Evaluation of stress relaxation in bentonite filled rubber under tensile load using scanner based digital image correlation method
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Date
2019-05
Authors
Poon, Heong Wai
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Abstract
Rubber stress relaxation behaviour is important to be studied and to be evaluated because it deals with the properties and function of rubber under stress condition. There are several methods that can be used to study rubber stress relaxation behaviour such as conventional tensile test and compression test. However, the surface deformation pattern and movement cannot be evaluated using these methods. The objective of this research isto develop a new method using scanner-based Digital Image Correlation (DIC) to evaluate the effect of various percentages of Bentonite loading in natural rubber on the physical stress relaxation behaviour. A flatbed scanner was used for the image acquisition. A motorized test rig was used to carry out the stress relaxation tests. Randomness test MATLAB algorithm was developed to investigate the randomness of speckles created on rubber specimen using different subset sizes. Scaling factor was determined at 0.042333 𝑚𝑚/𝑝𝑖𝑥𝑒𝑙 which was needed to be use in length calculations. Spring tensile test was carried out to determine spring constant for rubber force calculation. Slip test was carried out to investigate the effectiveness of the clamp system of the test rig. Rubber tensile tests were carried out to study different Bentonite loading rubber specimen stress-strain behaviour. Then, stress relaxation tests were carried out for all the rubber specimens. The results shows that the higher the Bentonite loading, the more the stress of the rubber decreased for a given period. DIC MATLAB algorithm was developed and this method was used to evaluate the rubber surface during stress relaxation and the results shows the ability of DIC to indicate surface abnormality and surface movement pattern. All findings form this research work indicate the capability of the new method developed to evaluate rubber stress relaxation behaviour.