塑性材料在对称循环变应力下的极限应力为( )。
A. σ s
B. σ B
C. σ 0
D. σ -1
零件的截面形状一定,当截面尺寸增大时,其疲劳极限值将随之()
A. 变大
B. 变小
C. 不变
在载荷和几何形状相同的情况下,钢制零件间的接触应力与铸铁零件间的接触应力相比()
A. 较高
B. 较低
C. 相同
feel / be at homea range ofcome into beingapply toa lack ofdebt of gratitude / thanksback and forthshower withLocal farmers regard the black soils as a "gift from the past" because they are naturally fertile and have the ability to support _______ crops.