In rotationally extruded fittings,high-density polyethylene(HDPE)pipes prepared using conventional processing methods often suffer from poor pressure resistance and low toughness.This study introduces an innovative ro...In rotationally extruded fittings,high-density polyethylene(HDPE)pipes prepared using conventional processing methods often suffer from poor pressure resistance and low toughness.This study introduces an innovative rotary shear system(RSS)to address these deficiencies through controlled mandrel rotation and cooling rates.We successfully prepared self-reinforced HDPE pipes with a three-layer structure combining spherical and shish-kebab crystals.Rotational processing aligned the molecular chains in the ring direction and formed shish-kebab crystals.As a result,the annular tensile strength of the rotationally processed three-layer shish-kebab structure(TSK)pipe increased from 26.7 MPa to 76.3 MPa,an enhancement of 185.8%.Notably,while maintaining excellent tensile strength(73.4 MPa),the elongation at break of the spherulite shishkebab spherulite(SKS)tubes was improved to 50.1%,as compared to 33.8%in the case of shish-kebab spherulite shish-kebab(KSK)tubes.This improvement can be attributed to the changes in the micro-morphology and polymer structure within the SKS tubes,specifically due to the formation of small-sized shish-kebab crystals and the low degrees of interlocking.In addition,2D-SAXS analysis revealed that KSK tubes have higher tensile strength due to smaller crystal sizes and larger shish dimensions,forming dense interlocking structures.In contrast,the SKS and TSK tubes had thicker amorphous regions and smaller shish sizes,resulting in reduced interlocking and mechanical performance.展开更多
The structural circumferential periodicity of inertial excitation produced by concentrated mass was utilized to establish the mathematical model of thin circular plate carrying eccentric concentrated mass and to analy...The structural circumferential periodicity of inertial excitation produced by concentrated mass was utilized to establish the mathematical model of thin circular plate carrying eccentric concentrated mass and to analyze its transverse vibration. The fundamental frequency coefficient, natural frequency and mode shape function are determined by this method. A clamped thin circular plate was taken as an example to study the mass effect on the vibrating system.Comparison between the present results and published ones exhibits excellent agreement, which shows that the analytical method in this paper can be used to predict the transverse vibration parameters accurately.展开更多
The presence of tip clearance not only ensures the structural safety of compression system in aero-engines,but also exerts significant negative impacts on internal flow stability due to the leakage flow.Previous studi...The presence of tip clearance not only ensures the structural safety of compression system in aero-engines,but also exerts significant negative impacts on internal flow stability due to the leakage flow.Previous studies by our team have shown that the induced shock resulting from the circumferentially diverging clearance structure has remarkable effect on suppressing leakage flow in transonic compressor rotors.Therefore,the inherent correlations between the characteristics of induced shock and leakage flow are further elucidated in this paper,and the influencing rules of induced shock wave on tip flow characteristic of transonic rotors are summarized as well.The results demonstrate that the enhancement of inhibitory effects on leakage flow and increase in the rotor’s stall margin can be achieved by both intensifying the induced shock wave and shifting its circumferential position away from the suction side edge of blade tip,which is possible by adjusting the circumferential expansion ratio of diverging clearance.The stall margin of the transonic rotor exhibits three distinct variations as the circumferential expansion ratio of the diverging clearance increases monotonically,and a maximum improvement of over 8.9%can be achieved through feature variations of the induced shock wave.The insufficient acceleration of the supersonic leakage jet flow over blade tip due to a smaller circumferential expansion ratio poses challenges in inducing a shock wave,resulting in an increased blockage effect and reduced stall margin of rotor.Meanwhile,excessive circumferential expansion ratio results in a pronounced adverse pressure gradient originating from the induced shock wave,leading to leakage flow separation at the blade tip and consequently weakening the intensity of induced shock waves while shifting its circumferential position towards the blade tip.As a result,further increasing the circumferential expansion ratio does not yield an enhanced rotor stall margin but instead exhibits a slight decreasing trend.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52373045 and 52033005).
文摘In rotationally extruded fittings,high-density polyethylene(HDPE)pipes prepared using conventional processing methods often suffer from poor pressure resistance and low toughness.This study introduces an innovative rotary shear system(RSS)to address these deficiencies through controlled mandrel rotation and cooling rates.We successfully prepared self-reinforced HDPE pipes with a three-layer structure combining spherical and shish-kebab crystals.Rotational processing aligned the molecular chains in the ring direction and formed shish-kebab crystals.As a result,the annular tensile strength of the rotationally processed three-layer shish-kebab structure(TSK)pipe increased from 26.7 MPa to 76.3 MPa,an enhancement of 185.8%.Notably,while maintaining excellent tensile strength(73.4 MPa),the elongation at break of the spherulite shishkebab spherulite(SKS)tubes was improved to 50.1%,as compared to 33.8%in the case of shish-kebab spherulite shish-kebab(KSK)tubes.This improvement can be attributed to the changes in the micro-morphology and polymer structure within the SKS tubes,specifically due to the formation of small-sized shish-kebab crystals and the low degrees of interlocking.In addition,2D-SAXS analysis revealed that KSK tubes have higher tensile strength due to smaller crystal sizes and larger shish dimensions,forming dense interlocking structures.In contrast,the SKS and TSK tubes had thicker amorphous regions and smaller shish sizes,resulting in reduced interlocking and mechanical performance.
基金Supported by the National High Technology Research and Development Program of China("863"Program,No.2012AA1117064)
文摘The structural circumferential periodicity of inertial excitation produced by concentrated mass was utilized to establish the mathematical model of thin circular plate carrying eccentric concentrated mass and to analyze its transverse vibration. The fundamental frequency coefficient, natural frequency and mode shape function are determined by this method. A clamped thin circular plate was taken as an example to study the mass effect on the vibrating system.Comparison between the present results and published ones exhibits excellent agreement, which shows that the analytical method in this paper can be used to predict the transverse vibration parameters accurately.
基金the General Program of National Natural Science Foundation of China(Grant No.52076124)the Joint Fund of the National Natural Science Foundation of China(No.U2441278).
文摘The presence of tip clearance not only ensures the structural safety of compression system in aero-engines,but also exerts significant negative impacts on internal flow stability due to the leakage flow.Previous studies by our team have shown that the induced shock resulting from the circumferentially diverging clearance structure has remarkable effect on suppressing leakage flow in transonic compressor rotors.Therefore,the inherent correlations between the characteristics of induced shock and leakage flow are further elucidated in this paper,and the influencing rules of induced shock wave on tip flow characteristic of transonic rotors are summarized as well.The results demonstrate that the enhancement of inhibitory effects on leakage flow and increase in the rotor’s stall margin can be achieved by both intensifying the induced shock wave and shifting its circumferential position away from the suction side edge of blade tip,which is possible by adjusting the circumferential expansion ratio of diverging clearance.The stall margin of the transonic rotor exhibits three distinct variations as the circumferential expansion ratio of the diverging clearance increases monotonically,and a maximum improvement of over 8.9%can be achieved through feature variations of the induced shock wave.The insufficient acceleration of the supersonic leakage jet flow over blade tip due to a smaller circumferential expansion ratio poses challenges in inducing a shock wave,resulting in an increased blockage effect and reduced stall margin of rotor.Meanwhile,excessive circumferential expansion ratio results in a pronounced adverse pressure gradient originating from the induced shock wave,leading to leakage flow separation at the blade tip and consequently weakening the intensity of induced shock waves while shifting its circumferential position towards the blade tip.As a result,further increasing the circumferential expansion ratio does not yield an enhanced rotor stall margin but instead exhibits a slight decreasing trend.
