It looks like crazing to me:
“Crazing is also called hairline craze. They can be fine, thin, tiny type cracks that may extend in an unreinforced or reinforced network on or under the surface or through a layer of a plastic material. Different conditions and effects occur depending on the type plastic, load conditions, and environment. The formation of crazes are like cracks in that they are wedge shaped and formed perpendicular to the applied stress. They differ from cracks by containing plastic that is stretched in a highly oriented manner perpendicular to the plane of the craze. They are parallel to the applied stress direction. Another major distinguishing feature is that unlike cracks, crazes are able to support stress.
With the application of static loading, the strain at which crazes start to form decreases as the applied stress decreases. In constant strain-rate testing crazes always start to form at a well-defined stress level. Crazes start sooner under high stress levels. When tensile stress is applied to an amorphous (Chapter 1) plastic such as acrylics, PVCs, PS, and PCs, crazing may occur before fracturing. Crazing occurs in crystalline plastics, but in those its onset is not readily visible. It also occurs in most fiber-reinforced plastics, at the time-dependent knee in the stress-strain curve”.
https://www.sciencedirect.com/topics/chemistry/crazing#:~:text=Crazing is also called hairline,%2C load conditions%2C and environment.
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