Fracture Behavior of Two Biopolymers Containing Notches: Effects of Notch Tip Plasticity

Sahel Shahbaz,Ali Reza Torabi,Sergio Cicero,Majid Reza Ayatollahi

doi:10.3390/app10238445

Sahel Shahbaz, Ali Reza Torabi + Show 2 more

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https://doi.org/10.3390/app10238445

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Abstract

This paper analyzes the notch effect on the fracture behavior of two biomaterials (a brittle bone cement and a ductile dental material) under mode I loading. U-notched Brazilian disk (UNBD) specimens of both materials were tested under remote compression, determining the corresponding fracture loads and load-displacement curves. Additionally, cracked rectangular and semicircular bend (SCB) specimens were tested under symmetric three-point bending in order to determine the fracture toughness of the two materials. Then, fracture loads were derived theoretically by applying the maximum tangential stress (MTS) and the mean stress (MS) criteria. Due to the brittle linear elastic behavior of the bone cement material, the MTS and MS criteria were directly applied to this material; however, given the significant nonlinear behavior of the dental material, the two fracture criteria were combined with the Equivalent Material Concept (EMC) for the fracture analyses of the dental material specimens. The results reveal a very good accuracy of both the MTS and the MS criteria for the fracture analysis of bone cement notched specimens. In the case of the dental material, very good results are also obtained when combining the MTS and the MS criteria with the EMC. The proposed approach can be useful for the fracture analysis of a wide range of biopolymers, from brittle to ductile behavior.

Highlights

Polymeric biomaterials are generally categorized, as many other families of materials, into three different groups, depending on their fracture behavior: brittle, quasi-brittle, and ductile
Fracture tests were carried out on U-notched Brazilian disk (UNBD) specimens with various notch tip radii made of two different biomaterials with different fracture behavior: linear elastic and elastic–plastic
While the behavior of the DM in tensile tests was clearly elastic–plastic, its behavior in UNBD tests did not present any evident nonlinear zone in the load-displacement curves before the critical point, given that the plastic zone around the notch is very localized in the notch tip vicinity

Summary

Introduction

Polymeric biomaterials are generally categorized, as many other families of materials, into three different groups, depending on their fracture behavior: brittle, quasi-brittle, and ductile. Fracture in brittle biomaterials usually takes place suddenly, with no plastic deformation from the pre-existing defect (crack or notch) tip. The fracture process in quasi-brittle biomaterials is still abrupt, but a small plastic zone is developed around the crack/notch tip at the fracture onset. Ductile biomaterials usually exhibit elastic–plastic stress–strain behavior, and fracture normally occurs with an intermediate or large plastic zone in the vicinity of the crack/notch tip. Bone cement is a well-known type of biomaterial. Bone cements are used in clinical applications for fixing joint prostheses in the hip and knee joints. Depending on the implant shape, notches of

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