P1 internal stress
P2 material complicated and interesting, 不太能避免internal stress好多东西都有internal stress, 有利有弊,analytical cmpetence
P3 proliferation of nontraditional materials. /triming of safety margins/reduction in the scale of many engineered systems
P1:压力在工业制作的基本用途;人们对压力的负面认识
P2: 对P1中人们误解的反驳,点出internal stress在工业中的必要性和应用;beneficial转折后为harmful
P3: 3个趋势 - 1. proliferation of nontraditional materials;2. trimming of safety margins;3. reduction in scale of engineered systems