Investigation of Interfaces Under Mechanical and Thermal Loading Using a Cohesive Zone Model
Abstract
Failures of structures is a great concern of engineering for longer and safer service
life. The ability to predict a damage and failure depends on understanding the deformation
and stress that develop in the material. Damage (micro level failures) and
failures often initiate at material interfaces. Interactions between different material
phases, as well as crack initiation and propagation, make fracture and damage processes
very difficult to analyze. The interfaces between dissimilar layers in the functionally
graded hybrid material (FGHC) are the most critical for reliability. The use
of different processes and materials to fabricate a hybrid material induce mismatch
strains, making interfacial failure a primary damage mechanism. As advanced materials
are introduced in load bearing structures in aerospace applications to improve
performance, maintenance, and manufacturing, designing safe interfaces becomes a
paramount goal. Creating seamless interfaces and mechanical locking between metal
and polymer matrix composite layers is possible by fabricating a metal surface with
various surface features. One of the joining methods is using carbon nano tube grown
on the fabric surface, with the subsequent infusion of resin. This method makes use
of grown forest of carbon nano tubes using carbon vapor deposition.
Experimental techniques are well established for determining interlaminar fracture
in composite material systems. The mode I interlaminar fracture toughness can
be obtained by the mode I test standard, which uses double cantilever beam specimen.
Similarly, mode II and mixed-mode properties are extracted by designated
test standards, such as end-notch flexure test and mixed mode bending test. Double
cantilever beam test is conducted to explore fracture toughness of hybrid interfacesmodi ed by carbon nanotube grown on carbon fabric and Ti-foil as a function of temperature
to assess its potential use within FGHC. It is seen that fracture toughness
of modi ed interfaces in mode I is higher than the unmodified ed interfaces.
In the present study, computational assessment of joining a metal laminate to
carbon ber reinforced polymer (CFRP) laminate was undertaken to investigate
interlaminar response and mode I and II delamination toughness. The objective of
the present research was to develop a computational model to study delamination in
laminated composite plates subjected to bending and extensional loads, and to study
di erent joining techniques, as well as to predict the thermomechanical interfacial
response. This model incorporates extreme environment conditions, such as high
temperature to study these joining techniques. Experimental data of DCB tests
were obtained in collaboration with Dr. Ochoa's group in order to validate and
verify the computational solutions.
The results of this study are expected to provide a better understanding of interface
mechanical behavior, thereby provide both materials scientists and designers in
selecting alternate material systems and interfaces so that enhanced structural properties
such as interfacial strength and durability of the joints subject to out-of-plane
bending, impact, and fatigue loading are realized.
Citation
Ozsoy, Ovul Ozgu (2014). Investigation of Interfaces Under Mechanical and Thermal Loading Using a Cohesive Zone Model. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /152579.