Glass transition plays a critical role to determine the dynamic behaviors of amorphous shape memory polymers(SMPs).However,the fundamental relationships between shape memory effect(SME)and dynamic glass transition hav...Glass transition plays a critical role to determine the dynamic behaviors of amorphous shape memory polymers(SMPs).However,the fundamental relationships between shape memory effect(SME)and dynamic glass transition have not been well understood,even though this topic has been studied for decades.In this study,we apply a mean-square displacement function of Adam-Gibbs(AG)domain size model to explore metastable glass transition between normal glass state and rubbery state of amorphous SMPs,based on both mode-coupling theory and mean-field model.A statistic viscosity equation is formulated to study the dynamic glass transition of metastable AG domains in an amorphous SMP.A dynamically spinodal model is also developed to connect dynamic glass transitions to thermomechanical processes,based on statistic viscosity equation and phase transition model.Furthermore,using the spinodal models,multiple shape memory behaviors have been predicted for amorphous SMPs with dual-,triple-and quadruple-SMEs,resulted from their different routes of themomechanical evolutions.Finally,the proposed models are verified using the experimental data reported in literature.展开更多
Electrospun fibers of shape memory triethoxysilane-terminated poly(epsilon-caprolactone)(PCL-TES)loaded with bioactive glasses(BG)are here presented.Unloaded PCL-TES,as well as PCL/BG nanocomposite fibers,are also con...Electrospun fibers of shape memory triethoxysilane-terminated poly(epsilon-caprolactone)(PCL-TES)loaded with bioactive glasses(BG)are here presented.Unloaded PCL-TES,as well as PCL/BG nanocomposite fibers,are also considered for comparison.It is proposed that hydrolysis and condensation reactions take place between triethoxysilane groups of the polymer and the silanol groups at the BG particle surface,thus generating additional crosslinking points with respect to those present in the PCL-TES system.The as-spun PCL-TES/BG fibers display excellent shape memory properties,in terms of shape fixity and shape recovery ratios,without the need of a thermal crosslinking treatment.BG particles confer in vitro bioactivity to PCL-based nanocomposite fibers and favor the precipitation of hydroxycarbonate apatite on the fiber surface.Preliminary cytocompatibility tests demonstrate that the addition of BG particles to PCL-based polymer does not inhibit ST-2 cell viability.This novel approach of using bioactive glasses not only for their biological properties,but also for the enhancement of shape memory properties of PCL-based polymers,widens the versatility and suitability of the obtained composite fibers for a huge portfolio of biomedical applications.展开更多
Bird strike studies on typical aluminium leading edges of the Horizontal Tail (HT) with and without Glass Fibre Shape Memory Polymer (GF-SMP) layers are carried out. A one-fifth scaled model of HT is designed and fabr...Bird strike studies on typical aluminium leading edges of the Horizontal Tail (HT) with and without Glass Fibre Shape Memory Polymer (GF-SMP) layers are carried out. A one-fifth scaled model of HT is designed and fabricated. The parameters like bird dimension and energy requirements are accordingly scaled to conduct the bird strike tests. Two leading-edge components have been prepared, namely one with AL 2024-T3 aluminium alloy and the other specimen of the same dimension and material, additionally having GF-SMP composite layers inside the metallic leading edge, in order to enhance its impact resistance. Bird strike experiments are performed on both the specimens, impacting at the centre of the leading edge in the nose tip region with an impact velocity of 115 m/s. The test component is instrumented with linear post-yield strain gauges on the top side and the PZT sensors on the bottom. Furthermore, the impact scenario is monitored using a high-speed camera at 7000 fps. The bird strike event is simulated by an equation of state model, in which the mass of the bird is idealized using smooth particle hydrodynamics element in PAMCRASH<sup>?</sup><sup> </sup>explicit solver. The strain magnitude and its pattern including time duration are found to be in a good correlation between test and simulation. Key metrics are evaluated to devise an SHM scheme for the load and impact event monitoring using strain gauges and PZT sensors. GF-SMP layers have improved the impact resistance of the aluminium leading edge which is certainly encouraging towards finding a novel solution for the high-velocity impact.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11725208,12172107)the International Exchange Grant(Grant No.201078)。
文摘Glass transition plays a critical role to determine the dynamic behaviors of amorphous shape memory polymers(SMPs).However,the fundamental relationships between shape memory effect(SME)and dynamic glass transition have not been well understood,even though this topic has been studied for decades.In this study,we apply a mean-square displacement function of Adam-Gibbs(AG)domain size model to explore metastable glass transition between normal glass state and rubbery state of amorphous SMPs,based on both mode-coupling theory and mean-field model.A statistic viscosity equation is formulated to study the dynamic glass transition of metastable AG domains in an amorphous SMP.A dynamically spinodal model is also developed to connect dynamic glass transitions to thermomechanical processes,based on statistic viscosity equation and phase transition model.Furthermore,using the spinodal models,multiple shape memory behaviors have been predicted for amorphous SMPs with dual-,triple-and quadruple-SMEs,resulted from their different routes of themomechanical evolutions.Finally,the proposed models are verified using the experimental data reported in literature.
文摘Electrospun fibers of shape memory triethoxysilane-terminated poly(epsilon-caprolactone)(PCL-TES)loaded with bioactive glasses(BG)are here presented.Unloaded PCL-TES,as well as PCL/BG nanocomposite fibers,are also considered for comparison.It is proposed that hydrolysis and condensation reactions take place between triethoxysilane groups of the polymer and the silanol groups at the BG particle surface,thus generating additional crosslinking points with respect to those present in the PCL-TES system.The as-spun PCL-TES/BG fibers display excellent shape memory properties,in terms of shape fixity and shape recovery ratios,without the need of a thermal crosslinking treatment.BG particles confer in vitro bioactivity to PCL-based nanocomposite fibers and favor the precipitation of hydroxycarbonate apatite on the fiber surface.Preliminary cytocompatibility tests demonstrate that the addition of BG particles to PCL-based polymer does not inhibit ST-2 cell viability.This novel approach of using bioactive glasses not only for their biological properties,but also for the enhancement of shape memory properties of PCL-based polymers,widens the versatility and suitability of the obtained composite fibers for a huge portfolio of biomedical applications.
文摘Bird strike studies on typical aluminium leading edges of the Horizontal Tail (HT) with and without Glass Fibre Shape Memory Polymer (GF-SMP) layers are carried out. A one-fifth scaled model of HT is designed and fabricated. The parameters like bird dimension and energy requirements are accordingly scaled to conduct the bird strike tests. Two leading-edge components have been prepared, namely one with AL 2024-T3 aluminium alloy and the other specimen of the same dimension and material, additionally having GF-SMP composite layers inside the metallic leading edge, in order to enhance its impact resistance. Bird strike experiments are performed on both the specimens, impacting at the centre of the leading edge in the nose tip region with an impact velocity of 115 m/s. The test component is instrumented with linear post-yield strain gauges on the top side and the PZT sensors on the bottom. Furthermore, the impact scenario is monitored using a high-speed camera at 7000 fps. The bird strike event is simulated by an equation of state model, in which the mass of the bird is idealized using smooth particle hydrodynamics element in PAMCRASH<sup>?</sup><sup> </sup>explicit solver. The strain magnitude and its pattern including time duration are found to be in a good correlation between test and simulation. Key metrics are evaluated to devise an SHM scheme for the load and impact event monitoring using strain gauges and PZT sensors. GF-SMP layers have improved the impact resistance of the aluminium leading edge which is certainly encouraging towards finding a novel solution for the high-velocity impact.
