1. (10 Points) A 6-m long by 50-mm diameter rod of aluminum alloy (E = 70 GPa, a = 22.5 x /℃, and v = 0.346) is attached at the ends to supports that yield to permit a change of 1.0 mm in the rod when stressed. When the temperature is 35℃, there is no stress in the rod. After the temperature of the rod drops to - 20 ℃, determine (a) the maximum normal stress in the rod and (b) the change in diameter of the rod.
四、 若您利用一塊磁鐵、一瓶海水以及一枝水泥鋼釘(硬度 50 HRC)及手感重量,將如何 在 48 小時內區分尺度均為 20 mm ✖ 10 mm ✖ 5 mm 且為經拋光表面處理的:鋁合金、白銅 75%Cu-25%Ni(10 元硬幣之材料)、淬火回火中碳合金鋼(硬度 58 HRC)、肥粒體系 430 不銹鋼(Fe-16Cr)及退火之沃斯田體系 304 不銹鋼(Fe-18Cr-8Ni)等五種金屬材料,並請說明 您的理由。【25 分】