PSI - Issue 19

Okan Yılmaz et al. / Procedia Structural Integrity 19 (2019) 302 – 311 Yılmaz et al. / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 1. A schematic of basic bolted connection under and out-of-plane bending and in-plane shear loading conditions.

the fatigue life is not a function of base material property. From this perspective, mechanical joints are promising to ripe the benefits from the improvements of the base material.

Nomenclature

HSS high-strength steel E Young’s modulus σ y yield modulus σ UTS ultimate tensile strength ε f elongation HV0 . 2 Vickers’ hardness R load ratio ∆ σ nom nominal stress range F fpb , max maximum applied force in four-point bending test SWT Smith-Watson-Topper parameter σ max maximum stress normal to the critical plane ∆ ε/ 2 the amplitude of the strain normal to the critical plane N f fatigue life

It should be noted that in bolted connections there exist additional failure modes, which need to be understood thoroughly. Connecting parts with bolts adds another layer of complexity as the parts are now in contact. Although the motion is limited with the pre-tension added to the bolt, it is one of the governing aspects of mechanical response under operational loads. The frictional forces created by the pre-tension carry shear loads but also damage locally the surface of the mating parts when cyclic loads are applied. The oscillatory movement between the surfaces in contact leads to very high local stresses and wear, which can lead to premature failure of the bolted component. This phenomena, known as fretting fatigue, has previously been reported for bolted connections in HSS [2, 3]. For the typical application areas such as trucks, trailers, and agricultural machinery, this type of failure can be resulted from the cyclic loading produced by unevenness in the road, sudden stops, accelerations, and the internal resonance of the part components. The position and loading direction of the bolted joints can be classified into two main di ff erent loading modes: in-plane shear and out-of-plane bending, which are schematically represented in Fig. 1. The aim of the study is to explore the possibilities of using conventional mechanical joining techniques for HSSs by analyzing the possible failure mechanisms via experimental and numerical e ff orts. The design of the test setups at tempts to reproduce the in-plane and out-of-plane loading conditions observed in typical applications. Section 2 details the methodology and di ff erent fatigue experiments we carry out in this study: (i) axial tests of holed specimens, (ii) shear lap bolted joints, and (iii) four-point bending tests of bolted assemblies. In Section 3, several e ff ects influencing the fatigue performance are investigated. These e ff ects are listed as the hole-making procedures (punching, drilling, water-jet cutting, plasma cutting, and laser cutting), pre-tension level, surface condition, and flange configuration. A finite-element simulation is carried out for the determination of the correct failure mode under out-of-plane bending