Impact and Toughness
Rapid material
fracture due to impact conditions may be a concern in many plastic
component designs. Components may be incidentally impacted by dropping,
transportation, accident etc, or they may be impacted by design.
Material toughness will contribute to resistance to failure but several
other factors including part geometry, working temperature and
environment and processing factors will also be significant.
B&B, table 6-8
lists some factors affecting part toughness.
Polymers
variously reported for their good toughness -
Polypropylene PE
Polyethylene PE
PTFE
Toughened PVC
High Impact PS
ABS
Acetal POM
Nylon PA
Polycarbonate PC
PC/ABS Blends
...and under
High Performance Plastics
Polyphenylene Oxide Blends -
PPO/PA, /ABS
etc
possible
PEEK (but depends on info source!)
It is interesting to note that many of these are the
cheaper general purpose plastics, with some
engineering polymers (POM,
PA, PC etc). High Performance plastics are not well represented.
Strong, table 7.1 includes impact data for some
engineering platics.
B&B, table 6-4 shows impact data for a range of polymers.
NB
B&B report that particle fillers & fibre
reinforcements can reduce toughness, this isn't the case for some
composite materials - check the particular polymer grade you are
interested in!
Abrasion Resistance
Generally the abrasion resistance of plastics when
compared to other engineering materials is not great. Alternative
materials with or without surface coatings might be used where high
levels of abrasion resistance are required in a design. However plastics
parts may see abrasive contacts eg carrying cases, exposed shells or
housings, and some plastics will be better at resisting damage than
others.
B&B, figure 9-14 gives wear volumes under sand abrasion
for a range of polymeric materials. It suggests that two materials are
most often associated with abrasion resistance -
Polyurethane PUR
and UHMWPE
PUR is also used as an abrasion resistant coating on, for
example, floors.
Nylons and
Acetals are commonly used in plastic bearing and gearing
applications and these are subjected to surface contact and wear effects.
Strong suggests that Polypropylene
PP is a better material with regard to abrasion resistance than
the Polyethylenes PE.
