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Instrumented nanoindentation is widely used to extract the material properties from the measured force-displacement curves. In this work, the uniqueness/non-uniqueness of the intrinsic viscoelastic properties of materials determined by nanoindentation during load-unload tests is investigated. A four-parameter viscoelastic law with constant Poisson's ratio is used to model the mechanical behavior of a polymer material and a 2D-axisymmetric Finite Element Model (FEM) is used to simulate the nanoindentation test. Firstly, a nanoindentation experimental triangular load-unload test is performed on a bulk sample of polypropylene (PP) with a Berkovich indenter tip at a depth rate of 1000 nm/min. The values of the four material parameters are estimated by the Finite Element Model Updating (FEMU). The numerical results can accurately fit the experimental data. However, several quasi-solutions are shown to exist. These load-unload data allow to identify only three viscoelastic parameters if the Poisson's ratio is known. Secondly, the effect of nanoindentation depth rate, loading type (triangular, trapezoidal, exponential, sinusoidal) and apex angle is numerically investigated using an identifiability index based on the conditioning of the inverse problem. We show a correlation between the identifiability index and the energy dissipated by the material during the tests. The extraction of all material parameters remains impossible using a single test. Finally, some combinations of several nanoindentation triangular tests and indenter tip angles are also investigated. We show that a dual nanoindentation technique (cube corner and Berkovich tips) with triangular load-unload tests is an interesting combination to reliably extract all the viscoelastic parameters, provided that plasticity is taken into account. This result illustrates the interest of using this numerical identifiability index to design nanoindentation experiments to ensure the robustness of the intrinsic viscoelastic properties extraction. [ABSTRACT FROM AUTHOR]

With the aim of providing better control of shooting experiments performed with replicas of prehistoric projectiles, we have conducted an instrumental archaeology study on the efficiency of prehistoric projectile points by placing emphasis on their adhesion and ballistic characteristics. In order to avoid any reproducibility problems, hafting adhesives were made with controlled mixtures of commercial rosin (also called 'colophany') and beeswax added as a plasticizer. An original experimental device has been developed to instrument a bow, allowing the control of both the trajectories and the velocities of the different shoots. In the course of an experimental programme on Sauveterrian microliths from the Mesolithic period of the South of France, the experimental system was applied to composite replica projectile tips of Mesolithic hunters. Arrows being shot at transparent targets were filmed in order to evaluate the penetration length and residual damage. Interestingly, this study reveals that the properties of the mixture are highly dependent on the velocity of the arrows. It was shown that-contrary to previous experiments that usually used a mixture in which rosin predominates- the most efficient adhesive is made of 70 wt% beeswax with only 30 wt% rosin. This result is of great importance for improving further shooting experiments and overcoming the problems frequently mentioned due to the loss of the flint armatures before they reach the animal target, or at least before penetration. When using this appropriate mixture, the lateral armatures are resistant to most of the shots. Experiments performed on real boars' flesh have also shown that the presence of lateral microliths allows the laceration inflicted on the target to be enlarged. Finally, a critical parameter has been identified, which is the location on the arrow of the microlithic element. [ABSTRACT FROM AUTHOR]

Fundamental deformation mechanisms of FCC materials under indentation have been probed at the grain scale. Experimental tests have been conducted on large-grained annealed and cold-worked polycrystalline nickel samples with a Berkovich indenter. Indentation axes have been chosen to be close to the three main crystallographic directions [001], [101] and [111]. Pile-ups and slip traces have been revealed around the residual imprints by analysing topographic measurements obtained by atomic force microscopy. It is shown that the indenter orientation in each indentation plane drives pile-ups and slip traces which in turn contain precious information about the crystallographic orientation and the hardening state of the studied grain. Imprint topographies after pile-up formation therefore carry information that one can exploit to assess some intrinsic material properties at the grain scale. A 3D finite element modelling of the nanoindentation test at the grain scale has been developed, making use of crystal plasticity constitutive laws. Six different virtual materials having the same macroscopic behaviour have been built. The simulation results show a good agreement with experimental tests and also a great pile-up sensitivity to interaction matrix components. These results pave the way to the interaction matrix identification using an inverse finite element method. [ABSTRACT FROM AUTHOR]

Highlights: [•] A bio-sourced adhesive made of 75%w/w rosin and 25%w/w beeswax was studied. [•] Tack and mechanical properties were highlighted by experimental nanoindentations. [•] They depend strongly of the applied strain rate and are dictated by a size effect. [•] A modelisation of these phenomena is proposed. [•] The experimental measurements and the numerical results are in good agreement. [Copyright &y& Elsevier]

Abstract: Austenitic and martensitic TiNi shape memory alloys were studied by means of cyclic instrumented indentation with the purpose of documenting the phase transformation. Recovery indexes were determined from the energy absorbed during loading, unloading and reloading and their relation with the microstructure and shape memory properties established. Significant changes on the load–displacement curves, associated to the transformation phenomenon, were exhibited by both materials. Under spherical cyclic nanoindentation, a classic pseudoelastic behavior was observed in the austenitic alloy, which was characterized by high recovery indexes and constitutes the first experimental evidence of this property under such testing conditions. On the other hand, the martensitic alloy showed lower recovery indexes, as a consequence of a faster stabilization process of the martensite plates. [Copyright &y& Elsevier]

This work deals with the indentation analysis of nanocolumnar thin films and the difficulties encountered to deduce relevant mechanical parameters by this methodology. SiO 2 thin films prepared by physical vapour oblique angle deposition with different nanocolumnar microstructures have been subjected to indentation analysis. Despite the fact that the films had been made of the same material, deposited on the same substrate and had similar thickness, their indentation responses were different and depended on their particular microstructure. It has been also reali s ed that the measured hardness and elastic modulus variation with the indentation depth were length scale dependent and that there is not a unique analytical thin-film nanoindentation model to extract the mechanical properties from the experimental nanoindentation curves. To overcome these limitations a numerical finite element model (FEM) of the nanocolumnar coatings has been built to figure out the contributions of the different physical phenomena intervening in the indentation process. This FEM simulation relies on a description of the elasto-plastic microstructural units of the coatings and the contact friction interactions between them. Based on this simulation a parametrical representation, incorporating two length scales and the contributions of densification and/or the buckling of nanocolumnar units, has been developed to account for the evolution of the apparent elastic modulus deduced from numerical indentation tests. A Hall-Petch modification of this description considering two length scales instead of the common approximation considering a single length scale has rendered the best agreement with the elastic values determined experimentally. Although, at the present stage, the particular microstructure of the films can not be deduced from the evolution of their elastic moduli with the indentation depth, the obtained results and their interpretation constitute a first though essential step for the elaboration of an inverse analysis methodology capable of correlating microstructure and elastic response of nanocolumnar coatings. • The indentation response of multi-layered PVOAD columnar coatings greatly depends on their microstructure. • Buckling but also densification drive the evolution of indentation elastic modulus and hardness with indentation depth. • FEM of a columnar structure under indentation allow s to reproduce the experimental response of multi-layered PVOAD coatings. • Size dependent model allows to extract length scale parameters from elastic response of PVOAD coatings. [ABSTRACT FROM AUTHOR]

Abstract: The ageing of zirconia under hydrothermal conditions is a key issue in many applications, as the properties and thickness of the degraded layer influence the reliability of the material. This paper presents a study by nanoindentation of the hydrothermal degradation of tetragonal zirconia polycrystals doped with yttria with a tetragonal grain size of 0.3μm and of the same material after heat-treatment at high temperature (1650°C) in order to develop a duplex cubic-tetragonal microstructure with a large tetragonal grain size. Nanoindentation is used to evaluate the Young’s modulus and hardness of the degraded surfaces as a function of indenter penetration depth. The mechanisms of hydrothermal degradation are also studied. Using Raman spectroscopy, atomic force microscopy and focused ion beam (FIB) cross-sections, we show that hydrothermal degradation induces t–m phase transformation and microcracking under the surface. Microcracks in degraded zirconia, clearly observed in FIB cross-sections, are associated with the decrease in hardness and Young’s modulus of the degraded surface. Nanoindentation is used to detect and quantify the degradation of zirconia by calculating the decrease in hardness and Young’s modulus with penetration depth. Using a thin-film model, the depth of the degraded layer and its mechanical properties are also extracted. As expected, we demonstrate that duplex zirconia with a large tetragonal grain size is more sensitive to hydrothermal degradation than monophasic small-grain tetragonal zirconia. [Copyright &y& Elsevier]

Electron beam-physical vapour deposited (EB-PVD) yttria-stabilized zirconia (YSZ) thermal barrier coatings have been investigated by nanoindentation. It is shown that the mechanical properties, and particularly the Young's modulus, of these coatings are closely related to their columnar microstructure. The transition from intracolumnar to intercolumnar deformation is characterized by a difference between the mechanical properties of the bulk YSZ and those of the coatings. The use of different indenter shape showed that the contact area was the parameter characteristic of this scale dependence. Deformation mechanisms studied by AFM have shown a good correlation with the evolution of the mechanical properties during the deformation. [ABSTRACT FROM AUTHOR]

This study investigates the incipient plasticity during a nanoindentation test with a spherical indenter in magnesium oxide single crystals. The load–displacement curves show multiple pop-ins, interspaced by elastic deformation, and reveal the transition from an initial elastic deformation regime to a continuous elastoplastic one. Nanoindentations have been stopped after the first pop-in and the dislocation structures have been three-dimensionally characterized by AFM observations of the surface deformation and by nanoetching. The dislocation pattern shows two activated slip systems. The resolved shear stress has been calculated just before the pop-in, for all of the activated slip systems. The final positions of the dislocations generated during the first pop-in reveal that they were all nucleated at the point of maximum resolved shear stress. [ABSTRACT FROM AUTHOR]

Abstract: Incipient plasticity in magnesium oxide single crystals has been investigated by nanoindentation with a spherical indenter. For very low loads, the surface deformation can be limited to a single slip line, making modelling of the deformation easier. The recently developed nanoetching technique has been used to investigate the corresponding dislocation structure. Single pile-ups of a few dislocation half loops have been observed and fully characterised. A simple elastic model, based upon the calculation of the Peach Koehler force induced by the pile-ups and the spherical indenter stress field, has been used to determine the equilibrium positions of dislocations in these pile-ups. A comparison between the experimental and calculated structures has led to the determination of the lattice friction stress for edge and screw dislocations in magnesium oxide single crystals. This stress is found to be 65MPa for edge dislocations and 86MPa for screw dislocations. [Copyright &y& Elsevier]

This letter is based on recent progress in the observation of dislocation distributions around nanoindentations by chemical etching. This so-called nanoetching technique is used to determine the dislocation mechanisms associated with the pop-in phenomenon in MgO and LiF. Successive stages of highly controlled chemomechanical polishing have revealed that these dislocations are half-loops lying in the classical slip systems of MgO or LiF. However, they do not extend on the surface in the classical rosette-arms pattern but stay concentrated around the imprint. A mechanism of dislocation interactions, enhanced by the fact that the dislocations are suddenly nucleated in a small volume, is proposed to explain this specific distribution. [ABSTRACT FROM AUTHOR]

In this paper, it is shown that combining AFM, chemical etching and controlled polishing, progressively removing thin layers of material, allows a three-dimensional reconstruction of the volume distribution of dislocations about and under nanoindentation imprints. To illustrate the method, results obtained in MgO, a material known for its simple plasticity, have been selected. It is shown, comparing surface deformation and etching pattern, that the entire dislocation distribution associated with small indents can be analysed in terms of individual dislocations, leading to a better understanding of the elementary mechanisms of plasticity associated with the early stages of indents formation in crystalline material. [Copyright &y& Elsevier]

We report a case of cerebral venous sinus thrombosis, bilateral adrenal hemorrhage, and thrombocytopenia in a 70-year-old man found dead. He had previously received the ChAdOx1 nCoV-19 vaccine (Vaxzevria®, AstraZeneca) 18 days before, and had since developed unspecific and undiagnosed characteristics of what proved to be a rare case of vaccine-associated thrombocytopenia with thrombosis syndrome (TTS). He was found dead 1 week after the beginning of symptoms (day 25 post-vaccine). Autopsy yielded venous hemorrhagic infarction with the presence of thrombi within dural venous sinuses, and extensive hemorrhagic necrosis of the central part of the adrenal glands. Antibodies against platelet factor 4 (PF4) were strongly positive in postmortem fluids, as measured with an enzyme-linked immunosorbent assay (ELISA). This difficult diagnosis is usually made during the patient's lifetime. After eliminating differential diagnoses, we concluded on a fatal case of vaccine-induced immune TTS with positive anti-PF4 antibodies in cadaveric blood, 3 weeks after ChAdOx1 nCoV-19 vaccination. Specific search for anti-PF4 antibodies in cadaveric blood appears therefore paramount to assess postmortem cases of TTS associated with anti-COVID vaccines. [ABSTRACT FROM AUTHOR]

Abstract: There is an increasing usage of PVD-coated hardmetals in applications where contact loads of cyclic nature between curved surfaces are common, e.g. cold forming tools and machine components. Thus, knowledge of both the mechanical response and the damage mechanisms involved during contact fatigue of these systems is required if they want to be used effectively. In this investigation this is approached by implementing spherical indentation testing techniques. Experimental work includes the evaluation of monotonic indentation stress–strain curves, cyclic indentation stress–number of cycles diagrams and subsurface damage evolution. Emphasis is placed on determining the indentation stress affiliated to the emergence of circular cracks at the coating, event here proposed and proved to be the critical failure stage for the columnar TiN film and the low cobalt/fine grained WC–Co hardmetal substrate under study. It is found that the coated system investigated is susceptible to contact fatigue. However, the corresponding fatigue sensitivity, assessed on the basis of an indentation stress analysis of the relative contact response under monotonic and cyclic conditions, is rather low. Such a result is rationalized by considering the ceramic nature as well as the high residual compressive stress state of the hard coating, the system component where the damage defined as critical takes place. [Copyright &y& Elsevier]

The instrumented indentation response of polycrystalline alumina and alumina-based ceramic multilayers with well-known residual stresses is investigated. Young's modulus and hardness were evaluated as a function of penetration depth with Berkovich and spherical indenters by continuous stiffness measurements. A size effect was observed due to the length scale of the microstructure. Values of hardness and Young's modulus were in good agreement with previous works. No significant differences in the P – h curves were observed for materials with and without residual stress, making it difficult to employ the various methodologies in the literature for estimation of residual stress or crack length evaluation. Crack length had, therefore, to be measured by direct observation. Thus, cube corner indentations did not produce well-developed radial cracks but chipping of the material, whereas indentations with Berkovich indenters produced radial cracks suitable for apparent fracture toughness estimation and, consequently, residual stress. [ABSTRACT FROM AUTHOR]

Highlights • Young's modulus and hardness of Co-Mo/TiO 2 nano-composite coatings. • Tribological properties and scratch resistance of Co-Mo/TiO 2 nano-composite coatings. • Corrosion behaviour of wear and scratch tracks in Ringer's solution at 25 °C. Abstract The micro-mechanical (Young's modulus and hardness) and tribological properties, as well as the scratch resistance of Co-Mo/TiO 2 nano-composite coatings were investigated. The coating was found to be harder and stiffer than the substrate (pure cobalt). Low residual stresses were also derived from Stoney's equation (type I stress). The corrosion behaviour after tribological and scratch tests was studied in Ringer's solution. Dry sliding of the coating against an alumina ball at the load of 1 N or 2 N over the same distance had nearly no influence on the anodic branch of the polarisation curves. By contrast, the current density in the cathodic branch (oxygen reduction reaction, ORR) increased significantly as the normal load of the sliding contact increased. Severe damage induced during scratch tests (with loads from 0 to 30 N) caused an increase in the current density, both in the anodic and cathodic branches. This increase was more pronounced in the cathodic domain (ORR). [ABSTRACT FROM AUTHOR]

The influence of internal casting defects on the fatigue properties of A357-T6 alloy has been studied. Specimens with artificial casting defects ( ∅ eq ≈ 2 mm) placed at the surface or in the bulk have been produced. A reference S–N curve has been obtained for the material containing only natural defects (microshrinkages). Cycling has been performed in air or under vacuum. In spite of their relatively large size, the internal artificial defects do not induce a reduction of the fatigue life compared to the reference material. When the artificial defects are placed at the surface, a decrease is observed when the specimens are cycled in air but it disappears again when cycling is performed in vacuum conditions. The detrimental effect of the casting defects is discussed in relation to their ability to initiate a crack growing in vacuum or not. It can be concluded that the increased fatigue lives observed for internal defects are the consequence of slower crack initiation and propagation mechanism occurring in vacuum. [ABSTRACT FROM AUTHOR]

Bone marrow (BM) analysis is of forensic interest for postmortem toxicological investigations where blood samples are unavailable or unusable. Due to the lack of studies, it remains difficult to interpret concentrations of xenobiotics measured in this matrix. Based on a statistical approach published previously to interpret meprobamate concentrations in bile and vitreous humor, we propose here a diagnostic test for interpretation of BM meprobamate concentrations from analysis of 99 sets of autopsy data. The mean age was 48 years (range 18-80 years, one unknown) for males and 50 years (range 19-80 years, one unknown) for females, with a male/female ratio at 0.768. A BM concentration threshold of 11.3 μg/g was found to be statistically equivalent to that of a blood meprobamate concentration threshold of 50 μg/ml in distinguishing overdose from therapeutic use. The intrinsic qualities of this diagnostic test were good with sensitivity of 0.82 and specificity of 0.92. Compared to previous tests published with the same objective on vitreous humor and bile, this study shows that BM is a useful alternative matrix to reveal meprobamate overdose when blood, vitreous humor, and bile are not available or unusable. [ABSTRACT FROM AUTHOR]

Abstract: Two cases of scavenging postmortem freshwater shrimps (Gammarus pulex) are presented. We report the two first illustrated observations of cutaneous postmortem injuries inflicted by a G. pulex population, a small freshwater crustacean, on two non putrefied drowning victims, and we describe their particular histological features and their potential in forensic investigations. [Copyright &y& Elsevier]

Abstract: Pharmacokinetic studies and postmortem toxicological investigations require a validated analytical technique to quantify drugs on a large number of matrices. Three-step liquid/liquid extraction with online derivatization (silylation) ahead of analysis by gas chromatography–tandem mass spectrometry was developed and validated on rabbit specimens in order to quantify citalopram and 4 benzodiazepines (diazepam, nordazepam, oxazepam and temazepam) in 11 biological matrices (blood, urine, bile, vitreous humor, liver, kidney, skeletal muscle, brain, adipose tissue, bone marrow (BM) and lung). Since the 11 biological matrices came from the same animal species, full validation was performed on 1 matrix, bone marrow (considered the most complex), while the other 10 underwent partial validation. Due to non-negligible matrix effects, calibration curves were performed on each matrix. Within-day and between-day precision (less than 12.0% and 12.6%, respectively) and accuracy (from 88.9% to 106.4%) were acceptable on BM at both low and high concentrations. Assessment on the other matrices confirmed accuracy and within-day precision (less than 12%, and generally between 85.1% and 114.5%, respectively). The lower limit of quantification of the method was 1ng/g for nordazepam, 5ng/g for citalopram and 10ng/g for oxazepam, diazepam and temazepam. The combination of 3-step extraction and MS/MS detection provided good selectivity in all matrices, including the most lipid-rich. Application to real-case samples showed that the method was sensitive enough to describe distribution patterns in an animal experiment, and specific enough to detect molecules in highly putrefied samples from human postmortem cases. [Copyright &y& Elsevier]

Abstract: Bone marrow (BM) analysis is of forensic interest in postmortem toxicological investigation in case of limited, unavailable or unusable blood samples. However, it remains difficult to determine whether a drug BM concentration is therapeutic or represents overdose, due to the lack of studies on this alternative matrix. Given the variations in BM composition in the body, sample location was suggested to be a relevant factor in assessing BM concentration. The aim of the present study was to compare postmortem caffeine concentrations in various BM sample locations and secondly to consider the correlation between BM and blood concentrations. Six BM samples (right and left side: proximal and medial femur and 5th rib) and a blood sample were collected from 21 forensic autopsies. Gas chromatography coupled to tandem mass spectrometry was performed. Blood caffeine concentrations ranged from 60 to 7591ng/mL. Femoral and rib BM concentrations ranged from 51 to 6171ng/g and 66 to 7280ng/g, respectively. Blood concentrations were always higher than BM concentrations. As a good correlation was demonstrated between blood and rib BM and between blood and the average of the four femoral BM concentrations, blood caffeine concentrations could be correctly extrapolated from BM concentrations. BM caffeine concentration was found to depend on sample location. Rib BM caffeine concentrations appeared to be systematically greater than averaged femur values and concentrations were much more variable between the 4 femur BM samples than between the 2 ribs. From a practical point of view, for caffeine analysis, rib BM appeared more relevant than femoral BM, which requires multisampling to overcome the concentration variability problem. [Copyright &y& Elsevier]