The mechanical properties and deformation mechanism of semi-continuously casting and as-extruded AZ70 magnesium alloys in a wide range of grain sizes(from 14 to 103μm)were investigated at 653 K and 1×10-3s -1.It...The mechanical properties and deformation mechanism of semi-continuously casting and as-extruded AZ70 magnesium alloys in a wide range of grain sizes(from 14 to 103μm)were investigated at 653 K and 1×10-3s -1.It is discovered that with reducing grain size,flow stress is weakened and plasticity is improved and even superplasticity exhibits.SEM and OM were used to clarify the deformation mechanism.It is suggested that dynamic recrystallization(DRX)is the coordination deformation mechanism of grain boundary sliding(GBS)for coarse grain,and cavity and intracrystalline slip are the coordination deformation mechanisms of GBS for fine grain.展开更多
In this paper, we study the kinematic mechanism and path planning for a two-caster nonholonomic vehicle (the Essboard) which is a recent variant of skateboard. Different from the most studied Snakeboard, the Essboard ...In this paper, we study the kinematic mechanism and path planning for a two-caster nonholonomic vehicle (the Essboard) which is a recent variant of skateboard. Different from the most studied Snakeboard, the Essboard consists of a torsion bar and two platforms, each of which contains a pedal and a caster. We first investigate the relationship between the tilt angles of the pedals and the wheel directions of the casters. This relationship reveals how to control the wheel directions by adjusting the tilt angles. Next, the rotational radius of the Essboard is derived for a given pair of tilt angles of both pedals. The rotational radius of the Essboard is much different than that of the Snakeboard. Then we develop a path-planning algorithm for the Essboard to move from a start position to the goal, using a series of consecutively connected arcs, which are tangent to each other at the connected points. It is shown from a kinematic point of view that the path planning of the Essboard can be solved by a series of pairs of pedals' tilt angles. Three experiments are conducted to confirm the correctness of the main results. The results in this paper are a foundation for further study of the Essboard.展开更多
基金Project(2008CB617509)supported by the National Basic Research Program of ChinaProject(30870634)supported by the National Natural Science Foundation of China
文摘The mechanical properties and deformation mechanism of semi-continuously casting and as-extruded AZ70 magnesium alloys in a wide range of grain sizes(from 14 to 103μm)were investigated at 653 K and 1×10-3s -1.It is discovered that with reducing grain size,flow stress is weakened and plasticity is improved and even superplasticity exhibits.SEM and OM were used to clarify the deformation mechanism.It is suggested that dynamic recrystallization(DRX)is the coordination deformation mechanism of grain boundary sliding(GBS)for coarse grain,and cavity and intracrystalline slip are the coordination deformation mechanisms of GBS for fine grain.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51105012 and 61175079)
文摘In this paper, we study the kinematic mechanism and path planning for a two-caster nonholonomic vehicle (the Essboard) which is a recent variant of skateboard. Different from the most studied Snakeboard, the Essboard consists of a torsion bar and two platforms, each of which contains a pedal and a caster. We first investigate the relationship between the tilt angles of the pedals and the wheel directions of the casters. This relationship reveals how to control the wheel directions by adjusting the tilt angles. Next, the rotational radius of the Essboard is derived for a given pair of tilt angles of both pedals. The rotational radius of the Essboard is much different than that of the Snakeboard. Then we develop a path-planning algorithm for the Essboard to move from a start position to the goal, using a series of consecutively connected arcs, which are tangent to each other at the connected points. It is shown from a kinematic point of view that the path planning of the Essboard can be solved by a series of pairs of pedals' tilt angles. Three experiments are conducted to confirm the correctness of the main results. The results in this paper are a foundation for further study of the Essboard.
