- UID
- 1521908
- 在线时间
- 小时
- 注册时间
- 2022-7-2
- 最后登录
- 1970-1-1
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P1 high-tech version of artisanship, engineers manipulate internal stress => desired properties
• Average ppl mildly alarmed: dental locked-in stress
• Hazy understanding: stress=>fracture=> stress-related failure
• Thus: material stress without redeeming value should be eliminated
P2 true picture is more complicated and interesting
• Difficult to work a rigid material without internal stress
} many operations set up internal stress, and many familiar objects subject to them
• But residual pressure is beneficial and harmful
• Indeed, manufacturers go to great lengths to introduce them
• New: the ability to directly measure stress rather than inferring nature
• Analytical competence important
P3
• First trend: the proliferation of nontraditional material
• Second trend: trimming safety margins
Not economiclly
• Third trend: reduction in scale of many engineered systems
Microscopic chip > cable
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