Determination of local density in components made by fused deposition modeling through indentation test

Abstract

The present study is aimed at determining the local density of components made by fused deposition modeling (FDM) through non-destructive indentation tests. An experimental campaign was performed to assess such a relationship. Specimens were made varying the amount of material flow and the direction of deposition. The specimen’s dimension and weight were measured to determine the average density. The internal porosity due to uncomplete filling produced due to the deposition process was also assessed through cross-sectioning. Instrumented indentation tests were conducted on the samples to determine a relationship between the density and the slopes during the loading and unloading phases. The tests were performed using flat cylindrical indenters of different diameters. The results indicated that the density of the specimens was strongly influenced by the adopted material flow and the orientation during deposition. An empirical relationship was determined between the slopes measured during indentation tests and the density. Such a relationship is independent of the deposition orientation. The optimized procedure represents a valuable tool to determine the local density of components made by fused deposition modeling through non-destructive indentation tests.

Analysis of the Manufacturing Porosity in Additively Manufactured Onyx/Long Fiber Reinforced Composites Using X-Ray Computed Tomography

“…8. In the Pure Onyx samples, the porosity content was found to be 0.68% with a standard deviation of 0.18%, a fact that is indicative of the relatively low replicability of the 3D printing process outcome, as indicated also in past works [31].…”

Mechanical characterization of FDM parts through instrumented flat indentation

“…Instrumented at indentation tests were performed at a constant travel speed of 0.1 mm/min, using a at-end cylindrical indenter with 4.0 mm diameter made of K720 high-strength steel by Bohler. The diameter of the indenter was selected based on the previous study [35]. The adoption of smaller indenters (i.e., 2 mm in diameter) led to lower test reliability since the results were susceptible to the surface morphology of the samples.…”

“…Still, it also greatly depends on the complexity of the component (such as concave-convex features) and the relative dimension of these geometrical features compared to the nozzle diameter. This also hinders the possibility of determining the mechanical characteristics of a component by testing a "standard" sample that should be representative of the actual component [35]. Besides, since the high plasticity of materials involved in FDM, machining a sample from the actual component is also challenging.…”

“…Non-destructive testing (NDT) of the actual component is highly demanded to provide reliable information concerning the component's behavior. Different methods have been adopted to characterize the mechanical behavior of the parts made by FDM and the relationship with the porosity, including X-ray Computed Tomography Analysis [36] and cross-sectional analysis [35]. Alternatively, non-destructive characterization tests (such as hardness tests) are performed through a technological test that does not directly measure a mechanical characteristic.…”

“…This is particularly important for testing materials with highly inhomogeneous properties, such as those produced through the FDM process. Among them, indentation tests have shown a great capability to predict the mechanical behavior of metals and plastics [46] and even the amount of porosity [35].…”