Mechanical capability and damage assessment of novel reinforced hybrid structures produced by laser additive manufacturing
Daniel Hülsbusch, TU Dortmund, Dortmund, GermanyMatthias Haack, Institute for Design and Materials Testing (IKW), Department of Materials Test Engineering (WPT)/ TU Dortmund University, Dortmund, GermanyAndreas Solbach, Institute of Laser and System Technologies (iLAS), Hamburg University of Technology, Hamburg, GermanyClaus Emmelmann, Institute of Laser and System Technologies (iLAS), Hamburg University of Technology; Laser Zentrum Nord (LZN), Hamburg, GermanyFrank Walther, Institute for Design and Materials Testing (IKW), Department of Materials Test Engineering (WPT)/ TU Dortmund University, Dortmund, Germany
The intended substitution of conventional materials by fibre-reinforced polymers (FRP) in manufacturing hybrid lightweight structures requires innovative joining strategies to combine materials with different physical and chemical properties. In this context, challenges remain with regard to a material-specific application of force to the load-bearing fibre structure of polymer composite parts. To address this matter, a hybrid interface for connecting metallic substrates to a fibre-reinforced polymer by application of integrated form-closure elements (pins) has been proposed and investigated by various groups of researchers. In recent years different manufacturing technologies were employed for adding the fabric-penetrating pin elements to the subsequent joining surfaces, for example arc welding (CMT) and more recently laser additive manufacturing. The latter technology is capable of manufacturing complex shaped parts with an equally complex arrangement of pin structures attached to the surface, which shows great potential for high-tech applications.
In the present study, a laser additively manufactured Ti-6Al-4V-substrate were combined with an in-situ cured carbon-fibre-reinforced polymer (CFRP). Quasi-static tensile (shear) tests and multiple step tests were carried out to assess the mechanical properties of specimens with two differently sized pin structures as well as a solely adhesively joined reference configuration. By the combined use of 3D deformation measurement and structure-borne noise emission analysis, different structure-related failure mechanisms were detected.
The results had been compared to light and SEM microstructural investigations in order to describe and assess the loading-induced damage behaviour. Multiple step tests have been used for time- and cost-efficient estimation of the fatigue strength and determination of the fatigue behaviour depending on the pin length. The results have been validated within constant amplitude tests. It was shown that the tensile shear strength increased in comparison to the normal adhesive interface up to 600 %, whereby different pin size-depending failure-initiating mechanisms have been detected.