PCB closeup with marked antenna

Photoelasticity describes changes in the optical properties of a material under mechanical deformation. It is a property of all dielectric media and is often used to experimentally determine the stress distribution in a material, where it gives a picture of stress distributions around discontinuities in materials. Photoelastic experiments (also informally referred to as photoelasticity) are an important tool for determining critical stress points in a material, and are used for determining stress concentration in irregular geometries.1

To see internal stresses in transparent object you can use / buy a polariscope or your IPS / LED monitor (displaying white background) and a camera polarizing filter / polarizing film used to capture outdoors pictures without strong light reflections.