FAILS. Peak 52.3 MPa on the 0.5 mm inside fillet (face 3) at (6.19, 12.6, 6.11). The part cracks at about 0.96x this load.

Confidence: high. passed mesh convergence, force balance, hand calculation, singularities, bolt bearing, units and sanity
Max deflection 3.47 mm at (90, 0, 6).
Material PLA (3D printed), limit 50 MPa; mass 30.29 g.
Loads: 40 N down @ top and within 12 of 65,12.5,6. Fixtures: bolt holes d=4.5; wall x=min.

Checks:
  [pass] mesh convergence: max principal stress settled: 43 -> 50.9 -> 53 -> 52.3 MPa over 4 meshes, last change 1.4%
  [pass] force balance: reactions balance the loads to 0.00014% (forces) and 8.4e-06% (moments)
  [pass] hand calculation: beam theory through the critical section gives 15.2 MPa nominal; FEA peak is 3.45x that, a stress concentration of about 3.4 from the local shape
  [pass] singularities: no sharp corner or support artifact is above the reported stress
  [pass] bolt bearing: worst hole of fix1 (d 4.5 mm) carries 2.7 N sideways and 45.7 N along its axis; bearing stress 0.1 MPa, safety factor 499.33 on bearing
  [pass] units and sanity: part 123 mm across, peak strain 0.015, max deflection 3.47 mm (2.8% of size): all plausible

Assumptions:
  - Linear elastic material and small deflections (no yielding redistribution, no buckling).
  - PLA (3D printed): E 3500 MPa, Poisson 0.36, max principal vs tensile strength 50 MPa (Prusament PLA technical data sheet; Ultimaker PLA TDS).
  - Loads are static and applied all at once; no impact, vibration or fatigue.
  - Printed part treated as isotropic at 100% infill; across the layers it is roughly 60% as strong. Pass --print-direction to check that.
  - Brittle failure: judged by the largest tensile principal stress.
  - Bolted holes are rigidly held over the hole and a washer sized ring (twice the hole radius).
  - Wall supports push but cannot pull (frictionless contact, solved iteratively).
  - Contact between separate parts, friction and preload are not modeled.

Suggested fixes:
  - Stress piles up in the 0.5 mm fillet. A fillet of 3 mm (about half the 6 mm wall) spreads it out. With that radius the peak is usually about 1.4x the 15.2 MPa beam stress, roughly 21.2 MPa (safety factor 2.35).
  - The wall through the peak is 6 mm. To reach safety factor 2.5 it needs 9.7 mm (+62%), because bending stress falls with thickness squared.
  - The peak sits where two walls meet and bend. A gusset as thick as the wall, with legs about half as long as the shorter wall, ties them together and usually cuts the corner stress by half or more.
  - The load acts 58.9 mm from the critical section. Moving a support or the load to within 22.5 mm brings the bending stress to the target.

Images: stress: images/stress.png, zoom: images/zoom.png, safety: images/safety.png, deformed: images/deformed.png, convergence: images/convergence.png, fix_before: images/stress.png, fix_after: fix-gusset/images/stress.png
Report: report.html
