问题 问答题 简答题

为什么能把钢材简化为理想的弹性材料?

答案

参考答案:

从钢材拉伸时的应力-应变曲线可以看到,钢材有较明显的弹性、屈服阶段,但当应力达屈服点后,钢材应变可达2%~3%,这样大的变形虽然没有破坏,但结构或构件已不适于再继续承受荷载,所以副忽略钢材强化阶段,又由于比例极限和屈服点比较接近,达到相应应力值时的应变也较接近,且数值很小。因此为了简化计算,通常假定屈服点前钢材为完全弹性的,而屈服点后则为完全塑性的,这样就把钢材视为理想的弹塑性体。

填空题


In the following passage, there are 20 blanks representing the words that are missing from the context. You are to put back in each of the blanks the missing worD.The time for this section is 20 minutes.
Many things about language are a mystery, and many will always remain so. But some things we do know.
First, we know that all human beings have a language of some sort. (1) is no race of men anywhere on earth so backward that it has (2) language, no set of speech sounds by which the people communicate with one (3) . Furthermore, in historical times, there has never been a race of men (4) a language.
Second, there is no such thing as a primitive language. There are many people (5) cultures are underdeveloped, who are, as we say, uncivilized, but the (6) they speak are not primitive. In all known languages we can see complexities (7) must have been tens of thousands of years in development.
This has not (8) been well understood; indeed, the direct contrary has often been stateD.Popular ideas (9) the language of the American Indians will illustrate. Many people have supposed that the Indians (10) in a very primitive system of noises. Study has proved this (11) be nonsense. There are, or were, hundreds of American Indian languages, and all of them (12) out to be very complicated and very old.They are certainly (13) from the languages that most of us are familiar with, but they are (14) more primitive that English and Greek.
A third thing we know about language (15) that all languages are perfectly adequate. That is, each one is a perfect (16) of expressing the culture of the people who speak the language.
Finally, we (17) that language changes. It is natural and normal for language to change; the (18) languages which do not change are the dead ones. This is easy to (19) if we look backward in time. Change goes in all aspects of language. (20) features change as do speech sounds, and changes in vocabulary are sometimes very extensive and may occur very rapidly. Vocabulary is the least stable part of any language.

选择题