Laser-Cut Hypo Tube Finite element analysis

Summary

I conducted this analysis intending to demonstrate how finite element analysis can reduce development costs . My goal was to identify the trends of laser cutting patterns on catheter hypo tubes.

During testing, I found that the cut patterns expected to be stiffer than the nominal cut pattern were actually noticeably softer. This sparked my curiosity about whether a simple finite element analysis simulation would show the same trends.

To do this, I created 3-D models of the nominal catheter hypo tube cut pattern and the test cut pattern used in the lab. I didn’t attempt to duplicate the force levels or analyze stresses.

The simulation involved three-inch sections of .066 diameter hypo tube with a .003 inch wall, covered with a .003 inch thick plastic tube bonded to the hypo tube. I modeled the material properties for both the stainless hypo tube and the PBAX plastic material.

I constrained the ends of the assembly completely and applied a 0.25-inch deflection to the FEA models.

The figures show the different cut patterns, constraints, and other details of the analysis models. The force required to deflect each cut pattern would show whether the trend was predicted.

Figure 1– model detail showing cut pattern and tube layers

Figure 2 – Deflected model

 

 

Figure 3 – nominal catheter hypo tube – meshed model

 

Figure 4 – nominal catheter hypo tube – meshed model closeup showing cut pattern  . Cut angle perpendicular to tube axis

 

 

 

Figure 5   test  cut pattern – meshed . Note cut angle

 

Results

catheter cut pattern                                     Force (lb)

baseline/nominal                                         1.20

test                                                                  0.67

Comments

The analysis model made accurate predictions. These predictions matched the trend seen in the catheter tests. Although it over-predicted the stiffness difference between the two cut patterns, the trend is in the right direction.

Finite element analysis is a useful tool in medical product development. It helps us predict how prototypes will behave before we build them. We tested different hypo tube cut patterns. They were less stiff than the standard design. Because of this, we could have saved time. Running 3-D models of hypo tubes using basic finite element analysis first would have helped before building prototypes.