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Title: Study on the characterization of mechanical properties of viscoelastic-plastic materials by nanoindentation
Author: Wang, Lei
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2014
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The aim of this PhD work is to develop a novel and effective instrument to characterize the mechanical properties of viscoelastic material. The principle of this system is based on nanoindentation technique, which is widely used in recent years to explore the mechanical properties of various materials. However, quite a few studies demonstrated that the determination of mechanical properties of viscoelastic material by using the standard Oliver Pharr method would lead to incorrect results. Based on this issue, a new improved tribological probe microscopy (TPM) system was established to carry out the investigation of mechanical properties of viscoelastic materials. Materials including polytetrafluoroethylere (PTFE), styrene rubber and nitrile rubber were measured under quasi-static mode of nanoindentation. The inaccurate results proved that static indentation analyzed by the Oliver Pharr method is not suitable for current work. In addition, dynamic indentation was performed to measure these samples. The results demonstrated that it is a good approach to explore time-dependent properties of polymer samples. The dynamic method offers more abundant viscous information. Moreover, another measurement function was added in this facility to perform creep nanoindentation on viscoelastic samples. It enables to generate instant and infinite modulus as well as time constant. The comparison between the results obtained by dynamic and creep indentation reveals that the more physical element should be considered to bridge the gap between these two approaches. Extra works focus on the relationship between surface topography and its mechanical properties. Finite element simulation as well as actual experiments were performed to investigate the tilt effect on the results of mechanical properties. The results revealed that the standard Oliver Pharr method underestimated the contact area, which will result in overestimating the hardness and elastic modulus of engineering materials. Above all, this study proved the ability of our home made facility to further explore the viscoelastic material. More importantly, it will pave a new way for the investigation of the relationship between the surface topography and viscous property of soft matter including various biomaterials in the near future.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)