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In 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.

This work reports a systematic and quantitative evaluation of the effects induced on the adhesive properties of carbon fiber reinforced polymer (CFRP) substrates by various vacuum cold-plasma treatments. In particular, surface activation of the CFRP substrates was performed using several combinations of exposure time, plasma power, and processing gas (air, O-2, Ar and N-2). By comparing these plasma treatments with conventional techniques of abrasion and peel ply, it was possible to substantially increase the performance of the adhesively bonded joints made by overlapping the CFRP substrates with a structural epoxy resin. On each differently treated surface, measurements of roughness and of wettability were performed, allowing the evaluation of the increase in surface energy after the plasma treatment. XPS analyses allowed the identification of the chemical state of the substrates and showed an in-depth functionalization of the outer layer of the CFRP material. The experimental results show that an engineered plasma treatment of the CFRP substrates allows one to modify the surface morphology and both wetting and chemical activation properties of the treated surfaces, resulting in an increased mechanical shear strength of the joints.

This work emphasizes the critical need of surface preparation to improve the performance of adhesively bonded 3D printed Acrylonitrile Butadiene Styrene (ABS) adherends obtained using Fused Filament Fabrication (FFF). In particular, mechanical abrasion and two different plasma pre-treatments, i.e., Atmospheric Pressure Plasma (APP) and Low-Pressure Plasma (LPP), were compared through the qualitative analysis of surface wettability, using static and dynamic contact angle measurements, and the quantitative evaluation of surface roughness measured using optical profilometry. In addition, mechanical tests were carried out using the single lap joint configuration and the interaction between the treated ABS substrates and three different adhesive materials, epoxy, polyurethane and modified silane, were carefully ascertained. The results indicated that the plasma process at low pressure (LPP) enabled a substantial decrease of contact angle (θ 80o). The improved wetting was accompanied by a relevant increase in the joint strength. The actual mechanism of fracture shifted from adhesive failure, typical of solvent cleaned and abraded surfaces, to full cohesive failure within either the substrates of the adhesive layer. Besides, a strong influence of the adhesive selected for manufacturing was reported. Indeed, using a tough bi-component epoxy adhesive in conjunction with the LPP pre-treatment led to substrate failure, representing the largest possible enhancement of joint strength. The shear strength was over 300% of that obtained with reference solvent cleaned, and 80% larger than that recorded on abraded surfaces.

Buildings are large consumers of energy everywhere and a substantial share of energy goes to heat and cool buildings. This heating and air-conditioning load can be reduced through many means; a notable possibility is the proper design and selection of the building envelope. Therefore the use of thermal insulation in buildings contributes to reducing the annual energy cost. The objective of this paper is to present a new coating based on waterborne matrix, which is modified with gamma-alumina to form an inorganic–organic composite paint. Characterizations and performance, in terms of thermal conductivity, are presented. Due to both the high surface area of particles and the presence of interstitial cavities in the thin film, the product seems to be very interesting as insulation material.

The use of adhesives in place of traditional joining techniques as welding and riveting is becoming increasingly common in structural design. Compared to other conventional joining processes, adhesive bonding offers several advantages: including acoustic insulation, vibration attenuation, structure lightening, corrosion reduction and uniform stress distribution. These benefits can be offset if the surfaces to be bonded are not carefully cleaned, degreased and prepared. Many approaches to surface treatments based on physical or chemical modifications have been developed in the years in order to improve the surface activity. Although widely used and very efficient, these techniques present several disadvantages. Physical methods based on mechanical abrasion are supposed to extend bonding area as they increase the roughness, but cause an extensive degradation to the specimens and they are often not easy to reproduce. On the other hand, chemical treatments are typically used with the aim of modifying both morphology and chemical structure of the substrates layers, but they present serious environmental problems of waste disposal, which has moved investigations to an industrial alternative to these processes. According, the use of energetic methods of surface cleaning, such as laser and plasma cleaning processes have been recently consolidated since they are useful to modify the topmost layers of the substrates, increasing their reactivity, without affecting the bulk material properties. These treatments offer an effective and environment-friendly processing of different materials, providing strong and durable bonds with adhesives through modification of the surface morphology and functionalities. In this study, the effects of laser and low pressure plasma treatments on mechanical properties of adhesive bonded joints has been investigated and compared performing lap-shear tests.

In this paper, the effects of low pressure plasma treatment on surface energy of polyethylene samples and on shear properties of adhesive bonded joints based on these substrates have been investigated. In particular, the optimization of two plasma process parameters, exposure time and power input, was studied performing contact angle evaluation and lap-shear tests. The plasma treatment was also compared with a conventional primer treatment, for which it is a clean and effective alternative. As a measure of the durability of both treatments, the bond shear strength immediately after bonding was compared with that after a storage period in the laboratory environment. The experimental results show that the optimized plasma process may remarkably increase wettability properties of polyethylene surfaces and shear strength of bonded joints, even higher than those treated with primer and that these good properties remain quite unchanged even after some days of storage in a laboratory.

Hybrid 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.

This paper presents a systematic investigation of the influence of sandblasting pretreatment parameters on the surface roughness and mechanical characteristics of adhesive-bonded joints. The preliminary surface treatment in a bonding process has two important aims: first of all, it eliminates contaminants (dust, grease, humidity and corrosion products) which can modify the wettability of the substrate, then it increases surface roughness and, consequently, the contact area between substrate and adhesive, creating a mechanical interlocking that maximizes adhesion. To enhance the strength and avoid the de-adhesive failure of the joint, it is therefore advisable to increase the contact substrate-adhesive by a mechanical treatment of sanding, grinding or preferably sandblasting, usually considered one of the most effective methods to control the desired level of surface roughness and joint strength. This process, apparently easy to manage, is controlled by a great number of operating parameters, which all contribute to creating a good result. With the aim of evaluating the influence that some of these parameters have on the mechanical characteristics of adhesive-bonded joints, an experimental campaign was carried out. In particular, a steel substrate, an epoxy adhesive and various types of sand, different in nature and granulometry were used. The variable parameters for the execution of blasting are sand, impact angle and pressure. The assessments departed from an investigation into their effect on surface roughness and thereafter the mechanical properties of the bonded joints were analyzed.

In aeronautics and aerospace construction, whenever a seam is needed between aluminum alloy parts, riveting, nailing or bolting are the preferred methods of junction. Friction stir welding technology has made possible the realization of high strength aluminum alloy joints, which are normally considered non-weldable with conventional welding techniques.

In this paper, laser weldability of neutral polypropylene has been investigated using fibre and carbon dioxide lasers. A design of experiment (DoE) was conducted in order to establish the influence of the main working parameters on the welding strength of the two types of laser. The welded samples were characterized by carrying out visual and microscopic inspection for the welding morphology and cross-section, and by distinguishing the tensile strength.The resulting weld quality was investigated by means of optical microscopy at weld cross-sections. The tensile strength of butt-welded materials was measured and compared to that of a corresponding bulk material.

Fiber laser techniques are increasing their use in many applications, including modification of material surface properties. In particular they are often used for materials’ marking as a non-contact processing. In spite of this, the impact of the laser beam on the surface causes metallurgical and morphological changes. The developments during the laser-material interaction can also affect other surface properties, especially corrosion properties which are crucial in the case of Iron-Nickel alloys. Effect of laser marking on a Fe-Cr-Ni alloy using a Tm-fibre laser (IPG Photonics TRL1904; maximum power: 50W, wavelength: 1904 nm), is described in this paper. In order to evaluate the effect of the laser on corrosion properties a specific ageing test in salt spray has been performed. Moreover, superficial morphology analyses have been performed on samples before and after corrosion tests. Possibilities and limitations of laser marking on these alloys have been discussed, in particular from the point of view of the marked surface corrosion resistance preservation.

In this paper the behaviour of the plastic flow during Friction Stir Welding of AA7075 T651 plates, realized with different shaped tools, has been investigated. In particular, the influence of the shape of three tools was studied using copper strips placed along the welds. After welding, radiography and metallurgical analysis were used in order to investigate the marker movement and its fragmentation.

Fiber Reinforced Polymer (FRP) sandwich panels are increasing their application as structural and non-structural components in all kinds of construction. By varying the material and thickness of core and face sheets, it is possible to obtain sandwich structures with different properties and performance. In particular, their advantages as lightweight and high mechanical properties make them extremely suitable for the transport industry. One of the most critical aspects regarding composite materials for engineering application is their performance after hygrothermal aging. The panels used in this study are composed of low density core, made by thermosetting resin foam with microspheres and glass fibers rolled until obtaining the required thickness, and two face sheets of the same material but realized in high density. In this study, the authors focused on the bending behaviour of this kind of sandwich panel, as received and after severe aging cycles.