This work investigates the feasibility of using friction stir welding (FSW) process as a groove filling welding technique to weld duplex stainless steel (DSS) that is extensively used by petroleum service companies and marine industries. For the FSW experiments, three different groove geometries without root gap were designed and machined in a DSS plates 6.5 mm thick. FSW were carried out to produce butt-joints at a constant tool rotation rate of 300 rpm, traverse welding speed of 25 mm/min, and tilt angle of 3o using tungsten carbide (WC) tool. For comparison, the same DSS plates were welded using gas tungsten arc welding (GTAW). The produced joints were evaluated and characterized using radiographic inspection, optical microscopy, and hardness and tensile testing. Electron back scattering diffraction (EBSD) was used to examine the grain structure and phases before and after FSW. The initial results indicate that FSW were used successfully to weld DSS joints with different groove designs with defect-free joints produced using the 60° V-shape groove with a 2 mm root face without root gap. This friction stir welded (FSWed) joint was further investigated and compared with the GTAW joint. The FSWed joint microstructure mainly consists of α and γ with significant grain refining; the GTWA weld contains different austenitic-phase (γ) morphologies such as grain boundary austenite (GBA), intragranular austenite precipitates (IGA), and Widmanstätten austenite (WA) besides the ferrite phase (α) in the weld zone (WZ) due to the used high heat input and 2209 filler rod. The yield strength, ultimate tensile strength, and elongation of the FSWed joint are enhanced over the GTAW weldment by 21%, 41%, and 66% and over the BM by 65%, 33%, and 54%, respectively. EBSD investigation showed a significant grain refining after FSW with grain size average of 1.88 µm for austenite and 2.2 µm for ferrite.

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An understanding into the macro kinetic and kinematic behaviour of fretted surfaces is provided. Making use of a modified version of a previously developed in‐house two‐dimensional elastic–plastic finite element analysis numerically simulates flat contact pad fretting fatigue tests. Basic macro mechanics concepts are adopted to idealise two bodies with rough contact surfaces and loaded at two different sites with arbitrary axial loading profiles. A time scale factor is devised to recognise the earliest candidate out of the events possibly accommodated at each loading increment. The present analysis utilises a relevant experimental set up developed in the Structural Integrity Research Institute of the University of Sheffield as an application. Computational results accurate to within 1.2% and corresponding to one contact pad span and six constant normal loads acting individually with four amplitudes of two sinusoidal axial load cycles are presented. The present computations include (1) the development of the global and local normal and tangential reactions and relative sliding displacement acting along the fretting surfaces and (2) contact pad deformation, generated stress fields and plasticity development within the neighbouring region of the fretted area.

A centrifugal mixing method was developed to disperse ceramic particles inside a thermosetting polymer. Horizontal centrifugal equipment was used to fabricate cylindrical rods from epoxy reinforced with silicon carbide particles. Silicon carbide particles (SiC) are used for the outer coating of epoxy to increase wear resistance. In the centrifugal mixing process, there are three important variables: rotational speed, ceramic percentage and, ceramic size which affect ceramic particle distribution. This paper aims to find the relationship between these variables and the distribution of ceramic particles then determine the optimum conditions to get maximum wear resistance and hardness. From the experiment and analysis, it can be concluded that when mixing speed was greater than 600 rpm, the possibility of air bubbles formation was increased especially for ultrafine particles. Otherwise, the maximum wear resistance and hardness values were found in ultrafine size SiC samples reinforced with 30 wt% which were mixed at a low speed of 300 rpm.

PurposeThe purpose of this paper is to estimate the number of cycles for fatigue crack initiation in notched plates.Design/methodology/approachPreviously published experimental results for tests with initially uncracked U‐shaped notches of different sizes and geometries are utilized. The present work defines the fatigue initiation period, Ni, as number of loading cycles required for the formation of a through‐thickness Mode I crack at the notch root macroscopically propagating along the plate width. Thus, backward extrapolation of the observed early decreasing fatigue growth rates of the initiated crack at the notch root on the specimen surface to zero surface crack size enables the estimation of Ni.FindingsA parameter based on the normal strain range and the maximum normal stress acting at the notch root best fitted Ni.Research limitations/implicationsThis paper provides an estimation of Ni in 3 mm thick mild steel plates subjected to constant amplitude uniaxial cyclic stresses. Initiated‐but‐non‐propagating cracks possibly found at the notch surface and at the notch root along the plate width are distinguished.Originality/valueBased on the present analysis, a threshold stress is devised to represent the minimum stress level required for the appearance of a through‐thickness crack at the notch root running along the specimen width. Notched plates simulate many engineering applications particularly in aerospace industry.