Introduction to practical FEA -3

A: 132 MPa drops the shear contribution and would under-predict yielding in combined loading. 98 MPa treats the state as uniaxial and ignores σy entirely, which masks biaxial effects. 156 MPa applies plane strain assumptions and inflates the equivalent stress for a thin section. 145 MPa comes from the plane stress von Mises formulation using all three terms without artificial constraint.

A: Low-cycle fatigue would leave widespread plastic deformation and fewer, wider striations. Brittle overload gives a granular fracture surface without progressive beach marks. Stress corrosion cracking needs a corrosive environment and typically shows branched cracks. High-cycle fatigue driven by stress concentration matches the beach marks, single origin, and elastic stress range.

A: 2024-T3 is prone to galvanic attack and pitting near stainless in wet conditions. Magnesium AZ91 accelerates galvanic loss and complicates corrosion modeling. Plain carbon steel shifts the problem to coating defects and different thermal expansion. 6061-T6 aluminum with isolation at fasteners reduces galvanic driving force while staying FEA-friendly.

A: 305 kN/mm forgets to convert length to consistent units and overshoots by three orders. 8.4 kN/mm uses shank diameter instead of tensile area. 121 kN/mm applies aluminum modulus by habit from joint members. 305 kN/m follows k = EA/L with consistent units for steel and the given geometry.