The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct ...The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct information of local stress and strain. Local stress/strain calculation methods are applied to determine the initial crush stresses and the strain rates at initial crush from a cell-based finite element model of irregular honeycomb under dynamic loadings. The initial crush stress under constant-velocity compression is identical to the quasi-static one, but less than the one under direct impact, i.e. the initial crush stresses under different dynamic loadings could be very different even though there is no strain-rate effect of matrix material. A power-law relation between the initial crush stress and the strain rate is explored to describe the strain-rate effect on the initial crush stress of irregular honeycomb when the local strain rate exceeds a critical value, below which there is no strain-rate effect of irregular honeycomb. Deformation mechanisms of the initial crush behavior under dynamic loadings are also explored.The deformation modes of the initial crush region in the front of plastic compaction wave are different under different dynamic loadings.展开更多
This paper has been done on study kinematic problem of Persian joint in a general way. In this study, instead of using simulation analysis method as in the previous researches, the 3D rotation matrix method is applied...This paper has been done on study kinematic problem of Persian joint in a general way. In this study, instead of using simulation analysis method as in the previous researches, the 3D rotation matrix method is applied to present the relationship of angular velocities of input shaft and output shaft. The result shows that when the angle between intersecting shafts changes from 0 to 135°, the angular velocity is maintained constant. This new result completely matches with analysis from kinematic simulation of this mechanism. The obtained result is an important base to solve dynamic problem in order to develop the applicability of this joint in reality.展开更多
This paper has been focused on investigating kinematics of Persian joint. In this study, instead of using the 3D （three dimensional） rotation matrix method as in the previous research, Persian joint is considered as...This paper has been focused on investigating kinematics of Persian joint. In this study, instead of using the 3D （three dimensional） rotation matrix method as in the previous research, Persian joint is considered as a robotic mechanism, and the methods and tools are applied to present the relationship of angular displacements of input shaft and output shaft. When the angle between intersecting shafts changes from 0 degree to 135 degrees, the results show that the velocities of input shaft and output shaft are almost the same with the actual values. This study provides a new method to investigate this mechanism in detail. The obtained results not only provide the sub-parameters （the displacement of guide arms and connecting arms）, but also help to have a deeper understanding about the operation of Persian joint in order to develop the design of Persian joint in the future.展开更多
基金supported by the National Natural Science Foundation of China (Grants 11372308, 11372307)the Fundamental Research Funds for the Central Universities (Grant WK2480000001)
文摘The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct information of local stress and strain. Local stress/strain calculation methods are applied to determine the initial crush stresses and the strain rates at initial crush from a cell-based finite element model of irregular honeycomb under dynamic loadings. The initial crush stress under constant-velocity compression is identical to the quasi-static one, but less than the one under direct impact, i.e. the initial crush stresses under different dynamic loadings could be very different even though there is no strain-rate effect of matrix material. A power-law relation between the initial crush stress and the strain rate is explored to describe the strain-rate effect on the initial crush stress of irregular honeycomb when the local strain rate exceeds a critical value, below which there is no strain-rate effect of irregular honeycomb. Deformation mechanisms of the initial crush behavior under dynamic loadings are also explored.The deformation modes of the initial crush region in the front of plastic compaction wave are different under different dynamic loadings.
文摘This paper has been done on study kinematic problem of Persian joint in a general way. In this study, instead of using simulation analysis method as in the previous researches, the 3D rotation matrix method is applied to present the relationship of angular velocities of input shaft and output shaft. The result shows that when the angle between intersecting shafts changes from 0 to 135°, the angular velocity is maintained constant. This new result completely matches with analysis from kinematic simulation of this mechanism. The obtained result is an important base to solve dynamic problem in order to develop the applicability of this joint in reality.
文摘This paper has been focused on investigating kinematics of Persian joint. In this study, instead of using the 3D （three dimensional） rotation matrix method as in the previous research, Persian joint is considered as a robotic mechanism, and the methods and tools are applied to present the relationship of angular displacements of input shaft and output shaft. When the angle between intersecting shafts changes from 0 degree to 135 degrees, the results show that the velocities of input shaft and output shaft are almost the same with the actual values. This study provides a new method to investigate this mechanism in detail. The obtained results not only provide the sub-parameters （the displacement of guide arms and connecting arms）, but also help to have a deeper understanding about the operation of Persian joint in order to develop the design of Persian joint in the future.
