An Experimental and Numerical Investigation Into Vibration of Delaminated 3D Printed PLA Beams

Abstract

<p>This report consists of several experimental and FEM-based numerical free vibration analyses of 3D printed PLA cantilever beam specimens. In the beginning, an introduction to the topic is given which includes an overview, organization of the report and literature review. Afterwards, the experimental setup including PLA specimens, Power supply, Laser interface and Input Laser sensors, is discussed. Experimental results, including frequency spectrum and fundamental frequency of defective, cantilevered, PLA beam specimens are evaluated, and average fundamental flexural (bending) frequencies are reported in the later section. The defect is considered to be a single, symmetric, through-the-width, centrally located delamination of various (0.5 mm, 0.25 mm, and 0.1 mm) delamination thicknesses, covering one-third of the beam specimens’ length. The average frequency values are calculated based on three different trials, conducted to ensure the accuracy of the obtained results. For the specimens with delamination thickness of 0.5mm, 0.25mm and 0.1mm, respectively, the fundamental frequencies are found to be 13.99 Hz, 13.36 Hz and 12.82 Hz. Theoretical results, including fundamental frequencies and corresponding mode shapes, obtained through simulations carried out using Finite Element Analysis (FEA) Software (Femap with NX Nastran) are also reported and discussed. For the PLA beam specimens with symmetric, through-the-width, centrally located, delamination of 0.5 mm, 0.25 mm, 0.1 mm, and 0 mm, respectively, the fundamental frequencies were found to be 16.26 Hz, 16.20 Hz, 15.89 Hz and 16.66 Hz. The mass of each PLA beam specimen (in kg) was also reported. The comparison is made between the numerical (FEM) and experimental results and reasonings are given for any discrepancies. </p> <p>Finally, the main findings are highlighted, and this report closes with conclusions, future </p> <p>considerations and. [sic] Future considerations include the possible aspect of the research that was not completed due to lack of time and resources. Appendix A includes an example of the theoretical and numerical vibrational analysis for a simple cantilever homogeneous (steel) beam. Appendix B explains numerical analysis of 3D-printed PLA beams, where the effect of system length on the fundamental frequency is demonstrated. It is observed that by increasing the length of the cantilever beam with 30mm (from 240 mm to 271 mm), the fundamental frequency decreases by 29.8%. Finally, Appendix C demonstrates a basic and introductory numerical contact analysis, assuming a coefficient of friction of 0.1, to calculate the contact pressure, contact force, contact traction, and contact stress. Contact analysis was done to understand the parameters such as contact force, contact stress and many more when the contact will occur. In contact analysis, certain parameters such as contact force, contact traction, and contact pressure was obtained through vibration analysis (without applied loading) and contact stress was obtained through static analysis (with applied loading). In this case, the gap was modelled with two surfaces touching each other. It was concluded from the results that very high loading will be needed to make contact happen. The content of this Appendix paves the way for the future vibration analysis of delaminated PLA beam including contact effects.</p>