A comparative numerical study of combined cold expansion and local torsion on fastener holes

Abstract

A B S T R A C T Cold expansion and local torsion processes provide controllable strengthening mechanisms for a fastener hole and therefore have engineering significance. They rely on the residual stress and the accumulated shearing strain, respectively, which are difficult to measure. Due to the complex closed form solutions for these mechanisms, their numerical study is of great importance. In this work, a combination of the cold expansion and the local torsion on a fastener hole has been investigated numerically to evaluate the amount and nature of the total accumulated residual stresses around a fastener hole. Different cases of the cold expansion and the local torsion processes were modelled and studied by finite element simulation to investigate the existence of a loading case which produces a beneficial compressive residual stress field in the vicinity of a hole. Sensitivity of the final residual stress with respect to a range of process parameters including adequate diametral interference and angle of rotation was investigated.Keywords elastic-plastic behaviour; finite element analysis; hole expansion technique; plastic strain localization; residual stress; torsion. N O M E N C L A T U R Eb = Rate at which size of yield surface changes C k = Initial kinematic hardening modulus d f = Final hole diameter d i = Initial hole diameter r = Radial distance, radial coordinate r i = Hole radius Q ∞ = Maximum change in size of yield surface z = Longitudinal coordinate a k = Back-stress (kinematic shift) y k = Rate at which kinematic hardening modulus changes ε pl = Equivalent plastic strain θ = Tangential coordinate ξ = Degree of cold expansion σ | 0 . = Size of yield surface at zero plastic strain σ 0 = Size of yield surface = Twist angle I N T R O D U C T I O NCreating stronger and tougher materials is a perpetual goal of design and materials engineers. Mechanical joints such as bolts and rivets, that require the use of drilled holes, are extensively used in mechanical structures. These joints are inherently vulnerable to failure due to stress Correspondence: S. Khoddam.

Interference fit effect on improving fatigue life of a holed single plate

“…For this reason, the local amplitude, depending on both the remote stress and interference level, has been calculated and analysed. Therefore, some FEA have been carried out in order to confirm what is stated earlier . In Fig.…”

“…The holes cause a geometrical discontinuity, which leads to stress concentration during the loading; furthermore, the drilling operation creates rough surfaces or localised damages, so that the fatigue life of component may be drastically reduced. Such situation forces a compensation of the fatigue life reduction that can be obtained with different techniques such as the cold expansion or the interference‐fit connections . The aim of the present paper was to characterise, from a microstructural and mechanical point of view, the 35 KB2 forging steel, investigating the effect of interference‐fit level on the fatigue life of holed plates, which are used in tracks chains of high power excavators (Fig.…”

Surface Modification and Nanocomposite Layering of Fastener-Hole through Friction-Stir Processing

“…However, there are no known reports of FSP performed on cylindrical or curved surfaces. Recently, Shamdani and Khoddam [22] performed a numerical study on a combination of cold expansion and local torsion on fastener holes. Although the results were not experimentally verified, they concluded that cold expansion combined with local torsion would have a beneficial effect on improving the overall mechanical performance of a hole.…”

A new conception for enhancement of fatigue life of large number of fastener holes in aircraft structures

“…An idea for a modified torsion straining, called internal torsion, was demonstrated, as an alternative to the existing mandrel cold working methods. The same authors offer a combination of mandrel cold working and local torsion of fastener hole, considering an idealized case . The material used is a Ti‐IF steel.…”