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P. Bowen - One of the best experts on this subject based on the ideXlab platform.
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Tensile and Fracture toughness properties of SiC_p reinforced Al alloys: Effects of particle size, particle volume fraction, and matrix strength
Journal of Materials Engineering and Performance, 2004Co-Authors: M. T. Milan, P. BowenAbstract:The goal of this work was to evaluate the effects of particle size, particle volume fraction, and matrix strength on the Monotonic Fracture properties of two different Al alloys, namely T1-Al2124 and T1-Al6061, reinforced with silicon carbide particles (SiC_p). From the tensile tests, an increase in particle volume fraction and/or matrix strength increased strength and decreased ductility. On the other hand, an increase in particle size reduced strength and increased the composite ductility. In Fracture toughness tests, an increase in particle volume fraction reduced the toughness of the composites. An increase in matrix strength reduced both K _crit and δ_crit values. However, in terms of K _Q (5%) values, the Al6061 composite showed a value similar to the corresponding Al2124 composite. This was mainly attributed to premature yielding caused by the high ductility/low strength of the Al6061 matrix and the testpiece dimensions. The effect of particle size on the Fracture toughness depends on the type of matrix and toughness parameter used. In general, an increase in particle size decreased the K _Q (5%) value, but simultaneously increased the amount of plastic strain that the matrix is capable of accommodating, increasing both δ_crit and K _crit values.
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Tensile and Fracture toughness properties of SiCp reinforced Al alloys: Effects of particle size, particle volume fraction, and matrix strength
Journal of Materials Engineering and Performance, 2004Co-Authors: Marcelo Tadeu Milan, P. BowenAbstract:The goal of this work was to evaluate the effects of particle size, particle volume fraction, and matrix strength on the Monotonic Fracture properties of two different Al alloys, namely T1-Al2124 and T1-Al6061, reinforced with silicon carbide particles (SiCp). From the tensile tests, an increase in particle volume fraction and/or matrix strength increased strength and decreased ductility. On the other hand, an increase in particle size reduced strength and increased the composite ductility. In Fracture toughness tests, an increase in particle volume fraction reduced the toughness of the composites. An increase in matrix strength reduced both K crit and δcrit values. However, in terms of K Q (5%) values, the Al6061 composite showed a value similar to the corresponding Al2124 composite. This was mainly attributed to premature yielding caused by the high ductility/low strength of the Al6061 matrix and the testpiece dimensions. The effect of particle size on the Fracture toughness depends on the type of matrix and toughness parameter used. In general, an increase in particle size decreased the K Q (5%) value, but simultaneously increased the amount of plastic strain that the matrix is capable of accommodating, increasing both δcrit and K crit values.
M. T. Milan - One of the best experts on this subject based on the ideXlab platform.
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Tensile and Fracture toughness properties of SiC_p reinforced Al alloys: Effects of particle size, particle volume fraction, and matrix strength
Journal of Materials Engineering and Performance, 2004Co-Authors: M. T. Milan, P. BowenAbstract:The goal of this work was to evaluate the effects of particle size, particle volume fraction, and matrix strength on the Monotonic Fracture properties of two different Al alloys, namely T1-Al2124 and T1-Al6061, reinforced with silicon carbide particles (SiC_p). From the tensile tests, an increase in particle volume fraction and/or matrix strength increased strength and decreased ductility. On the other hand, an increase in particle size reduced strength and increased the composite ductility. In Fracture toughness tests, an increase in particle volume fraction reduced the toughness of the composites. An increase in matrix strength reduced both K _crit and δ_crit values. However, in terms of K _Q (5%) values, the Al6061 composite showed a value similar to the corresponding Al2124 composite. This was mainly attributed to premature yielding caused by the high ductility/low strength of the Al6061 matrix and the testpiece dimensions. The effect of particle size on the Fracture toughness depends on the type of matrix and toughness parameter used. In general, an increase in particle size decreased the K _Q (5%) value, but simultaneously increased the amount of plastic strain that the matrix is capable of accommodating, increasing both δ_crit and K _crit values.
M.-h. Herman Shen - One of the best experts on this subject based on the ideXlab platform.
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A Robust Optimization Technique for Calculating Scaling Coefficients in an Energy-Based Fatigue Life Prediction Method
Journal of Engineering for Gas Turbines and Power, 2013Co-Authors: Todd Letcher, John Wertz, M.-h. Herman ShenAbstract:The energy-based lifing method is based on the theory that the cumulative energy in all hysteresis loops of a specimens' lifetime is equal to the energy in a Monotonic tension test. Based on this theory, fatigue life can be calculated by dividing Monotonic tensile energy by a hysteresis energy model, which is a function of stress amplitude. Due to variations in the empirically measured hysteresis loops and Monotonic Fracture area, fatigue life prediction with the energy-based method shows some variation as well. In order to account for these variations, a robust design optimization technique is employed. The robust optimization procedure uses an interval uncertainty technique, eliminating the need to know an exact probability density function for the uncertain parameters. The robust optimization framework ensures that the difference between the predicted lifetime at a given stress amplitude and the corresponding experimental fatigue data point is minimized and within a specified tolerance range while accounting for variations in hysteresis loop energy and Fracture diameter measurements. Accounting for these experimental variations will boost confidence in the energy-based fatigue life prediction method despite a limited number of test specimens.
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Damage Parameter Assessment for Energy Based Fatigue Life Prediction Methods
Volume 7: Structures and Dynamics Parts A and B, 2012Co-Authors: Casey Holycross, Onome Scott-emuakpor, M.-h. Herman Shen, John Wertz, Todd Letcher, Tommy GeorgeAbstract:An energy-based method used to predict fatigue life and critical life of various materials has been previously developed, correlating strain energy dissipated during Monotonic Fracture to total cyclic strain energy dissipation in fatigue Fracture. This method is based on the assumption that the Monotonic strain energy and total hysteretic strain energy to Fracture is equivalent. The Fracture processes of Monotonic and cyclic failure modes can be of stark contrast, with ductile and brittle Fracture dominating each respectively. This study proposes that a more appropriate damage parameter for predicting fatigue life may be to use low cycle fatigue (LCF) strain energy rather than Monotonic energy. Thus, the new damage parameter would capture similar Fracture processes and cyclic behavior. Round tensile specimens machined from commercially supplied Al 6061-T6511 were tested to acquire LCF failure data in fully reversed loading at various alternating stresses. Results are compared to both Monotonic and cyclic strain energy dissipation to determine if LCF strain energy dissipation is a more suitable damage parameter for fatigue life prediction.© 2012 ASME
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A Robust Optimization Technique for Calculating Scaling Coefficients in an Energy-Based Fatigue Life Prediction Method
Volume 7: Structures and Dynamics Parts A and B, 2012Co-Authors: Todd Letcher, John Wertz, M.-h. Herman ShenAbstract:The energy-based lifing method is based on the theory that the cumulative energy in all hysteresis loops of a specimens’ lifetime is equal to the energy in a Monotonic tension test. Based on this theory, fatigue life can be calculated by dividing Monotonic tensile energy by a hysteresis energy model, which is a function of stress amplitude. Due to variations in the empirically measured hysteresis loops and Monotonic Fracture area, fatigue life prediction with the energy-based method shows some variation as well. In order to account for these variations, a robust design optimization technique is employed. The robust optimization procedure uses an interval uncertainty technique, eliminating the need to know an exact probability density function for the uncertain parameters. The robust optimization framework ensures that the difference between the predicted lifetime at a given stress amplitude and the corresponding experimental fatigue data point is minimized and within a specified tolerance range while accounting for variations in hysteresis loop energy and Fracture diameter measurements. Accounting for these experimental variations will boost confidence in the energy-based fatigue life prediction method despite a limited number of test specimens.Copyright © 2012 by ASME
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A new distortion energy-based equivalent stress for multiaxial fatigue life prediction
International Journal of Non-Linear Mechanics, 2012Co-Authors: Onome Scott-emuakpor, Tommy George, Charles Cross, John Wertz, M.-h. Herman ShenAbstract:Abstract A new equivalent stress amplitude expression has been developed for the assessment of fatigue life in components under multiaxial loading. The expression was generated by incorporating non-linear/plastic stress–strain relation into a mechanical energy calculation, and then applying the calculation to the distortion energy theory for a cyclic loading case. Therefore, the new uniaxial equivalent stress expression determines an appropriate stress amplitude value for multiaxial cyclic loading. The purpose of the equivalent stress value is to determine multiaxial fatigue failure using an energy-based fatigue life prediction criterion. The governing understanding behind the criterion states that the physical damage quantity for failure is equal to the accumulated strain energy in a Monotonic Fracture, which is also equal to the accumulated strain energy during fatigue failure. Using the new equivalent stress amplitude expression and the energy-based life prediction method, a comparison is made between prediction results and multiaxial empirical data. The multiaxial data was acquired by a vibration-based biaxial bending fatigue test and a torsion fatigue test with an assumed axial misalignment. The results of the comparison provide encouragement regarding the capability of the newly developed equivalent stress amplitude expression for fatigue life prediction.
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An Energy-Based Axial Isothermal- Mechanical Fatigue Lifing Procedure
Journal of Engineering for Gas Turbines and Power, 2011Co-Authors: John Wertz, Onome Scott-emuakpor, M.-h. Herman Shen, Tommy George, Charles CrossAbstract:An energy-based fatigue lifing procedure for the determination of full-life and critical-life of in-service structures subjected to axial isothermal-mechanical fatigue (IMF) has been developed. The foundation of this procedure is the energy-based axial room-temperature fatigue model, which states: the total strain energy density accumulated during both a Monotonic Fracture event and a fatigue process is the same material property. The energy-based axial IMF lifing framework is composed of the following entities: (1) the development of an axial IMF testing capability; (2) the creation of a testing procedure capable of assessing the strain energy accrued during both a Monotonic Fracture process and a fatigue process at various elevated temperatures; and (3), the incorporation of the effect of temperature into the axial fatigue lifing model. Both an axial IMF capability and a detailed testing procedure were created. The axial IMF capability was employed in conjunction with the Monotonic Fracture curve testing procedure to produce fifteen Fracture curves at four operating temperatures. The strain energy densities for these Fracture curves were compared, leading to the assumption of constant Monotonic Fracture energy at operating temperatures below the creep activation temperature.
Robert L Taylor - One of the best experts on this subject based on the ideXlab platform.
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microstructural studies of friction stir welds in 2024 t3 aluminum
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: Michael A Sutton, Bangcheng Yang, Anthony P Reynolds, Robert L TaylorAbstract:Friction stir welds in 7 mm thick, 2024-T351 aluminum rolled sheet material have been completed. Metallurgical, hardness and quantitative energy dispersive X-ray measurements have been performed which demonstrate that a segregated, banded, microstructure consisting of alternating hard particle rich and hard particle poor regions is developed. Mixed-mode I/II Monotonic Fracture experiments confirm that the observed banded microstructure affects the macroscopic Fracture process. Since the band spacing is directly correlated with the welding tool advance per revolution, our results indicated that the opportunity exists to manipulate the friction stir weld process parameters in order to modify the weld microstructure and improve a range of material properties, including Fracture resistance.
Onome Scott-emuakpor - One of the best experts on this subject based on the ideXlab platform.
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Damage Parameter Assessment for Energy Based Fatigue Life Prediction Methods
Volume 7: Structures and Dynamics Parts A and B, 2012Co-Authors: Casey Holycross, Onome Scott-emuakpor, M.-h. Herman Shen, John Wertz, Todd Letcher, Tommy GeorgeAbstract:An energy-based method used to predict fatigue life and critical life of various materials has been previously developed, correlating strain energy dissipated during Monotonic Fracture to total cyclic strain energy dissipation in fatigue Fracture. This method is based on the assumption that the Monotonic strain energy and total hysteretic strain energy to Fracture is equivalent. The Fracture processes of Monotonic and cyclic failure modes can be of stark contrast, with ductile and brittle Fracture dominating each respectively. This study proposes that a more appropriate damage parameter for predicting fatigue life may be to use low cycle fatigue (LCF) strain energy rather than Monotonic energy. Thus, the new damage parameter would capture similar Fracture processes and cyclic behavior. Round tensile specimens machined from commercially supplied Al 6061-T6511 were tested to acquire LCF failure data in fully reversed loading at various alternating stresses. Results are compared to both Monotonic and cyclic strain energy dissipation to determine if LCF strain energy dissipation is a more suitable damage parameter for fatigue life prediction.© 2012 ASME
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The Effect of Compressive Damage on Tensile Loading Failure of Titanium 6Al-4V
Volume 7: Structures and Dynamics Parts A and B, 2012Co-Authors: Onome Scott-emuakpor, Tommy George, John Wertz, Casey HolycrossAbstract:In order to explore the belief that total strain energy accumulation during Monotonic tensile Fracture is a universal damage parameter, the effect of compressive preloads on specimens failed via tensile loading is analyzed. The motivation behind this analysis is due to the theory of an energy-based life prediction model, which states that the total strain energy required for Monotonic tensile Fracture is defined as the physical damage quantity for the fatigue lifing model. Two things are observed in order to determine the effects of a compressive preload on tensile Monotonic Fracture. First, the compressive work is viewed as accumulated damage, thus adding to the total work necessary for failure. Second, tensile works of Fractured specimens with and without stored compressive energy are compared to see if the damage parameter is affected. The analysis is conducted through experimental data acquisition from round stock Titanium 6Al-4V dogbone specimens. The results from this study show that compressive damage has a negligible effect on Monotonic tensile work to Fracture, and combined half-cycle tension and compression preloads have an unnoticeable effect on the tensile work of the final pull to Fracture. These results contradict the theory and research validations of the energy-based predictions; however, they provide a platform for future efforts to understand the strain energy correlation between Monotonic, low cycle and high cycle failures.© 2012 ASME
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An energy‐based critical fatigue life prediction method for AL6061‐T6
Fatigue & Fracture of Engineering Materials & Structures, 2012Co-Authors: Todd Letcher, Onome Scott-emuakpor, Tommy George, M.-h. H. Shen, Charles CrossAbstract:An energy-based critical fatigue life prediction method is developed and analysed. The original energy-based fatigue life prediction theory states that the number of cycles to failure is estimated by dividing the total energy accumulated during a Monotonic Fracture by the strain energy per cycle. Because the accuracy of this concept is heavily dependent on the cyclic behaviour of the material, a precise understanding of the strain energy behaviour throughout each failure process is necessary. Examination of the stress and strain during fatigue tests shows that the cyclic strain energy behaviour is not perfectly stable as initially presumed. It was discovered that fatigue hysteresis energy always accumulates to the same amount of energy by the end of the stable energy region, which has led to a new ‘critical energy’ material property. Characterization of strain energy throughout the fatigue process has thus improved the understanding of an energy-based fatigue life prediction method.
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A new distortion energy-based equivalent stress for multiaxial fatigue life prediction
International Journal of Non-Linear Mechanics, 2012Co-Authors: Onome Scott-emuakpor, Tommy George, Charles Cross, John Wertz, M.-h. Herman ShenAbstract:Abstract A new equivalent stress amplitude expression has been developed for the assessment of fatigue life in components under multiaxial loading. The expression was generated by incorporating non-linear/plastic stress–strain relation into a mechanical energy calculation, and then applying the calculation to the distortion energy theory for a cyclic loading case. Therefore, the new uniaxial equivalent stress expression determines an appropriate stress amplitude value for multiaxial cyclic loading. The purpose of the equivalent stress value is to determine multiaxial fatigue failure using an energy-based fatigue life prediction criterion. The governing understanding behind the criterion states that the physical damage quantity for failure is equal to the accumulated strain energy in a Monotonic Fracture, which is also equal to the accumulated strain energy during fatigue failure. Using the new equivalent stress amplitude expression and the energy-based life prediction method, a comparison is made between prediction results and multiaxial empirical data. The multiaxial data was acquired by a vibration-based biaxial bending fatigue test and a torsion fatigue test with an assumed axial misalignment. The results of the comparison provide encouragement regarding the capability of the newly developed equivalent stress amplitude expression for fatigue life prediction.
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An Energy-Based Axial Isothermal- Mechanical Fatigue Lifing Procedure
Journal of Engineering for Gas Turbines and Power, 2011Co-Authors: John Wertz, Onome Scott-emuakpor, M.-h. Herman Shen, Tommy George, Charles CrossAbstract:An energy-based fatigue lifing procedure for the determination of full-life and critical-life of in-service structures subjected to axial isothermal-mechanical fatigue (IMF) has been developed. The foundation of this procedure is the energy-based axial room-temperature fatigue model, which states: the total strain energy density accumulated during both a Monotonic Fracture event and a fatigue process is the same material property. The energy-based axial IMF lifing framework is composed of the following entities: (1) the development of an axial IMF testing capability; (2) the creation of a testing procedure capable of assessing the strain energy accrued during both a Monotonic Fracture process and a fatigue process at various elevated temperatures; and (3), the incorporation of the effect of temperature into the axial fatigue lifing model. Both an axial IMF capability and a detailed testing procedure were created. The axial IMF capability was employed in conjunction with the Monotonic Fracture curve testing procedure to produce fifteen Fracture curves at four operating temperatures. The strain energy densities for these Fracture curves were compared, leading to the assumption of constant Monotonic Fracture energy at operating temperatures below the creep activation temperature.