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Strength Values (strength + value)

Distribution by Scientific Domains
Polymers and Materials Science45%
Medical Sciences36%
Chemistry9%
Physics and Astronomy6%

Kinds of Strength Values

  • bond strength value
    		•
  • flexural strength value
    		•

    Selected Abstracts

    Improvement of the interfacial compatibility between sugar cane bagasse fibers and polystyrene for composites

    POLYMER COMPOSITES, Issue 2 2004
    Edgar García-Hernández
    Sugar cane bagasse fibers were modified by surface treatments using either physical or chemical methods in order to improve their adhesion to polystyrene matrices. The surface treatment methods used were alkaline treatment, treatment with silane coupling agents, physical coating with polystyrene and grafting of polystyrene with and without crosslinker. Fiber modifications were monitored by Fourier Transform Infrared Spectroscopy (FTIR), Differential Thermal Analysis coupled with Thermogravimetric Analysis (DTA-TGA) and Scanning Electron Microscopy (SEM). On the other hand, the improvement of the adhesion between sugar cane modified fibers and polystyrene was assessed by micromechanical pull-out and by macromechanical Iosipescu tests. It was found, from Interfacial Shear Strength values (IFSS), that substantial improvements in fiber-matrix compatibility were achieved. According to micro- and macromechanical test results, the IFSS increased for all treated fibers as compared to non-treated fibers. Particularly, both the coating the fibers or grafting with polystyrene using crosslinker resulted in substantial adhesion improvement to the polystyrene matrix in comparison with the non-treated fibers and fibers treated by alkaline and silane methods only. Polym. Compos. 25:134,145, 2004. © 2004 Society of Plastics Engineers. [source]

    Effect of Net Fiber Reinforcement Surface Treatment on Soft Denture Liner Retention and Longevity

    JOURNAL OF PROSTHODONTICS, Issue 4 2010
    MPhil, 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]

    Alumina/Silicon Carbide Laminated Composites by Spark Plasma Sintering

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009
    Vincenzo M. Sglavo
    Ceramic laminates composed of alumina/silicon carbide composite layers were produced by spark plasma sintering (SPS). Monolithic composite disks containing up to 30 vol% of silicon carbide were fabricated by stacking together and cosintering by SPS green layers prepared by tape casting water-based suspensions. An engineered laminate with a specific layer combination that is able to promote the stable growth of surface defects before final failure was also designed and produced. Fully dense materials with an optimum adhesion between the constituting layers and a homogeneous distribution of the two phases were obtained after SPS. Monolithic composites showed an increasing strength with SiC load, and biaxial strength values as high as 700 MPa were observed for a SiC content of 30 vol%. The engineered laminate showed a peculiar crack propagation that is responsible for the high strength value of about 600 MPa and for the evident insensitivity to surface defects. [source]

    Enhanced Mechanical Performance of Self-Bundled Electrospun Fiber Yarns via Post-Treatments

    MACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2008
    Xuefen Wang
    Abstract A new route to high-performance electrospun polymer fibers was developed using a self-bundling electrospinning technique combined with post-treatments such as stretching and annealing under conditions similar to those used for conventional fibers. Self-bundled electrospun PAN fiber yarns were characterized by SEM, mechanical tests, polarized FT-IR spectroscopy and WAXD. The obtained results revealed that the PAN nanofiber yarns possessed enhanced alignment, a higher degree of crystallinity and higher molecular orientation after treatments, resulting in a remarkable improvement in mechanical performance, approaching the strength value of the corresponding conventional fibers. [source]

    Continuous surface modification process with ultraviolet/ozone for improving interfacial adhesion of poly(ethylene terephthalate)/epoxy composites

    POLYMER COMPOSITES, Issue 5 2006
    Paisan Khanchaitit
    This study proposed a continuous UV/ozone surface modification process for the production of polymeric fiber-reinforced polymer composite. A gas phase photoreactor using the conventional low-pressure mercury UV lamps and the economically made ozone generators were designed and constructed. Poly(ethylene terephthalate) (PET) fibers and epoxy resin were chosen as a reinforcement and a matrix, respectively. The synergistic effects of UV and various gas species (nitrogen, air, oxygen, air/ozone, and oxygen/ozone) exposure as well as the effects of exposure time, i.e., 2, 5, and 10 min, on the morphology and chemistry of PET-fiber surfaces were investigated by using a scanning electron microscope coupled with energy dispersive x-ray analysis (SEM/EDX). The tensile testing and analysis of fractography of the resulted composites were performed to evaluate the effectiveness of the process. The SEM/EDX results showed that the effects of the treatment were dependent on both the concentration of reactive species present in the gases and the exposure time. The PET fibers treated under UV/O2 + O3 exposure for 5 min yielded the resulting composite with the highest tensile strength value. Under this condition, the tensile strength of the composite can be increased up to 63% in comparison with that of the untreated PET fiber/epoxy composite. The results are of interest for application as an in-line surface modification for composite productions. POLYM. COMPOS., 27:484,490, 2006. © 2006 Society of Plastics Engineers [source]

    Comparative assessment of time-related bioactive glass and calcium hydroxide effects on mechanical properties of human root dentin

    DENTAL TRAUMATOLOGY, Issue 1 2009
    Monika Marending
    These materials have a disinfecting capacity similar to Ca(OH)2, but bear the advantage of bioactivity. However, because bioactive glasses initially act as alkaline biocides just as Ca(OH)2 does, they may also negatively affect mechanical dentin properties over time. This was assessed in the current study using standardized human root dentin bars. Specimens were immersed in 1:20 (wt vol,1) suspensions of nanometric bioactive glass 45S5 or calcium hydroxide for 1, 10, or 30 days. Control specimens were immersed in pure saline for 30 days (n = 20 per group). Subsequently, modulus of elasticity (E) and flexural strength (FS) of the specimens were determined. Results were compared between groups using one-way anova and Scheffé's post-hoc test. Ca(OH)2 caused a significant (P < 0.001) 35% drop in mean flexural strength values compared to the control treatment after 10 days. No further change was observed between 10 days and 30 days. Bioactive glass caused a 20% drop in mean flexural strength as compared to the control after 10 days. However, this difference did not reach statistical significance (P > 0.05). No effects of either material on dentin modulus of elasticity values were observed. It was concluded that the calcium hydroxide suspension affected the dentin more than the bioactive glass counterpart; however, the effect was self-limiting and probably restricted to superficial dentin layers, as suggested by the mere decrease in flexural strength but not in modulus of elasticity values. [source]

    Physicochemical evaluation of silica-glass fiber reinforced polymers for prosthodontic applications

    EUROPEAN JOURNAL OF ORAL SCIENCES, Issue 3 2005
    Gökçe Meriç
    This investigation was designed to formulate silica-glass fiber reinforced polymeric materials. Fused silica-glass fibers were chosen for the study. They were heat-treated at various temperatures (500°C, 800°C and 1100°C), silanized, sized and incorporated in two modified resin mixtures (A and B). The flexural properties in dry and wet conditions were tested and statistically analyzed, and the content of residual methyl methacrylate (MMA) monomer, dimensional changes with temperature, water sorption and solubility were determined. Woven fibers [36.9% (wt/wt)], heat-treated at 500°C, gave the highest strength values for the polymeric composites (an ultimate transverse strength of 200 Mpa and a flexural modulus of 10 GPa) compared with the fibers heat-treated at other temperatures. There was no statistically significant difference in the measured flexural properties between resins A and B regarding fiber treatment and water storage time. These fiber composites had a small quantity of residual MMA content [0.37 ± 0.007% (wt/wt)] and very low water solubility, indicating good biocompatibility. It was suggested that silica-glass fibers could be used for reinforcement as a result of their anticipated good qualities in aqueous environments, such as the oral environment. [source]

    Influence of the mineral content and morphological pattern of artificial root caries lesion on composite resin bond strength

    EUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2004
    Anderson T. Hara
    Dentine substrates with different mineral contents and morphological patterns were created by submitting root slabs to the following treatments: (A) immersion in artificial saliva during the experimental period (control), (B) demineralization for 32 h to induce caries lesion (demineralized group), and (C) demineralization for 32 h followed by remineralization for 8 d (remineralized group). The slabs were longitudinally sectioned, the mineral content was determined by cross-sectional microhardness, and the bond strength of an adhesive system/composite resin was assessed using a microtensile bond strength test. The dentine morphology after the treatments as well as the failure pattern of the debonded specimens was examined by scanning electron microscopy. Statistically significant differences were found in mineral content. Morphological analysis showed marked differences between the patterns of demineralized and remineralized substrates. The bond strength mean value of the control A did not differ from the group B, but was statistically higher than the group C. Since no linear relationship was found between dentine mineral content and bond strength values, it could be suggested that the morphological pattern may be more relevant than the mineral content to explain the bond strength of composite resin to dentine. [source]

    Beneficial Effects of AlN as Sintering Aid on Microstructure and Mechanical Properties of Hot-pressed ZrB2,

    ADVANCED ENGINEERING MATERIALS, Issue 7 2003
    F. Monteverde
    Higher density of ZrB2 ceramics than with the pure material is achieved when 4.6,% of aluminum nitride are added before hot-pressing as a sintering aid. AlN supports densification and prevents grain coarsening, mainly by virtue of its ability to remove the boron oxide layer that otherwise covers ZrB2 particles. The new material (see Figure for an SEM image of a polished section) has outstanding mechanical properties, e.g. strength values of 600 and 200 MPa at 25 and 1500,°C. [source]

    Rapid risk assessment using probability of fracture nomographs

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2009
    R. PENMETSA
    ABSTRACT Traditional risk-based design process involves designing the structure based on risk estimates obtained during several iterations of an optimization routine. This approach is computationally expensive for large-scale aircraft structural systems. Therefore, this paper introduces the concept of risk-based design plots that can be used for both structural sizing and risk assessment for fracture strength when maximum allowable crack length is available. In situations when crack length is defined as a probability distribution the presented approach can only be applied for various percentiles of crack lengths. These plots are obtained using normalized probability density models of load and material properties and are applicable for any arbitrary load and strength values. Risk-based design plots serve as a tool for failure probability assessment given geometry and applied load or they can determine geometric constraints to be used in sizing given allowable failure probability. This approach would transform a reliability-based optimization problem into a deterministic optimization problem with geometric constraints that implicitly incorporate risk into the design. In this paper, cracked flat plate and stiffened plate are used to demonstrate the methodology and its applicability. [source]

    Polymerization stress, flow and dentine bond strength of two resin-based root canal sealers

    INTERNATIONAL ENDODONTIC JOURNAL, Issue 10 2009
    S. F. C. Souza
    Abstract Aim, To compare two resin-based root canal sealers (AH Plus and dual cure Epiphany) in terms of flow, polymerization stress and bond strength to dentine. Methodology, Flow was evaluated by measuring the diameter of uncured discs of sealer (0.5 mL) after 7 min compression (20N) between two glass plates (n = 5). Polymerization stress was monitored for 60 min in 1-mm thick discs bonded to two glass rods (Ø = 5 mm) attached to a universal testing machine (n = 3). Bond strength was analyzed through micropush-out test (n = 10) and failure mode was examined with scanning electron microscope (100× and 2500×). Data were statistically analyzed using the Student's t -test (, = 0.05). Results, Polymerization stress was 0.32 ± 0.07 MPa for Epiphany self-cure, 0.65 ± 0.08 MPa for Epiphany light-cure and zero for AH Plus (P < 0.05). Flow data and bond strength values were 30.9 ± 1.1, 28.6 ± 0.7 mm and 6.3 ± 5.3, 17.8 ± 7.5 MPa for Epiphany and AH Plus, respectively (P < 0.001). Failure mode was predominantly cohesive in the sealer for both materials. Conclusions, Epiphany had higher flow and polymerization stress and lower bond strength values to dentine than AH Plus. In view of these findings it can be implied that AH Plus would provide a better seal. [source]

    Bond strength of AH Plus and Epiphany sealers on root dentine irradiated with 980 nm diode laser

    INTERNATIONAL ENDODONTIC JOURNAL, Issue 9 2008
    E. Alfredo
    Abstract Aim, To evaluate the bond strength of AH Plus and Epiphany sealers to human root canal dentine irradiated with a 980 nm diode laser at different power and frequency parameters, using the push-out test. Methodology, Sixty canine roots were sectioned below the cementoenamel junction to provide 4-mm-thick dentine discs that had their root canals prepared with a tapered bur and irrigated with sodium hypochlorite, ethylenediaminetetraacetic acid and distilled water. The specimens were assigned to five groups (n = 12): one control (no laser) and four experimental groups that were submitted to 980 nm diode laser irradiation at different power (1.5 and 3.0 W) and frequency (continuous wave and 100 Hz) parameters. Half of specimens in each group had their canals filled with AH Plus sealer and half with Epiphany. The push-out test was performed and data (MPa) were analysed statistically by anova and Tukey's test (P < 0.05). The specimens were split longitudinally and examined under SEM to assess the failure modes after sealer displacement. Results, The specimens irradiated with the diode laser and filled with AH Plus had significantly higher bond strength values (8.69 ± 2.44) than those irradiated and filled with Epiphany (3.28 ± 1.58) and the nonirradiated controls (3.86 ± 0.60). The specimens filled with Epiphany did not differ significantly to each other or to the control (1.75 ± 0.69). There was a predominance of adhesive failures at Epiphany,dentine interface (77%) and mixed failures at AH Plus,dentine interface (67%). Conclusions, The 980 nm diode laser irradiation of root canal dentine increased the bond strength of AH Plus sealer, but did not affect the adhesion of Epiphany sealer. [source]

    Development of hydrogel patch for controlled release of alpha-hydroxy acid contained in tamarind fruit pulp extract

    INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 2 2005
    J. Viyoch
    Synopsis The aim of this study was to develop hydrogel patch using crosslinked chitosan,starch as polymeric matrix for controlling the release of the natural alpha-hydroxy acid (AHA) contained in the extract of tamarind's fruit pulp. The chitosan (MW 100 000) was blended with corn, tapioca or rice starch in various ratios and then crosslinked with glutaraldehyde. The physical characteristics, mechanical resistance, bio-adhesion property and surface morphology of the prepared hydrogel patches with and without the extract were investigated. The release patterns of the hydrogel patches containing the extract were investigated by measuring the amount of tartaric acid, a major AHA present in the tamarind's fruit pulp extract, accumulated in the receptor medium of the vertical diffusion cell at various time intervals over a period of 6 h. The results indicated that the formulations of chitosan : corn starch 4.5 : 0.5 with glutaraldehyde 0.02% w/w (C4.5C0.5G0.02) or 0.04% w/w (C4.5C0.5G0.04), chitosan : tapioca starch 4.5 : 0.5 with glutaraldehyde 0.04% w/w (C4.5T0.5G0.04) or 0.05% w/w (C4.5T0.5G0.05), and chitosan : rice starch 4.5 : 0.5 with glutaraldehyde 0.04% w/w (C4.5R0.5G0.04) and chitosan : rice starch 4.0 : 1.0 with glutaraldehyde 0.03% w/w (C4.0R1.0G0.03) provided the flexible and elastic patches with good bio-adhesive property. The tensile strength values ranged from 5 to15 N mm,2 and the elasticity ranged from 30 to 60%. The addition of the extract in these formulations significantly increased the tensile strength values of the obtained patches. The patch of C4.0R1.0G0.03 formulation containing the extract showed relatively highest porosity, corresponding to its highest amount (12.02 ± 0.33 mg) and rate (0.452 ± 0.012 mg mm,2 min,1/2) of tartaric acid released. The amounts of tartaric acid released from the developed hydrogel patches were proportional to a square root of time (Higuchi's model), particularly the release from C4.0R1.0G0.03 (R2, 0.9978 ± 0.0020) and C4.5R0.5G0.04 (R2, 0.9961 ± 0.0024) patches. Résumé Le but de cette étude était de développer un patch hydrogel en utilisant, en tant que matrice polymère, un mélange chitosane/amidon réticulé pour le contrôle du relargage d', -hydroxyacide naturel contenu dans l'extrait de la pulpe du fruit du tamarinier. Du chitosane (MW 100 000) a été mélangéà des farines de maïs, de tapioca ou de riz dans différentes proportions, les mélanges ont été réticulés avec du glutaraldéhyde. Les caractéristiques physiques, résistance mécanique, propriétés de bio adhésion et morphologie de surface des patchs hydrogels préparés avec et sans extrait ont étéétudiées. Le profil de relargage des patchs hydrogels contenant l'extrait a étéétudié en mesurant la quantité d'acide tartarique, , -aminoacide majoritaire présent dans l'extrait, accumulé dans le milieu récepteur d'une cellule à diffusion verticale en fonction du temps sur une période de 6 heures. Les résultats ont montré que les formulations contenant: ,,un mélange chitosane/amidon de maïs dans un rapport 4.5 : 0.5 réticulé avec 0.02% ou 0.04% poids/poids de glutaraldéhyde (respectivement C4.5C0.5G0.02 et C4.5 C0.5 G0.04) ou ,,un mélange de chitosane/amidon de tapioca dans un rapport 4.5 : 0.5 réticulé avec 0.04% ou 0.05% poids/poids de glutaraldéhyde (C4.5T0.5 G0.04ou C4.5 T0.5 G0.05) ,,ainsi que le mélange chitosane/amidon de riz dans un rapport 4.5 : 0.5 réticulé avec 0.04% poids/poids de glutaraldehyde (C4.5R0.5 G0.04) ,,et le mélange chitosane/amidon de riz dans un rapport 4.0 : 1.0 réticulé avec 0,03% poids/poids de glutaraldehyde (C4.0 R1.0 G0.03) conduisaient à des patchs flexibles et élastiques avec de bonnes propriétés bio adhésives. Leur résistance mécanique varie de 5 à 15 N/m2 et leur élasticité de 30 à 60%. L'addition de l'extrait de fruit à ces formules augmente significativement la résistance mécanique des patchs. Le patch C4.0R1.0 G0.03 contenant l'extrait montre la plus grande porosité correspondant à la quantité d'acide tartarique relargué la plus élevée (12.02 ± 0.33 mg), ainsi qu'à la plus grande vitesse de relargage (0.452 ± 0.012 mg mm- 2 mn- 1/2). Les quantités d'acide tartarique relarguées à partir de patchs hydrogels développés sont proportionnelles à la racine carrée du temps (modèle d'Higuchi), en particulier pour les patchs C4.0 R1.0G0.03 (R2, 0.9978 ± 0.0020) et C4.5R0.5 C0.004 (R2, 0.9061 ± 0.0024). [source]

    The electronic and optical properties of oligo(trans -1,2-di(2-thienyl)-1,3-butadiene): A theoretical study

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2008
    Nei Marçal
    Abstract In the present work we investigated the theoretical electronic structure of poly(trans -1,4-di(2-thienyl)-1,3-butadiene) (PTB) and determined the optical properties of its neutral and doped oligomers. Geometrical optimizations were at the semiempirical level by using the Austin method 1 (AM1). The band structure of , electrons regarding to the neutral PTB polymer was obtained by using a tight-binding Hamiltonian. The densities of electronic states (DOS) for neutral and doped copolymers were calculated by using the negative factor counting technique. The spatial charge distribution of the oligomeric chain was also analyzed. The energy of the electronic transitions and their associated oscillator strength values were calculated for the neutral, double, and single charged oligomers to determine the UV,vis absorption spectra. The calculations were performed using the intermediate neglect of differential overlap Hamiltonian in combination with the single configuration-interaction technique in order to include correlation effects. The band gap obtained in the PTB was about 2.101 eV for the optics absorption and 1.73 eV for the DOS. The bipolaron states appear in the gap, about 0.57 eV and 0.48 eV below and above the conduction and valence bands, respectively. When the dopants concentration is increased the DOS showed that the energy gap tends to vanish, which may lead to semiconductor,metal transition. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

    The influence of the impregnating chemicals on the bonding strength of impregnated wood materials

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
    Ayhan Özçifçi
    Abstract In this study, it is aimed to determine the bonding strength of white oak (Quercus petreae L.) and chestnut (Castanea sativa Mill.) woods impregnated with borax and zinc chloride. Within this purpose, the experimental samples were bonded with Polyvinyl-acetate and polyurethane based Desmodur-VTKA (D-VTKA) adhesives according to BS EN 205 standards after they had been prevacuumed with a pressure equal to 760 mmHg,1 with impregnating at 2 atm pressures for 60 min according to ASTM-D 1413 standards and applied vacuum-impregne-vacuum method. During the experiments, the retention amount, the retention proportion, and the bonding strength values of the samples were determined. According to the test results, the highest values of retention amount, and bonding strength were obtained from the wood material impregnated with zinc chloride. The impregnating materials had a negative effect on bonding strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Manufacturing, mechanical characterization, and in vitro performance of bioactive glass 13,93 fibers

    JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2006
    E. Pirhonen
    Abstract Fibers were manufactured from the bioactive glass 13,93 by melt spinning. The fibers were further characterized by measuring their tensile and flexural strength, and their in vitro performance was characterized by immersing them in simulated body fluid, which analyzed changes in their mass, their flexural strength, and surface reactions. The strength of glass fibers is highly dependent on fiber diameter, test method, and possible surface flaws, for example, cracks due to abrasion. In this study, the thinnest fibers (diameter between 24 and 33 ,m) possessed the highest average tensile strength of 861 MPa. The flexural strength was initially 1353.5 MPa and it remained at that level for 2 weeks. The Weibull modulus for both tensile and flexural strength values was initially about 2.1. The flexural strength started to decrease and was only ,20% of the initial strength after 5 weeks. During the weeks 5,40, only a slight decrease was detected. The flexural modulus decreased steadily from 68 to 40 GPa during this period. The weight of the samples initially decreased due to leaching of ions and further started to increase due to precipitation of calcium phosphate on the fiber surfaces. The mass change of the bioactive glass fibers was dependent on the surface area rather than initial weight of the sample. The compositional analysis of the fiber surface after 24 h and 5 weeks immersion did confirm the initial leaching of ions and later the precipitation of a calcium phosphate layer on the bioactive glass 13,93 fiber surface in vitro. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source]

    Lifetime prediction of CAD/CAM dental ceramics,

    JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 6 2002
    Ulrich Lohbauer
    Abstract The dynamic fatigue method was used to obtain subcritical crack growth parameters n and A for a commercial feldspathic dental porcelain and for a lanthanum-glass-infiltrated alumina glass ceramic. Five stress rates d,/dt ranging from 50 to 0.01 MPa s,1 were applied. The inert strength values were calculated with the use of Weibull statistics and maximum-likelihood approaches for the Weibull parameter m. Strength,probability,time (SPT) diagrams were derived for both materials. The alumina glass composite showed a high fracture strength ,0 (442 MPa) at a failure probability of PF = 63.2% and a high resistance against subcritical crack growth (n = 36.5). The development of strength under fatigue conditions was calculated for exemplary 1 year. The strength of the alumina glass material dropped to 228 MPa within this period. This fact is due to a low content of infiltrated lanthanum glass phase in the composite material (25 wt%). In contrast, for the high-silica-glass-containing porcelain a distinct decrease of strength ,0 from initial 133 to 47 MPa after 1 year was predicted. This, mainly because of a low crack growth resistance (n = 16.8) of the feldspathic porcelain. Much lower strength values were calculated, assuming a failure probability of PF = 5%. The decrease is mainly caused by the sensitivity of high,glass-containing ceramics against water corrosion. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 780,785, 2002 [source]

    Bond Strength of Two Resin Cements on Dentin Using Different Cementation Strategies

    JOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 4 2010
    RENATA MARQUES MELO MS
    ABSTRACT Purpose:, This study evaluated the microtensile bond strength of two resin cements to dentin either with their corresponding self-etching adhesives or employing the three-step "etch-and-rinse" technique. The null hypothesis was that the "etch-and-rinse" adhesive system would generate higher bond strengths than the self-etching adhesives. Materials and Methods:, Thirty-two human molars were randomly divided into four groups (N = 32, n = 8/per group): G1) ED Primer self-etching adhesive + Panavia F; G2) All-Bond 2 "etch-and-rinse" adhesive + Panavia F; G3) Multilink primer A/B self-etching adhesive + Multilink resin cement; G4) All-Bond 2 + Multilink. After cementation of composite resin blocks (5 × 5 × 4 mm), the specimens were stored in water (37°C, 24 hours), and sectioned to obtain beams (±1 mm2 of adhesive area) to be submitted to microtensile test. The data were analyzed using 2-way analysis of variance and Tukey's test (, = 0.05). Results:, Although the cement type did not significantly affect the results (p = 0.35), a significant effect of the adhesive system (p = 0.0001) was found on the bond strength results. Interaction terms were not significant (p = 0.88751). The "etch-and-rinse" adhesive provided significantly higher bond strength values (MPa) with both resin cements (G2: 34.4 ± 10.6; G4: 33.0 ± 8.9) compared to the self-etching adhesive systems (G1: 19.8 ± 6.6; G3: 17.8 ± 7.2) (p < 0.0001). Pretest failures were more frequent in the groups where self-etching systems were used. Conclusion:, Although the cement type did not affect the results, there was a significant effect of changing the bonding strategy. The use of the three-step "etch-and-rinse" adhesive resulted in significantly higher bond strength for both resin cements on dentin. CLINICAL SIGNIFICANCE Dual polymerized resin cements tested could deliver higher bond strength to dentin in combination with "etch-and-rinse" adhesive systems as opposed to their use in combination with self-etching adhesives. (J Esthet Restor Dent 22:262,269, 2010) [source]

    Shear Bond Strength of Enamel Treated with Seven Carbamide Peroxide Bleaching Agents

    JOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 4 2004
    ROBERTA TARKAN.
    ABSTRACT Purpose:: Lower average values of bond strength of adhesive systems to enamel bleached with 10% carbamide peroxide agents have been reported, but the effects of higher concentrations of carbamide peroxide bleaching agents are still unknown. The aim of this in vitro study was to evaluate the shear bond strength of enamel treated with different concentrations of carbamide peroxide to an adhesive system after a postbleaching period of storage in artificial saliva for 15 days. Materials and Methods: Seven carbamide peroxide bleaching agents with concentrations varying from 10 to 22% were analyzed. A placebo agent was used as a control group. The agents were applied on the enamel fragments for 8 h/d for 42 days. During the remaining time, the specimens were stored in artificial saliva. After that time, the fragments were stored individually in artificial saliva for 15 days. An adhesive system was used to bond resin-based composite cylinders on the enamel surface. Shear bond strength tests were performed and the fractured surfaces of the specimens were visually examined with a stereomicroscope at ×30. Results: The analysis of variance did not show differences in shear bond strength among the treatment agents. The fractures for all treatment agents were predominantly adhesive. Conclusion: After 15 days storage in artificial saliva, different concentrations of carbamide peroxide bleaching agents and a placebo agent had the same enamel shear bond strength values. [source]

    Experimental deformation of partially melted granite revisited: implications for the continental crust

    JOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2005
    C. L. ROSENBERG
    Abstract A review and reinterpretation of previous experimental data on the deformation of partially melted crustal rocks reveals that the relationship of aggregate strength to melt fraction is non-linear, even if plotted on a linear ordinate and abscissa. At melt fractions, , < 0.07, the dependence of aggregate strength on , is significantly greater than at , > 0.07. This melt fraction (, = 0.07) marks the transition from a significant increase in the proportion of melt-bearing grain boundaries up to this point to a minor increase thereafter. Therefore, we suggest that it is the increase of melt-interconnectivity that causes the dramatic strength drop between the solidus and a melt fraction of 0.07. We term this drop the ,melt connectivity transition' (MCT). A second, less-pronounced strength drop occurs at higher melt fractions and corresponds to the breakdown of the solid (crystal) framework. This is the ,solid-to-liquid transition' (SLT), corresponding to the well known ,rheologically critical melt percentage'. Although the strength drop at the SLT is about four orders of magnitude, the absolute value of this drop is small compared with the absolute strength of the unmelted aggregate, rendering the SLT invisible in a linear aggregate strength v. melt-fraction diagram. On the other hand, the more important MCT has been overlooked in previous work because experimental data usually are plotted in logarithmic strength v. melt-fraction diagrams, obscuring large strength drops at high absolute strength values. We propose that crustal-scale localization of deformation effectively coincides with the onset of melting, pre-empting attainment of the SLT in most geological settings. The SLT may be restricted to controlling flow localization within magmatic bodies, especially where melt accumulates. [source]

    The effect of thermocycling and dentine pre-treatment on the durability of the bond between composite resin and dentine

    JOURNAL OF ORAL REHABILITATION, Issue 5 2004
    M. S. Huang
    Summary, The high bond strength between restorative resin and dentine plays an important role in long-term performance of restorations in the oral environment. A variety of treatment techniques have been described to enhance the bond strength of composite resin to dentine. Unfortunately, few studies have reported available bond durability of adhesive resins to dentine. The purpose of this research was to study the shear bond strength of composite resin to dentine pre-treated with phosphoric acid, self-etching agent or Nd:YAP laser irradiation. The durability of bond strength between resin and dentine stored in the artificial saliva thermocycling between 5 and 55 °C was also evaluated. The scanning electron microscope was used to assess the treated-dentine surfaces. The mean value of the shear bond strength in the acid-etching group (18·2 ± 4·9 MPa) was the highest among the three dentine treatments (self-etching system: 12·6 ±3·0 MPa, Nd:YAP laser: 13·4 ± 3·3 MPa) prior to thermocycling. After thermocycling, shear strength values of all treated dentines decreased with increasing number of the cycles. When subjected to 3000 thermocycles, the mean bond strengths of these pre-treated samples to composite resin became 9·1 ± 1·4, 7·8 ± 1·8, and 8·1 ± 1·7 MPa for acid-etching, self-etching and laser-irradiation, respectively, with a significant reduction of 38,50%. [source]

    Effect of Net Fiber Reinforcement Surface Treatment on Soft Denture Liner Retention and Longevity

    JOURNAL OF PROSTHODONTICS, Issue 4 2010
    MPhil, 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]

    Alumina/Silicon Carbide Laminated Composites by Spark Plasma Sintering

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009
    Vincenzo M. Sglavo
    Ceramic laminates composed of alumina/silicon carbide composite layers were produced by spark plasma sintering (SPS). Monolithic composite disks containing up to 30 vol% of silicon carbide were fabricated by stacking together and cosintering by SPS green layers prepared by tape casting water-based suspensions. An engineered laminate with a specific layer combination that is able to promote the stable growth of surface defects before final failure was also designed and produced. Fully dense materials with an optimum adhesion between the constituting layers and a homogeneous distribution of the two phases were obtained after SPS. Monolithic composites showed an increasing strength with SiC load, and biaxial strength values as high as 700 MPa were observed for a SiC content of 30 vol%. The engineered laminate showed a peculiar crack propagation that is responsible for the high strength value of about 600 MPa and for the evident insensitivity to surface defects. [source]

    Fracture Strength of Plate and Tubular Forms of Monolithic Silicon Carbide Produced by Chemical Vapor Deposition

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2002
    Brian Vern Cockeram
    The fracture strength of silicon carbide (SiC) plate deposits produced by chemical vapor deposition (CVD) was determined from room temperature to 1500°C using a standard 4-point flexural test method (ASTM C1161). CVD SiC materials produced by two different manufacturers are shown to have only slightly different flexural strength values, which appear to result from differences in microstructure. Although CVD deposition of SiC results in a textured grain structure, the flexural strength was shown to be independent of the CVD growth direction. The orientation of machining marks was shown to have the most significant influence on flexural strength, as expected. The fracture strength of tubular forms of SiC produced by CVD deposition directly onto a mandrel was comparable to flexural bars machined from a plate deposit. The tubular (O-ring) specimens were much smaller in volume than the flexural bars, and higher strength values are predicted based on Weibull statistical theory for the O-ring specimens. Differences in microstructure between the plate deposits and deposits made on a mandrel result in different flaw distributions and comparable strength values for the flexural bar and O-ring specimens. These results indicate that compression testing of O-rings provides a more accurate strength measurement for tubular product forms of SiC due to more representative flaw distributions. [source]

    Microtensile bond strength of different adhesive systems in dentin irradiated with Er:YAG laser

    LASER PHYSICS LETTERS, Issue 7 2008
    L.M.G. Sierpinsky
    Abstract The objective this study was to evaluate in vitro the bond strength of two etch-and-rise and one self-etching adhesive system after dentin irradiation with Er:YAG (erbium: yttrium aluminum garnet) laser using microtensile test. The results revealed that the groups treated with laser Er:YAG presented less tensile bond strength, independently to the adhesive system used. The prompt L-pop adhesive presented less microtensile bond strength compared to the other adhesives evaluated. There was no difference between single bond and excite groups. The adhesive failures were predominant in all the experimental groups. The Er:YAG laser influenced negatively bond strength values of adhesive systems tested in dental substrate. (© 2008 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

    Tensile bond strength of a flowable composite resin to ER:YAG-laser-treated dentin,

    LASERS IN SURGERY AND MEDICINE, Issue 5 2005
    Juliana Donadio-Moura MSD
    Abstract Background and Objectives This in vitro study evaluated the influence of a flowable composite resin (FCR) on the tensile bond strength of resin to dentin treated with the Er:YAG Laser (L) and diamond bur (DB). Study Design/Materials and Methods Ninety dentin surfaces obtained from 45 third molars were ground and randomly divided into six groups (n,=,15): G1,DB, G2,DB+FCR, G3,L (100 mJ, 10 Hz, 37.04 J/cm2), G4,L (100 mJ, 10 Hz, 37.04 J/cm2)+FCR, G5,L (250 mJ, 2 Hz, 92.60 J/cm2), and G6,L (250 mJ, 2 Hz, 92.60 J/cm2)+FCR. After surface etching with 37% phosphoric acid and the application of an adhesive system, inverted conical specimens were prepared with a hybrid composite resin. In groups G2, G4, and G6 a FCR was placed before the hybrid composite resin. After 24 hours-storage in distilled water, the tensile test was performed in a universal testing machine (0.5 mm/minute, 500 N). Results Data were submitted to Kruskal Wallis test (P,=,0.01). The mean bond strength values (MPa±SD) were: G1,13.54 (±2.99), G2,14.67 (±2.32), G3,9.49 (±3.09), G4,14.60 (±2.76), G5,8.97 (±3.89), and G6,13.02 (±2.18). Groups G1 and G2 presented the highest bond strength values, which were statistically similar to those of G4 and G6. The groups treated with laser and without the FCR (G3 and G5) showed the lowest shear bond strength values. Conclusions FCR can increase the adhesion to dentin treated with Er:YAG laser within different parameters. © 2005 Wiley-Liss, Inc. [source]

    Total reflectance and Raman studies in AlyInxGa1-x-yN epitaxial layers

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2010
    A. Margarida Bola
    Abstract This study comprises a set of AlyInxGa1-x-yN thin films grown on GaN/sapphire substrate by MOVPE, with In content between 2 and 8% and Al between 21 and 38%. The thin films were optically characterized by means of UV-Visible total reflectance and ,-UV-Raman scattering, performed at room temperature. It is shown that the [Al]/[In] ration influences strongly the Reflectance spectra and a good correlation has been found between the reflectance maximum located at higher energy and the band gap predicted by Vegard's law for quaternary alloys. The Raman results indicate that the LO-AlGaN-like vibration mode is the dominated vibration in good agreement with the oscillator strength values obtained theoretically [12] for this alloys. It is shown how the influence of competing effects, such as composition and strain influences the frequency observed for the LO-AlGaN-like mode (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Morphology and compression-after-impact strength relationship in interleaved toughened composites

    POLYMER COMPOSITES, Issue 1 2003
    B. J. Derkowski
    Morphology and compression after impact (CAI) strength relationships in interleaved toughened high performance composites are investigated using a quantitative two-dimensional image analysis approach. A group of six quasi-isotropic carbon fiber-epoxy composites with identical compositions, but having variations in CAI strengths, were analyzed to study how the interleaf particle size, particle size distribution, and location of particles in the interlaminar region affect the CAI strength values and the corresponding damage mechanisms. It is found that the CAI strength of interleaved-toughened composites is significantly affected by the size and size distribution of toughener particles in the interlaminar regions of the composite. In general, high CAI strength composites exhibit more uniform particle size distribution throughout the interlaminar regions. Whereas, for low CAI strength composites, the interleaf particles tend to cluster together and have varied size distribution. [source]

    Changes in the mechanical properties of tooth-colored direct restorative materials in relation to time

    POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2003
    Gülbin Sayg
    Abstract The objective of this study was to determine the flexural strength, flexural modulus, Vickers hardness of a packable composite (Surefil), and an ormocer (Definite) in comparison with a microhybrid composite (Z-100), a microfil composite (Silux Plus) and a polyacid-modified composite resin (Dyract). Flexural strength and flexural modulus were determined using a three-point bending device. Microhardness was measured with a Vickers indentor. The specimens of each material were prepared according to manufacturer's instructions. The specimens were stored in artificial saliva at pH 6, all at 37°C. The groups were tested at the beginning of the test, at 3 months and at 6 months. Flexural strength values of Surefil and Definite showed a progressive increase. The highest MPa values were determined for Surefil (134.4,MPa) and the lowest MPa values were obtained for Dyract (59.6,MPa). The highest flexural modulus values were revealed for Surefil (10.000 GPa). Z-100, Silux Plus and Definite showed a tendency to decline in relation to time for their flexural modulus. GPa values of Silux Plus were stable at 3 and 6 months. Vickers hardness numbers showed that Surefil was the hardest and Dyract was the weakest material. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Compatibilized poly(ether imide)/LCP blends: drawing ability and mechanical properties of the ribbons

    POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2002
    F. J. Vallejo
    Abstract The effects of the addition of polyarylate (PAr) on the drawing ability of poly(ether imide) (PEI)/Rodrun liquid-crystalline 5000 (Ro LC5000) (Ro) blends and on the mechanical properties of their ribbons were studied. The compatibilizing effect of the PAr led to an increase in the drawing ability of the blends, as seen by the fact that the maximum Ro content compatible with the drawing process increased from 15 to 30%. This may lead to new applications in the field of gas barrier materials. The presence of PAr also led to an increase in the adhesion between the two phases of the blends and consequent improved ductility. However, the very high modulus of elasticity and tensile strength in the direction of orientation (up to three-fold those of the matrix) due to the less developed fibrillation were smaller than the corresponding values before compatibilization. These very large modulus of elasticity and tensile strength values and those perpendicular to the direction of orientation, which were similar to those of the matrix, led to a high anisotropy in the extruded ribbons that increased with the draw ratio (DR) and the Ro contents. The high mechanical properties of the ribbons may be used and the anisotropy diminished by layering the ribbons in, and perpendicular to, the direction of orientation, according to the expected external load. Copyright © 2002 John Wiley & Sons, Ltd. [source]