Browsing by Author "Chen, Yanyun"

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    Overview of Aluminum Alloy Mechanical Properties During and After Fires
    Summers, Patrick T.; Chen, Yanyun; Rippe, Christian; Allen, Ben; Mouritz, Adrian; Case, Scott W.; Lattimer, Brian Y. (Springer, 2015)
    Aluminum alloys are increasingly being used in a broad spectrum of load-bearing applications such as lightweight structures, light rail, bridge decks, marine crafts, and off-shore platforms. A major concern in the design of land-based and marine aluminum structures is fire safety, at least in part due to mechanical property reduction at temperatures significantly lower than that for steel. A substantial concern also exists regarding the integrity and stability of an aluminum structure following a fire; however, little research has been reported on this topic. This paper provides a broad overview of the mechanical behavior of aluminum alloys both during and following fire. The two aluminum alloys discussed in this work, 5083-H116 and 6061-T651, were selected due to their prevalence as lightweight structural alloys and their differing strengthening mechanisms (5083 – strain hardened, 6061 – precipitation hardened). The high temperature quasi-static mechanical and creep behavior are discussed. A creep model is presented to predict the secondary and tertiary creep strains followed by creep rupture. The residual mechanical behavior following fire (with and without applied stress) is elucidated in terms of the governing kinetically-dependent microstructural mechanisms. A review is provided on modeling techniques for residual mechanical behavior following fire including empirical relations, physically-based constitutive models, and finite element implementations. The principal objective is to provide a comprehensive description of select aluminum alloys, 5083-H116 and 6061-T651, to aid design and analysis of aluminum structures during and after fire.
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    Stress-induced Damage and Post-fire Response of Aluminum Alloys
    Chen, Yanyun (Virginia Tech, 2015-01-15)
    Aluminum alloys have increasing applications in construction and transportation industries. Both 5xxx-series (Al-Mg) and 6xxx-series (Al-Mg) alloys are frequently used in marine construction because of their light weight, high strength, and corrosion resistance. One of the major concerns regarding the marine application of aluminum alloys is their mechanical performance in fire scenarios. The material strength may be degraded due to both thermal and mechanical damage during fire exposure. This work emphasizes the stress-induced mechanical (physical) damage and its impact on the residual (post-fire) performance of 5083-H116 and 6061-T651 aluminum alloy. Thermo-mechanical tests were performed at various temperatures and stresses to study the stress-induced damage at induced plastic creep strain levels. Unstressed thermally exposed and thermo-mechanically damaged samples were examined to separate the stress-induced microstructural damage. The stress-induced microstructural damage primarily manifests itself as dynamic recovery at low creep temperatures, while cavitation, dynamic recrystallization and dynamic precipitation (in Al6061) are the types of damage developed in the high creep strains at high exposure temperatures. Different creep mechanisms are also studied for both Al5083 and Al6061. The post-fire mechanical response at room temperature after thermo-mechanical damage was investigated with reference to the damaged microstructure present in the material. Residual material strengths based on deformed cross sectional area after the creep test were calculated to provide insight into how microstructural damage affects the post-fire material performance. The competing effects of strength degradation caused by cavitation and strengthening due to grain elongation and subgrain refinement were investigated. Engineering residual material strengths calculated based on the original cross sectional area prior to creep tests were also studied to provide guidance for structural design.