Tail Light Crazing

Anybody seeing tail lights craze like this?

There has been no impact to this area and the external surface is smooth. The turn signals in the mirrors have similar issues.

 

I didn't know that "crazing" was even a word. And this was not what I was expecting when I clicked on this thread. But thanks!... I'm guessing that maybe heat could be causing it?? I'm really not sure... Thanks again for the word, tho

 

Seriously, I thought that this was going to be some weird shit like fan girls over-obsessing about tail lights... But here is what I've learned so far with the help of the online universe...

"Crazing is the phenomenon that produces a network of fine cracks on the surface of a material, for example in a glaze layer. Crazing frequently precedes fracture in some glassy thermoplastic polymers. As it only takes place under tensile stress, the plane of the crazing corresponds to the stress direction. The effect is visibly distinguishable from other types of fine cracking because the crazing region has different refractive indices from surrounding material. Crazing occurs in regions of high hydrostatic tension, or in regions of very localized yielding, which leads to the formation of interpenetrating micro-voids and small fibrils. If an applied tensile load is sufficient, these bridges elongate and break, causing the micro-voids to grow and coalesce; as micro-voids coalesce, cracks begin to form.

Polymers:
Crazing occurs in polymers, because the material is held together by a combination of weaker Van der Waals forces and stronger covalent bonds. Sufficient local stress overcomes the Van der Waals force, allowing a narrow gap. Once the slack is taken out of the backbone chain, covalent bonds holding the chain together hinder further widening of the gap. The gaps in a craze are microscopic in size. Crazes can be seen because light reflects off the surfaces of the gaps. The gaps are bridged by fine filament called fibrils, which are molecules of the stretched backbone chain. The fibrils are only a few nanometers in diameter, and cannot be seen with a light microscope, but are visible with an electron microscope.

The thickness profile of a crazing is like a sewing needle: the very tip of the crazing may be as thin as several atoms, as the distance from the tip increase, it tends to thicken gradually with the rate of the increase diminishing with distance. Therefore, the growth of crazing has a critical distance from the tip. The opening angle of the crazing lies between 2° to 10°. The boundary between crazing and surrounding bulk polymer is very sharp, the micro-structure of which can be scaled down to 20Å or less, which means it can only be observed by electron microscopy.

A craze is different from a crack in that it cannot be felt on the surface and it can continue to support a load. Furthermore, the process of craze growth prior to cracking absorbs fracture energy and effectively increases the fracture toughness of a polymer. The initial energy absorption per square meter in a craze region has been found to be up to several hundred times that of the uncrazed region, but quickly decreases and levels off. Crazes form at highly stressed regions associated with scratches, flaws, stress concentrations and molecular inhomogeneities. Crazes generally propagate perpendicular to the applied tension. Crazing occurs mostly in amorphous, brittle polymers like polystyrene (PS), acrylic (PMMA), and polycarbonate; it is typified by a whitening of the crazed region. The white color is caused by light-scattering from the crazes.

Besides, the production of crazing is a reversible process, after applied compressive stress or elevated temperature (higher than glass transformation temperature), it may disappear and the materials will return to optically homogeneous state.

Shear banding is the narrow region with high level of shearing strain from local strain softening, it is also very common during the deformation of thermoplastic materials. One of the main differences between crazing and shear banding, is that crazing occurs with an increase in volume, which shear banding does not. This means that under compression, many of these brittle, amorphous polymers will shear band rather than craze, as there is a contraction of volume instead of an increase. In addition, when crazing occurs, one will typically not observe "necking," or concentration of force upon one spot in a material. Rather, crazing will occur homogeneously throughout the material."


So basically, it occurs because after production, internal stresses can remain in the material eventually causing the crazing. It also sounds like you MAY be able to CAREFULLY take a heat gun to it to see if it helps. I will not be liable if this doesn't work or causes more damage. Sorry. You can also try bringing it up to the dealer if the vehicle is still under warranty. But honestly, I would probably forget about it. It's so small that only you will probably ever notice it. Good luck... & thanks for the inspiration to actually get me to learn something new today. For a while there, I thought that I already knew everything, lol...

 

Crazy didn't know craze was a word. Thanks!

 

Ceramics and chinaware will craze on the surface. Looks like a shattered phone screen, just on the very surface.

 

And it’s only Tuesday... Well done though

 

It's from UV. Yes, I've seen it often. My headlights did it a long time ago.
Knew it was coming when starting to see all these bulbous lights on new vehicles that are more and more pronounced to the sun.

 

Knowledge is power.