S. de Barros

Influence of mechanical surface treatment on fatigue life of bonded joints

ABSTRACT Adhesively bonded joints can support a longer fatigue life if compared to conventional joining techniques, provided that a set of requirements is fulfilled. One of the most important requirements is the mechanical preparation of the bonded joint surface, which improves the joint interface adhesion. The aim of this work is to investigate the influence of surface roughness of mild steel substrates on fatigue behavior in adhesive bonded plates. To accomplish this objective, three different surface treatments were used on A36 steel substrate specimens, namely sand blasting, grit blasting, and bristle blasting. Bonded plate specimens, using end-notched flexure format, with a thin adhesive epoxy layer were manufactured and tested, under mode II loading condition, in both static and dynamic tests. The results confirm the importance of surface treatment of the substrate on the fatigue life, confirming that adhesively bonded joints have significant performance differences when subjected to static and dynamic loadings.

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.

Experimental analysis of metal-composite repair of floating offshore units (FPSO)

ABSTRACT This work presents the analysis of the fatigue behaviour of a repaired metal-composite panel under mixed-mode loading conditions and also discusses a composite repair of the damaged tube on an offshore unit application. A carbon steel plate (A36) as a parent substrate and an epoxy resin was used. The composite material for the repair was a biaxial +45°/−45° non-crimp carbon fabric. Static and dynamic three-point bending tests were performed. It was found that the fatigue load must be lower than 60% of the static load for fatigue life >105, as recommended by Det Norske Veritas (DNV). It is likely that the findings of this study will be a boost to improve the understanding of the long-term performance of bonded repair in an offshore environment.

Debonding on command of multi-material adhesive joints

ABSTRACT In this work an innovative technique for multi-material adhesive joints debonding by combining the inductive heating method and the use of thermally expandable particles (TEPs) is presented. First, single lap joints (SLJs) using various combinations of adherends (high-strength steel (HS), aluminum (Al), and carbon fiber reinforced plastics (CFRP)) were fabricated and tested to assess the influence of TEP content on the lap-shear strength of the joints. Further, the ability of the TEP-modified joints to support temperature-controlled debonding was evaluated. It was shown that the control of debonding process by temperature is possible. The temperature needed for debonding is a function of TEP content and can be lowered by increasing the TEP content. Relatively similar debonding temperatures were found for multi-material/dissimilar joints debonding compared with similar joints, but more induction heating power is generally necessary to disassemble multi-material adhesive joints.

Application of Geopolymeric Adhesives in Ceramic Systems Subjected to Cyclic Temperature Environments

The Brazilian experience with the use of ceramic tiles in facades dates back to the 17th century. Many modern buildings still use such an architectural option, which leads to an increasing industry of cementious adhesives. Despite several recommendations in standards, there is still a huge problem with ceramic detachments. This paper discusses observations in some field case scenarios as well as assesses the potential use of a new type of adhesive, characterized by having low CO2 emissions in its productions chain. In this study, the adhesive properties were determined in a porcelain tiles-adhesive-substrate system through the pullout test. The roughness of the tiles was also determined. Three types of adhesives were used: a high-performance commercial adhesive, classified by the Brazilian standard as high adherence (ACIII-E), and two alkaline type adhesives [alkaline-activated metakaolinite (MK) and alkaline-activated weathered soils (SI)]. These geopolymeric adhesives were activated with alkaline metals using sodium and potassium silicates. The bonded systems were subjected to room temperature, 55°C, and cyclic regimen. In field cases, it has been observed that detachments most often occur in facades subjected to a greater incidence of sunlight on their surfaces. The experimental study points out that the alkaline activation of aluminum silicates improved adhesive and thermo mechanical properties in comparison with commercial adhesives. In general, the geopolymeric adhesives had better adhesion than those which were adhered with the commercial adhesive ACIII-E, especially under increased temperature.

Functionally graded adhesive joints by using thermally expandable particles

ABSTRACT The main objective of this work was to use thermally expandable particles (TEPs) in order to create a graded adhesive along the overlap by local mixing of the particles. Different amounts of TEPs were used along the overlap with two different adhesives used in automotive industry. Tensile and four-point bend tests were performed on single lap joints with hard steel adherends in order to investigate the behaviour of TEPs-modified graded joints. It was found that the strength of the joints under tension decrease with increasing TEPs content even for small amount of particles (i.e. 1 and 5%). However, a slight increase in strength was found for the graded joints compared to homogeneous joints modified with the same %wt TEPs. In the four-point bending test, the graded joints presented slightly higher strength, if compared with the homogeneous joints modified with the same wt% TEPs. 5%wt TEPs-modified joints presented the highest strength when submitted to bending loading. The experimental results are compared with a finite element model and generally a reasonably good agreement was found.

Bonded repair of composite structures in aerospace application: a review on environmental issues

Over the last two decades, the repair of existing engineering structures using fiber reinforced polymer composites has attracted a great attention by aerospace industry, as it is more economical than replacing new. With an increased use of composite material in aerospace field, it is thus essential to restore the structural integrity by repair of damaged part. Concerns regarding the long term durability of composite repair bonded joints have been a major obstacle for critical component of aerospace structures. This paper reviews the current research on the environmental durability of adhesive bonded repair of composite structures to focus on the durability concerns and suggestion on the research needed in this area. The most important environmental factors (moisture and temperature) are reviewed thoroughly and also combined environmental effect. Finite element methods used to predict the environmental influence on the composite bonded joints are briefly reviewed. Finally, the paper concludes with key findings, opportunities and future research topics in order to develop cost effective, better quality and reliable composite repair bonded joints.

Test methods for bond strength of glass fiber posts to dentin: A review

ABSTRACT In this paper, a review of the test methods for bond strength of glass fiber posts to dentin is presented. The main variables that influence the bond strength tests are related to substrate, to specimen properties, specimen preparation, and test methodology. The impact of these variables on the test outcome is analyzed. The search was performed on studies published between 2007 and 2015. Most of the tests carried out, in the literature, were the push-out (75%), pull-out (13%), and microtensile (11.9%) tests, showing an inversion compared to the results found in studies published between 2005 and 2010, when push-out test was used in a proportion of 2% and microtensile test in a proportion of 67%. The push-out test emerged as a practical tool for evaluating the interfacial shear strength between fiber post and root canal walls.

The Influence of Alloying Elements on Adhesive Properties of Epoxy-Quasicrystal Composites

Quasicrystals (QC) are materials that exhibit good surface properties such as high hardness, low surface energy, low friction coefficient, and good resistance to oxidation and corrosion. Despite these properties, QC alloys are highly brittle, discouraging their uses in applications requiring mechanical stresses. Hence, the development of composites using quasicrystalline materials as reinforcement to ductile matrices is an interesting alternative. In this work, Al-Cu-Fe quasicrystals were used as a reinforcement to epoxy resin in order improve adhesion with metallic substrates. Adhesive properties were evaluated by single lap joint (SLJ) tests and the QC/epoxy interface was analyzed by scanning electron microscopy (SEM). Aluminum, copper, and iron, individual elements, were used to investigate the contribution of each element to the adhesive. Results show that it was possible to significantly enhance adhesion properties when 25% QC was added to epoxy and that the effect of QC amount on SLJ bond strength did not follow a linear trend. Moreover, the contribution of each alloying element was important to explain the influence of QC addition on adhesive properties of the epoxy-based composites.