Modeling the Creep of Hastelloy X and the Fatigue of 304 Stainless Steel Using the Miller and Walker Unified Viscoplastic Constitutive Models

Hastelloy X (HX) and 304 stainless steel (304SS) are widely used in the pressure vessel and piping industries, specifically in nuclear and chemical reactors, pipe, and valve applications. Both alloys are favored for their resistance to extreme environments, although the materials exhibit a rate-dependent mechanical behavior. Numerous unified viscoplastic models proposed in literature claim to have the ability to describe the inelastic behavior of these alloys subjected to a variety of boundary conditions; however, typically limited experimental data are used to validate these claims. In this paper, two unified viscoplastic models (Miller and Walker) are experimentally validated for HX subjected to creep and 304SS subjected to strain-controlled low cycle fatigue (LCF). Both constitutive models are coded into ansys Mechanical as user-programmable features. Creep and fatigue behavior are simulated at a broad range of stress levels. The results are compared to an exhaustive database of experimental data to fully validate the capabilities and performance of these models. Material constants are calculated using the recently developed Material Constant Heuristic Optimizer (macho) software. This software uses the simulated annealing algorithm to determine the optimal material constants through the comparison of simulations to a database of experimental data. A qualitative and quantitative discussion is presented to determine the most suitable model to predict the behavior of HX and 304SS.

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Modeling the Creep of Hastelloy X Using the Miller and Walker Unified Viscoplastic Constitutive Models

Volume 6A: Materials and Fabrication ◽

10.1115/pvp2015-45108 ◽

2015 ◽

Author(s):

Luis A. Varela J. ◽

Calvin M. Stewart ◽

Ali P. Gordon

Keyword(s):

Experimental Data ◽

Creep Behavior ◽

Simulated Annealing Algorithm ◽

Extreme Environments ◽

Constitutive Models ◽

Suitable Model ◽

Inelastic Behavior ◽

Hastelloy X ◽

Material Constants ◽

Viscoplastic Models

Hastelloy X is widely used in the pressure vessel and piping (PVP) industries, specifically in nuclear and chemical reactors, pipes and valves applications. Hastelloy X is favored for its resistance to extreme environments, although it exhibits a rate-dependent mechanical behavior. Numerous unified viscoplastic models proposed in literature claim to have the ability to describe the inelastic behavior of superalloys subjected to a variety of boundary conditions; typically limited experimental data is used to validate their performance. In this paper, two unified viscoplastic models (Miller and Walker) were experimentally validated for Hastelloy X creep behavior. Both constitutive models are coded into ANSYS Mechanical as user programmable features (UPF). Creep behavior is simulated at a broad range of stress levels. The results are compared to an exhaustive database of experimental data to fully validate the capabilities and performance of these models. Material constants are calculated using the recently developed Material Constant Heuristic Optimizer (MACHO) software. This software uses the simulated annealing algorithm to determine the optimal material constants by using an extensive database of experimental data. A qualitative and quantitative discussion is presented to determine the most suitable model for Hastelloy X PVP components.

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Development of a Novel Hybrid Unified Viscoplastic Constitutive Model

Volume 9: Mechanics of Solids, Structures and Fluids ◽

10.1115/imece2015-50390 ◽

2015 ◽

Author(s):

Luis A. Varela J. ◽

Calvin M. Stewart

Keyword(s):

Experimental Data ◽

Stainless Steel ◽

Hybrid Model ◽

Material Constant ◽

Inelastic Behavior ◽

Hastelloy X ◽

Material Constants ◽

Stainless Steel 304 ◽

Simulation Results ◽

Optimal Material

Hastelloy X and stainless steel 304 are alloys widely used in industrial gas turbines components, petrochemical industry and energy generation applications; In the Pressure Vessel and Piping (PVP) industries they are used in nuclear and chemical reactors, pipes and valves applications. Hastelloy X and stainless steel 304 are favored for these types of applications where elevated temperatures are preferred for better systems’ efficiencies; they are favored due to its high strength and corrosion resistance at high temperature levels. A common characteristic of these alloys, is its rate-dependent mechanical behavior which difficult the prediction of the material response for design and simulation purposes. Therefore, a precise unified viscoplastic model capable to describe Hastelloy X and stainless steel 304 behaviors under a variety of loading conditions at high temperatures is needed to allow a better and less conservative design of components. Numerous classical unified viscoplastic models have been proposed in literature, to predict the inelastic behavior of metals under extreme environments. Based on Miller and Walker classical unified constitutive models a novel hybrid unified viscoplastic constitutive model is introduced in the present work, to describe the inelastic behavior caused by creep and fatigue effects at high temperature. The presented hybrid model consists of the combination of the best aspects of Miller and Walker model constitutive equations, with the addition of a damage rate equation which provides a description of the damage evolution and rupture prediction capabilities for Hastelloy X and stainless steel 304. A detailed explanation on the meaning of each material constant is provided, along with its impact on the hybrid model behavior. Material constants were calculated using the recently developed Material Constant Heuristic Optimizer (MACHO) software, to ensure the use of the optimal material constants values. This software uses the simulated annealing algorithm to determine the optimal material constants in a global surface, by comparing numerical simulations to an extensive database of experimental data. To validate the capabilities of the proposed hybrid model, numerical simulation results are compared to a broad range of experimental data at different stress levels and strain amplitudes; besides the consideration of two alloys in the present work, would demonstrate the model’s capabilities and flexibility to model multiple alloys behavior. Finally a quantitative analysis is provided to determine the percentage error and coefficient of determination between the experimental data and numerical simulation results to estimate the efficiency of the proposed hybrid model.

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