Machine Design and Analysis: Stress, Fatigue, and Components
From stress state to failure
Machine Design and Analysis rewards a disciplined path: determine loads, compute nominal stresses, apply stress concentration only where appropriate, combine into principal or von Mises stresses, then compare with the correct allowable.
Concepts to master. Principal stresses and Mohr's circle; von Mises versus Tresca for ductile static failure; maximum normal stress for brittle materials; K_t (geometric) versus K_f (fatigue notch factor, often K_f = 1 + q(K_t - 1)); S-N curves and endurance limit with Marin factors; mean-stress diagrams (Goodman, Gerber, ASME elliptic); Miner's cumulative damage; shaft design under combined bending and torsion; bearing L10 life; AGMA gear bending and contact stress; bolt preload and joint separation; spring Wahl factor; weld throat area; critical speed and buckling.
Common traps. Treating rotating-shaft bending as steady; applying K_f to mean stress as well as alternating stress; substituting S_ut for S_e; omitting the speed term in bearing life (L10 hours = 10^6(C/P)^3/(60n)); using yield strength in a fatigue check; confusing gear ratio with torque ratio.
Worked example (Goodman). 1/n = sigma_a/S_e + sigma_m/S_ut. With sigma_a = 20 ksi, sigma_m = 30 ksi, S_e = 30 ksi, and S_ut = 90 ksi: 1/n = 0.667 + 0.333 = 1.00, so n = 1.0. If sigma_a rises 10%, 1/n = 0.733 + 0.333 = 1.067 and n falls to 0.94-small load changes matter near the limit.