弯幽应力( Stresses in Beams) §5-2纯弯曲时的正应力 (Normal stresses in pure beams Examine the deformation, deformation 观察变形, then propose the hypothesis 提出假设 geometric relationship Distribution regularity of deformation 变形的分布规律 physical relationship Distribution regularity of stress static 变形几何关系物理关系静力关系 应力的分布规律 elationship Establish the formula 建立公式(Stresses in Beams) deformation geometric relationship Examine the deformation， then propose the hypothesis Distribution regularity of deformation Distribution regularity of stress Establish the formula 变 形 几 何 关 系 物 理 关 系 静 力 关 系 观察变形， 提出假设 变形的分布规律 应力的分布规律 建立公式 physical relationship static relationship §5-2 纯弯曲时的正应力 (Normal stresses in pure beams )