Investigation on Mechanical Properties of Austenitic Stainless-Steel Pipes Welded by TIG Method

هذا البحث يدرس الخواص الميكانيكية للأنابيب الفولاذية الاوستنايتي (نوع 204) الملحومة بطريقة اللحام بغاز التنغستن الخامل. اجريت فحوصات اختبار الصلادة روكويل C، قوة الشد وقوة الانحناء لأنابيب الصلب الملحومة بدرجتين مختلفتين من درجة حرارة اللحام 700 درجة مئوية و900 درجة مئوية مع وبدون استخدام حشوة اللحام. كذلك تم إجراء فحص البنية المجهرية لمناطق اللحام. أظهرت الخصائص أن اللحامات الفولاذية المكتملة عند 900 درجة مئوية مع استخدام حشوة اللحام أعلى مقاومة شد ومقاومة انحناء مقارنة بتلك الملحومة بدرجة 700 بدون حشوة اللحام ويعزى ذلك الى ان حشوة اللحام انصهرت بدرجة حرارة كافية وقد ملئت النقص الحاصل لمعدن النيكل في المادة الاساس اثناء فترة اللحام.This paper investigates the mechanical properties of austenitic stainless steel (type 204) pipes welded by Tungsten Inert Gas (TIG) welding process. Testing of hardness (HRC), tensile strength and bending strength was performed for the steel pipes welded at two different welding temperatures (700 °C and 900 °C) with and without using the weld filler wire. The microstructure of the welding regions was examined by using an optical microscopy. The properties showed that the steel pipes welded by 900 °C with using the weld filler obtained the highest tensile strength and bending strength versus these welded by 700 °C without the use of the weld filler. This is attributed to the weld filler heated and melt at sufficient temperature (900 °C) and compensate losing in the Ni metal occurred in the base steel metal during the welding process

Electrochemical performance of ternary s-GN/PANI/CNTs nanocomposite as supercapacitor power electrodes

In this paper, binary carbon nanotubes (CNTs) reinforced conducting polyaniline (PANI) and ternary sulfonated Graphene nanosheets (s-GN) decorated CNT@PANI nanocomposites were prepared using a solution mixing followed by ultrasonic dispersion. The SEM and XRD analysis found that the s-GN and CNTs have uniformly sandwiched the PANI. The cyclic voltammetry (CV) results showed that the sulfonated graphene along with CNTs have led to increase the electrochemical capacitance from 305 F/g for the binary CNT20@PANI to 419 F/g for the ternary CNT20@PANI@s-GN20 nanocomposites (37 % increase). This increase is attributed to the free mobility of the electronic carriers on the s-GN surface for the larger surface area and presence of the SO-3 groups. The electrochemical impedance spectroscopy (EIS) measurements exhibited that the s-GN embedded PANI@CNT nanocomposite resulted in a higher energy density of 209 Wh/kg with a power density of 381 W/kg at scan rate of 5 mV/s in an electrolyte of 0.5M H2SO4. The prepared s-GN@PANI@CNTs nanocomposites are promising electrode’s materials for the electrochemical capacitors power systems

Effect of SiC addition on mechanical and wear characteristics of WC-32(W-Ti)C-6Co cemented carbides

The effect of silicon carbide (SiC) addition on mechanical and wear properties of cemented carbides was investigated in this study. Different percentages (1-7 wt.%) of SiC were added to the cemented carbides mixture of WC/32 wt. % (Ti-W) C/6 wt.% Co. The microstructural characteristics of the developed materials was identified using scanning electron microscopy (SEM) and Rockwell-A macrohardness (HRA), Vickers microhardness (Hv) as well as transverse rupture strength (TRS) were measured. The experimental results revealed that inserting SiC inclusion into the cemented carbides is found to be useless for two reasons. First, the microstructure of the developed carbides has more aggregations of largely contiguous SiC grains led to presence of rich/poor regions and consequently poor compatibility between carbides and the binder. Second, all properties of the cemented carbides greatly declined with the addition of SiC particles

The effects of material formulation and manufacturing process on mechanical and thermal properties of epoxy/clay nanocomposites

A holistic study was conducted to investigate the combined effect of three different pre-mixing processes, namely mechanical mixing, ultrasonication and centrifugation, on mechanical and thermal properties of epoxy/clay nanocomposites reinforced with different platelet-like montmorillonite (MMT) clays (Cloisite Na+, Cloisite 10A, Cloisite 15 or Cloisite 93A) at clay contents of 3–10 wt%. Furthermore, the effect of combined pre-mixing processes and material formulation on clay dispersion and corresponding material properties of resulting composites was investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), flexural and Charpy impact tests, Rockwell hardness tests and differential scanning calorimetry (DSC). A high level of clay agglomeration and partially intercalated/exfoliated clay structures were observed regardless of clay type and content. Epoxy/clay nanocomposites demonstrate an overall noticeable improvement of up to 10 % in the glass transition temperature (Tg) compared to that of neat epoxy, which is interpreted by the inclusion of MMT clays acting as rigid fillers to restrict the chain mobility of epoxy matrices. The impact strength of epoxy/clay nanocomposites was also found to increase by up to 24 % with the addition of 3 wt% Cloisite Na+ clays. However, their flexural strength and hardness diminished when compared to those of neat epoxy, arising from several effects including clay agglomeration, widely distributed microvoids and microcracks as well as weak interfacial bonding between clay particles and epoxy matrices, as confirmed from TEM and SEM results. Overall, it is suggested that an improved technique should be used for the combination of pre-mixing processes in order to achieve the optimal manufacturing condition of uniform clay dispersion and minimal void contents

Cracks, microcracks and fracture in polymer structures: Formation, detection, autonomic repair

The first author would like to acknowledge the financial support from the European Union under the FP7 COFUND Marie Curie Action. N.M.P. is supported by the European Research Council (ERC StG Ideas 2011 n. 279985 BIHSNAM, ERC PoC 2015 n. 693670 SILKENE), and by the EU under the FET Graphene Flagship (WP 14 “Polymer nano-composites” n. 696656)

Fracture toughness and toughening mechanisms of unsaturated polyester-based clay nanocomposites

In this study, the role of nanoclay particles (MMT) on micro- and nano-scale deformation and fracture behaviour of a crosslinked unsaturated polyester (UPE)-based nanocomposites is explored. Nanocomposites from well-dispersed MMT particles and the UPE resin were prepared by a combination of mechanical mixing and ultrasonication process. The morphological characteristics of nanocomposites were examined by TEM. Critical stress intensity factor (KIc) based on linear elastic fracture mechanics (LEFM) and compact tension (CT) configuration is evaluated. The fracture modes and toughening mechanisms of the fractured-surfaces were identified by SEM analysis. An intercalation/partially exfoliation structure of UPE/MMT nanocomposite with moderate enhancement in fracture toughness is observed. The addition of 3 wt.% MMT exhibits the highest KIc value of nanocomposite by a 61% improvement over the neat UPE. The fracture surface of the neat UPE seems to be a highly brittle fracture without crazing and a coarser surface with the appearance of plastic deformation zones of the nanocomposites

Effect of alumina inclusions on microstructure and mechanical properties of 62 WC, 32 (Ti-W) C and 6 Co compacts

This investigation is aimed at understanding the role of adding ceramic inclusion, alumina (Al2O3) on the densification, microstructure and mechanical properties of cemented carbide cutting inserts. The samples were prepared of an initial mixture of 62 WC, 32 (Ti-W) C and 6 Co wt% particulates; different additions of Al2O3 of 1, 2, 3 and 4 wt% were introduced to that mixture. The testing specimens were compacted via powder metallurgy at 200 MPa and sintered at 1,410°C under vacuum. The green and sintered densities have decreased; the figures of macrohardness, Vickers hardness and transverse rupture strength have also deteriorated with the increase of alumina content. The macrohardness has almost declined of 30% at 3% alumina. This is ascribed to the interfacial grain-boundary decohesion between Al2O3 and carbide particles as can be observed from scanning electron microscopy images which depicts the monolithic clusters in the final consolidation of the compacts

Morphological structures and tribological performance of unsaturated polyester based untreated/silane-treated halloysite nanotubes

In this study, pristine halloysite nanotubes (HNT) and silane-treated halloysite (s-HNT) particles were incorporated into highly crosslink unsaturated polyester (UPE) to explore the morphological structure and tribological performance of UPE-HNT nanocomposite. Wear resistance of cured UPE/HNT and UPE/s-HNT nanocomposites were systematically evaluated using block-on-ring (BOR) configuration against stainless steel counterpart under a certain dry sliding conditions. TEM micrographs revealed a uniform morphological dispersion of halloysite particles in the UPE matrix. Both pristine and silane-treated HNT particles induced a modest decrease in a specific wear rate and coefficient of friction of nanocomposites. There was a pronounced reduction in the specific wear rate of the polyester composites at more than 5 wt.% of halloysite. However, the addition of silane exhibited insignificant results especially at higher percentages of HNT. The investigation of worn surface morphology and wear mechanism of materials by using SEM is also discussed