Three Tips for Fatigue-Resistant Bracket Design

Brackets under cyclic loads often fail from fatigue cracks starting at stress concentrations. To boost fatigue life, focus on geometry, material, and assembly. Each aspect can prevent crack initiation or slow growth.

First, eliminate sharp corners. Use generous fillet radii—at least 0.5 times the bracket thickness—to lower stress concentration factors. Even a small radius drastically reduces peak stress. Also avoid sudden cross-section changes.

Second, choose a material with a high endurance limit, like 7075-T6 aluminum or 4140 steel quenched and tempered. Surface finish matters: polishing or shot peening removes machining notches and introduces compressive residual stress, further resisting crack initiation.

Third, design bolted joints to keep brackets in compression. Preload bolts to 75% of yield strength to prevent separation and reduce alternating stress. Ensure bolts see pure tension, not bending. Cantilevered brackets should be avoided or stiffened.

Apply these guidelines with FEA verification. Investing in fillet radii and preload pays off in longer service life with minimal cost increase.

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