Vibration Loosening Performance of Additively-Manufactured Bolted Joints

Abstract The vibration loosening performance of threaded joints made of Additively Manufactured (AM) and Cast AlSi10Mg clamped members is investigated. Measurements of under-head friction coefficient are correlated to the vibration loosening results. AM parts are manufactured in 3 different orientations, affecting the angle between the deposition planes and the underhead surface. Loosening rates of AM parts are compared to cast and AM samples with machined surfaces. Conventional flange head M8x1.5 Class 8.8 fasteners are tightened to 5 levels of initial clamp load, ranging from 1 to 18 kN. All samples demonstrate comparable steady-state loosening rates, albeit with different wear patterns. Non-machined AM samples exhibit lower underhead friction compared to machined surfaces at lower preloads. At higher preloads, non-machined AM samples experience a notable increase in the bearing friction coefficient due to surface alterations caused by the sliding bolt head. Furthermore, non-machined AM specimens display significantly higher initial preload loss than machined specimens whereas machined AM joints exhibit similar vibration loosening characteristics to machined cast joints, with comparable loosening rates and sample-to-sample variance. Data variance is also higher for non-machined AM samples. More significant differences between the groups of specimens are observed at lower preloads; higher bolt tension, together with the underhead fretting, alters the surface of the AM samples, and its tribological characteristics. No significant load relaxation/creep is observed for any of the tested specimens. Discussion of the results and conclusions are provided.