An apparent or pseudo change in the sign occurs when a stresstrajectory passes through an isotropic point.
当一个主应力迹线通过一个各向同性点时，该符号会发生一个表面上的或虚假的改变。
2
We may draw curves which have everywhere one of these directions for a tangent, these curves are called stresstrajectory.
我们可以画一簇曲线，这簇曲线处处都有一个主方向作为切线，这些曲线叫做应力轨线。
3
Effects of Well Trajectory in Directional Hole on Casing Stress under Different In-situ Stress Conditions, Progress in safety science and technology, 2005.