问题 多项选择题

金属材料的蠕变也是一种塑性变形,但它与一般的塑性变形相比,具有()几个特点。

A.金属材料的蠕变是在一定的温度下才能发生的,如钢在400℃以上才能发生蠕变

B.发生蠕变现象时间长,一般要经过几百甚至几万小时才发生蠕变现象

C.发生蠕变现象时的应力较小,低于本身的屈服点甚至低于弹性极限

D.金属材料的蠕变是在冲击载荷作用下产生

E.金属材料的蠕变是结构长期失稳条件下的塑性变形

答案

参考答案:A, B, C

填空题
单项选择题

I remember my math teacher Mr. Young very well. He stood out because the kids made fun of him. He was missing one of his fingers, and always pointed at students with his middle finger.

I was not very good at English and math. No matter how hard I tried, I just could not figure out why I did not understand what all the other kids found so easy to learn.

One day, I was told that if I got one more E on my report card, I would be taken to the" big prison for kids".

I tried really hard for weeks. I just couldn’t understand how to make different parts of members into whole things.

The day before report cards were to come out, I knew that Mr. Young would give me an E ,just like he always did.

I went to Mr. Young and told him that the orphanage was going to send me to the big prison if I got another E on my report card. He told me there was nothing he could do;it would be unfair to the other kids if he gave me a better grade than I had actually earned.

I smiled at him and said, "Mr. Young, do you know how the kids make fun of you because you’re missing your finger" He looked at me, moved his mouth to one side and said nothing.

"They shouldn’t do that to you because you can’t help having a finger, Mr. Young. Just like I can’t help not being able to learn numbers and stuff like that. "I said.

The next day, when I got my report card, I tucked it into one of my books. While on the school bus, I opened it : Geography, B+ ; Mechanical Drawing, C- ; English, D- ; History, C- ; Gym, B+ ; Art, C ; Math, D-.

That math grade was the most favorite one I ever received. Because I knew that someone in the world finally understood what it was like for me to be missing a finger inside my head.

Where may the boy live according to the passage()

A. In an orphanage.

B. In a big prison.

C. In the school dormitory.

D. In his home.