×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Rubber degradation under cyclic loads

Rubber degradation under cyclic loads

Rubber degradation under cyclic loads

(OP)
Do the properties of "Natural Rubber" degrade quicker under cyclic stress conditions or will it be more environment dependant?  The point in case is a car shock ansorber and "perishing" (aging/loss of elasticity) of the rubber.

RE: Rubber degradation under cyclic loads

Steve,

It depends on cyclic stresses, the geometry of the part, and the environmental conditions.

For example, suspension bushes on a intensively used off highway truck will always fail through fatigue or mechanical damage before ageing becomes an issue, often around the 5,000 hour mark. Mechanical fatigue results in a loss of stiffness- a part is considered to have failed if the stiffness has dropped by 25-30%

Ageing of a rubber part is bought about by ozone attack, UV radiation, and high operating temperatures.
Ozone attack causes a hardening and cracking the rubber surface, but in practice this rarely results in the failure of components. As it is a diffusion process, it is dependent on the exposed area of the rubber, compared to its' volume. For most load bearing parts the exposed area is quite small, and most natural rubber elastomers are compounded to resist ozone attack with the addition  of waxes to the polymer. To be frank, degradation due to exposure to fuel and mineral oils is more likely.

Ageing of a rubber depends on temperature to a certain extent, and will result in a gradual stiffening over time (7-10 years is reasonable), and a deterioration in noise isolation performance.For a part loaded in compression it is unlikely that this would cause the component to fail.

To summarise, if you drive your car fast over rough roads, deterioration through fatigue, leading to a loss of stiffness and breakdown of the part is more likely. However, gradual ageing (and stiffening) will predominate in a gently driven  vehicle.

For a shock abosorber bush, the shock absorber itself will probably need changing before the bushes fail!

I hope this goes some way to answering your question

Regards

Tom Aspin

RE: Rubber degradation under cyclic loads

Besides the environmental conditions the natural rubber part is exposed to , including the type and intensity of use it undergoes. Degradation of natural rubber parts will depend very much on the rubber curing formulation and the type of crosslinking formed during vulcanisation. This will all depend on the chemicals and conditions used to cure the natural rubber.

Cyclic loadings can be designed into a rubber part by skilled rubber technologists using thier knowledge of the properities  obtained by varying the type and levels of accelerators, thiurams, and sulphur donors.

Newer vulcanisers such as AS100, TBUT and SAA30 can be used to improve the  dynamic properities obtained from traditional chemicals such as DPTT and TMTD

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources