Notch Fracture in Polymeric Specimens under Compressive Stresses: The Role of the Equivalent Material Concept in Estimating the Critical Stress of Polymers

Abstract

In this paper, the fracture of notched polymeric specimens under compressive stresses was investigated both experimentally and theoretically. In the experimental section, to determine the load-carrying capacity (LCC) of U-notched specimens made of general-purpose polystyrene (GPPS) and polymethyl-methacrylate (PMMA) polymers, tests were performed on notched square samples under compression, i.e., negative mode I loading. In the observation of the nonlinear behavior of the two polymers in the standard compressive tests, for the first time, the equivalent material concept (EMC) was used under compressive loading to theoretically estimate the critical stresses of the two polymers, which were shown to be significantly different from the ultimate strengths obtained from the standard compression tests. By linking the EMC to the maximum tangential stress (MTS) and mean stress (MS) criteria, the LCC of the notched specimens was predicted. The outcomes are twofold: First, MTS, MS, EMC–MTS, and EMC–MS criteria provide accurate predictions of the experimental critical loads observed in the U-notched polymeric specimens; second, the combination of the EMC with the MTS and MS criteria, allow such predictions to be obtained without any need for experimental calibration.

Fracture Load Predictions in Additively Manufactured ABS U-Notched Specimens Using Average Strain Energy Density Criteria

“…In a recent publication, Seibert et al [ 30 ] successfully applied the ASED criterion in additive manufactured polylactic acid (PLA) material by using an alternative approach to determine the control volume used in this criterion (see Section 2 ). Alternatively, in the presence of non-linear behaviour, Torabi proposed the Equivalent Material Concept (EMC) [ 31 ], with the idea of transforming a non-linear material (in terms of tensile behaviour) into an equivalent linear-elastic material and allowing the use of the corresponding (generally simpler) elastic assessment tools (e.g., TDC [ 32 ], ASED [ 32 , 33 ], Maximum Tangential Stress [ 34 ], etc.). However, the EMC was not accurate enough for materials that present non-linear behaviour in both the tensile and the fracture behaviours, for which the same author developed the Fictitious Material Concept (FMC) [ 35 ], with a similar purpose to that of the EMC.…”

“…However, the EMC was not accurate enough for materials that present non-linear behaviour in both the tensile and the fracture behaviours, for which the same author developed the Fictitious Material Concept (FMC) [ 35 ], with a similar purpose to that of the EMC. Since the moment when these methodologies (ASED, EMC and FMC) were conceptualized, their validation has been extended not only to metals but also to polymeric and composite materials [ 33 , 34 , 36 , 37 , 38 , 39 , 40 ].…”