1,720,973 research outputs found
Low pressure plasma treatment of CFRP substrates for adhesive bonding: an investigation of joint durability under severe temperature-moisture conditioning
No full textThis work reports a quantitative evaluation of the aging behavior of adhesively bonded joints manufactured using a toughened epoxy adhesive applied on CFRP substrates. Low-pressure plasma (LPP) treatment was employed, adopting air and pure oxygen as process gases and varying working parameters such as power and exposure time. A preliminary testing campaign was performed under standard laboratory conditions to evaluate shear strength of single-lap joints (SLJ), comparing effectiveness of LPP treatments to a traditional mechanical abrasion of the adherends. Even at this early stage, experimental findings highlighted how this physical method provides for competitive performance over abrasion, resulting in a remarkable enhancement of the shear resistance. Four sets of LPP-treatment conditions were selected and then subjected to accelerated aging (consisting of 56 cycles of 5 h at T = 70 °C, RH>90% and 5 h at T = −40 °C each). Their behavior was compared to that of abraded joints, employed as a reference. To assess the durability of the CFRP-epoxy adhesive system under accelerated aging conditions, tensile shear strength (TSS) testing and wedge cleavage test (WT) were performed in parallel. The experimental results showed that low-pressure plasma treatment of the CFRP substrates results in increased short-term quality of the adhesive joint as well as in enhancement of its durability even under severe aging conditions
A design-of-experiments approach to estimate the effect of plasma-treatment parameters on the mechanical resistance of adhesive-bonded joints
No full textIn this study, the design of experiments (DoE) approach was used to identify the effect of low-pressure plasma surface treatment parameters on the lap-shear strength of adhesive bonded joints realized using different substrates. In particular, four different polymeric substrates were considered: 5- and 7-layer carbon-fiber reinforced polymers and polyamide 6 and 6.6. Two-level, full-factorial designs were used to investigate the effects of two varying principal parameters, namely, plasma power and treatment time, for each type of substrate. The analysis was carried out by considering different types of processing gases. The objective function was the tensile shear strength of the adhesively bonded joints. For each set of joints, the shear strength values were compared using the DoE approach to detect any systematic behavior among different substrates. Finally, it was possible to identify the set-up parameters that gave the best performance in terms of shear strength, considering any equivalent conditions from a statistical point of view. This aspect is particularly important in consideration of the process optimization of the manufacturing cycle; indeed, it allows the maximization of the joint efficiency by limiting the energy cost for treatment
A Response Surface Methodology Approach to Improve Adhesive Bonding of Pulsed Laser Treated CFRP Composites
No full textIn this work, a response surface-designed experiment approach was used to determine the optimal settings of laser treatment as a method of surface preparation for CFRP prior to bonding. A nanosecond pulsed Ytterbium-doped-fiber laser source was used in combination with a scanning system. A Face-centered Central Composite Design was used to model the tensile shear strength (TSS) of adhesive bonded joints and investigate the effects of varying three parameters, namely, power, pitch, and lateral overlap. The analysis was carried out considering different focal distances. For each set of joints, shear strength values were modeled using Response Surface Methodology (RSM) to identify the set-up parameters that gave the best performance, determining any equivalent conditions from a statistical point of view. The regression models also allow the prediction of the behavior of the joints for not experimentally tested parameter settings, within the operating domain of investigation. This aspect is particularly important in consideration of the process optimization of the manufacturing cycle since it allows the maximization of joint efficiency by limiting the energy consumption for treatment
Influence of silica aerogel filler on strength-to-weight ratio of carbon/epoxy composite made by vacuum resin infusion
No full textDurability of polyamide bonded joints: influence of surface pre-treatment
No full textThe aim of this study was to evaluate the influence of surface pre-treatment on the durability of bonded joints between polyamide pieces. Various surface preparations of the substrates were carried out and a wedge test was performed to evaluate the joint behaviour over time. Joints composed of polyamide 6 and polyamide 66 were made using a two-component acrylic adhesive. Four different surface treatments were compared: only degreasing, degreasing + abrasion, degreasing + plasma and degreasing + abrasion + plasma. The tests carried out highlighted the extreme importance of choosing the right surface preparation if one wishes to guarantee high performance over time. For both substrates, superficial preparations with cold plasma yielded the best results
Experimental investigation of the static and fatigue behavior of hybrid ductile adhesive-RSWelded joints in a DP 1000 steel
No full textHybrid joining is gaining wide space in automotive industry thanks to the possibility of concentrating advantages of different joining methods in a unique technique. Producers’ main interest is indeed to obtain quality joints, which are able to maintain their properties under severe load conditions, increasing the life of their components and, thus, safety for the final users. In particular, the use of adhesive-bonding combined with resistance spot welding (RSW) offers several advantages both over adhesive joints, increasing stiffness and static strength of the assemblies, and over the welded-only joints extending fatigue life of the components. This work relates the properties of hybrid RSWeld-bonded joints in an Advanced High-Strength Steel (AHSS) to the performance of joints made by using the two joining techniques separately, i.e. spot welding only and adhesive-bonding using a semi-structural epoxy-polyurethane adhesive. The experimental findings showed that this hybrid system presents excellent static and dynamic qualities over the two more conventional techniques and also suggest its use in production
Effect of process gases in vacuum plasma treatment on adhesion properties of titanium alloy substrates
No full textThe subject of this paper is the quantitative evaluation of the correlation which exists between the surface characteristics of parts in a titanium alloy, Ti-6Al-4V, and the mechanical strength of the joints, made linking these parts using a structural epoxy adhesive. In particular, the surfaces were prepared by using vacuum plasma as a prebonding treatment with various process gases (air, Ar and O2). For each of these treatments, tests were performed for the mechanical characterisation of the joints, and surveys on the wettability properties were carried out by using a sessile drop method in order to estimate the surface energy of plasma treated surfaces. The results were related to the morphological and electrical properties of the substrates, defined in parallel through SKPM assessment. Further XPS analyses of their chemical state allowed the evaluation of the effect of vacuum plasma on both contaminant removal and formation of a weak oxide layer. The results obtained highlighted interesting relationships between vacuum plasma surface preparation and mechanical resistance of the bonded joints, as well as synergy between the morphological, electrical and chemical properties present in adhesive phenomena
Laser surface pre–treatment of polyolefin substrates for adhesive bonding
No full textAdhesive bonding offers many advantages over mechanical fastening, but requires accurate surface preparation, which is widely recognized as the key step to producing reliable and durable adhesive bonds. The use of laser cleaning processes helps to increase the reactivity of the topmost layers of substrates, without affecting the bulk material properties. These methods are often applied to treat polymers, which are generally characterized by high chemical inertia, very low surface energy values and, consequently, poor adhesive properties and this is particularly true for polyolefins. Furthermore, laser treatment provides an alternative to the polluting and less accurate practices such as manual abrasion and primer. In this paper the effect of different laser pre-treatments on polypropylene (PP) and high density polyethylene (HDPE) substrates was studied, by microscopic investigation and single lap- shear tests. As a comparison, untreated and primer treated specimens were also included in the experimental campaign. The results show that laser treatment significantly affected the substrates' surface and the mechanical properties of adhesive bonded joints. Finding the optimal combination of the working parameters, it is possible to enhance the strength of both untreated and primer-treated joints
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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