2nd International Workshop on Physics-Based Modelling of Material Properties and Experimental Observations with special focus on Fracture and Damage Mechanics: Book of Abstracts

This report covers the book of abstracts of the 2nd International Workshop on Physics Based Modelling of Material Properties and Experimental Observations, with special focus on Fracture and Damage Mechanics. The workshop is organized in the context of European Commission’s Enlargement and Integration Action, by the Joint Research Centre in collaboration with the TOBB University of Economics and Technology (TOBB ETU) on 15th-17th May 2013 in Antalya, Turkey. The abstracts of the keynote lectures and all the technical presentations are included in the book. This workshop will give an overview of different physics-based models for fracture and degradation of metallic materials and how they can be used for improved understanding and more reliable predictions. Models of interest include cohesive zones to simulate fracture processes, ductile-brittle transition for ferritic steels, ductile fracture mechanisms such as void growth or localized shear, fatigue crack initiation and short crack growth, environmental assisted cracking. Experimental studies that support such models and case studies that illustrate their use are also within the scope. The workshop is also an opportunity for scientists and engineers from EU Member States and target countries to discuss research activities that could be a basis for future collaborations.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen

Fundamentals of interface phenomena in advanced bulk nanoscale materials

The review is devoted to a study of interface phenomena influencing advanced properties of nanoscale materials processed by means of severe plastic deformation, high-energy ball milling and their combinations. Interface phenomena include processes of interface defect structure relaxation from a highly nonequilibrium state to an equilibrium condition, grain boundary phase transformations and enhanced grain boundary and triple junction diffusivity. On the basis of an experimental investigation, a theoretical description of the key interfacial phenomena controlling the functional properties of advanced bulk nanoscale materials has been conducted. An interface defect structure investigation has been performed by TEM, high-resolution x-ray diffraction, atomic simulation and modeling. The problem of a transition from highly non-equilibrium state to an equilibrium one, which seems to be responsible for low thermostability of nanoscale materials, was studied. Also enhanced grain boundary diffusivity is addressed. Structure recovery and dislocation emission from grain boundaries in nanocrystalline materials have been investigated by analytical methods and modeling

Features of change of V-4Ti-4Cr alloy hardness during microstructure evolution under severe plastic deformation

Features of changes of microhardness and nanohardness of V–4Ti–4Cr alloy at different stages of microstructure transformation during severe plastic deformations by torsion under pressure are presented. Microstructure features and mechanisms of its transformation affecting the hardness of studied alloy are discussed. Local temperature increase and activization of relaxation processes of nonequilibrium nanostructure states with high (hundreds of degrees/µm) elastic curvature of the crystal lattice are considered as main factors that define nonmonotonic character of changes in the microhardness at the stage of formation and evolution of the two-level structural states. In alloy under study at a value of true logarithmic deformation e ≥ 6.6 the formation of areas consisting of nanocrystals several nanometers in size with a high density of large-angle boundaries and elastic curvature of the crystal lattice hundreds of degrees/µm was found. Hardness of the material (Hnano ≈ E/16) differs little from its theoretical (limit) hardness

Field-control, phase-transitions, and life's emergence

Instances of critical-like characteristics in living systems at each organizational level as well as the spontaneous emergence of computation (Langton), indicate the relevance of self-organized criticality (SOC). But extrapolating complex bio-systems to life's origins, brings up a paradox: how could simple organics--lacking the 'soft matter' response properties of today's bio-molecules--have dissipated energy from primordial reactions in a controlled manner for their 'ordering'? Nevertheless, a causal link of life's macroscopic irreversible dynamics to the microscopic reversible laws of statistical mechanics is indicated via the 'functional-takeover' of a soft magnetic scaffold by organics (c.f. Cairns-Smith's 'crystal-scaffold'). A field-controlled structure offers a mechanism for bootstrapping--bottom-up assembly with top-down control: its super-paramagnetic components obey reversible dynamics, but its dissipation of H-field energy for aggregation breaks time-reversal symmetry. The responsive adjustments of the controlled (host) mineral system to environmental changes would bring about mutual coupling between random organic sets supported by it; here the generation of long-range correlations within organic (guest) networks could include SOC-like mechanisms. And, such cooperative adjustments enable the selection of the functional configuration by altering the inorganic network's capacity to assist a spontaneous process. A non-equilibrium dynamics could now drive the kinetically-oriented system towards a series of phase-transitions with appropriate organic replacements 'taking-over' its functions.Comment: 54 pages, pdf fil

Structural relaxation of nanocrystalline PdAu alloy: Mapping pathways through the potential energy landscape

Preparation history and processing have a crucial influence on which configurational state material systems assume. Glasses and nanocrystalline materials usually reside in nonequilibrium states at room temperature, and as a consequence, their thermodynamic, dynamical, and physical properties change with time—even years after manufacture. Such changes, entitled aging or structural relaxation, are all manifestations of paths taken in the underlying potential energy landscape. Since it is highly multidimensional, there is a need to reduce complexity. Here, we demonstrate how to construct a one-dimensional pathway across the energy landscape using strain/volume as an order parameter. On its way to equilibrium, we map the system’s release of energy by calorimetry and the spectrum of barrier heights by dilatometry. The potential energy of the system is reduced by approximately B during relaxation, whereas the crossing of saddle points requires activation energies in the order of 1eV/atom relative to the energy minima. As a consequence, the system behaves as a bad global minimum finder. We also discovered that aging is accompanied by a decrease in the non-ergodicity parameter, suggesting a decline in density fluctuations during aging

Recent Advancements in Metallic Glasses

The Special Issue “Recent Advancements in Metallic Glasses” presents ten original papers, considering both scientific and application issues related to metallic glasses. The papers are devoted to general consideration of the formation and defects of the glassy structure, defect evolution due to heat treatment, deformation behavior upon compression and high-pressure torsion, amorphous-crystalline transformation, hydrogenation behavior, and biomedical applications

The role of local structure in dynamical arrest

Amorphous solids, or glasses, are distinguished from crystalline solids by their lack of long-range structural order. At the level of two-body structural correlations, glassformers show no qualitative change upon vitrifying from a supercooled liquid. Nonetheless the dynamical properties of a glass are so much slower that it appears to take on the properties of a solid. While many theories of the glass transition focus on dynamical quantities, a solid's resistance to flow is often viewed as a consequence of its structure. Here we address the viewpoint that this remains the case for a glass. Recent developments using higher-order measures show a clear emergence of structure upon dynamical arrest in a variety of glass formers and offer the tantalising hope of a structural mechanism for arrest. However a rigorous fundamental identification of such a causal link between structure and arrest remains elusive. We undertake a critical survey of this work in experiments, computer simulation and theory and discuss what might strengthen the link between structure and dynamical arrest. We move on to highlight the relationship between crystallisation and glass-forming ability made possible by this deeper understanding of the structure of the liquid state, and emphasize the potential to design materials with optimal glassforming and crystallisation ability, for applications such as phase-change memory. We then consider aspects of the phenomenology of glassy systems where structural measures have yet to make a large impact, such as polyamorphism (the existence of multiple liquid states), aging (the time-evolution of non-equilibrium materials below their glass transition) and the response of glassy materials to external fields such as shear.Comment: 70 page

Extreme Laser-Driven Regimes in Covalently Bonded Planetary Materials

Our study focused on two materials: diamond (component in exoplanets and National Ignition Facility capsules) and perovskite (predominant component of the Earth mantle). High-power, pulsed, laser-driven shock compression experiments conducted on [001] oriented single crystalline diamond reveal stacking faults, dislocations, nano-twins and amorphous bands, upon the recovery and characterization of the specimens. Three laser energy levels are applied to specimens encapsulated in impedance matched momentum traps, generating shock pressures of 69, 93, and 115 GPa at a pulse duration of approximately 1 ns. At the lowest laser energy level (generating a pressure of 69 GPa), the defect-free lattice is retained, and diamond only exhibits elastic deformation. At the highest energy level (generating a pressure of 115 GPa) defects are generated in the structure to relax the deviatoric stresses resulting from the uniaxial strain compression of the lattice. The high shear stresses are relaxed by stacking faults, dislocations, twins, and amorphous bands. These shear-induced lattice defects on crystallographic slip planes are crucial to the onset of amorphization. Transmission electron microscopy reveals that the amorphous bands are extremely localized and as narrow as a few nanometers. This amorphization is consistent with other covalently bonded materials with negative Clapeyron behavior subjected to extreme loading. Consequently, shock-induced amorphization is proposed as a new deformation mechanism of diamond under extremely high strain rate deformation.Laser shock compression was employed on [010] oriented CaTiO3 under extreme pressure and temperature conditions comparable to those in the Earth’s mantle. The shear stress generated by the 70 GPa shock stress was equal to approximately 20 GPa, assuming elasticity. This is significantly higher than the Peierls-Nabarro stress required to move dislocations, around 10 GPa. TEM also revealed the generation of profuse perpendicular dislocations in [110](001) and [1 ̅10](001) slip systems. Dislocation density ranged from 15×1012 m-2 to 2×1012 m-2 within 12 µm from the shocked surface. Additionally, antiphase domain boundaries along [010] and [100] were observed under the high-pressure shock conditions. CaTiO3 deforms mainly through dislocation motion due to its positive Clapeyron slope and high atomic packing factor