Search results

1 – 10 of over 15000
Article
Publication date: 24 July 2019

Ting Qi, Haihong Zhu, Xiaoyan Zeng and Jie Yin

It is a crucial issue to eliminate cracks for selective laser melting (SLM) 7xxx series aluminum alloy. This paper aims to study the effect of silicon content on the…

Abstract

Purpose

It is a crucial issue to eliminate cracks for selective laser melting (SLM) 7xxx series aluminum alloy. This paper aims to study the effect of silicon content on the cracking behavior and the mechanism of eliminating crack of SLMed Al7050 alloy.

Design/methodology/approach

Six different silicon contents were added to the Al7050 powder. The crack density and crack count measuring from optical micrographs were utilized to judge the cracking susceptibility. The low melting phases analyzing from Jmatpro and the microstructure observing by EPMA and SEM were used to discuss the mechanism of eliminating the crack.

Findings

The cracking susceptibility of SLMed Al7050 alloy decreases with the increase of adding silicon content. When adding silicon, two new low-melting phases appeared: Mg2Si and Al5Cu2Mg8Si6. These low-melting phases offer much liquid feeding along the grain boundary and decrease the cracking susceptibility. Moreover, the grains are obviously refined after adding silicon. The fine grain can increase the total surface area of the grain boundary, which can reinforce the matrix and decrease the cracking susceptibility. High silicon content results in more low-melting phases and fine grains, which decreases the cracking susceptibility.

Originality/value

The investigation results can help to obtain crack-free SLMed Al7050 parts and deep knowledge on eliminating cracking mechanism of high-strength aluminum alloy fabricated by SLM.

Details

Rapid Prototyping Journal, vol. 25 no. 10
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 5 March 2018

Wei Zhang, Beibing Dai, Zhen Liu and Cuiying Zhou

The cracking of a reinforced concrete lining has a significant influence on the safety and leakage of pressure tunnels. This study aims to develop, validate and apply a…

Abstract

Purpose

The cracking of a reinforced concrete lining has a significant influence on the safety and leakage of pressure tunnels. This study aims to develop, validate and apply a numerical algorithm to simulate the lining cracking process during the water-filling period of pressure tunnels.

Design/methodology/approach

Cracks are preset in all lining elements, and the Mohr−Coulomb criterion with a tension cutoff is used in determining whether a preset crack becomes a real crack. The effects of several important factors such as the water pressure on crack surfaces (WPCS) and the heterogeneity of the lining tensile strength are also considered simultaneously.

Findings

The crack number and width increase gradually with the increase in internal water pressure. However, when the pressure reaches a threshold value, the increase in crack width becomes ambiguous. After the lining cracks, the lining displacement distribution is discontinuous and steel bar stress is not uniform. The measured stress of the steel bar is greatly determined by the position of the stress gauge. The WPCS has a significant influence on the lining cracking mechanism and should not be neglected.

Originality/value

A reliable algorithm for simulating the lining cracking process is presented by which the crack number and width can be determined directly. The numerical results provide an insight into the development law of lining cracks and show that the WPCS significantly affects the cracking mechanism.

Details

Engineering Computations, vol. 35 no. 1
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 1 March 1999

W.L. Yao and Ming C. Leu

This paper presents a numerical and experimental investigation of ceramic shell cracking during the burnout process in investment casting with internally webbed laser…

1348

Abstract

This paper presents a numerical and experimental investigation of ceramic shell cracking during the burnout process in investment casting with internally webbed laser stereolithography patterns. Considered are the cracking temperature of the ceramic shell, the buckling temperature of the web link, and the glass transition temperature of the epoxy resin. Our hypothesis is that shell cracking will occur if the ceramic rupture temperature is lower than the temperature of glass transition and the temperature of web buckling. This hypothesis is validated by a good agreement we obtained between experimental observations and numerical simulations. It is found that the shell cracking and web link buckling are strongly related to the cross‐sectional dimensions and span length of the web structure and the shell thickness, and that shell cracking can be prevented by buckling of the epoxy webbed pattern in early stages of the burnout process.

Details

Rapid Prototyping Journal, vol. 5 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 15 June 2015

Luke N. Carter, Khamis Essa and Moataz M Attallah

The purpose of this paper is to optimise the selective laser melting (SLM) process parameters for CMSX486 to produce a “void free” (fully consolidated) material, whilst…

1459

Abstract

Purpose

The purpose of this paper is to optimise the selective laser melting (SLM) process parameters for CMSX486 to produce a “void free” (fully consolidated) material, whilst reducing the cracking density to a minimum providing the best possible fabricated material for further post-processing. SLM of high temperature nickel base superalloys has had limited success due to the susceptibly of the material to solidification and reheat cracking.

Design/methodology/approach

Samples of CMSX486 were fabricated by SLM. Statistical design of experiments (DOE) using the response surface method was used to generate an experimental design and investigate the influence of the key process parameters (laser power, scan speed, scan spacing and island size). A stereological technique was used to quantify the internal defects within the material, providing two measured responses: cracking density and void per cent.

Findings

The analysis of variance (ANOVA) was used to determine the most significant process parameters and showed that laser power, scan speed and the interaction between the two are significant parameters when considering the cracking density. Laser power, scan speed, scan spacing and the interaction between power and speed, and speed and spacing were the significant factors when considering void per cent. The optimum setting of the process parameters that lead to minimum cracking density and void per cent was obtained. It was shown that the nominal energy density can be used to identify a threshold for the elimination of large voids; however, it does not correlate well to the formation of cracks within the material. To validate the statistical approach, samples were produced using the predicted optimum parameters in an attempt to validate the response surface model. The model showed good prediction of the void per cent; however, the cracking results showed a greater deviation from the predicted value.

Originality/value

This is the first ever study on SLM of CMSX486. The paper shows that provided that the process parameters are optimised, SLM has the potential to provide a low-cost route for the small batch production of high temperature aerospace components.

Details

Rapid Prototyping Journal, vol. 21 no. 4
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 5 May 2015

Babruvahan Pandurang Ronge and Prashant Maruti Pawar

– This paper aims to focus on the stochastic analysis of composite rotor blades with matrix cracking in forward flight condition.

Abstract

Purpose

This paper aims to focus on the stochastic analysis of composite rotor blades with matrix cracking in forward flight condition.

Design/methodology/approach

The effect of matrix cracking and uncertainties are introduced to the aeroelastic analysis through the cross-sectional stiffness properties obtained using thin-walled beam formulation, which is based on a mixed force and a displacement method. Forward flight analysis is carried out using an aeroelastic analysis methodology developed for composite rotor blades based on the finite element method in space and time. The effects of matrix cracking are introduced through the changes in the extension, extension-bending and bending matrices of composites, whereas the effect of uncertainties are introduced through the stochastic properties obtained from previous experimental and analytical studies.

Findings

The stochastic behavior of helicopter hub loads, blade root forces and blade tip responses are obtained for different crack densities. Further, assuming the behavior of progressive damage in same beam is measurable as compared to its undamaged state, the stochastic behaviors of delta values of various measurements are studied. From the stochastic analysis of forward flight behavior of composite rotor blades at various matrix cracking levels, it is observed that the histograms of these behaviors get mixed due to uncertainties. This analysis brings out the parameters which can be used for effective prediction of matrix cracking level under various uncertainties.

Practical implications

The behavior is useful for the development of a realistic online matrix crack prediction system.

Originality/value

Instead of introducing the white noise in the simulated data for testing the robustness of damage prediction algorithm, a systematic approach is developed to model uncertainties along with damage in forward flight simulation.

Details

Aircraft Engineering and Aerospace Technology: An International Journal, vol. 87 no. 3
Type: Research Article
ISSN: 0002-2667

Keywords

Article
Publication date: 1 November 1990

Z.A. Foroulis

This paper presents a brief summary of the stress corrosion cracking experience of carbon steel in amine acid gas scrubbing units. In addition, it discusses the current…

Abstract

This paper presents a brief summary of the stress corrosion cracking experience of carbon steel in amine acid gas scrubbing units. In addition, it discusses the current views of the most probable mechanism of cracking of carbon steel equipment in amine acid gas scrubbing units and the probable role of the nature of the amine molecule.

Details

Anti-Corrosion Methods and Materials, vol. 37 no. 11
Type: Research Article
ISSN: 0003-5599

Article
Publication date: 7 April 2021

Emanuel Tamir and Sherry Ganon-Shilon

The study explores characteristics of strong school cultures through principals' exploitation of additional resources within implementation of a national reform.

Abstract

Purpose

The study explores characteristics of strong school cultures through principals' exploitation of additional resources within implementation of a national reform.

Design/methodology/approach

An interpretive approach was utilized to analyze qualitative data from semi-structured interviews with 35 Israeli high school principals who implemented a national reform in state and religious-state schools from all school districts.

Findings

The article presents four types of cracking cultures led by the principals: (1) a school values-based culture, such as respect; (2) a caring culture based on trust and a positive atmosphere; (3) a maintenance achievement-oriented culture; and (4) a creative culture that supports the teachers and takes risks in using resources beyond their intended purpose.

Originality/value

Exploring principals' exploitation of resources within a cracking culture may promote school improvement and innovation during national reform implementation.

Details

Journal of Educational Administration, vol. 59 no. 5
Type: Research Article
ISSN: 0957-8234

Keywords

Article
Publication date: 1 September 1972

J.C. Scully

Introduction Stress corrosion cracking is a phenomenon that is of interest to a wide range of metal users. When it occurs under service conditions, often without any prior…

Abstract

Introduction Stress corrosion cracking is a phenomenon that is of interest to a wide range of metal users. When it occurs under service conditions, often without any prior indication of impeding failure, its effect may be catastrophic.

Details

Anti-Corrosion Methods and Materials, vol. 19 no. 9
Type: Research Article
ISSN: 0003-5599

Article
Publication date: 1 September 1965

L. Fairman

Background to tests. Cathodic protection has been used on an industrial scale for the protection of pipelines and underwater structures for many years. It has not…

Abstract

Background to tests. Cathodic protection has been used on an industrial scale for the protection of pipelines and underwater structures for many years. It has not, however, been applied to structures in which, although the general corrosion resistance is high, there is likelihood of failure by stress‐corrosion cracking. The purpose of the investigation reported here was to determine the effect of cathodic polarisation in a range of commercial alloys which were liable to this type of failure. The idea of using cathodic protection is especially attractive, as metallic or non‐metallic coatings, though they delay the onset of stress corrosion, are not suitable preventive measures. Pitting in the coatings soon results in earlier failure and some materials, such as stainless steel, are difficult to coat.

Details

Anti-Corrosion Methods and Materials, vol. 12 no. 9
Type: Research Article
ISSN: 0003-5599

Article
Publication date: 14 February 2019

Weishan Huang, Jing-Li Luo, Hani Henein and Josiah Jordan

This paper aims to evaluate the sulfide stress cracking (SSC) resistance of L80 casing steels with different alloying chemistries (e.g. Ti-B and Mn-Cr-Mo) by correlating…

Abstract

Purpose

This paper aims to evaluate the sulfide stress cracking (SSC) resistance of L80 casing steels with different alloying chemistries (e.g. Ti-B and Mn-Cr-Mo) by correlating the reduction in area ratio with the mechanical property, inclusion and carbide.

Design/methodology/approach

SSC tests were conducted in 5.0 Wt.% sodium chloride and 0.5 Wt.% acetic acid solution saturated with H2S using constant load tensile method. The microstructure and fracture morphology of the steel were observed using scanning electron microscope. The inclusion and carbide were identified by energy dispersive spectroscopy and auger electron microscope.

Findings

Among all the testing steels, electric resistance welding (ERW) L80-0.5Mo steel demonstrates the highest SSC resistance because of its appropriate mechanical properties, uniform microstructure and low inclusion content. The SSC resistance of L80 steels generally decreases with the rising yield strength. The fracture mode of steel with low SSC resistance is jointly dominated by transgranular and intergranular cracking, whereas that with high SSC resistance is mainly transgranular cracking. SSC is more sensitive to inclusions than carbides because the cracks are easier to be initiated from the elongated inclusions and oversized oxide inclusions, especially the inclusion clusters. Unlike the elongated carbide, globular carbide in the steel can reduce the negative effect on the SSC resistance. Especially, a uniform microstructure with fine globular carbides favors a significant improvement in SSC resistance through precluding the cracking propagation.

Originality/value

The paper provides the new insights into the improvement in SSC resistance of L80 casing steel for its application in H2S environment through optimizing its alloying compositions and microstructure.

Details

Anti-Corrosion Methods and Materials, vol. 66 no. 4
Type: Research Article
ISSN: 0003-5599

Keywords

1 – 10 of over 15000