Mechanical characterisation of PA‐Al₂O₃ composites obtained by selective laser sintering

Abstract

PurposeThis paper aims to develop a deep characterization of PA‐Al2O3 composite for selective laser sintering (SLS). Tension test is used to determine main mechanical characteristics of the material, both at room temperature and at 100°C. An accurate knowledge of the parts' performances as a function of the building orientation, is fundamental to understand the manufacturing anisotropy. Particular attention is dedicated to the joining and failure micromechanisms ruling the macroscopic characteristics, on the basis of the knowledge developed by the authors on SLS of both metal and polymeric powders.Design/methodology/approachSpecimens have been built with different orientations in regard to powder deposition plane and laser path. Tension test is used to determine main mechanical characteristics of the material, both at room temperature and at 100°C. A particular attention is dedicated to the joining and failure micromechanisms ruling the macroscopic characteristics of the composite material by means of optical and scanning electron microscope (SEM) observations.FindingsThe sintered material shows an evident anisotropy in the growth direction (z‐axis), as well as it seems to be not sensitive to the sintering direction at room temperature (x, y, xy). At 100°C the effect of sintering direction becomes more evident and a different behaviour results considering x‐ and y‐direction, respectively. Accurate SEM characterization has been carried out to understand the effect of the manufacturing anisotropy on the mechanical performances, both in terms of additive construction and laser sintering strategy. The observation of the rupture surfaces showed that cracks originate from the external surface and propagate initially by the ductile failure of the polymeric matrix, up to the sudden fracture of the whole section.Originality/valuePrevious studies concerning polyamide charged parts confirm the importance of fabrication parameters and geometry on the final performances, due to anisotropic heat supply and transfer phenomena. The originality of the paper is in the investigation on both at room temperature and at 100°C. Moreover, a model is proposed where it is hypothesized that the layer‐by‐layer construction is only marginally responsible of the anisotropic behaviour of the material.

Process for reinforcing SLS parts by epoxy resin

“…Similar conclusions related to anisotropy in the growth direction (z axis) are observed in the research carried out by Berti et al (2010) applied to PA-Al2O3 composite for selective laser sintering (SLS) and in the work carried out by E. Bassoli et al (2012) in the case of metal or ceramic filler. In conclusion either the design or the material of SLS part has to be changed if this technology is wanted to be used for this kind of clutch pedal.…”

Fracture mechanics of laser sintered cracked polyamide for a new method to induce cracks by additive manufacturing

“…Polyamide (PA) specimens manufactured by SLS; three different configurations were manufactured with the purpose of evaluating the effect of building direction on Mode I fracture mechanic properties of the material. Similar studies on PA-Al2O3 composites have been presented by [5,6], mainly focused on tensile or bending properties. The novelty of this work lays in its focus on the fracture mechanics properties of PA for SLS, and on the investigation on the capability of AM processes to build 3D artificial cracks, otherwise impossible to create by classic methods.…”

“…[4] performed a rigorous analysis of the Young's modulus, ultimate tensile strength, and strain-to-failure of a glassfilled nylon PA12 composite called DuraForm®, demonstrating the variability of the material properties throughout the built volume and between builds. Berti et al [5] also tensile tested specimens built with different orientations, at two different temperatures. They found that the most important anisotropy is located between the vertical direction and the horizontal plane, but near the upper operative temperature the mechanical difference between specimens built with longitudinal axis parallel to the two horizontal directions becomes important.…”

Joining mechanisms and mechanical properties of PA composites obtained by selective laser sintering

“…It offers high throughput, no need for supports except from the first layers to be detached from the machine worktable, no post-processing, wide range of materials, high automation possibilities (Eyers and Dotchev, 2010;Bassoli et al, 2005;Caulfield et al, 2007). Fully functional components can be obtained for example in polyamide (unfilled or reinforced with glass fibres/beads, Aluminium and carbon), flame retardant polyamides and Polyetheretherketone (PEEK) for automotive, aerospace and military industries, but also biomedical devices and consumer goods (Eyers and Dotchev, 2010;Berti et al, 2010;Senthilkumaran et al, 2009). Polyamide-matrix composite parts can be produced directly from the CAD model, without any post-treatment.…”