Effects of Surface Treatments on the Fatigue Response of High Strength Fasteners

Abstract

The aim of the present work was the assessment of the impact of deep-rolling and shot-peening performed in the underhead and in the unthreaded shank of two high strength screws (36 NiCrMo and 42 CrMoV) for fatigue life enhancement. The experimental campaign consisted of six combinations, including the non-treated state. The aforementioned treatments were evaluated alone or with shot-peening performed after deep-rolling in the underhead fillet of the screws. Deep rolling was carried out at the optimal rolling force, whereas two shot diameters were considered for shot-peening (Z100 and UFS70). The results have been evaluated in terms of fatigue limits and factor effects have been assessed by marginal mean plots.

Experimental Investigation on the Effect of Shot Peening and Deep Rolling on the Fatigue Response of High Strength Fasteners

“…Connecting rod screws with a reduced shank that is made of two high strength steels has been investigated in the present study, while considering the most frequent failure mode under fatigue with fracture occurring in the region of the underhead fillet radius (with 0.35 mm radius). A two-factor (shot-peening and deep rolling) design has been set-up and two experimental campaigns with different process parameters have been performed, the second one being arranged following the results that were yielded by a former set of tests, already partially reported in [23] and here included for completeness of the work.…”

“…Upon manufacturing, these screws underwent similar treatments (except that they were not ground) to achieve an hardness up to 47 HRC and the static specifications consisted in a tensile strength between 1400 MPa and 1450 MPa, a yield strength of 1250 MPa, and a minimum elongation at fracture of 11%, which were also verified by experimental characterization. factor (shot-peening and deep rolling) design has been set-up and two experimental campaigns with different process parameters have been performed, the second one being arranged following the results that were yielded by a former set of tests, already partially reported in [23] and here included for completeness of the work. Limited by the geometry of the underhead, the residual stress measurement was not feasible with the use of conventional techniques, such as hole-drilling or laboratory X-ray diffraction (XRD).…”

Optimization of Bolted Joints: A Literature Review

“…The outcomes demonstrated a favorable effect of deep rolling on fatigue, particularly for the 42CrMoV steel. Contrarily, the outcome of shot-peening was highly dependent on the set of parameters used, and it might either improve or deteriorate the fatigue life in response to the level of induced surface roughness [48]. A study conducted by Croccolo et al [49] examined the impact of shot-peening and lubrication conditions on the performance of 42CrMoV screws subjected to several tightening passes.…”