An M36X4 ISO metric bolt is used in a joint at recommended preload of 0.85 proof

Question

An M36X4 ISO metric bolt is used in a joint at recommended preload of 0.85 proof load. The bolt and the members are all made up of steel (PS= 650 MPa, S_ut=900 MPa, Se=140 MPa). The joint s subjected to a repeated tensile fatigue load of 0 to 120 kN. The joint stiffness factor C = 0.22. Find: Factor of safety against infinite fatigue life (N_f). Assume K_fm= i and K_fa = 5.7 +0.02682d (where, d is me nominal or me major ammeter in 'mm'). Use Table 15-2, Page 897for bolt tensile stress area and diameter. Coarse threads.

Explanation / Answer

Factor of safety , Nf = Kfm * (Ps/Sut) * sqrt(5.7 + 0.02682d) * C * Se/Lmax

                                        =   1 * (650/900) * sqrt(5.7 + 0.02682 * 0.85) * 0.22 * 140/120

                                 = 0.4434

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