PSI - Issue 42

Stefan Sieberer et al. / Procedia Structural Integrity 42 (2022) 72–79 S. Sieberer et al. / Structural Integrity Procedia 00 (2019) 000–000

73

2

tape laying or winding machines. Here, AM is at an advantage. The eye structures are usually small in size, which allows to economically manufacture such parts on most commercially available CCF AM printers (Matsuzaki et al. (2018)). Precise tangential fibre placement around the eye is crucial, which can be achieved with the AM process. Previously, lug structures were investigated using traditionally manufactured fibre reinforced polymers (FRP) (Ai et al. (2021) Garcia et al. (2021)), and CCF AM was used to produce woven open hole tension specimens with high performance (Dickson and Dowling (2019)). A study by Pyl et al. (Pyl et al. (2019)) on the comparison of traditional and AM CCF reinforced open hole tension specimens gave beneficial strain distribution, however the strength of the AM specimens was not superior to traditional specimen with drilled holes. The matrix influence in transverse direc tion in the specimen was one of the main reasons for this. More studies on topologically optimal use of the CCF AM technology avoided this limitation by using topologically optimised beam structures (Chen and Ye (2021); Fedulov et al. (2021)). In addition to traditional optimisation goals, AM gives potential of stacking and layer angle freedom to increase e.g. energy absorption (Peng et al. (2020)), or variable sti ff ness and strength by fibre content variation (Hou et al. (2020)). For AM CCF structures with already optimised fibre placement, the fibre content is an e ff ective measure to obtain required part strength whilst keeping manufacturing and material costs for the AM part to a minimum. For the current investigation, the motivating factor is to understand and elaborate the relation between layer height and fibre volume fraction and its influence on the mechanical properties of CCF AM composite lugs. In this contribution, AM CCF lug eye specimens were designed to lightweight principles, subjected to static tensile, and the occurred fracture analysed. The specimens and the test procedure are introduced in the next section, followed by test results and discussion of the obtained data.

Nomenclature

AM Additive Manufacturing CCFContinuous Carbon Fibre DIC Digital Image Correlation FE Finite Element SCFRSPhort Carbon Fibre Reinforced Polymer TP Thermoplastic

2. Specimens and Test Set-up

2.1. Specimen manufacture

The specimens for the testing were manufactured on an Anisoprint 3d-CCF printer using proprietary Anisopring CCF fibre bundles with thermoset matrix (Azarov et al. (2017)) and co-extruded with thermoplastic (TP) matrix material. The TP is Prirevo N6C4, from Prirevo 3D-solutions GmbH, a PA6 reinforced with short carbon fibres (20Wt%). The fibre steering slicing (NanoGcode) software and Composer A4 were used in pre-processing. More on the printing process can be found in e.g. (Savandaiah et al. (2022a,b)). The specimen design followed a Finite Element (FE) analysis and principal strain trajectories were obtained with methods as can be found in (Schaberger (2016)). Figure 1 shows the printed layer structure. Alternative layers of fibre reinforcement and short carbon fibre reinforced polymer (SCFRP) were printed at the eye. The fibre reinforcement was aligned tangentially at the eye and followed the major principal strain trajectories as precise as possible under the boundary conditions of the AM laying process. In the shaft region, the SCFRP layer was replaced by CCF in the minor principal strain direction because of transverse stresses in the connecting region between eye and shaft (Schu¨rmann (2007)). Figure 2 shows a printed specimen with a fibre layer visible. Boundary SCFRP on the outside and at the shaft are visible, and are printed to give shape consistency. All specimens were printed to the same dimensions, including the CCF shaft cross-section A CCF . Two di ff erent layer heights were printed for the di ff erent specimens to investigate the influence of the resulting di ff erence in fibre volume