Fabrication of hybrid composite T-joints by co-curing with 3D printed dual cure epoxy

Review of Tailoring Methods for Joints with Additively Manufactured Adherends and Adhesives

“…Some authors explored the feasibility of using additive manufacturing to tailor the bondline by controlling the adhesive composition or shape [ 39 , 40 , 41 , 42 , 43 ]. The main benefits of this approach are the compatibility with non-additively manufactured adherends and the improved joint quality, as the adhesive layer is relatively free from porosities and possesses high geometrical accuracy and reproducibility.…”

“…The work of Dahmen et al [ 40 ] was based on the work by Redmann et al [ 39 ] and used the same 3D printing set up and materials to assess if the proposed AM adhesive deposition method could be suitable for industrial application. As a case study, the authors considered a T-joint configuration, a non-standardized joint but highly relevant in aerospace industry applications, as it is commonly used in the spar-skin joints of aircraft wings.…”

“…The work by Schmidt et al [ 42 ] completed the previous works [ 39 , 40 , 41 ] by assessing the effect of various deposition strategies on the physical and mechanical properties of UV and thermally cured adhesives. Schidt et al, changing the AM process, were able to overcome the limitation of SLA and manufacture flawless bond lines, confirming the results obtained in [ 39 ].…”

“…This can be achieved with a finer control over the final geometries, adopting voxel-oriented material tailoring, enhancing reproducibility and lowering the porosity in the adhesive. The next main challenges will be in engineering the proposed methods for different adhesives and different scales, from large aircraft wings [ 40 ], integrating the deposition of the long fiber reinforced matrix, to micro scale, electronic applications using new tailoring approaches such as the one presented in [ 46 ] where a patterned adhesive, controlled by droplets in size from 0.5 to 6.0 µL, outperformed a continuous adhesive with an increment of ~70% in shear strength.…”

Enhancement of 3D-Printable Materials by Dual-Curing Procedures

“…Intermediate printed materials were soft gels with a glass transition temperature of 14 • C, which increased up to 155-160 • C after the epoxy reaction was carried out in the thermal treatment, which consisted of a slow multistep curing process at temperatures up to 220 • C. The authors optimized the thermal curing process from 9 h to 3 h without compromising the thermalmechanical properties, while controlling the maximum conversion rate to moderate values. Later on, Dahmen et al [61] studied the application of a similar EPX 81 system exploiting the adhesive properties of the intermediate, partially cured material for the fabrication of hybrid composite T-joints. Specimens for lap-shear tests were prepared using printed adhesive layers that were sandwiched between prepreg plies on each side and cured in an oven under vacuum to ensure good contact within the prepreg plies, and between the prepreg plies and the adhesive layer.…”