Catheter Analysis tab
The Analysis tab reports the predicted static properties of each section once the model is built. Until you build, it shows a short "build the model first" state with a button that takes you to Catheter Setup.
Sections are read one at a time. Pick one from the Sections list in the left rail and its KPI cards fill the page, with that section's peel-away and cross-section drawings beside them. The catheter's color bar runs down the outer margin, proximal at the top, and clicking a band jumps to that section. Figures that belong to the whole catheter rather than to one section sit in the Catheter Total card under the picker. The drawings and the numbers are both the model you built: edit the design in Catheter Setup and nothing here moves until you build again.
At a glance
| KPI | What it tells you | Section below |
|---|---|---|
| Tensile: First Yield (estimated) | Axial pull at which the first layer starts to take a permanent set. | Failure Mode Analysis |
| Tensile: Peak Force (estimated) | Axial pull at which the first material reaches its tensile strength: an onset, not the higher ultimate rupture load. | Failure Mode Analysis |
| Torque: First Yield (estimated) | Applied torque at which the first layer starts to take a permanent set in twist. | Failure Mode Analysis |
| Torque at Failure (estimated) | Applied torque at which the first material reaches its shear capacity. | Failure Mode Analysis |
| Min. Bend Radius (first yield) | Core sections: bend radius at which the core polymer first takes a measurable permanent set. | Failure Mode Analysis |
| Yield Moment (first yield) | Core sections: the bending moment at that first-yield radius. | Failure Mode Analysis |
| Burst: First Yield (estimated) | Internal pressure at which the first layer starts to take a permanent set. | Failure Mode Analysis |
| Burst Pressure (estimated) | Internal fluid pressure at which the wall ruptures. | Failure Mode Analysis |
| Crush: First Yield (estimated) | External pressure at which the first layer starts to take a permanent set. | Failure Mode Analysis |
| Crush Pressure (estimated) | External pressure at which the structure collapses inward. | Failure Mode Analysis |
| Kink Mandrel | Simulated: largest mandrel the section can be wrapped on before it kinks. | Kink Radius |
| Kink Mode | Simulated: which event set the kink, the collapse onset or 50 % lumen loss (the ISO kink). | Kink Radius |
| Collapse Onset Mandrel | Simulated: the mandrel at which the bending moment peaks, the onset of collapse. | Kink Radius |
| Collapse Mode | Simulated: how the section ends when bent tighter: moment peak, snap-through, lumen closure, or not applicable. | Kink Radius |
| 50 % Lumen Loss Mandrel | Simulated: the mandrel at which the lumen has lost half its area. | Kink Radius |
| Snap-Through Mandrel | Simulated: the tightest mandrel at which the section still holds a stable shape. | Kink Radius |
| Bending Stiffness (EI) | Resistance to bending. Drives trackability and tip behavior. | Stiffness Properties |
| Bending Stiffness (EIx / EIy) | Anisotropic sections: the device-axis bending pair, in place of the single EI. | Stiffness Properties |
| Torsional Stiffness (GJ) | Resistance to twisting. | Stiffness Properties |
| Axial Stiffness (EA) | Resistance to stretching/compression along the axis. | Stiffness Properties |
| Axial Compliance (L/EA) | How far a section stretches or compresses per unit axial load. Sums over sections to a catheter total. | Stiffness Properties |
| Torsional Compliance (L/GJ) | How far a section twists per millinewton-meter of torque. Sums over sections to a catheter total. | Stiffness Properties |
| Linear Density | Mass per unit length. | Stiffness Properties |
| Braid / Coil characteristics | Angle, pitch, coverage, fill factor and wire length, per reinforced layer. | Reinforcement Characteristics |
| Total Length, Total Mass | Whole-catheter dimensions. | Catheter Total |
| Stiffness Transitions | The EI step between each pair of adjacent sections. | Catheter Total |
Units adapt to the global Metric/Imperial setting (see Menu Bar > Units). See Model accuracy for typical accuracy by regime.
Failure Mode Analysis
Kink and collapse are not predicted by a closed form here: a single number cannot see the bend direction, the pull-wire lumens, a guidewire in the bore, or which layer takes a set first. They are simulated instead by the Kink Radius tab, which publishes its results to the Kink Radius card below.
Each failure value has a First Yield (estimated) row above it: an estimate of where the first layer starts to take a permanent set, which is the margin to design against. No catheter standard defines a yield endpoint (the ISO 10555-1 tensile and burst tests report a peak or break value), so treat it as a design margin, not a test result. Each layer's limit is its material's Yield Strength from the Materials Library (for nitinol, the strain at which it starts to take a set). Hover any of these rows to see which layer and material set the value. A First Yield row reads --.-- when it cannot be given with confidence, and its hover says why: a layer that could yield first has no published yield (the material is named), or no layer has a yield point at all (soft elastomers). A material that breaks without yielding, such as tungsten, gives a First Yield equal to the point where it fails. A row that has no value for any section is hidden.
- Tensile: First Yield (estimated): the axial pulling force at which the first layer in the section starts to take a permanent set, the first wire or polymer reaching its yield. A layer with no yield point, such as a soft elastomer, never sets it.
- Tensile: Peak Force (estimated): The axial pulling force at which the first material in the section is predicted to reach its tensile strength. As the section stretches, its wall narrows, so a braid wire stretches less than the section does (and a near-circumferential wire not at all). Polymers are taken as linear up to their tensile strength, so this is not a polymer's yield point (a polymer that yields first, as most stiffer grades do, starts to deform permanently at a lower load), and not the ultimate rupture load, which is higher because ductile wires keep carrying load past it. The First Yield row above it gives the load at which the first layer starts to set.
- Torque: First Yield (estimated): the applied torque at which the first layer starts to take a permanent set in twist, a polymer reaching its shear yield or a wire reaching its yield. Pull-wire liners are included.
- Torque at Failure (estimated): The applied torque at which the first material in any layer is predicted to reach its shear capacity.
- Min. Bend Radius (first yield) and Yield Moment (first yield): shown for multi-lumen core sections only, where a solid shaped core replaces the round bore these pressure limits assume.
Column buckling is not reported as a per-section number here: a single Euler load says little about a real push, where the free length, the tip's end condition and vessel support change the answer by an order of magnitude. Use the Pushability tab for the push-force / buckling curve of the free distal length under the end conditions, vessel support, and friction you choose.
- Burst: First Yield (estimated): the internal pressure, tip closed off, at which the first layer starts to take a permanent set, on the same wall the burst pressure uses.
- Burst Pressure (estimated): The internal fluid pressure at which the wall bursts, with the tip closed off as in a burst test. The layers stretch together around the tube and the tube is free to lengthen, so a braid takes hoop load only as far as its wire angle lets it. The reinforcement wires reach their limit early and stop carrying load, and the polymer carries the rest until it bursts, with the swelling of the tube taken into account. Beside a pull-wire lumen only the wall around the lumen, and the lumen's liner, carry load. Hover the row to see which material set the value.
- Crush: First Yield (estimated): the external pressure at which the first layer starts to take a permanent set in hoop compression, on the same wall the crush pressure uses. It reads
--.--when the wall would buckle as a ring before any layer yields, or when a layer that could yield first has no published yield. - Crush Pressure (estimated): The external pressure at which the section fails inward: the lower of the wall buckling as a ring and the wall crushing through its strength. The ring is taken at its weakest section, the thin wall beside any pull-wire lumens, and bends about its own neutral surface, with the external pressure acting on its outer surface and the wall's shear through its thickness included. Braid and coil bands carry the hoop stiffness the wire-level model gives them (the same trained band stiffness the Kink Radius section model uses). Braid and coil wires are not credited in the strength limit. With the legacy stiffness calculator (Help > About) the ring is the older laminate value, in which coil wires are not credited. On a very soft wall, one squashed more than about 10 % around the hoop at that pressure, treat the value as optimistic: the wall closes before it fails.
Kink Radius
This section is the one part of the tab that is not produced by the build. It is filled in by the Kink Radius tab, which bends the section's real cross-section step by step, and it reports what that run simulated.
The tool runs one section at a time, so after a run that section shows its numbers while the others still read Not run. Three different blanks appear on these rows, and they are three different facts:
- Not run: nobody has simulated this section yet. The only one of the three with an action behind it.
- Not reached: the section was simulated and this event never happened on the bend ramp. That is an answer, not a gap.
--.--: the tab's marker for "computed, not applicable here". On these rows it means the section can never be meshed at all, however many times the tool is run: a manual-stiffness section has no layup, and a rigid section is not in the flexible model.
Rebuilding the model clears these rows: the events were simulated on the previous cross-section, so re-run the sections you care about.
Each event is one row, given as the mandrel a bench wrap would use: mandrel = 2R − OD, the pin, because that is what a bench test measures directly. A mandrel depends on the section's OD, so it does not compare between sections of different diameter; each row's hover says so, and the Kink Radius tab prints the centerline radius beside every event, which does compare. The rows sit in the same order as that tab's results.
- Kink Mandrel: The largest mandrel this section can be wrapped on before it kinks: the earlier of the collapse onset (the section stops resisting the bend and starts to flatten) and 50 % lumen loss (the ISO kink). This is the number to design to.
- Kink Mode: WHICH event set the Kink Mandrel above: the collapse onset or 50 % lumen loss (ISO kink), whichever the bend meets first. None reached means the ramp finished without a kink.
- Collapse Onset Mandrel: The mandrel at which the section stops getting harder to bend and starts getting easier: the peak of its moment-curvature curve. It is a criterion, not a mechanism: on a round tube it is classical Brazier collapse (the bore flattens); on a multi-lumen core the same peak comes from whatever gives first: the webs between lumens folding, a lumen flattening. Nothing has yielded at the peak itself, but the section is losing stiffness from here on and bending past it may damage it. Blank when the moment was still rising where the model stopped: there is no peak to report, and the row's hover says so and gives the bend it stopped at.
- Collapse Mode: HOW this section ends when it is bent tighter and tighter, which a blank Collapse Onset row cannot tell you on its own. A moment peak is the best-converged answer. Snap-through means the run snapped without ever peaking, so the snap becomes the onset, a much wider error band. Lumen closure means it ovalizes shut with no peak and no snap, which is a real answer: this section does not kink, it closes. A solid multi-lumen core reports Not applicable, because it has no bore to ovalize into a limit point and its real failure mode is material strain. Not determined means the bend ramp ended before any of those happened: the only one of them that means "we did not measure it".
- 50 % Lumen Loss Mandrel: The mandrel at which the lumen has lost 50 % of its undeformed cross-sectional area: the ISO 25539-2 / EN 13868 definition of a kink.
- Snap-Through Mandrel: The tightest mandrel at which the section still holds a stable shape. Past it there is no shape it can settle into: it snaps, and the bore closes. This is not the 50 % lumen loss above it: the lumen is often still well open here, and the ISO kink may never be reached at all. What ends here is the section's stability, not its lumen. The model carries no self-contact between the bore walls, so read this as the end of what was solved, and as a bound on anything tighter: an event reported as Not reached may simply lie past it.
- Permanent Set Mandrel (estimated): The largest mandrel at which a layer reaches its permanent-set strain, so the section starts to take a lasting set: it no longer springs back straight. On a reinforced shaft it often comes after the kink, or not at all. Permanent set means the lasting (non-recovering) set of each layer, from each material's published or derived limit; elastomers keep a stiffness-based estimate until measured. The bend it happens at is simulated, so treat it as a guide rather than a number to design a margin against. Hover the row for the layers in the order the bend meets them and the basis of the limit that set it (published, derived or estimated (stiffness law)).
Braid or coil wires lifting out of the wall is a three-dimensional effect the section model can only flag, with a trigger known to within about 2–3×. It is not a row here or on the Kink Radius tab; when the model rates it likely, that tab says so under About this run.
A Design Sweep with its per-section kink simulation enabled reports the same events as centerline radii, so a sweep surface and this page are describing the same measurements. They are not interchangeable numbers: the sweep solves a deliberately coarser screening preset (a 48-point section mesh against this tool's 96, twelve ramp steps against twenty), which is what buys it hundreds of design points instead of one. Where the two disagree, the Kink Radius tab is the better estimate. Mandrels have no sweep column at all: a mandrel depends on the OD, so it cannot be compared across designs of different diameter.
Stiffness Properties
- Bending Stiffness (EI): This value, also known as Flexural Rigidity, defines the catheter section's resistance to bending.
- Bending Stiffness (EIx / EIy): For anisotropic designs, the direction-dependent pair shown in place of the single EI (see Multi-lumen core sections).
- Torsional Stiffness (GJ): This value, also known as Torsional Rigidity, defines the catheter section's resistance to twisting.
- Axial Stiffness (EA): This value represents the resistance to stretching and compression along the axis.
- Axial Compliance (L/EA): How far a section stretches or compresses per unit of axial load: its length divided by its axial stiffness. The reciprocal view of EA, and the one that adds up: sections load in series, so the per-section values sum to the Catheter Total row for it.
- Torsional Compliance (L/GJ): How far a section twists per millinewton-meter of applied torque: its length divided by its torsional stiffness. Sections twist in series, so these also sum to a Catheter Total. Useful for estimating how much handle rotation is absorbed by the shaft before the tip responds.
- Linear Density: This is the mass per unit length of the section.
Reinforcement Characteristics
Calculated for each reinforced layer in each catheter section. Braid layers report:
- Braid Angle: Wrap angle of the braid wire.
- Braid Pitch: The axial distance between successive wraps of the braid wire.
- Braid Coverage: The percentage of the catheter's surface area covered by the reinforcing wires.
- Braid Fill Factor: The volume fraction of the reinforced layer occupied by braid wire.
- Braid Total Wire Length: The total unspooled length of wire required to construct this specific layer for the current section length.
- Filars per Carrier: Wires running side by side within each carrier (a multi-filar or multi-end braid). They widen the band a carrier lays down, so coverage saturates sooner and the weave jams at a lower PPI.
- Axial Wires and Axial Coverage: on a triaxial braid, the number of straight axial wires and the share of the surface they cover, reported separately from the bias-wire coverage above.
Coil layers report Coil Angle, Coil Coverage, and Coil Total Wire Length.
Catheter Total
The card under the section picker holds the figures that belong to the catheter rather than to any one section:
- Total Length.
- Total Mass, when every section's mass is known.
- Axial Compliance (L/EA) and Torsional Compliance (L/GJ) summed over the sections, since both add in series.
- Stiffness Transitions: one row per adjacent pair of sections, giving the ratio of their bending stiffness (EI). A large step concentrates curvature at the joint, which is where whipping and joint kinking start; the step is invisible while you read one section page at a time, which is why it is reported here. Where a section bends differently about its two axes, the ratio uses each section's stiffer axis and the row's hover says so.
Multi-lumen core sections
Sections built on a multi-lumen extruded core report a slightly different KPI set, because a solid shaped core is not a thin-walled round tube:
- Min. Bend Radius (first yield) and Yield Moment (first yield): the bend at which the core polymer first takes a measurable permanent set, from the same per-material limit the Kink Radius tab uses, the meaningful bend limit for a solid core. Conservative: it ignores stress concentration at the lumen webs.
- Bending Stiffness (EIx / EIy): anisotropic designs (shaped cores, ovals, pull-wire-dominated tips with >1% anisotropy) show the device-axis bending pair in place of the single EI row (EIx resists deflection along X, EIy along Y), matching the independent X/Y stiffness the dynamic simulation uses. Isotropic sections within such a design read EIx = EIy = EI; fully isotropic designs show only the single EI row.
- Bending EI (min / max): the principal EI range (which can differ from the X/Y pair on rotated cores) is reported on the wizard's Review page and in the PDF/Excel reports.
- Burst Pressure and Crush Pressure, and their First Yield rows, show N/A: those formulas assume a single round bore. The Kink Radius tab meshes the core itself (its lumens, webs and septa) and is the tool for a core section's bend limit.
Model accuracy
The stiffness values shown above (EA, EI, GJ) and the derived failure-mode KPIs come from VirtuCath's trained stiffness calculator. On seven trusted bench measurements its median error is 6.9%; on a blind test of 400 new designs its median error against the wire-level model it learned from is about 8% in bending and torsion and under 3% in axial stiffness, with the bending of a coil under a braid the least accurate case. Two similar designs share much of the same error, so the difference between them is predicted 3–4× more closely than either absolute value.
See Model Accuracy for the full regime guidance, including accuracy by construction family, how A/B-style design comparisons stay useful where absolute accuracy is wider, and how variation in material properties versus the Materials Library defaults affects predictions.
Related pages
- Catheter Setup Tab: where braid coverage, angle, pattern, and polymer choice are defined.
- Kink Radius: the simulation that fills in the bend limits above.
- Pushability: the push-force and buckling curve that replaced the per-section Euler load.
- Simulation Readouts: runtime metrics (bending moment, bend radius) that reference the same EI used here.
- Model Accuracy: calculator + simulator accuracy characterization, with verification report PDFs.