Hygrothermal effects on the shear properties of carbon fiber/epoxy composites

The environmental factors, such as humidity and temperature, can limit the applications of composites by deteriorating the mechanical properties over a period of time. Environmental factors play an important role during the manufacture step and during composite's life cycle. The degradation of composites due to environmental effects is mainly caused by chemical and/or physical damages in the polymer matrix, loss of adhesion at the fiber/matrix interface, and/or reduction of fiber strength and stiffness. Composite's degradation can be measure by shear tests because shear failure is a matrix dominated property. In this work, the influence of moisture in shear properties of carbon fiber/epoxy composites ( laminates [0/0](s) and [0/90](s)) have been investigated. The interlaminar shear strength (ILSS) was measured by using the short beam shear test, and Iosipescu shear strength and modulus (G(12)) have been determinated by using the Iosipescu test. Results for laminates [0/0](s) and [0/90](s), after hygrothermal conditioning, exhibited a reduction of 21% and 18% on the interlaminar shear strenght, respectively, when compared to the unconditioned samples. Shear modulus follows the same trend. A reduction of 14.1 and 17.6% was found for [0/0](s) and [0/90](s), respectively, when compared to the unconditioned samples. Microstructural observations of the fracture surfaces by optical and scanning electron microscopies showed typical damage mechanisms for laminates [0/0](s) and [0/90](s).

The Effect of Water Immersion and UV Radiation Aging on the Shear Behavior of Woven Continuous Fiber/PEI Laminates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Shear strength evaluation of composite-composite resin associations

Objective: The aim of this study was to investigate the shear strength between distinct associations of different commercial composite resins and their fracture modes.Methods: Nine composite-composite associations (n = 90) were prepared for shear strength evaluation and separated into the following groups: Z/Z (Filtek Z250 UD + Filtek Z250 A2); Z/ D (Filtek Z250 UD + Durafill VS A2); Z/S (Filtek Z250 UD + Filtek Supreme YT); C/C (Charisma OA2 + Charisma A2); C/D (Charisma OA2 + Durafill VS A2); C/S (Charisma OA2 + Filtek Supreme YT); H/H (Herculite XRV B2D + Herculite XRV B2E); H/D (Herculite XRV B2D + Durafill VS A2); H/S (Herculite XRV B2D + Filtek Supreme YT). Shear tests were carried out using universal mechanical test equipment with a load of 200 kgf and speed of 0.5 mm/min. Ultimate shear strength data (MPa) from all tested groups were submitted to analysis of variance (one-way ANOVA) and the Tukey test. The fractured surfaces of the test samples were visually evaluated by binocular stereomicroscope at 20 times magnification. Fractures were classified as either adhesive or cohesive or mixed.Results: The highest ultimate shear strength observed for composite-composite associations was found for the groups: Z/Z, C/S, H/H, H/S, Z/S and C/C. Those associations containing the Durafill resin were weaker than the others.Conclusion: Microparticle RBC associations presented lower shear strength than hybrid and/or nanoparticle RBC associations, once the only significant difference was found when the Durafill resin was involved. (c) 2008 Elsevier Ltd. All rights reserved.

The effect of water immersion on the shear bond strength between chairside reline and denture base acrylic resins: Basic science research

Purpose: The effect of water immersion on the shear bond strength (SBS) between 1 heat-polymerizing acrylic resin (Lucitone 550-L) and 4 autopolymerizing reline resins (Kooliner-K, New Truliner-N, Tokuso Rebase Fast-T, Ufi Gel Hard-U) was investigated. Specimens relined with resin L were also evaluated. Materials and Methods: One hundred sixty cylinders (20 × 20 mm) of L denture base resin were processed, and the reline resins were packed on the prepared bonding surfaces using a split-mold (3.5 × 5.0 mm). Shear tests (0.5 mm/min) were performed on the specimens (n = 8) after polymerization (control), and after immersion in water at 37°C for 7, 90, and 180 days. All fractured surfaces were examined by scanning electron microscopy (SEM) to calculate the percentage of cohesive fracture (PCF). Shear data were analyzed with 2-way ANOVA and Tukey's test; Kruskall-Wallis test was used to analyze PCF data (α = 0.05). Results: After 90 days water immersion, an increase in the mean SBS was observed for U (11.13 to 16.53 MPa; p < 0.001) and T (9.08 to 13.24 MPa, p = 0.035), whereas resin L showed a decrease (21.74 MPa to 14.96 MPa; p < 0.001). The SBS of resins K (8.44 MPa) and N (7.98 MPa) remained unaffected. The mean PCF was lower than 32.6% for K, N, and T, and higher than 65.6% for U and L. Conclusions: Long-term water immersion did not adversely affect the bond of materials K, N, T, and U and decreased the values of resin L. Materials L and U failed cohesively, and K, N, and T failed adhesively. © 2007 by The American College of Prosthodontists.

Effect of fiber orientation on the shear behavior of glass fiber/epoxy composites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Pulsed Nd:YAG laser seam welding of AISI 316L stainless steel thin foils

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Estudo mecânico da estabilidade dorsal da osteossíntese intramedular associada à fixação externa (método de Ulson)

OBJETIVO: Avaliar o método de Ulson de fixação intramedular associado à fixação externa variando a altura do travamento externo dos fios de Kirschner e sem fixação externa. MÉTODO: Foram utilizadas 18 tíbias de porcos, sendo realizada osteotomia transversal na região da tuberosidade e introduzidos dois fios de Kirschner intramedulares em cada peça, em três diferentes padrões de montagem: grupo I - travamento com minifixador externo com 3,0cm de altura; grupo II - travamento com 4,5cm de altura; grupo III: sem travamento externo. Realizaram-se ensaios mecânicos de cisalhamento, obtendo-se: carga máxima, limite de proporcionalidade e coeficiente de rigidez. RESULTADOS: Não foram encontradas diferenças significativas de carga máxima e limite de proporcionalidade entre os grupos; o grupo II apresentou maior coeficiente de rigidez. CONCLUSÃO: A altura do travamento dos fios de Kirschner no método de Ulson, dentro dos limites avaliados, não prejudicou a estabilidade do sistema de fixação da fratura.

Effect of methyl methacrylate monomer on bond strength of denture base resin to acrylic teeth

Bond failures at the acrylic teeth and denture base resin interface are still a common clinical problem in prosthodontics. The effect of methyl methacrylate (MMA) monomer on the bond strength of three types of denture base resins (Acron MC, Lucitone 550 and QC-20) to two types of acrylic teeth (Biotone and Trilux) was evaluated. Twenty specimens were produced for each denture base resin/acrylic tooth combination and were randomly divided into control (acrylic teeth received no surface treatment) and experimental groups (MMA was applied to the surface of the acrylic teeth for 180 s) and were submitted to shear tests (1 mm/mm). Data (MPa) were analyzed using three-way ANOVA/Student's test (alpha = 0.05). MMA increased the bond strength of Lucitone denture base resins and decreased the bond strength of QC-20. No difference was detected for the bond strength of Acron MC base resin after treatment with MMA. (C) 2008 Elsevier Ltd. All rights reserved.

Effect of disinfection on adhesion of reline polymers

Cylinders (3.5 x 5.0 mm) of the reline resins Kooliner (K), New Truliner (N), Tokuso Rebase Fast (T), and Ufi Gel Hard (U) were bonded to cylinders (20 x 20 mm) of the denture base resin Lucitone 550 (L), and samples were divided into two controls and four test groups (n = 8). Shear tests (0.5 mm/min) were performed after polymerization or immersion in water (37 degrees C) for 7 days (controls); two or seven cycles of disinfection by immersion in sodium perborate (50 degrees C/10 min) or microwave irradiation (650 W/6 min). Statistical analyses (alpha = 0.05) revealed that two cycles of microwave and chemical disinfection increased the mean bond strengths of materials T (9.08 to 12.93 MPa) and L (18.89 to 23.02 MPa). For resin L, seven cycles of chemical (15.72 MPa) and microwave (17.82 MPa) disinfection decreased the shear bond strength compared with the respective control (21.74 MPa). Resins U (13.12 MPa), K (8.44 MPa), and N (7.98 MPa) remained unaffected.

Effect of microwave disinfection on the bond strength of denture teeth to acrylic resins

During microwave disinfection, the dentures are exposed to water at high temperature and this may affect the bond between the denture teeth and the acrylic resin from which dentures are made. In this study, a shear test was used to evaluate the effect of microwave disinfection (650W/6 min) on the bond strength of two types of denture teeth to three acrylic resins, with different polymerization methods. The specimens were submitted to the shear tests (0.5 mm/min) after: immersion in water (37 degrees C) for 48 h or 8 days (controls); two or seven cycles of microwave disinfection (test groups). Data (MPa) were analyzed using three-way ANOVA and Tukey HSD test (alpha = 0.05). Microwave disinfection did not adversely affect the bond strength of all tested materials with the exception of QC-20 bonded to SR Vivodent PE, for which a significant reduction was recorded after seven cycles of irradiation. (C) 2007 Elsevier Ltd. All rights reserved.

Influência da energia de soldagem em uniões de lâminas finas através de laser pulsado de Nd:YAG

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Estudo reológico de sistemas gelatina/colágeno/amido para obtenção de géis e aplicação dietéticas de gelatina

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo dos mecanismos de instabilidade em solos residuais de biotita-gnaisse da bacia do ribeirão Guaratinguetá

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A influência do processo de cura nas propriedades do compósito estrutural carbono/epóxi fabricado via VARTM: processamento e caracterização

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efeito do armazenamento prolongado em água sobre a resistência de união entre resinas para reembasamento e resina para base de prótese

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)