Seawater carbonate chemistry and biological processes of oysters Crassostrea virginica during experiments, 2010

Estuarine organisms are exposed to periodic strong fluctuations in seawater pH driven by biological carbon dioxide (CO2) production, which may in the future be further exacerbated by the ocean acidification associated with the global rise in CO2. Calcium carbonate-producing marine species such as mollusks are expected to be vulnerable to acidification of estuarine waters, since elevated CO2 concentration and lower pH lead to a decrease in the degree of saturation of water with respect to calcium carbonate, potentially affecting biomineralization. Our study demonstrates that the increase in CO2 partial pressure (pCO2) in seawater and associated decrease in pH within the environmentally relevant range for estuaries have negative effects on physiology, rates of shell deposition and mechanical properties of the shells of eastern oysters Crassostrea virginica (Gmelin). High CO2 levels (pH ~7.5, pCO2 ~3500 µatm) caused significant increases in juvenile mortality rates and inhibited both shell and soft-body growth compared to the control conditions (pH ~8.2, pCO2 ~380 µatm). Furthermore, elevated CO2 concentrations resulted in higher standard metabolic rates in oyster juveniles, likely due to the higher energy cost of homeostasis. The high CO2 conditions also led to changes in the ultrastructure and mechanical properties of shells, including increased thickness of the calcite laths within the hypostracum and reduced hardness and fracture toughness of the shells, indicating that elevated CO2 levels have negative effects on the biomineralization process. These data strongly suggest that the rise in CO2 can impact physiology and biomineralization in marine calcifiers such as eastern oysters, threatening their survival and potentially leading to profound ecological and economic impacts in estuarine ecosystems.

Ground-penetrating radar (GPR) point measurements of ice thickness in Austria

Glacier thickness is an important factor in the course of glacier retreat in a warming climate. Thiese study data presents the results (point data) of GPR surveys on 66 Austrian mountain glaciers carried out between 1995 and 2014. The glacier areas range from 0.001 to 18.4 km**2, and their ice thickness has been surveyed with an average density of 36 points/km**2 . The glacier areas and surface elevations refer to the second Austrian glacier inventory (mapped between 1996 and 2002). According to the glacier state recorded in the second glacier inventory, the 64 glaciers cover an area of 223.3±3.6 km**3. Maps of glacier thickness have been calculated by Fischer and Kuhn (2013) with a mean thickness of 50±3 m and contain an glacier volume of 11.9±1.1 km**3. The mean maximum ice thickness is 119±5 m. The ice thickness measurements have been carried out with the transmitter of Narod and Clarke (1994) combined with restively loaded dipole antennas (Wu and King, 1965; Rose and Vickers, 1974) at central wavelengths of 6.5 (30 m antenna length) and 4.0 MHz (50 m antenna length). The signal was recorded trace by trace with an oscilloscope. 168 m/µs as used by Haeberli et al. (1982), Bauder (2001), and Narod and Clarke (1994), the signal velocity in air is assumed to be 300 m/µs. Details on the method can be are found in Fischer and Kuhn (2013), as well as Span et al. (2005) and Fischer et al. (2007).

Nanoindentation of Bridgman YBCO samples

In this study, the mechanical properties of YBa2Cu3O7−x, obtained by the Bridgman technique, were examined using a Berkovich tip indenter on the basal plane (0 0 1). Intrinsic hardness was measured by nanoindentation tests and corrected using the Nix and Gao model for this material. Furthermore, Vickers hardness tests were performed, in order to determine the possible size effect on these measurements. The results showed an underestimation of the hardness value when the tests were performed with large loads. Moreover, the elastic modulus of the Bridgman samples was 128 ± 5 GPa. Different residual imprints were visualised by atomic force microscopy and a focused ion beam, in order to observe superficial and internal fracturing. Mechanical properties presented a considerable reduction at the interface. This effect could be attributed to internal stress generated during the texturing process. In order to corroborate this hypothesis, an observation using transmission electron microscopy was performed.

Mapping of mechanical properties of cement paste microstructures

The presented study is related to the EU 7 th Framework Programme CODICE (COmputationally Driven design of Innovative CEment-based materials). The main aim of the project is the development of a multi-scale model for the computer based simulation of mechanical and durability performance of cementitious materials. This paper reports results of micro/nano scale characterisation and mechanical property mapping of cementitious skeletons formed by the cement hydration at different ages. Using the statistical nanoindentation and micro-mechanical property mapping technique, intrinsic properties of different hydrate phases, and also the possible interaction (or overlapping) of different phases (e.g. calcium-silcate-hydrates) has been studied. Results of the mapping and statistical indentation testing appear to suggest the possible existence of more hydrate phases than the commonly reported LD and HD C-S-H and CH phases

Bond modelling of prestressed concrete during the prestressing force release

This paper presents an analytical model for simulating the bond between steel and concrete, in precast prestressed concrete elements, during the prestressing force release. The model establishes a relationship between bond stress, steel and concrete stress and slip in such concrete structures. This relationship allows us to evaluate the bond stress in the transmission zone, where bond stress is not constant, along the whole prestressing force release process. The model is validated with the results of a series of tests, considering different steel indentation depths and concrete covers and is extended to evaluate the transmission length. This capability has been checked by comparing the transmission length predicted by the model and one measured experimentally in two series of tests.

Determination of the mechanical properties of amorphous materials through instrumented nanoindentation

A novel methodology based on instrumented indentation is developed to determine the mechanical properties of amorphous materials which present cohesive-frictional behaviour. The approach is based on the concept of a universal hardness equation, which results from the assumption of a characteristic indentation pressure proportional to the hardness. The actual universal hardness equation is obtained from a detailed finite element analysis of the process of sharp indentation for a very wide range of material properties, and the inverse problem (i.e. how to extract the elastic modulus, the compressive yield strength and the friction angle) from instrumented indentation is solved. The applicability and limitations of the novel approach are highlighted. Finally, the model is validated against experimental data in metallic and ceramic glasses as well as polymers, covering a wide range of amorphous materials in terms of elastic modulus, yield strength and friction angle.

Flow and fracture behaviour of FV535 steel at different triaxialities, strain rates and temperatures

The new generation jet engines operate at highly demanding working conditions. Such conditions need very precise design which implies an exhaustive study of the engine materials and behaviour in their extreme working conditions. With this purpose, this work intends to describe a numerically-based calibration of the widely-used Johnson–Cook fracture model, as well as its validation through high temperature ballistic impact tests. To do so, a widely-used turbine casing material is studied. This material is the Firth Vickers 535 martensitic stainless steel. Quasi-static tensile tests at various temperatures in a universal testing machine, as well as dynamic tests in a Split Hopkinson Pressure Bar, are carried out at different triaxialities. Using ABAQUS/Standard and LS-DYNA numerical codes, experimental data are matched. This method allows the researcher to obtain critical data of equivalent plastic strain and triaxility, which allows for more precise calibration of the Johnson–Cook fracture model. Such enhancement allows study of the fracture behaviour of the material across its usage temperature range.

Study of bond stress-slip relationship and radial dilation in prestressed concrete

This paper presents two test procedures for evaluating the bond stress–slip and the slip–radial dilation relationships when the prestressing force is transmitted by releasing the steel (wire or strand) in precast prestressed elements. The bond stress–slip relationship is obtained with short length specimens, to guarantee uniform bond stress, for three depths of the wire indentation (shallow, medium and deep). An analytical model for bond stress–slip relationship is proposed and compared with the experimental results. The model is also compared with the experimental results of other researchers. Since numerical models for studying bond-splitting problems in prestressed concrete require experimental data about dilatancy angle (radial dilation), a test procedure is proposed to evaluate these parameters. The obtained values of the radial dilation are compared with the prior estimated by numerical modelling and good agreement is reached

Comportamiento mecánico de la aleación W+1%Y2O3 en función de la atmósfera y la temperatura

Mediante ensayos de flexión en tres puntos se compara y evalúa el comportamiento mecánico de la aleación W- 1wt%Y2O3 con el W puro fabricados ambos mediante HIP. Se ha obtenido la tenacidad de fractura, la resistencia a flexión y el límite elástico en atmósfera oxidante y de vacío en un intervalo de temperaturas comprendido entre -196 ºC, ensayos de inmersión en nitrógeno líquido, y 1200 ºC. Previamente, se ha medido la densidad, la dureza mediante ensayos Vickers y el módulo de elasticidad dinámico de los materiales. Además, la dureza y el módulo de elasticidad se han comparado con los obtenidos mediante ensayos instrumentados de nanoindentación. Finalmente se ha realizado un pequeño estudio de las superficies de fractura de las muestras ensayadas mediante microscopía electrónica de barrido para poder relacionar el modo de rotura de los materiales y las propiedades mecánicas macroscópicas con los micromecanismos de fallo involucrados en función de la temperatura.

Microestructura y propiedades mecánicas del material masivo superconductor YBCO a 300 Y 77 K.

En este trabajo se realiza una caracterización mecánica y microestructural del material masivo superconductor YBCO. El material ha sido procesado mediante dos técnicas distintas, Top-Seeding Melt Growth (TSMG) y Bridgman, y este estudio profundiza en el efecto de la microestructura, el método de procesado y la temperatura de ensayo en el comportamiento mecánico de material. Con el fin de conseguir un amplio conocimiento de sus propiedades mecánicas se han realizado ensayos de resistencia a flexión, tenacidad de fractura y dureza Vickers a 300 y 77 K. Asimismo, se llevaron a cabo ensayos de nanoindentación y el tamaño crítico del defecto semielíptico. Los resultados obtenidos muestran que el comportamiento mecánico de los dos materiales está controlado por defectos y grietas, introducidas durante el procesado. También se ha encontrado un buen acuerdo entre el tamaño del defecto critico detectado experimentalmente con los valores obtenidos mediante de análisis de mecánica de fractura.

Laser shock peening without absorbent coating (LSPwC) effect on 3D surface topography and mechanical properties of 6082-T651 Al alloy

The influence of nanosecond laser pulses applied by laser shock peening without absorbent coating (LSPwC) with a Q-switched Nd:YAG laser operating at a wavelength of λ = 1064 nm on 6082-T651 Al alloy has been investigated. The first portion of the present study assesses laser shock peening effect at two pulse densities on three-dimensional (3D) surface topography characteristics. In the second part of the study, the peening effect on surface texture orientation and micro-structure modification, i.e. the effect of surface craters due to plasma and shock waves, were investigated in both longitudinal (L) and transverse (T) directions of the laser-beam movement. In the final portion of the study, the changes of mechanical properties were evaluated with a residual stress profile and Vickers micro-hardness through depth variation in the near surface layer, whereas factorial design with a response surface methodology (RSM) was applied. The surface topographic and micro-structural effect of laser shock peening were characterised with optical microscopy, InfiniteFocus® microscopy and scanning electron microscopy (SEM). Residual stress evaluation based on a hole-drilling integral method confirmed higher compression at the near surface layer (33 μm) in the transverse direction (σmin) of laser-beam movement, i.e. − 407 ± 81 MPa and − 346 ± 124 MPa, after 900 and 2500 pulses/cm2, respectively. Moreover, RSM analysis of micro-hardness through depth distribution confirmed an increase at both pulse densities, whereas LSPwC-generated shock waves showed the impact effect of up to 800 μm below the surface. Furthermore, ANOVA results confirmed the insignificant influence of LSPwC treatment direction on micro-hardness distribution indicating essentially homogeneous conditions, in both L and T directions.

A novel methodology to determine the mechanical properties of amorphous materials through instrumented nanoindentation

A novel methodology based on instrumented indentation was developed to characterize the mechanical properties of amorphous materials. The approach is based on the concept of a universal postulate that assumes the existence of a characteristic indentation pressure proportional to the hardness. This hypothesis was numerically validated. This method overcomes the limitation of the conventional indentation models (pile-up effects and pressure sensitivity materials).

Cohesive-frictional modelling of bond and splitting action of prestressing wire

This work shows a numerical procedure for bond between indented wires and concrete, and the coupled splitting of the concrete. The bond model is an interface, non-associative, plasticity model. It is coupled with a cohesive fracture model for concrete to take into account the splitting of such concrete. The radial component of the prestressing force, increased by Poisson’s effect, may split the surrounding concrete, decreasing the wire confinement and diminishing the bonding. The combined action of the bond and the splitting is studied with the proposed model. The results of the numerical model are compared with the results of a series of tests, such as those which showed splitting induced by the bond between wire and concrete. Tests with different steel indentation depths were performed. The numerical procedure accurately reproduces the experimental records and improves knowledge of this complex process.

An analytical model for simulating the bond of prestressed concrete during the prestressed force release

A bond analytical model is proposed in this paper. The model is capable of reproducing the bond stress developed between the steel and concrete, in precast prestressed elements, during the entire process of prestressing force release. The bond stress developed in the transmission zone, where the bond stress is not constant, is also obtained. The steel and concrete stresses as well as the slip between both materials can be also estimated by means of the relation established in the model between these parameters and the bond stress. The model is validated with the results of a series of tests, considering different steel indentation depths and concrete covers and it is extended to evaluate the transmission length. This has been checked by comparing the transmission length predicted by the model and one measured experimentally in two series of tests.