select the Stress
Trajectories 
button in the toolbar, OR
select the Stress
Trajectories checkbox under the General tab of the Display Options
dialog.
Stress Trajectories indicate the orientation and relative magnitude of the in-plane major and minor principal stresses. To display Stress Trajectories:
select the Stress
Trajectories button in the toolbar, OR
select the Stress
Trajectories checkbox under the General tab of the Display Options
dialog.
The Stress Trajectories are displayed as intersecting orthogonal lines (a long line for s1 and a short line for s3), displayed at each grid point of the stress grid.
Stress trajectories displayed with Sigma1 contours
Scale Stress Trajectories
The Scale Trajectories checkbox is available under the General tab of the Display Options dialog.
If the Scale Trajectories checkbox is selected, then the size of the stress trajectory lines indicate the relative magnitude of sigma1 and sigma3. If only one line (sigma1 trajectory) appears at a grid point, then sigma3 = 0 (or is very small).
If the Scale Trajectories checkbox is NOT selected, then all stress trajectory symbols will have the same size, regardless of stress magnitude (i.e. the stress trajectories will indicate orientation only).
If a square dot ¨ appears instead of the stress trajectory symbol, this indicates that the in-plane stresses are hydrostatic (s1 = s3) at that point. This symbol will only appear if the Scale Trajectories checkbox is NOT selected.
Complete Plane Strain
If you are using the Complete Plane Strain analysis option, then the Stress Trajectories option will NOT be available. This is because the principal stress orientations are 3-dimensional for Complete Plane Strain, and cannot be represented on the 2-dimensional model. The Stress Trajectories option in Examine2D is only intended to represent the in-plane principal stresses for a Plane Strain analysis.