Silvio de Barros

INFLUENCE OF ADHEREND SURFACE ROUGHNESS ON THE ADHESIVE BOND STRENGTH

SURFACE TREATMENT OF THE ADHERENDS PRIOR TO ADHESIVE BONDING PLAYS AN IMPORTANT ROLE IN THE ENHANCING OF STRENGTH AND DURABILITY OF BONDED JOINTS. IN THIS WORK, AN INVESTIGATION ON EFFECT OF ADHEREND SURFACE ROUGHNESS ON ADHESIVE BOND STRENGTH WAS PERFORMED. SINGLE STRAP JOINTS WITH DIFFERENT ADHERENDS (MILD STEEL AND ALUMINIUM) BONDED WITH AN EPOXY RESIN (ARALDITE® 2015) WERE TESTED. THE ADHEREND SURFACE WAS TREATED BY MECHANICAL ABRASION PROCESS USING AN EMERY PAPER. CONTACT ANGLE MEASUREMENT AND SEM ANALYSIS TO UNDERSTAND THE WETTABILITY AND THE FAILURE MECHANISM OF THE JOINTS WERE PERFORMED. IT WAS FOUND THAT AN OPTIMUM SURFACE ROUGHNESS EXISTS FOR A MAXIMUM BONDING STRENGTH AND THE ROUGHNESS RANGE DEPENDS ON THE ADHEREND MATERIAL. THE JOINT STRENGTH CHANGES ARE ASSOCIATED NOT ONLY SIMPLY BY THE INCREASED BONDING AREA, SURFACE TEXTURE OR MECHANICAL INTERLOCKING, BUT ALSO BY THE CHEMICAL CHARACTERISTICS OF THE SURFACE AND THE CHEMICAL BOND BETWEEN THEM.

Numerical simulations of crack propagation tests in adhesive bonded joints

Mainly due to their low weight, low cost and ease of assembly, the adhesive bonds have emerged as a promising technology. However, the lack of adequate tools of design and control remain an obstacle to the use of the adhesives. In this work a cohesive interface model formulated within the framework of damage mechanics is applied for the simulation of decohesion during crack propagation tests. Considering the mechanical tests of aluminium/epoxy specimens, comparisons between experimental and numerical results are presented.

Adhesive joint computations using cohesive zones

BackgroundThe cohesive zone approach has gained increasing success in recent years for simulating debonding and fracture via finite element methods and is ideally suited for simulating adhesive joints, the potential crack paths being generally known in advance in most cases. In the paper the determination of the size of the so-called cohesive process zone is discussed, i.e. the region wherein the stress and damage state have to be correctly resolved in order to properly quantify the dissipated energy and the load bearing capacity of the structure. An a priori estimate for the size of the active process zone is provided based on the beam on elastic foundation model in which the material parameters of the cohesive law are incorporated.MethodsThe formulation of the cohesive model in a damage mechanics format is first provided. The beam on elastic foundation model is then recalled and an approximate solution for the cohesive zone length is found that depends on a material length and a geometric parameter as well.Results and discussionNumerical results are presented for a Double Cantilever Beam (DCB) geometry with varying thickness for which bilinear and exponential cohesive laws are considered. The influence of the geometry and of the shape of the cohesive law are put forward in terms of global response and evolution of the cohesive process zone.ConclusionsThe size of the process zone is found to be quite sensitive to the specimen characteristic size, whose influence is well captured even using a simplified modeling wherein the original cohesive law is changed into an ideal perfectly brittle one. This leads to fairly good estimates of the size of the cohesive zone compared to finite element results.

Mechanical Performance of Natural Fibers Reinforced Geopolymer Composites

The use of geopolymers as matrix in composites with syntactical fibers have been studied and proposed in the literature. Nonetheless, for the best know of the authors, there are no researches about the use of geopolymers as matrix in composites with natural fibers. The use of natural fibers is increasing in the automotive industries. One of the problems to expand the use of natural fibers in composite materials is the low fire resistance of the classical type of polymers. In this sense, geopolymeric matrices open up horizons for this type of application. This paper studies composites with geopolymeric matrices reinforced with two types of natural fibers: sisal (Agave Sisalana) and pineapple leaf fiber (PALF-Ananas Comosus). The mechanical properties of these new composites are investigated by mechanical tests. The results confirm the increasing in the mechanical performance whenever the fibers are under traction stress.

Effect of periodontal disease on the bond strength of fiber post cemented with different adhesive systems and resin luting agents

The objective of the present study was to determine the effect periodontal disease on the bond strength of fiberglass posts, different adhesive systems and resin cements. Ninety human maxillary central incisors roots extracted due to periodontal disease or prosthetic reasons were endodontically treated and divided into six experimental groups: NPD-ARC – no periodontal disease/RelyX ARC and Adper Single Bond 2; NPD-PF – no periodontal disease/Panavia F and ED Primer; NPD-U – no periodontal disease/RelyX U100; PD-ARC – periodontal disease/RelyX ARC and Adper Single Bond 2; PD-PF – periodontal disease/Panavia F and ED Primer; and PD-U – periodontal disease/RelyX U100. Specimens were subjected to push-out test and data were analyzed by two-way ANOVA and Tukey’s test (p = 0.05). The periodontal disease groups showed that the Panavia F/ED Primer group presented no significantly higher mean values compared with RelyX U100, and that both presented significantly higher mean values when compared with RelyX ARC/Single Bond 2 group. These results were also observed in roots with no periodontal disease. There were no differences in bond strength mean values of roots related or not to periodontal disease.

Interlaminar adhesion assessment of carbon-epoxy laminates under salt water ageing using peel tests

The aim of this study is to assess the interlaminar adhesion of carbon-epoxy laminates under salt water condition. Carbon-epoxy laminate specimens were immersed in a salt water tank for 60 days. Some specimens were then dried at room temperature for 280 days, until recovering their initial weight. Specimens were tested using the composite peel test, an adaptation of the floating roller peel tests for composite materials. The results showed a degradation of peel strength in some areas due to the ageing process. The drying process did not affect the test results. A scanning electron microscopic analysis carried out on the fracture surface of the specimens revealed a typical mode I failure microstructure. A mixture of matrix failure and fibre/matrix interfacial failure was observed in non-aged specimens. Finally, a chemical characterization of the fracture surfaces with energy-dispersive spectroscopy confirmed the penetration of salt water in regions near the edge of the specimens. A degradation of the fibre/matrix interface adhesion was observed in affected areas. Floating roller peel tests proved to be a fast and effective method to access the interlaminar adhesion performance of composite laminates.

Effect of Babassu Natural Filler on PBAT/PHB Biodegradable Blends: An Investigation of Thermal, Mechanical, and Morphological Behavior

Blending of biodegradable polymers in combination with low-price organic fillers has proven to be a suitable approach to produce cost-effective composites in order to address pollution issues and develop products with superior mechanical properties. In the present research work PBAT/PHB/Babassu composites with 25, 50, and 75% of each polymer and 20% of Babassu were produced by melting extrusion. Their thermal, mechanical, and morphological behavior was investigated by differential scanning calorimetry (DSC), tensile testing, and scanning electron microscopy (SEM). Blending PBAT with PHB inhibited the crystallization of both polymers whereas adding Babassu did not significantly change their melting behaviour. Incorporation of Babassu reduced the tensile strength of its respective blends between 4.8 and 32.3%, and elongation at break between 26.0 and 66.3%. PBAT as highly ductile and low crystalline polymer may be seen as a crystallization tool control for PHB as well as a plasticizer to PBAT/PHB blends and PBAT/PHB/Babassu composites. As PBAT content increases: (i) elongation at break increases and (ii) surface fracture becomes more refined indicating the presence of more energy dissipation mechanisms. As PBAT/PHB/Babassu composites are biodegradable, environmental friendly, and cost effective, products based on these compounds have a great potential since their mechanical properties such as ductility, stiffness, and tensile strength are still suitable for several applications even at lower temperatures (−40 °C).

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.

Papers from the 2nd Luso-Brazilian Conference on Adhesion and Adhesives (CLBA2014), Porto, Portugal, 24–25 July 2014

This special issue of The Journal of Adhesion (JA) contains selected papers presented at the 2nd Luso-Brazilian Conference on Adhesion and Adhesives (CLBA 2014) held in Porto, Portugal, during 24–25 July 2014. CLBA 2014 was chaired by both of us and was co-organized by the Brazilian Association of Adhesion and Adhesives (ABAA) and the Portuguese Association of Adhesion and Adhesives (APAA). The goal of the conference was to join the Portuguese and Brazilian communities to discuss issues related to adhesive bonding research lately developed in both countries. Approximately 50 papers were presented by researchers from many universities and research centres. In order to disseminate the work presented at CLBA 2014, selected papers were prepared which resulted in the present special issue. The first three papers focus on methods to investigate adhesion. Antunes et al. investigate the adhesive strength of FeCr and FeCoCr coatings produced by electric arc thermal spray process on carbon steel plates. The physical properties of coatings were evaluated by pull-off test and microhardness measurement. The main conclusion is that the FeCrCo deposition, with an epoxy sealing, is suitable to be used as an efficient coating of carbon steel in aggressive marine environments. In Lopes et al., the pull-off test is used to characterize the in-service performance of ceramic tile claddings. An experimental campaign is performed in laboratory and in situ, analysing the variability of the pull-off testing technique. The tests performed in the laboratory showed a variation coefficient from 8% to 25% whereas for tests on walls the variation coefficient was comprised between 15% and 26%. Martins et al. present a study on the curing conditions of several resin-impregnated papers and its impact on the performance of HPL (high-pressure decorative laminate). A new methodology for evaluating the bond strength development between the different layers of a HPL (overlay, decorative, and kraft papers) was developed using ABES (automated bonding evaluation system) equipment. The two following contributions address adhesive properties and development. Paiva et al. developed a model capable to predict and optimize the peel strength from the composition of adhesives for the footwear industry. The design variables are the weight percentages of the solid raw material

Editorial for thematic series: 1st Luso-Brazilian conference on adhesion and adhesives

© A m This special issue of Applied Adhesion Science (AAS) contains selected papers presented at the 1 Luso-Brazilian Conference on Adhesion and Adhesives (CLBA 2012) held in Rio de Janeiro, Brazil during November 8–9, 2012. CLBA 2012 was chaired by both of us and was co-organized by the Brazilian Association of Adhesion and Adhesives (ABAA) and the Portuguese Association of Adhesion and Adhesives (APAA). The goal of the conference was to join the Portuguese and Brazilian communities to discuss issues related to adhesive bonding research lately developed in both countries. Approximately 60 papers were presented by researchers from many universities and research centers. In order to disseminate the work presented in CLBA 2012, selected papers were prepared which resulted in the present Special Issue. In the first paper, Queiroz et al. study the creep behavior of single-lap joints (SLJ). They developed a pneumatic creep equipment capable of testing ten specimens simultaneously. Results show that the average tensile strength is not enough to guarantee project safety, for long term applications. An initial model for the creep behavior of bonded joints was also proposed. In the next paper, Sales et al. investigated the effect of periodontal disease on the bond strength of fiberglass posts. Push-out tests were performed in specimens prepared with different adhesive systems and resin cements. It was possible to conclude that periodontal disease did not affected the bond strength mean values of fiberglass posts cementation. In the third paper, Silva Neto et al. present a numerical and experimental investigation on the adhesion between the steel tube and cement paste in petroleum wells. Push-out tests were performed with three different interface conditions in order to validate the numerical model. They observed the influence of the different conditions used in the experiments and the sensibility of the model variables to these changes. Antunes et al. worked on the characterization of FeCr and FeCoCr alloy coatings of carbon steels for marine environment applications. The adhesive strength of alloy coatings using thermal spray process was studied and related to chemical composition. Five combinations of wires and intermediate bonds were used. The coatings were characterized by morphological aspects, corrosion and adhesion tests. They concluded that the FeCoCr deposition, with an epoxy sealing, is suitable to be used as an efficient coating of carbon steel in aggressive marine environments. The last paper by Souza and Reis is related to the thermal behavior of DGEBA (Diglycidyl Ether of Bisphenol A) adhesives. Three different epoxy adhesives used in the offshore industry are characterized by Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA). The