Akademik Veri Yönetim Sistemi
Tezin Türü: Doktora
Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Bilimleri Enstitüsü, Fen Bilimleri Enstitüsü, Türkiye
Tezin Onay Tarihi: 2014
Öğrenci: MEHMET MACAR
Danışman: RAİF ORHAN YILDIRIM
Özet:The main objective of this research is to investigate the dynamic behavior of aluminum alloys (such as 5083-H131, 7039-T64 and 2139-T8) commonly used in lightweight armored military vehicles in a comparative manner and establish a robust experimental database as well as constitutive models for their dynamic response over a wide range of strain rates and temperatures typically encountered in penetration and impact events. Unlike quasi-static deformation processes, impact and dynamic penetration events often involve high strain rates, large strains and rapid changes in temperature due to severe thermoplastic heating and adiabatic deformation conditions. Therefore, any reliable simulation and/or design of armor systems require the development of rate and temperature dependent predictive constitutive models that heavily rely on extensive experimentation at high strain rates and elevated temperatures. In the first phase of study, high strain rate experiments were conducted by using split-Hopkinson pressure bar (SHPB) apparatus at both room temperature and elevated temperatures to understand and document the constitutive behavior of selected aluminum alloys. Quasi-static experiments were also conducted to establish a basis for comparison and more comprehensive analysis of the constitutive response. Then, building on the experimental results and observations, the competition between strain hardening, strain rate hardening and thermal softening mechanisms were evaluated for each alloy to develop a comprehensive analysis of their dynamic deformation and failure behavior. In the second phase, the emphasis was placed on developing predictive constitutive models and finding the model parameters. Both phenomenological (Johnson-Cook, Modified Johnson-Cook) and physics based (Zerilli-Armstrong, Modified Zerilli-Armstrong, Turkkan-Vural Modified Zerilli-Armstrong) models were utilized and their performances were evaluated. According to these results, a new modified model was proposed by combining Modified Johnson-Cook and Turkkan-Vural Modified Zerilli-Armstrong models depending on their ability in capturing the experimental data. The new proposed model eliminates the weakness of the existing models and fits the experimental data better, especially at elevated temperatures. This study has also led to an advanced understanding of aluminum alloy armor materials’ tendency to shear localization in the form of adiabatic shear banding (ASB) by using shear-compression specimens (SCS) in controlled dynamic experiments followed by detailed microstructural examination.