Assessment of Surface Treatment Degree of Steel Sheets in the Bonding Process

Surface Properties of Graffiti Coatings on Sensitive Surfaces Concerning Their Removal with Formulations Based on the Amino-Acid-Type Surfactants

Water-in-oil (w/o) nanoemulsions stabilized with amino acid surfactants (AAS) are one example of nanotechnology detergents of the "brush on, wipe off"-type for removing graffiti coatings from different sensitive surfaces. The high-pressure homogenization (HPH) process was used to obtain the nanostructured fluids (NSFs), including the non-toxic and eco-friendly components such as AAS, esterified vegetable oils, and ethyl lactate. The most effective NSF detergent was determined by response surface methodology (RSM) optimization. Afterwards, several surface properties, i.e., topography, wettability, surface free energy, and the work of water adhesion to surfaces before and after their coverage with the black graffiti paint, as well as after the removal of the paint layers by the eco-remover, were determined. It was found that the removal of graffiti with the use of the NSF detergent is more dependent on the energetic properties and microporous structure of the paint coatings than on the properties of the substrates on which the layers were deposited. The use of NSFs and knowledge of the surface properties could enable the development of versatile detergents that would remove unwanted contamination from various surfaces easily and in a controlled way.

Influence of Temperature, Humidity and Load Coupling on Mechanical Properties of Adhesive Joints and Establishment of Creep Model

To study the creep and property degradation behavior of adhesive joints under the coupling action of temperature, humidity and load, polyurethane shear joints were prepared and tested. Different static loads were applied to joints at high temperature (80 °C) and high temperature and humidity (80 °C/95% RH) to test and analyze the creep deformation, and a suitable creep model was established. At the same time, the performance degradation test of the joints under the effect of multifactor coupling was carried out to obtain the variation law of the failure load, and the failure mechanism was discussed based on the failure section. The research shows that the creep strain of the joint at high temperature and humidity was significantly larger than that at high temperature, and the failure fracture time was shorter, in which water molecules played a role of softening and hydrolysis. The viscoelastic multi-integral creep model was used to analyze and predict the creep behavior of the joints. It was found that the creep model could better describe the creep behavior of the joints under uniaxial constant loading. Under the coupling effect of temperature, humidity and load, the failure load decreased with time, and with the increase in static load, the decline range and rate of failure load increased. It was found that the mechanical properties in the high temperature and humidity environment decreased significantly more than those in the high temperature environment. When a static load was applied during creep, cracks easily occurred inside the adhesive layer, and water molecules easily diffused inside the cracks, which increased the decay rate of the mechanical properties. This study provides good theoretical significance and engineering value for the application of polyurethane adhesion structures in rail vehicles.

Adhesive Joint Degradation Due to Hardener-to-Epoxy Ratio Inaccuracy under Varying Curing and Thermal Operating Conditions

This paper presents the results of an experimental study of adhesive joint strength with consideration of the inaccuracy of the hardener dosage, in the context of evaluating the degradation of joints when used either at ambient or elevated temperatures. The butt joint strength characteristics were assessed for two types of adhesives-rigid and flexible-and two curing scenarios-with and without heat curing. An excess hardener was shown to be significantly more unfavourable than its deficiency, which can ultimately be considered as a recommendation for forming epoxy adhesive joint assemblies. In order to fully understand the relationship between the analysed mechanical properties of the material and the influence of component ratio excesses and heating, a process of fitting basic mathematical models to the obtained experimental data was also performed.