The Stress in first principal direction result shows the first principal stress (maximum normal stress) in the part (Warp or Stress analysis), or in the wire or paddle (Microchip Encapsulation analysis), at the selected position through the cross-section, after ejection.
Positive values correspond to tension in the part, and negative values correspond to compression.
Consider the first principal stress result when the material is brittle. Consider the areas with a high level of stress and compare the results against the relevant material criteria. If the absolute value of the first principal stress of an element is greater than the relevant material criteria, then the part will fail.
Note that the plot corresponds to one particular position through the cross-section, as specified by a normalized thickness value where -1 is the bottom of the element, 0 is the centerline through the element, and +1 is the top of the element.
The normalized thickness value can be viewed or modified on the Animation tab of the Plot Properties dialog.
Also consider the second principal stress when the material is brittle. It is possible for the absolute value of the second principal stress to be greater than the absolute value of the first principal stress if an element is in compression.