Today's KNOWLEDGE Share:(linear elastic fracture mechanics)
Today's KNOWLEDGE Share:
Time for some really basic "LEFM" (linear elastic fracture mechanics).
Fracture Mechanics essentially assumes all materials or parts do contain "defects".
It is a reasonable assumption if you think about dust and all sorts of contaminants (including fillers with poor surface treatments) present in our polymer plants, compounding facilities and molding shops.
If a defect is small enough, a tensile stress (steady or dynamic) will trigger a relatively stable and slow crack growth rate.
This is captured by the exponent "m", i.e. the slope of the linear region II of the graph shown above.
When the crack "a" reaches some critical length, the stress intensity factor K reaches the value K1c where the crack enters the unstable crack growth region, quickly leading to part failure.
Some polymers are good because the stable crack growth is really slow (low value of "m"), some polymers are good because they survive despite the presence of a large crack (high K1c value).
The overall performance of a polymer, for instance under a fatigue test, is a combination of these two fundamental characteristics.
It is time to brush-up your knowledge about polymer mechanical performance and failure mechanisms.
Source:Vito leo
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#polymers #failuremechanism #crack #compounding #injectionmolding
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