From October 2003 to April 2008 a systemic reform of the Mechanical Engineering program at The Ci... more From October 2003 to April 2008 a systemic reform of the Mechanical Engineering program at The City College of New York was undertaken with the goal of incorporating emerging technologies (such as nanotechnology, biotechnology, Micro-Electro-Mechanical Systems (MEMS), intelligent systems) and new teaching methodologies (such as project based learning, hands-on laboratory experiences, inquiry based learning, home experiments) into the curriculum. This reform activity was supported by NSF and affected all the courses taught by the Department. Almost all faculty participated in the effort. In this paper, we describe the modifications introduced in four courses of the curriculum, namely, Mechatronics, Mechanics of Materials, Heat Transfer and System Modeling, Analysis and Control. The modifications consisted both of topics related to emerging technologies and new teaching methodologies. Results of assessment conducted to ascertain the effect of the changes are presented. For example student opinions about course outcomes before and after the modifications were surveyed for the four courses discussed above. Based on the limited assessment data available thus far, it appears that students' confidence and overall academic performance has improved in some courses following the reform. It is the authors' opinion that these will see further improvement in coming years as the specifics of the reform elements are refined.
Liaw received his Ph.D. degree from the University of Washington in 1983. After a year of post-do... more Liaw received his Ph.D. degree from the University of Washington in 1983. After a year of post-doctoral research study at University of Washington, he joined the faculty of CCNY in 1984, where he is a Full Professor at Department of Mechanical Engineering. During 2000-2002 he was also appointed Acting Associate Dean for Undergraduate Studies, School of Engineering. His interests include (1) the design, analysis, manufacturing and testing of composites and smart materials, and (2) improving engineering education through innovative teaching and research techniques, with emphasis on attracting underrepresented minorities and women. Through years he has published more than 70 refereed papers with funding support from NSF, NASA, ARPA, AFOSR, ARO, U.S. Army TACOM-TARDEC and ARDEC-Picatinny Arsenal, AT&T, Digital Equipment Corporation, Alliant Techsystems, Frontier Performance Polymers, NYS GRI and PSC CUNY. In addition to being active in research, he had also served as the ECSEL Project Director at CCNY in 1993-2001. The main charge of the NSF-funded ECSEL Coalition is to improve undergraduate engineering education through design for manufacturing across the curriculum.
Liaw received his Ph.D. degree from the University of Washington in 1983. After a year of post-do... more Liaw received his Ph.D. degree from the University of Washington in 1983. After a year of post-doctoral research study at University of Washington, he joined the faculty of the City College of the City University of New York (CCNY) in 1984, where he is a Full Professor at Department of Mechanical Engineering. During 2000-2002 he was also appointed Acting Associate Dean for Undergraduate Studies, School of Engineering. His interests include (1) the design, analysis, manufacturing and testing of composites and smart materials, and (2) improving engineering education through innovative teaching and research techniques, with emphasis on attracting under-represented minorities and women. Through years he has published more than 70 refereed papers with funding support from NSF, NASA, ARPA, AFOSR, ARO, U.S. Army TACOM-TARDEC and ARDEC-Picatinny Arsenal, AT&T, Digital Equipment Corporation, Alliant Techsystems, Frontier Performance Polymers, NYS GRI and PSC CUNY. In addition to being active in research, he had also served as the ECSEL Project Director at CCNY in 1993-2001. The main charge of the NSF-funded ECSEL Coalition is to improve undergraduate engineering education through design across the curriculum.
I RF 447239 6a. NAME OF PERFORMING ORGANIZATION |6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZ... more I RF 447239 6a. NAME OF PERFORMING ORGANIZATION |6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION
In this study, pure Fe and Fe matrix composites (5 wt. % nano-Al2O3, 5 wt. % micron-B4C and 2.5 w... more In this study, pure Fe and Fe matrix composites (5 wt. % nano-Al2O3, 5 wt. % micron-B4C and 2.5 wt. % nano-Al2O3-2.5 wt. % micron-B4C) were manufactured via powder metallurgy. The density and phase analysis of the produced samples were performed. The electrochemical corrosion behaviour of the samples in a 3.5 wt. % NaCl solution was studied using potentiodynamic polarization at 25, 50 and 75 ºC. The corrosion rate of the samples significantly increased with increasing test temperature. Also, the effect of reinforcement particulates leads to deteriorate corrosion resistance of pure Fe due to the presence of galvanic reactions.
Volume 10: Mechanics of Solids and Structures, Parts A and B, 2007
A combined experimental and 3-D dynamic nonlinear finite element approach was adopted to study co... more A combined experimental and 3-D dynamic nonlinear finite element approach was adopted to study composite beams subject to drop-weight or ballistic impact. The composite specimens, made of S2 glass-reinforced toughened epoxy (44% fiber volume fraction, cured at 350°F), had 24 layers (approximately 6.35 mm) with various stacking sequences. They were damaged by impacts using either an Instron-Dynatup 8520 instrumented drop-weight impact tester (lowvelocity impact) or an in-house high-speed gas gun (ballistic impact). For both types of tests, the time-histories of dynamic strains induced during impact were recorded using strain gages mounted on the front and back of the composite beam specimen. For drop-weight impact tests, the time history of impact force was also recorded; whereas for ballistic impact tests, only the impact velocity was calculated from the recorded change in voltage outputs, which resulted from the traversing of the impactor through two optical paths formed by two sets of diode laser-amplified photo diode pairs. The commercially available 3-D dynamic nonlinear finite element software, LS-DYNA, incorporated with a proposed nonlinear anisotropic damage model, was then used to simulate the experimental results. Good agreement between experimental and FEM results can be seen from comparisons of dynamic strain and impact force histories and damage patterns. Once the proposed nonlinear anisotropic damage model was verified by experimental results, further finite element simulations were conducted to predict the ballistic limit velocity (V 50) for penetration prevention.
Volume 12: Processing and Engineering Applications of Novel Materials, 2010
A new class of thermal microactuators, Z-shaped thermal actuator, is introduced in comparison wit... more A new class of thermal microactuators, Z-shaped thermal actuator, is introduced in comparison with the well-established V-shaped thermal actuator. Though they share many features in common, Z-shaped thermal actuator offers several advantages: compatibility with anisotropic etching, smaller feature size, larger displacement, and larger variety of stiffness and output force. While the Z-shaped thermal actuator was modeled analytically and verified by multiphysics finite element analysis (FEA), the beam width and length of the central beam were identified as the major design parameters in tuning the device displacement, stiffness, stability and output force. Experimental measurements were taken on three arrays of Z-shaped thermal actuator with variable parameters. Results agreed well with the finite element analysis. The development of Z-shaped thermal actuator is applicable in simultaneous sensing and actuating applications. During the quasi-static test of individual Z-shaped thermal ...
Volume 9: Mechanics of Solids, Structures and Fluids, 2010
This paper investigated the effect of temperature on hybrid and non-hybrid woven composite panels... more This paper investigated the effect of temperature on hybrid and non-hybrid woven composite panels (100mm×100mm×6.35mm) drop-weight impacted at five different temperatures:60C,20C, room temperature, 75C and 125C. The studies were conducted by combining experimental and 3-D dynamic finite element approaches. The specimens tested were made of plain-weave hybrid S2 glass-IM7graphite fibers/toughened epoxy. The composite panels were damaged using an instrumented drop-weight impact tester equipped with an environmental chamber for temperature control. The time-histories of impact-induced dynamic strains and impact forces were recorded. The damaged specimens were inspected visually and using the ultrasonic C-scan method. A 3-D dynamic finite element (FE) software package, with Chang-Chang composite damage model, was then used to simulate the experimental results of the drop-weight tests. Good agreement between experimental and FE results has been achieved. It is observed that the variation of results obtained from our experiments for the hybrid composites was very small (about 8%) when compared to those of non-hybrid composites. Also, when looking at the hybrid or non-hybrid composite, the effect of temperature at 60C, 20C was not significant whereas at 75C and 125C the results were more distinct.
The self-sensing damage detection method based on the electrical resistance measurement of carbon... more The self-sensing damage detection method based on the electrical resistance measurement of carbon fiber polymer-matrix composites has been investigated for a decade. In order to eliminate the effect of contact resistance when using the two-probe method, the four-probe methods, which include the resistance, potential and voltage change methods, were proposed in literature. However, the basic problems involved in the four-probe methods remain unclear, i.e., the validity range and the applicability of the four-probe methods. In this paper, beam-type specimens with and without delamination damage are used to carry out numerical analyses for the above-mentioned problems. It is found that the four-probe resistance method is valid only when the through-thickness conductivity is comparable to or larger than the longitudinal conductivity. For the potential method, which measures directly the voltage values between the voltage contacts, the present results show that the percentage change in damage-induced voltage between a pair of voltage contacts is not consistent with the percentage change in resistance. The underlying reason is that the damage-induced voltage change depends on the location of the applied current, while the resistance change does not.
Monotonic tensile tests are conducted on seven different Glare grades of fiber metal laminates. I... more Monotonic tensile tests are conducted on seven different Glare grades of fiber metal laminates. In-situ stress–strain curves of glass/epoxy laminate interleaved in Glare 2(3/2) are exposed with the application of metal volume fraction method using the stress–strain curves of Glare 2(3/2) and Aluminum 2024-T3 in unidirectional and transverse directions. The strain–stress curves of cross-ply Glares are predicted by the modification of this method with an empirical parameter and a second parameter considering the relative glass/epoxy laminate thickness ratios of Glare grades. Modified metal volume fraction method presented in this study can be used as a preliminary estimation of stress–strain curves of multiple possible fiber metal laminate configurations without testing.
This article was published in the above mentioned Springer issue. The material, including all por... more This article was published in the above mentioned Springer issue. The material, including all portions thereof, is protected by copyright; all rights are held exclusively by Springer Science + Business Media. The material is for personal use only; commercial use is not permitted. Unauthorized reproduction, transfer and/or use may be a violation of criminal as well as civil law. Abstract Impact responses and damage of various fiber-metal laminates were studied using a drop-weight instrument with the post-impact damage characteristics being evaluated through ultrasonic and mechanical sectioning techniques. The first severe failure induced by the low-velocity drop-weight impact occurred as delamination between the aluminum and fiber-epoxy layers at the non-impact side. It was followed by a visible shear crack in the outer aluminum layer on the non-impact face. Through-thickness shear cracks in the aluminum sheets and severe damage in the fiber laminated layers (including delamination between adjacent fiber-epoxy laminae with different fiber orientations) developed under higher energy impacts. The impact properties of fiber-metal laminates varied with different constituent materials and fiber orientations. Since it was punched through easily, the aramid-fiber reinforced fiber-metal laminates (ARALL) offered poorer impact resistance than the glass-fiber reinforced fiber-metal laminates (GLARE). Tougher and more ductile aluminum alloys improved the impact resistance. GLARE made of cross-ply prepregs provided better impact resistance than GLARE with unidirectional plies. Keywords Drop-weight (low-velocity) impact. Fiber-metal laminates (GLARE and ARALL). Ultrasound
From October 2003 to April 2008 a systemic reform of the Mechanical Engineering program at The Ci... more From October 2003 to April 2008 a systemic reform of the Mechanical Engineering program at The City College of New York was undertaken with the goal of incorporating emerging technologies (such as nanotechnology, biotechnology, Micro-Electro-Mechanical Systems (MEMS), intelligent systems) and new teaching methodologies (such as project based learning, hands-on laboratory experiences, inquiry based learning, home experiments) into the curriculum. This reform activity was supported by NSF and affected all the courses taught by the Department. Almost all faculty participated in the effort. In this paper, we describe the modifications introduced in four courses of the curriculum, namely, Mechatronics, Mechanics of Materials, Heat Transfer and System Modeling, Analysis and Control. The modifications consisted both of topics related to emerging technologies and new teaching methodologies. Results of assessment conducted to ascertain the effect of the changes are presented. For example student opinions about course outcomes before and after the modifications were surveyed for the four courses discussed above. Based on the limited assessment data available thus far, it appears that students' confidence and overall academic performance has improved in some courses following the reform. It is the authors' opinion that these will see further improvement in coming years as the specifics of the reform elements are refined.
Liaw received his Ph.D. degree from the University of Washington in 1983. After a year of post-do... more Liaw received his Ph.D. degree from the University of Washington in 1983. After a year of post-doctoral research study at University of Washington, he joined the faculty of CCNY in 1984, where he is a Full Professor at Department of Mechanical Engineering. During 2000-2002 he was also appointed Acting Associate Dean for Undergraduate Studies, School of Engineering. His interests include (1) the design, analysis, manufacturing and testing of composites and smart materials, and (2) improving engineering education through innovative teaching and research techniques, with emphasis on attracting underrepresented minorities and women. Through years he has published more than 70 refereed papers with funding support from NSF, NASA, ARPA, AFOSR, ARO, U.S. Army TACOM-TARDEC and ARDEC-Picatinny Arsenal, AT&T, Digital Equipment Corporation, Alliant Techsystems, Frontier Performance Polymers, NYS GRI and PSC CUNY. In addition to being active in research, he had also served as the ECSEL Project Director at CCNY in 1993-2001. The main charge of the NSF-funded ECSEL Coalition is to improve undergraduate engineering education through design for manufacturing across the curriculum.
Liaw received his Ph.D. degree from the University of Washington in 1983. After a year of post-do... more Liaw received his Ph.D. degree from the University of Washington in 1983. After a year of post-doctoral research study at University of Washington, he joined the faculty of the City College of the City University of New York (CCNY) in 1984, where he is a Full Professor at Department of Mechanical Engineering. During 2000-2002 he was also appointed Acting Associate Dean for Undergraduate Studies, School of Engineering. His interests include (1) the design, analysis, manufacturing and testing of composites and smart materials, and (2) improving engineering education through innovative teaching and research techniques, with emphasis on attracting under-represented minorities and women. Through years he has published more than 70 refereed papers with funding support from NSF, NASA, ARPA, AFOSR, ARO, U.S. Army TACOM-TARDEC and ARDEC-Picatinny Arsenal, AT&T, Digital Equipment Corporation, Alliant Techsystems, Frontier Performance Polymers, NYS GRI and PSC CUNY. In addition to being active in research, he had also served as the ECSEL Project Director at CCNY in 1993-2001. The main charge of the NSF-funded ECSEL Coalition is to improve undergraduate engineering education through design across the curriculum.
I RF 447239 6a. NAME OF PERFORMING ORGANIZATION |6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZ... more I RF 447239 6a. NAME OF PERFORMING ORGANIZATION |6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION
In this study, pure Fe and Fe matrix composites (5 wt. % nano-Al2O3, 5 wt. % micron-B4C and 2.5 w... more In this study, pure Fe and Fe matrix composites (5 wt. % nano-Al2O3, 5 wt. % micron-B4C and 2.5 wt. % nano-Al2O3-2.5 wt. % micron-B4C) were manufactured via powder metallurgy. The density and phase analysis of the produced samples were performed. The electrochemical corrosion behaviour of the samples in a 3.5 wt. % NaCl solution was studied using potentiodynamic polarization at 25, 50 and 75 ºC. The corrosion rate of the samples significantly increased with increasing test temperature. Also, the effect of reinforcement particulates leads to deteriorate corrosion resistance of pure Fe due to the presence of galvanic reactions.
Volume 10: Mechanics of Solids and Structures, Parts A and B, 2007
A combined experimental and 3-D dynamic nonlinear finite element approach was adopted to study co... more A combined experimental and 3-D dynamic nonlinear finite element approach was adopted to study composite beams subject to drop-weight or ballistic impact. The composite specimens, made of S2 glass-reinforced toughened epoxy (44% fiber volume fraction, cured at 350°F), had 24 layers (approximately 6.35 mm) with various stacking sequences. They were damaged by impacts using either an Instron-Dynatup 8520 instrumented drop-weight impact tester (lowvelocity impact) or an in-house high-speed gas gun (ballistic impact). For both types of tests, the time-histories of dynamic strains induced during impact were recorded using strain gages mounted on the front and back of the composite beam specimen. For drop-weight impact tests, the time history of impact force was also recorded; whereas for ballistic impact tests, only the impact velocity was calculated from the recorded change in voltage outputs, which resulted from the traversing of the impactor through two optical paths formed by two sets of diode laser-amplified photo diode pairs. The commercially available 3-D dynamic nonlinear finite element software, LS-DYNA, incorporated with a proposed nonlinear anisotropic damage model, was then used to simulate the experimental results. Good agreement between experimental and FEM results can be seen from comparisons of dynamic strain and impact force histories and damage patterns. Once the proposed nonlinear anisotropic damage model was verified by experimental results, further finite element simulations were conducted to predict the ballistic limit velocity (V 50) for penetration prevention.
Volume 12: Processing and Engineering Applications of Novel Materials, 2010
A new class of thermal microactuators, Z-shaped thermal actuator, is introduced in comparison wit... more A new class of thermal microactuators, Z-shaped thermal actuator, is introduced in comparison with the well-established V-shaped thermal actuator. Though they share many features in common, Z-shaped thermal actuator offers several advantages: compatibility with anisotropic etching, smaller feature size, larger displacement, and larger variety of stiffness and output force. While the Z-shaped thermal actuator was modeled analytically and verified by multiphysics finite element analysis (FEA), the beam width and length of the central beam were identified as the major design parameters in tuning the device displacement, stiffness, stability and output force. Experimental measurements were taken on three arrays of Z-shaped thermal actuator with variable parameters. Results agreed well with the finite element analysis. The development of Z-shaped thermal actuator is applicable in simultaneous sensing and actuating applications. During the quasi-static test of individual Z-shaped thermal ...
Volume 9: Mechanics of Solids, Structures and Fluids, 2010
This paper investigated the effect of temperature on hybrid and non-hybrid woven composite panels... more This paper investigated the effect of temperature on hybrid and non-hybrid woven composite panels (100mm×100mm×6.35mm) drop-weight impacted at five different temperatures:60C,20C, room temperature, 75C and 125C. The studies were conducted by combining experimental and 3-D dynamic finite element approaches. The specimens tested were made of plain-weave hybrid S2 glass-IM7graphite fibers/toughened epoxy. The composite panels were damaged using an instrumented drop-weight impact tester equipped with an environmental chamber for temperature control. The time-histories of impact-induced dynamic strains and impact forces were recorded. The damaged specimens were inspected visually and using the ultrasonic C-scan method. A 3-D dynamic finite element (FE) software package, with Chang-Chang composite damage model, was then used to simulate the experimental results of the drop-weight tests. Good agreement between experimental and FE results has been achieved. It is observed that the variation of results obtained from our experiments for the hybrid composites was very small (about 8%) when compared to those of non-hybrid composites. Also, when looking at the hybrid or non-hybrid composite, the effect of temperature at 60C, 20C was not significant whereas at 75C and 125C the results were more distinct.
The self-sensing damage detection method based on the electrical resistance measurement of carbon... more The self-sensing damage detection method based on the electrical resistance measurement of carbon fiber polymer-matrix composites has been investigated for a decade. In order to eliminate the effect of contact resistance when using the two-probe method, the four-probe methods, which include the resistance, potential and voltage change methods, were proposed in literature. However, the basic problems involved in the four-probe methods remain unclear, i.e., the validity range and the applicability of the four-probe methods. In this paper, beam-type specimens with and without delamination damage are used to carry out numerical analyses for the above-mentioned problems. It is found that the four-probe resistance method is valid only when the through-thickness conductivity is comparable to or larger than the longitudinal conductivity. For the potential method, which measures directly the voltage values between the voltage contacts, the present results show that the percentage change in damage-induced voltage between a pair of voltage contacts is not consistent with the percentage change in resistance. The underlying reason is that the damage-induced voltage change depends on the location of the applied current, while the resistance change does not.
Monotonic tensile tests are conducted on seven different Glare grades of fiber metal laminates. I... more Monotonic tensile tests are conducted on seven different Glare grades of fiber metal laminates. In-situ stress–strain curves of glass/epoxy laminate interleaved in Glare 2(3/2) are exposed with the application of metal volume fraction method using the stress–strain curves of Glare 2(3/2) and Aluminum 2024-T3 in unidirectional and transverse directions. The strain–stress curves of cross-ply Glares are predicted by the modification of this method with an empirical parameter and a second parameter considering the relative glass/epoxy laminate thickness ratios of Glare grades. Modified metal volume fraction method presented in this study can be used as a preliminary estimation of stress–strain curves of multiple possible fiber metal laminate configurations without testing.
This article was published in the above mentioned Springer issue. The material, including all por... more This article was published in the above mentioned Springer issue. The material, including all portions thereof, is protected by copyright; all rights are held exclusively by Springer Science + Business Media. The material is for personal use only; commercial use is not permitted. Unauthorized reproduction, transfer and/or use may be a violation of criminal as well as civil law. Abstract Impact responses and damage of various fiber-metal laminates were studied using a drop-weight instrument with the post-impact damage characteristics being evaluated through ultrasonic and mechanical sectioning techniques. The first severe failure induced by the low-velocity drop-weight impact occurred as delamination between the aluminum and fiber-epoxy layers at the non-impact side. It was followed by a visible shear crack in the outer aluminum layer on the non-impact face. Through-thickness shear cracks in the aluminum sheets and severe damage in the fiber laminated layers (including delamination between adjacent fiber-epoxy laminae with different fiber orientations) developed under higher energy impacts. The impact properties of fiber-metal laminates varied with different constituent materials and fiber orientations. Since it was punched through easily, the aramid-fiber reinforced fiber-metal laminates (ARALL) offered poorer impact resistance than the glass-fiber reinforced fiber-metal laminates (GLARE). Tougher and more ductile aluminum alloys improved the impact resistance. GLARE made of cross-ply prepregs provided better impact resistance than GLARE with unidirectional plies. Keywords Drop-weight (low-velocity) impact. Fiber-metal laminates (GLARE and ARALL). Ultrasound
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Papers by Benjamin Liaw