Interface Loads Analysis - % Error

[irq]

Hello group!

today a question regarding interface loads deviation between different models & techniques, global & local models, hand calculation etc.
It is well known if the different techniques and model discretizations will be used (especially the very coarse meshes, remember complete aircraft model to estimate the global forces which are used in more detailed models) the results will deviate from each other.

What is your procedure & experience in this regard? What percent of load deviation are generally acceptable? Is rough 10% to high to say my model is good enough? As per my experience you need very often to build some models, as even the size of the elements has big difference (say within 5-10%) for load distribution at SPC's. Is there any rule to estimate the max. size of the element to not significantly impact the stiffness & load distributions at the interfaces?

I'm looking forward for interesting discussion.
Irq

 

[rb1957]

if you're using "interface loads" to create free bodies within your structure, then the sum of the interface loads should equal your applied loads to within 0.0001% (ie they should balance).

if your free body is statically determinate then each loadpath will be within 0.000000001% (ie there's one and only one solution).

if your fre body is indeterminate, then the loadpaths can vary slightly, very slightly, as the models define the stiffness of each loadpath differently.

another day in paradise, or is paradise one day closer ?

 

[stressebookllc]

From an aircraft interiors standpoint, I can tell you that 1.0" is a very decent size for laminate elements, even 2.0" is acceptable. Other than that, even if your structure is statically determinate, there could be a difference compared to 3D rigid body analysis loads. Like rb1957 said, statically indeterminate means FEA is the only way as the stiffness of the discretized structure will impact the interface loads. Hand calculations may not compare very well (except maybe along some degrees of freedom).

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