On the fracture of thin laminates

DSpace Repository

On the fracture of thin laminates

Show full item record

Files for download

Find Full text There are no files associated with this item.

Facebook

Simple item record

Publication Doctoral Thesis
Title On the fracture of thin laminates
Author(s) Kao-Walter, Sharon
Date 2004
English abstract
This thesis concerns mechanical and fracture properties of a thin aluminium foil and polymer laminate that is widely used as packaging material. The possibility of controlling the path of the growing crack propagation by adjustment of the adhesion level and the property of the polymer layer is investigated. First, the fracture process of the aluminium foil is investigated experimentally. It is found that fracture occurs at a much lower load than what is suggested by standard handbook fracture toughness. Observations in a scanning electron microscope with a tensile stage show that small-scale stable crack growth occurs before the stress intensity factor reaches its maximum. An examination using an optical profilometric method shows almost no plastic deformation except for in a small necking region at the crack tip. However, accurate predictions of the maximum load are obtained using a strip yield model with a geometric correction. Secondly, the mechanical and fracture properties of the laminate are studied. A theory for the mechanics of the composite material is used to evaluate a series of experiments. Each of the layers forming the laminate is first tested separately. The results are analysed and compared with the test results of the entire laminate with varied adhesion. The results show that tensile strength and strain at peak stress of the laminate, with or without a crack, increase when the adhesion of the adhesive increases. It is also found that a much larger amount of energy is consumed in the laminated material at tension compare with the single layers. Possible explanations for the much higher toughness of the laminate are discussed. Finally, the behaviour of a crack in one of the layers, perpendicular to the bimaterial interface in a finite solid, is studied by formulating a dislocation superposition method. The stress field is investigated in detail and a so-called T stress effect is considered. Furthermore, the crack tip driving forces are computed numerically. The results show that the analytical methods for an asymptotically small crack extension can also be applied for a fairly large amount of crack growth. By comparing the crack tip driving force of the crack deflected into the interface with that of the crack penetrating into the polymer layer, it is shown how the path of the crack can be controlled by selecting a proper adhesion level of the interface for different material combinations of the laminate.
Link http://www.bth.se/fou/forskinfo.nsf/alfs/8234b0fbc62f096ac1256f9500478384 (external link to publication)
Publisher Blekinge Institute of Technology
Series/Issue Blekinge Institute of Technology Dissertation Series;7
ISSN 1650-2159
ISBN 91-7295-048-X
Pages 128 p
Language eng (iso)
Subject(s) Technology
Research Subject Categories::TECHNOLOGY::Materials science
Handle http://hdl.handle.net/2043/10933 (link to this page)

This item appears in the following Collection(s)

Show full item record

Search


Browse

My Account

Statistics