Analysis and modelling of 3D printed springs for use in spacecraft

• Main Author: Sacco, Enea
• Other Authors: Moon Seung Ki
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Aeronautical engineering::Aircraft
• Online Access: https://hdl.handle.net/10356/141038
• Institution: Nanyang Technological University

The use of additive manufacturing in the space industry is growing and there are many developments being made in a wide variety of fields, from tools for astronauts to rocket combustion chambers to habitats on other worlds. Yet there are still several knowledge gaps that slow the development of standards and therefore the widespread use of 3D printing in the space industry. One of the gaps is the application of 3d printing to springs for use in spacecraft mechanisms. Consequently, the objective of this research is to analyse and model the behaviour of these widespread components. The first step is to characterise the material, which in this case is PLA printed using material extrusion with two different in-fills, using the orthotropic model. Another material, ULTEM 9085, was also used later in the research. The results showed that the two in-fill are mechanically similar but one is slightly better under shear stresses. Based on the understanding of the material characteristics, simulations are conducted using tensile coupons with varying numbers of perimeters and then compared to samples printed with the same characteristics. The simulations and experimental results are in close agreement with some slight differences that are negligible. Following this, 3D printed springs are investigated and design guidelines are developed: square wire cross-section is easier to print and mono directional in-fill produces stronger springs. The springs are tested both in the pre and post-deformation regions of the force-displacement plots. Testing showed that springs still behave semi-elastically while after plastic deformation. Comparison between ULTEM 9085 and PLA springs lead to the observation that smaller layers increase the stiffness of the springs. The next step of the research is the derivation of an equation for the calculation of the stiffness of 3D printed springs. Two methods are attempted and one is successful, leading to an equation that predicted spring constants that agreed very closely with experimental data. Finally a cost analysis of springs printed with ULTEM 9085 is performed, PLA was not considered because it was only used for developing the model. Various methods for reducing the cost are then investigated. The research presented in this thesis increases the knowledge of 3D printed materials in several ways. First a characterization of printed PLA is made which can be used as reference, given the printing settings. The behaviour of 3D printed springs in the plastic region can be used as a safety feature. Finally, the equation that predicts the spring constant can be used to save time in design processes and is the starting point for developing more equations that allow the full use of 3D printing’s design freedom for springs.