Today's KNOWLEDGE Share
Why would glass fibers possibly help with Stress-Cracking resistance in molded parts?
Fibers get strongly aligned in the flow direction by the shear stress, specifically in the frozen skin layers. The core section always shows some more orientation randomness. As a consequence a strong residual stress will appear, because the core "wants" to shrink more than the skin. This accounts easily for a 10-30 MPa stress in a stiff GF filled material (a fractional % of the modulus). The good news is that the core, desperately trying to shrink more, will put the skin under significant compression, protecting your part from Environmental Stress-Cracking, which can only operate in Tension.
Not very different from "rebars in concrete", if you see what I mean.
Source:Vito leo
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