Estimation of the residual stress on the thread root generated by thread rolling process

Abstract

Yoshimoto had been presented a hypothesis concerning the fatigue strength of a bolt in bolt/nut assembly using Ishibashi's hypothesis on the relationship between the fatigue notch factor and the local stress distribution on the first thread root of a bolt mated with nut. By using Yoshimoto's hypothesis, the effect of the manufacturing process (sequence or order of thread rolling and heat treatment processes) on the fatigue strength can be explained in connection with the axial residual stress at the first thread root of a bolt as a change of mean stress level. However, this hypothesis has not yet been verified quantitatively since the axial residual stress which may exist locally around the thread root could neither be measured nor estimated with sufficient accuracy. This study aims to quantify the axial residual stress on the thread root generated by thread rolling process. For this purpose, a method for simulating thread rolling process by using 3D elastic-plastic FEM was proposed to estimate the axial residual stress distribution by using precisely determined material property. Calculated results for two types of test specimens, one is grooved specimen with larger root radius and the other is leadless bolt specimen having the same thread profile as M10×1.25 bolts, show that the axial compressive residual stress of 1000 MPa level is generated at the root of the specimens. Finally, the validity of the simulation was confirmed through the X-ray stress measurement for grooved specimen, and the fatigue tests for leadless bolt specimen.

Fatigue analysis of preloaded bolted joints

“…The magnitude of the residual stress in a Grade 8.8 bolt (minimum tensile stress of 800MPa) as calculated by Furukawa and Hagiwara (2014) [11] was greater than the magnitude of residual stress, as estimated in this paper, for the bolts with a tensile strength of 1154MPa as tested by Marcelo et. al.…”

“…The process of thread rolling has been simulated by Furukawa and Hagiwara (2014) [11] using 3D elasticplastic Finite Element Methods. The heat treatment process, quench hardening and tempering, was not simulated within the model hence, the results are representative of thread rolling after heat treatment.…”

Fatigue performance of prosthetic screws used in dental implant restorations: Rolled versus cut threads

“…21,28,41,42 The surface finish was mainly influenced by the residual compressive stresses on the thread surface by the rolling process, found to be larger than the ones left by cutting. 25,31 Using synchrotron radiation to evaluate surface properties should improve the quality of the data and allow the extrapolation of stress more accurately. [43][44][45] The prosthetic screws had a significantly better fatigue response with thread rolling, consistent with roll-threaded screws used in industry.…”

“…The rolling process is less time-consuming because the thread may be obtained in a single pass 21,22 with no need for secondary operations, 23 which significantly increases productivity 24 and reduces unit product cost. 21 Regarding mechanical behavior, the thread rolling process introduces compressive residual stresses 25 on the thread surface, increasing hardness from strain hardening. 26 Furthermore, as no material is removed, good grain flow is obtained, 21,27 improving surface quality.…”

An empirical approach to a comprehensive damage-equivalent stress function for fatigue

“…This means that whilst a bolt may be preloaded to, say, 80% of proof load, only the core of the thread is subjected to that level of pre-stress, and the thread root would experience lower stress. Furukawa and Hagiwara's (2015) [9] work estimated that a thread's compressive residual stress, rolled after heat treatment, was 830MPa. Importantly, this was for a thread rolled after heat treatment; however, bolt manufactures prefer to heat treat after thread rolling.…”