An experimental and analytical study of graded materials under thermo-mechanical dynamic loading

Addis Asmelash Kidane, University of Rhode Island

Abstract

A fundamental study is conducted to evaluate dynamic fracture and failure in functionally graded materials (FGM) at room and high temperatures. ^ Asymptotic analysis in conjunction with displacement potentials is used to develop thermo-mechanical stress fields for a mixed mode propagating crack in homogenous and FGMs. First, asymptotic temperature fields are derived for an exponential variation of thermal conductivity and later these temperature fields are used in deriving stress fields. Using asymptotic thermo-mechanical stress fields the variation of maximum shear stress, circumferential stress and strain energy density as a function of temperature around the crack-tip are generated. Finally, utilizing the minimum strain energy density criterion and the maximum circumferential stress criterion, the crack growth direction for various crack-tip speeds, non-homogeneity coefficients and temperature fields are determined.^ An experimental investigation is conducted to evaluate the thermo-mechanical constitutive behavior of a Ti/TiB layered FGM under dynamic loading. A split Hopkinson pressure bar (SHPB) apparatus with infrared spot heaters is used to investigate the effect of temperature on mechanical response of the FGM. A series of experiments are conducted at different temperatures and the stress strain relation for different temperatures is obtained.^ Quasi-static and dynamic fracture initiation toughness of Ti/TiB layered FGM is investigated using a three point bend specimen. The modified SHPB apparatus in conjunction with induction coil heating system is used during elevated temperature dynamic loading experiments. A simple and accurate technique has been developed to identify the time corresponding to the load at which the fracture initiates. A series of experiments are conducted at different temperatures ranging from room temperature to 800°C, and the effect of temperature and loading rate on the fracture initiation toughness is investigated.^ A model transparent graded material is used to investigate the steady state and transient crack propagation in a functionally graded material. High-speed digital photography combined with photoelasticity technique is used to record the full-field stress data around the propagating crack. By analyzing the photoelastic fringe patterns, the propagation crack tip velocity and displacement are obtained.^

Subject Area

Engineering, Mechanical

Recommended Citation

Addis Asmelash Kidane, "An experimental and analytical study of graded materials under thermo-mechanical dynamic loading" (2009). Dissertations and Master's Theses (Campus Access). Paper AAI3380532.
http://digitalcommons.uri.edu/dissertations/AAI3380532

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