The role of oxides in the formation of hole defects in friction stir welded joint of 2519-T87 aluminum alloy has been investigated by using optical microscope, scanning electron microscope, electron backscatter diffra...The role of oxides in the formation of hole defects in friction stir welded joint of 2519-T87 aluminum alloy has been investigated by using optical microscope, scanning electron microscope, electron backscatter diffraction and electron probe microanalyzer to examine the distribution of oxides and the features of hole defects, and using ABAQUS 3D thermo-mechanical coupling finite element model based on arbitrary Lagrangian-Eulerian method to simulate the material flow behavior. Oxides exist at the edge of tunnel hole and in the micropores in the joint. Based on distribution of oxygen and material flow behavior, it is believed that the oxides on the surface of the alloy tend to flow down into the bulk along the flow direction of plastic material during friction stir welding, aggregate in the weak region of material flow at the intersection of the shoulder affected zone and the stir pin-tip affected zone, and consequently prevent the material from contacting and diffusing. Due to the insufficient material flow and therefore the small plastic deformation,the pressure is not high enough to compress the accumulated oxides, resulting in hole defects.展开更多
一尼采的《苏鲁支语录》有一节:Von allem Geschriebenen liebe ich nur das,was einer mit-seinem Blute schreibt.Schreibe mit Blut:und duwirsterfahren,daβ Blut Geist ist.(凡一切已经写下的,我只爱其人用其血写下的。用血写:然...一尼采的《苏鲁支语录》有一节:Von allem Geschriebenen liebe ich nur das,was einer mit-seinem Blute schreibt.Schreibe mit Blut:und duwirsterfahren,daβ Blut Geist ist.(凡一切已经写下的,我只爱其人用其血写下的。用血写:然后你将体会到,血便是精义。)血便是精义,要懂得旁人的血是不易的。展开更多
By using Schwarz alternating method, this paper presents asimplified alternating algorithm for the problems of two holes having arbitrary shapes and arrangements in an isotropic homogeneous linear elastic infinite reg...By using Schwarz alternating method, this paper presents asimplified alternating algorithm for the problems of two holes having arbitrary shapes and arrangements in an isotropic homogeneous linear elastic infinite region, and obtains stress and displacement fields for random times of iteration. After precision analysis it is found that the results for twenty times of iteration are of very high precision, and those with higher precision can be acquired if the iteration solving is further conducted. The comparison of the results from FEM further proves the reliability of the simplified alternating algorithm presented by this paper.展开更多
Determining how to achieve sustainable development and protection of historical districts is a worthwhile research topic.As a vital way to update urban space,tourism development in historical districts is an effective...Determining how to achieve sustainable development and protection of historical districts is a worthwhile research topic.As a vital way to update urban space,tourism development in historical districts is an effective tool for redistributing urban functions and increasing urban vitality.This paper takes the Insa-dong in South Korea as a case study for the evaluation of tourist satisfaction in historical districts,based on 550 questionnaires.The questionnaire contains 33 evaluation indicators,and the subjects’subjective judgment and satisfaction with Insa-dong are measured in the form of the Likert scale.Using SPSS to analyze tourists’satisfaction with historical districts,this studyfinds that:(1)The tourist satisfaction evaluation of Insa-dong includes six dimensions in total:"Embodiment of historical elements","The blend of tradition and modernity","Industry distribution and type","Consumer demand","Street layout and function"and"Landscaping".(2)"The blend of tradition and modernity"has the highest weight while"Industry distribution and type"has the lowest one in the analysis of factors influencing overall satisfaction.(3)The analysis of the common factor weights and the common factor satisfaction levels shows that"The blend of tradition and modernity"and"Street layout and function"are the parts that need to be improved."Consumer demand"also has a lot of room for promotion.The research results will be beneficial for enhancing the tourist experiences of historical districts and they provide a theoretical basis and practical experience reference for effective protection and sustainable development of historical districts.展开更多
This paper explores the influence of the local meteoric conditions, the overlying soil on the concentrations of Ca, Mg, and St, and the ratios of Mg/Ca, Sr/Ca, and Mg/Sr in soil infiltrating water （SIW）. An in situ ...This paper explores the influence of the local meteoric conditions, the overlying soil on the concentrations of Ca, Mg, and St, and the ratios of Mg/Ca, Sr/Ca, and Mg/Sr in soil infiltrating water （SIW）. An in situ monitoring program was carried out above the Furong Cave throughout 2010 to collect data on SIW, monthly temperature and rainfall, and the geochemical com- position and granularity of soils. The discharge of SIW responded quickly to the local rainfall, and its residence time was the primary factor affecting the Ca, Mg, and Sr content of the SIW. The high concentrations of Ca, Mg, and Sr in the SIW during April should be attributed primarily to the prolonged residence of SIW in the soil during the local dry seasons of winter and early spring. The maximum Mg/Sr ratio also occurred in April. The ratio of Mg/Ca in SIW is positively correlated with pro- longed residence time and with high temperatures, which do not strongly affect the ratio of Sr/Ca. The Mg/Ca ratio was lowest when the Sr/Ca ratio was highest because plant metabolism increased the absorption of Ca and Mg, but not St, and also be- cause higher temperatures enhanced the dissolution of Mg more than that of Sr. These different responses of Mg and Sr to temperature increases resulted in high Mg/Sr ratios during July and August.展开更多
文摘The role of oxides in the formation of hole defects in friction stir welded joint of 2519-T87 aluminum alloy has been investigated by using optical microscope, scanning electron microscope, electron backscatter diffraction and electron probe microanalyzer to examine the distribution of oxides and the features of hole defects, and using ABAQUS 3D thermo-mechanical coupling finite element model based on arbitrary Lagrangian-Eulerian method to simulate the material flow behavior. Oxides exist at the edge of tunnel hole and in the micropores in the joint. Based on distribution of oxygen and material flow behavior, it is believed that the oxides on the surface of the alloy tend to flow down into the bulk along the flow direction of plastic material during friction stir welding, aggregate in the weak region of material flow at the intersection of the shoulder affected zone and the stir pin-tip affected zone, and consequently prevent the material from contacting and diffusing. Due to the insufficient material flow and therefore the small plastic deformation,the pressure is not high enough to compress the accumulated oxides, resulting in hole defects.
文摘一尼采的《苏鲁支语录》有一节:Von allem Geschriebenen liebe ich nur das,was einer mit-seinem Blute schreibt.Schreibe mit Blut:und duwirsterfahren,daβ Blut Geist ist.(凡一切已经写下的,我只爱其人用其血写下的。用血写:然后你将体会到,血便是精义。)血便是精义,要懂得旁人的血是不易的。
基金the National Natural Science Foundation of China (Grant No. 49772166).
文摘By using Schwarz alternating method, this paper presents asimplified alternating algorithm for the problems of two holes having arbitrary shapes and arrangements in an isotropic homogeneous linear elastic infinite region, and obtains stress and displacement fields for random times of iteration. After precision analysis it is found that the results for twenty times of iteration are of very high precision, and those with higher precision can be acquired if the iteration solving is further conducted. The comparison of the results from FEM further proves the reliability of the simplified alternating algorithm presented by this paper.
基金The National Key Research and Development Program(2019YFC0507802)The National Natural Science Foundation of China(41801139)。
文摘Determining how to achieve sustainable development and protection of historical districts is a worthwhile research topic.As a vital way to update urban space,tourism development in historical districts is an effective tool for redistributing urban functions and increasing urban vitality.This paper takes the Insa-dong in South Korea as a case study for the evaluation of tourist satisfaction in historical districts,based on 550 questionnaires.The questionnaire contains 33 evaluation indicators,and the subjects’subjective judgment and satisfaction with Insa-dong are measured in the form of the Likert scale.Using SPSS to analyze tourists’satisfaction with historical districts,this studyfinds that:(1)The tourist satisfaction evaluation of Insa-dong includes six dimensions in total:"Embodiment of historical elements","The blend of tradition and modernity","Industry distribution and type","Consumer demand","Street layout and function"and"Landscaping".(2)"The blend of tradition and modernity"has the highest weight while"Industry distribution and type"has the lowest one in the analysis of factors influencing overall satisfaction.(3)The analysis of the common factor weights and the common factor satisfaction levels shows that"The blend of tradition and modernity"and"Street layout and function"are the parts that need to be improved."Consumer demand"also has a lot of room for promotion.The research results will be beneficial for enhancing the tourist experiences of historical districts and they provide a theoretical basis and practical experience reference for effective protection and sustainable development of historical districts.
基金supported by National Natural Science Foundation of China(Grant Nos.41302138,40971122,41030103 and 41172165)the Fundamental Research Funds for the Central Universities of Southwest University(Grant Nos.XDJK2013A012 and XDJK2009C106)State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences(Grant No.SKLLQG1310)
文摘This paper explores the influence of the local meteoric conditions, the overlying soil on the concentrations of Ca, Mg, and St, and the ratios of Mg/Ca, Sr/Ca, and Mg/Sr in soil infiltrating water （SIW）. An in situ monitoring program was carried out above the Furong Cave throughout 2010 to collect data on SIW, monthly temperature and rainfall, and the geochemical com- position and granularity of soils. The discharge of SIW responded quickly to the local rainfall, and its residence time was the primary factor affecting the Ca, Mg, and Sr content of the SIW. The high concentrations of Ca, Mg, and Sr in the SIW during April should be attributed primarily to the prolonged residence of SIW in the soil during the local dry seasons of winter and early spring. The maximum Mg/Sr ratio also occurred in April. The ratio of Mg/Ca in SIW is positively correlated with pro- longed residence time and with high temperatures, which do not strongly affect the ratio of Sr/Ca. The Mg/Ca ratio was lowest when the Sr/Ca ratio was highest because plant metabolism increased the absorption of Ca and Mg, but not St, and also be- cause higher temperatures enhanced the dissolution of Mg more than that of Sr. These different responses of Mg and Sr to temperature increases resulted in high Mg/Sr ratios during July and August.
