ORALS

SESSION: MultiscaleMonPM1-R8	Horstemeyer International Symposium (7th Intl. symp. on Multiscale Material Mechanics & Sustainable Applications)
Mon. 28 Nov. 2022 / Room: Similan 1
Session Chairs: Seongwoo Woo; Session Monitor: TBA

14:00: [MultiscaleMonPM105] OS Plenary
Renormalization Group and Catastrophe Theory in geomechanics: From universal (fractal) material properties to scale-invariant constitutive laws
Alberto Carpinteri¹ ; ¹Politecnico di Torino, Torino, Italy;
Paper Id: 295 [Abstract]

The present paper deals with the opposite natural trends in composite systems: catastrophe and chaos arising from simple nonlinear rules, as well as order and structure emerging from heterogeneity and randomness. Part I deals with Nonlinear Fracture Mechanics models (in particular, the Cohesive Crack Model to describe strain localization both in tension and in compression) and their peculiar consequences: fold catastrophes (post-peak strain-softening and snap-through instabilities) or cusp catastrophes (snap-back instabilities) in plain or reinforced structural elements. How can a relatively simple nonlinear constitutive law, which is scale-independent, generate a size-scale dependent ductile-to-brittle transition? Constant reference is made to Dimensional Analysis and to the definition of suitable nondimensional brittleness numbers that govern the transition. These numbers can be defined in different ways, according to the selected theoretical model. The simplest way is that of directly comparing critical LEFM conditions and plastic limit analysis results. This is an equivalent way --although more effective for finite-sized cracked plates-- to describe the ductile-to-brittle size-scale transition, if compared to the traditional evaluation of the crack tip plastic-zone extension in an infinite plate. In extremely brittle cases, the plastic zone or process zone tends to disappear and the cusp catastrophe conditions prevail over the strain-softening ones and tend to coincide with the LEFM critical conditions in the case of initially cracked plates. Part II deals with the occurrence of self-similar and fractal patterns in the deformation, damage, fracture, and fragmentation of heterogeneous disordered materials, and with the consequent apparent scaling in the nominal mechanical properties of the same materials. Such a scaling is negative (lacunar fractality) for tensile strength and fatigue limit, whereas it is positive (invasive fractality) for fracture energy, fracture toughness, and fatigue threshold. At the same time, corresponding fractal (or renormalized) quantities emerge, which are the true scale-invariant properties of the material. They appear to be the constant factor (the universal property) in the power-law relating the nominal canonical quantity to the size-scale of observation. When the reference sets from self-similar become self-affine, we obtain Multi-fractal Scaling Laws, which are asymptotic and present a decreasing fractality for increasing structural sizes. They reproduce the experimental data very consistently. On the other hand, Critical Phenomena are always associated with the emergence of self-similar or self-affine patterns, to fractal (renormalized) or multi-fractal quantities, and to spontaneous self-organization. Typical examples are represented by: phase transformations, laminar-to-turbulent fluid flow transitions, avalanches in granular media, earthquakes, micro-cracking, and fracture in structural materials. In a fractal framework, it is then possible to define a scale-invariant constitutive law: the so-called Fractal Cohesive Crack Model, in which stress and strain are defined over lacunar fractal sets and the fracture energy in an invasive fractal set, which is the Cartesian product of the two previous sets.

References:
A. Carpinteri, Fracture and Complexity, Springer-Nature, Berlin, 2021.

SESSION: MultiscaleMonPM1-R8	Horstemeyer International Symposium (7th Intl. symp. on Multiscale Material Mechanics & Sustainable Applications)
Mon. 28 Nov. 2022 / Room: Similan 1
Session Chairs: Seongwoo Woo; Session Monitor: TBA

14:25: [MultiscaleMonPM106] OS Plenary
Correlation between Nano-Mechanics Instabilities, TeraHertz Phonons, and Sub-Atomic Particle Emissions: Implications to Geophysics and Geochemistry
Alberto Carpinteri¹ ; ¹Politecnico di Torino, Torino, Italy;
Paper Id: 260 [Abstract]

TeraHertz phonons are produced in solids and fluids by mechanical instabilities at the nano-scale (fracture and cavitation). They present a frequency that is close to the resonance frequency of the atomic lattices and an energy that is close to that of thermal neutrons. A series of fracture experiments on natural rocks and the systematic monitoring of seismic events have demonstrated that TeraHertz phonons are able to induce fission reactions on medium-weight elements (in particular, iron and calcium) with neutron and/or alpha particle emissions. The same phenomenon appears to have occurred in several different situations and to explain puzzles related to the history of our planet, like the primordial carbon pollution (and correlated iron depletion) or the ocean formation (and correlated calcium depletion), as well as scientific mysteries, like the so-called cold fusion or the correct radio-carbon dating of organic materials. Very important applications to earthquake precursors, climate change, and energy production are likely to develop in the next future. Three different forms of energy might be used as earthquake precursors. At the tectonic scale, Acoustic Emission (AE) prevails, as well as Electro-Magnetic Emission (EME) at the meso-scale, and Neutron Emission (NE) at the nano-scale. The three fracto-emissions tend to anticipate the next seismic event with an evident and chronologically ordered shifting: high frequencies and neutron emission about one week before, then lower frequencies and electromagnetic and acoustic waves. The experimental observations reveal a strong correlation between the three fracto-emission peaks and the major earthquakes occurring in the closest areas. Regarding cold fusion, despite the great amount of experimental results, the comprehension of these phenomena still remains unsatisfactory. On the other hand, as reported by most of the articles devoted to cold fusion, one of the principal features is the appearance of micro-cracks on the electrode surfaces after the experiments. A mechanical explanation is proposed as a consequence of hydrogen embrittlement of the electrodes during electrolysis. The preliminary experimental activity was conducted using a Ni-Fe anode and a Co-Cr cathode immersed in a potassium carbonate solution. Emissions of neutrons and alpha particles were measured during the experiments as well as evident chemical composition changes of the electrodes revealing the effects of fission reactions occurring in the host lattices. The symmetrical fission of Ni appears to be a clear evidence. Such reaction would produce two Si atoms or two Mg atoms with alpha particles and neutrons as additional fragments. In order to confirm the preliminary investigation, further electrolytic tests have been conducted using Pd and Ni electrodes. As for the early experiments, relevant compositional changes and the appearance of ligther elements previously absent have been observed. The most relevant process emerging from the experiments is the primary fission of palladium (decrement of 30%) into iron and calcium. Then, secondary fissions appear in turn producing oxygen atoms, alpha particles, and neutrons. The chemical composition changes were confirmed by four repetitions of the same experiment. An extensive evaluation of the heat generation has been carried out showing a positive energy balance in correspondence to the major neutron emission peaks.

References:
A. Carpinteri et al. (Eds), Acoustic, Electromagnetic, Neutron Emissions from Fracture and Earthquakes, Springer International, Switzerland, 2015.