Technical Paper Archive

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Microscopy Investigation of Crack Precursors and Fracture Surfaces

A40 tunnicliffe paper

Event: 198th Technical Meeting - Fall 2020
Location: Virtual
Date: October 19, 2020
Author: Lewis Tunnicliffe
Paper Number: A40

Price: $20.00

  • Simple tension stress-strain testing was used to investigate fracture behavior of carbon black (CB)-reinforced styrene-butadiene rubber (SBR), using 50 replicate specimens to quantify distributions of tensile strength and crack precursor size. Four vulcanized rubber compounds were studied: a CB-filled SBR with standard mixing conditions (Control); the same formulation with intentional poor mixing of the CB; and materials formed by adding minor amounts of 0.5 mm diameter glass microspheres (beads) – serving as large model defects/inclusions – to the Control compound using a two-roll mill at two levels corresponding to average values of 0.78 and 6.24 beads per gauge section region of the tensile test specimen. This paper focuses on analyzing the fracture surfaces with microscopy to complement our recent publication on Weibull failure statistics for distributions of tensile strength and crack precursor size (Polymers 12, 203 (2020)). For all 200 fractured test specimens that were imaged with light optical microscopy (LOM), the SBR material exhibited fracture surfaces that were characterized by relatively smooth planes there were perpendicular to the uniaxial loading direction. LOM also revealed concentric fracture rings emanating from the crack precursors, and interferometric microscopy (IFM) confirmed that these zones were defined by distinct micro-roughness features. The fractures initiated by the presence of the glass beads were obvious from LOM, and these failures resided in the low strength regions of the tensile strength distributions. Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) was also employed for distinguishing crack initiation from CB agglomerates versus zinc oxide particles.

    Papers from 198th Technical Meeting - Fall 2020

    Items from 198th Technical Meeting - Fall 2020