Metallic micro parts are playing an important role in micro-fabrication industry. Recently, we ha... more Metallic micro parts are playing an important role in micro-fabrication industry. Recently, we have demonstrated a new deformation mechanism for micro-formability of polycrystalline materials. Different depressed micro-features smaller than the grain size have been successfully fabricated on 6061 aluminum alloy (AA6061) substrates with good fidelity. To further verify this proposed deformation mechanism that grain size is not a limiting factor, we demonstrate here that in addition of depressed features, protruded micro-features on a polycrystalline substrate can similarly be fabricated.
Environmental sustainability has been the focus of recent construction trends. Adopting efficient... more Environmental sustainability has been the focus of recent construction trends. Adopting efficient construction technologies and minimizing the usage of raw materials are a few of many ways to achieve such sustainability. In the past few years, 3D printing of concrete has received considerable attention for its potential to be the next disruptive technology for construction industry. By eliminating and/or reducing the amount of in-situ construction, combined with the need for skilled personnel, 3D printing can help in achieving good quality control at construction site, which has long been an issue in traditional construction industry. Singapore is dependent on neighboring countries for raw construction materials. Using recycled materials as a substitute for aggregates not only minimizes the usage of raw materials, but also help in reducing the Singapore’s dependency on other countries in long-term. In this study, preliminary findings of a 3D printed cementitious material with recycl...
The inorganic polymer, e.g. geopolymer, is well known as a green construction material with its r... more The inorganic polymer, e.g. geopolymer, is well known as a green construction material with its remarkable mechanical and durability properties compared to other ceramic and Portland cement-based materials. It is worth promising to explore such geopolymer properties processed by a recent innovative technology, i.e. 3D concrete printing, which has established its ground in the construction industry. This study is focused on examining the directional effect of 3D printing process on compressive strengths of geopolymer mortar made from different industry by-products such as fly ash, slag, silica fume, etc. For a comparison, the same geopolymer mix was casted and cured in ambient temperature prior to its mechanical test with printed samples. Results from experimental tests revealed an anisotropy in the compressive strengths caused due to layered deposition of the geopolymer mortar.
This study investigated the properties of alkali activated slag (AAS) binders formulated for extr... more This study investigated the properties of alkali activated slag (AAS) binders formulated for extrusion-based 3D printing. The fresh properties of AAS mixes were tailored through the use of nanoclay (NC) and nucleation seeds. The printability criteria employed were the ease of extrusion (extrudability) and the stability of the layered structure (buildability). Introduction of 0.4% NC in AAS mixes led to improved thixotropic properties due to the flocculation effect, which accounted for the extrudability and shape fidelity of the binder. Inclusion of 2% hydromagnesite seeds in this mix design provided additional nucleation sites for the increased precipitation of hydrate phases, resulting in denser microstructures. This enhanced the hydration reaction and improved the structural build-up rate necessary for large-scale 3D printing. The developed AAS mix containing 0.4% NC and 2% hydromagnesite seeds was used in the printing of an actual 3D structure to demonstrate its feasibility to be used in 3D printing applications.
3D concrete printing technology greatly facilitates automation in construction which enhances eff... more 3D concrete printing technology greatly facilitates automation in construction which enhances efficiency, productivity and sustainability. This study develops a slag-based mixture as a cementless material for sustainable spray-based 3D printing. Effects of MgO and fly ash cenosphere (FAC) addition on setting, hydration and rheological properties of fresh mixtures are investigated to obtain the optimal mixture. Results show that inclusion of MgO effectively reduces initial setting time of the fresh mixtures. With 40 wt.% of GGBS replaced by MgO, initial setting time is greatly reduced from 305 min to 67 min (78% reduction). Fourier-Transformed Infrared (FTIR) spectra suggest the acceleration is plausibly due to the physical aspects. Furthermore, the FTIR spectra show that MgO can effectively activate the slag and also improve water retention. Rheological tests reveal that FAC addition generally reduces dynamic yield stress and plastic viscosity while increases static yield stress of the fresh mixtures, resulting in lower pumping pressures and higher critical ratios. The mixture with 20 wt.%/40 wt.% FAC addition has 29%/31% lower pumping pressure and 78%/68% higher critical ratio compared with plain MgO-activated slag material, respectively. Hence, the material with tailored rheology leads to better delivery and deposition performance of the mixture and overall spray-printing quality. An optimal mixture was finally selected based on setting, hydration, rheological properties and spray performance. The developed cementless mixture was successfully applied in the vertical spray-based 3D printing of filament and profile, which confirmed its feasibility in engineering applications.
3D printing of cementitious materials is an innovative and promising approach in the construction... more 3D printing of cementitious materials is an innovative and promising approach in the construction sector, attracting much attention over the past few years. Use of waste cementitious materials in the production of 3D printable components increases the sustainability and cost-effectiveness of this process. This work proposes an environmentally friendly 3D printable cementitious material involving the use of magnesium potassium phosphate cement (MKPC) with various ratios of fly ash replacement ranging from 0 to 60 wt% to increase the working time of the binder. Silica fume was used at up to 10 wt% to adjust rheological and mechanical properties. The performance of the developed MKPC binders with different formulations in the context of 3D printing was assessed via a detailed investigation of the workability, extrudability, buildability, compressive strength, porosity and microstructural analysis. Amongst the mixtures studied, the optimum MKPC formulation involving 60 wt% fly ash and 10 wt% silica fume with a borax-to-magnesia ratio of 1:4 was selected for a small-scale printing demonstration in line with its rheological and mechanical 2 properties. Finally, a 20-layer component with a height of 180 mm was printed in min to demonstrate the feasibility of the adopted mixture in 3D printing.
Empirical models to predict rheological properties of fiber reinforced cementitious composites fo... more Empirical models to predict rheological properties of fiber reinforced cementitious composites for 3D printing.
There has been much recent interest in aluminium matrix composites as candidates for materials wi... more There has been much recent interest in aluminium matrix composites as candidates for materials with higher specific properties (e.g. strength and stiffness) and temperature properties compared to conventional aluminium alloys in current use. However, these improvements have been accompanied by a general degradation of the fracture properties, such as dt,~ctility and toughness. In this work a novel reinforcement, Ni in the preform state, and the rates of deformation on the mechanical properties of this reinforcement system are explored. It is found that improved mechanical properties can be obtained by appropriate design of the reinforcement a~d powders systems and consolidation techniques.
Computer Methods in Applied Mechanics and Engineering, 2004
A mesh-free kp-Ritz method of solution based on the kernel particle approximation for the field v... more A mesh-free kp-Ritz method of solution based on the kernel particle approximation for the field variables is proposed for the large deflection flexural analysis of laminated composite plates. The first-order shear deformation theory (FSDT) is used for modeling the flexure. The nonlinear solution algorithm is based on the total Lagrangian formulation with Green's strain measures and von Kármán assumptions. The
Proceedings of the International Symposium on Automation and Robotics in Construction (IAARC), 2017
In recent years, digital fabrication is termed as "third industrial revolution" and its interacti... more In recent years, digital fabrication is termed as "third industrial revolution" and its interaction with extrusion based cementitious material has been well known as concrete printing. In concrete printing, a gantry/robotic system deposits concrete layer by layer following G-codes generated from slicing of the 3D component. However, the robotic system does not consider the material (concrete) properties and component geometry which sometimes cause failure in the printing process. Concrete properties are usually attributed with time and therefore the system parameters such as extruder velocity and layer height are necessarily to be controlled accordingly to obtain an uninterrupted smooth flow. In line with this, our current research aims to automate the printing process by collecting material's fresh properties through a feedforward control system. A six-axis industrial Denso® robot was used for 3D printing of geopolymer concrete with the help of screw pump and ten-millimeter circular extruder. The obtained experimental results confirmed the validity and robustness of this automated set up.
3D printing (3DP), commonly known as additive manufacturing (AM), is a promising technology that ... more 3D printing (3DP), commonly known as additive manufacturing (AM), is a promising technology that can fabricate three dimensional complex shape prototypes directly from computer-aided design (CAD) model without any tooling and human intervention. Owing to its peculiar characteristics, AM is widely used in many industries to assist in the design, manufacture and commercialization of a product. More recently, this technology has been extended to building and construction (B&C) application in order to mitigate some of the critical issues such as shortage of skilled labour, high production cost and construction time, health and safety concerns of the workers in the hazardous environment etc. However for successful implementation, proper selection of materials and their mix design is highly recommended, which is a challenging task. This paper summarizes the current available 3DP systems from literature and the respective materials that have been used thus far by various experts, industrie...
The effects of heat treatment on the microstructure, tensile property and fracture behavior of as... more The effects of heat treatment on the microstructure, tensile property and fracture behavior of as-extruded AZ91 magnesium alloy were studied with OM and SEM. The results show that the grains of as-cast AZ91 alloy are refined by hot extrusion due to dynamic recrystallization, and the mechanical properties are improved obviously. The ductility is significantly enhanced after solution treatment of the as-extruded AZ91 alloy, tensile strength is almost the same as before, and hardness is significantly reduced after solution treatment and artificial aging treatment. The tensile strength reduced and the ductility is significantly enhanced of as-extruded after annealing processes. The fracture surface of as-extruded AZ91 magnesium alloy has the mixed modes of ductile and brittle characteristics. But after T6 or annealing treatment, the dimple number increases evidently.
Journal of Biomedical Materials Research Part A, 2007
Hydroxyapatite has been successfully deposited onto Fecralloy substrate (a metal alloy with 22% C... more Hydroxyapatite has been successfully deposited onto Fecralloy substrate (a metal alloy with 22% Cr, 4.8% Al) by electrophoretic deposition in an attempt to promote the adhesion between coating and substrate, consequently to extend the lifetime of implants. Fecralloy has the ability to generate a dense and stable alpha-Al(2)O(3) layer "in situ" during thermal treatment, which will highly improve the adhesion and the corrosion resistance of the coating system. Phases and morphologies of HA coating were found to vary after sintering according to XRD and SEM analysis. Besides the physicochemical characterization, the effects of the Fecralloy, thermally generated oxide layer, and HA coating on the early and late responses of osteoblasts in vitro were determined. Cellular morphology and proliferation were studied up to 7 days. Quantitative assays of mineralization were conducted up to 14 days. Osteoblasts showed increased cell spreading and cell proliferation on metal substrates, with significantly higher mineralization on HA coating. The results in this study proved that Fecralloy is a biocompatible metal and the HA coating on Fecralloy provides a good candidate for orthopaedic and dental implants.
Proceedings of SPIE - The International Society for Optical Engineering, 2001
ABSTRACT With the recent growth of microelectromechanical systems (MEMS), RF capacitive microswit... more ABSTRACT With the recent growth of microelectromechanical systems (MEMS), RF capacitive microswitches are becoming popular. As such there is a need to accurately characterize the performance of the RF capacitive microswitches. To realize this goal, the paper proposes both electrical and static mechanical models to precisely extract the performance parameters of the RF capacitive microswitches. The electrical model proposed in this paper provides a means to represent the RF capacitive microswitches for use to determine the resistance, capacitance, and inductance. The static mechanical model predicts the effective stiffness constant and the pull-in voltage. Deformation of the bridge and its contact behavior with the dielectric layer are also precisely analyzed using Finite Element Method. Finally this paper discusses the fabrication of the RF capacitive microswitches.
Purpose: The purpose of the paper is to study the cavitation and grain growth during superplastic... more Purpose: The purpose of the paper is to study the cavitation and grain growth during superplastic forming. Design/methodology/approach: Superplastic alloys exhibit the extremely large elongation to failure by their high strain rate sensitivity. Cavities have widely been observed during superplastic deformation of metals and alloys and lead to the degradation of material properties such as tensile, creep, fatigue and stress-corrosion behavior. In this work, a finite element method is developed, which considers the grain growth and the effect of material damage. Findings: The effects of material parameters and deformation damage on the superplastic deformation process are numerically analyzed, and the means to control cavitation growth is discussed. The microstructural mechanism of grain growth during superplastic deformation is also studied. A new model considering the grain growth is proposed and applied to conventional superplastic materials The relationships between the strain, the strain rate, the test temperature, the initial grain size and the grain growth respectively in superplastic materials are discussed. Practical implications: The effect of variation of strain rate sensitivity (m value) on the strain limit of the superplastic deformation is investigated, and the theoretically calculated values are compared with the experimental results. Originality/value: A new microstructure model based on the microstructural mechanism of superplastic deformation has been proposed. This model has been successfully applied to analyze conventional superplastic materials.
International Journal of Mechanical Sciences, 2002
... The work of Whiteney and Pagano [30], Bert and Chen [31], and Reddy and Chao [32] are typical... more ... The work of Whiteney and Pagano [30], Bert and Chen [31], and Reddy and Chao [32] are typical of studies using first-order shear deformation theory (FSDT), while that of Liu et al. [33], and Pandya and Kant [34] use higher order theories. A comparative assessment of various ...
Friction stir processing is a solid-state welding technology capable of joining metal parts witho... more Friction stir processing is a solid-state welding technology capable of joining metal parts without the melting. The microstructure of the material evolved during the process vary from columnar grain along the thermal gradient in the melt pool to fine equiaxed grains. Evaluation on its mechanical properties in terms of micro-hardness was performed. A significant decrease in microhardness was observed in the processed region. The decrease in the microhardness is mainly attributed to the dissolution of hardening precipitates in the aluminium matrix.
Metallic micro parts are playing an important role in micro-fabrication industry. Recently, we ha... more Metallic micro parts are playing an important role in micro-fabrication industry. Recently, we have demonstrated a new deformation mechanism for micro-formability of polycrystalline materials. Different depressed micro-features smaller than the grain size have been successfully fabricated on 6061 aluminum alloy (AA6061) substrates with good fidelity. To further verify this proposed deformation mechanism that grain size is not a limiting factor, we demonstrate here that in addition of depressed features, protruded micro-features on a polycrystalline substrate can similarly be fabricated.
Environmental sustainability has been the focus of recent construction trends. Adopting efficient... more Environmental sustainability has been the focus of recent construction trends. Adopting efficient construction technologies and minimizing the usage of raw materials are a few of many ways to achieve such sustainability. In the past few years, 3D printing of concrete has received considerable attention for its potential to be the next disruptive technology for construction industry. By eliminating and/or reducing the amount of in-situ construction, combined with the need for skilled personnel, 3D printing can help in achieving good quality control at construction site, which has long been an issue in traditional construction industry. Singapore is dependent on neighboring countries for raw construction materials. Using recycled materials as a substitute for aggregates not only minimizes the usage of raw materials, but also help in reducing the Singapore’s dependency on other countries in long-term. In this study, preliminary findings of a 3D printed cementitious material with recycl...
The inorganic polymer, e.g. geopolymer, is well known as a green construction material with its r... more The inorganic polymer, e.g. geopolymer, is well known as a green construction material with its remarkable mechanical and durability properties compared to other ceramic and Portland cement-based materials. It is worth promising to explore such geopolymer properties processed by a recent innovative technology, i.e. 3D concrete printing, which has established its ground in the construction industry. This study is focused on examining the directional effect of 3D printing process on compressive strengths of geopolymer mortar made from different industry by-products such as fly ash, slag, silica fume, etc. For a comparison, the same geopolymer mix was casted and cured in ambient temperature prior to its mechanical test with printed samples. Results from experimental tests revealed an anisotropy in the compressive strengths caused due to layered deposition of the geopolymer mortar.
This study investigated the properties of alkali activated slag (AAS) binders formulated for extr... more This study investigated the properties of alkali activated slag (AAS) binders formulated for extrusion-based 3D printing. The fresh properties of AAS mixes were tailored through the use of nanoclay (NC) and nucleation seeds. The printability criteria employed were the ease of extrusion (extrudability) and the stability of the layered structure (buildability). Introduction of 0.4% NC in AAS mixes led to improved thixotropic properties due to the flocculation effect, which accounted for the extrudability and shape fidelity of the binder. Inclusion of 2% hydromagnesite seeds in this mix design provided additional nucleation sites for the increased precipitation of hydrate phases, resulting in denser microstructures. This enhanced the hydration reaction and improved the structural build-up rate necessary for large-scale 3D printing. The developed AAS mix containing 0.4% NC and 2% hydromagnesite seeds was used in the printing of an actual 3D structure to demonstrate its feasibility to be used in 3D printing applications.
3D concrete printing technology greatly facilitates automation in construction which enhances eff... more 3D concrete printing technology greatly facilitates automation in construction which enhances efficiency, productivity and sustainability. This study develops a slag-based mixture as a cementless material for sustainable spray-based 3D printing. Effects of MgO and fly ash cenosphere (FAC) addition on setting, hydration and rheological properties of fresh mixtures are investigated to obtain the optimal mixture. Results show that inclusion of MgO effectively reduces initial setting time of the fresh mixtures. With 40 wt.% of GGBS replaced by MgO, initial setting time is greatly reduced from 305 min to 67 min (78% reduction). Fourier-Transformed Infrared (FTIR) spectra suggest the acceleration is plausibly due to the physical aspects. Furthermore, the FTIR spectra show that MgO can effectively activate the slag and also improve water retention. Rheological tests reveal that FAC addition generally reduces dynamic yield stress and plastic viscosity while increases static yield stress of the fresh mixtures, resulting in lower pumping pressures and higher critical ratios. The mixture with 20 wt.%/40 wt.% FAC addition has 29%/31% lower pumping pressure and 78%/68% higher critical ratio compared with plain MgO-activated slag material, respectively. Hence, the material with tailored rheology leads to better delivery and deposition performance of the mixture and overall spray-printing quality. An optimal mixture was finally selected based on setting, hydration, rheological properties and spray performance. The developed cementless mixture was successfully applied in the vertical spray-based 3D printing of filament and profile, which confirmed its feasibility in engineering applications.
3D printing of cementitious materials is an innovative and promising approach in the construction... more 3D printing of cementitious materials is an innovative and promising approach in the construction sector, attracting much attention over the past few years. Use of waste cementitious materials in the production of 3D printable components increases the sustainability and cost-effectiveness of this process. This work proposes an environmentally friendly 3D printable cementitious material involving the use of magnesium potassium phosphate cement (MKPC) with various ratios of fly ash replacement ranging from 0 to 60 wt% to increase the working time of the binder. Silica fume was used at up to 10 wt% to adjust rheological and mechanical properties. The performance of the developed MKPC binders with different formulations in the context of 3D printing was assessed via a detailed investigation of the workability, extrudability, buildability, compressive strength, porosity and microstructural analysis. Amongst the mixtures studied, the optimum MKPC formulation involving 60 wt% fly ash and 10 wt% silica fume with a borax-to-magnesia ratio of 1:4 was selected for a small-scale printing demonstration in line with its rheological and mechanical 2 properties. Finally, a 20-layer component with a height of 180 mm was printed in min to demonstrate the feasibility of the adopted mixture in 3D printing.
Empirical models to predict rheological properties of fiber reinforced cementitious composites fo... more Empirical models to predict rheological properties of fiber reinforced cementitious composites for 3D printing.
There has been much recent interest in aluminium matrix composites as candidates for materials wi... more There has been much recent interest in aluminium matrix composites as candidates for materials with higher specific properties (e.g. strength and stiffness) and temperature properties compared to conventional aluminium alloys in current use. However, these improvements have been accompanied by a general degradation of the fracture properties, such as dt,~ctility and toughness. In this work a novel reinforcement, Ni in the preform state, and the rates of deformation on the mechanical properties of this reinforcement system are explored. It is found that improved mechanical properties can be obtained by appropriate design of the reinforcement a~d powders systems and consolidation techniques.
Computer Methods in Applied Mechanics and Engineering, 2004
A mesh-free kp-Ritz method of solution based on the kernel particle approximation for the field v... more A mesh-free kp-Ritz method of solution based on the kernel particle approximation for the field variables is proposed for the large deflection flexural analysis of laminated composite plates. The first-order shear deformation theory (FSDT) is used for modeling the flexure. The nonlinear solution algorithm is based on the total Lagrangian formulation with Green's strain measures and von Kármán assumptions. The
Proceedings of the International Symposium on Automation and Robotics in Construction (IAARC), 2017
In recent years, digital fabrication is termed as "third industrial revolution" and its interacti... more In recent years, digital fabrication is termed as "third industrial revolution" and its interaction with extrusion based cementitious material has been well known as concrete printing. In concrete printing, a gantry/robotic system deposits concrete layer by layer following G-codes generated from slicing of the 3D component. However, the robotic system does not consider the material (concrete) properties and component geometry which sometimes cause failure in the printing process. Concrete properties are usually attributed with time and therefore the system parameters such as extruder velocity and layer height are necessarily to be controlled accordingly to obtain an uninterrupted smooth flow. In line with this, our current research aims to automate the printing process by collecting material's fresh properties through a feedforward control system. A six-axis industrial Denso® robot was used for 3D printing of geopolymer concrete with the help of screw pump and ten-millimeter circular extruder. The obtained experimental results confirmed the validity and robustness of this automated set up.
3D printing (3DP), commonly known as additive manufacturing (AM), is a promising technology that ... more 3D printing (3DP), commonly known as additive manufacturing (AM), is a promising technology that can fabricate three dimensional complex shape prototypes directly from computer-aided design (CAD) model without any tooling and human intervention. Owing to its peculiar characteristics, AM is widely used in many industries to assist in the design, manufacture and commercialization of a product. More recently, this technology has been extended to building and construction (B&C) application in order to mitigate some of the critical issues such as shortage of skilled labour, high production cost and construction time, health and safety concerns of the workers in the hazardous environment etc. However for successful implementation, proper selection of materials and their mix design is highly recommended, which is a challenging task. This paper summarizes the current available 3DP systems from literature and the respective materials that have been used thus far by various experts, industrie...
The effects of heat treatment on the microstructure, tensile property and fracture behavior of as... more The effects of heat treatment on the microstructure, tensile property and fracture behavior of as-extruded AZ91 magnesium alloy were studied with OM and SEM. The results show that the grains of as-cast AZ91 alloy are refined by hot extrusion due to dynamic recrystallization, and the mechanical properties are improved obviously. The ductility is significantly enhanced after solution treatment of the as-extruded AZ91 alloy, tensile strength is almost the same as before, and hardness is significantly reduced after solution treatment and artificial aging treatment. The tensile strength reduced and the ductility is significantly enhanced of as-extruded after annealing processes. The fracture surface of as-extruded AZ91 magnesium alloy has the mixed modes of ductile and brittle characteristics. But after T6 or annealing treatment, the dimple number increases evidently.
Journal of Biomedical Materials Research Part A, 2007
Hydroxyapatite has been successfully deposited onto Fecralloy substrate (a metal alloy with 22% C... more Hydroxyapatite has been successfully deposited onto Fecralloy substrate (a metal alloy with 22% Cr, 4.8% Al) by electrophoretic deposition in an attempt to promote the adhesion between coating and substrate, consequently to extend the lifetime of implants. Fecralloy has the ability to generate a dense and stable alpha-Al(2)O(3) layer "in situ" during thermal treatment, which will highly improve the adhesion and the corrosion resistance of the coating system. Phases and morphologies of HA coating were found to vary after sintering according to XRD and SEM analysis. Besides the physicochemical characterization, the effects of the Fecralloy, thermally generated oxide layer, and HA coating on the early and late responses of osteoblasts in vitro were determined. Cellular morphology and proliferation were studied up to 7 days. Quantitative assays of mineralization were conducted up to 14 days. Osteoblasts showed increased cell spreading and cell proliferation on metal substrates, with significantly higher mineralization on HA coating. The results in this study proved that Fecralloy is a biocompatible metal and the HA coating on Fecralloy provides a good candidate for orthopaedic and dental implants.
Proceedings of SPIE - The International Society for Optical Engineering, 2001
ABSTRACT With the recent growth of microelectromechanical systems (MEMS), RF capacitive microswit... more ABSTRACT With the recent growth of microelectromechanical systems (MEMS), RF capacitive microswitches are becoming popular. As such there is a need to accurately characterize the performance of the RF capacitive microswitches. To realize this goal, the paper proposes both electrical and static mechanical models to precisely extract the performance parameters of the RF capacitive microswitches. The electrical model proposed in this paper provides a means to represent the RF capacitive microswitches for use to determine the resistance, capacitance, and inductance. The static mechanical model predicts the effective stiffness constant and the pull-in voltage. Deformation of the bridge and its contact behavior with the dielectric layer are also precisely analyzed using Finite Element Method. Finally this paper discusses the fabrication of the RF capacitive microswitches.
Purpose: The purpose of the paper is to study the cavitation and grain growth during superplastic... more Purpose: The purpose of the paper is to study the cavitation and grain growth during superplastic forming. Design/methodology/approach: Superplastic alloys exhibit the extremely large elongation to failure by their high strain rate sensitivity. Cavities have widely been observed during superplastic deformation of metals and alloys and lead to the degradation of material properties such as tensile, creep, fatigue and stress-corrosion behavior. In this work, a finite element method is developed, which considers the grain growth and the effect of material damage. Findings: The effects of material parameters and deformation damage on the superplastic deformation process are numerically analyzed, and the means to control cavitation growth is discussed. The microstructural mechanism of grain growth during superplastic deformation is also studied. A new model considering the grain growth is proposed and applied to conventional superplastic materials The relationships between the strain, the strain rate, the test temperature, the initial grain size and the grain growth respectively in superplastic materials are discussed. Practical implications: The effect of variation of strain rate sensitivity (m value) on the strain limit of the superplastic deformation is investigated, and the theoretically calculated values are compared with the experimental results. Originality/value: A new microstructure model based on the microstructural mechanism of superplastic deformation has been proposed. This model has been successfully applied to analyze conventional superplastic materials.
International Journal of Mechanical Sciences, 2002
... The work of Whiteney and Pagano [30], Bert and Chen [31], and Reddy and Chao [32] are typical... more ... The work of Whiteney and Pagano [30], Bert and Chen [31], and Reddy and Chao [32] are typical of studies using first-order shear deformation theory (FSDT), while that of Liu et al. [33], and Pandya and Kant [34] use higher order theories. A comparative assessment of various ...
Friction stir processing is a solid-state welding technology capable of joining metal parts witho... more Friction stir processing is a solid-state welding technology capable of joining metal parts without the melting. The microstructure of the material evolved during the process vary from columnar grain along the thermal gradient in the melt pool to fine equiaxed grains. Evaluation on its mechanical properties in terms of micro-hardness was performed. A significant decrease in microhardness was observed in the processed region. The decrease in the microhardness is mainly attributed to the dissolution of hardening precipitates in the aluminium matrix.
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Papers by Ming-Jen Tan