User login

Navigation

What we talked about

You are here

Home » Forums » Ask iMechanica

Rubber fatigue testing. Displacement Controlled tests vs Force Controlled test

Wed, 2010-04-14 09:50 - Álvaro Sañudo Acosta

Hi,

 I need some advice about the next topic. I've been asked to develop a Haigh Diagram for Natural Rubber as André et al.{1} or Saintier et al. {2} do, and from it, be able to predict the fatigue life of a train suspension. This authors carried out the fatigue tests under displacement control and they considered that the sample had failed when a 1mm crack appeared, because they were studing the crack initiation.

However, train´s suspension supplier I work with is asked to test its product under controlled force. The reason is that the suspension works under cyclical forces due to the car weight, centrifugal forces in curves etc. The failure criterion must be a 20% drop in the suspension's stiffness. 

Then the following question arises:

 It is possible to determine the fatigue life of suspension that have to be tested under force control (due to manufacturers' requirement) from a Haigh Diagram developed with test conducted under displacement control?

Could you recommend me links related to the topic?

 Thanks,

Alvaro.

 {1} N.André, G. Cailletaud, R.Piques. Haigh diagram for fatigue crack initiation prediction of natural rubber components. Kautschuk Und Gummi Kunstoffe 1999; 52:120-3

{2}N.Saintier, G.Cailletaud, R.Piques. Multiaxial fatigue life predictor for a natural rubber. International Journal fo Fatigue 28(2006) 530-539

 

Forums: 
Ask iMechanica
»

Submitted by Álvaro Sañudo Acosta on Wed, 2010-04-21 06:47.

Hi again,

My doubt is due to:

  • As the stiffness drops due to the crack growth, and if we take into account the large displacements that the rubber withstand, in tests under controlled force the test piece is submited to a slightly bigger quantity of elastic energy. The opposite happens in a test under controlled displacement.

Notice that due to the large displacements, we have to define the Haigh diagram with Cauchy Stress, which is obtained from strains s=f(e); where s=stress, e=strain.

 Thus, only under displacement control we can assure that during the initiation and/or slow crack growths phase any material's plane is submited to a "constant" cyclical deformation (Obviously except those ones which are fixed) and therefore, to "constant" cyclical strain and stress state.

So in my oppinion it can be formidably difficult to predict the fatigue life of a sample with an acceptable accuracy from tests conducted under controlled force. Am I right? 

 Has anybody worked in the topic before?

I'm doing some research in the topic. I let you know my advances

Thanks,

Álvaro

 

»
Subscribe to Comments for "Rubber fatigue testing. Displacement Controlled tests vs Force Controlled test"

Recent comments

More comments

Syndicate

Subscribe to Syndicate