Publikationsserver der RWTH Aachen University
Polymer crystallization and micromechanical behavior of fiber reinforced polymer composites : a microstructural view on advanced polymer composites
Abstract
dc:descriptionThe final properties of a polymer composite are determined by its internal structure, which is formed during processing of the product. Therefore, phenomenon of crystallization plays a significant role in the development of the morphology of semicrystalline polymers such as isotactic polypropylene (iPP). The amount of strain experienced during the flow influences the number and the type of the nuclei formed and thereby the final crystalline structure. Therefore, the kinetics and topology of spherulite growth during crystallization of iPP has been studied by using a 3D cellular automaton model. The new automaton approach also predicted the intricate spherulite topologies and the kinetic details. The presence of fibers and other additives in semicrystalline polymer matrices like iPP reduces the free energy barrier for nucleation which can increase the local or overall rate of nucleation. Such influences can induce transcrystallinity and results in the formation of a heterogeneous microstructure at different length scales. These microstructural inhomogeneities can induce anisotropic strain distribution under external loads especially at the interface/interphase regions between the fibers and the polymer matrix. Strain-field analysis via digital image correlation (DIC), which is also referred to as photogrammetry, was applied in the present study to map lateral surface microstrain distributions at different length scales. DIC provided a direct and strong experimental support to the heterogeneous behaviors of reinforced polymer composites therefore the application of high-resolution DIC technique in this research is unique and valuable. However, it is still underutilized to investigate the micromechanical behavior of complex polymer composites especially at higher optical resolution. Therefore, in this work scanning electron microscopy (SEM) in-situ experimentation in conjunction with a micro-tensile testing machine was conducted to overcome the resolution limits of the conventional light optical setup. This novel combination proved to be very useful in resolving the microstrain distribution behavior in non-conductive materials such as polymer composites at submicron level. The formation of heterogeneous strain patterns revealed the anisotropic micromechanical behavior which necessitated to thoroughly examine the localized micromechanical properties. Such microscale changes were more important for one of the investigated material in this study i.e. polyether(ether)ketone (PEEK) reinforced with short carbon fibers (CF) which is commercially used as a medical implant (bone implant). Sterilization is a mandatory process for the materials used as bone-implants. A combination of nanoindentation and nanoscratch tests were performed to characterize the local micromechanical properties of the material emphasizing the influence of the sterilization processes on the interphase region. The results reveal that the bulk polymer is largely unaffected in terms of the measured parameters by sterilization and only a slight modification in the properties of the PEEK matrix occurs at the interphase. This applies in particular for the steam sterilization process. Scanning electron microscopy (SEM) was used to examine fracture surfaces, which revealed multiple localized failure mechanisms attributed to the different fiber orientations.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2007
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Godara, Ajay
- Contributors dc:contributor
-
- Raabe, Dierk
Subjects
dc:subject × 11Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- eng
Identifiers
dc:identifier.*- OAI identifier oai:identifier
- oai:publications.rwth-aachen.de:62436