Date of Award


Document Type

Master Thesis

Degree Name

Master of Engineering (Research)


Biomedical, Manufacturing & Facilities Engineering

First Advisor

Dr. Ger Kelly

Second Advisor

Dr. Rauri McCool

Third Advisor

Professor Noel O'Dowd


The creep behaviour of hand laminated, glass fiber reinforced polyester composites were studied at coupon level, due to the use of similar materials in long term load bearing civil and structural engineering applications. Creep predictions were made by fitting the parameters of several viscoelastic models to experimental creep data as well as two accelerated test methods, time temperature superposition (TTS) and frequency time transformations (FTT). TTS experiments were carried out in a dynamic mechanical analyzer (DMA) in three point bending mode for three types of material systems. Creep compliance master curves representing the linear viscoelastic creep response at reference temperatures of 35‘^C, 45”C and 55°C were generated by using a manual curve shifting procedure, while the validity of TTS was explored by assessment of the temperature dependence of the curve shifting.

The FTT method of synthesizing the linear viscoelastic creep response was used by initially carrying out a series of oscillatory measurements in three point bending mode in the DMA. The dynamic stiffness as a function of frequency was transformed into time domain creep compliance by means of an inverse fast Fourier transform and numerical integration routine implemented in National Instruments’ LabView 8.2. The technique was also initially tested by synthesizing a number of known exact functions in order to give confidence in the results. The synthesized functions were generated for periods of two and four hours and compared to actual time domain creep tests carried out over a two hour period. The results show good potential for using FTT as a creep characterization technique, provided that the frequency dependent properties can be successfully extrapolated to the low frequencies required for synthesis.

Procedures for theoretically estimating the static and transient response of a polymer composite structure in flexure were also explored through a combination of theoretical and finite element approaches. The results showed excellent correlation between theoretical and finite element models for static analysis while transient finite element analysis suggests that increased temperature can dramatically increase the creep rate of a polymer composite structure in flexure.


Supervisor Dr. Ger Kelly, Department of Manufacturing, Facilities and Biomedical Engineering, Cork Institute of Technology.

Internal Examiner Dr. Rauri McCool, Department of Mechanical Engineering, Cork Institute of Technology.

External Examiner Professor Noel O’ Dowd, Department of Mechanical and Aeronautical Engineering, University of Limerick.

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