This study presents a semi-analytical solution to describe the behavior of shape memory polymers(SMPs) based on the nonlinear thermo-visco-hyperelasticity which originates from the concepts of internal state variables...This study presents a semi-analytical solution to describe the behavior of shape memory polymers(SMPs) based on the nonlinear thermo-visco-hyperelasticity which originates from the concepts of internal state variables and rational thermodynamics.This method is developed for the finite bending of multilayers in a dual-shape memory effect(SME) cycle.The layer number and layering order are investigated for two different SMPs and a hyperelastic material.In addition to the semi-analytical solution,the finite element simulation is performed to verify the predicted results,where the outcomes demonstrate the excellent accuracy of the proposed solution for predicting the behavior of the multilayer SMPs.Since this method has a much lower computational cost than the finite element method(FEM),it can be used as an effective tool to analyze the SMP behavior under different conditions,including different materials,different geometries,different layer numbers,and different layer arrangements.展开更多
The properties of functionally graded(FG) cellular structures vary spatially, and the varying properties can meet the requirements of different working environments. In this study, we fabricated FG cellular structures...The properties of functionally graded(FG) cellular structures vary spatially, and the varying properties can meet the requirements of different working environments. In this study, we fabricated FG cellular structures with shape memory effect by 4D printing and evaluated the compressive performance and shape memory behavior of these structures with temperature through experimental analysis and finite element simulations. The results show that the maximum energy absorption gradually decreases but the compressive modulus gradually increases with increasing gradient parameters. Moreover, the finite element simulations also show that the compressive deformation mode of the structure shifts from uniform to non-uniform deformation with increasing gradient parameters. The compressive modulus and compressive strength of 4D printed FG structures decrease with increasing temperature due to the influence of the shape memory polymer, and they exhibit outstanding shape recovery capability under high-temperature stimulus. The proposed 4D printed FG structures with such responsiveness to stimulus shed light on the design of intelligent energy-absorbing devices that meet specific functional requirements.展开更多
It is of theoretical and engineering interest to establish a macro-mechanical constitutive model of the shape memory polymer (SMP), which includes the mechanical constitutive equation and the material parameter functi...It is of theoretical and engineering interest to establish a macro-mechanical constitutive model of the shape memory polymer (SMP), which includes the mechanical constitutive equation and the material parameter function, from the viewpoint of practical application. In this paper, a new three-dimensional macro-mechanical constitutive equation, which describes the mechanical behaviors associated with the shape memory effect of SMP, is developed based on solid mechanics and the viscoelasticity theorem. According to the results of the DMA test, a new material parameter function is established to express the relationship of the material parameters and temperature during the glass transition of SMP. The new macro-mechanical constitutive equation and material parameter function are used to numerically simulate the process producing the shape memory effect of SMP, which includes deforming at high temperature, stress freezing, unloading at low temperature and shape recovery. They are also used to investigate and analyze the influences of loading rate and temperature change rate on the thermo-mechanical behaviors of SMP. The numerical results and the comparisons with Zhou’s material parameter function and Tobushi’s mechanical constitutive equation illustrate that the proposed three-dimensional macro-mechanical constitutive model can effectively predict the thermo-mechanical behaviors of SMP under the state of complex stress.展开更多
Polylactic acid(PLA)is one of the most promising shape memory polymers with outstanding biocompatibility,while poly(ether ether ketone)(PEEK)is a special engineering plastic with excellent mechanical performance.In th...Polylactic acid(PLA)is one of the most promising shape memory polymers with outstanding biocompatibility,while poly(ether ether ketone)(PEEK)is a special engineering plastic with excellent mechanical performance.In this work,PEEK was selected to modify PLA,and a series of PLA blended with different PEEK contents(PLA/PEEK blends)were obtained.The effects of PEEK on thermodynamic,mechanical and shape memory properties of PLA/PEEK blends were investigated.The results showed that the thermal stabillity of the PL A/PEEK blend was improved with the PEEK content increase.The tensile strength reached the highest value of 20.6 MPa when the PEEK content was 10%.While the best shape memory performance occurred with the PEEK content of 15%,the shape recovery time was less than 2 s,and the shape fixation/recovery ratio was more than 99%.Furthermore,the programmable mimetic flower opening process was achieved by using PLA/PEEK blends with different PEEK content ratios.The above results indicated that the blend of an appropriate proportion of PEEK had positive effects on mechanical and deformation performances of PLA.展开更多
Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheat...Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheating,and heat accumulation during DED leads to the spatial heterogeneous distribution of columnar crystal and equiaxed crystal,a gradient distribution of Ni4Ti3 precipitates along the building direction,and preferential formation of Ni4Ti3 precipitates in the columnar zone.The austenite transformation finish temperature(Af)varies from-12.65℃(Z=33 mm)to 60.35℃(Z=10 mm),corresponding to tensile yield strength(σ0.2)changed from 120±30 MPa to 570±20 MPa,and functional properties changed from shape memory effect to superelasticity at room temperature.The sample in the Z=20.4 mm height has the best plasticity of 9.6%and the best recoverable strain of 4.2%.This work provided insights and guidelines for the spatial characterization of DEDed NiTi.展开更多
基金Project supported by the Iran National Science Foundation (INSF)(No.98027408)。
文摘This study presents a semi-analytical solution to describe the behavior of shape memory polymers(SMPs) based on the nonlinear thermo-visco-hyperelasticity which originates from the concepts of internal state variables and rational thermodynamics.This method is developed for the finite bending of multilayers in a dual-shape memory effect(SME) cycle.The layer number and layering order are investigated for two different SMPs and a hyperelastic material.In addition to the semi-analytical solution,the finite element simulation is performed to verify the predicted results,where the outcomes demonstrate the excellent accuracy of the proposed solution for predicting the behavior of the multilayer SMPs.Since this method has a much lower computational cost than the finite element method(FEM),it can be used as an effective tool to analyze the SMP behavior under different conditions,including different materials,different geometries,different layer numbers,and different layer arrangements.
基金supported by the National Natural Science Foundation of China (Grant Nos.12072094 and 12172106)。
文摘The properties of functionally graded(FG) cellular structures vary spatially, and the varying properties can meet the requirements of different working environments. In this study, we fabricated FG cellular structures with shape memory effect by 4D printing and evaluated the compressive performance and shape memory behavior of these structures with temperature through experimental analysis and finite element simulations. The results show that the maximum energy absorption gradually decreases but the compressive modulus gradually increases with increasing gradient parameters. Moreover, the finite element simulations also show that the compressive deformation mode of the structure shifts from uniform to non-uniform deformation with increasing gradient parameters. The compressive modulus and compressive strength of 4D printed FG structures decrease with increasing temperature due to the influence of the shape memory polymer, and they exhibit outstanding shape recovery capability under high-temperature stimulus. The proposed 4D printed FG structures with such responsiveness to stimulus shed light on the design of intelligent energy-absorbing devices that meet specific functional requirements.
基金supported by the National Natural Science Foundation of China (Grant No. 95505010)the National High Technology Research and Development Program of China (Grant No. 2006AA03Z109)+2 种基金the China Postdoctoral Science Foundation (Grant No. 20080430933)the Harbin Talent Foundation of Scientific and Technical Innovation (Grant No.RC2009QN017046)the Fundamental Research Funds for Central Universities (Grant No. HEUCF: Z1004).
文摘It is of theoretical and engineering interest to establish a macro-mechanical constitutive model of the shape memory polymer (SMP), which includes the mechanical constitutive equation and the material parameter function, from the viewpoint of practical application. In this paper, a new three-dimensional macro-mechanical constitutive equation, which describes the mechanical behaviors associated with the shape memory effect of SMP, is developed based on solid mechanics and the viscoelasticity theorem. According to the results of the DMA test, a new material parameter function is established to express the relationship of the material parameters and temperature during the glass transition of SMP. The new macro-mechanical constitutive equation and material parameter function are used to numerically simulate the process producing the shape memory effect of SMP, which includes deforming at high temperature, stress freezing, unloading at low temperature and shape recovery. They are also used to investigate and analyze the influences of loading rate and temperature change rate on the thermo-mechanical behaviors of SMP. The numerical results and the comparisons with Zhou’s material parameter function and Tobushi’s mechanical constitutive equation illustrate that the proposed three-dimensional macro-mechanical constitutive model can effectively predict the thermo-mechanical behaviors of SMP under the state of complex stress.
基金supported by the Project of National Key Research and Development Program of China(2018YFB1105100,2018YFC2001300 and 2018YFA0703300)the National Natural Science Foundation of China(Grant Nos.51822504,51675223 and 91848204)+4 种基金the Joint Foundation for Equipment Preresearch of Ministry of Education(2018G944.00084)the Key Scientific and Technological Project of Jilin Province(20180201051GX)the Program for JLU Science and Technology Innovative Research Team(2017TD-04)the National Postdoctoral Program for Innovative Talents(BX20180126)the China Postdoctoral Science Foundation(2018M641769).
文摘Polylactic acid(PLA)is one of the most promising shape memory polymers with outstanding biocompatibility,while poly(ether ether ketone)(PEEK)is a special engineering plastic with excellent mechanical performance.In this work,PEEK was selected to modify PLA,and a series of PLA blended with different PEEK contents(PLA/PEEK blends)were obtained.The effects of PEEK on thermodynamic,mechanical and shape memory properties of PLA/PEEK blends were investigated.The results showed that the thermal stabillity of the PL A/PEEK blend was improved with the PEEK content increase.The tensile strength reached the highest value of 20.6 MPa when the PEEK content was 10%.While the best shape memory performance occurred with the PEEK content of 15%,the shape recovery time was less than 2 s,and the shape fixation/recovery ratio was more than 99%.Furthermore,the programmable mimetic flower opening process was achieved by using PLA/PEEK blends with different PEEK content ratios.The above results indicated that the blend of an appropriate proportion of PEEK had positive effects on mechanical and deformation performances of PLA.
基金the financial support of the Hunan Innovation Platform and Talent Plan(2022RC3033)Natural Science Foundation of Shandong Province(ZR2020ZD04)Ganzhou Science and Technology Planning Project(Grant No.Ganshikefa[2019]60)。
文摘Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheating,and heat accumulation during DED leads to the spatial heterogeneous distribution of columnar crystal and equiaxed crystal,a gradient distribution of Ni4Ti3 precipitates along the building direction,and preferential formation of Ni4Ti3 precipitates in the columnar zone.The austenite transformation finish temperature(Af)varies from-12.65℃(Z=33 mm)to 60.35℃(Z=10 mm),corresponding to tensile yield strength(σ0.2)changed from 120±30 MPa to 570±20 MPa,and functional properties changed from shape memory effect to superelasticity at room temperature.The sample in the Z=20.4 mm height has the best plasticity of 9.6%and the best recoverable strain of 4.2%.This work provided insights and guidelines for the spatial characterization of DEDed NiTi.
