Influence of relative density on quasi-static and fatigue failure of lattice structures in Ti6Al4V produced by laser powder bed fusion

Abstract

Lattice structures produced by additive manufacturing have been increasingly studied in recent years due to their potential to tailor prescribed mechanical properties. Their mechanical performances are influenced by several factors such as unit cell topology, parent material and relative density. In this study, static and dynamic behaviors of Ti6Al4V lattice structures were analyzed focusing on the criteria used to define the failure of lattices. A modified face-centered cubic (FCCm) lattice structure was designed to avoid the manufacturing problems that arise in the production of horizontal struts by laser powder bed fusion. The Gibson–Ashby curves of the FCCm lattice were obtained and it was found that relative density not only affects stiffness and strength of the structures, but also has important implications on the assumption of macroscopic yield criterion. Regarding fatigue properties, a stiffness based criterion was analyzed to improve the assessment of lattice structure failure in load bearing applications, and the influence of relative density on the stiffness evolution was studied. Apart from common normalization of S–N curves, a more accurate fatigue failure surface was developed, which is also compatible with stiffness based failure criteria. Finally, the effect of hot isostatic pressing in FCCm structures was also studied.

Damage-induced failure analysis of additively manufactured lattice materials under uniaxial and multiaxial tension

“…Due to the presence of noise in the DIC results (arising from lighting noise and unsmooth surface of samples), the notation of "active beams" in experimental contours may not be as clear as it is in the Having significant discrepancies in experimentally and numerically characterized mechanical properties of additively manufactured lattice materials is a common issue, e.g. see (Drücker et al, 2021;Alaña et al, 2021;Xiao et al, 2020). This is because there are many manufacturing defects which are not included in the numerical model.…”

“…Yet, their mechanical testing and characterization have been mainly performed under compressive loading, e.g. see (Roos et al, 2019;Xiao et al, 2015;Liu et al, 2017;Cao et al, 2020;Wang and Li, 2018;Epasto et al, 2019;Großmann et al, 2019;Alaña et al, 2021;Wang et al, 2020), while tensile behavior is less explored. This may be due to the challenges associated with the design of tensile samples and the early failure resulting from the stiffness jump.…”

A dimensional assessment of small features and lattice structures manufactured by laser powder bed fusion

“…In this work, we calculated the nominal interconnected porosity, which corresponds to the volume fraction compared to a solid neck sample of designed samples, and defined by the difference of the nominal volume and the proportion of the volume within the lattice structure. This term differs from relative density due to it is defined by the proportion of the material (dry weight) with a total specimen volume [26].…”

Hydrogen embrittlement in micro-architectured materials

“…[1], [2], [3], [4], [5] and [6], while others investigate the failure (quasi-static and fatigue) under compression, e.g. [7], [8], [9], [10] and [11], and (more recently) under tension, e.g. [12], [13], [14], [15], [16] and [17].…”

“…Most of these failure-related studies highlighted the role of manufacturing imperfections, and some thoroughly investigated the topic, e.g. see [8], [9], [14] and [16]. These imperfections (like void, strut waviness and surface roughness) often arise from additive manufacturing processes, and noticeably influence the material behavior.…”