Long term stress relaxation behaviour of polyethylene terephthalate subjected to thermally activated restrained shrinkage

Long term stress relaxation behaviour of polyethylene terephthalate subjected to thermally activated restrained shrinkage

Hazelwood, T.
Jefferson, A.D.
Lark, R.J.

2013-06-16

Research has been carried out with the aim of better understanding the relevant properties of materials to be used in a new self-healing cementitious composite material system. The system consists of shape memory polymer tendons embedded within a cementitious matrix, upon heat activation these tendons undergo a shrinkage process which closes any cracks present. After this heat activation, autogenous healing of the cracks is enhanced by the ongoing application of pressure to the cracked faces. In a previous study the build-up of stress in a restrained poly(ethylene terephthalate) specimen upon heat activation was investigated. In the current study, the long term stress relaxation behaviour of such a restrained specimen has been investigated so that its potential for use in the material system described above can be better understood. Both experimental and numerical approaches have been undertaken. A specimen of poly(ethylene terephthalate) was restrained against longitudinal shrinkage and a heat of 90oC applied for a duration of 10 minutes to simulate the conditions it would be subject to within the system. The stress in the specimen was continuously monitored during heat activation, cooling, and for approximately 6 months after this. This data was used to quantify the stress relaxation of the specimen. The stress relaxation over the period studied was found to be very low; the peak stress was 32.80MPa, this fell to a minimum value of 30.84MPa after a period of approximately 97 days had elapsed. These low levels of stress relaxation are beneficial to the system since a larger shrinkage force will be applied for a longer period of time, which should also lead to improved autogenous healing of cracks.

concrete
self-healing
shape memory polymer
thermo-mechanical behaviour
long-term stress relaxation

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Conference proceedings

conference paper

(c) 2013 Hazelwood, T.; Jefferson, A.D.; Lark, R.J.