Biomechanics
Stent Analysis Lab
1. Introduction
The objective of this lab was to analyse the stresses placed on a stent as it was being
delivered, with two varying deployment diameters of 3.5mm and 6.5mm. The percentagechange in the diameter of this stent due to post-crimping and post-deployment recoil will be
calculated. Any relevant plots of stresses and strains will also be presented.
Initially, the stent analysed had an uncrimped diameter of 1.56mm, before being crimped to a
diameter of 0.8mm, in which the stent goes through recoiling. The stent then experiences
post-crimp recoil, followed by deployment to 3.5mm/6.5mm. After the balloon deflation,
recoil takes place, and the stent undergoes fatigue loading.
Below, in Figure 1, is the True Stress Strain Curve of 316L Stainless Steel calculated in this
lab.
True Stress Strain Curve for 316L Stainless Steel
700
True Stress σ (MPa)
600
500
400
300
True Stress/Strain Curve
200
100
0
-0.1
0
0.1
0.2
0.3
0.4
True Strain (ε)
Figure 1: True Stress Strain Curve for 316L Stainless Steel.
2. Results of 3.5mm stent deployment
0.5
Contour Plots
Figure 2: Von-Mises Stress during the crimping (3.5mm deployment)
Figure 3: Equivalent Plastic Strain during crimping (3.5mm deployment)
Figure 4: Von-Mises Stress during deployment (3.5mm)
Figure 5: Equivalent Plastic Strain during deployment (3.5mm)
Figure 6: Maximum Principal Stress during deployment (3.5mm)
Goodman Diagram
Goodman Diagram for Stent with 3.5mm deployment
400
Alternating Stress (MPa)
350
300
250
200
Alternating Stress vs Mean Stress
150
Safety Line
100
50
0
-100
0
-50
100
200
300
400
500
600
700
Mean Stress (MPa)
Figure 7: Goodman's Diagram for stent with 3.5mm deployment diameter
Percentage Change in Stent Diameter due to post-crimp recoil
Both distances, 𝑑𝑟 and 𝑑𝑐 seen below were measured using the Distance tool present in
Abaqus.
Percentage Change in Stent Diameter due to post-deployment recoil
Both distances, 𝑑𝑟 and 𝑑d seen below were measured using the Distance tool present in
Abaqus.
Paris Law
3. Results of 6.5mm stent deployment
Contour Plots
Figure 8: Von Mises Stress during crimping (6.5mm)
Figure 9: Equivalent Plastic Strain during crimping (6.5mm)
Figure 10: Von Mises Stress during deployment (6.5mm)
Figure 11: Equivalent Plastic Strain during deployment (6.5mm)
Figure 12: Maximum Principal Stress during deployment (6.5mm)
Goodman Diagram
Goodman Diagram for Stent with 6.5mm
deployment
400
Alternating Stress (MPa)
350
-200
300
250
200
150
100
50
0
-100
-50 0
100
200
300
400
500
Mean Stress (MPa)
Alternating Stress vs Mean Stress
Safety Line
Figure 13: Goodman's Diagram for stent with 6.5mm deployment diameter
600
700
Percentage Change in Stent Diameter due to post-crimp recoil
Both distances, 𝑑𝑟 and 𝑑𝑐 seen below were measured using the Distance tool present in
Abaqus.
Percentage Change in Stent Diameter due to post-deployment recoil
Both distances, 𝑑𝑟 and 𝑑d seen below were measured using the Distance tool present in
Abaqus.
Paris Law
4. Conclusion
A higher percentage of recoil can be seen in the stent with 3.5mm diameter than the stent with
6.5mm diameter.
The overextended stent also showed higher values of plastic strain (PEEQ), which implies
that the recoil percentage decreases as the plastic strain experienced increases, due to
excessive deformation causing damage to the sent and reducing its recoiling capacity.
Stent over-deployment causes damage to the stent, while stent under-deployment can cause
the stent to dislodge; both scenarios that could be fatal to a patient’s life.
From the Goodman’s Diagram, it is clear neither stent exceed the safety line, making these
two stents safe. The maximum crack size seen were 2.91μm and 79.9μm for the 3.5mm and
6.5mm radius respectively, both of which were calculated through FDA standards.