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Thursday, July 16, 2015

Stiffness comparison of welded parts - Part 2

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From [Stiffness comparison of welded parts - Part 1], we have 3 different designs of supports subjected to the same loads which we're going to compare their stiffness. Let's start with the Finite Element Analysis (FEA) model of design A.
finite element model with mesh, face loads and fixations
Finite element analysis (FEA) model of Design A
The mounting plate on the right is constrained so that there is no displacement in x, y and z directions. The flange on the left is subjected to face loads in x and z directions which means the support is under bending and torsion. After solving the equations, we get the post processor result as follows.
finite element result of design A (displacement)
FEA result: Displacement of Design A -- typical welding connection
The max displacement magnitude is 14.77 mm and displacement in x, y, and z are as follows.
  • Max displacement in x = -12.2 mm
  • Max displacement in y = 4.4 mm
  • Max displacement in z = -7.5 mm
The same conditions applied on design B and C. And these are the FEA results.
finite element result showing less displacement of design B
FEA result: Displacement of Design B -- additional square tube
The max displacement magnitude is 10.77 mm (27% decreased) and displacement in x, y, and z are as follows.
  • Max displacement in x = -10.1 mm (17% decreased)
  • Max displacement in y = 3.2 mm (27% decreased)
  • Max displacement in z = -2.4 mm (68% decreased)
The displacement in z direction reduces 68% since the additional square tube helps support the bending. The third tube also helps reduce torsion which result in reduction of displacement in x direction by 17%.
finite element result showing less displacement with minimal mass
FEA result: Displacement of Design C -- reinforced plate inserted between square tubes
The max displacement magnitude is 9.7 mm (34% decreased) and displacement in x, y, and z are as follows.
  • Max displacement in x = -8 mm (34% decreased compared to design A)
  • Max displacement in y = 3.1 mm (29% decreased compared to design A)
  • Max displacement in z = -4.8 mm (36% decreased compared to design A)
The displacement in z direction reduces 36% which is less than design B. However, when subjected to torsion, the displacement in x direction is much less than design B. This design is only adding a small piece of steel plate.

Summary:
  • Displacement Magnitude:
    • Design A = 14.77 mm (100%)
    • Design B = 10.77 mm (-27%)
    • Design C = 9.7 mm (-34%)
  • Mass:
    • Design A = 0.9 kg (100%)
    • Design B = 1.3 kg (+44%)
    • Design C = 0.92 kg (+2%)
So design C could improve stiffness with small increment of mass and it isn't difficult to do. There may be other better designs compared to design C, but this is one of the improvements that we can easily gain by minor changes to design.

The following video shows the 3D model in Unigraphics and finite element analysis model with results in LISA finite element analysis software.

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