On initiation of chemically assisted crack growth and crack propagation paths of branching cracks in polycarbonate

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On initiation of chemically assisted crack growth and crack propagation paths of branching cracks in polycarbonate

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Publication Licentiate Thesis
Title On initiation of chemically assisted crack growth and crack propagation paths of branching cracks in polycarbonate
Author(s) Hejman, Ulf
Date 2010
English abstract
Stress corrosion, SC, in some cases gives rise to stress corrosion cracking, SCC, which differs from purely stress intensity driven cracks in many aspects. They initiate and grow under the influence of an aggressive environment in a stressed substrate. They grow at low load and may branch. The phenomenon of SCC is very complex, both the initiation phase and crack extension itself of SCC is seemingly associated with arbitrariness due to the many unknown factors controlling the process. Such factors could be concentration of species in the environment, stress, stress concentration, electrical conditions, mass transport, and so on. In the present thesis, chemically assisted crack initiation and growth is studied with special focus on the initiation and branching of cracks. Polycarbonate plates are used as substrates subjected to an acetone environment. Experimental procedures for examining initiation and branching in polycarbonate are presented. An optical microscope is employed to study the substrate. The attack at initiation is quantified from pits found on the surface, and pits that act as origin for cracks is identified and the distribution is analysed. A growth criterion for surface cracks is formulated from the observations, and it is used to numerically simulate crack growth. The cracks are seen to coalesce, and this phenomenon is studied in detail. Branching sites of cracks growing in the bulk of polycarbonate are inspected at the sample surface. It is found that the total width of the crack branches are approximately the same as the width of the original crack. Also, angles of the branches are studied. Further, for comparison the crack growth in the bulk is simulated using a moving boundary problem based algorithm and similar behaviour of crack branching is found.
Publisher Ulf Hejman/Media-Tryck AB
ISBN 978-91-633-6462-4
Pages 77
Language eng (iso)
Subject(s) stress corrosion
crack initiation
multiple cracking
polycarbonate
three point bending
stress corrosion cracking
polycarbonate
dissolution
branching
experiment
finite element modelling
Sciences
Research Subject Categories::MATHEMATICS::Applied mathematics::Numerical analysis
Research Subject Categories::TECHNOLOGY::Engineering mechanics::Solid mechanics
Research Subject Categories::TECHNOLOGY::Materials science::Surface engineering
Included papers
  1. U. Hejman, C. Bjerkén. "Environmentally assisted initiation and growth of multiple surface cracks". Submitted for publication.

  2. U. Hejman, C. Bjerkén. "Branching cracks in a layered material - Dissolution driven crack growth in polycarbonate". Submitted for publication.

Handle http://hdl.handle.net/2043/9955 (link to this page)

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