Ozsoy, Ovul Ozgu (2014-05). Investigation of Interfaces Under Mechanical and Thermal Loading Using a Cohesive Zone Model. Doctoral Dissertation.
Thesis
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.
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.
