Fatigue Analysis — validation & limitations

What it calculates

• Goodman, Gerber and Soderberg fatigue safety factor with von Mises combined bending + torsion (σ_a_eq, σ_m_eq)
• Marin endurance-limit correction factors ka (surface), kb (size), kc (load type), ke (reliability) — 40+ built-in materials. Room-temperature only: the temperature factor kd is fixed at 1.0 and is not an input
• S-N (Wöhler) curve with Basquin slope b and operating-point overlay on the log-log plot
• Palmgren-Miner linear damage rule for variable-amplitude loading — up to six stress-range levels with per-level di = n/Nf and cumulative damage D. Enter pre-counted blocks (count them per ASTM E1049); the tool does not perform rainflow counting itself
• Coffin-Manson strain-life (LCF) for low-cycle fatigue below ~10 000 cycles, with elastic/plastic separation and transition-life Nt (ASTM E606)
• Stress concentration factor Kt/Kf interactive interpolator (Peterson/Neuber) for shoulder fillets, grooves, transverse holes and keyways

Validation evidence — independent reference cases (3)

Each case runs the tool's engine on a worked example whose values come from a published source or a hand derivation from the cited equations, and an automated regression test asserts the engine against those values within the stated tolerance. "Conservative" means the engine is known to sit on the safe side of the reference and the test asserts that side. Sources are cited; their text is not reproduced.

• Endurance limit Se through the full Marin factor chain

  Agrees

  Source: Shigley's Mechanical Engineering Design, 9th/10th ed. (SI), §6-7 to §6-9: Eq. 6-8, 6-18, 6-19 (Table 6-2), 6-20, 6-26, Table 6-5; worked Examples 6-3 and 6-4 as anchors

  Inputs: Sut 690 MPa, Sy 580 MPa, machined surface, d 32 mm, rotating bending, 99 % reliability

  Quantity	Reference value	Tolerance
  Surface factor ka	0.797777	1e-5 relative
  Size factor kb	0.855797	1e-6 relative (0.5 % vs book 0.858)
  Reliability factor ke	0.814	1e-12 relative
  Endurance limit Se	191.7325 MPa	1e-4 relative

  tests/golden/REF-fatigue-endurance-limit.golden.test.ts

• Finite life on the S-N line and Palmgren-Miner cumulative damage

  Agrees

  Source: Shigley's Mechanical Engineering Design, 9th/10th ed. (SI): §6-9 Eqs. 6-13/6-14/6-16 (S-N line, f 0.9), §6-12 (Goodman equivalent reversed stress), §6-15 (Palmgren-Miner); AISI 1020 CD from Table A-20

  Inputs: Sut 470, Sy 390 MPa, machined, d 20 mm, bending, 50 % reliability, Kt 1; spectrum 230 MPa × 5e4, 200 MPa × 1e5, 150 MPa × 1e6 cycles

  Quantity	Reference value	Tolerance
  Endurance limit Se	186.7884 MPa	1e-5 relative
  Life at 230 MPa fully reversed	172 275 cycles	2e-4 relative
  Life at σa 150 / σm 120 MPa	528 510 cycles	2e-4 relative
  Miner total damage D	0.468399 (SAFE)	2e-4 relative

  tests/golden/REF-fatigue-finite-life-miner.golden.test.ts

• Fatigue safety factor (Goodman, Gerber, Soderberg) and Langer yield

  Agrees

  Source: Shigley's Mechanical Engineering Design, 9th/10th ed., §6-10 and §6-12: Eq. 6-32 (Kf), Eq. 6-46 (Goodman), Table 6-7 (Gerber), Eq. 6-45 (Soderberg), Eq. 6-49 (Langer)

  Inputs: Sut 690, Sy 580, Se 191.7325 MPa, Kt 1.65, q 0.84; nominal σa 55 / σm 80 MPa (case 1), σa 100 / σm 120 MPa (case 2)

  Quantity	Reference value	Tolerance
  Goodman nf (case 1)	1.605835	1e-5 relative
  Gerber nf (case 1)	1.972892	1e-5 relative
  Soderberg nf (case 1)	1.522710	1e-5 relative
  Goodman nf / Langer nY (case 2)	0.930058 (FAIL) / 1.705280	1e-5 relative

  tests/golden/REF-fatigue-mean-stress-criteria.golden.test.ts

Limitations

Not checked by this tool

• Rainflow counting of a measured load history — Enter pre-counted blocks in the Miner panel; count cycles per ASTM E1049
• Welded joints (detail categories) — The Marin / Goodman method is for machined parts; use the /welds fatigue panel (EN 1993-1-9)
• Crack growth and damage tolerance (fracture mechanics) — Not computed; use a fracture-mechanics assessment for flawed or inspected parts
• Corrosion fatigue and fretting — No endurance limit exists in a corrosive medium; use test data for the environment
• Residual stresses and surface treatments (peening, nitriding, rolling) — No credit or penalty is taken; use test data for treated or ground surfaces
• Elevated temperature and creep-fatigue — kd is fixed at 1.0; above about 250 C apply kd (Shigley Table 6-4) and check creep