The effect of interference‐fit fasteners on the fatigue life of central hole specimens

Abstract

A B S T R A C T Fatigue tests were carried out on 2024-T351, thickness 1.6 mm, central hole specimens containing pins installed with five different interference-fit levels. Tests clearly demonstrated the beneficial effect of interference fit on fatigue resistance, up to the maximum value examined, 2.5%. A three-dimensional (3D) finite-element model was used in order to characterize the stress field around the hole. A large specimen, with a 40-mmdiameter hole filled with interference-fit pin, was instrumented by strain gauges and statically tested in order to check FEM results. A very good correlation existed between measured and numerically evaluated strains. FEM results demonstrated the well-known effect of interference-fit fasteners on reducing stress ranges. By increasing the interference level, the stress range was practically unchanged, while the mean stress decreased.Interference-fit produces a biaxial stress state, which must be taken into account for fatigue evaluation. In the present case, a simple criterion, based on hoop strain, predicted the fatigue results quite well with the exception of open hole fatigue test results, which were overestimated.Keywords biaxial stresses; experimental measurements; finite-element analysis; interference fit. N O M E N C L A T U R EK f = fatigue stress concentration factor i = interference R = stress ratio = S min /S max S = nominal applied stress S eq = equivalent uniaxial stress S min = minimum stress in fatigue cycle S max = maximum stress in fatigue cycle S x = radial stress S y = longitudinal stress I N T R O D U C T I O NThe fatigue resistance of mechanical joints in aircraft structures is a problem not completely solved and continuously studied because, nearly always, the fatigue resistance of aircraft structures corresponds to the fatigue resistance of the joints contained in these structures. Limiting our attention to mechanical joints, so many different elements are used that even their classification is difficult. A possible distinction can be made between solid rivets, which are plastically deformed during installation, and threadedCorrespondence: A. Lanciotti.

Fatigue life variability due to variations in interference fit of steel bushings in 7075-T651 aluminum lugs

“…With this outlier removed, the angle change with interference fit becomes more apparent. It was shown in [16] that as interference fit increased the failure location occurred at a greater angle above the horizontal, opposite of what testing here showed. There are two major differences between the test in [16] and here that may be a cause; (1) the testing referenced used a much higher level of interference fit and (2) the testing referenced was for a central hole specimen loaded in tension with no external load applied to the bolt.…”

Numerical and experimental study of an interference fitted joint using a large deformation Chaboche type combined isotropic–kinematic hardening law and mortar contact method

“…(6) Stop augmentation if desired contact traction or gap function tolerances are achieved and go to next time step. is also a portion of total global virtual work and updated traction can be placed in this contact virtual work and consequently in its equilibrium equation contribution.…”

“…̅ is the pull-back of Kirchhof stress into the intermediate configuration and since it is symmetric, ̅ ( ̅ ̅ ) is equal to zero. Using equation (6) and then rearranging the equation (16), we have:…”

“…These joints have inherent stress concentration and they are a potential source for crack nucleation and propagation under cyclic loading. To overcome this issue, several innovative methods have been investigated such as cold expansion [1][2][3], Bolt clamping [4,5], interference fit [6][7][8] and mixed methods [9][10][11]. In interference fit process an oversized fastener pin or bolt is inserted into a hole by force that causes the hole to stretch.…”

Interference fit effect on holed single plates loaded with tension-tension stresses

“…Since some catastrophic failures may occur in this type of joints, it was decided to investigate the relation between the amount of interference and the fatigue life. There are a lot of studies concerning the effect of interference fit on the fatigue life [8][9][10][11][12]; however, these papers are mainly devoted to the study of aluminium alloys (2xxx and 7xxx series) or the direct effect of interference fit is shadowed by either cold expansion or bolt clamping effect. On the opposite the material investigated in this paper is high strength steel so that no previous tests or results can be found concerning this application.…”