问题 问答题 简答题

简述冷加工纤维组织、带状组织和变形织构的成因及对金属材料性能的影响。

答案

参考答案:

冷加工纤维组织是纯金属和单相合金在冷塑性变形时和变形度很大的条件下,各晶粒伸长成纤维状;带状组织是复相合金在冷塑性变形和变形度大的条件下第二相被破碎或伸长,沿变形方向成带状分布而形成的;变形织构是金属和合金在在冷塑性变形时晶粒发生择优取向而形成的。

上述冷加工纤维组织、带状组织和变形织构都使材料的性能具有方向性,即在各个方向上的性能不均,对使用性能有不良影响,但少数金属材料,如用作变压器的硅钢片,各向异性能更好满足使用要求。

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单项选择题

Proper arrangement of classroom space is important to encouraging interaction. Most of us have noticed how important physical setting is to efficiency and comfort in our work. College classroom space should be designed to encourage the activity of critical thinking. We may be approaching the twenty-first century, but step into almost any college classroom and you step back in time at least a hundred years. Desks are normally in straight rows, so students can clearly see the teacher but not all their classmates. The assumption behind such an arrangement is obvious. Everything of importance comes from the teacher.
With a little imagination and effort, unless desks are fixed to the floor, the teacher can correct this situation and create space that encourages interchange among students. In small or standard-size classes, chairs, desks, and tables can be arranged in a variety of ways. The primary goal should be for everyone to be able to see everyone else. Larger classes, particularly those held in lecture halls, unfortunately, allow much less flexibility.
Arrangement of the classroom should also make it easy to divide students into small groups for discussion or problem-solving exercises. Small classes with movable desks and tables present no problem. Even in large lecture halls, it is possible for students to turn around and form groups of four to six. Breaking a class into small groups provides more opportunities for students to interact with each other, think out loud, and see how other students’ thinking processes operate all essential elements in developing new modes of critical thinking. In courses that regularly use a small group format, students might be asked to stay in the same small groups throughout the course. A colleague of mine, John, allows students to move around during the first two weeks, until they find a group they are comfortable with. John then asks them to stay in the same seat, with the same group, from that time on. This not only creates a comfortable setting for interaction but helps him learn students’ names and faces.

The author mentioned John in Paragraph 4 in order to ______.

A. describe a good seat-arrange mode in courses with small group format
B. give an example that students stay in the same seat throughout the course
C. create a comfortable setting for interaction
D. learn students’ names and faces