In order to control cutting force and its direction i n milling operation, a new milling head was developed. The head has two milling cutters, which are connected by a pair of gears and rotate in opposite direction re...In order to control cutting force and its direction i n milling operation, a new milling head was developed. The head has two milling cutters, which are connected by a pair of gears and rotate in opposite direction respectively. Both up-cut and down-cut can be carried out simultaneously by t hese milling cutters. The each depth of cut, the ratio of up/down cutting depth , by these cutters can be also selected. The cutting force characteristics were experimentally discussed by changing the ratio. The cutting force and its locus can be also changed by the selection of the ratio of up/down cutting depth. For practical usage of the head the analytical prediction method of the cutting forc e characteristics under selected cutting condition was proposed based on the ene rgy approach method proposed, in which both of cutting force characteristics of a single milling cutter and the combined milling cutter under a selected up/dow n cutting depth ratio were analytically estimated based on the two dimensional c utting data. It was experimentally shown that in NC milling machine the cutting force locus was controlled in pre-determined direction under various tool paths .展开更多
Aluminum foam is widely used in diverse areas to minimize the weight and maximize the absorption of shock energy in lightweight structures and various bio-materials.It presents a number of advantages,such as low densi...Aluminum foam is widely used in diverse areas to minimize the weight and maximize the absorption of shock energy in lightweight structures and various bio-materials.It presents a number of advantages,such as low density,incombustibility,non-rigidity,excellent energy absorptivity,sound absorptivity and low heat conductivity.The aluminum foam with an air cell structure was placed under the TDCB Mode II tensile load by using Landmark equipment manufactured by MTS to examine the shear failure behavior.The angle of the tapered adhesively-bonded surfaces of specimens was designated as a variable,and three models were developed with the inclined angles differing from one another at 6°,8° and 10°.The specimens with the inclined angles of 6°,8° and 10° have the maximum reaction forces of 168 N,194 N when the forced displacements are 6,5 and 4.2 mm respectively.There are three specimens with the inclined angles of 10°,8° and 6° in the order of maximum reaction force.As the analysis result,the maximum equivalent stresses of 0.813 MPa and 0.895 MPa happened when the forced displacements of 6 mm and 5 mm proceeded at the models of 6° and 8°,respectively.A simulation was carried out on the basis of finite element method and the experimental design.The results of the experiment and the simulation analysis are shown not different from each other significantly.Thus,only a simulation could be confirmed to be performed in substitution of an experiment,which is costly and time-consuming in order to determine the shearing properties of materials made of aluminum foam with artificial data.展开更多
In slab column-shear wall structures,both the whole structure′s seismic behavior and failure mode are greatly influenced by the distribution of horizontal seismic forces between slab-column and shear wall.In this pap...In slab column-shear wall structures,both the whole structure′s seismic behavior and failure mode are greatly influenced by the distribution of horizontal seismic forces between slab-column and shear wall.In this paper,a pushover analysis of topical slab column-shear wall structure was carried out,the seismic shear force that the slab-column and shear wall should undertake was worked out,the influences of plastic internal force redistribution and structure stiffness characteristic value on horizontal seismic distribution were studied and the calculation formula was given.The analysis results showed that with the yield of the shear walls,the story shear force was undertaken by slab-columns correspondingly increased while with the decrease of characteristic value of stiffness of a structure,and the horizontal seismic force was undertaken by slab-columns correspondingly decreased.According to the code,the design of horizontal force distribution may be cause insecurity problems,so it is necessary to give the distribution law of horizontal seismic forces in slab-column shear wall structures as the supplement to the corresponding regulation of the Code.展开更多
第二代负泊松比(second-generation negative Poisson’s ratio bolts,2G-NPR)锚杆逐渐应用于裂隙岩体加固,为研究2G-NPR锚杆在充填结构面中的抗剪性能,采用室内直剪试验对比分析了不同充填厚度下2G-NPR锚杆和普通钢筋(Q235)锚杆锚固结...第二代负泊松比(second-generation negative Poisson’s ratio bolts,2G-NPR)锚杆逐渐应用于裂隙岩体加固,为研究2G-NPR锚杆在充填结构面中的抗剪性能,采用室内直剪试验对比分析了不同充填厚度下2G-NPR锚杆和普通钢筋(Q235)锚杆锚固结构面的剪切力学行为。结果表明,相同充填厚度下,2G-NPR锚杆较Q235锚杆弹性阶段剪切刚度低,峰值抗剪强度高、峰值剪切位移大;随着充填厚度增加,虽然两类锚杆的峰值抗剪强度变化相差不大,但由于2G-NPR锚杆的高吸能、高延展特性,其峰值剪切位移优势明显,使得试样延性得到一定提升。锚杆轴力监测数据表明,2G-NPR锚杆能够有效补偿其与灌浆体解耦造成的轴力突降,且持荷能力更持久;其平均峰值轴力为Q235锚杆的3.17倍,且随着充填厚度增加,峰值轴力持续上升,锚固性能更为稳定。进一步结合声发射监测发现,相同充填厚度下,2G-NPR锚杆的最大累计计数和最大累计能量更低,b值(声发射小事件数与大事件数的比值)下降时间更晚,试样破坏程度更小,揭示2G-NPR锚杆提升试样延性的原因在于其有效吸收了剪切应变能,减缓了裂纹的扩展。研究结果可为2G-NPR锚杆在软硬互层岩体支护工程中的应用提供指导。展开更多
目的力角特性是永磁直线同步电机(permanent magnet linear synchronous motor,PMLSM)运行稳定性的重要特性,是评价电机性能和控制电机的依据。但在低频工况下,PMLSM的力角特性因电枢电阻的影响而存在偏移现象,进而导致利用现有忽略电...目的力角特性是永磁直线同步电机(permanent magnet linear synchronous motor,PMLSM)运行稳定性的重要特性,是评价电机性能和控制电机的依据。但在低频工况下,PMLSM的力角特性因电枢电阻的影响而存在偏移现象,进而导致利用现有忽略电枢电阻的力角特性分析计算电机低速运行特性会存在较大的偏差。为此,对PMLSM低频低速下的力角特性偏移原因及其影响规律展开深入研究,并确定力角特性偏移的临界条件。方法首先,建立考虑电枢电阻的PMLSM力角特性的解析模型,分析力角特性产生偏移的原因;其次,基于建立的解析模型,通过峰值推力及其对应的功角研究不同因素对推力特性的影响规律,并建立有限元模型对分析结果进行验证。然后,利用解析法确定PMLSM力角特性产生偏移的临界条件,即当力角偏移系数k(k=X_(t)/R_(a))≥11.43可以近似认为峰值推力对应的功角等于90°,可以忽略力角偏移现象;最后,搭建PMLSM样机测试平台,将有限元结果、实验结果与理论分析进行比较,验证推力特性曲线产生偏移的原因和临界条件。结果研究发现,与常用的忽略电枢电阻的力角特性相比,PMLSM力角特性向左偏移。力角特性偏移现象会导致两方面的影响,一是导致推力和电枢电流的关系不单调,出现小负载的电流比大负载的还要大的现象,二是低频运行时峰值推力减小,因此低频时不能保持恒推力运行。结论研究结果对PMLSM的设计和精确控制具有重要的参考价值。展开更多
文摘In order to control cutting force and its direction i n milling operation, a new milling head was developed. The head has two milling cutters, which are connected by a pair of gears and rotate in opposite direction respectively. Both up-cut and down-cut can be carried out simultaneously by t hese milling cutters. The each depth of cut, the ratio of up/down cutting depth , by these cutters can be also selected. The cutting force characteristics were experimentally discussed by changing the ratio. The cutting force and its locus can be also changed by the selection of the ratio of up/down cutting depth. For practical usage of the head the analytical prediction method of the cutting forc e characteristics under selected cutting condition was proposed based on the ene rgy approach method proposed, in which both of cutting force characteristics of a single milling cutter and the combined milling cutter under a selected up/dow n cutting depth ratio were analytically estimated based on the two dimensional c utting data. It was experimentally shown that in NC milling machine the cutting force locus was controlled in pre-determined direction under various tool paths .
基金Project(2011-0006548)supported by Basic Science Research Program through the National Research Foundation of Korea
文摘Aluminum foam is widely used in diverse areas to minimize the weight and maximize the absorption of shock energy in lightweight structures and various bio-materials.It presents a number of advantages,such as low density,incombustibility,non-rigidity,excellent energy absorptivity,sound absorptivity and low heat conductivity.The aluminum foam with an air cell structure was placed under the TDCB Mode II tensile load by using Landmark equipment manufactured by MTS to examine the shear failure behavior.The angle of the tapered adhesively-bonded surfaces of specimens was designated as a variable,and three models were developed with the inclined angles differing from one another at 6°,8° and 10°.The specimens with the inclined angles of 6°,8° and 10° have the maximum reaction forces of 168 N,194 N when the forced displacements are 6,5 and 4.2 mm respectively.There are three specimens with the inclined angles of 10°,8° and 6° in the order of maximum reaction force.As the analysis result,the maximum equivalent stresses of 0.813 MPa and 0.895 MPa happened when the forced displacements of 6 mm and 5 mm proceeded at the models of 6° and 8°,respectively.A simulation was carried out on the basis of finite element method and the experimental design.The results of the experiment and the simulation analysis are shown not different from each other significantly.Thus,only a simulation could be confirmed to be performed in substitution of an experiment,which is costly and time-consuming in order to determine the shearing properties of materials made of aluminum foam with artificial data.
文摘In slab column-shear wall structures,both the whole structure′s seismic behavior and failure mode are greatly influenced by the distribution of horizontal seismic forces between slab-column and shear wall.In this paper,a pushover analysis of topical slab column-shear wall structure was carried out,the seismic shear force that the slab-column and shear wall should undertake was worked out,the influences of plastic internal force redistribution and structure stiffness characteristic value on horizontal seismic distribution were studied and the calculation formula was given.The analysis results showed that with the yield of the shear walls,the story shear force was undertaken by slab-columns correspondingly increased while with the decrease of characteristic value of stiffness of a structure,and the horizontal seismic force was undertaken by slab-columns correspondingly decreased.According to the code,the design of horizontal force distribution may be cause insecurity problems,so it is necessary to give the distribution law of horizontal seismic forces in slab-column shear wall structures as the supplement to the corresponding regulation of the Code.
文摘第二代负泊松比(second-generation negative Poisson’s ratio bolts,2G-NPR)锚杆逐渐应用于裂隙岩体加固,为研究2G-NPR锚杆在充填结构面中的抗剪性能,采用室内直剪试验对比分析了不同充填厚度下2G-NPR锚杆和普通钢筋(Q235)锚杆锚固结构面的剪切力学行为。结果表明,相同充填厚度下,2G-NPR锚杆较Q235锚杆弹性阶段剪切刚度低,峰值抗剪强度高、峰值剪切位移大;随着充填厚度增加,虽然两类锚杆的峰值抗剪强度变化相差不大,但由于2G-NPR锚杆的高吸能、高延展特性,其峰值剪切位移优势明显,使得试样延性得到一定提升。锚杆轴力监测数据表明,2G-NPR锚杆能够有效补偿其与灌浆体解耦造成的轴力突降,且持荷能力更持久;其平均峰值轴力为Q235锚杆的3.17倍,且随着充填厚度增加,峰值轴力持续上升,锚固性能更为稳定。进一步结合声发射监测发现,相同充填厚度下,2G-NPR锚杆的最大累计计数和最大累计能量更低,b值(声发射小事件数与大事件数的比值)下降时间更晚,试样破坏程度更小,揭示2G-NPR锚杆提升试样延性的原因在于其有效吸收了剪切应变能,减缓了裂纹的扩展。研究结果可为2G-NPR锚杆在软硬互层岩体支护工程中的应用提供指导。
文摘目的力角特性是永磁直线同步电机(permanent magnet linear synchronous motor,PMLSM)运行稳定性的重要特性,是评价电机性能和控制电机的依据。但在低频工况下,PMLSM的力角特性因电枢电阻的影响而存在偏移现象,进而导致利用现有忽略电枢电阻的力角特性分析计算电机低速运行特性会存在较大的偏差。为此,对PMLSM低频低速下的力角特性偏移原因及其影响规律展开深入研究,并确定力角特性偏移的临界条件。方法首先,建立考虑电枢电阻的PMLSM力角特性的解析模型,分析力角特性产生偏移的原因;其次,基于建立的解析模型,通过峰值推力及其对应的功角研究不同因素对推力特性的影响规律,并建立有限元模型对分析结果进行验证。然后,利用解析法确定PMLSM力角特性产生偏移的临界条件,即当力角偏移系数k(k=X_(t)/R_(a))≥11.43可以近似认为峰值推力对应的功角等于90°,可以忽略力角偏移现象;最后,搭建PMLSM样机测试平台,将有限元结果、实验结果与理论分析进行比较,验证推力特性曲线产生偏移的原因和临界条件。结果研究发现,与常用的忽略电枢电阻的力角特性相比,PMLSM力角特性向左偏移。力角特性偏移现象会导致两方面的影响,一是导致推力和电枢电流的关系不单调,出现小负载的电流比大负载的还要大的现象,二是低频运行时峰值推力减小,因此低频时不能保持恒推力运行。结论研究结果对PMLSM的设计和精确控制具有重要的参考价值。
