E.M. Sampaio

Adhesion of Geopolymer Bonded Joints Considering Surface Treatments

In this study the adhesion properties of a geopolymer-based adhesive on metallic substrates are investigated, considering different surface conditions. Mechanical treatments (grit-blasting and sand-blasting) and chemical treatments (nitro-phosphoric acid and silanization) were performed on steel and aluminium plates. Single lap joint specimens were tested in order to access the influence of these pretreatments on the shear bond strength. The surfaces were scanned and the average surface roughness parameters were used in order to assess their effect on bond strength. The results indicated that the effect of individual surface roughness parameters alone is not statistically significant when correlated with bond strength. In general, chemical treatments were usually less effective than mechanical treatments alone for both steel and aluminium joints with geopolymers as adhesives.

Analysis of gap formation at tooth-composite resin interface: effect of C-factor and light-curing protocol

Objective: The aim of this study was to evaluate the effect of C-factor and light-curing protocol on gap formation in composite resin restorations. Material and Methods: Cylindrical cavities with 5.0 mm diameter and three different depths (A=1.0, B=2.0 and C=3.0 mm) were prepared on the occlusal surface of 30 human molars and restored in a single increment with P 60. The composite resin was light-cured according to two protocols: standard - 850 mW/cm2 / 20 s and gradual - 100 up to 1000 mW/cm2/ 10 s + 1000 mW/cm2 / 10 s. After storage in distilled water (37°C/7 days), the restorations were cut into three slices in a buccolingual direction and the gap widths were analyzed using a 3D-scanning system. The data were submitted to ANOVA and Student-Newman-Keuls test (α=0.05). Results: ANOVA detected a significant influence for the C-factor and light-curing protocol as independent factors, and for the double interaction C-factor vs. light-curing protocol. Cavities with higher C-factor presented the highest gap formation. The gradual light-curing protocol led to smaller gap formation at cavity interfaces. Conclusions: The findings of this study suggest that the C-factor played an essential role in gap formation. The gradual light-curing protocol may allow relaxation of composite resin restoration during polymerization reaction.

Influence of C-factor and Light-curing Mode on Gap Formation in Resin Composite Restorations

To investigate the influence of the C-factor (Cf) and light-curing mode (LCM) on gap formation in resin composite (RC) restorations. Cylindrical Class I cavities with a 5.0 mm diameter andthree different depths (1.0, 2.0 and 3.0 mm) were prepared in the occlusal surfaces of 60 human molars and restored with P60 (P) and Supreme (Su). RCs were light-cured in accordance with two modes: Standard (S)--850mW/cm2/20 seconds and Ramp (R)-100 up to 1000mW/cm2/10 seconds +1000mW/cm2/10 seconds. After storage in distilled water, the restorations were cut into three slices and the gap widths were analyzed in a 3D-scanning system. The data were analyzed by ANOVA and Student-Newman-Keuls test (alpha = 0.05). ANOVA detected significant influence for the RC, Cf and LCM independent factors and for the double interactions RC vs Cf and LCM vs Cf. Smaller gap formation was found for cavities restored with Su. R was responsible for the smaller gap formation. The highest gap formation was found for cavities with Cf = 3.4, followed by Cf = 2.6 and 1.8 without statistical differences between them. These findings suggest that Cf played an essential role in gap formation. R LCM may allow RC relaxation during polymerization reaction. Finally, nanocomposites (Su) may lead to less gap formation at the resin-dentin interface.

Evaluación de la adherencia de uniones adhesivas metálicas con adhesivos epoxídicos modificados

In this work the adhesive properties of epoxy resins based on diglycidyl ether of bisphenol A have been evaluated. The epoxy resin was modified with butadiene and acrylic copolymers to obtain toughened adhesives. The aliphatic primary amines triethylenetetramine, N-(2-aminoethyl)piperazine and isophorone diamine were investigated as curing agents. The adhesive properties were investigated using the epoxy resins as independent systems as well as the modified resin. The adhesive properties of modified and unmodified epoxy resins were studied using steel alloy (ASTM A36) as adherent. The adherence has been evaluated using three geometric assays of steel-steel bonded joints. The rheological behavior of the adhesives was investigated under isothermal conditions. The rheological parameters associated with the curing reaction such as reaction rate, pot life and gel time of the pure adhesives were related to the chemical structure of the curing agents. The cloud point and the gel time of the modified adhesives were related to the morphology and the reaction rate, respectively. The morphology was characterized by scanning electronic microscopy. The adherence of the adhesive joints at different mechanical solicitations was related to the generated morphology by the dispersed phase of each modifier and the networks structures of the epoxy adhesives.

Study on the creep behavior of bonded metallic joints

Bonded joints have been used as the main alternative to join components made of different materials or not. Literature shows that although prior studies focused on the characterization of several mechanical properties related to joints, little is known about the creep behavior of bonded joints. Creep test’s main disadvantage is the low productivity of results since testing machines are not able to perform simultaneous multiple tests. In this case, the statistical treatment is based on a small amount of results, reducing the reliability of the predictions obtained. With this in mind, the Laboratory of Adhesion and Adherence (LAA) developed the pneumatic creep equipment (PCE), capable of testing ten specimens simultaneously, with distinct parameters. This work studies the behavior of single-lap joints (SLJ) made of metallic substrate and bonded with epoxy and polyurethane adhesives. The joints were fabricated in conformity with the ASTM D 1002 standard. Results show that, for long term applications, the average tensile strength isn’t enough to guarantee project safety. An initial model for the creep behavior of bonded joints is proposed.

Fatigue and quasi-static analysis of a new type of surface preparation used for the CFRP repair of steel offshore structures

ABSTRACT In recent years, there has been an increasing interest in repairing offshore steel structures by using adhesively joined carbon fiber reinforced polymers (CFRP). For such procedure, surface preparation plays a vital role to maintain the integrity of the joint and to ensure proper load transfer. The primary surface preparation used by the oil and gas industry is the grit blasting due to its known quality. However, the logistic required is a major drawback limiting the use of adhesively joined repairs. Other surface preparation procedures available are unable to promote proper treatment. In this paper, an alternative surface preparation methodology employing a portable machine that uses rotation and impact to treat the steel surface was evaluated by quasi-static and fatigue tests of CFRP/steel adhesively bonded using the double-lap joints. The joints were prepared using non-corroded and severely corroded steel surfaces treated by grit blasting or rotating impact machine. The corroded plate was used to evaluate the efficiency of the rotating impact machine in removing deeply penetrating oxides. Test results showed that the performance of the machine was comparable to grit blasting even for the severely corroded surface with deep pitting. Corrosion in the metallic substrate impaired the quasi-static and fatigue properties.

An assessment of composite repair system in offshore platform for corroded circumferential welds in super duplex steel pipe

The main aim of this study is to assess the effectiveness of a composite repair system in severely corroded circumferential welds in super duplex stainless steel pipes as a preventive measure against the premature corrosion damage at the welds. Artificial defects were fabricated on the super duplex steel tube in order to reproduce the localized corrosion damage defects found in real welded joints. Three kinds of through thickness defects were considered: 25%, 50% and 96% of the perimeter of the pipe. The performance of the repaired pipe was assessed by hydrostatic tests as per ISO 24817 standard. The results showed that the composite repair system can sustain the designed failure pressure even for the pipe damaged with through-wall defect up to 96% of the perimeter of the pipe. Hence, the composite repair system can be used as a preliminary tool to protect the unexpected or premature failure at the welds and maintain an adequate level of mechanical strength for a given operating pressure. This composite repair system can assure that the pipe will not leak until a planned maintenance of the line. Nevertheless, further work is still desirable to improve the confidence in the long-term performance of bonded composite.