Hardening of a dual-cure resin cement using QTH and LED curing units

Objective: This study evaluated the surface hardness of a resin cement (RelyX ARC) photoactivated through indirect composite resin (Cristobal) disks of different thicknesses using either a light- emitting diode (LED) or quartz tungsten halogen (QTH) light source. Material and Methods: Eighteen resin cement specimens were prepared and divided into 6 groups according to the type of curing unit and the thickness of resin disks interposed between the cement surface and light source. Three indentations (50 g for 15 s) were performed on the top and bottom surface of each specimen and a mean Vickers hardness number (VHN) was calculated for each specimen. The data were analyzed using two-way ANOVA and Tukey-Kramer test was used for post-hoc pairwise comparisons. Results: Increased indirect resin disk thickness resulted in decreased mean VHN values. Mean VHN values for the top surfaces of the resin cement specimens ranged from 23.2 to 46.1 (QTH) and 32.3 to 41.7 (LED). The LED curing light source produced higher hardness values compared to the QTH light source for 2- and 3-mm-thick indirect resin disks. The differences were clinically, but not statistically significant. Increased indirect resin disk thickness also resulted in decreased mean VHN values for the bottom surfaces of the resin cement: 5.8 to 19.1 (QTH) and 7.5 to 32.0 (LED). For the bottom surfaces, a statistically significant interaction was also found between the type of curing light source and the indirect resin disk thickness. Conclusions: Mean surface hardness values of resin cement specimens decreased with the increase of indirect resin disk thickness. The LED curing light source generally produced higher surface hardness values.

Optimization procedures in the design of continuous induction hardening and tempering installations for magnetic steel bars

An inverse problem concerning the industrial process of steel bars hardening and tempering is considered. The associated optimization problem is formulated in terms of membership functions and, for the sake of comparison, also in terms of quadratic residuals; both geometric and electromagnetic design variables have been considered. The numerical solution is achieved by coupling a finite difference procedure for the calculation of the electromagnetic and thermal fields to a deterministic strategy of minimization based on modified Flctcher and Reeves method. © 1998 IEEE.

Caracterização mecânica e microestrutural de aços Bake hardening graus 180 e 210 aplicados na indústria automotiva

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo do efeito bake hardening nos aços BH 180 e BH 220 galvanizados pelo processo de imersão a quente

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effects of substituting ytterbium for scandium on the microstructure and age-hardening behaviour of Al-Sc alloy

In order to reduce the cost of Al-Sc alloys and maintain their mechanical properties, the microstructure and mechanical properties of Al-0.24 wt% Sc-0.07 wt% Yb in comparison with Al-0.28 wt% Sc alloys were studied. The aging behaviour, precipitate morphologies, precipitate coarsening and precipitation hardening of both alloys were investigated. The average diameter and the size distribution of nanoscale Al3Sc and Al-3(Sc,Yb) precipitates at various aging conditions were measured. Transmission electron microscopy (TEM) and high-resolution TEM were used to deeply understand the precipitate evolution. A maximum hardness around 73 (HV30) was obtained with a precipitate diameter from 4.3 to 5.6 nm for both alloys. (c) 2014 Elsevier B.V. All rights reserved.

Effect of beam hardening on arterial enhancement in thoracoabdominal CT angiography with increasing patient size: an in vitro and in vivo study

To assess the effect of beam hardening on arterial enhancement in thoracoabdominal computed tomographic (CT) angiography in various body sizes in a phantom and in a clinical study.

The Age-Hardening of Duralumin

The development of wrought alloys of aluminum to which high strength and ductility can be imparted by heat treatment began with the work of Wilm and Claesser in Germany, 1905­-1911. During this time an alloy was developed which was later commercially produced in that country under the tradename of duralumin. The need for strong, light alloys for aircraft during the World War greatly hastened the development of duralumin.

Age Hardening of Silver-Platinum Alloys

The alloy system selected for study was the binary alloy of platinum and silver. An examination of the various silver alloy diagrams revealed that of several possible alloys, the silver platinum was the most suit­able with regard to solubility.

The Age Hardening of Copper with Manganese Silicide.

The increase in hardness is attributed to the manganese silicide being precipitated from solid solution and deposited between crystal planes. The subsequent softening which occurs on prolonging the period of reheating is believed to be due to an agglomeration of the dispersed hardening agent.

The Age Hardening of Silver with Copper-Silicide

The successful application of the phenomenon of pre­cipitation hardening to aluminum and copper has indicated the possibility of hardening all metals in the same way. The phenomenon of age hardening was discoveredin 1911, and since that time much research has been car­ried on in all parts of the world on various alloy sys­tems.

The Age-Hardening of Magnesium with Aluminum and Zinc

Magnesium is one of the most active elements and forms oxides, nitrides, and carbides, but not hydrides. Due to its activity, low melting point, low strength when unalloyed, and the difficulty with which it is worked, magnesium has not been and is not at present well developed.

The Age-Hardening of Aluminum with MgZn2

The purpose of this thesis is to investigate the age-hardening of aluminum with magnesium and zinc in such proportions as to conform to the compound MgZn2. Because of a lack of time and proper equipment, the only property investigated was the hardness as indicated by the Rockwell Superficial Hardness Tester.

An Experimental Investigation of the Age Hardening of Copper with Manganese Silicide

The subject of the thesis was based upon the theory of precipitation or age hardening of the copper by the compound formed by the Manganese and silicon present in the ternary Cu-Mn-Si alloy. The effect of the heat treat­ment to such an alloy was to be studied and the best aging time and temperature was to be determined.

An Experimental Investigation of the Age Hardening of Nickel with Boron

Since 1911, at which time, the age hardening phenomenon of duralumin was discovered by Film, much re­search has been carried on investigating the various alloy systems. The successful application of age hardening to the copper aluminum system (duralumin) has indicated the possibility of hardening practically all the metals in the same way.

An Investigation of the Age-Hardening of Copper with Nickel-Boron Compounds

Boron is an element whose metallurgical possibil­ities have never been fully investigated. The principal reason for this fact seems to lie in the difficulties encountered in preparing elemental boron and its various intermetallic compounds.