在塑性区，水平及垂直应力均是上凹的。
The horizontal and vertical stresses are concave upward in plastic zone.
峰后泊松比与轴向压应力之间的关系可能是一条直线，也可能是上凸的，或上凹的。
It is possible for linear, upwards concave or upwards convex relations between the post-peak Poisson's ratio and the flow compressive stress.
数以百计的旅客在塑料凹背椅子上，等待广播通知。
Hundreds of passengers, sitting in plastic bucket seats, awaited the boarding announcement.
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