Student:	Vahap VAHAPOĞLU
Supervisor:	Prof. Dr. Sami KARADENİZ
Department:	Mechanical Engineering
Institution:	Graduate School of Natural and Applied Sciences
University:	Karadeniz Technical University, Turkey

Title of the Thesis:	Experimental Investigation of the Inelastic Properties of Rubber-like Materials
Level:	Ph.D.
Acceptance Date:	12/5/2006
Number of Pages:	235
Registration Number:	di540

Summary:

In this thesis, the effects of the stress relaxation, Mullins effects, permanent set,

strain rate of straining, and hysteresis on the stress–strain behaviours of SBR (Stiren-

crystallization and NR (natural rubber) which shows strain induced crystallization are

investigated experimentally.

A special purpose uni-axial testing machine was designed and manufactured for the

study. All the hardware and the sensors used in the experimental set up were controlled by

a software written in the NI-LABVIEW platform. To investigate the inelastic properties of

the rubbers used seven different loading procedures were proposed and then fed into the

software. Hence, all the experiments were performed by the full assistance of a computer.

In the fist stage, the effects of the every one of these inelastic properties on the stressstrain

behaviours of the chosen rubbers were investigated and then their combined effects

were studied. Hence the stress-strain data which are independent of the inelastic properties

of the rubbers were obtained. The effects of the application of pre-conditioning on the

inelastic properties of the studied rubbers were also investigated.

Experimental investigation showed that the pre-conditioning experiments can be

carried out at a strain rate of 200mm/min. for the SBR. The corresponding strain rate for

NBR and NR is 80 mm/min. In order to obtain the Mulins effects free data it is necessary

that the rubber specimens should be subjected to 10 to 12 pre loading cycles. After these

loading cycles the effects of the stress relaxation, permanent set, hysterisis on the stress -

strain behavior settled down. For the SBR is possible to obtain the stress-stain data which

are independent from the inelastic properties of this rubber. On the other hand, such data

can not be obtained for of the NBR and NR since there remains some hysteresis area

between the uploading and unloding curves for these rubbers.

Key Words: Rubber-Like Materials, Mullins Effects, Hysteresis, Stress Relaxation,

Permanent Set, Strain Rate, Pre Conditioning, Uniaxial Testing Machine