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<p>Composite materials have become widely used in engineering applications, in order to reduce the overall weight of structures while retaining their required strength.
Due to their light weight, relatively high stiffness properties, and formability into
complex shapes, discontinuous fiber composites are advantageous for producing small
and medium size components. However, qualifying their mechanical properties can
be expensive, and therefore there is a need to improve predictive capabilities to help
reduce the overall cost of large scale testing. To address this challenge, a composite
material consisting of discontinuous glass fibers in a polypropylene matrix is studied
at the microstructural level through coupled experiments and simulations, in order
to uncover the mechanisms that cause microvoids to initiate and progress, as well
as certain fiber breakage events to occur, during macroscopic tension. Specifically,
this work coupled in-situ X-ray micro computed tomography (μ-CT) experiments
with a finite element simulation of the exact microstructure to enable a 3D study
that tracked damage initiation and propagation, and computed the local stresses and
strains in the microstructure. In order to have a comprehensive 3D understanding
of the evolution of the microstructure, high fidelity characterization procedures were
developed and applied to the μ-CT images in order to understand the exact morphology of the microstructure. To aid in this process, ModLayer - an interactive
image processing tool - was created as a MATLAB executable, and the 3D microstructural feature detection techniques were compared to traditional destructive
optical microscopy techniques. For damage initiation, this work showed how high
hydrostatic stresses in the matrix can be used as a metric to explain and predict the exact locations of microvoid nucleation within the composite’s microstructure. From
a damage propagation standpoint, matrix cracking - a mechanism that has been
notably difficult to predict because of its apparent stochastic nature - was studied
during damage propagation. The analysis revealed the role of shear stress in fiber
mediated flat matrix cracking, and the role of hydrostatic stress in fiber-avoidance
conoidal matrix cracking. Overall, a sub-fiber simulation and an in-situ experimental
analysis provided the microstructural physical phenomena that govern certain damage initiation and progression mechanisms, further enabling the strength and failure
predictions of short fiber thermoplastic composites.
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| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12214379 |
| Date | 29 April 2020 |
| Creators | Imad A Hanhan (8780756) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Investigating_damage_in_discontinuous_fiber_composites_through_coupled_in-situ_X-ray_tomography_experiments_and_simulations/12214379 |
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