Sounds like a fascinating thesis.  I hope I will read this one day.  I have grown believe that cyclic compression loading can drive a Mode-II crack.  I think I can buy that this can also drive Mode-I (if material has fallen out and there is then a moment at the crack front).  Mode-III ... not so much. 

- Jay Eppinga

Firstly it depends on how you are going to load the component for Mode-1 or 2 or 3 type of fracture. In case of cyclic compressive load you apply, you are generating fatigue stresses in the component. These stresses tend to concentrate on the tip of the crack along with a plastic zone created at its tip. Fatigue stresses are more dangerous than normal stresses and can increase the crack propagation rate. You have to choose the material with good fracture toughness (Kt) depending on what load amplitudes you apply as crack propagation once reached critical speed cannot be controlled.  To study the propagation rate it is advisable to have a material with higher value of Kt.

- Akhil  Deshpande 

I think it is a very much debatable topic to realize crack initiation under cyclic compression loading, There is no crack opening delta K, only delta K closure or 0 delta K, I think that will make definition of crack initiation threshold a bit complex as the threshold becoming negative, now people are thinking to study the deviatoric nature of loading intensities, of course that should not mean that crack will propagate in Mixed mode or pure mode II,  those are only the possibilities it may be the crack gets arrested at that site only, obviously microstructures will play a role and very interestingly it may not start from the surface, it may get arrested at inititiation then can initiate in subsurface, ok these stuffs are only speculations from our understanding of compressive contact fatigue tests of rail steel but should not be a reflective when you are doing full scale testing in an UTM, let's see. I am also becoming interested toread your thesis, for initial design of your expts you can take help of some old papers like

10.1111/j.1460-2695.1987.tb00459.x

http://ac.els-cdn.com/S0013794485800382/1-s2.0-S0013794485800382-main.pdf?_tid=7f521064-2588-11e7-ad75-00000aab0f6c&acdnat=1492665564_877d0f2aa6e2772fe76b3a6b713add71

best of luck and looking forward to see the updates and new challenges solved by you

We are working on this problem too! Now we have encountered 2 major problems.

A: Fatigue Crack Growth(FCG) Rate

Crack growth under compression may cause a lot of problems. Since the crack closure and the crack face friction take place during cyclic loading. The crack driving force may be changed by the (tangential) friction force, and fractography may also be destroyed for same reason, which means we could barely find any clue on fractography under compression.

B: Fatigue Crack Growth Path

Opening crack grows in its local Mode I direction, based on LEFM (also MTS criterion), the maximum tensile stress plane. However, tensile stress cannot be find under compression at the crack tip, which means a totally different propagation mechanism. We are trying to figure out what the FCG mechanism is and build up some relationship between the mechanism and FCG path.

Best wishes! Looking forward your solution!

Hi everyone,

Thanks very much for the responses, all my research so far is pointing to cellular buckling and as you have said negative values as in no crack opening! But the opposite happening.

Compression cracks growing from space/areas left damaged from cell collapse leading to crack propagation.

Martin,

This paper by Prof. Suresh may be helpful to your research:

http://www.sciencedirect.com/science/article/pii/S0013794485800382

Again thanks everyone for some good ides and papers to review.

what material are you studying

Aluminium Alloy to EN2635-AL-P2014A

Condition T6511.

I assume that (1) the crack is aligned along the applied compression direction after fracture propagation over large distance and (2) dislocation arrangements form ahead of the crack tip. Internal stresses may develop from these dislocations. Your thesis will be successful if you are able to identify and measure internal tensile stresses perpendicular to the propagating crack. I recommend you to use transmition electron microscopy and, from my own experience, to do this technical job by yourself. Good luck

Sincerely yours