Derek Covill's blog for teaching and research

a collection of subject notes, guides and projects

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# finite element analysis (FEA)

Linear elastic models: linear = proportional, elastic = recoverable (not plasticly deformed)

• tension (pulling); stress (MPa) = normal  force (N) /area (mm2)…= F/A
• compression (pushing);  stress (negative MPa) = normal force (N) /area (mm2)… = F/A
• shear (along surface); stress = shear force (N) / area (mm)… = F/A
• bending (flexure); bending stress = moment (Nm) X distance from neutral axis (m) / second moment of area (m4)…= My/I
• torsion (twisting); shear stress = torque (Nm) x radius (m) / polar second moment of area (m4)…Tr/J
• peel (bond strength)
• cleavage (rigid peel)

second moment of area calculator

polar second moment of area calculator (Ip)

Bending stress formulas

Main failure modes to consider:

• yielding (plastically deformed): stress (MPa) < yield strength (MPa); safety factor =  yield strength (MPa) / max stress (MPa);  if safety factor <= 1 then yielding occurs. Run static study.
• buckling (under compression + high aspect ratio): if buckling load factor < 1 then buckling occurs. Run buckling study.
• fatigue (accumulated damage, e.g. comet plane): Fatigue strength (MPa) = stress at which failure occurs after n cycles (see S-N curve); If the max stress > fatigue strength, then fatigue failure occurs. Run static study but compare to fatigue strength, not yield.
• delamination (separation of layers): difficult to simulate.

Some useful videos on creating, editing and using various tools in FEA using Solidworks Simulation:

https://blogs.brighton.ac.uk/covill/category/guides/fea/