slimjimmy
Nuclear
- Apr 5, 2011
- 16
Hi Everybody.
I'm modelling Nitinol stent crimp and expansion into an idealised artery in Abaqus/Explicit. I am having numerous problems with the ratio of kinetic energy to internal energy with the analysis. I was hoping somebody may provide me with some insight on this.
I am modelling the crimp stage using a C3D8 elements for the stent and have defined a surface section for the crimper surface. I am using kinetic contact and surface to node contact (surface to surface or genral contact do not work) Everything is in mm so my density for my Nitinol stent is 6.9e-9. I am using semi automatic mass scaling with a time period of 1, scaling to a target time of 1e-5 and at a frequeny of approx every 5 increments. I am getting resonable results for the crimp step, strains at about 8 - 10%. However on expansion of the stent is where the difficulties lie.
Allowing the stent to undergo free expansion into the artery I get a ballooning effect of the stent, (ends start to curve inwards- looks like the opposite to dogboning) and when my stent contacts my artery i get crazy stresses in my stent struts ( 10,000 MPa compared to 300 - 900 MPa in the literature) I am using using penalty contact with surface surface interaction with the stent and artery.
Can anybody tell me why my stresses are so high in my stent? I have looked at my time vs energy graph of both internal energy vs kinetic energy. My energies are way off with the kinetic energies being much higher than the internal erengy in the second step, (should be within 5% of internal energy at all times). Is my mass scaling strategy wrong? Anybody have any ideas.
Any help would be greatly appreciated.
thanks
Slim Jimmy
I'm modelling Nitinol stent crimp and expansion into an idealised artery in Abaqus/Explicit. I am having numerous problems with the ratio of kinetic energy to internal energy with the analysis. I was hoping somebody may provide me with some insight on this.
I am modelling the crimp stage using a C3D8 elements for the stent and have defined a surface section for the crimper surface. I am using kinetic contact and surface to node contact (surface to surface or genral contact do not work) Everything is in mm so my density for my Nitinol stent is 6.9e-9. I am using semi automatic mass scaling with a time period of 1, scaling to a target time of 1e-5 and at a frequeny of approx every 5 increments. I am getting resonable results for the crimp step, strains at about 8 - 10%. However on expansion of the stent is where the difficulties lie.
Allowing the stent to undergo free expansion into the artery I get a ballooning effect of the stent, (ends start to curve inwards- looks like the opposite to dogboning) and when my stent contacts my artery i get crazy stresses in my stent struts ( 10,000 MPa compared to 300 - 900 MPa in the literature) I am using using penalty contact with surface surface interaction with the stent and artery.
Can anybody tell me why my stresses are so high in my stent? I have looked at my time vs energy graph of both internal energy vs kinetic energy. My energies are way off with the kinetic energies being much higher than the internal erengy in the second step, (should be within 5% of internal energy at all times). Is my mass scaling strategy wrong? Anybody have any ideas.
Any help would be greatly appreciated.
thanks
Slim Jimmy