Atomic mechanism of fracture of solid polymers

Zhurkov, S. N.; Korsukov, V. E.

doi:10.1002/pol.1974.180120211

Cited by 221 publications

(136 citation statements)

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“…To expose the deteriorated region near the tip electrode so that spectroscopic 14 study could be made, it was necessary to cut the sample into 1 00-micron thick slices. This introduces physical damage and may have influenced the results, especially as it is known that mechanical working of polymers can generate free radicals [Zhurkov et al (1974)]. …”

Section: Discussionmentioning

confidence: 99%

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Investigation of the structural changes in LDPE and XLPE induced by high electrical stress

Sayers¹

2000

Eighth International Conference on Dielectric Materials, Measurements and Applications

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SummaryHigh voltage electrical cables play an immensely important, although largely unseen, part in the lives of everybody in the world today. They are mostly buried underground and provide trouble free operation for the majority of their operational lives. However, the polymer based insulation that is used for a large number of high voltage cables is subject to long term ageing which can eventually lead to electrical breakdown. This ageing manifests itself as the appearance of tree like structures in the bulk polymer insulator. The growth of a tree frequently starts on the boundary of the polymer at the so-called "polymer-semicon" interface.This thesis is concerned, however, with the changes that must take place in the polymer before the tree is formed.Previous investigations of field induced changes occurring within polymer insulation have involved cutting the polymer to expose the region of interest: this is not a satisfactory as the cutting process can produce changes in the polymer. To avoid this a novel technique was developed whereby the polymer-semicon interface can be exposed without cutting the polymer.The interface region of the polymer in contact with the plane electrode was examined and even though the field in this region is less than at the point, it can be sufficiently large to induce structural change in the polymer, readily detectable by Raman spectroscopy.In studies of both LDPE and XLPE, we find evidence of structural change within the polymer and most significantly of considerable Raman fluorescence which is indicative of defect states in the polymer. The latter becomes modified as the polymer structure approaches electrical failure.The observations reported are set in context by the examination of the work of relevant authors and some conclusions deduced. The evidence supports a model in which the forces induced by the electrical field lead to failure by the mechanisms of local yield, microvoid craze and crack formation commonly invoked for the mechanical fracture of polymeric solids. Acknowledgments I would like to thank the School of Informatics, University of Wales, Bangor for all the help and assistance provided not only through the period of this PhD but also during my degree course. I would like to thank the people who worked at BICC Cables Limited before it became BICC General and then was sold to Pirelli Cables who closed BICC down. I would also like to thank the EPSRC for funding this work through a Co-operative Award in Science and Engineering (CASE) studentship.As a result of these connections I have had the pleasure and honour of working with Professor T. J. Lewis and Doctor J. P. Llewellyn both of whom continue to astound me with their ability to absorb new ideas, generate original ideas and furthermore to critically review those ideas and theories. Doctor Carl. Griffiths, previously of BICCGeneral provided invaluable critical appraisal of the work, results and interpretations presented here. I would also like to thank Dr Steven Befteridge, also previously of BICCGeneral, for h...

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Section: Discussionmentioning

confidence: 99%

“…In addition it has also been shovvn that ruptured bonds can localise into micro regions forming sub-microvoids Mich have been found to lead to the physical breakdown of the polymer. [Zhurkov et al (1974)] Crystallinity There has been a significant amount of published work carried out with…”

Section: -46mentioning

confidence: 99%

Investigation of the structural changes in LDPE and XLPE induced by high electrical stress

Sayers¹

2000

Eighth International Conference on Dielectric Materials, Measurements and Applications

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“…For polymers it was not clear whether covalent bonds within molecules were being broken or van der Waal bonds between polymer molecules, allowing the latter to slip past one another. However, in 1974 Zhurkov and Kursukov used infrared spectroscopy to monitor the breaking of covalent polymer bonds and showed that this process was paramount in determining the dependence of fracture on stress [25]. They also showed that the values of U o calculated from the dependence of fracture time on temperature in Eq.…”

Section: If Dry Chloride Of Silver In Powder Be Triturated In a Mortamentioning

confidence: 99%

“…[24,25]. From the above it can be seen that, by the end of the 1950s, the stress-augmented thermal activation approach pioneered by Prandtl and Eyring had been successfully used in models of plastic deformation, liquid viscosity, kinetic friction, and chemical bond dissociation.…”

Section: Early Historymentioning

confidence: 99%

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Stress-augmented thermal activation: Tribology feels the force

2018

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Abstract:In stress-augmented thermal activation, the activation energy barrier that controls the rate of atomic and molecular processes is reduced by the application of stress, with the result that the rate of these processes increases exponentially with applied stress. This concept has particular relevance to Tribology, and since its development in the early twentieth century, it has been applied to develop important models of plastic flow, sliding friction, rheology, wear, and tribochemistry. This paper reviews the development of stress-augmented thermal activation and its application to all of these areas of Tribology. The strengths and limitations of the approach are then discussed and future directions considered. From the scientific point of view, the concept of stress-augmented thermal activation is important since it enables the development of models that describe macroscale tribological performance, such as friction coefficient or tribofilm formation, in terms of the structure and behaviour of individual atoms and molecules. This both helps us understand these processes at a fundamental level and also provides tools for the informed design of lubricants and surfaces.

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Mechanochemical Reactions of Polymers

Beyer

2014

Encyclopedia of Polymer Science and Technology

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An external mechanical force is able to activate covalent bonds. Grinding, milling, or extrusion of polymers and polymeric materials leads to polymer degradation, because covalent bonds are broken. Mechanoradicals are generated by homolytic rupture of covalent bonds, but bond hydrolysis or other bimolecular reactions may as well be mechanically activated. Rubber mastication, thermomechanical treatment of food polymers, and recycling of postconsumer plastic waste are technological applications of mechanochemical reactions of polymers. The design of mechanophores opens new possibilities for mechanoresponsive materials. Weak linkages introduce defined rupture points in polymers. Mechanochromic mechanophores lead to color change of polymer solids when exposed to excessive mechanical stress, even before macroscopic damage becomes visible. Further examples are chemiluminescent mechanophores, cross‐linking mechanophores, or mechanophores acting as mechanocatalysts. A quantitative understanding of mechanochemical reactions is reached with a wide variety of experimental and theoretical methods. Defined force can be applied to the bulk material, as well as to individual molecules embedded in macrocycles, or single polymer chains manipulated with an atomic force microscope. The latter method forms the basis for single molecule force spectroscopy, which is performed either in the force‐ramp or force‐clamp mode. The theoretical framework ranges from one‐dimensional description of covalent bonds with a Morse potential via the constrained geometries simulate external force method to full‐dimensional quantum chemical methods like external force explicitly included or the force‐modified potential energy surface. Ab initio molecular dynamics simulations, transition state optimizations, or intrinsic reaction paths following are routinely performed on molecules exposed to a defined mechanical force.

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Atomic mechanism of fracture of solid polymers

Cited by 221 publications

References 13 publications

Investigation of the structural changes in LDPE and XLPE induced by high electrical stress

Investigation of the structural changes in LDPE and XLPE induced by high electrical stress

Stress-augmented thermal activation: Tribology feels the force

Mechanochemical Reactions of Polymers

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