Numerical Modeling of Shockwaves Driven by High-Energy Particle Beam Radiation in Tungsten-Made Structures

The investigation of wave propagation in solids requires the development of reliable methods for the prediction of such dynamic events in which the involved materials cover wide ranges of different possible states, governed by plasticity, equation of state, and failure. In the present study, the wave propagation in metals generated by the interaction of high-energy proton beams with solids was considered. In this condition, axisymmetric waves were generated, and, depending on the amount of the delivered energy, different regimes (elastic, plastic, or shock) can be reached. Nonlinear numerical analyses were performed to investigate the material response. The starting point was the energy map delivered into the component as the consequence of the beam impact. The evolution of both hydrodynamic and mechanical quantities was followed starting from the impact and the effects induced on the hit component were investigated. The results showed the portion of the component close to the beam experiences pressure and temperature increase during the deposition phase. The remaining part of the component is traversed by the generated shockwave, which induces high values of strain in a short time or even the failure of the component

Temperature dependence of material behaviour at high strain-rate Proceedings of 24th DYMAT Technical Meeting 9-11 September 2019, Stresa (Italy)

In recent years, interest in material characterization at high strain-rates while varying the temperature has been continuously increasing. Consequently, the study and modelling of material behavior in such conditions has been promoted. In many applications such as machining, metal forming, high velocity impact or high energy deposition of metals, materials are deformed at very high rates. This produces self-heating to high temperatures due to adiabatic processes. In this case, the stress-strain response will be a balance between the effects of hardening (due to strain and strain-rate) and thermal softening. In other cases, the working temperature may be different to room temperature. Hence both the mechanical response of the material and the effect of strain-rate should be investigated in the domain of interest. At high temperature, materials generally become much more ductile and can also exhibit microstructural changes due to recrystallization phenomena. By contrast, at low temperatures the material strength usually increases and the mechanical behavior changes from ductile to brittle. From these considerations, it appears evident that temperature and strain-rate are variables of fundamental importance in the prediction of the mechanical response of materials, playing an important role in many deformation processes. Hence, it is clear there is a need to define proper material models which could be implemented in numerical Finite Element simulations from which it should be possible to predict and estimate the responses of structures, components and materials under different loading conditions and scenarios. Of course, the development of methodologies and facilities for the complete investigation of the mechanical response of materials in the whole temperature and strain-rate field of interest is required and has to be addressed, by also taking into account the fact that temperature and strain-rate are mutually related. This means that the thermal effects obtained from quasi-static tests cannot always be used to predict material response under dynamic loading conditions. Moreover, this reveals that in order to consider the coupled effects of temperature and strain-rate, material models should be used in which the thermal component of stress is also considered

An advanced identification procedure for material model parameters based on image analysis

Inverse methods for the material strength model calibration are widespread techniques, which allow taking into account for the actual strain, strain-rate, temperature and triaxiality fields inside the specimen. An optimization procedure generally starts from experimental measurement of force-stroke time history and is based on the minimization of the difference between experimental and numerically computed quantities. In this work, the strength model identification is performed also on the basis of the specimen shape recorded during the test. This information is imposed as boundary condition, which forces the experimental profile to the external surface of the specimen. The optimization is based on the minimization of the reaction force of the imposed boundary condition. This technique could be applied both to quasi-static and dynamic tests, also at different temperatures, since the only additional requirement is a video of the test with a good compromise in terms of spatial and time resolutions. The methodology is compared with a standard numerical optimization procedure, in order to evaluate the reliability of the method and the advantages/disadvantages of this new approach

Dynamic mechanical behavior of syntactic iron foams with glass microspheres

In this work, the mechanical behavior of syntactic foams made of hollow glass microspheres mixed in an iron matrix was investigated. This type of material is interesting since, when compared to other types of metal foams, it offers greatly increased quasi-static compressive strength, though at lower maximum porosity and thus higher density. Moreover it maintains the advantages and useful properties of metal foams such as thermal and environmental resistance. In particular, the strain-rate sensitivity response was studied. The experimental characterization was performed by means of compression tests at three strain-rate levels: at the highest strain-rate level a SHPB was used. Type and content of glass microspheres were also studied. The experimental results showed that the compression behavior of syntactic foams, similarly to the other types of foams, is strongly affected by all the examined factors. For what concerns the strain-rate, it was found to increase material characteristics in almost all cases. The influence of the matrix behavior on the composite was identified as the determining parameter in this respect. In order to evaluate the results obtained with the described tests campaign, the experimental data were further elaborated by means of an empirical analytical strain-rate sensitive model. The dependency of the material response on model parameters was widely discusse

ANALISI DELLA CURVA DI FLUSSO PLASTICO DI MATERIALI METALLICI BASATA SULLA MISURA SPERIMENTALE DEL PROFILO DI NECKING

L’identificazione dei modelli di flusso plastico a partire dalla realizzazione di prove di trazione, nonostante la semplicità della prova, presenta alcuni problemi legati allo sviluppo di condizioni di sollecitazione triassiale conseguenti al raggiungimento della condizione di necking. Numerosi approcci sono stati proposti in passato per correggere la misurazione canonica di forza e allungamento rilevata durante la prova, al fine di determinare la legge true stress-true strain del materiale e identificare, così, i parametri di modelli costitutivi elasto-plastici. Nel presente lavoro viene proposto un approccio basato su una combinazione di analisi digitale dell’immagine e ottimizzazione numerica di modelli FEM: l’evoluzione del profilo del provino dogbone rilevato durante una prova di trazione viene impiegata direttamente per l’identificazione della legge di flusso plastico del materiale. La metodologia presentata è stata applicata per il rame HDHC e comparata con le tecniche di indagine convenzionali

ASCs-exosomes recover coupling efficiency and mitochondrial membrane potential in an in vitro model of ALS

The amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by motoneurons death. Mutations in the superoxide dismutase 1 (SOD1) protein have been identified to be related to the disease. Beyond the different altered pathways, the mitochondrial dysfunction is one of the major features that leads to the selective death of motoneurons in ALS. The NSC-34 cell line, overexpressing human SOD1(G93A) mutant protein [NSC-34(G93A)], is considered an optimal in vitro model to study ALS. Here we investigated the energy metabolism in NSC-34(G93A) cells and in particular the effect of the mutated SOD1(G93A) protein on the mitochondrial respiratory capacity (complexes I-IV) by high resolution respirometry (HRR) and cytofluorimetry. We demonstrated that NSC-34(G93A) cells show a reduced mitochondrial oxidative capacity. In particular, we found significant impairment of the complex I-linked oxidative phosphorylation, reduced efficiency of the electron transfer system (ETS) associated with a higher rate of dissipative respiration, and a lower membrane potential. In order to rescue the effect of the mutated SOD1 gene on mitochondria impairment, we evaluated the efficacy of the exosomes, isolated from adipose-derived stem cells, administrated on the NSC-34(G93A) cells. These data show that ASCs-exosomes are able to restore complex I activity, coupling efficiency and mitochondrial membrane potential. Our results improve the knowledge about mitochondrial bioenergetic defects directly associated with the SOD1(G93A) mutation, and prove the efficacy of adipose-derived stem cells exosomes to rescue the function of mitochondria, indicating that these vesicles could represent a valuable approach to target mitochondrial dysfunction in ALS

Sirtuin 6 localization at cortical brain level of young diabetic mice

The metabolic syndrome, characterized by visceral obesity, dyslipidaemia, hyperglycaemia and hypertension, has become one of the major public-health challenges worldwide and it is strictly associated with the development of type II diabetes and neurodegenerative diseases (Alberti et al. 2005; Panza et al. 2010). Increased metabolic flux to the brain during overnutrition can orchestrate stress response, blood-brain barrier alteration, microglial cells activation and neuroinflammation (Nerurkar et al., 2011). The protein sirtuin family is a class of nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylase that act on a variety of targets and so play a key role in central physiological regulation (Sebastian et al., 2012; Wang et al., 2012). To assess the physiopathological significance of sirtuin6 (SIRT6) at brain cortical level, we analysed its specific expression and subcellular localization in young db/db mice, animal model of type II diabetes mellitus, and respective control lean mice. In particular, we analysed the cytoarchitecture of the brain cortex, evaluated SIRT6 expression and its localization by immunohistochemistry comparing young db/db mice to lean control mice, distinguishing among the six cortical layers and between motor and somatosensory cortex. We observed that SIRT6 is mainly localized in the nucleus of both lean and db/db mice. Diabetic mice showed few SIRT6 positive cells respect to lean control mice in all cortical layers without significant differences between motor and somatosensory cortex. No morphological alteration have been find. In conclusion, our findings contribute to further understand SIRT6 protein expression in the early steps of type II diabetes mellitus and suggest its implication in the pathogenic processes of diabetes mellitus and diabetes–induced neurodegeneration

Sirtuin 6 localization at cortical brain level of young diabetic mice

The metabolic syndrome, characterized by visceral obesity, dyslipidaemia, hyperglycaemia and hypertension, has become one of the major public-health challenges worldwide and it is strictly associated with the development of type II diabetes and neurodegenerative diseases (Alberti et al. 2005; Panza et al. 2010). Increased metabolic flux to the brain during overnutrition can orchestrate stress response, blood-brain barrier alteration, microglial cells activation and neuroinflammation (Nerurkar et al., 2011). The protein sirtuin family is a class of nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylase that act on a variety of targets and so play a key role in central physiological regulation (Sebastian et al., 2012; Wang et al., 2012). To assess the physiopathological significance of sirtuin6 (SIRT6) at brain cortical level, we analysed its specific expression and subcellular localization in young db/db mice, animal model of type II diabetes mellitus, and respective control lean mice. In particular, we analysed the cytoarchitecture of the brain cortex, evaluated SIRT6 expression and its localization by immunohistochemistry comparing young db/db mice to lean control mice, distinguishing among the six cortical layers and between motor and somatosensory cortex. We observed that SIRT6 is mainly localized in the nucleus of both lean and db/db mice. Diabetic mice showed few SIRT6 positive cells respect to lean control mice in all cortical layers without significant differences between motor and somatosensory cortex. No morphological alteration have been find. In conclusion, our findings contribute to further understand SIRT6 protein expression in the early steps of type II diabetes mellitus and suggest its implication in the pathogenic processes of diabetes mellitus and diabetes–induced neurodegeneration

Diamond-based sensors for in vitro cellular radiobiology: Simultaneous detection of cell exocytic activity and ionizing radiation

The investigation of secondary effects induced by ionizing radiation represents a new and ever-growing research field in radiobiology. This new paradigm cannot be investigated only using standard instrumentation and methodologies, but rather requires novel technologies to achieve significant progress. In this framework, we developed diamond-based sensors that allow simultaneous real-time measurements with a high spatial resolution of the secretory activity of a network of cells cultured on the device, as well as of the dose at which they are exposed during irradiation experiments. The devices were functionally characterized by testing both the above-mentioned detection schemes, namely: amperometric measurements of neurotransmitter release from excitable cells (such as dopamine or adrenaline) and dosimetric evaluation using different ionizing particles (alpha particle and X-ray photons). Finally, the sensors were employed to investigate the effects induced by X-rays on the exocytotic activity of PC12 neuroendocrine cells by monitoring the modulation of the dopamine release in real-time

behaviour of advanced materials impacted by high energy particle beams

Beam Intercepting Devices (BID) are designed to operate in a harsh radioactive environment and are highly loaded from a thermo-structural point of view. Moreover, modern particle accelerators, storing unprecedented energy, may be exposed to severe accidental events triggered by direct beam impacts. In this context, impulse has been given to the development of novel materials for advanced thermal management with high thermal shock resistance like metal-diamond and metal-graphite composites on top of refractory metals such as molybdenum, tungsten and copper alloys. This paper presents the results of a first-of-its-kind experiment which exploited 440 GeV proton beams at different intensities to impact samples of the aforementioned materials. Effects of thermally induced shockwaves were acquired via high speed acquisition system including strain gauges, laser Doppler vibrometer and high speed camera. Preliminary information of beam induced damages on materials were also collected. State-of-the-art hydrodynamic codes (like Autodyn®), relying on complex material models including equation of state (EOS), strength and failure models, have been used for the simulation of the experiment. Preliminary results confirm the effectiveness and reliability of these numerical methods when material constitutive models are completely available (W and Cu alloys). For novel composite materials a reverse engineering approach will be used to build appropriate constitutive models, thus allowing a realistic representation of these complex phenomena. These results are of paramount importance for understanding and predicting the response of novel advanced composites to beam impacts in modern particle accelerators