Modified Archimedes Method for Density Measurements of Samples With Open Porosity

Abstract As prototyped parts transition into scalable manufacturing research and industries, cost-effective and non-destructive testing methods are continuously needed to characterize obtained parts and components. This becomes even more significant in powder-based additive manufacturing (AM), where porosity – known to be linked to mechanical properties –, is nearly inevitable. Amongst the non-destructive methods for density measurements, x-ray computed tomography is a costly and time-consuming approach, whereas the cost-effective Archimedes measurement method fails to accurately characterize parts with open porosities. Alternatively, pycnometry provides a precise method for measuring the density of both solid and porous samples, although it is size-restricted. This study introduces a modified Archimedes measurement technique, that accounts for both open and enclosed porosities. This method makes use of a thin film of polytetrafluoroethylene (PTFE) that works as a shape-conforming layer, sealing open pores and including their volume into density calculations. The density of the PTFE film which is needed in the final density estimation is measured under the same conditions as in the modified method and it is found to be 0.88±0.06 g/cm3. When compared to traditional Archimedes measurements, this novel modified method reveals lower density values of porous parts, while displaying a downward trend with decreasing printing energy density, at which porosity is expected to increase. This discrepancy evidences the overestimation of density values by traditional Archimedes, since open pores volume are disregarded. Repeatability assessments confirm the modified method’s reliability, with a standard deviation of 0.02 g/cm3. This method demonstrates potential as an inexpensive, nondestructive, and dependable tool for parameter optimization research and accurate density measurements of highly porous components that are obtained by manufacturing processes, including but not limited to metal AM.