Dear Professor Miyazaki, I appreciate your brilliant jobs on shape memory alloys. I always refer to your works in my research area and Ph.D thesis.
May I ask you what exactly you mean by complex stress state? Does it mean studying multiaxial loading or stress state at stress risers? Whether this study corresponds to fatigue performance or quasi-static fracture behavior or etc?
Many thanks in advance
Pejman
Complex stress state means multiaxial loading performed on athin wall tubular specimen subjected to different combination of an axial force and a torque.
Dear Lech Dietrich,
Many thanks for your kind explanations.
As most of the stent configurations are fabricated through laser cut of such thin-walled micro-tubes, and due to the fact that zigzag-shaped stent struts undergo either the compression-compression or tension-tension at critical points (in operation conditions under blood pulsation), I am curious in the results of the strain-controlled bending-rotation tests especially under different percentage of completion of phase transformation. The combined rotation can then mimic the stent twisting due to the unique anatomical, biomechanical and hemodynamic forces applied to (specially) superficial femoral and popliteal arteries during daily leg movements. Another factor that I could not see in the literature of "micro-tubes" to be investigated, is the role of "Af-Test Temperature difference" (in strain controlled fatigue loading) on the fatigue performance of micro-tubes. As we know, the high amount of such temperature difference lead to suppressed martensitic transformation and in strain controlled tests it results in very high stress amplitudes; in other side, very small such temperature difference (in strain-controlled conditions) result in lower stress levels but higher level of completion of cyclic martensitic transformation. When we can obtain an optimum point between these parameters (in point of view of better fatigue performance), we can determine the desired Af, that can be assessed by specific heat treatments. Fairly, I imagine that, if the mean strain and strain amplitude for the tests, are estimated through finite element simulations, then the exerted results can be of more interest of the industry.
Because the range of the stent diameters and the proposed vessel diameters' rang are available from the stent producer webpages. Then by a set of finite element simulations, fairly we can obtain the rang of mean-strain and strain amplitude at the critical points of the stent struts (under the pulsation), and establish the corresponding experiments.
These all, make me really interested in this project and your future results.
Kind regards and good luck for your project
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