On the Cyclic Inelastic Behavior and Shakedown-Based Design of Metallic Materials and Structures: Analysis and Experiments

Metallic structures in many engineering disciplines are subject to repeated and extreme thermomechanical loading conditions. The conventional design of these types of structures, that are not limited by high-cycle fatigue, employs first-yield criteriain order to avoid failure due to cyclic plasticity. However, yield-limited designs often fail to produce acceptable solutions for multifunctional structures in extreme environments. In order to overcome these limitations and capitalize on the elastoplasticload-bearing reserve, this dissertation analytically, numerically, and experimentally demonstrates inelastic design methods that exploit shakedown for metallic structures. Several analytic and numerical case studies are presented that are relevant to aerospaceand civil engineering applications. These include built-in beam structures, auxetics, and reinforced concrete structures. Experimentally, new macroscopic demonstrations of shakedown behavior and shakedown design (avoiding alternating plasticityand ratchetting) at ambient and elevated temperatures are made for two common engineering materials: the nickel-based superalloy IN625 and stainless steel 316L. The results indicate that allowing shakedown can significantly expand the feasible design space (2-4 times) compared to conventional first-yield. It is found that interactions with other material and structural behaviors such as dynamic strain aging, creep, and buckling can have both propitious and detrimental effects on the macroscopic shakedown response. In this way, this dissertation serves to promote more wide-spread adoption of shakedown-based analysis in realizing new structural concepts and accurately assessing the structural integrity of existing components.