Materials with a negative Poisson＇s ratio（PR）are called auxetics;they are characterized by expansion/contraction when tensioned/compressed.Given this counterintuitive behavior,they present very particular character...Materials with a negative Poisson＇s ratio（PR）are called auxetics;they are characterized by expansion/contraction when tensioned/compressed.Given this counterintuitive behavior,they present very particular characteristics and mechanical behavior.Geometrical models have been developed to justify and artificiall reproduce such materials＇ auxetic behavior.The focus of this study is the exploration of a reentrant model by analyzing the variation in the PR of reentrant structures as a function of geometrical and base material parameters.It is shown that,even in the presence of protruding ribs,there may not be auxetic behavior,and this depends on the geometry of each reentrant structure.Values determined for these parameters can be helpful as approximate reference data in the design and fabrication of auxetic lattices using reentrant geometries.展开更多
The effect of high intensity ultrasound based on the novel multi-frequency multimode modulated technology on the final density, porosity, mechanical and fatigue properties of an AlSi<sub>9</sub>Cu<sub&g...The effect of high intensity ultrasound based on the novel multi-frequency multimode modulated technology on the final density, porosity, mechanical and fatigue properties of an AlSi<sub>9</sub>Cu<sub>3</sub>(Fe) alloy after different processing time was studied. Reduced pressure test was used to evaluate the density of alloys. The tensile and fatigue tests were used to evaluate the static and dynamic properties for the different time of ultrasonic degassing, respectively. It is found that ultrasonic degassing is effective in reduction porosity as well as to improve the final density of castings. Furthermore, the experimental results suggest that the porosity level does not have a substantial influence on the static properties contrary to what is observed on fatigue properties.展开更多
Magnesium-based materials show great potential for producing biodegradable stents,but their high corrosion rates are a roadblock.This study investigates whether ultrasound melt treatment can change the corrosion respo...Magnesium-based materials show great potential for producing biodegradable stents,but their high corrosion rates are a roadblock.This study investigates whether ultrasound melt treatment can change the corrosion response of an extruded AZ91D-1.0%Ca(wt.%)in Earle's Balanced Salt Solution by tailoring the intermetallics'morphology in the as-extruded state.The results showed that the wires from ultrasound-treated ingots corroded faster than non-treated ones in immersion for up to 6 hours.This trend shifted for longer periods,and ultrasound-treated material showed lower corrosion rates and uniform corrosion,while the non-treated material displayed localized corrosion signs.Tensile testing of the wires demonstrated that immersion in EBSS lowered the tensile strength and elongation at fracture due to material degradation,regardless of the processing route.Nonetheless,this decline was sharper in the non-treated material.These findings suggest that ultrasound melt processing can be a promising method for improving the corrosion resistance of magnesium-based materials,paving the way for their use in manufacturing biodegradable stents.展开更多
文摘Materials with a negative Poisson＇s ratio（PR）are called auxetics;they are characterized by expansion/contraction when tensioned/compressed.Given this counterintuitive behavior,they present very particular characteristics and mechanical behavior.Geometrical models have been developed to justify and artificiall reproduce such materials＇ auxetic behavior.The focus of this study is the exploration of a reentrant model by analyzing the variation in the PR of reentrant structures as a function of geometrical and base material parameters.It is shown that,even in the presence of protruding ribs,there may not be auxetic behavior,and this depends on the geometry of each reentrant structure.Values determined for these parameters can be helpful as approximate reference data in the design and fabrication of auxetic lattices using reentrant geometries.
基金supported by FEDER/COMPETE fundsnational funds through FCT-Portuguese Foundation for Science and Technology and was developed on the aim of the research project PTDC/EME-TME/119658/2010 and the Post-Doctoral grant SFRH/BPD/76680/2011
文摘The effect of high intensity ultrasound based on the novel multi-frequency multimode modulated technology on the final density, porosity, mechanical and fatigue properties of an AlSi<sub>9</sub>Cu<sub>3</sub>(Fe) alloy after different processing time was studied. Reduced pressure test was used to evaluate the density of alloys. The tensile and fatigue tests were used to evaluate the static and dynamic properties for the different time of ultrasonic degassing, respectively. It is found that ultrasonic degassing is effective in reduction porosity as well as to improve the final density of castings. Furthermore, the experimental results suggest that the porosity level does not have a substantial influence on the static properties contrary to what is observed on fatigue properties.
基金This work was supported by Portuguese FCT under the project UIDB/04436/2020the doctoral grant PD/BD/140094/2018 and SFRH/BD/145285/2019.
文摘Magnesium-based materials show great potential for producing biodegradable stents,but their high corrosion rates are a roadblock.This study investigates whether ultrasound melt treatment can change the corrosion response of an extruded AZ91D-1.0%Ca(wt.%)in Earle's Balanced Salt Solution by tailoring the intermetallics'morphology in the as-extruded state.The results showed that the wires from ultrasound-treated ingots corroded faster than non-treated ones in immersion for up to 6 hours.This trend shifted for longer periods,and ultrasound-treated material showed lower corrosion rates and uniform corrosion,while the non-treated material displayed localized corrosion signs.Tensile testing of the wires demonstrated that immersion in EBSS lowered the tensile strength and elongation at fracture due to material degradation,regardless of the processing route.Nonetheless,this decline was sharper in the non-treated material.These findings suggest that ultrasound melt processing can be a promising method for improving the corrosion resistance of magnesium-based materials,paving the way for their use in manufacturing biodegradable stents.
