Papers by George Pantazopoulos
Intergranular Cracking of High Strength Extruded Brass Alloys
The Minerals, Metals & Materials Series, 2018
In this paper, a failure analysis investigation is presented concerning the intergranular crackin... more In this paper, a failure analysis investigation is presented concerning the intergranular cracking of three different diameter (O26.6, O10.8, O8.5 mm) high strength brass rods which failed after extrusion. Optical, Scanning Electron Microscopy and Electron Backscatter Diffraction are employed in order to reveal the mechanisms and the root causes of the failures. The microstructural characteristics, exhibited by the brass rods, pertaining mainly to phase, grain structure, size and distribution of intermetallic particles, are considered to exert a detrimental effect, impairing the mechanical properties, facilitating the environmentally-induced degradation and assisting the occurrence of brittle fractures. Revision of preheating and extrusion conditions could be further implemented in order to minimize the risk of such failure in the future.
Cracking Failures of Copper Alloy Hot Rolled Plates: Phenomenological Approach and Root Cause Analysis
Contributed Papers from MS&T17, 2018
Characterization of HTS Powders and Components
Processing of High-Temperature Superconductors at High Strain Rates, 2019
Synthesis of Ceramic Superconductors
Processing of High-Temperature Superconductors at High Strain Rates, 2019
Fundamentals of Superconductors
Processing of High-Temperature Superconductors at High Strain Rates, 2019
Fundamental Aspects of Rolled Zn Alloy Sheet Formability: Structure-Property and Failure Mode Relationships
Materials Science Forum, 2016
In the present work, critical testing methods are employed in order to assess the formability of ... more In the present work, critical testing methods are employed in order to assess the formability of a Zn-Ti-Cu alloy, evaluating, therefore, the anisotropic properties of the produced sheet. The determination of plastic strain ratios and the induced combined mathematical expressions, utilizing bi-axial strain measurements for the various test directions (0, 45 and 90 degrees towards the RD), together with the performance of cupping tests are compiled, aiming to rank and interpret the bending and sheet metal roll-forming capability. Moreover, the microstructural characterization is realized to address the influence of grain and phase structure on the sheet metal formability and identify potential optimization routes. Fracture analysis approach elucidated the micro-mechanisms prevailed in damage evolution and accumulation during monotonic loading, signifying the importance of microstructure development during thermomechanical process history.
Engineering Failure Analysis, 2016
Two components of a water pump installed in a casting shop for recirculation of cooling water exp... more Two components of a water pump installed in a casting shop for recirculation of cooling water experienced severe and accelerated corrosion after two months in service. The received pieces of the water pump assembly were a shaft and a conical tube, which was used as connector with the impeller. The shaft exhibited circumferential pitting corrosion behavior in specific areas where it was in contact with another pump component. Light optical microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy were mainly used as analytical techniques for corrosion process evaluation and for the identification of the morphology and chemical composition of corrosion products, in order to draw safe conclusions concerning the type of the corrosion and the respective root-source. The main findings of the investigation indicated that pitting corrosion was the dominant failure mechanism for both water pump components influenced by the presence of aggressive environmental conditions, characterized by the presence of chlorides and sulfates that accelerate corrosion process above a certain temperature range (T N 50-55°C).
Surface Modification Technologies XI
The Institute of Materials, …, 1998
Fabrication of thick layered superconductive ceramic (BiPbSrCaCuO)/metal composite strips by explosive cladding and rolling
Journal of Materials Processing Technology, 1995
Explosive cladding, subsequent rolling and heat treatment are employed to fabricate a composite (... more Explosive cladding, subsequent rolling and heat treatment are employed to fabricate a composite (sandwich) strip consisting of an intermediate high temperature superconducting ceramic layer of the BiPbSrCaCuO compound and two metal silver plates. Macro- and micro- structural experimental observations regarding the quality of the product at the various stages of the fabrication were evaluated using optical and scanning electron microscopy and X-ray diffraction techniques, whilst the superconducting properties of the composite strips were obtained using ac-magnetic susceptibility techniques; preliminary dc-resistivity measurements were made also to evaluate further the superconductive properties of the material. Post-fabrication heat-treatment in air resulted in improved superconductivity of the heat-treated strips as compared to the residual superconductivity obtained after rolling, leading therefore to useful conculsions regarding the applicability of the fabricated composite plates in the electrical and electronic industries.
Net shape manufacturing of silver-sheathed high-Tc superconductive ceramic (YBaKCuO) strip by explosive compaction/cladding and rolling
Journal of Materials Processing Technology, 1996
Explosive compaction/cladding and subsequent rolling are employed to fabricate a sandwich metal/c... more Explosive compaction/cladding and subsequent rolling are employed to fabricate a sandwich metal/ceramic strip consisting of two silver plates and two intermediate high-temperature superconducting ceramic paths of the Y Ba Cu O system. Macro-and ...
Journal of Failure Analysis and Prevention, 2006
The tensile properties and failure mode of heat treated and liquid nitrocarburized tool steels we... more The tensile properties and failure mode of heat treated and liquid nitrocarburized tool steels were studied. The tested steels are used as die and tool materials for plastic molds and punching/blanking dies, where wear resistance is required. In addition to intense friction, the main die block and other die components are subjected to tensile and repetitive stresses during operation (tension and fatigue loading). Therefore, hardness, tensile, and fatigue resistance are also critical quality parameters that contribute to material reliability and tool life. However, this study is an initial component of research and does not include fatigue data.
Engineering Failure Analysis, 2009
Fabrication of multi-layered steel/superconductive ceramic (YBaKCuO)/silver rods by explosive powder compaction and extrusion
Journal of Materials Processing Technology, 1996
Axisymmetric explosive powder compaction and subsequent direct extrusion are employed to fabricat... more Axisymmetric explosive powder compaction and subsequent direct extrusion are employed to fabricate a multi-layered metal/high-Tc ceramic rod consisting of a silver mandrel, a potassium doped YBa2Cu3O7 core and a steel sheath. Experimental investigations regarding the ‘soundness’ and the superconducting properties of the component at the various stages of the fabrication are reported. Microstructural/crystallographic changes, macro- and micro-defects of the ‘green’ compacted billet and the extruded rod are also indicated and discussed.
Texture Analysis and Anisotropic Properties of a Rolled CuZn36 Brass Alloy
In this study, the mechanical properties of an annealed CuZn36 rolled brass alloy with 0.2 mm thi... more In this study, the mechanical properties of an annealed CuZn36 rolled brass alloy with 0.2 mm thickness with respect to anisotropy expressed in terms of plastic strain ratio measurements (r-values, normal and planar anisotropy) are related with the development of specific rolling and recrystallization texture components obtained by EBSD. Anisotropic behaviour is primarily controlled by the crystallographic texture and constitutes an indicator of multi-axial mechanical behaviour, affecting directly the drawability and sheet metal formability. Microstructure examination employing optical and Scanning Electron Microscopy of tensile specimens are performed in order to investigate the emergent damage mechanisms in relation to the texture and structure evolution of the final product.
Fabrication of HTS Films
Processing of High-Temperature Superconductors at High Strain
Fatigue failure analysis of a Ø14 B500C steel rebar: Metallurgical evaluation and numerical simulation
Engineering Failure Analysis
Abstract In the present work, the investigation of an early fatigue failure of steel rebar sample... more Abstract In the present work, the investigation of an early fatigue failure of steel rebar samples, of dimensions of O 14 mm, during standard fatigue tests is performed. The rebar failed after approximately 1.67 × 106 fatigue cycles, much below of the specified 5.0 × 106 cycles according to BS 4449 standard. The rebar tested sample exhibited a crack initiation site close to the root of a surface geometric discontinuity (“nipple”), which is considered as a stress concentration point. Light optical microscopy, microhardness testing, SEM/EDS, and numerical simulation were employed as the main investigation methods. Fractographic examination depicted the presence of clearly resolved fine fatigue striations elucidating the continuous crack growth period, under Paris law regime, followed by a dimpled ductile zone as the instant ultimate fracture zone. An evaluation of the steel inclusions (MnS, Fe-Si-Mn-Al-Mg-O) was achieved by optical metallography and SEM/EDS analysis. In addition, the results of the numerical analysis, verified that the existence of manufacturing imperfections or geometric irregularities, such as the “nipple” marking of the bar, imposed a significant stress raise up to 2 to 3.3 times of the applied mean stress level, leading to an effective reduction of the expected lifetime of the specimen.
Microstructure and properties of lead-free brasses using post-processing heat treatment cycles
Materials Science and Technology
We report the tailoring of the microstructure of lead-free brasses with a view to improving their... more We report the tailoring of the microstructure of lead-free brasses with a view to improving their machinability via the controlled augmentation of the β-phase. This should be performed while keeping the mechanical properties within the EN standard, as β-phase augmentation can lead to embrittlement. Twenty seven heat treatment protocols were performed in order to transform the microstructure and consequently modify the properties of three lead-free brasses. The most successful heat treatment was chosen for each studied alloy according to the above criteria. The selected protocols led to a combination of β-phase augmentation with mechanical properties conforming to standards providing a promising ground for improved machinability performance. This paper is part of a Themed Issue on Brass Alloys.
Journal of Failure Analysis and Prevention, 2016
Investigation of Fatigue Failure of Roll Shafts in a Tube Manufacturing Line
Journal of Failure Analysis and Prevention, 2010
A failure analysis of steel shafts operating as roll components in a tube drawing machine was con... more A failure analysis of steel shafts operating as roll components in a tube drawing machine was conducted. Visual inspection, optical microscopy, SEM fractography, and hardness testing were used as the principal analytical tools for the failure investigation. The findings showed that the failure mechanism is rotating bending fatigue under low stress–high stress concentration conditions. The primarily inadequate component design resulted
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Papers by George Pantazopoulos