Nano-indentation instrumented tests are carried out at shallow depths on PAN-based and MPP-based carbon fibres. Indentation moduli are obtained by performing the tests at ten different measured ...orientations with respect to the fibre axis. They are used to identify the elastic constants of the fibres, assuming a transversely isotropic behaviour, by minimising a cost function between measured and estimated values. Inconstancies between the identified in-plane shear and transverse moduli and reported literature values are pointed out, and some drawbacks of the nano-indentation method are highlighted. An improved method taking into account the buckling mechanisms of crystallites at stake during the indentation process, and visible in the hysteretic behaviour of force-penetration nanoindentation curves, is proposed. It allows to identify values of elastic constants that are in accordance with literature values. These elastic properties of carbon fibres are in turn used to estimate the elastic properties of epoxy matrix composites containing these fibres. Very good agreement is found with experimentally available values of unidirectional ply properties. An excellent correlation between experiments and Finite Element Analyses of the indentation response of carbon fibres is eventually found.
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The mechanical response of amorphous silica (or silica glass) under hydrostatic compression for very high pressures up to 25GPa is modelled via an elastic–plastic constitutive equation (continuum ...mechanics framework). The material parameters appearing in the theory have been estimated from the ex situ experimental data of Rouxel et al. Rouxel T, Ji H, Guin JP, Augereau F, Rufflé B. J Appl Phys 2010;107(9):094903. The model is shown to capture the major features of the pressure–volume response changes from the in situ experimental work of Sato and Funamori Sato T, Funamori N. Phys Rev Lett 2008;101:255502 and Wakabayashi et al. Wakabayashi D, Funamori N, Sato T, Taniguchi T. Phys Rev B 2011;84(14):144103. In particular, the saturation of densification, the increase in elasticity parameters (bulk, shear and Young’s moduli) and Poisson’s ratio are found to be key parameters of the model.
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Borosilicate glasses are considered for the long-term confinement of high-level nuclear wastes. External irradiations with 1 MeV He+ ions and 7 MeV Au5+ ions were performed to simulate effects ...produced by alpha particles and by recoil nuclei in the simulated SON68 nuclear waste glass. To better understand the structural modifications, irradiations were also carried out on a 6-oxides borosilicate glass, a simplified version of the SON68 glass (ISG glass). The mechanical and macroscopic properties of the glasses were studied as function of the deposited electronic and nuclear energies. Alpha particles and gold ions induced a volume change up to −0.7% and −2.7%, respectively, depending on the glass composition. Nano-indentations tests were used to determine the mechanical properties of the irradiated glasses. A decrease of about −22% to −38% of the hardness and a decrease of the reduced Young's modulus by −8% were measured after irradiations. The evolution of the glass structure was studied by Raman spectroscopy, and also 11B and 27Al Nuclear Magnetic Resonance (MAS-NMR) on a 20 MeV Kr irradiated ISG glass powder. A decrease of the silica network connectivity after irradiation with alpha particles and gold ions is deduced from the structural changes observations. NMR spectra revealed a partial conversion of BO4 to BO3 units but also a formation of AlO5 and AlO6 species after irradiation with Kr ions. The relationships between the mechanical and structural changes are also discussed.
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•Mechanical and structural properties of two borosilicate glass compositions irradiated with alpha particles and heavy ions were investigated.•Both kinds of particles induced a decrease of the hardness, reduced Young's modulus and density.•Electronic and nuclear interactions are responsible for the changes observed.•The evolution of the mechanical properties under irradiation is linked to the changes occured in the borosilicate network.
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When subjected to constrained deformation loadings, such as during an indentation test, silica glass experiences complex deformation mechanisms including densification and volume-conservative shear ...plasticity. The densification mechanism may increase the density up to more than 21%. The question of the mechanical behaviour of an already fully densified glass sample naturally arises. This issue is one of the key points to address when one tries to propose a constitutive model of pristine silica glass. Indeed, during an indentation test, which is a popular test for this task, beneath the indenter tip, some regions might be fully densified. What is their behaviour, after saturation in densification and during loading, is therefore an issue to address. Moreover, this is a crucial point for exploring the transition from plasticity to cracking, which is of paramount importance and a long-term objective for predicting the lifetime of glass products subjected to contact loadings such as impact or scratching.
In this paper, a quantitative identification of fully densified silica mechanical constitutive behaviour is made by using instrumented indentation testing and finite element analyses. The use of such an indirect method to assess the mechanical behaviour of this material comes from its brittle behaviour in unconstrained deformation modes usually employed in metals plasticity. It is shown here that fully densified silica behaves as a von Mises material (rate-independent shear plasticity without strain-hardening) like some crystalline metals. The yield strength and yield strains are, at the contrary, much higher than for alloys: respectively 6.5 GPa and 6.1%. This mechanical modelling, as well as the plastic parameters values found, are in excellent agreement with very recent experimental and numerical simulations on silica glass and silicate glasses.
The high value of the yield strain is found to explain unusual indentation features such as a unusual long range residual piling-up while sinking-in is predicted during loading, as well as low values of the ratio hardness-to-yield strength.
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The region of permanent densification beneath a Berkovich indentation imprint in silica glass is investigated using a novel chemical dissolution technique. The use of the similitude regime in sharp ...indentation testing allows one to record reliable data with a good spatial resolution that makes it possible to deal with low loads (typically below 10 mN) and, more importantly, crack-free imprints. The densified zone dissolves more quickly than the non densified regions. The analysis of the results, along the vertical axis, indicates that the densification zone is rather homogeneous with a steep transition to the non densified zone. The size of the densification zone, with respect to the initial free surface, is estimated to be around two times the maximum penetration depth of the instrumented indentation test. These findings are compared with those obtained by numerical simulations using different constitutive equations from the literature. A very good concordance between Raman spectroscopy and chemical probe results is found for imprints made with no or few cracking events during indentation testing.
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The determination of the contact area is a key step in deriving mechanical properties such as hardness or an elastic modulus by instrumented indentation testing. Two families of procedures are ...dedicated to extracting this area: on the one hand, post-mortem measurements that require residual imprint imaging, and on the other hand, direct methods that only rely on the load vs. penetration depth curve. With the development of built-in scanning probe microscopy imaging capabilities such as atomic force microscopy and indentation tip scanning probe microscopy, last-generation indentation devices have made systematic residual imprint imaging much faster and more reliable. In this paper, a new post-mortem method is introduced and further compared to three existing classical direct methods by means of a numerical and experimental benchmark covering a large range of materials. It is shown that the new method systematically leads to lower error levels regardless of the type of material. The pros and cons of the new method vs. direct methods are also discussed, demonstrating its efficiency in easily extracting mechanical properties with enhanced confidence.
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As part of a recent study Li et al. (2018) 1 proposed as a proof of inhomogeneous shear flow at indentation site in oxide glasses the existence of both a nano pattern on the residual imprint as ...revealed by atomic force microscopy and numerous discrete events on the load displacement curve, called bursts. Both were reported to be loading rate dependent. Here, using the same experimental set up, we provide experimental evidence that discrete bursts existence and loading rate sensitivity can be attributed to the displacement sensor noise floor and to data sampling rate issues respectively. We also show the nano pattern present on the faces of the indentation imprint to be extremely repeatable, to not depend neither on glass composition nor on loading rate as it is the result of the stamping onto the glass surface of the indenter surface roughness generated by its machining process.
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Fused silica samples were subjected to laser induced shock loading. Laser flux was varied in order to obtain different amounts and characteristics of damage in the samples. Three dimensional damage ...and fracture maps of two identical samples impacted by high and low laser flux values were obtained using both optical microscopy and X-ray computed micro-tomography. Three prevalent fracture and damage patterns were identified. Peridynamic approach was used to simulate the laser impact conditions on the samples in order to explain the causes of the observed fracture and damage morphologies. A proprietary shock physics code, ESTHER, was used to calculate the transient kinetic energy imparted to the samples based on the experimental laser flux values. The kinetic energy values were then integrated over time and provided target values to match for the peridynamic impact conditions. The main fracture patterns were captured by peridynamic simulations with reasonable quantitative accuracy. Explanations for initiation and propagation of each of the fracture patterns were presented based on the peridynamic dynamic fracture simulations. Limitations of the computational approach and recommendations for future work is provided.
•X-ray micro-CT reveals 3-D interconnected fracture system in laser impacted silica.•Peridynamic approach helps identify initiation and propagation of dynamic fracture.•Laser impact damage away from the impact site propagates in spurts.•Lingering wave interactions near crack tips leads to fracture propagation.
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Amorphous chalcogenide films play a motivating role in the development of integrated planar optical circuits due to their potential functionality in near infrared (IR) and mid-IR spectral regions. ...More specifically, the photoluminescence of rare earth ions in amorphous chalcogenide films can be used in laser and amplifier devices in the IR spectral domain. The aim of the present investigation was to optimize the deposition conditions for the fabrication of undoped and Er3+ doped sulphide and selenide thin films with nominal composition Ga5Ge20Sb10S(Se)65 or Ga5Ge23Sb5S67 by pulsed laser deposition (PLD). The study of compositional, morphological and structural characteristics of the layers was realized by scanning electron microscopy-energy dispersive spectroscopy, atomic force microscopy and Raman spectroscopy analyses, respectively. Some optical properties (transmittance, index of refraction, optical band gap, etc.) of prepared chalcogenide films and optical losses were investigated as well. The clear identification of near-IR photoluminescence of Er3+ ions was obtained for both selenide and sulphide films. The decay of the 4I13/2 a' 4I15/2 transition at 1.54Akm in Er3+ doped Ga5Ge20Sb10S65 PLD sulphide films was studied to assess the effects of film thickness, rare earth concentration and multilayer PLD deposition on their spectroscopic properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The development of infrared sensing platform requires adapted materials. In this work, we used sputtered gold nanoparticles on a chalcogenide glass to demonstrate that these infrared materials can be ...used as substrate for surface enhanced infrared absorption (SEIRA) spectroscopy. The sputtering parameters were optimized to get the highest possible enhancement. To assess it, a self-assembled monolayer of 4-nitrothiophenol was used. These preliminary results are promising and pave the way for various configurations of waveguide for integrated optical components.
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