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Length-scale effects in yielding and damage development in polymer materials
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 13 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0394
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-485OAI: oai:DiVA.org:kth-485DiVA: diva2:14190
Presentation
2005-11-16, B3, KTH, Brinellvägen 23, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20101123

Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2013-01-15Bibliographically approved
List of papers
1. Influence of molecular weight on strain-gradient yielding in polystyrene
Open this publication in new window or tab >>Influence of molecular weight on strain-gradient yielding in polystyrene
2004 (English)In: Polymer Engineering and Science, ISSN 0032-3888, E-ISSN 1548-2634, Vol. 44, no 10, 1987-1997 p.Article in journal (Refereed) Published
Abstract [en]

Experimental observations have indicated that the presence of strain gradients has an influence on the inelastic behavior of polymers as well as in other materials such as ceramics and metals. The present study has experimentally quantified length-scale effects in inelastic deformations of the polymer material polystyrene (PS) with respect to the molecular length. The experimental technique that has been used is nano-indentation to various depths with a Berkovich indenter. The hardness has been calculated with the method by Oliver and Pharr, and also by direct measurements of the area from atomic force microscopy. The experiments showed that the length-scale effects in inelastic deformations exist in polystyrene at ambient conditions. The direct method gave a smaller hardness than the Oliver-Pharr method. It was also shown that the length-scale parameter according to Nix and Gao increases with increasing molecular weight. For high molecular weights above a critical value of entanglement, there was no pertinent increase in the length-scale parameter. The length-scale parameter for strain-gradient plasticity has a size of around 0.1 μm for polystyrene.

Keyword
Data reduction, Deformation, Hardness, Microelectromechanical devices, Molecular weight, Parameter estimation, Shear strength, Thin films, Molecular length, Strain-gradient yielding, Temperature fields
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7943 (URN)10.1002/pen.20202 (DOI)000224842300020 ()2-s2.0-9144252706 (Scopus ID)
Note
QC 20100910 QC 20110922Available from: 2008-01-31 Created: 2008-01-31 Last updated: 2011-09-22Bibliographically approved
2. Length-scale effects on damage development in tensile loading of glass-sphere filled epoxy
Open this publication in new window or tab >>Length-scale effects on damage development in tensile loading of glass-sphere filled epoxy
2006 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 43, no 24, 7337-7357 p.Article in journal (Refereed) Published
Abstract [en]

Particle-reinforced polymers are widely used in load-carrying applications. The effect of particle size on damage development in the polymer is still relatively unexplored. In this study, the effect of glass-sphere size on the damage development in tensile loaded epoxy has been investigated. The diameter of the glass spheres ranged from approximately 0.5-50 mu m. The first type of damage observed was debonding at the sphere poles, which subsequently grew along the interface between the glass spheres and epoxy matrix. These cracks were observed to kink out into the matrix in the radial direction perpendicular to the applied load. The debonding stresses increased with decreasing sphere diameter, whereas the length to diameter ratio of the resulting matrix cracks increased with increasing sphere diameter. These effects could not be explained by elastic stress analysis and linear-elastic fracture mechanics. Possible explanations are that a thin interphase shell may form in the epoxy close to the glass spheres, and that there is a length-scale effect in the yield process which depends on the strain gradients. Cohesive fracture processes can contribute to the influence of sphere size on matrix-crack length. Better knowledge on these underlying size-dependent mechanisms that control damage development in polymers and polymer composites is useful in development of stronger materials. From a methodology point of view, the glass-sphere composite test can be used as an alternative technique (although still in a qualitative way) to hardness vs. indentation depth to quantify length-scale effects in inelastic deformation of polymers.

Keyword
length-scale effects, particle composite, polymer matrix, interfacial debonding, matrix cracking
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7944 (URN)10.1016/j.ijsolstr.2006.05.026 (DOI)000241539200008 ()2-s2.0-33749350399 (Scopus ID)
Note
QC 20100910. Conference: Colloquium on Size-Dependent Mechanics of Materials. Groningen, NETHERLANDS. JUN 13-15, 2005Available from: 2008-01-31 Created: 2008-01-31 Last updated: 2011-09-29Bibliographically approved

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