Thermomechanical analysis of the crack tip zone in stretched crystallizable natural rubber by using infrared thermography and digital image correlation

J.R Samaca Martinez,X Balandraud,E Toussaint,J.-B Le Cam,D Berghezan

doi:10.1016/j.polymer.2014.10.010

Abstract

This paper provides the first characterization of heat source field in the crack tip zone in carbon black filled natural rubber (NR). It focuses more especially on the calorific effects of strain induced crystallization (SIC). For this purpose, full thermal and kinematic fields are measured simultaneously. Initial image processing based on motion compensation enables us to track the temperature of any material point at the specimen surface. A second image processing stage, based on the heat diffusion equation, enables us to obtain the fields of heat sources produced and absorbed by the material during the test. The heterogeneity of the stretch states is analyzed from the kinematic measurements. In terms of heat production, crystallization acts in two opposite ways in the crack tip zone: the crystallization process produces additional heat, but crystallites act as fillers, which increases material stiffness in the crack tip zone. Moreover, the heat sources in the crack tip zone remain positive and small during unloading. This phenomenon is due to the production of mechanical dissipation and probably a continuation of the crystallization process. The results attained are compared with those recently obtained in non-crystallizing carbon black filled styrene butadiene rubber (SBR50).

Highlights

Fracture mechanics in rubber is classically addressed through phenomenological approaches, especially through the strain energy release rate, named tearing energy [1]
In terms of heat production, crystallization acts in two opposite ways in the crack tip zone: the crystallization process produces additional heat, but crystallites act as fillers, which increases material stiffness in the crack tip zone
Infrared thermography and digital image correlation have been used simultaneously to analyze the thermomechanical behavior at the crack tip of a filled crystallizable rubber (NR50) and a filled noncrystallizable rubber (SBR50)

Summary

Introduction

Fracture mechanics in rubber is classically addressed through phenomenological approaches, especially through the strain energy release rate, named tearing energy [1]. To account for the physical phenomena involved in crack growth, the expression of the tearing energy can be modified, for instance by weighting it with a dissipative energy function to model the effects of dissipation at the crack tip [2]. Such approaches remain a description of fracture on the global scale and do not enable us to satisfactorily predict crack propagation paths or to understand how changes in the microstructure affect crack growth. This should be all the more interesting since the continuum quantities measured are energies (making the link with tearing energy)

Methods

Results

Conclusion