<p>图示为三角形单元体，已知ab、ca两斜面上的正应力为σ，剪应力为零。在竖正面bc上有:<img alt="" src="https://file.gaojiufeng.cn/learnAppQuestion/9f/f0/9ff0fd22a0091c6f3e47b07d5286c150.jpg" style="width: 100%;height: auto;"><img alt="" src="https://file.gaojiufeng.cn/learnAppQuestion/be/c8/bec8d70698fc291d0800f649e6f2c05b.jpg" style="width: 100%;height: auto;"></p>