December 21, 2021 at 9:41 am
Rameez_ul_Haq
Subscriber
,I mean we know that the failure region (Inverse Reserve Factors greater than 1) is not gonna go away at all even if thats a singularity. But due to decrease in element size, it might shrink (i.e. still happening at the same elements and not any extra elements, but the size of it will decrease with increase IRF values).
Pardon me for not answering about the direction of ply, and yes the fiber direction (of a UD fiber) of ply 1 (bonded to the spar) is along the length of the wing. And thank you for the feedback on the ply oreintation in figuring out the failure mode.
To be honest, I haven't done a detailed analysis check to figure out if this ply is failing in the direction of fiber (X direction) or the direction of matrix (Y direction). Ofcourse, if the stresses in X direction are higher than the tensile/compressive strength of ply in that direction, then it fails in fiber breakage whereas if stresses in Y direction are higher than the tensile/compressive strength in that direction of the ply, then it fails in Matrix mode (maybe matrix cracking). This can be done easily using the sampling point tool and in the same figure that I posted for IRF of plys in my question, the stresses along the X and Y both directions can be written on the same figure. The problem is sir, I don't know how does a singularity affect the results for composite surfaces. For example, I might be seeing stresses higher in the fiber direction than its strength so I might be thinking that it is because of fiber breakage, but that might be actually a singularity. Similarly, the stresses might be higher in the matrix direction than the strength along that direction and I might be assuming that it is because of matrix failure, but that might be a result of singluarity. You understand, right, where I am going with this?
So the singularity problem is easier for an isotropic material, like I can conduct a mesh convergence study. For a composite material, near me it is not easy at all. That is why I was saying that mesh convergence near the failure region might result in the regions having IRFs greater than 1, to shrink since the mesh size has decreased. If they do, then yes its a singularity, but if they don't instead the region tends to increase, then I am sure that it is not because of singularity (no matter if the ply is failing in fiber breakage mode or matrix failure mode, and how much the stress has increased). In this case, I have to spend much more time in trying to diagnose the actual failure mode, and taking necessary measures to avoid this failure.
Pardon me for not answering about the direction of ply, and yes the fiber direction (of a UD fiber) of ply 1 (bonded to the spar) is along the length of the wing. And thank you for the feedback on the ply oreintation in figuring out the failure mode.
To be honest, I haven't done a detailed analysis check to figure out if this ply is failing in the direction of fiber (X direction) or the direction of matrix (Y direction). Ofcourse, if the stresses in X direction are higher than the tensile/compressive strength of ply in that direction, then it fails in fiber breakage whereas if stresses in Y direction are higher than the tensile/compressive strength in that direction of the ply, then it fails in Matrix mode (maybe matrix cracking). This can be done easily using the sampling point tool and in the same figure that I posted for IRF of plys in my question, the stresses along the X and Y both directions can be written on the same figure. The problem is sir, I don't know how does a singularity affect the results for composite surfaces. For example, I might be seeing stresses higher in the fiber direction than its strength so I might be thinking that it is because of fiber breakage, but that might be actually a singularity. Similarly, the stresses might be higher in the matrix direction than the strength along that direction and I might be assuming that it is because of matrix failure, but that might be a result of singluarity. You understand, right, where I am going with this?
So the singularity problem is easier for an isotropic material, like I can conduct a mesh convergence study. For a composite material, near me it is not easy at all. That is why I was saying that mesh convergence near the failure region might result in the regions having IRFs greater than 1, to shrink since the mesh size has decreased. If they do, then yes its a singularity, but if they don't instead the region tends to increase, then I am sure that it is not because of singularity (no matter if the ply is failing in fiber breakage mode or matrix failure mode, and how much the stress has increased). In this case, I have to spend much more time in trying to diagnose the actual failure mode, and taking necessary measures to avoid this failure.
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