Cliff Butcher | University of Waterloo (original) (raw)

Papers by Cliff Butcher

International Journal of Energy Research, 2009

The influence of operating conditions such as reheat, intercooling, ambient temperature and press... more The influence of operating conditions such as reheat, intercooling, ambient temperature and pressure ratio are analyzed from a second law perspective on the performance of a natural gas-fired gas turbine cogeneration system. The effect of these operating parameters on carbon dioxide emissions is also discussed. The second law efficiency of gas turbine cogeneration system increases markedly with reheat option. Higher pressure ratios lead to decreased second law cogeneration efficiency but this effect can be reduced with a higher level of reheat option. The effect of intercooling on second law efficiency is strongly related to pressure ratio with higher pressure ratios significantly decreasing efficiency. The second law efficiency is not so sensitive to the environment temperature for levels of reheat or intercooling greater than 50%. Copyright © 2009 John Wiley & Sons, Ltd.

International Journal of Fracture, 2011

Two constitutive models for porous ductile materials are employed together to predict the yield b... more Two constitutive models for porous ductile materials are employed together to predict the yield behaviour of ductile materials containing void clusters. In this dual bound approach, the upper and lower bound constitutive models of Gurson (1977) and Sun and Wang (1989) are each evaluated in order to obtain upper and lower estimates for the material behaviour. By combining these two solutions, a predictive band can be created to capture the experimental variation in the yielding behaviour. Although these constitutive models have been derived with the assumption of a periodic void distribution, real materials contain void clusters that can significantly alter the onset of yielding and fracture. Therefore it is of great interest to determine if using dual constitutive models can produce an acceptable first-order approximation of the yielding behaviour in these materials. In the present work, the upper and lower bound yield loci are superimposed over numerical data available in the literature for the yielding of materials containing void clusters. It is shown that the dual bound approach is able to capture the material behaviour over a wide range of practically encountered stress triaxialities.

International Journal of Fracture, 2009

Numerical simulations of straight tube hydroforming of a dual phase (DP600) advanced high strengt... more Numerical simulations of straight tube hydroforming of a dual phase (DP600) advanced high strength steel were performed using a variant of the Gurson–Tvergaard–Needleman (GTN) constitutive model to account for the influence of void shape and shear on coalescence. The effect of axial-feed (end-feed) on damage development and formability is investigated for end-feed loads of zero and 133 kN. A parametric study was conducted to determine an appropriate void nucleation stress and strain and the numerical values compared with the experimental data. The calibrated GTN damage model gives good agreement with the experimentally determined burst pressure, formability and failure location with the best performance occurring for the high end-feed load.

International Journal of Fracture, 2006

Numerical simulation of stretch flange forming of Al–Mg sheet AA5182 was performed using the uppe... more Numerical simulation of stretch flange forming of Al–Mg sheet AA5182 was performed using the upper and lower bound constitutive models of Gurson–Tvergaard–Needleman (GTN) and Sun and Wang, respectively. Stress and strain-controlled nucleation rules are adopted for both models. The lower bound model of Sun and Wang has been extended to include the void coalescence criterion of Tvergaard and Needleman to form the so-called Sun–Tvergaard–Needleman (STN) model. Upper and lower bound formability predictions are combined to create a predictive formability band as actual formability lies between these limits. The resulting formability predictions are compared with experimental results and an appropriate void nucleation stress and strain suggested.

Theoretical and Applied Fracture Mechanics, 2011

An experimental and numerical test programme was conducted to investigate damage-induced ductile ... more An experimental and numerical test programme was conducted to investigate damage-induced ductile fracture in notched tensile sheet specimens of an aluminum-magnesium alloy. An upper bound, damage-based constitutive model was employed to estimate the formability of the material over a range of stress states found in sheet metal forming. Stress-and strain-based nucleation models are evaluated to characterize damage initiation and fracture of the material. The ligament strain-to-failure, elongationto-failure and load-displacement curves can be captured using either nucleation rule. The advantages of each nucleation model are discussed in relation to quantitative measurements of damage available in the literature. Stress-based nucleation provides a promising approach for characterizing the nucleation behaviour over a range of stress states compared to strain-based nucleation.

International Journal of Energy Research, 2009

The influence of operating conditions such as reheat, intercooling, ambient temperature and press... more The influence of operating conditions such as reheat, intercooling, ambient temperature and pressure ratio are analyzed from a second law perspective on the performance of a natural gas-fired gas turbine cogeneration system. The effect of these operating parameters on carbon dioxide emissions is also discussed. The second law efficiency of gas turbine cogeneration system increases markedly with reheat option. Higher pressure ratios lead to decreased second law cogeneration efficiency but this effect can be reduced with a higher level of reheat option. The effect of intercooling on second law efficiency is strongly related to pressure ratio with higher pressure ratios significantly decreasing efficiency. The second law efficiency is not so sensitive to the environment temperature for levels of reheat or intercooling greater than 50%. Copyright © 2009 John Wiley & Sons, Ltd.

International Journal of Fracture, 2011

Two constitutive models for porous ductile materials are employed together to predict the yield b... more Two constitutive models for porous ductile materials are employed together to predict the yield behaviour of ductile materials containing void clusters. In this dual bound approach, the upper and lower bound constitutive models of Gurson (1977) and Sun and Wang (1989) are each evaluated in order to obtain upper and lower estimates for the material behaviour. By combining these two solutions, a predictive band can be created to capture the experimental variation in the yielding behaviour. Although these constitutive models have been derived with the assumption of a periodic void distribution, real materials contain void clusters that can significantly alter the onset of yielding and fracture. Therefore it is of great interest to determine if using dual constitutive models can produce an acceptable first-order approximation of the yielding behaviour in these materials. In the present work, the upper and lower bound yield loci are superimposed over numerical data available in the literature for the yielding of materials containing void clusters. It is shown that the dual bound approach is able to capture the material behaviour over a wide range of practically encountered stress triaxialities.

International Journal of Fracture, 2009

Numerical simulations of straight tube hydroforming of a dual phase (DP600) advanced high strengt... more Numerical simulations of straight tube hydroforming of a dual phase (DP600) advanced high strength steel were performed using a variant of the Gurson–Tvergaard–Needleman (GTN) constitutive model to account for the influence of void shape and shear on coalescence. The effect of axial-feed (end-feed) on damage development and formability is investigated for end-feed loads of zero and 133 kN. A parametric study was conducted to determine an appropriate void nucleation stress and strain and the numerical values compared with the experimental data. The calibrated GTN damage model gives good agreement with the experimentally determined burst pressure, formability and failure location with the best performance occurring for the high end-feed load.

International Journal of Fracture, 2006

Numerical simulation of stretch flange forming of Al–Mg sheet AA5182 was performed using the uppe... more Numerical simulation of stretch flange forming of Al–Mg sheet AA5182 was performed using the upper and lower bound constitutive models of Gurson–Tvergaard–Needleman (GTN) and Sun and Wang, respectively. Stress and strain-controlled nucleation rules are adopted for both models. The lower bound model of Sun and Wang has been extended to include the void coalescence criterion of Tvergaard and Needleman to form the so-called Sun–Tvergaard–Needleman (STN) model. Upper and lower bound formability predictions are combined to create a predictive formability band as actual formability lies between these limits. The resulting formability predictions are compared with experimental results and an appropriate void nucleation stress and strain suggested.

Theoretical and Applied Fracture Mechanics, 2011

An experimental and numerical test programme was conducted to investigate damage-induced ductile ... more An experimental and numerical test programme was conducted to investigate damage-induced ductile fracture in notched tensile sheet specimens of an aluminum-magnesium alloy. An upper bound, damage-based constitutive model was employed to estimate the formability of the material over a range of stress states found in sheet metal forming. Stress-and strain-based nucleation models are evaluated to characterize damage initiation and fracture of the material. The ligament strain-to-failure, elongationto-failure and load-displacement curves can be captured using either nucleation rule. The advantages of each nucleation model are discussed in relation to quantitative measurements of damage available in the literature. Stress-based nucleation provides a promising approach for characterizing the nucleation behaviour over a range of stress states compared to strain-based nucleation.