Cracked taillight...? [UPDATED]

A couple months ago I realized my drivers side taillight had all types of spiderweb like cracks/scratches (hairline) and it keeps getting worse... these cracks don’t go all the way through (because no condensation inside) but they are reaching the edges where the 2 sides of the taillights meet. Should I have them replaced? Also, there is no specific impact spot where something could of hit it. Anyone else have this issue?





these cracks cover a good portion of the whole taillight as well which is weird



Edit: Over the summer of 2020 the same thing happened again to both taillights. Ended up throwing them away and installing TRD Pro taillights. That seemed to fix the issue.

 

Tough to tell the cause. Did someone try to pry them out? And yes, if it bothers you, replacing seems like the fix

 

Are they on the surface or actually on the inside of the lens? Wondering if they are on the inside of the lens and there is no impact spot, maybe it could be a manufacturing defect and be covered under warranty

 

Almost looks like stress cracks. Possibly a manufacturing defect or could have occurred at installation.
I’d check with your dealer.

 

That’s what I was thinking. I have my inspection here soon so I’ll bring it up then

 

This is know as "crazing". See below...

"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."

 

[UPDATE] I had the driver's side taillight replaced under warranty. The main cause of the cracking was a manufacturing defect in the backside and the right side of the housing which caused the cracks to take place inside, rather than outside of the taillight.

New taillight:

 

Good deal

 

As /having worked in plastic molding ..... There is another thing that can cause this as well ....... Virgin plastics QC is well controlled - but once the raw plastic hits the molder there are a lot of variables. When Starting a run or having problems that cause unacceptable parts - the defective parts (of same/similar? resin and color) are usually thrown into a grinder/chopper to "pelletize" the bad molded plastics. Then the ground material is re mixed with new virgin resin and reused (Toyota parts Spec may be may 10%?? or other % regrind with virgin max). Every time the plastics get reheated and molded some of the capability / "Spec" (i.e., Flex, hardness, uv, etc.) diminish. Some molders will greatly exceed the "10%" or spec for regrind. It reduces scrap and saves money on mfg. SO ... a plastic that has too much, and too many times recycled plastic produces Crap parts such as these. I'd have the supplier "crush and destroy" 1 piece per xxxx made to ensure the parts/resin is still to spec ...... JMO.