Duplicate node output when using fieldoutput

When using fieldoutput, if a node is used more than once (e.g. a node contacts with more than one master surface), multiple field output will be created for the same node. It will cause that created XY data has a duplicate X value and fail any XY data operation with different XY data.

Stent design parameters

1. Flexibility: Apply angular displacement on both ends and measure the reaction moment. The unit for this study is Moment(Nmm) vs. Angle/length (rad/mm)
2. Radial recoil: (R_load-R_unload)/R_load
3. Foreshortening: (L-L_load)/L
4. Radial Strength: force per unit of length when stent suddenly collapse
5. Fatigue Safety Factor (FSF).The FSF was estimated by using the modified Goodman relationship (Shigley, 2001)

FSF ≡ Fatigue Safety Factor response
• Sa ≡ Alternating Stress response
• Sm ≡ Mean Stress response
• Se ≡ Stent Material’s Endurance Limit (10 year fatigue life equivalent of blood pressure
loading)
• Suts ≡ Stent Material’s Ultimate Tensile Stress (defined in terms of true stress)

Reference: Baillargeon et al SCC 2011

Stent expansion methods

Three approaches:
(i) ignoring the balloon and applying an increasing uniform pressure directly on the stent inner surface.
(ii) accounting for balloon-stent interaction and enforcing a radial
displacement-driven process on a cylindrical balloon (using rigid body surface RSURFU).
(iii) accounting for balloon-stent interaction and applying an increasing uniform pressure inside of balloon (using hydrostatic element or surface).

Using membrane elements to better capture surface strains

There has always been some concern with finite element analyses using solid elements that the most exact characterization of field quantities occurs at the integration points, which are located in the interior of the part being modeled, whereas often (particularly where significant bending or torsion is involved) the largest strains occur at the surface, which are traditionally available only by extrapolation from the integration points to the nodal points using the element’s shape functions. The M3D4R membrane elements in this study is to “trick” the solver into providing surface values that are more exact and are not interpolated. (DeHerrera 2009)