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To quantify the influence of absorbed water in PA6 on the pre-treatment and bonding process, an unfilled and unreinforced PA6 material is investigated in a dried and saturated state. The material is pre-treated by atmospheric pressure plasma jet (APPJ) with varying jet distances. The surfaces are investigated by contact angle measurements, DSC and FTIR to detect molecular and morphological changes in the surface. To evaluate the bonding strength, samples are bonded with a two-component polyurethane adhesive and a two-component acrylate adhesive and tested in a lap shear and a tensile configuration. The results show that water content has a significant influence on the effectivity of the pre-treatment process and the resulting bonding strength and failure mechanism. The adhesion is majorly affected, however these effects do not influence the macroscopic wetting behavior and cannot be measured in contact angles. FTIR spectra and DSC scans do not show significant changes in molecular groups or crystallinity that would explain the observed adhesion improvement in dried samples. High bonding strength is only achieved with adherents at low water content. [ABSTRACT FROM AUTHOR]

In ultrasonic metal welding, low specific resistances and large joining surface cross-sections require the use of mechanical testing to quantify the joint quality. In this study, different quality features of ultrasonically welded joints made of pure copper sheet are investigated during the successive phases of joint formation. Two test series with different workpiece geometries are examined. It is shown that mechanical quality features such as shear and peel forces behave differently over the formation of the joint and are not transferable. As an alternative to these, laser scanning microscopy is used to record images of the fracture surface that describe the growth of the joint area during formation. The study finds that shear tensile force growth and joint area growth are non-linear and comparable, with optimized welds achieving joint areas of 30 mm2 out of 64 mm2 and 6 mm2 out of 16 mm2. Although overall quality increases with increasing welding time, the material strength in the joint zone decreases. Depending on the original rolling condition, between 43% and 59% of the original material strength can be identified as the joint strength. The automatic analysis of fracture images is a suitable alternative to mechanical testing for similar joints. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) bonding technology is widely used across industries. As the curing reaction is initiated via an external light source, the use of fast-curing structural UV acrylates has so far been limited to joint designs with at least one transparent joining part. By introducing a side-emitting polymer optical fiber textile into the adhesive layer, which acts as an embedded light source, the technology can be made accessible for applications with nontransparent substrates such as metals. This paper describes the development of extra thin polymer optical fiber narrow fabrics designed to enable curing of structural adhesive joints. Polymer optical fibers (warp) were combined with different low-titer polyester weft yarns in two fabric design types with different primary out-coupling mechanisms: undulation and surface modification of the polymer optical fibers. The effect of yarn properties, thread densities and weave on fabric quality, geometry and lateral light intensity of each type were investigated. Results showed that narrow fabric production within the tight geometric limits required is feasible. Fabrics manufactured with nontextured yarns at low titers and low weft densities exhibited the highest lateral light intensities for the surface modification type fabric. To compensate for intensity loss over fabric length, investigating light coupling from both sides is recommended for this fabric type. For the undulation type fabric, the lateral light intensity characteristics indicated that the high tenacity yarns are promising candidates for the fabrication of low sidelight attenuation fabrics through modulation of the weft density. [ABSTRACT FROM AUTHOR]

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Fiber-reinforced plastics (FRP) are widely used in the automotive industry due to their lightweight construction potential. Especially, injection-molded components are very popular because of their short cycle times. Unfortunately, this manufacturing process results in some disadvantages for delayed adhesive bonding. On the one hand, such thermoplastics have a very low surface energy (Polyamide 6 (PA6) 36 mJ/m), on the other hand residues of release agents on the surface hinder adhesion between product and adhesive. These disadvantages have to be overcome by the right surface pre-treatment process. Currently, a solvent-containing process is usually used for this purpose. If necessary, the use of primer is common. In the presented paper, the pre-treatment process of an injection-molded component made of polyamide 6 reinforced with glass short-fibers is presented. First, material-specific properties are measured. The influence of laser pre-treatment at 355 nm and 1064 nm wavelength is investigated. Measurements of surface free energy and surface roughness are conducted. The bonding strength is validated by peel test and tensile shear tests. The shear strength was doubled by laser pre-treatment at a medium energy level, partially cohesive failure of the adhesive was achieved. Both investigated wavelengths led to a great improvement of bonding strength at suitable parameters. [ABSTRACT FROM AUTHOR]