When designing plastic parts, it is necessary to know the mechanical properties of the resin to be used.
Especially when used as a structural part, if you do not know the S-S curve (stress-strain curve) of the material to be used, there is a possibility of fracture during use.
Failure to know the S-S curve (stress-strain curve) of the material to be used may result in fracture during use.
Below are typical S-S curve diagrams for non-reinforced plastics.
Figure1. non-reinforced plastic
Elastic region means the region that returns to the original state (the amount of strain returns to zero) after the stress is removed.
The plastic region is the region that does not return to the original state (the amount of strain remains) after the stress is removed.
For example, if a plastic underlay is bent lightly, it will return to straightness, but if it is bent strongly, the underlay will turn white or remain bent.
(This means that the underlay has been deformed to the plastic region by the strong bending.
Most non-reinforced plastics have a plastic region even beyond the elastic region, so even if stresses exceeding the material strength occur, they rarely result in immediate failure.
So what happens in the case of fiber-reinforced plastics?
Figure2 . reinforced plastic
There is almost no plastic region, and the pattern often leads to failure as soon as the stress reaches the fracture strength. Fiber-reinforced plastics tend to have a higher Young's modulus than non-reinforced plastics, but lower fracture strain, due to the physical properties of the fibers.
Fiber-reinforced plastics are being actively considered as an alternative to metals due to their high Young's modulus.
However, they are susceptible to fracture when subjected to loads or stresses outside of the expected range, so the operating environment and safety factor settings must be carefully considered.
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