[考古] 刚看到有楼主放出“残余应力”这篇阅读，求大神拎一下文章结构

还原出来的原文（加粗的是做题时需要参考的定位）：

The average person is likely to feel mildly alarmed on being told that dental fillings contain locked-in stresses. We all have a somewhat hazy understanding that stress leads to fracture and can vaguely recall dramatic instances of stress-related failures. Thus we are likely to feel that all material stresses are without redeeming value and should, if possible, be eliminated.

A truer picture of the behavior of materials is both more complicated and more interesting. It turns out that it is difficult to work a rigid material without introducing permanent internal stresses. Most common manufacturing operations, such as turning, grinding, and peening, can set up internal stresses, and many familiar objects are subject to them, including dental fillings, computer chips, and pipelines. But these residual stresses can be beneficial as well as harmful. Indeed, manufacturers sometimes go to great lengths to introduce them. Many stress-related effects and recipes for obtaining them have long been known to artisans. What is new is the ability to measure the stress fields directly rather than inferring their nature from warpage and breakage. Several trends in engineering design make this analytical competence important.

One of the trends is the proliferation of nontraditional materials. The best way to work a sword or to coil a spring may be known, but no comparable body of lore exists for ceramic transducers or semiconductor wafers or composite airfoils. A second trend is the trimming of safety margins. Bridges and other load-bearing structures have traditionally been built with large safety factors, but the lavish use of materials required by this practice is increasingly uneconomic（原文在这里有改动，给了一些比较具体的数字）; in the case of objects that must be lofted into space, a large safety factor is totally impractical. A third trend is the reduction in scale of many engineered systems. Residual stresses play a much more important role in the microscopic metal interconnects on the surface of a chip than they do in a thick electrical cable.