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# Understanding the Spine Simulation Method in Fibersim

Community Manager

When choosing among some of the more complex options for running producibility simulations in Fibersim, understanding the differences among the options and how they interact becomes very important. The most critical thing when exploring these options is to realize that these options exist to simulate different lay-up methodologies, even if these differences are very subtle.

Having a strong understanding of how an actual ply is laid up in the real world is the first step in defining the ply properly in Fibersim. Let’s consider the case of a stringer/spar model that has a high degree of in-plane curvature. The term, “in-plane”, refers to the stringer bending primarily in the same “plane” as the flange (as opposed to “out-of-plane curvature”, which would mean bending in a plane normal to the flange).

If we consider a full-body ply with its origin point near the bottom, right-hand portion of the stringer (as shown), a Traditional simulation with Standard propagation—along with its associated flat pattern—is simple to envision. The layup operator places the piece of material down onto the tool at the origin point, then smooths out the fabric in all directions out from that point.

This methodology may not be desirable, however. Another option is to steer the material around the bend in the stringer by constraining the propagation of the primary fiber to the spine of the stringer. Instead of the layup operator laying down the fabric on the tool at the origin point and smoothing outwards from there, it’s as though the layup operator were folding the ply in half along its length, touching that folded edge down onto the tool along the spine, then smoothing out the ply laterally from the spine:

A third option, however, is available as well. This option is subtly different from the second method above in that we are using a Spine Simulation Method, which requires the same To Curve Propagation. The real-world analog to this is when the layup operator consolidates the majority of the deformation in the main bend near the middle of the stringer, then continues to steer the material along the spine. Further, this methodology more closely matches automated deposition (machine-laid) processes:

[In addition to using a Spine Simulation Method, one can use a Spine-Based Rosette to test for fiber Deviation when the ply’s warp fibers are meant to be constrained along the stringer’s spine, while the weft fibers are to run transverse to the spine.

Again, the subtleties among these three layup methods are important to understand—both in how the Ply objects are defined in Fibersim and in how the actual plies in real life are laid down and smoothed out onto the tool. Depending on different manufacturability concerns (managing deformation) or strength requirements (managing fiber deviation), one method may be more appropriate than another.

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