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Thermal Cycles (thermal + cycle)
Selected AbstractsMethodology for Thermomechanical Simulation and Validation of Mechanical Weld-Seam Properties,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Wolfgans Bleck A simulation and validation of the mechanical properties in submerged-arc-weld seams is presented, which combines numerical simulation of the thermal cycle in the weld using the SimWeld software with an annealing and testing procedure. The weld-seam geometry and thermal profile near the weld seam can be computed based on the simulation of an equivalent heat source describing the energy input and distribution in the weld seam. Defined temperature,time cycles are imposed on tensile specimens allowing for annealing experiments with fast cooling rates. The direct evaluation of welded structures and the simple generation of input data for mechanical simulations in FE software packages are possible. [source] Dynamic Self-Assembly of the Liquid-Crystalline Smectic,A Phase,ADVANCED MATERIALS, Issue 17 2005K. Prasad A photoinduced transition in an azobenzene-containing liquid crystal leads to a phase that does not exist in the thermal cycle. The smectic,A phase is induced and stabilized only in the presence of UV light, producing fan-shaped focal conic textures typical of the SmA phase, as observed by polarized-light microscopy (see Figure). This dynamic self-assembly is explained by photoinduced nanophase segregation and a frustrated spin-gas model. [source] Effect of three adhesive primers for a noble metal on the shear bond strengths of three resin cementsJOURNAL OF ORAL REHABILITATION, Issue 1 2001K. Yoshida The purpose of this study was to evaluate the durability and shear bond strengths of the different combinations of three adhesive primers and three resin cements to a silver,palladium,copper,gold (Ag,Pd,Cu,Au) alloy. The adhesive primers Alloy Primer® (AP), Metal PrimerII® (MPII) and Metaltite® (MT), and the resin cements BistiteII® (BRII), Panavia Fluoro Cement® (PFC) and Super-Bond C&B® (SB) were used. Two sizes of casting alloy disks were either non-primed or primed and cemented with each of the three resin cements. The specimens were stored in a 37 °C water bath for 24 h and then immersed alternately in 4 and 60 °C water baths for 1 min each for up to 100 000 thermal cycles. Shear mode testing at a crosshead speed of 0·5 mm/min was then performed. The application of MPII or MT was effective for improving the shear bond strength between each of the three resin cements and the Ag,Pd,Cu,Au alloy compared with non-primed specimens. However, when primed with MPII or MT and cemented with SB, the bond strength at 100 000 thermal cycles was significantly lower than that at thermal cycle 0. When primed with AP, the specimens cemented with BRII or PFC showed lower bond strength than non-primed specimens and failed at the metal,resin cement interface at 100 000 thermal cycles. On the other hand, AP was effective in enhancing the shear bond strength of SB to the Ag,Pd,Cu,Au alloy. The five combined uses of an adhesive metal primer and resin cement (combinations of MPII or MT and BRII or PFC and AP and SB) are applicable to the cementation of prosthodontic restorations without complicated surface modification of the noble alloy. [source] Influence of contamination on resin bond strength to nano-structured alumina-coated zirconia ceramicEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 4 2010Shanchuan Zhang Zhang S, Kocjan A, Lehmann F, Kosma, T, Kern M. Influence of contamination on resin bond strength to nano-structured alumina-coated zirconia ceramic. Eur J Oral Sci 2010; 118: 396,403. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci The purpose of this study was to evaluate the influence of contamination and subsequent cleaning on the bond strength and durability of an adhesive resin to nano-structured alumina-coated zirconia ceramic. Zirconia ceramic disks were coated with nano-structured alumina, utilizing the hydrolysis of aluminum nitride powder. After immersion in saliva or the use of a silicone disclosing agent, specimens were cleaned with phosphoric acid etching or with tap water rinsing only. Uncontaminated specimens served as controls. Plexiglas tubes filled with composite resin were bonded with a phosphate monomer [10-methacryloxydecyl-dihydrogenphosphate (MDP)]-containing resin (Panavia 21). Subgroups of eight specimens each were stored in distilled water at 37°C, either for 3 d without thermal cycling (TC) or for 150 d with 37,500 thermal cycles from 5 to 55°C. The tensile bond strength (TBS) was determined using a universal testing machine at a crosshead speed of 2 mm min,1. The topography of the debonded surface was scrutinized for fractographic features, utilizing both optical and scanning electron microscopy. The TBS to uncontaminated nano-structured alumina-coated zirconia ceramic was durable, while contamination significantly reduced the TBS. Phosphoric acid cleaning was effective in removal of saliva contamination from the coated bonding surface but was not effective in removal of the silicone disclosing agent. Nano-structured alumina coating improves resin bonding to zirconia ceramic and eliminates the need for air-abrasion before bonding. [source] Determination of elastic modulus of demineralized resin-infiltrated dentin by self-etch adhesivesEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2007Genta Yasuda The purpose of this study was to determine ultrasonically the changes in elastic modulus of demineralized adhesive-infiltrated dentin. Dentin disks were obtained from bovine incisors and shaped into a rectangular form. The specimens were immersed in single-step self-etch adhesives, then stored in distilled water and run through thermal cycles between 5 and 60°C. The longitudinal and shear wave sound velocities and the elastic modulus were determined using ultrasonic equipment composed of a pulser-receiver, transducers, and an oscilloscope. After 24 h of storage, the elastic modulus of mineralized dentin was 16.9 GPa and that of demineralized dentin was 2.1 GPa. The immersion of demineralized dentin in adhesives significantly increased the elastic modulus to 3.3,5.9 GPa. After 30,000 thermal cycles, the elastic modulus of dentin was 32.4 GPa, whereas that of demineralized adhesive infiltrated dentin was 3.1,4.1 GPa. Thermal stresses did not cause adhesive-infiltrated demineralized dentin to deteriorate, as measured by elastic modulus. [source] Diel variation in surface and subsurface microbial activity along a gradient of drying in an Australian sand-bed streamFRESHWATER BIOLOGY, Issue 10 2003Cecile Claret Summary 1. Microbes play key roles in nutrient transformation and organic matter mineralisation in the hyporheic zone but their short-term responses to diel variations in discharge and temperature are unknown. Rates of microbial esterase activity were hypothesised to vary vertically and along a gradient of moisture in a drying sand-bed stream where discharge fluctuated daily in response to evapotranspiration. 2. At ,fully saturated', ,moist' and ,dry' locations in three sites along a drying Australian sand-bed stream, microbial activity at three depths (surface, 10 and 30 cm) was assessed using fluorescein diacetate hydrolysis. Samples were collected in mid-summer in the late afternoon and again at dawn to assess diel variation in hydrolytic activity at each site and depth. Data loggers tracked diel variations in temperature at each depth. 3. Hydrolytic activity was up to 10-fold greater in the surface sediments in late afternoon than at dawn in all habitats, and was correlated with surface sediment temperature. Diel differences in activity were not detected at 10 cm, although daily thermal cycles were evident at this depth. Unexpectedly, activity was marginally higher at dawn at 30 cm in all habitats, perhaps reflecting lags in temperature at that depth. 4. Overall, microbial activity declined with depth, strongly correlated with vertical trends in total organic matter and concentrations of dissolved phosphorus. Particulate organic matter, probably buried during a flood 35 days earlier, appeared largely responsible for these vertical trends. On the other hand, there was little evidence for hydrological exchange between much of the hyporheic zone and the surface stream, implying that processes in the subsurface zone of this stream are effectively isolated during baseflow in mid-summer. 5. Diel cycles of wetting and drying in the moist habitats did not enhance esterase activity relative to the dry or fully saturated habitats. Sediment moisture was not correlated with microbial activity, and mats of senescent algae appeared to inhibit water loss from surface sediments in the moist habitat. In this sand-bed stream, local diel fluctuations in water level appear to have less influence on microbial activity and mineralisation of organic matter in the sediments than occasional floods that bury leaf litter and renew many hyporheic zone functions. Subreach-scale processes seem to be the major driving force of microbial processes and nutrient cycling in this sand-bed river. [source] Improvements and algorithmical considerations on a recent three-dimensional model describing stress-induced solid phase transformationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2002Ferdinando Auricchio Abstract During mechanical loading,unloading cycles shape-memory alloys (SMA) are able to undergo large deformations without showing residual strains (pseudoelasticity) or recovering them through thermal cycles (shape memory effect). Motivated by stress-induced solid phase transformations, these unique behaviours induce the SMA exploitation in innovative and commercially valuable applications, stimulating, consequently, the interest in the development of constitutive models. Also if many models are now available in the literature, effective three-dimensional proposals are still few and limited in several aspects. In this paper, a three-dimensional thermomechanical model recently proposed by Souza et al. (European Journal of Mechanics,A/Solids, 1998; 17: 789,806.) is taken into consideration; such a model is of particular interest for its effectiveness and flexibility, but it also shows some limitations and missing links in the algorithmical counterparts. This work discusses some improvements to the original model as well as the development and the implementation of a robust integration algorithm to be adopted in a numerical scheme, such as a finite-element framework. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effect of three adhesive primers for a noble metal on the shear bond strengths of three resin cementsJOURNAL OF ORAL REHABILITATION, Issue 1 2001K. Yoshida The purpose of this study was to evaluate the durability and shear bond strengths of the different combinations of three adhesive primers and three resin cements to a silver,palladium,copper,gold (Ag,Pd,Cu,Au) alloy. The adhesive primers Alloy Primer® (AP), Metal PrimerII® (MPII) and Metaltite® (MT), and the resin cements BistiteII® (BRII), Panavia Fluoro Cement® (PFC) and Super-Bond C&B® (SB) were used. Two sizes of casting alloy disks were either non-primed or primed and cemented with each of the three resin cements. The specimens were stored in a 37 °C water bath for 24 h and then immersed alternately in 4 and 60 °C water baths for 1 min each for up to 100 000 thermal cycles. Shear mode testing at a crosshead speed of 0·5 mm/min was then performed. The application of MPII or MT was effective for improving the shear bond strength between each of the three resin cements and the Ag,Pd,Cu,Au alloy compared with non-primed specimens. However, when primed with MPII or MT and cemented with SB, the bond strength at 100 000 thermal cycles was significantly lower than that at thermal cycle 0. When primed with AP, the specimens cemented with BRII or PFC showed lower bond strength than non-primed specimens and failed at the metal,resin cement interface at 100 000 thermal cycles. On the other hand, AP was effective in enhancing the shear bond strength of SB to the Ag,Pd,Cu,Au alloy. The five combined uses of an adhesive metal primer and resin cement (combinations of MPII or MT and BRII or PFC and AP and SB) are applicable to the cementation of prosthodontic restorations without complicated surface modification of the noble alloy. [source] Effect of Net Fiber Reinforcement Surface Treatment on Soft Denture Liner Retention and LongevityJOURNAL OF PROSTHODONTICS, Issue 4 2010MPhil, Muhanad M. Hatamleh BSc Abstract Purpose: To evaluate shear bond strength of Molloplast-B soft liner attached to different acrylic surfaces (smooth, rough, and Sticktech net fiber-reinforced interfaces) after 3000 thermal cycles. Materials and Methods: Sixty-nine specimens were fabricated by attaching Molloplast-B soft liner to acrylic bases of three interfaces (n= 23); smooth (Group 1, control), rough (Group 2), and Sticktech net fiber-reinforced interface (Group 3). The specimens underwent 3000 thermocycles (5 and 55°C) before being subject to a shear bond test at 2 mm/min crosshead speed. Debonding sites were investigated using an optical microscope at 40× magnification. Bond failures were categorized as adhesive, cohesive, or mixed. Results: Mean (SD) bond strength values (MPa) were: 0.71 (0.15); 0.63 (0.07); and 0.83 (0.12) for smooth, rough, and fiber-reinforced acrylic interfaces, respectively. The mean values were analyzed using one-way ANOVA and Bonferroni post hoc test for pairwise comparisons (p, 0.05). The net fiber-reinforced acrylic interface exhibited a statistically significantly higher bond strength value when compared to smooth and rough acrylic interfaces (P= 0.003 and P= 0.000, respectively). Modes of failure were mainly cohesive (91%), followed by mixed failures (9%). Conclusions: Molloplast-B exhibited a stronger bond to StickTech Net fiber-reinforced surfaces when compared to smooth and rough acrylic interfaces after thermocycling. This may enhance prosthesis serviceability during clinical use. [source] An investigation of the effect of thermal cycling on plasma-sprayed zirconia/NiCoCrAlY thermal barrier coatingMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2004A. El-Turki Abstract The microstructural change, crack initiation and spallation of a vacuum plasma sprayed (VPS) thermal barrier coating on an INCONEL-738 superalloy substrate were investigated after successive 300 h thermal cycles at 1050°C. The coating was characterised using Raman spectroscopy, scanning electron microscopy (SEM) energy dispersive X-ray analysis (EDX) and Auger electron spectroscopy (AES). Localised micro-cracks at the yttrium (III) oxide stabilised zirconium (IV) oxide (YSZ) ceramic coating/thermally grown oxide (TGO) interface were observed after 8 cycles. Spallation of the YSZ coating occurred after approximately 21 cycles. Significant amounts of the elements titanium, tantalum and chromium were found within the TGO together with the formation of nickel, cobalt and chromium-rich oxides at this TGO/YSZ interface. [source] In situ deformation of thin films on substratesMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2009Marc Legros Abstract Metallic thin-film plasticity has been widely studied by using the difference between the coefficients of thermal expansion of the film and the underlying substrate to induce stress. This approach is commonly known as the wafer curvature technique, based on the Stoney equation, which has shown that thinner films have higher yield stresses. The linear increase of the film strength as a function of the reciprocal film thickness, down to a couple hundred nanometers, has been rationalized in terms of threading and interfacial dislocations. Polycrystalline films also show this kind of dependence when the grain size is larger than or comparable to the film thickness. In situ TEM performed on plan-view or cross-section specimens faithfully reproduces the stress state and the small strain levels seen by the metallic film during wafer curvature experiments and simultaneously follows the change in its microstructure. Although plan-view experiments are restricted to thinner films, cross-sectional samples where the film is reduced to a strip (or nanowire) on its substrate are a more versatile configuration. In situ thermal cycling experiments revealed that the dislocation/interface interaction could be either attractive or repulsive depending on the interfacial structure. Incoherent interfaces clearly act as dislocation sinks, resulting in a dislocation density drop during thermal cycles. In dislocation-depleted films (initially thin or annealed), grain boundaries can compensate for the absence of dislocations by either shearing the film similarly to threading dislocations or through fast diffusion processes. Conversely, dislocations are confined inside the film by image forces in the cases of epitaxial interfaces on hard substrates. To increase the amount of strain seen by a film, and to decouple the effects of stress and temperature, compliant substrates can also be used as support for the metallic film. The composite can be stretched at a given temperature using heating/cooling straining holders. Other in situ TEM methods that served to reveal scaling effects are also reviewed. Finally, an alternate method, based on a novel bending holder that can stretch metallic films on rigid substrates, is presented. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source] Internal friction investigation of reverse martensitic transformation in oil-quenched Ni64Al36 alloyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2008Z. C. Zhou Abstract Low-frequency internal friction investigation of reverse martensitic transformation in oil-quenched Ni64Al36 alloy has been carried out using a multifunctional internal friction apparatus from room temperature to 400 °C and additionally differential scanning calorimetry and X-ray diffraction experiments were also completed. It has been shown that an internal friction peak presents at about 220 °C in the internal friction,temperature curve during heating for the oil-quenched Ni64Al36 alloy but not for the furnace-cooled Ni64Al36 alloy. The peak still appears during cooling and the peak temperature shifts to lower temperature. The changes of the peak temperature positions cannot be visibly observed when the vibration frequency is changed. The peak heights increase with decreasing vibration frequency and increasing heating rate, being linearly directly proportional to It has been suggested that the internal friction peak results from reverse martensitic transformation of L10 , , during heating and originates from martensitic transformation of , , L10 during the subsequent cooling process. The influence of the thermal cycles on the transformation is not observed for the limited thermal cycles. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature dependence of electrical resistivity in carbon nanofiber/unsaturated polyester nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 7 2008Toshiaki Natsuki This article described the temperature dependence of electrical resistivity for carbon nanofiber (CNF)/unsaturated polyester resin (UPR) nanocomposites prepared by a solvent evaporation method. It was found that the CNF/UPR nanocomposites had quite low electrical percolation threshold due to CNFs having a large aspect ratio and being well dispersed into the UPR matrix. A sharp decrease in the electrical resistivity was observed at about 1 wt% CNF content. The influence of CNF content on the electrical resistivity was investigated as a function of temperature in detail. The nanocomposites showed a positive temperature coefficient effect for the resistivity, and had a strong temperature dependence near the percolation threshold. When the number of thermal cycles was increased, the electrical resistivity decreased and had a weak temperature dependence, especially in the case of melting temperature. Moreover, the size influences of CNFs on the electrical properties of nanocomposites were analyzed and discussed. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Determining Thermal Test Requirements for Automotive ComponentsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 2 2004Dustin S. Aldridge Abstract Component thermal response is dependent upon numerous factors including the atmospheric temperature, heat sinks and sources, vehicle use time, etc. The number of significant thermal cycles and time at temperature for many components will be related to the number of times the engine is started. This paper provides a methodology to determine the number of significant thermal cycles and time at temperature a product will experience in 10 years which will depend upon engine starts. These calculations provide the basis for an accelerated test requirement to qualify the product based upon customer usage measurements. Because of the trace ability and linkage, the methodology is more marketable to internal and external customers, and less likely to be questioned or arbitrarily overruled. It also enables relative severity assessments for historical customer requirements compared with field needs. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||||||||