Fatigue Strength of Screw Joints

Endurance limit and allowable preload range for infinite-life design.

Section A

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Strength class

Minimum clamping force F_m kN

Joint stiffness factor C_m

Key results

Max. bolt fluctuation P_b

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Min. preload F_i,min

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Max. preload F_i,max

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Total fluctuation P

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Endurance strength σ_e

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Load at yield F_0.2	—	kN
Clamped-part fluctuation P_m	—	kN	P_b(1−C_m)/C_m

Design for infinite fatigue life (>10⁶ cycles): keep working stresses below the endurance limit. Endurance strength σ_e = 0.75(180/d + 52) MPa (d = nominal diameter). P_b = 2A_tσ_e; P_m = P_b(1−C_m)/C_m; F_i,min = F_m + P_m; F_i,max = F_0.2 − P_b.