ABSTRACTVarious models and calculation methods for the description of shape memory behaviour have... more ABSTRACTVarious models and calculation methods for the description of shape memory behaviour have been developed in recent years by different research groups. Some of the models have already been extended towards the thermomechanical and functional behaviour of matrix materials with embedded SMA-wires. The basic concepts of a thermomechanical model which has found widespread use in the literature on smart materials, are critically reviewed.A recently developed model based on a generalised thermodynamic analysis of the underlying martensitic transformation is discussed more into detail. Experimental verifications indicate that this thermodynamic model can be developed to an effective tool for the materials design of matrix materials with embedded SMA-wires.
This paper introduces a phenomenological algorithm for simulation of rate independent hysteretic ... more This paper introduces a phenomenological algorithm for simulation of rate independent hysteretic responses of shape memory alloys (SMAs) in cyclic uniaxial thermomechanical loads. The algorithm is proposed in a compact differential form that uses only seven well-defined material parameters and is adjustable to a particular alloy by fitting a single experimental pseudoelastic loop. It has been developed as a tool for predictions of history dependent uniaxial σ-e-T responses of SMA elements to be embedded into the smart structures and composites. Simulated model responses to a variety of thermomechanical loading paths, including partial internal loop behaviours, are demonstrated. The computer program with a numerically implemented algorithm is available on the Internet.
... A small endothermic peak related to the SAM fraction appeared on the DSC curve and the POM fr... more ... A small endothermic peak related to the SAM fraction appeared on the DSC curve and the POM fraction caused a global shift of the baseline. ... Kelly Tsoi acknowledges the financial support of Zonta International through the Amelia Earhart Fellowship Award. ...
Recovery stresses generated by shape memory alloys (SMAs) deformed in the martensitic state and s... more Recovery stresses generated by shape memory alloys (SMAs) deformed in the martensitic state and subsequently heated with constrained shape are, besides the pseudoelasticity and shape memory effects, the most useful and unique property of these materials. It is a basis on ...
Adaptive composites integrate actuating and sensing materials into a structural material (e.g., t... more Adaptive composites integrate actuating and sensing materials into a structural material (e.g., the integration of thin shapememory alloy [SMA] wires can function as actuating elements into fiber-reinforced polymer composites). SMA composites can open new perspectives on the development of engineering structures and devices with adaptive shape, stiffness, damping, and other properties. Materials design involving the constitutive modeling of SMA composite thermomechanical responses is a key topic in the development of the adaptive composites. As such, example simulation results obtained using a recently developed composite model are presented.
Adaptive materials integrate actuating and sensing technologies into a structural material. The a... more Adaptive materials integrate actuating and sensing technologies into a structural material. The approach discussed here is the integration of shape memory alloy (SMA) wires as actuating elements in fibre reinforced polymer composites. SMA's offer attractive potentials such as reversible strains of several percent, generation of high recovery stresses, and high power/weight ratios. T he development of polymer composites with embedded SMA's can open new perspectives with respect to the development of engineering structures with adaptive shape, stiffness, damping and other properties. The development of these advanced composites with embedded SMA-wires is still in an early stage. An overview is given of the current state-of-the-art and of the many fundamental issues which require further research before these adaptive composites can be used in industrial applications.
Production of the NiTi slotted tube stents by laser cutting leads to strong burr formation and de... more Production of the NiTi slotted tube stents by laser cutting leads to strong burr formation and depositions on the material surface. Acid pickling is one of the major methods to remove the burr and the depositions. In this study, as a pre-treatment of polishing the NiTi stents, pickling was tested for various times in an acid solution at room temperature. Its effect on the surface morphology, dimension changes, and mechanical behaviour of the NiTi stents was evaluated. The burr and depositions could be removed practically. The removal (weight loss) of the material increases linearly with the pickling time. The burr and depositions were removed totally from the cutting zone when pickling time reached a specific value. Experimental relations among weight loss, dimensions, mechanical properties and pickling time of the NiTi stents were established.
ÐA uni®ed thermodynamic analysis has been developed which allows the combined complex eects of ap... more ÐA uni®ed thermodynamic analysis has been developed which allows the combined complex eects of applied stresses and alloy composition on the martensite start temperature, M s (s), to be explained and predicted. In this uni®ed analysis, a thermodynamic analysis of the eect of applied stress on the relative stability of the high and low temperature phase is combined with existing thermodynamic descriptions of the alloy system. The calculated results are compared with experimental results for the g 4 e martensitic transformation in Fe±Mn±Si shape memory alloys. For single crystals, the comparison shows that the inuence of applied stresses can be directly predicted with a reasonable accuracy for a wide composition range. By integrating a polycrystallinity parameter in the analysis it is shown that the calculations are also valid for polycrystalline alloys. Application of this analysis to experimental values of M s (s) can also generate useful data for future optimizations of the thermodynamic description of several alloy systems. # 1998 Acta Metallurgica Inc.
The superelastic behaviors of different isothermal treated Cu-13.8Al-4.0Ni (mass fraction) single... more The superelastic behaviors of different isothermal treated Cu-13.8Al-4.0Ni (mass fraction) single crystals were studied by applying tensile stress along ＜001＞ of the β phase. The different isothermal specimens have different superelastic behavior due to the change of the ratio of stress-induced γ＇1 andβ＇1. The superelasticity of γ＇1 phase tends to that ofβ＇1 phase with cycling.Typical stabilization of stress-induced martensite above Ap*P results in residual deformation. Due to the reverse transformation of γ＇1, there is a deviation of pseudo-yield stress from linear relation with temperature at relatively low stress.
ABSTRACTVarious models and calculation methods for the description of shape memory behaviour have... more ABSTRACTVarious models and calculation methods for the description of shape memory behaviour have been developed in recent years by different research groups. Some of the models have already been extended towards the thermomechanical and functional behaviour of matrix materials with embedded SMA-wires. The basic concepts of a thermomechanical model which has found widespread use in the literature on smart materials, are critically reviewed.A recently developed model based on a generalised thermodynamic analysis of the underlying martensitic transformation is discussed more into detail. Experimental verifications indicate that this thermodynamic model can be developed to an effective tool for the materials design of matrix materials with embedded SMA-wires.
This paper introduces a phenomenological algorithm for simulation of rate independent hysteretic ... more This paper introduces a phenomenological algorithm for simulation of rate independent hysteretic responses of shape memory alloys (SMAs) in cyclic uniaxial thermomechanical loads. The algorithm is proposed in a compact differential form that uses only seven well-defined material parameters and is adjustable to a particular alloy by fitting a single experimental pseudoelastic loop. It has been developed as a tool for predictions of history dependent uniaxial σ-e-T responses of SMA elements to be embedded into the smart structures and composites. Simulated model responses to a variety of thermomechanical loading paths, including partial internal loop behaviours, are demonstrated. The computer program with a numerically implemented algorithm is available on the Internet.
... A small endothermic peak related to the SAM fraction appeared on the DSC curve and the POM fr... more ... A small endothermic peak related to the SAM fraction appeared on the DSC curve and the POM fraction caused a global shift of the baseline. ... Kelly Tsoi acknowledges the financial support of Zonta International through the Amelia Earhart Fellowship Award. ...
Recovery stresses generated by shape memory alloys (SMAs) deformed in the martensitic state and s... more Recovery stresses generated by shape memory alloys (SMAs) deformed in the martensitic state and subsequently heated with constrained shape are, besides the pseudoelasticity and shape memory effects, the most useful and unique property of these materials. It is a basis on ...
Adaptive composites integrate actuating and sensing materials into a structural material (e.g., t... more Adaptive composites integrate actuating and sensing materials into a structural material (e.g., the integration of thin shapememory alloy [SMA] wires can function as actuating elements into fiber-reinforced polymer composites). SMA composites can open new perspectives on the development of engineering structures and devices with adaptive shape, stiffness, damping, and other properties. Materials design involving the constitutive modeling of SMA composite thermomechanical responses is a key topic in the development of the adaptive composites. As such, example simulation results obtained using a recently developed composite model are presented.
Adaptive materials integrate actuating and sensing technologies into a structural material. The a... more Adaptive materials integrate actuating and sensing technologies into a structural material. The approach discussed here is the integration of shape memory alloy (SMA) wires as actuating elements in fibre reinforced polymer composites. SMA's offer attractive potentials such as reversible strains of several percent, generation of high recovery stresses, and high power/weight ratios. T he development of polymer composites with embedded SMA's can open new perspectives with respect to the development of engineering structures with adaptive shape, stiffness, damping and other properties. The development of these advanced composites with embedded SMA-wires is still in an early stage. An overview is given of the current state-of-the-art and of the many fundamental issues which require further research before these adaptive composites can be used in industrial applications.
Production of the NiTi slotted tube stents by laser cutting leads to strong burr formation and de... more Production of the NiTi slotted tube stents by laser cutting leads to strong burr formation and depositions on the material surface. Acid pickling is one of the major methods to remove the burr and the depositions. In this study, as a pre-treatment of polishing the NiTi stents, pickling was tested for various times in an acid solution at room temperature. Its effect on the surface morphology, dimension changes, and mechanical behaviour of the NiTi stents was evaluated. The burr and depositions could be removed practically. The removal (weight loss) of the material increases linearly with the pickling time. The burr and depositions were removed totally from the cutting zone when pickling time reached a specific value. Experimental relations among weight loss, dimensions, mechanical properties and pickling time of the NiTi stents were established.
ÐA uni®ed thermodynamic analysis has been developed which allows the combined complex eects of ap... more ÐA uni®ed thermodynamic analysis has been developed which allows the combined complex eects of applied stresses and alloy composition on the martensite start temperature, M s (s), to be explained and predicted. In this uni®ed analysis, a thermodynamic analysis of the eect of applied stress on the relative stability of the high and low temperature phase is combined with existing thermodynamic descriptions of the alloy system. The calculated results are compared with experimental results for the g 4 e martensitic transformation in Fe±Mn±Si shape memory alloys. For single crystals, the comparison shows that the inuence of applied stresses can be directly predicted with a reasonable accuracy for a wide composition range. By integrating a polycrystallinity parameter in the analysis it is shown that the calculations are also valid for polycrystalline alloys. Application of this analysis to experimental values of M s (s) can also generate useful data for future optimizations of the thermodynamic description of several alloy systems. # 1998 Acta Metallurgica Inc.
The superelastic behaviors of different isothermal treated Cu-13.8Al-4.0Ni (mass fraction) single... more The superelastic behaviors of different isothermal treated Cu-13.8Al-4.0Ni (mass fraction) single crystals were studied by applying tensile stress along ＜001＞ of the β phase. The different isothermal specimens have different superelastic behavior due to the change of the ratio of stress-induced γ＇1 andβ＇1. The superelasticity of γ＇1 phase tends to that ofβ＇1 phase with cycling.Typical stabilization of stress-induced martensite above Ap*P results in residual deformation. Due to the reverse transformation of γ＇1, there is a deviation of pseudo-yield stress from linear relation with temperature at relatively low stress.
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Papers by Rudy Stalmans