Why longitudinal and shear wave velocities increases after every round of fatigue testing

[student85]

Hi all,

 

Currently i'm have obtained results which shows that both longtiudinal and shear wave velocities increases after every round of fatigue test. Is there anyone can help me explain this phenomenon? is it due to the atomic structure in the material? if possible, plz give some websites or sources that can read more about them. thanks

[John Cuthber]

Not strictly my field but, how do the wave velocities vary with density and stiffness?

How does fatigue testing affect those parameters?

[Enthalpy]

As sqrt(stiffness/density), where the stiffness must match the wave: shear, Young, Young with no side expansion allowed...

 

The observation surprises me. Cold work alone should not change the stiffness, and the density less so - but maybe the material is special? Austenitic stainless steel can transform into martensite by cold work, and martensite is stiffer and lighter than austenite. The effect is even more important with many polymers, for instance polyamide.