为研究界面黏着,利用表面力仪在高离子强度电解质水溶液中测量负电云母表面之间的法向力.在纯水中,因范德华吸引,两表面跳跃至直接接触(间距0A),分离两表面时测得界面黏着力为-46.7 m N/m.在0.1 mol/L K_(2)SO_(4)中,因K^(+)离子牢固吸...为研究界面黏着,利用表面力仪在高离子强度电解质水溶液中测量负电云母表面之间的法向力.在纯水中,因范德华吸引,两表面跳跃至直接接触(间距0A),分离两表面时测得界面黏着力为-46.7 m N/m.在0.1 mol/L K_(2)SO_(4)中,因K^(+)离子牢固吸附于云母,表面间距稳定于5A,黏着力仅-2.9 m N/m;在0.1 mol/L Ca(NO_(3))_(2)中,云母表面吸附的Ca^(2+)离子产生显著短程水合排斥,但在较低载荷下解吸附,导致两表面直接接触,黏着力高达-40.7 m N/m.加入Ca(OH)_(2)于0.1 mol/L K_(2)SO_(4)仅产生微弱短程排斥,黏着状态几乎与纯K_(2)SO_(4)水溶液中相同.聚电解质PCE从0.1 mol/L K_(2)SO_(4)中吸附于云母表面且诱导远程空间位阻排斥,但在中等载荷下解吸附,导致两表面轻度黏着(间距5A);牢固吸附于云母表面的PNS高分子薄膜之间的空间位阻完全阻止云母界面黏着.牢固吸附是电解质吸附层稳定阻止界面黏着的必要条件.展开更多
A line contact model of elastic coated solids is presented based on the influence coefficients(ICs) of surface displacement and stresses of coating-substrate system and the traditional contact model. The ICs of displa...A line contact model of elastic coated solids is presented based on the influence coefficients(ICs) of surface displacement and stresses of coating-substrate system and the traditional contact model. The ICs of displacement and stresses are obtained from their corresponding frequency response functions(FRF) by using a conversion method based on fast Fourier transformation(FFT). The contact pressure and the stress field in the subsurface are obtained by employing conjugate gradient method(CGM) and discrete convolution fast Fourier transformation(DC-FFT). Comparison of the contact pressure and subsurface stresses obtained by the numerical method with the exact analytical solutions for Hertz contact is conducted, and the results show that the numerical solution has a very high accuracy and verify the validity of the contact model. The effect of the stiffness and thickness of coatings is further numerically studied. The result shows that the effects on contact pressure and contact width are opposite for hard and soft coatings and are intensified with the increase of coating thickness; the locations of crack initiation and propagation are different for soft and hard coatings; the risk of cracks and delaminations of coatings can be brought down by improving the lubrication condition or optimizing the non-dimensional parameter h/bh. This research offers a tool to numerically analyze the problem of elastic coated solids in line contact and make the blindness and randomness of trial-type coating design less.展开更多
针对国Ⅵ排放标准,对某柴油机用EGR(排气再循环,Exhaust Gas Recirculation)冷却器进行了换热性能分析与优化。首先通过仿真分析对比打坑管式与内翅片式模型的温度场、压力场和换热效率,确定内翅片式模型各项指标均有较明显优势;为进一...针对国Ⅵ排放标准,对某柴油机用EGR(排气再循环,Exhaust Gas Recirculation)冷却器进行了换热性能分析与优化。首先通过仿真分析对比打坑管式与内翅片式模型的温度场、压力场和换热效率,确定内翅片式模型各项指标均有较明显优势;为进一步满足设计要求,同时尽量减小气侧压差,又对翅片波纹幅值进行优化,确定当幅值A=0.9 mm时,仿真换热效率为86.43%。最后进行了样件制造以及换热性能实验台测试,实测换热效率为88.55%,实验与仿真数据符合度较高。所设计的EGR冷却器换热效率较高,且具有一定设计余量,经仿真和实验验证可行。展开更多
文摘为研究界面黏着,利用表面力仪在高离子强度电解质水溶液中测量负电云母表面之间的法向力.在纯水中,因范德华吸引,两表面跳跃至直接接触(间距0A),分离两表面时测得界面黏着力为-46.7 m N/m.在0.1 mol/L K_(2)SO_(4)中,因K^(+)离子牢固吸附于云母,表面间距稳定于5A,黏着力仅-2.9 m N/m;在0.1 mol/L Ca(NO_(3))_(2)中,云母表面吸附的Ca^(2+)离子产生显著短程水合排斥,但在较低载荷下解吸附,导致两表面直接接触,黏着力高达-40.7 m N/m.加入Ca(OH)_(2)于0.1 mol/L K_(2)SO_(4)仅产生微弱短程排斥,黏着状态几乎与纯K_(2)SO_(4)水溶液中相同.聚电解质PCE从0.1 mol/L K_(2)SO_(4)中吸附于云母表面且诱导远程空间位阻排斥,但在中等载荷下解吸附,导致两表面轻度黏着(间距5A);牢固吸附于云母表面的PNS高分子薄膜之间的空间位阻完全阻止云母界面黏着.牢固吸附是电解质吸附层稳定阻止界面黏着的必要条件.
基金Project(2013CB632305)supported by the National Basic Research Program of ChinaProject(51375108)supported by the National Natural Science Foundation of China
文摘A line contact model of elastic coated solids is presented based on the influence coefficients(ICs) of surface displacement and stresses of coating-substrate system and the traditional contact model. The ICs of displacement and stresses are obtained from their corresponding frequency response functions(FRF) by using a conversion method based on fast Fourier transformation(FFT). The contact pressure and the stress field in the subsurface are obtained by employing conjugate gradient method(CGM) and discrete convolution fast Fourier transformation(DC-FFT). Comparison of the contact pressure and subsurface stresses obtained by the numerical method with the exact analytical solutions for Hertz contact is conducted, and the results show that the numerical solution has a very high accuracy and verify the validity of the contact model. The effect of the stiffness and thickness of coatings is further numerically studied. The result shows that the effects on contact pressure and contact width are opposite for hard and soft coatings and are intensified with the increase of coating thickness; the locations of crack initiation and propagation are different for soft and hard coatings; the risk of cracks and delaminations of coatings can be brought down by improving the lubrication condition or optimizing the non-dimensional parameter h/bh. This research offers a tool to numerically analyze the problem of elastic coated solids in line contact and make the blindness and randomness of trial-type coating design less.
文摘针对国Ⅵ排放标准,对某柴油机用EGR(排气再循环,Exhaust Gas Recirculation)冷却器进行了换热性能分析与优化。首先通过仿真分析对比打坑管式与内翅片式模型的温度场、压力场和换热效率,确定内翅片式模型各项指标均有较明显优势;为进一步满足设计要求,同时尽量减小气侧压差,又对翅片波纹幅值进行优化,确定当幅值A=0.9 mm时,仿真换热效率为86.43%。最后进行了样件制造以及换热性能实验台测试,实测换热效率为88.55%,实验与仿真数据符合度较高。所设计的EGR冷却器换热效率较高,且具有一定设计余量,经仿真和实验验证可行。
