The Experts below are selected from a list of 4920 Experts worldwide ranked by ideXlab platform
Ange-therese Akono - One of the best experts on this subject based on the ideXlab platform.
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fracture toughness of one and two dimensional nanoreinforced cement via Scratch Testing
Philosophical Transactions of the Royal Society A, 2021Co-Authors: Ange-therese AkonoAbstract:Cement is the most widely consumed material globally, with the cement industry accounting for 8 of human-caused greenhouse gas emissions. Aiming for cement composites with a reduced carbon footprin...
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microstructure toughness relationships in calcium aluminate cement polymer composites using instrumented Scratch Testing
Journal of Materials Science, 2017Co-Authors: K R Anderson, Ange-therese AkonoAbstract:We investigate the influence of the microstructure on the fracture properties of calcium aluminate cement/polymer composites. We carry out microscopic Scratch tests during which a Rockwell C diamond probe pushes across the surface of a polished specimen under a linearly increasing vertical force. We extend the Scratch fracture method to heterogeneous materials. The Scratch test induces a ductile-to-brittle transition as the penetration depth increases. Scanning electron microscopy imaging shows that the low porosity and the strong cement-binder interphase favor toughening mechanisms such as crack trapping and bridging. Nonlinear fracture mechanics theory yields the fracture toughness in the fracture-driven regime. The fracture toughness of macro-defect-free (MDF) cement is found to decrease as the polymer-to-cement ratio increases. This decrease in the fracture resistance can be explained by the decrease in anhydrous cement content and the increase in the inter-particle distance between cement grains. By evaluating the fracture toughness of the micro-constituents of MDF cement, we show that the high value of the fracture toughness at the composite level stems from tough calcium aluminate phases and a highly packed non-porous granular microstructure.
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fracture properties of the alkali silicate gel using microscopic Scratch Testing
Cement & Concrete Composites, 2017Co-Authors: Caroline V Johnson, Nicole P Hasparyk, Paulo J.m. Monteiro, Jiaxin Chen, Ange-therese AkonoAbstract:We carry out a multi-scale investigation of the fracture properties of the gel produced by the alkali-silica reaction in concrete. Milimeter-sized alkali gels are tested via Scratch tests at the micrometer level. Scanning electron microscopy reveals curved fracture surfaces produced during the Scratch test, warranting a fracture mechanics analysis. By application of a nonlinear fracture mechanics model to the recorded load and depth data, we estimate the fracture toughness of ASR gel to be Kc=0.62Kc=0.62 MPam. In turn, by combining micro-indentation and Scratch tests, we can estimate the fracture energy Gf=11.2Gf=11.2 J/m2. These experimental results are important for the multi-scale modeling of the alkali-aggregate reaction.
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microscopic fracture characterization of gas shale via Scratch Testing
Mechanics Research Communications, 2016Co-Authors: Ange-therese Akono, Pooyan KabirAbstract:Abstract We investigate the fracture properties of organic-rich shale at the microscopic scale by coupling advanced imaging techniques, fracture mechanics and micro-scale mechanical Testing methods. We study three shale systems: Toarcian (Paris Basin, France), and Lower and Upper Woodford shale (Oklahoma, US). A material preparation procedure is designed so as to visualize the microstructure. Optical microscopy and scanning electron microscopy reveal a porous granular fabric with the grain size ranging from 30 to 100 μm as well as micron-sized air voids. Microscopic Scratch tests are carried out, during which a stylus is pushed across the surface of a material under a prescribed monotonically increasing vertical load. We develop a fracture mechanics approach that takes into account the heterogeneity and anisotropy of gas shale. The microscopic Scratch toughness predicted by the Scratch fracture model is 2.35–2.98 MPa m , which is two times higher than the macroscopic fracture toughness. A microscopic examination of the fracture surface reveals toughening mechanisms such as particle pull out, crack front roughening and crack bridging. The methodology presented is new and will pave the way toward a mechanistic physics-based understanding of the fracture behavior of gas shale at multiple length scales. In turn, this will accelerate the design of optimum and efficient schemes to extract natural gas from unconventional shale.
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Energetic Size Effect Law at the Microscopic Scale: Application to Progressive-Load Scratch Testing
Journal of Nanomechanics and Micromechanics, 2016Co-Authors: Ange-therese AkonoAbstract:AbstractA Scratch test consists in pulling a diamond stylus across the surface of a weaker material; it is widely applied in several fields of science and engineering, including polymer damage, metal wear, thin-film quality control, and strength of rocks. Recently, there has been an upsurge of interest in the fracture analysis of materials via Scratch Testing. In this study, the energetic size effect law (SEL) is applied at the microscopic scale for progressive-load Scratch tests using a Rockwell C diamond probe. First, we employ dimensional analysis to connect the Scratch force to the projected load-bearing area and to the perimeter for an axisymmetric Scratch probe. In a second step, based on geometrical considerations, we approximate the real Scratch probe geometry with a cone of equivalent half-apex angle, θeq. Then, we express the dependence of the nominal strength, σN, on the structural size, Λ, via a scaling relationship. The theoretical developments are later implemented in an experimental procedu...
Terence G Langdon - One of the best experts on this subject based on the ideXlab platform.
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indentation and Scratch Testing of dlc zr coatings on ultrafine grained titanium processed by high pressure torsion
Wear, 2013Co-Authors: Chuan Ting Wang, R J K Wood, Terence G Langdon, A Escudeiro, T Polcar, A Cavaleiro, Nong GaoAbstract:Abstract High-pressure torsion was employed to refine the microstructure of grade 2 Ti under an imposed pressure of 3.0 GPa at room temperature. The microhardness of grade 2 Ti increased from 1.82 GPa for the coarse grain state to 3.05 GPa after high-pressure torsion processing, where this value is very close to the hardness of the Ti–6Al–4V alloy. Subsequently, several diamond-like carbon (DLC) coatings with thicknesses of ∼1.4 μm were deposited on as-received Ti, high-pressure torsion processed Ti and Ti–6Al–4V samples via physical vapour deposition. Both indentation and Scratch tests showed a much improved adhesion of DLC-7Zr, DLC:H-7Zr and DLC-9Zr coatings with high-pressure torsion processed Ti as the substrate by comparison with the same coatings on coarse-grained Ti. The results suggest that commercial pure Ti processed by high-pressure torsion and coated with a diamond-like carbon coating provides a potential candidate material for bio-implant applications.
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tribology Testing of ultrafine grained ti processed by high pressure torsion with subsequent coating
Journal of Materials Science, 2013Co-Authors: Chuan Ting Wang, R J K Wood, Terence G LangdonAbstract:A grade 2 pure Ti was processed by high-pressure torsion (HPT) under 3.0 GPa for 10 revolutions to achieve an improved strength. Wear tests revealed that HPT only slightly improved the wear resistance of pure Ti. Subsequently, a TiN coating with a thickness of 2.5 μm was deposited on different Ti substrates to improve the wear resistance. Both indentation and Scratch Testing demonstrated a much improved load-bearing capacity when ultrafine-grained Ti was chosen as the substrate compared with coarse-grained Ti. All results indicate that pure Ti processed by HPT, when combined with a subsequent coating, represents a good candidate material for bio-implant applications.
Jürgen Malzbender - One of the best experts on this subject based on the ideXlab platform.
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measuring mechanical properties of coatings a methodology applied to nano particle filled sol gel coatings on glass
Materials Science & Engineering R-reports, 2002Co-Authors: Jürgen Malzbender, Den Jmj Jaap Toonder, A R BalkenendeAbstract:The main aim of this paper is to demonstrate the practical use of nano-indentation and Scratch Testing in determining mechanical properties of thin coatings. We place our emphasis on how information obtained using both techniques can be combined to give a more complete representation of the properties of a coating–substrate system. Part I of the paper gives an overview of approaches to determine mechanical properties of thin coatings that have been proposed in the literature, and develops them further to be useful tools in the analysis of coatings. This results in methods for measuring the mechanical properties of thin coatings. We particularly emphasise the determination of the elastic modulus, hardness, coating and interfacial fracture toughness and residual stress using indentation and Scratch Testing. Part II of the paper illustrates the application of these methods to relatively soft coatings of methyltrimethoxysilane (MTMS) filled with colloidal silica or alumina particles on glass. The coatings were prepared using a sol–gel process. We report results of the dependence of the mechanical properties on the filler particle content, illustrating that microstructural changes can also be tracked using these techniques. The effects of the nature and volume fraction of the filler particles are discussed.
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Fracture toughness and adhesion energy of sol-gel coatings on glass
Journal of Materials Research, 2002Co-Authors: Jaap Den Toonder, G. De With, Jürgen Malzbender, Ruud BalkenendeAbstract:The reliability of coatings that are used in industrial applications critically depends on their mechanical properties. Nanoindentation and Scratch Testing are well-established techniques to measure some of these properties, namely the elastic modulus and hardness of coatings. In this paper, we investigate the possibility of also assessing the coating fracture toughness and the energy of adhesion between the coating and the substrate using indentation and Scratch Testing. Various existing and new methods are discussed, and they are illustrated by measurements on particle-filled sol-gel coatings on glass. All methods are based on the occurrence of cracking, and they are therefore only applicable to coating systems that act like brittle materials and exhibit cracking during indentation and Scratching. The methods for determining the fracture toughness give comparable results, but the values still differ to within about 50%. The values of the adhesion energy obtained from different measurements are consistent, but it remains uncertain to which extent the obtained values are quantitatively correct. The results show that the methods used are promising, but more research is needed to obtain reliable quantitative results.
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Scratch Testing of hybrid coatings on float glass
Surface & Coatings Technology, 2001Co-Authors: Jürgen MalzbenderAbstract:Abstract Results of Scratch Testing on hybrid organic–inorganic coatings on float glass are reported. The effects of the preparation conditions on the apparent Scratch resistance are tested using a sphere. As parameters to quantify the Scratch resistance the load and the area of delamination as well as the length and number of surface cracks are considered. It is concluded that the main reason for delamination is the deflection of cracks at the interface. A model is proposed to estimate the distance between cracks.
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Analysis of Scratch Testing of organic-inorganic coatings on glass
Thin Solid Films, 2001Co-Authors: Jürgen MalzbenderAbstract:Results on Scratch Testing of hybrid, organic-inorganic coatings are reported. The behavior of the friction coefficient as well as the load of cracking, delamination and chipping are analyzed using spheres of different radii. The effects of a variation of the loading and displacement rate are tested. Models to predict the friction coefficient are tested and related to the observations. The apparent fracture toughness and its relationship to the deformation of the coating and substrate are discussed. Parameters are given that are independent of the indenter radius and coating thickness and, therefore, permit an objective assessment of the failure of coatings.
Ben D Beake - One of the best experts on this subject based on the ideXlab platform.
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Elevated temperature repetitive micro-Scratch Testing of AlCrN, TiAlN and AlTiN PVD coatings
International Journal of Refractory Metals & Hard Materials, 2017Co-Authors: Ben D Beake, Jose Luis Endrino, Christine Kimpton, German S. Fox-rabinovich, Stephen C. VeldhuisAbstract:Abstract In developing advanced wear-resistant coatings for tribologically extreme highly loaded applications such as high speed metal cutting a critical requirement is to investigate their behaviour at elevated temperature since the cutting process generates frictional heat which can raise the temperature in the cutting zone to 700–900 °C or more. High temperature micro-tribological tests provide severe tests for coatings that can simulate high contact pressure sliding/abrasive contacts at elevated temperature. In this study ramped load micro-Scratch tests and repetitive micro-Scratch tests were performed at 25 and 500 °C on commercial monolayer coatings (AlCrN, TiAlN and AlTiN) deposited on cemented carbide cutting tool inserts. AlCrN exhibited the highest critical load for film failure in front of the moving Scratch probe at both temperatures but it was prone to an unloading failure behind the moving probe. Scanning electron microscopy showed significant chipping outside the Scratch track which was more extensive for AlCrN at both room and elevated temperature. Chipping was more localised on TiAlN although this coating showed the lowest critical loads at both test temperatures. EDX analysis of Scratch tracks after coating failure showed tribo-oxidation of the cemented carbide substrate. AlTiN showed improved Scratch resistance at higher temperature. The von Mises, tensile and shear stresses acting on the coating and substrate sides of the interface were evaluated analytically to determine the main stresses acting on the interface. At 1 N there are high stresses near the coating-substrate interface. Repetitive Scratch tests at this load can be considered as a sub-critical load micro-scale wear test which is more sensitive to adhesion differences than the ramped load Scratch test. The analytical modelling showed that a dramatic improvement in the performance of AlTiN in the 1 N test at 500 °C could be explained by the stress distribution in contact resulting in a change in yield location due to the high temperature mechanical properties. The increase in critical load with temperature on AlTiN and AlCrN is primarily a result of the changing stress distribution in the highly loaded sliding contact rather than an improvement in adhesion strength.
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nano Scratch Testing of ti fe nx thin films on silicon
Surface & Coatings Technology, 2017Co-Authors: Ben D Beake, Vladimir Vishnyakov, Adrian L HarrisAbstract:Abstract Thin films of (Ti,Fe)N x have been produced on silicon wafers with a wide range of compositions and mechanical properties to investigate correlations between the mechanical properties measured by indentation and crack resistance in the highly loaded sliding contact in a nano-Scratch test. The nano-Scratch test data on the thin films using a well-worn Berkovich indenter with ~ 1 μm end radius were supported by high resolution scanning electron microscopic (SEM) imaging and analytical stress modelling. The results show that mechanical properties of the coating, its thickness and the substrate properties all influence the deformation process. They affect the critical loads required, the type of failures observed and their location relative to the moving probe. The differences in coating mechanical properties affect how the interface is weakened (i.e. by initial substrate or coating yielding or both) and determine the deformation failure mechanism. The load dependence of the friction coefficient provides details of the sliding contact zone and the location of failure relative to the sliding probe. Improved performance was achieved at intermediate hardness and H 3 / E 2 in the nano-Scratch tests on thin films. The friction and modelling results strongly suggest that failure at low load on the hardest coatings is due to a combination of high tensile stress at the rear of the contact zone and substrate yield. Designing thin films for protective coatings with in-built dissipative structures (such as soft and low elastic modulus inclusions) and mechanisms to combat stress may be a more successful route to optimise their toughness in highly loaded sliding conditions than aiming to minimise plasticity by increasing their hardness.
L Llanes - One of the best experts on this subject based on the ideXlab platform.
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indentation and Scratch Testing of a wc 6 wtco cemented carbide corrosion effects on load bearing capability and induced damage
Ceramics International, 2020Co-Authors: Y F Zheng, Gemma Fargas, Olivier Lavigne, L LlanesAbstract:Abstract In this work, corrosion effects on the indentation and Scratch response of a WC-6%Co hardmetal are investigated. Experimental variables include relative long corrosion times as well as indentation and Scratch Testing conditions yielding damage scenarios whose depths are similar to length scale of the degraded surface layers. It is found that load-bearing capability and crack extension resistance of the cemented carbide grade studied are significantly reduced after exposure to corrosive media. This is related to relevant changes within the microstructural assemblage of the material, from an effective bulk ceramic-metal composite into a porous layer consisting of a binderless carbide network on top of a pristine-like hardmetal substrate. However, such lessening effects are found to be dependent on the ratio between indentation and/or Scratch depth and thickness of the corroded layer. Hence, relative changes decrease as corrosion time increases, and no differences are discerned after seven days of immersion. Similar pronounced corrosion influence is evidenced in surface and subsurface damage scenario resulting after indentation and Scratch tests. In this regard, a transition from well-defined cracking systems into a scenario consisting of multiple, branched and less shallow fissures is evidenced when comparing pristine and corroded specimens respectively. The experimental fact that referred cracking features for corroded specimens are confined within the porous-like degraded layers points out that it is the result of small length-scale interaction between cracks and the cavities within the binderless WC skeleton, left after the metallic binder has been leached away.