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1 – 10 of 129
Article
Publication date: 11 June 2018

Halyna Krechkovska, Oleksandra Student, Grzegorz Lesiuk and José Correia

The purpose of this paper is to assess the technical state of old and repair steels of Shukhov’s tower elements after operation during ~ 110 and 70 years of the water…

Abstract

Purpose

The purpose of this paper is to assess the technical state of old and repair steels of Shukhov’s tower elements after operation during ~ 110 and 70 years of the water tower in Nikolaev, basing on their mechanical tests, metallography and fractography investigations.

Design/methodology/approach

For their certification, the fractographic and structural features and mechanical properties (hardness, strength, plasticity and impact toughness) were analyzed. Both the steels under consideration were characterized by low values of hardness and brittle fracture resistance. The mechanical characteristics of the old steel are lower compared with the repair one. It cannot be only explained by the quality of metal rolling. Moreover, the plasticity characteristics of both steels, defined in synthetic acid rain environment, are lower than in the air. Using fractography investigation, the operational damages in the bulk metal in the form of the elements of cleavage fracture in the central part of the fracture surfaces of specimens tested at the hydrogenation condition by synthetic acid rain environment were revealed.

Findings

The results of this study suggested a degradation of steels’ characteristics caused by the development of scattering damages during their operation. Higher relative elongation of the old steel at lower hardness and impact toughness were also evidenced in that. The metallography and fractography investigations also supported this finding.

Originality/value

This original study aimed at characterizing the microstructural and mechanical degradation of mild steels that was collected from Shukhov’s tower structural elements.

Details

International Journal of Structural Integrity, vol. 9 no. 3
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 1 August 1973

W.J. Van Der Vet

Introduction Visual inspection or observation at low magnification with an optical microscope has been of great help in analysing fracture surfaces. Optical microscopy…

Abstract

Introduction Visual inspection or observation at low magnification with an optical microscope has been of great help in analysing fracture surfaces. Optical microscopy, however, has distinct limitations, such as low resolution and small depth of field. The transmission electron microscope does not have these limitations.

Details

Anti-Corrosion Methods and Materials, vol. 20 no. 8
Type: Research Article
ISSN: 0003-5599

Article
Publication date: 30 August 2011

Simon A. Barter

This paper aims to present some aspects associated with the life prediction of structures with fatigue cracks growing from small natural discontinuities in aluminium alloy…

Abstract

Purpose

This paper aims to present some aspects associated with the life prediction of structures with fatigue cracks growing from small natural discontinuities in aluminium alloy (AA)7050‐T7451 for a surface condition that is present in F/A‐18 A/B aircraft critical structure.

Design/methodology/approach

Fatigue results are presented for thick section AA7050 plate coupons loaded with a representative fighter aircraft wing root bending moment loading spectrum. Detailed quantitative fractography (QF) was used to gain a deeper understanding of issues relevant to an improved fatigue life predictive capacity for this material by using the QF results to investigate the “effectiveness” of the fatigue initiating discontinuities.

Findings

Estimates of the “effectiveness” of the fatigue initiating discontinuities as quasi pre‐existing fatigue cracks (“equivalent pre‐crack size” (EPS) here) were made with the aid of a simple crack growth model. This model, based on experience, was found to be valid for the applied spectrum and stress levels used. These stress levels were chosen to represent those that may be found in highly stressed locations of fighter aircraft; and as such would usually lead to the limiting fatigue life of such a structure.

Research limitations/implications

The method has been extended to other crack growth situations and is being used to build a database large enough to determine the best probability distribution of the “effectiveness” of the fatigue initiating discontinuities for not only the surface condition reported here but several other surface conditions typical of aircraft metallic structure.

Practical implications

The EPS of the discontinuities from which the cracks grew were used to investigate distributions that may be used in a risk‐based assessment using deterministic crack growth measurements from such discontinuities. Some of the problems that remain to be resolved in such an analysis, prior to its use in a risk‐based assessment are discussed.

Originality/value

This work improves the understanding of the interaction of small fatigue cracks generated by representative loading spectra with the small discontinuities from which they grow and shows that the fatigue process is remarkably consistent down to very small sizes.

Details

International Journal of Structural Integrity, vol. 2 no. 3
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 1 October 2005

Hassan Malik and Fahd Nawaz

To discover if stress corrosion cracking (SCC) of C−Mn steel is possible at ambient pressure and temperature in a CO−CO2−H2O environment.

Abstract

Purpose

To discover if stress corrosion cracking (SCC) of C−Mn steel is possible at ambient pressure and temperature in a CO−CO2−H2O environment.

Design/methodology/approach

Approach involved electrochemical testing, slow strain rate testing (SSRT) and fractography. The chemistry within a crack or crevice during SCC differs from that of the bulk environment. To simulate this condition, a specimen was designed containing a steel plate, microelectrodes and artificial crevice. Electrochemical tests were performed to discover if conditions likely to cause SCC could be achieved. Slow strain rate tests and fractography was also carried out to support the electrochemical data.

Findings

Results indicated that CO can adsorb onto the metal and that localized corrosion occurred at defects in the adsorbed CO layer due to CO2, which led to the onset of SCC. Consequently, larger anodic and cathodic currents were measured with or without a crevice, when CO2 was in solution. Similar behaviour was observed on the microelectrodes. Regions of brittle fracture were discovered on the specimen surface after SSRT were conducted in a vapour phase environment. After such tests, the ductility of the steel was found to be impaired.

Practical implications

Practically the results could help to predict the potential range in which SCC may occur.

Originality/value

Paper is new because previous results were at high pressures. However, results indicate that SCC is a danger at atmospheric pressure. The paper is of value to people in the oil and gas industry.

Details

Anti-Corrosion Methods and Materials, vol. 52 no. 5
Type: Research Article
ISSN: 0003-5599

Keywords

Article
Publication date: 23 October 2020

Wilco M.H. Verbeeten, Miriam Lorenzo-Bañuelos, Rubén Saiz-Ortiz and Rodrigo González

The purpose of the present paper is to quantify and analyze the strain-rate dependence of the yield stress for both unfilled acrylonitrile-butadiene-styrene (ABS) and…

228

Abstract

Purpose

The purpose of the present paper is to quantify and analyze the strain-rate dependence of the yield stress for both unfilled acrylonitrile-butadiene-styrene (ABS) and short carbon fiber-reinforced ABS (CF-ABS) materials, fabricated via material extrusion additive manufacturing (ME-AM). Two distinct and opposite infill orientation angles were used to attain anisotropy effects.

Design/methodology/approach

Tensile test samples were printed with two different infill orientation angles. Uniaxial tensile tests were performed at five different constant linear strain rates. Apparent densities were measured to compensate for the voided structure. Scanning electron microscope fractography images were analyzed. An Eyring-type flow rule was evaluated for predicting the strain-rate-dependent yield stress.

Findings

Anisotropy was detected not only for the yield stresses but also for its strain-rate dependence. The short carbon fiber-filled material exhibited higher anisotropy than neat ABS material using the same ME-AM processing parameters. It seems that fiber and molecular orientation influence the strain-rate dependence. The Eyring-type flow rule can adequately describe the yield kinetics of ME-AM components, showing thermorheologically simple behavior.

Originality/value

A polymer’s viscoelastic behavior is paramount to be able to predict a component’s ultimate failure behavior. The results in this manuscript are important initial findings that can help to further develop predictive numerical tools for ME-AM technology. This is especially relevant because of the inherent anisotropy that ME-AM polymer components show. Furthermore, short carbon fiber-filled ABS enhanced anisotropy effects during ME-AM, which have not been measured previously.

Article
Publication date: 1 February 2016

Spiros Pantelakis, Dorothea Setsika, Apostolos Chamos and Anna Zervaki

The purpose of this paper is to quantify the corrosion damage evolution that has occurred on the aircraft aluminum alloy 2024 after the exposure to Exfoliation Corrosion…

Abstract

Purpose

The purpose of this paper is to quantify the corrosion damage evolution that has occurred on the aircraft aluminum alloy 2024 after the exposure to Exfoliation Corrosion Test (EXCO) solution. Moreover, the effect of the evolving corrosion damage on the materials mechanical properties has been assessed. The relevance of the corrosion damage induced by the exposure to the laboratory EXCO for linking it to the damage developed after the exposure of the material on several outdoor corrosive environments or in service is discussed.

Design/methodology/approach

To induce corrosion damage the EXCO has been used. For the quantification of corrosion damage the metallographic features considered have been pit depth, diameter, pitting density and pit shape. The effect of the evolving corrosion damage on the materials mechanical properties has been assessed by means of tensile tests on pre corroded specimens.

Findings

The results have shown that corrosion damage starts from pitting and evolves to exfoliation, after the development of intergranular corrosion. This evolution is expressed by the increase of the depth of attack, as well as through the significant growth of the diameter of the damaged areas. The results of the tensile tests performed on pre corroded material made an appreciable decrease of the materials tensile properties evident. The decrease of the tensile ductility may become dramatic and increases on severity with increasing corrosion exposure time. SEM fractography revealed a quasi-cleavage zone beneath the depth of corrosion attack.

Originality/value

The results underline the impact of corrosion damage on the mechanical behavior of the aluminum alloy 2024 T3 and demonstrate the need for further investigation of the corrosion effect on the structural integrity of the material. This work provides an experimental database concerning the quantification of corrosion damage evolution and the loss of material properties due to corrosion.

Details

International Journal of Structural Integrity, vol. 7 no. 1
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 15 August 2016

Ben Brown, Wes Everhart and Joe Dinardo

In the development of powder bed additive manufacturing (AM) process parameters, the characterization of mechanical properties is generally performed through relatively…

Abstract

Purpose

In the development of powder bed additive manufacturing (AM) process parameters, the characterization of mechanical properties is generally performed through relatively large mechanical test samples that represent a bulk response. This provides an accurate representation of mechanical properties for equivalently sized or larger parts. However, as feature size is reduced, mechanical properties transition from a standard bulk response to a thin wall response where lower power border scans and surface roughness have a larger effect.

Design/methodology/approach

For this study, samples of wall thickness varying between 4.0 and 0.25 mm were built in 304L on the selective laser melting (SLM) platform and Ti-6Al-4V on the electron beam melting (EBM) platform. Samples were then mechanically tested, and fractography was performed for analysis.

Findings

This study experimentally identifies the threshold between bulk and thin wall mechanical properties for 304L SS on the SLM platform and Ti-6Al-4V on the EBM platform. A possible method for improving those properties and shifting the transition from bulk to thin wall response to smaller wall thicknesses by manipulation of scan pattern was investigated.

Originality/value

This study is a novel investigation into the effect of reduced wall thickness on the mechanical properties of a part produced by powder bed AM.

Details

Rapid Prototyping Journal, vol. 22 no. 5
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 1 April 1960

P.J.E. Forsyth and D.A. Ryder

IN 1950 Zapffe and Worden used the metal‐lurgical microscope for the examination of fatigue fracture surfaces, a technique which they called fractography. They suggested…

Abstract

IN 1950 Zapffe and Worden used the metal‐lurgical microscope for the examination of fatigue fracture surfaces, a technique which they called fractography. They suggested, as a result of their observations, that fatigue fractures showed two characteristics:

Details

Aircraft Engineering and Aerospace Technology, vol. 32 no. 4
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 February 1994

J.S. Hwang, Z. Guo and G. Lucey

Conventional solder materials are generally low temperature and low strength materials which are particularly vulnerable to temperature and stress. Even under ambient…

Abstract

Conventional solder materials are generally low temperature and low strength materials which are particularly vulnerable to temperature and stress. Even under ambient temperature, 298±5°K, the homologous temperature of most soft solder compositions exceeds 0.5. It is therefore anticipated that the properties and behaviour of such solder compositions could alter significantly when they are exposed to temperature change, temperature rise and/or a moderate level of stresses. With the continued innovation and development of microelectronic packages along with the intense global competition, the reliability of solder joints and the quality and yield of making solder joints in production become increasingly important. This research is to address the fundamental material deficiencies of conventional solders in an effort to develop superior solder materials. Several material principles have been considered including both intrinsic material and soldering process approaches. This paper presents the preliminary results of strengthening effects from the intrinsic material approach. The soldering process effects will be presented in a separate paper. The strengthening effects were evaluated by the combined consideration of monotonic shearing, creep and isothermal low cycle fatigue tests. Fatigue fractography and microstructure of the strengthened solder were characterised in comparison with conventional 63Sn/37Pb solder. The results showed that the proprietary solder system possesses a higher monotonic flow resistance as cyclic frequency decreases to 10−4 Hz. Deformation mechanisms and fatigue failure modes are also discussed in this paper.

Details

Soldering & Surface Mount Technology, vol. 6 no. 2
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 7 March 2022

Raghuraj Panwar and Pankaj Chandna

This paper aims to predict the performance of friction stir welded AA8090 joint.

Abstract

Purpose

This paper aims to predict the performance of friction stir welded AA8090 joint.

Design/methodology/approach

In the present study, Al-Li AA8090 plates are butt joined using friction stir welding (FSW). The experiments are designed and optimized using a Taguchi-orthogonal array. The experiments are conducted at three different process parameters, i.e. tool rotational speed (TRS), tool transverse speed (TTS) and dwell time (DT). The ultimate tensile strength (UTS) and microhardness (MH) are considered as response parameters. In addition, a statistical tool (ANOVA) is used to check the adequacy of experiment results.

Findings

The maximum UTS of 220 MPa is obtained at a TRS of 1,400 rpm, tool TTS of 40 mm/min and DT of 15 s. The maximum microhardness is obtained for 1,400 rpm, 25 mm/min and 8 s, i.e. 108.6 HV. The microstructural showed that the minimum grain is observed at the nugget zone. Fractography analysis revealed the ductile behaviour of fractured surfaces.

Originality/value

From the reported literature, it has been observed that very limited work is reported on the FSW of AA8090 alloy. Further, the thermal behaviour of welded joint is also observed in this experimental work.

Details

Aircraft Engineering and Aerospace Technology, vol. 94 no. 7
Type: Research Article
ISSN: 1748-8842

Keywords

1 – 10 of 129