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1 一材料直徑為10mm,若經拉伸試驗後,直徑變為9.8mm,則斷面的收縮率為
A 2.0%
B 1.96%
C 4.12%
D 3.96%

斷面收縮率 = Ao-A'Ao×100%

=π/4×102-π/4×9.82π/4×102×100%=3.96%