Abstract
The material properties of 3D printed continuous fiber composites have been studied many times in the last years. However, only a minimal number of samples were used to determine the properties in each of the reported studies. Moreover, reported results can hardly be compared due to different sample geometries. Consequently, the variability of the mechanical properties (from one sample to the other) is a crucial parameter that has not been well quantified yet. In the present work, the flexural properties of 3D printed continuous carbon fiber/nylon composite specimens were experimentally quantified, using batches of 15 test specimens. In order to account for the possible influence of the quality of the prepreg filaments on the observed variability, three different filament rolls were used to manufacture the different batches. Also, two configurations were tested, with a fiber direction parallel (longitudinal) or perpendicular (transverse) to the main axis of the specimens. The results show moderate to high variabilities of the flexural modulus, flexural strength and maximum strain. The coefficient of variation was more than twice as high in the transverse case as in the longitudinal case.
Highlights
For ultra-lightweight applications, composite materials are often the preferred choice in the material selection process due to their superior strength-to-weight ratio
The bending test specimens were manufactured using a Markforged prepreg filament made of a 1K roving of continuous carbon fiber, which was pre-impregnated with a nylon matrix (CF/PA6) [51]
For the 3D printing process, the prepreg filament, ambient conditions, manufacturing process parameters and machine inaccuracies all influence the structure of the printed material and the resulting material properties
Summary
For ultra-lightweight applications, composite materials are often the preferred choice in the material selection process due to their superior strength-to-weight ratio. Dickson et al [9] determined tensile and flexural properties of specimens with eight reinforced layers, leading to a fiber volume fraction of around 8–11%, and compared isotropic and concentric printing patterns. Despite the large amount of scientific work carried out to characterize the mechanical properties of CFC, the previous experimental results are hardly comparable and cannot be combined in a high-quality material model Reasons for this are that the dimensions of test specimens and applied test standards differ and that the different studies used different fiber volume contents and reinforcement strategies. A CFF desktop 3D printer (Mark Two, Markforged) and carbon fiber reinforced nylon filament were used to manufacture the test specimens. A conclusion and an outlook on future work constitute the final section of this paper
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