Bolts are important fasteners indispensable in the manufacturing field for their advantages, which include convenient assembly and disassembly, easy maintenance, refastenability to prevent looseness, and the avoidance...Bolts are important fasteners indispensable in the manufacturing field for their advantages, which include convenient assembly and disassembly, easy maintenance, refastenability to prevent looseness, and the avoidance of a phase change in the connected material composition. The precise control of the tightening force in bolts is closely related to the safety and reliability of the connected equipment or structure. Although there are many methods for estimating the tightening force applied to a bolt during assembly, poor accuracy in controlling the preload during the tightening process and a lack of monitoring to determine the residual axial force in service remain issues in evaluating the safety of bolted assemblies. As a nondestructive testing technology, ultrasonic measurement can be applied to successfully address these issues. In order to help researchers understand the theoretical basis and technological development in this field and to equip them to conduct further in-depth research, in this review, the basic knowledge describing the state of stress and deformation of bolts, as well as conventional testing methods are summarized and analyzed. Then, through a review of recent research of the ultrasonic measurement of the axial stress in bolts, the influence of the e ective stressed length and temperature are analyzed and proposed methods of calibration and compensation are reviewed. In order to avoid coupling errors caused by traditional piezoelectric transducers, two newly proposed ultrasonic coupling technologies, the electromagnetic acoustic transducer(EMAT) and the permanent mounted transducer system(PMTS), are reviewed. Finally, the new direction of research of the detection of residual axial stress in in-service bolts that have been assembled to yield is discussed.展开更多
Urban development in arid and semi-arid regions is largely constrained by fragile physical environ- ments. The characteristics of an urban settlement are different from those in other regions of China. This paper anal...Urban development in arid and semi-arid regions is largely constrained by fragile physical environ- ments. The characteristics of an urban settlement are different from those in other regions of China. This paper analyses the coupling characteristics and spatio-temporal variations for oasis urban development and water-land resources at the northern slopes of the Tianshan Mountains by principal component analysis and a coupling degree model. The result shows that the degree and change in regional use of water and land resources are different among the studied cities/counties during their development. The built-up areas of these cities/counties have changed little with increasing populations and urbanization levels, which well reflects that the urban development in arid and semi-arid regions is limited by oasis areas. Per capita amount of water supplied, however, presented a trend of slowed growth with increasing levels of urbanization. Water consumption gradually increased with urban development and the improvement of people＇s living standards, accompanied by enhanced water use efficiency. The level of urbanization can be assessed through the coupling degree between oasis urban development and the use of water and land resources. A high coupling degree represents a high level of comprehensive urban devel- opment and use of water-land resources. Alternatively, a low coupling degree denotes a low level of urban devel- opment and water-land resource use.展开更多
中高纬度森林地区由于气候条件变化剧烈,土壤温室气体排放量的估算存在很大的不确定性,并且不同碳氮气体通量的主控因子与耦合关系尚不明确。以长白山温带针阔混交林为研究对象,采用静态箱-气相色谱法连续4a(2005—2009年)测定土壤二氧...中高纬度森林地区由于气候条件变化剧烈,土壤温室气体排放量的估算存在很大的不确定性,并且不同碳氮气体通量的主控因子与耦合关系尚不明确。以长白山温带针阔混交林为研究对象,采用静态箱-气相色谱法连续4a(2005—2009年)测定土壤二氧化碳(CO2)、甲烷(CH4)和氧化亚氮(N2O)净交换通量以及温度、水分等相关环境因子。研究结果表明:温带针阔混交林土壤整体上表现为CO2和N2O的排放源和CH4的吸收汇。土壤CH4、CO2和N2O通量的年均值分别为-1.3 kg CH4hm-2a-1、15102.2 kg CO2hm-2a-1和6.13 kg N2O hm-2a-1。土壤CO2通量呈现明显的季节性规律,主要受土壤温度的影响,水分次之;土壤CH4通量的季节变化不明显,与土壤水分显著正相关;土壤N2O通量季节变化与土壤CO2通量相似,与土壤水分、温度显著正相关。土壤CO2通量和CH4通量不存在任何类型的耦合关系,与N2O通量也不存在耦合关系;土壤CH4和N2O通量之间表现为消长型耦合关系。这项研究显示温带针阔混交林土壤碳氮气体通量主要受环境因子驱动,不同气体通量产生与消耗之间存在复杂的耦合关系,下一步研究需要深入探讨环境变化对其耦合关系的影响以及内在的生物驱动机制。展开更多
基金Supported by Project of Basic Technology Research which is funded by Technology and Quality Division of the Ministry of Industry and Information Technology(Grant No.JSZL2017602B002).
文摘Bolts are important fasteners indispensable in the manufacturing field for their advantages, which include convenient assembly and disassembly, easy maintenance, refastenability to prevent looseness, and the avoidance of a phase change in the connected material composition. The precise control of the tightening force in bolts is closely related to the safety and reliability of the connected equipment or structure. Although there are many methods for estimating the tightening force applied to a bolt during assembly, poor accuracy in controlling the preload during the tightening process and a lack of monitoring to determine the residual axial force in service remain issues in evaluating the safety of bolted assemblies. As a nondestructive testing technology, ultrasonic measurement can be applied to successfully address these issues. In order to help researchers understand the theoretical basis and technological development in this field and to equip them to conduct further in-depth research, in this review, the basic knowledge describing the state of stress and deformation of bolts, as well as conventional testing methods are summarized and analyzed. Then, through a review of recent research of the ultrasonic measurement of the axial stress in bolts, the influence of the e ective stressed length and temperature are analyzed and proposed methods of calibration and compensation are reviewed. In order to avoid coupling errors caused by traditional piezoelectric transducers, two newly proposed ultrasonic coupling technologies, the electromagnetic acoustic transducer(EMAT) and the permanent mounted transducer system(PMTS), are reviewed. Finally, the new direction of research of the detection of residual axial stress in in-service bolts that have been assembled to yield is discussed.
基金supported by the Dr.Western-funded Projects of Chinese Academy of Sciences(XBBS200805)the National Natural Science Foundation of China(40901092)
文摘Urban development in arid and semi-arid regions is largely constrained by fragile physical environ- ments. The characteristics of an urban settlement are different from those in other regions of China. This paper analyses the coupling characteristics and spatio-temporal variations for oasis urban development and water-land resources at the northern slopes of the Tianshan Mountains by principal component analysis and a coupling degree model. The result shows that the degree and change in regional use of water and land resources are different among the studied cities/counties during their development. The built-up areas of these cities/counties have changed little with increasing populations and urbanization levels, which well reflects that the urban development in arid and semi-arid regions is limited by oasis areas. Per capita amount of water supplied, however, presented a trend of slowed growth with increasing levels of urbanization. Water consumption gradually increased with urban development and the improvement of people＇s living standards, accompanied by enhanced water use efficiency. The level of urbanization can be assessed through the coupling degree between oasis urban development and the use of water and land resources. A high coupling degree represents a high level of comprehensive urban devel- opment and use of water-land resources. Alternatively, a low coupling degree denotes a low level of urban devel- opment and water-land resource use.
文摘中高纬度森林地区由于气候条件变化剧烈,土壤温室气体排放量的估算存在很大的不确定性,并且不同碳氮气体通量的主控因子与耦合关系尚不明确。以长白山温带针阔混交林为研究对象,采用静态箱-气相色谱法连续4a(2005—2009年)测定土壤二氧化碳(CO2)、甲烷(CH4)和氧化亚氮(N2O)净交换通量以及温度、水分等相关环境因子。研究结果表明:温带针阔混交林土壤整体上表现为CO2和N2O的排放源和CH4的吸收汇。土壤CH4、CO2和N2O通量的年均值分别为-1.3 kg CH4hm-2a-1、15102.2 kg CO2hm-2a-1和6.13 kg N2O hm-2a-1。土壤CO2通量呈现明显的季节性规律,主要受土壤温度的影响,水分次之;土壤CH4通量的季节变化不明显,与土壤水分显著正相关;土壤N2O通量季节变化与土壤CO2通量相似,与土壤水分、温度显著正相关。土壤CO2通量和CH4通量不存在任何类型的耦合关系,与N2O通量也不存在耦合关系;土壤CH4和N2O通量之间表现为消长型耦合关系。这项研究显示温带针阔混交林土壤碳氮气体通量主要受环境因子驱动,不同气体通量产生与消耗之间存在复杂的耦合关系,下一步研究需要深入探讨环境变化对其耦合关系的影响以及内在的生物驱动机制。
