In this paper,a multiscale model is developed for the mass functionally graded(FG)beam-fluid system to investigate its static and dynamic responses based on 3D printed porous beam free vibration tests,which are determ...In this paper,a multiscale model is developed for the mass functionally graded(FG)beam-fluid system to investigate its static and dynamic responses based on 3D printed porous beam free vibration tests,which are determined by two aspects.At the microstructural level,the gradient variation is realized by arbitrary distribution of matrix pores,and the effective moduli under specific distribution are obtained using the micromechanics homogenization theory.In the meantime,at the structural level,the mechanical responses of FG porous beams subjected to mass loading are considered in a static fluid environment.Then,the explicit expressions of local finite-element(FE)expressions corresponding to the static and dynamic responses are given in the appendices.The present results are validated against numerical and experimental results from the literature and mechanical tests of 3D printed structures,with good agreement generally obtained,giving credence to the present model.On this basis,a comprehensive parametric study is carried out,with a particular focus on the effects of boundary conditions,fluid density,and slenderness ratio on the bending and vibration of FG beams with several different gradations.展开更多
Aimed at the problem of store separation from internal cavity,this paper innovatively puts forward a separation scheme of using lateral jet to assist store safe separation.The jet ensures that the store is continuousl...Aimed at the problem of store separation from internal cavity,this paper innovatively puts forward a separation scheme of using lateral jet to assist store safe separation.The jet ensures that the store is continuously subjected to down head moment during separation,so as to ensure safe separation.The wind tunnel free drop test technique with lateral jet is established,which can ensure that there is no support interference in the motion process of the store and more truly simulate the motion of the store.The feasibility of the new separation scheme is proved by wind tunnel test.The test shows that the new scheme can also change the more dangerous state into a safe state.Through the analysis of the test data,the pitching moment coefficients of the store under different pressures in the high-pressure cylinder are obtained,and the effects of aircraft and cavity on the pitching moment of the store are obtained.The 3 stages of store passing through cavity shock wave are found.The results show that the lateral jet provides the store with continuous head down moment,and makes the store overcome the head up moment caused by the shock wave in front of the cavity,so as to ensure the safety of separation.展开更多
着重研究了机械冲击和应力对无铅BGA 封装焊点可靠性的影响,介绍了BGA 封装的可靠性力学试验(跌落、弯曲试验)及其分析方法。通过对力学试验中失效焊点的分析以及借助A N S Y S 模拟工具,找出引起失效的根本原因,为开发性能更好、高可...着重研究了机械冲击和应力对无铅BGA 封装焊点可靠性的影响,介绍了BGA 封装的可靠性力学试验(跌落、弯曲试验)及其分析方法。通过对力学试验中失效焊点的分析以及借助A N S Y S 模拟工具,找出引起失效的根本原因,为开发性能更好、高可靠性的无铅材料、改进无铅工艺提供依据。展开更多
为研究我国钢轨固定式闪光焊接头静弯试验的极限破断载荷及挠度水平,参考欧洲相关标准,分析了128个焊态接头的静弯试验结果;同时进行了160个接头的落锤试验,分析了静弯和落锤试验结果的相关性。试验结果表明:参考欧洲标准,96.9%的接头...为研究我国钢轨固定式闪光焊接头静弯试验的极限破断载荷及挠度水平,参考欧洲相关标准,分析了128个焊态接头的静弯试验结果;同时进行了160个接头的落锤试验,分析了静弯和落锤试验结果的相关性。试验结果表明:参考欧洲标准,96.9%的接头正压载荷>1 600 k N不断,挠度全部>20 mm;96.9%的接头反压载荷>1 500 k N不断;相同条件下的钢轨焊接接头落锤和静弯试验结果相关性不明显;灰斑是导致接头静弯性能降低的主要原因;顶锻量>11.5 mm的接头其静弯性能很好,而落锤性能较差;U71Mn轨出现灰斑的概率远大于U75V轨,但U75V轨的灰斑面积通常更大。展开更多
基金supported by the National Key Research and Development Program of China(No.2020YFA0711700)the National Natural Science Foundation of China(No.12322206,No.52378158,No.12302205)ZJU-ZCCC Institute of Collaborative Innovation(No.ZDJG2021002).
文摘In this paper,a multiscale model is developed for the mass functionally graded(FG)beam-fluid system to investigate its static and dynamic responses based on 3D printed porous beam free vibration tests,which are determined by two aspects.At the microstructural level,the gradient variation is realized by arbitrary distribution of matrix pores,and the effective moduli under specific distribution are obtained using the micromechanics homogenization theory.In the meantime,at the structural level,the mechanical responses of FG porous beams subjected to mass loading are considered in a static fluid environment.Then,the explicit expressions of local finite-element(FE)expressions corresponding to the static and dynamic responses are given in the appendices.The present results are validated against numerical and experimental results from the literature and mechanical tests of 3D printed structures,with good agreement generally obtained,giving credence to the present model.On this basis,a comprehensive parametric study is carried out,with a particular focus on the effects of boundary conditions,fluid density,and slenderness ratio on the bending and vibration of FG beams with several different gradations.
基金supported by the National Natural Science Foundation of China(Nos.U21B2054,11772317)supported by the Open Fund of Key Laboratory of Icing and Anti/Deicing,China(No.IADL20200408).
文摘Aimed at the problem of store separation from internal cavity,this paper innovatively puts forward a separation scheme of using lateral jet to assist store safe separation.The jet ensures that the store is continuously subjected to down head moment during separation,so as to ensure safe separation.The wind tunnel free drop test technique with lateral jet is established,which can ensure that there is no support interference in the motion process of the store and more truly simulate the motion of the store.The feasibility of the new separation scheme is proved by wind tunnel test.The test shows that the new scheme can also change the more dangerous state into a safe state.Through the analysis of the test data,the pitching moment coefficients of the store under different pressures in the high-pressure cylinder are obtained,and the effects of aircraft and cavity on the pitching moment of the store are obtained.The 3 stages of store passing through cavity shock wave are found.The results show that the lateral jet provides the store with continuous head down moment,and makes the store overcome the head up moment caused by the shock wave in front of the cavity,so as to ensure the safety of separation.
文摘为研究我国钢轨固定式闪光焊接头静弯试验的极限破断载荷及挠度水平,参考欧洲相关标准,分析了128个焊态接头的静弯试验结果;同时进行了160个接头的落锤试验,分析了静弯和落锤试验结果的相关性。试验结果表明:参考欧洲标准,96.9%的接头正压载荷>1 600 k N不断,挠度全部>20 mm;96.9%的接头反压载荷>1 500 k N不断;相同条件下的钢轨焊接接头落锤和静弯试验结果相关性不明显;灰斑是导致接头静弯性能降低的主要原因;顶锻量>11.5 mm的接头其静弯性能很好,而落锤性能较差;U71Mn轨出现灰斑的概率远大于U75V轨,但U75V轨的灰斑面积通常更大。
