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1 – 10 of over 6000Ömer Demir and Süleyman Sadi Seferoğlu
The lack of a reliable and valid measurement tool for coding achievement emerges as a major problem in Turkey. Therefore, the purpose of this study is to develop a Scratch-based…
Abstract
Purpose
The lack of a reliable and valid measurement tool for coding achievement emerges as a major problem in Turkey. Therefore, the purpose of this study is to develop a Scratch-based coding achievement test.
Design/methodology/approach
Initially, an item pool with 31 items was created. The item pool was classified within the framework of Bayman and Mayer’s (1988) types of coding knowledge to support content validity of the test. Then the item pool was applied to 186 volunteer undergraduates at Hacettepe University during the spring semester of the 2017-2018 academic year. Subsequently, the item analysis was conducted for construct validity of the test.
Findings
In all, 13 items were discarded from the test, leaving a total of 18 items. Out of the 18-item version of the coding achievement test, 4, 5 and 9 items measured syntactic, conceptual and strategic knowledge, respectively, among the types of coding knowledge. Furthermore, average item discrimination index (0.531), average item difficulty index (0.541) and Cronbach Alpha reliability coefficient (0.801) of the test were calculated.
Practical implications
Scratch users, especially those who are taking introductory courses at Turkish universities, could benefit from a reliable and valid coding achievement test developed in this study.
Originality/value
This paper has theoretical and practical value, as it provides detailed developmental stages of a reliable and valid Scratch-based coding achievement test.
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Gang Wang, Zihan Wang, Yue Zhang, GuangTao Xu, MingHao Zhao and Yanmin Li
The purpose of this paper is to find a new method to evaluate the hydrogen embrittlement performance of heterogeneous materials and thin film materials.
Abstract
Purpose
The purpose of this paper is to find a new method to evaluate the hydrogen embrittlement performance of heterogeneous materials and thin film materials.
Design/methodology/approach
The changes of hydrogen embrittlement properties of steel were studied by electrochemical hydrogen charging test and scratch test. The microstructure and properties of the alloy were analyzed by hardness tester, scanning electron microscope and three-dimensional morphology. The fracture toughness before and after hydrogen charging was calculated based on the scratch method.
Findings
The results showed that the hydrogen-induced hardening phenomenon occurs in the material after hydrogen charging. The scratch depth and width increased after hydrogen charging. The fracture toughness obtained by the scratch method showed that hydrogen reduces the fracture toughness of the material. The comparison error of fracture toughness calculated by indentation method was less than 5%.
Originality/value
The results show that the scratch method can evaluate the hydrogen embrittlement performance of the material. This method provides a possibility to evaluate the hydrogen embrittlement of thin-film and heterogeneous materials.
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Q.M Mehran, A.R Bushroa, M.A Fazal and M.M. Quazi
– The purpose of this study is to design and develop a new functional coating system for aerospace AL7075-T6 alloy that would evaluate the mechanical properties of the coating.
Abstract
Purpose
The purpose of this study is to design and develop a new functional coating system for aerospace AL7075-T6 alloy that would evaluate the mechanical properties of the coating.
Design/methodology/approach
This paper outlines the scratch adhesion characterisation of Cr/CrAlN coating using a combination of radio frequency (RF) and direct current (DC) physical vapour deposition (PVD) magnetron sputtering. The surface morphology, microstructure and chemical composition of the Cr/CrAlN film were evaluated by optical microscopy (OM), field emission scanning electron microscopy (FESEM) integrated with energy-dispersive X-Ray spectroscopy (EDX) and atomic force microscopy (AFM). The film-to-substrate adhesion was measured by a scratch test machine manufactured with a detection system, motorized stages, penetration depth sensors, optical microscope and tangential frictional load sensors.
Findings
The AFM and ultra-micro hardness results showed an increase in surface roughness to about 20 per cent and hardness to about 74 per cent. Moreover, the film-to-substrate adhesion strength of 1,814 mN was obtained with PVD deposition process.
Research limitations/implications
The main limitation of this work is caused by PVD deposition process. Besides, surface defects such as pinholes contribute to a decrease in adhesion strength.
Practical implications
The higher hardness of CrAlN coating is used to improve the properties of softer aluminium substrates. This hardness prevents ploughing-induced wear and provides greater adhesion strength by preventing coating delamination.
Originality/value
Until now, CrAlN is coated only on ferrous alloys. It has not yet been tried on aluminium alloys. Moreover, coating functionality depends on higher adhesion and failure mechanisms involved in the film-to-substrate system, which is significant in aerospace applications.
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Yunhai Ma, Hubiao Wang, Xin Zhang, Wenbo Shang, Jin Tong and Zhiyong Chang
Nature provides a wide range of structures with different functions, which can serve as a source of research concepts. Based on the bionics principle, a bionic structure was…
Abstract
Purpose
Nature provides a wide range of structures with different functions, which can serve as a source of research concepts. Based on the bionics principle, a bionic structure was applied to drill pipe specimens to compare the bond strength of paint coatings with and without a bionic ring groove pattern machined on the substrate.
Design/methodology/approach
Using the Revetest Xpress Plus scratch tester, the bond strengths of the coatings on the drill pipe with and without the bionic structure were measured and the difference in bond strength was observed.
Findings
The critical scratch loads of the surface coatings were 12.77 and 5.4 N. Furthermore, the scratch curve from the plain sample had a larger fluctuation compared to the curve of the samples with bionic ring grooves.
Originality/value
This indicated that the application of a bionic pattern to the surface of the substrate could enhance the bond strength and the degree of mechanical adhesion between the coating and the surface of the drill pipe, which is beneficial for the anti-corrosion performance of the drill pipe.
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Khaled Elleuch, Salah Mezlini, Siegfried Fouvry and Philippe Kapsa
Damage of aluminium alloy under contact loading is detected in different cases independent of contact configuration and operating conditions. An investigation of two industrial…
Abstract
Damage of aluminium alloy under contact loading is detected in different cases independent of contact configuration and operating conditions. An investigation of two industrial cases is proposed to describe how it is possible to study the material degradation under friction. The experimental simulation of aluminium damage in laboratory conditions is carried out. Two contact configurations are studied in order to reproduce the industrial damage of aluminium alloys. Varying experimental conditions relative to a specific contact body for each test have demonstrated a realistic correlation between damage, test configuration and material properties. Independent of the tribological system, plastic deformation seems to be the major parameter controlling the wear of aluminium alloy under friction in the studied cases.
Bingjing Lin, A. Kiet Tieu, Hongtao Zhu, Buyung Kosasih and Oyong Novareza
This paper aims to assess the adsorption behaviour and the adhesion strength of lubricant films formed by polypropylene oxide-polyethylene oxide-polypropylene oxide (PPO-PEO-PPO…
Abstract
Purpose
This paper aims to assess the adsorption behaviour and the adhesion strength of lubricant films formed by polypropylene oxide-polyethylene oxide-polypropylene oxide (PPO-PEO-PPO) with phosphate ester additive on Ti-coated surface and to identify the influence of molecular architecture and phosphate ester additive.
Design/methodology/approach
The thickness of the adsorbed PPO-PEO-PPO with phosphate ester lubricant films on Ti surfaces was measured by ellipsometry. The adhesion strength of the copolymer and the copolymer with phosphate ester lubricants was studied by the micro-scratch tests; the scratch tracks on the surfaces were observed by atomic force microscopy and scanning electronic microscopy.
Findings
The copolymer with a higher weight percentage of PPO not only formed a thicker film but also showed stronger adhesion and better lubrication performance. The added phosphate ester increased the film thickness and improved the tribological behaviour. The finding reveals that the adsorbed film thickness which depends on the PPO chain length and the presence of phosphate ester has a considerable effect on the scratch behaviour.
Originality/value
This paper fulfils the studies about adsorption behaviour and lubrication mechanism of this new lubricant which has not been adequately investigated on the metal surface.
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Abstract
Purpose
This paper aims to investigate the structure and scratch resistance properties of gas nitrided pure iron samples.
Design/methodology/approach
The effects of material strain hardening and amount of grain boundaries exposed on nitriding surface were evaluated by cold rolling the starting samples to different reduction levels before gas nitriding.
Findings
The study finds that nitriding without any prior cold rolling produced a comparatively wide compound layer with a large fraction of porous zone featuring low scratch hardness values but no evidence of damage. On the contrary, cold rolling before nitriding led to a more irregular and thinner compound layer with reduced amount of porous zone and much finer nitrides in the diffusion zone. Scratch hardness was increased but failure mechanism changed by generation of conformal cracks within the track groove and the appearance of discontinuous spallation at high loads.
Originality/value
One of the issues of great industrial importance concerning nitriding of steels is the need to predict the extent of the nitrided layer in products showing small variations in microstructure or in extent of cold working due to complex manufacturing cycles. Despite the practical importance, relatively little information is available in literature about these issues. The present paper is therefore aimed at investigating the structure and mechanical properties of pure iron samples, gas nitrided with different amounts of cold working and microstructural conditions.
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A.P. Kabra, P. Mahanwar, V. Shertukde and V. Bambole
The purpose of this paper is to formulate two component polyurethane coatings based on acrylic polyol, to study the effects of variable nanosilica loadings in these coatings on…
Abstract
Purpose
The purpose of this paper is to formulate two component polyurethane coatings based on acrylic polyol, to study the effects of variable nanosilica loadings in these coatings on different morphological, optical, mechanical, corrosion resistance and weather resistance properties and to study the intercalation of acrylic polyol molecules into nanosilica crystals by XRD technique.
Design/methodology/approach
Two component polyurethane coatings were synthesised using acrylic polyol and isocyanate HDI. The nanosilica was incorporated in polyurethane formulation at the weight ratios of 1%, 3% and 5% based on total weight of polyol and isocyanate. The performance of nanocoatings was compared for variable loads of nanosilica for different properties such as morphological, optical, mechanical, corrosion resistance, weather resistance and were studied for intercalation of acrylic polyol into nanosilica crystals by XRD technique.
Findings
Improvement in the properties of polyurethane coatings is achieved with the incorporation of nanosilica. The improvement is the result of inherently high properties of inorganic nanosilica. Tensile strength, scratch hardness, abrasion resistance, corrosion and weathering resistance show significant improvement in performance with the incorporation of nanosilica. Properties are found to deteriorate beyond a certain loading of nanosilica; hence it is important to optimise loading level. The optimal range for high performance was found to be in the range of 1% to 3%. The improvement was a result of synergistic behaviour and good interfacial interaction between polyurethane and nanosilica at optimal levels.
Research limitations/implications
The method used for incorporation of nanosilica into polyurethane was direct incorporation method. The other method of incorporation, i.e. in situ addition and its effect on properties can also be studied.
Practical implications
With the addition of optimal loading level of nanosilica to polyurethane coatings, properties can be enhanced up to the mark. The addition is relatively easy and cost effective.
Originality/value
The paper proves the significance of incorporation of nanosilica on original properties of polyurethane coatings and widens the area of applications of two component polyurethane coatings from acrylic polyol by strengthening them in their properties. The coatings can be applicable in high performance topcoats especially for automotive topcoats.
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Luciano Castro Lara, Henara Costa and José Daniel Biasoli de Mello
This paper aims to analyse the influence of the thickness of different layers [diamond-like-carbon (DLC) and chromium nitride (CrN)] on the sliding wear behaviour of a…
Abstract
Purpose
This paper aims to analyse the influence of the thickness of different layers [diamond-like-carbon (DLC) and chromium nitride (CrN)] on the sliding wear behaviour of a multifunctional coating on AISI 1020 substrates. When small and cheap components need to be manufactured in large scale, they are often produced using soft metals, such as unhardened low carbon steels and pure iron.
Design/methodology/approach
Two families, one with thicker films and the other with thinner films, were deposited onto a soft carbon steel substrate by plasma-enhanced chemical vapour deposition (PECVD). Reciprocating linear tests with incremental loading assessed the durability of the coatings. In addition, friction coefficient and wear rates of both specimens and counterbodies were measured at a constant load.
Findings
Thinner layers presented lower sliding wear rates (four-five times lower) for both specimens and counterbodies, less spalling and protective tribolayers on the wear tracks.
Originality/value
Although multilayered CrN–DLC coatings on relatively hard substrates such as HSS and cemented carbide tools are already a proven technology, much less is known about its deposition on a much softer substrate such as low carbon steel. In previous works, we have analysed the influence of layer thickness on hardness and scratch resistance of the same coatings. This paper presents results for their performance under wear sliding conditions using an original approach (three-dimensional triboscopic maps) for two distinct configurations (increasing load and constant load).
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D. Bhatia, M. Alam and P.C. Sarkar
To study the changes occurring in lac‐polyvinyl butyral (PVB) resin blends at molecular levels on baking the blends at 200°C for different intervals of time. It was also to…
Abstract
Purpose
To study the changes occurring in lac‐polyvinyl butyral (PVB) resin blends at molecular levels on baking the blends at 200°C for different intervals of time. It was also to ascertain the changes in key physico‐chemical parameters of these blends, before and after applying thermal stress on these blends.
Design/methodology/approach
Films of lac‐PVB blends, applied on tin panels were baked at 200°C for different time intervals. The FTIR spectra of the blends were recorded using specular reflectance spectroscopic techniques. The results obtained were compared and reported. The blends were also tested for different physico‐chemical parameters such as scratch hardness, flexibility, adhesion, acid resistance, etc.
Findings
On baking the blends of lac‐PVB resin at 200°C for different time intervals; fragmentation reaction, that is breakdown of products into small molecules, takes place in lac‐PVB blends. Side products such as acetic acid emerge on baking the blends. Probably hydrolysis of oxirane ring also takes place leading to the release of free alcoholic groups. The lac‐PVB blends do not show any improvement in scratch hardness and are also not resistant to the action of acids. The blends made by lac‐PVB resin baked at 200°C do not seem to be compatible as no improvement in any of the physico‐chemical parameters was seen.
Research limitations/implications
Mixtures of solvents were tried for dissolving the PVB resin. In most of the solvent mixtures, PVB resin forms big lumps and is not soluble so there is a need for universal solvent for dissolving the PVB resin. The spectral studies on lac‐PVB blends were conducted qualitatively, although desirable, quantitative studies could not be carried out, due to the inherent difficulties in handling the resins.
Practical implications
The parent resins in lac‐PVB blends (baked at 200°C) do not seem to be compatible with one another as there was no improvement in any of the physico‐chemical parameters of the lac‐PVB blends. For making lac‐PVB blends, low range of baking temperature may be tried.
Originality/value
In literature, there is not much evidence of making lac‐PVB blends. This paper is the first one in attempting to obtain and correlate FTIR spectra of the lac‐PVB blends with physico‐chemical changes of the blends. This paper also highlights the convenience of the method and the scope of sophisticated data analysis such as derivative spectrometry.
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