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Production and Evaluation of Fracture Behavior of Al-Dra Laminated Composites

Jamali, Mohsen |

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39086 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Bagheri, Reza; Seyyed Reihani, Morteza
  7. Abstract:
  8. Particulate ceramic reinforced aluminum matrix composites have high specific strength and stiffness; however, low fracture toughness and deformability have restricted their industrial applications. Among the methods introduced to overcome this shortcoming is fabricating the layered composites which contain alternative layers of aluminum (Al) and discontinuously reinforced aluminum (DRA). In this study, two different routes; i.e., "Powder extrusion - Casting - Rolling" and "Powder extrusion - Roll bonding" were employed to produce layered Al-DRA composites. After production of Al6061/SiCp composites via hot powder extrusion, mentioned processes were utilized to make DRA-Al-DRA laminate. In the first route aluminum melt was poured between DRA layers and the samples were finally hot rolled; while, in the second one after surface cleaning of Al and DRA layers, they were alternatively arranged and hot rolled. Impact test results showed that adding SiC particles decrease the impact resistance of Al/SiCp composites, for example adding 10 and 20 vol.% of particulate SiC to Al6061 resulted in 86 and 93% decrease in its impact energy, respectively. In addition, by increasing the volume fraction of reinforcement from 0 to 20%, fracture toughness (KQ) of Al/SiCp composites reduced from 37 to 26 MPa√m in static condition and 31 to 4 MPa√m in semi-dynamic condition. Particle fracture and particle-matrix debonding were the dominant micromechanisms of Al/SiCp composites' fracture. Fracture behavior of composites and particularly their resistance to crack growth were positively affected by layered structure. Comparison of the area under load – load point displacement curves of composites having same content of SiC indicated that fracture energy of layered samples was 35 to 100% more than those of monolithic ones. Unlike the Al/SiCp composites, catastrophic failure did not occur in Al-DRA composites. As a result of delamination of Al and DRA layers, plastic deformation of Al layer took place in the near plane stress condition and therefore, higher amount of energy was consumed during fracture process. There were no significant differences in the fracture micromechanisms of layered and monolithic composites with exception of elongated microvoids in Al layer which had been created during its shear fracture
  9. Keywords:
  10. Composite Laminate ; Fracture Toughness ; Powder Metallurgy ; Rolling Process ; Al6061/SiCp composite

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