Abstract
The primary objective of this work is to study and model the
fracture process and durability of paperboard cores in cyclic loading.
The results are utilized in creating analytic model to estimate the life
time of cores in printing industry. The life time means here the maximum
number of winding-unwinding cycles before the core delaminates. This
study serves also as an example of use of board as a constructional
engineering material.
Board is an example of complicated, fibrous, porous, hydroscopic,
time dependent and statistic material. Different core board grades are
typically made of recycled fibers. The material model in this work is
linear-elastic, homogeneous and orthotropic.
The material characteristics, elastic and strength properties are
studied first. Then the material is studied from the points of view of
fracture and fatigue mechanics. Some of the analysis and test methods
are originally developed for fiber composites but have been applied
successfully here also for laminated board specimen. An interesting
finding is that Scott Bond correlates well with the sum of mode I and
mode II critical strain energy release rates. It was also possible to
apply Paris' law and Miner's cumulative damage theory in the studied
example situations.
The creation of the life time model starts by FEM-analysis of
cracked and non cracked cores in a typical loading situation. The
elastic-linear material model is used here. The calculated stresses are
utilized in analytic J-integral model. The agreement between analytic
and numerical J-integral estimations is good.
The analytic life time model utilizes the analytic J-integral
model, Miner's cumulative damage theory and analytically formulated
Wöhler-curves which were constructed by applying the Paris' law.
The
Wöhler-curves were constructed also by testing cores to validate the
theoretical results. The testing conditions are validated by
FEM-analysis.
The cores heat up when tested or used with non expanding chucks
and a temperature correction was needed in the life time model to
consider this. Also, single or multi crack model was used depending on
the studied case. The calculated and tested durability prediction curves
show good correspondence. The results are finally reduced to correspond
to certain confidence level.
| Identifer | oai:union.ndltd.org:oulo.fi/oai:oulu.fi:isbn951-42-7400-8 |
| Date | 27 August 2004 |
| Creators | Ilomäki, M. (Marko) |
| Publisher | University of Oulu |
| Source Sets | University of Oulu |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess, © University of Oulu, 2004 |
| Relation | info:eu-repo/semantics/altIdentifier/pissn/0355-3213, info:eu-repo/semantics/altIdentifier/eissn/1796-2226 |
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