1. Don’t – underestimate stress
Stress in a component can be caused in different ways and these can be cumulative. Its not just the operational loads that need to be considered. Don’t forget residual stresses locked-in from the moulding process; Assembly stresses; and thermal expansion.
2. Don’t – rely on short term properties
Strength and stiffness values are normally given based on instant tests. But the properties of plastics are dependent on the rate of load application and the time under load. Effects such as creep, fatigue and relaxation can lead to cracking at lower stress than expected, unless the long term properties are considered.
3. Don’t – overlook temperature
Properties of plastics will change significantly as temperature rises. Over typical ambient temperature ranges the properties of metals do not change significantly. For thermoplastics increasing temperature by 10-20 degrees can have a dramatic effect on creep or fatigue.
4. Don’t – ignore the operating environment
In a lot of applications chemical resistance of thermoplastics is excellent. However certain combination of polymer and chemical can have a dramatic effect on durability. Often chemical resistance data does not highlight these effects, which can take several years to occur.
5. Don’t – forget about processing
Manufacturing processes like injection moulding are complex and have a big influence on the final properties of a component. A lack of understanding in the process can cause a wide range of problems.
6. Don’t - be left in the dark
Smithers Rapra have a wealth of experience in the successful use of plastics and rubbers in demanding applications. We can provide designers with assistance in material selection and services to help improve design durability.
FOR MORE INFORMATION
Contact Andrew Hulme
Smithers Rapra Design Services