PSI - Issue 47

G. Morettini et al. / Procedia Structural Integrity 47 (2023) 296–309 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The main objective of this research activity will be to present for PLA material, FDM processed, a simple criterion and robust, also applicable in an industrial context, based on the combined concepts of the Average Strain Energy Density (ASED) (Lazzarin (2001)) with Equivalent Material Concept (EMC) (Torabi at al. (2018)) correction for the prediction of the breaking load of notched PLA specimens. To achieve this, the first chapters of this article will be devoted to illustrating the ASED failure method used for prediction and possible corrections that could be applied to it to improve accuracy. Subsequently, the results of the experimental tests carried out on PLA U-notched specimens will be presented. finally, the experimental numerical comparison will highlight the limits and advantages of this application.

2. Theoretical Background 2.1. The Average Strain Energy Density (ASED) criterion

The Average Strain Energy Density (ASED) approach introduced and developed by professors Lazzarin and Berto (Berto (2013), lazzarin (2001), lazzarin (2005)) is currently one of the most widely used methods in the evaluation of the static and fatigue resistance of notched and welded structures (Foti at al. (2021), Sanchez at al. (2022)). For the application of this criterion, the concept of "elementary" volume introduced by Neuber (Neuber at al. (2013) and subsequently deepened by the same (Berto at al. (2011)) according to which the sensitivity of a material to brittle failure does not depend so much on the stress peaks in one point (which, moreover, cannot be defined analytically), but from the average stress state which is evaluated within a control volume. The main idea is that continuum mechanics is applicable from a certain distance from the tip of the notch Berto at al. (2009). The material element is always kept at a distance from the crack or notch tip where the inhomogeneity of the material due to microcracks, dislocations and grain boundaries, precludes an accurate analytical solution. The basic idea of ASED consists of the fact that brittle failure occurs when the average value of the average strain energy density � defined on a given control volume equals a critical value � which depends only on the material propriety. � � � (1) Critical strain energy evaluation � The critical value of energy density � can be evaluated simply by using a convenient resistance limit � obtained, for example, from quasi-static tensile tests performed on unnotched specimens having a cross-sectional area equal to that of the notched specimens as indicated by the equation (2). � � � �� �� (2) Where represents the Young's modulus of the material. As can be immediately deduced from the equation, the criterion must comply with the hypothesis of linear or quasi-linear behavior up to failure. In other words, it has to behave in a brittle way. Average strain energy density evaluation � Assuming the most general case of an isotropic linear elastic material, the Average strain energy density is evaluated as the ratio between the total strain energy, calculated within a control volume, and the control volume itself. This is expressed by equation (3).