Surface Preparation of Alumina for Improved Adhesive Bond Strength in Armor Applications
Surface treatments of alumina have been investigated with the aim of increasing the strength of the bond created between the alumina and a toughened epoxy adhesive. Four surface conditions have been assessed: as-fired; grit blasted; and krypton fluoride excimer laser treated under two sets of conditions. Compared with the as-fired surface, the grit blasted surface was rougher with poorer wettability, probably due to surface contamination. It was found that the laser treatments removed some of the sintering additives and caused rounding of the alumina grains, slightly increasing the surface roughness. Further, the laser treatment led to an increased surface energy and wettability, which has been linked tentatively to an observed increase in the hydroxyl groups on the surface. The adhesive bond strength was assessed by testing joints in tension and shear. It was found that the laser treated surfaces demonstrated slight improvements in bond strength, with a cohesive failure of the adhesive in tension for surfaces subjected to one of the two laser treatments, compared with failure at the interface for the as-fired, grit blasted and other laser treated samples in tension and for all samples in shear. Thus, it has been demonstrated that modifications to the surface of alumina can result in mechanical and chemical changes which affect roughness, wettability, bond strength and the locus of failure.
Study of the effect of substrate roughness on adhesive joints by SEM image analysis
The effect of adherend surface roughness on epoxy bonded aluminium joints has been studied. Several epoxy adhesives were tested to evaluate the influence of adhesive nature on the roughness effect. The aluminium pre-treatments applied were abrasion and impression processes, generating different texture levels. The abrasion with grinding papers of different grain sizes provides surfaces with high density of low summits. In contrast, the surfaces subjected to impression process present low density of very deep valleys. The roughness measurements were made by image analysis of micrographs obtained by Environmental Scanning Electron Microscopy (ESEM). In addition to the average roughness, other surface descriptors were determined to characterise completely the surfaces, allowing to evaluate the influence on the adhesive strength of different texture variables, such as the height, shape and density of the peaks and valleys which constitute the roughness profile. An optimum value of surface roughness was found for the joint strength measured by the lap shear tensile test. An increase of adherend roughness causes an increase of effective area but, at the same time, decreases the ability for adhesive penetration. It has also been shown that the joint strength depends on the main characteristics of the adherend surface, such as the density and depth of the protuberances. Finally, it has been found that the roughness effect seems be influenced by the adhesive nature. Different epoxy adhesives with similar mechanical properties present different joint strengths due to their different penetration abilities.
Designing surface properties of textile fibers by UV-laser irradiation
Abstract The irradiation of polymeric material by pulsed UV lasers generates characteristic modifications of the surface topography of the polymer beside other effects. The resulting surface properties may have an important impact in textile processing, as they can affect technical properties of synthetic and even natural fibers, e.g. particle and coating adhesion or wetting properties, in a dry process. An overview is given over microscopic and macroscopic properties of the generated surfaces in dependence on laser parameters and material constants. Various understandings of the genesis of the characteristic geometry and structure of irradiated surfaces are compared to experimental observations from polymer films and a number of textile fibers. With respect to specific fiber properties the experimental data give evidence of cooperative transport phenomena in a superheated polymer as the prime driving forces of the effect.