D.I. Pantelis

Determination of onset of plasticity (yielding) and comparison of local mechanical properties of friction stir welded aluminum alloys using the micro‐ and nano‐indentation techniques

Purpose – The purpose of this paper is to determine if the nanoindentation technique is a reliable method and whether it can be used to measure the surface hardness (H) in friction stir welded aluminum alloys. In order to test the reliability of nanoindentation technique, nanohardness values for friction stir welded aluminum alloys were compared to microhardness values. Additionally, the onset of plasticity (yielding) is investigated.Design/methodology/approach – Nanoindentation experiments were performed for the determination of onset on plasticity (yielding) and comparison of local mechanical properties of both welded alloys. In order to test the reliability of nanoindentation technique, nanohardness values for friction stir welded AA6082 were compared to microhardness values. The specimen was tested using two different instruments – a Vickers microhardness tester and a nanoindenter tester for fine scale evaluation of H.Findings – The results of this study indicate that nanohardness values with a Berkov...

The Accurate Prediction of the Thermal Response of Welded Structures Based on the Finite Element Method: Myth or Reality?

The thermal and metallurgical response of thin welded plates made of Ck45 steel during shielded metal arc welding is investigated through numerical results using the finite element method (FEM) and by in situ experimental measurements.

Dissimilar friction stir welding of aluminum alloys reinforced with carbon nanotubes

This chapter is devoted to studying the possibility of incorporating carbon nanotubes (CNTs) as reinforcing fillers in dissimilar metal matrices joints produced by friction stir welding (FSW), as well as the impact of this incorporation on the microstructural and mechanical properties of these joints. Carbon nanotubes are extensively used as a reinforcing material in nanocomposites, due to their high stiffness and strength. FSW is a solid-state welding process of joining aluminum and other metallic alloys and has been employed in the aerospace, rail, automotive, and marine industries. Recently, friction stir processing (FSP), a derivative method of FSW, has been employed as an alternative for the production of metal matrix composites (MMCs). In this work, the process parameters were optimized in order to achieve nondefective welds, with and without the addition of CNTs. Two main cases were studied: (1) FSP was optimized by changing the tool rotational and travel speed as well as the number and direction of FSW passes, and (2) a Taguchi design scheme was adopted to further investigate the FSP in relevance to three factors (number, direction of passes, and tool rotational speed). Mechanical behavior was studied, and the local mechanical properties of the produced MMCs were compared with their bulk counterparts and parent materials. More specifically, the measured mechanical properties in the micro- and nanoscale (namely hardness and elastic modulus) are correlated with the microstructure and the presence of fillers.

Rapid evaluation of temperature distribution of coatings during atmospheric plasma sprayed process

This study presents the experimental results of coating AISI 1045 steel substrate by low alloyed carbon steel powder using atmospheric plasma spraying (APS). Thermocouples were used to monitor the temperature history at specified positions during the spraying process. A simplified thermal finite element model of APS coating is presented. The transient temperature field is calculated first. An appropriate numerical filter implementing the thermal time response of the thermocouple is created and applied to the raw FEM results. Agreement between experiment and numerical model for temperature were deemed promising despite the simplifications adopted in the numerical model.

Hydrogen Effect on Fracture Toughness of API 5L X70, X65 and X52 Pipeline Steel Welds: An Overview

Steel welds representing three generations of pipeline steel were studied against hydrogen effect, using the fracture toughness parameter J integral which is a measure of the plastic work. The influence of hydrogen on the growth of a partial wall defect is studied and comparisons with the growth of the same defect in air are presented. The tests conducted were three-point bending fracture toughness tests, in air and in a hydrogen environment simulated by electrolysis. Reduction in J0 was observed in all pipeline steel grades as the current density increases, which was more pronounced in the base metal rather than in the heat affected zone. The different microstructures of the welded steels are observed and correlated to the reduction in plasticity. It is concluded that microstructure seems to be the decisive parameter for the selection of a pipeline steel for service in a hydrogen environment.Copyright