Aerogels,as competitive thermal insulating sub-stitutes,are seriously plagued by the deterioration of mechanical and insulating properties at high temperatures as well as energy-consuming drying methods.Herein,organic...Aerogels,as competitive thermal insulating sub-stitutes,are seriously plagued by the deterioration of mechanical and insulating properties at high temperatures as well as energy-consuming drying methods.Herein,organic-inorganic biomass composite aerogels with ablative properties are fabricated by a straightforward and environmentally friendly ambient-pressure-dried method,utilizing gellan gum,hollow glass microspheres,and phenolic resin.This method uses air bubbles as pore templates for constructing aerogels without additional modification or organic solvent consumption.The robust cross-linking networks formed within the aerogels significantly mitigate volume shrinkage induced by surface tension during mild drying while endowing the aerogels with a high modulus of 37.8 MPa and robust resistance to diverse rigors.Remarkably,upon exposure to high temperatures or fire,it spontaneously transforms into ceramic-like hybrid char with low volume shrinkage,continuous pore structures,and high stability.The ablative property of these aerogels enables them to maintain a high modulus of 8.22 MPa even after being treated at 900℃,while also exhibiting excellent high-temperature insulation,flame retardance,and smoke suppression.This work provides a facile and ecofriendly way for developing advanced hybrid biomass aerogels that combine high stiffness with superior thermal protection across a wide temperature range.展开更多
In order to achieve large tolerance capture and high stiffness connection for space payload operations,a Chinese large-scale space end-effector (EER) was developed.Three flexible steel cables were adopted to capture t...In order to achieve large tolerance capture and high stiffness connection for space payload operations,a Chinese large-scale space end-effector (EER) was developed.Three flexible steel cables were adopted to capture the payload with large capture allowance.Ball screw transmission mechanism and plane shape-constraint four bar linkage mechanism were utilized to connect the payload with high stiffness.The experiments show that capture tolerances in X,Y,Z,Pitch,Yaw,Roll directions are 100 mm,100 mm,120 mm,10.5°,10.5°,12°,respectively.The maximum connection stiffness is 4 800 N·m.The end-effector could meet the requirements for space large tolerance capture and high stiffness connection in the future.展开更多
This paper presents a novel four degrees of freedom(DOF) parallel mechanism with the closed-loop limbs, which includes two translational(2 T) DOF and two rotational(2 R) DOF. By connecting the proposed parallel mechan...This paper presents a novel four degrees of freedom(DOF) parallel mechanism with the closed-loop limbs, which includes two translational(2 T) DOF and two rotational(2 R) DOF. By connecting the proposed parallel mechanism with the guide rail in series,the 5-DOF hybrid robot system is obtained, which can be applied for the composite material tape laying in aerospace industry. The analysis in this paper mainly focuses on the parallel module of the hybrid robot system. First, the freedom of the proposed parallel mechanism is calculated based on the screw theory. Then, according to the closed-loop vector equation, the inverse kinematics and Jacobian matrix of the parallel mechanism are carried out. Next, the workspace stiffness and dexterity analysis of the parallel mechanism are investigated based on the constraint equations, static stiffness matrix and Jacobian condition number. Finally, the correctness of the inverse kinematics and the high stiffness of the parallel mechanism are verified by the kinematics and stiffness simulation analysis, which lays a foundation for the automatic composite material tape laying.展开更多
Protein-based hydrogels are promising materials for biomedical and materials science applications.However,engineer-ing hydrogels with both high stiffness and high toughness,a key requirement for many applications,rema...Protein-based hydrogels are promising materials for biomedical and materials science applications.However,engineer-ing hydrogels with both high stiffness and high toughness,a key requirement for many applications,remains challenging.Recently,by using the denatured crosslinking method,we developed highly stiff and tough protein hydrogels based on the polyprotein(FL)8 via introducing chain entanglements into the hydrogel network,which allow for stiffening the hydrogel without sacrificing toughness.These hydrogels exhibited a Young’s modulus of∼0.7 MPa and breaking strain of∼100%in tensile tests.To further enhance their stretchability and toughness,here we report the engineering of a protein/alginate hybrid hydrogel,in which the protein and alginate networks are covalently joined.Alginate was chemically modified with tyramine to introduce phenol groups,allowing the modified alginate to be photochemically crosslinked together with the polyprotein(FL)8 to form a hybrid network hydrogel.Using calcium-mediated ionic crosslinking,we demonstrated the feasibility to tune the Young’s modulus and breaking strain of these hydrogels by controlling the degree of tyramine modification of alginate.Our results showed that incorporating noncovalent ionic crosslinking into the hydrogel network increased the hydrogel’s stretchability from∼100%to over 200%without compromising stiffness,significantly improving the hydrogel’s toughness.This work expands the mechanical tunability of protein hydrogels and the repertoire of strategies for engineering hydrogels with a broad range of mechanical properties.展开更多
基金support by the National Natural Science Foundation of China(22205184,U22A20150,and 22475177)the Sichuan Science and Technology Program(2023NSFSC1955)+1 种基金the Hunan Provincial Key Research and Development Program(2023GK2090)the Hunan Provincial Science and Technology Innovation Program Project(2022RC1079)are sincerely acknowledged.
文摘Aerogels,as competitive thermal insulating sub-stitutes,are seriously plagued by the deterioration of mechanical and insulating properties at high temperatures as well as energy-consuming drying methods.Herein,organic-inorganic biomass composite aerogels with ablative properties are fabricated by a straightforward and environmentally friendly ambient-pressure-dried method,utilizing gellan gum,hollow glass microspheres,and phenolic resin.This method uses air bubbles as pore templates for constructing aerogels without additional modification or organic solvent consumption.The robust cross-linking networks formed within the aerogels significantly mitigate volume shrinkage induced by surface tension during mild drying while endowing the aerogels with a high modulus of 37.8 MPa and robust resistance to diverse rigors.Remarkably,upon exposure to high temperatures or fire,it spontaneously transforms into ceramic-like hybrid char with low volume shrinkage,continuous pore structures,and high stability.The ablative property of these aerogels enables them to maintain a high modulus of 8.22 MPa even after being treated at 900℃,while also exhibiting excellent high-temperature insulation,flame retardance,and smoke suppression.This work provides a facile and ecofriendly way for developing advanced hybrid biomass aerogels that combine high stiffness with superior thermal protection across a wide temperature range.
基金Project(2006AA04Z228) supported by the National High Technology Research and Development Program of China
文摘In order to achieve large tolerance capture and high stiffness connection for space payload operations,a Chinese large-scale space end-effector (EER) was developed.Three flexible steel cables were adopted to capture the payload with large capture allowance.Ball screw transmission mechanism and plane shape-constraint four bar linkage mechanism were utilized to connect the payload with high stiffness.The experiments show that capture tolerances in X,Y,Z,Pitch,Yaw,Roll directions are 100 mm,100 mm,120 mm,10.5°,10.5°,12°,respectively.The maximum connection stiffness is 4 800 N·m.The end-effector could meet the requirements for space large tolerance capture and high stiffness connection in the future.
基金by Fundamental Research Funds for the Central Universities(No.2018JBZ007).
文摘This paper presents a novel four degrees of freedom(DOF) parallel mechanism with the closed-loop limbs, which includes two translational(2 T) DOF and two rotational(2 R) DOF. By connecting the proposed parallel mechanism with the guide rail in series,the 5-DOF hybrid robot system is obtained, which can be applied for the composite material tape laying in aerospace industry. The analysis in this paper mainly focuses on the parallel module of the hybrid robot system. First, the freedom of the proposed parallel mechanism is calculated based on the screw theory. Then, according to the closed-loop vector equation, the inverse kinematics and Jacobian matrix of the parallel mechanism are carried out. Next, the workspace stiffness and dexterity analysis of the parallel mechanism are investigated based on the constraint equations, static stiffness matrix and Jacobian condition number. Finally, the correctness of the inverse kinematics and the high stiffness of the parallel mechanism are verified by the kinematics and stiffness simulation analysis, which lays a foundation for the automatic composite material tape laying.
基金supported by the Natural Sciences and Engineering Research Council of Canada.
文摘Protein-based hydrogels are promising materials for biomedical and materials science applications.However,engineer-ing hydrogels with both high stiffness and high toughness,a key requirement for many applications,remains challenging.Recently,by using the denatured crosslinking method,we developed highly stiff and tough protein hydrogels based on the polyprotein(FL)8 via introducing chain entanglements into the hydrogel network,which allow for stiffening the hydrogel without sacrificing toughness.These hydrogels exhibited a Young’s modulus of∼0.7 MPa and breaking strain of∼100%in tensile tests.To further enhance their stretchability and toughness,here we report the engineering of a protein/alginate hybrid hydrogel,in which the protein and alginate networks are covalently joined.Alginate was chemically modified with tyramine to introduce phenol groups,allowing the modified alginate to be photochemically crosslinked together with the polyprotein(FL)8 to form a hybrid network hydrogel.Using calcium-mediated ionic crosslinking,we demonstrated the feasibility to tune the Young’s modulus and breaking strain of these hydrogels by controlling the degree of tyramine modification of alginate.Our results showed that incorporating noncovalent ionic crosslinking into the hydrogel network increased the hydrogel’s stretchability from∼100%to over 200%without compromising stiffness,significantly improving the hydrogel’s toughness.This work expands the mechanical tunability of protein hydrogels and the repertoire of strategies for engineering hydrogels with a broad range of mechanical properties.
