency was compared to that from numerical simulations performed using a RANS model with a shear stress transport (SST) turbulence closure. The proposed semi-empirical velocity formula was also validated against the numerical solutions for cross-flow turbines with different geometries and boundary c…