BackgroundIn recent decades adhesively bonded joints gained attention in many industries such as automotive, aeronautics and offshore, increasing structural mechanical repair services and thus promoting technological advances. It is a trend to nowadays replace welded and bolted joint for adhesively bonded joint. Advantages over welded and bolted joints are don't need a fire exposure, fast manufacturing, fatigue and corrosion resistance. Although the geometry of bonded joint is complex considering particularities at the end of joint, adhesive joint promotes a decrease of stress concentration [1,2].A relation between adherend and adhesive material and consequently the load transfer of joint is intrinsically related to surface state. The correct preparation requires total removal of contaminants (remaining corrosion layers, dirt, lubricating and bio-organisms) is needed [3]. A strong adhesion depends on bonding surface treatment in order to improve a joint strength, although bond strength doesn't increase with increase of roughening [4]. The surface roughness modifications in the bonded area of the joint promote an expressive effect in the bonded structures [5,6].The main techniques for surface modification are sandblasting, grinding and chemical cleaning that makes a generation of specific surface topographies at bonding area. The advantages of bonding area preparation are a great mechanical coupling of the adhesive AbstractAdhesively bonded joints are being widely used in the fabrication process of aircraft and automobile structures. Surface roughness is an important parameter of product quality that strongly affects the performance of mechanical parts, as wel as production costs. This parameter highly influences the mechanical properties overall of such structures. The effects of UV radiation on the single lap joints manufactured with different types of surface preparation and temperature were examined before and after UV exposure. Sandblasting, sanding and chemical cleaning were used as surface preparation and two test temperatures were used for investigation, 25 and 115 °C. The results of those tests showed that surface preparation highly influences shear strength, but does not affect the stiffness of the tested joints. Temperature also influences the shear strength and stiffness. UV radiation contributes to increase shear strength and do not degrade the tested single lap joints.
The research of natural fiber composites is growing due to the fact that the green materials combine low weight with good mechanical properties. Curaua fiber arises as a competitive natural fiber due to its abundance, low cost and a variety of applications. In this work, different weight fractions of Curaua fiber were used in order to obtain this natural composite material. Specimens of Curaua/Epoxy composites were tested in tensile and in flexion to observe the quasi-static mechanical properties and its physical properties due to temperature variation were evaluated by Dynamic Mechanical Analyses (DMA) analyses. An increase in fiber quantity showed an increase in both the modulus and the strength, leading to a stiff and less ductile material. The results also showed an increase in the viscoelastic stiffness of the epoxy matrix by the incorporation of Curaua fibers. The interaction between Curaua fibers and epoxy matrix affects segmental mobility of the epoxy chains.
Diesel is an important fuel, partly because of the longevity and cleanliness of diesel engines. Often, polymers are in direct contact with diesel and understanding compatibility is critical. Polyoxymethylene (POM) is a thermoplastic used to manufacture automotive fuel pump gears and rotors due to its low coefficient of friction and thermal and dimensional stability. In this study, tensile tests were performed on plain and glass fiber reinforced (POM and POMGF) after immersion in diesel at different temperatures (−10°C, 23°C, and 60°C) for 1000, 2000, 3000, 5000, and 10 000 hour. A mathematical model was developed using data from just three tensile stress‐strain curves obtained at two different fluid temperatures and three different immersion times. Model and experimental results show good agreement with one another for all conditions tested.
The present paper investigates the effect of temperature of unplasticized polyvinyl chloride (UPVC) under tension. UPVC specimens were tensile tested across a range of temperatures (from À20 C to 60 C). The UPVC, like other polymers, was strongly affected by temperature. Those below room temperature were more fragile but had greater tensile strength and stiffness. When room temperature is exceeded, the UPVC test specimens became softer, with lower strength and stiffness. Considering the results, an analytical expression to predict the mechanical behavior of UPVC in tensile tests at different temperatures-more specifically a description of the experimental tensile stress-strain curves by an algebraic equation is proposed. A reasonable approximation of the stress-strain curve was possible to obtain with a minimum of three tests performed at different temperatures. The analytical results were in good agreement with experimental ones.
Composite repair systems have been gaining each time more space in industry, especially when it comes to repairing through-wall defects in pipes. They are simpler to apply, have no costly downtime and provide lower risks to the environment when compared to metallic repairs. ASME PCC-2 and ISO 24817 standards are responsible for defining the parameters necessary to a successful repair, however neither of them addresses a very common practice in such repairs, which is the addition of a bonded metallic patch over the defect. Several companies are adepts of such practice and it has already been proven that is actually the metallic patch and not the composite sleeve itself that sustains most of the load applied on the repair, and for that reason it becomes necessary to conduct further studies regarding the behavior of the patch alone. One important issue is to understand why the strength of similar repairs due to operation errors with very similar amplitude of pressure transients seems to vary randomly, with unexplained early failures. The present paper is concerned with an experimental study about how pressure variations can generate cyclic inelastic strains in the pipe, which can weaken the adhesion between pipe and patch, leading the repair to fail prematurely.
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