Editorial Type:
Article Category: Research Article
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Online Publication Date: 01 Dec 2007

Dynamic Fracture of Natural Rubber3

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Page Range: 252 – 275
DOI: 10.2346/1.2803268
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Abstract

This paper illustrates how the fracture energy of a tensile strip made of unfilled and 25 phr carbon black-filled natural rubber varies with far-field strain rate in the range 0.01–71 s−1. Quasistatic and dynamic fracture tests were performed at room temperature with an electromechanical INSTRON machine, a servo-hydraulic MTS machine, and Charpy tensile apparatus, respectively. It was found that the fracture energy of the unfilled natural rubber did not vary significantly over the range of sample strain rate, but there was significant variation in the fracture energy of the 25 phr carbon black-filled natural rubber from 0.01 to 71 s−1 sample strain rate. The fracture energy of the 25 phr carbon black-filled natural rubber at a sample strain rate of 0.1 s−1 was about three times greater than it was at the 10 s−1 sample strain rate. While the carbon black fillers increased the fracture energy of natural rubber by about 200% at quasistatic sample strain rates (0.01–0.1 s−1) and at 71 s−1, the carbon black fillers did nothing to improve the fracture energy of natural rubber at sample strain rates between 5 and 29 s−1. In this strain rate range, the fracture energy of 25 phr carbon black-filled natural rubber was almost the same as that in the unfilled natural rubber. The variation in the fracture energy with far-field strain rate was due to changes in the material behavior of natural rubber at high strain rates. Finite element analysis using a high-strain-rate constitutive equation for the 25 phr carbon black rubber specimen was used to calculate the fracture energy of the specimen at a sample strain rate of 55 s−1, and good agreement was found between the test and finite element results.

Keywords: dynamic fracture; fracture energy; crack speed; natural rubber
Copyright: The Tire Society
FIG. 1.
FIG. 1.

Geometry of single-edge notched strip.

FIG. 2.
FIG. 2.

Schematic diagram of tensile impact apparatus: (a) side view of Charpy impact apparatus and (b) top view of tensile impact apparatus.

FIG. 3.
FIG. 3.

Snapshots of single-edge notched strip of unfilled natural rubber at 26 s−1 deformation rate: (a) start of test, t=0 s; (b) blunting, t=0.0251 s; (c) fracture onset, t=0.0410 s; (d) intermediate fracture propagation, t=0.0422 s; (e) tearing and necking, t=0.0428 s; and (f) final fracture, t=0.0430 s.

FIG. 4.
FIG. 4.

Data synchronization of force and grip displacement for 26 s−1 strain rate: (a) force versus time from piezoelectric load cell and (b) grip displacement versus time from high-speed camera.

FIG. 5.
FIG. 5.

Crack displacement versus time.

FIG. 6.
FIG. 6.

Variation of fracture energy with far-field sample strain rate for unfilled natural rubber.

FIG. 7.
FIG. 7.

Variation of crack speed with sample strain rate for unfilled natural rubber.

FIG. 8.
FIG. 8.

Comparison of unfilled natural rubber data with Lake et al. [7] data.

FIG. 9.
FIG. 9.

Variation of fracture energy with sample strain rate for 25 phr carbon black-filled natural rubber.

FIG. 10.
FIG. 10.

Variation of crack speed with sample strain rate for 25 phr carbon black-filled natural rubber.

FIG. 11.
FIG. 11.

Comparison of the variation of fracture energy with the sample strain rate between unfilled and 25 phr carbon black-filled natural rubber.

FIG. 12.
FIG. 12.

Tensile fracture specimens at sample strain rate 0.1 s−1: (a) unfilled natural rubber and (b) 25 phr carbon black-filled natural rubber.

FIG. 13.
FIG. 13.

Tensile fracture specimens at sample strain rate 10 s−1: (a) unfilled natural rubber and (b) 25 phr carbon black-filled natural rubber.

FIG. 14.
FIG. 14.

Finite element analysis mesh of upper half of tensile fracture specimen.

FIG. 15.
FIG. 15.

Variation of specimen force with extension for 25 phr carbon black-filled natural rubber at 55 s−1 sample strain rate.

FIG. 16.
FIG. 16.

Tensile fracture specimen at 55 s−1 sample strain rate: (a) experiment and (b) finite element analysis prediction.

FIG. 17.
FIG. 17.

Contour plot of the strain energy density in the tensile fracture test at incipient fracture for sample strain rate 55 s−1.

FIG. 18.
FIG. 18.

Variation of material toughness with first invariant of left Cauchy Green deformation tensor (taken from Al-Quraishi [13]).

FIG. 19.
FIG. 19.

Variation of potential energy of tensile specimen with initial crack length.

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