Fracture testing and estimation of critical loads in a PMMA-based dental material with nonlinear behavior in the presence of notches

Abstract

The goal of the present investigation is twofold: first, to provide new experimental data on the fracture behavior of biopolymer specimens containing notches, and second, to validate new fracture criteria to predict the corresponding experimental fracture loads. For this purpose, nine fracture experiments are conducted on U-notched rectangular specimens with different notch tip radii made of polymer-based dental material under monotonic tension. As the main outcomes of the experimental program, the fracture loads of the specimens, as well as the corresponding load-displacement curves, were recorded. Due to the nonlinear behavior of the dental material being tested, considerable plastic deformations are developed in the U-notch vicinity and, hence, the use of linear elastic notch fracture mechanics (LENFM) criteria (e.g., the maximum tangential stress (MTS) and mean stress (MS) criteria) for fracture (critical) load predictions provides inaccurate results. Consequently, the Equivalent Material Concept (EMC), which equates the nonlinear biopolymer material with a virtual brittle material having perfectly linear elastic behavior, is combined with the MTS and the MS criteria, allowing the use of LENFM for fracture load predictions of the U-notched biopolymer specimens being tested. It is observed that the two resulting criteria, EMC-MTS and EMC-MS, provide very good predictions of the experimental results. From the viewpoint of mechanical design, the EMC-MTS criterion may be preferred to the EMC-MS criterion, given its inherent simplicity.