Extreme Loading Conditions Research Articles

Meshfree Simulations for Additive Manufacturing Process of Metals

We present a meshfree direct numerical simulation (DNS) capability for the additive manufacturing (AM) process of metals based on the hot optimal transportation meshfree (HOTM) method. The HOTM method is a meshfree thermomechanical Lagrangian computational framework for material behaviors under extreme thermomechanical loading conditions. It combines the optimal transportation meshfree (OTM) method and the variational thermomechanical constitutive updates. In the HOTM method, the linear momentum and energy conservation equations are solved simultaneously in a monolithic way. A phase-aware constitutive model is developed to predict the melting/solidification phase change of metals and multiphase mixing during the AM process automatically. The HOTM method is validated in the simulations of the laser welding process over Inconel 625 bare plate by applying heat flux models for the laser beam, the convective heat loss, and radiation heat loss. The performance measurements of the simulation results, including the melt pool geometric dimensions and cooling rates, are comparable to the experimental data measured in the AM benchmark tests. The influence of various laser powers and laser scanning speeds on the melt pool thermodynamics is also studied.

Desert Dust, Industrialization, and Agricultural Fires: Health Impacts of Outdoor Air Pollution in Africa

AbstractThe African continent continuously experiences extreme aerosol load conditions, during which the World Health Organization clean air standard of 10 μg/m3 of PM2.5 mass is systematically exceeded. Africa holds the world largest source of desert dust emissions, undergoes strong industrial growth, and produces approximately a third of the Earth's biomass burning aerosol particles. Sub‐Saharan biomass burning is driven by agricultural practices, such as burning fields and bushes in the postharvest season for fertilization, land management, and pest control. Thus, these emissions are predominantly anthropogenic. Here we use global atmospheric composition, climate, and health models to simulate the chemical composition of the atmosphere and calculate the mortality rates for Africa by distinguishing between purely natural, industrial/domestic, and biomass burning emissions. Air quality‐related deaths in Africa rank within the top leading causes of death in Africa. Our results of ~780,000 premature deaths annually point to the extensive health impacts of natural emissions, high mortality rate caused by industrialization in Nigeria and South Africa, and a smaller extent by fire emissions in Central and West Africa. In Africa, 43,000 premature deaths are linked to biomass burning mainly driven by agriculture. Our results also show that natural sources, in particular windblown dust emissions, have large impacts on air quality and human health in Africa.

Fracture and mechanical characteristics of CO2-saturated sandstone at extreme loading conditions

Dynamic compression and Brazilian disc tests were performed on dry, water- and brine-saturated sandstone with and without scCO2 (supercritical carbon dioxide) injection. Split Hopkinson pressure bar (SHPB) tests were conducted under different strain rates. The full-field deformation and fracturing process were investigated by the high-speed 3D digital image correlation (DIC) technique with a resolution of 256 × 256 pixels at 200,000 frames per second (fps). The presence of CO2 attenuated the dynamic compressive strength for dry and water-saturated sandstone. The dry sandstone has a greater brittleness with the saturation of CO2, but there was an opposite trend for water-saturated sandstone saturated by CO2. The presence of CO2 had less effect on the dynamic mechanical properties on the brine-saturated sandstone. The normalised stress threshold for crack initiation became lower for the dry and water treated specimen but was less effective in brine-saturated sandstone. The injection of CO2 intensified the fracturing degree, branching and altered the crack initiation position under dynamic loading. The mechanism of CO2 effect was studied from mineralogical structure alteration based on the observation by scanning electron microscope (SEM).

Anisotropic corrections for the downwelling radiative heat transfer flux from various types of aerosols

Comprehensive Monte Carlo simulations are used to correct deviations in the atmospheric downwelling longwave (DLW) radiative flux calculated by isotropic scattering assumptions. The widely used δ-M approximation is validated for low to medium values of aerosol loading. For very high aerosol loading conditions, the δ-M approximation incurs an error. Here we propose scaling corrections for extreme loading conditions routinely found in selected urban areas in Asia, but also in other continental and coastal areas susceptible to large-scale wildfire pollution (Western USA) or dust storms (Mediterranean regions and Northern Africa). The scaling rules are expressed as functions of the normalized aerosol optical depth t∗ and the scattering asymmetry factor eg. An exponential relationship between the DLW deviation that assumes isotropic scattering and t∗ is found, and the corresponding fitting coefficients are correlated for different types of aerosols (sample internal mixing, urban, continental and marine aerosols). The δ-M approximation is sufficiently accurate when aerosol optical depths (AOD) at the ground level are smaller than 0.5. For AOD beyond this threshold, the proposed scaling rule corrections should be used for estimation of downwelling thermal radiative fluxes. The effects of moisture content on aerosol composition and on DLW radiative fluxes are also investigated for all conditions of interest.

Dynamic mechanical behavior of lithium-ion pouch cells subjected to high-velocity impact

With broad-scale deployment of lithium-ion batteries, mechanical-abuse induced failure events such as short circuits and thermal runaway have made safety a focus of attention in battery design. Most previous studies have focused on quasi-static and low-velocity impact analyses, which could not represent the mechanical behavior of lithium-ion batteries in realistic situations. Here we report a combined experimental and computational study on the dynamic response of lithium-ion pouch cells subjected to high-velocity (200–1000 m/s) impact. Dynamic finite element simulations were performed to study the effects of internal interfacial behavior and external loading and boundary conditions on the dynamic mechanical behavior of pouch cells. Specifically, mechanical resistance across interfaces between different cell components has a pronounced impact on energy distribution and absorption, thereby determining the evolution of subsequent failure events. These results have practical implications for designing cells with liquid versus gel-type electrolytes, for example. Furthermore, finite element simulations on different external loading and boundary conditions indicate that a direct interaction between the impactor and the cell boundaries lead to a significant change in residual velocity, while the response of the pouch cell is independent of the prescribed far-field boundary conditions. In other words, there is not a significant difference in the response of pouch-format cells that have stacked electrodes versus wound electrodes at such high strain rates. These results are significantly different from quasi-static simulations wherein the evolution of failure events follows a very different pathway. In addition, the impact velocity profiles under different initial impact velocities offer the ballistic limit for the pouch cell and inform subsequent propagation analyses at the battery module level. Collectively, the findings presented here not only offer new perspectives on the role of the interfacial resistances and external boundary conditions on the mechanical safety of lithium-ion pouch cells, but also have implications for further investigations on cell design, modeling approaches, and test method development to study the safety of lithium-ion batteries under extreme loading conditions.

Rate and temperature dependent relations for CFSTs and CFFTs subject to post-impact fire conditions

Experimental research on the behaviour of conventional construction materials subject to extreme loading condition of post-impact-fire has indicated the effect of rate dependent loading history on the temperature performance of these materials. In order to analyse and design structures to withstand such combined loading, it is desirable to develop models that can reflect the mechanical properties of materials under initial impulsive loading and subsequent elevated temperature. In this study, a rate-pre-damage-temperature dependent empirical expression is proposed to predict the residual strength of partially damaged steel-concrete and fibre rein-forced polymer-concrete composite materials, in the form of concrete-filled steel tubes (CFST) and Concrete filled carbon-fibre reinforced polymer tubes (CFFT), at high temperatures up to 600 °C. The developed model is calibrated and validated on the basis of actual experimental data published by the authors. The proposed expression proves to be capable of successfully reproducing material strengths by considering the extent of high strain rate induced pre-damage together with temperature exposure.

Modified embedded-atom method potential of niobium for studies on mechanical properties

Niobium (Nb) as a refractory metal has appealing mechanical properties due to high ductility at room temperature. Density functional theory (DFT) calculations confirmed its intrinsic ductility by showing its perfect lattice generates an elastic shear deformation preceding its cleavage fracture under 〈100〉 ideal tensile deformation. Based on DFT calculations of simple atomic configurations, we applied an evolution strategy method to build a modified embedded-atom method (MEAM) spline-interpolation potential that can reproduce the intrinsic ductility of Nb during ideal tensile deformation. Further examinations show that simulations based on this MEAM potential can exhibit other essential characteristics of deformation behavior, such as ideal shear strengths, generalized stacking fault energies, twin boundary energies, phonon spectrum, etc., that are consistent with DFT calculations. This potential also outputs the structures, energetic stability and glide mechanism of 12〈111〉 screw dislocations, such as dislocation core structures, core energies, migration barriers and dislocation core trajectories, consistent with DFT calculations. Therefore, this MEAM potential is suitable to study the mechanical behaviors of Nb, especially those under extreme loading conditions and considering non-Schmid effects.

Experiment Analysis To Examine The Effects Of Adhesive And Adherent Type Of Geometrical Configuration On Joint Failure Loads

Abstract The intention of trialing’s is to calculate the effects of adhesive and adherent type on CFRP joints and to encounter the relation between the durability of adhesive joints and substantial properties on joint failure loads. The traditional practices to join two metals or any constituents were riveting, welding, brazing, bolting etc., On the other hand, for fibre materials, the above-stated techniques won’t effort out, for fibre materials epoxies are essential. During the extreme loading conditions, (adhesive or cohesive) bonding may bust. This paper is testing the adhesive bonding and cohesive bonding properties between CFRP with diverse conditions such as, varying overlap lengths, loading conditions, pre-treatment process, treating conditions of epoxies. The adhesive bonding is virtuous and captivating maximum load is premeditated. Currently, the analysis of adhesive A: Cold-cure epoxy (Araldite 2021), adhesive B: Toughened Acrylic (F246), adhesive C: Heat-cured toughened epoxy (ESP110), are led through varied loads with distinct lap joints were tested and results were plotted. Adhesive C has high strength compered to all other adhesives and maximum strength of joint depends on pre-treatment, thickness and overlap of joints.

Upwind 2MW Horizontal Axis Wind Turbine Tower Design and Analysis

Wind energy is one of the quickest growing renewable energies in the world due to era of wind energy is smooth and non-polluting; it does now not produce any byproducts dangerous to the environment. Large scale machines are in particular nicely appropriate for wind energy. The fee of foundations doesn’t upward push in share to the dimensions of the device, and protection costs are largely impartial of the size of the system. In areas where it is difficult to find sites for more than a single turbine, a large turbine with a tall tower uses the existing wind resource more efficiently. Different subcomponents are designed depend on the purpose of the turbines among these the tower of a wind turbine helps the nacelle and the rotor and affords the necessary elevation of the rotor to hold it clear off the floor and produce it as much as the level where the wind sources are. The towers for large wind turbines are typically made from steel; however concrete towers are every so often used. The tower is normally connected to its helping basis by using a bolted flange connection or a weld. The tower constitutes a low-generation aspect whose layout is easy to optimize, and which therefore for the duration of the layout manner lends itself easily as an item for possible fee discount. This may additionally are available in useful because the fee of a tower typically establishment a sizeable a part of the entire fee of a wind turbine. The design and analysis of the tower focused on large wind turbines. It examines the result of loading on the tower, the optimum tower height and the verification of safety against bending and buckling. The buckling of 2 MW horizontal axis wind turbine tower tube with tower base diameter of 3.9m, top tower diameter of 2m and length of 80m is studied by theoretical analysis and numerical simulation by using ANSYS and MATLAB software. Based on this study the results are calculated based on theoretical and FEM method and their error is shown, buckling modes and vibrational analysis are done, shear and bending diagrams are shown, extreme loading conditions are also shown.

Variation of damping behaviour of T105Mn120 castings, used for railway safety systems, as an effect of extreme loading conditions

Abstract Hadfield steel, invented by Sir Robert Hadfield in 1882, has an exceptional hardness and toughness, which recommend it for the construction of executive elements of railway passages and digging equipment. In the former case, the structures are subjected mainly to dynamic deformation, when the texture of austenite is mainly controlled by slip. In a previous work on solution-treated T105Mn120, we observed a marked work hardening tendency during strain sweep cycles, with average rates of 5.3 GPa/μm, which was further augmented by frequency increase, causing storage moduli growth up to 176 GPa in the fifth cycle. In the present paper, the limit frequencies were chosen as 0.5 and 16.66 Hz, replicating the extreme dynamic loading conditions of the parts cast from Hadfield steel at minimum and maximum train wagons, respectively. Dynamic mechanical analysis (DMA) were performed in strain sweep mode, at the above two frequencies, at 233 K and 323K, aiming to reproduce the extreme weather conditions on the ground. The structural changes, observed by electron-scanning microscopy, were corroborated with strain sweep results.

COASTAL FLOODING-INDUCED DEBRIS MOTION

Extreme coastal events such as the 2004 Indian Ocean Tsunami, the 2011 Tohoku Tsunami as well as the 2005 Katrina and 2012 Sandy hurricanes demonstrated that, hydrodynamic loading aside, debris loading represents a major factor in the extreme loading conditions experienced by inland infrastructure. While extreme hydrodynamic loading due to coastal flooding events has been the object of intense research over the past decade, few studies dealing with debris impact due to coastal flooding have been conducted. Post-tsunami forensic engineering field investigations conducted by the authors (Nistor et al. 2005; Shibayama et al., 2006; Nistor et al. 2010) or other researchers (Chock et al. 2012, Sato et al. 2014;) revealed that debris loading and debris damming have a significant effect on the structural integrity of buildings and infrastructure in general, especially in high-density urban areas. Current design guidelines (FEMA P-55, 2011; FEMA P-646, 2012) and the new ASCE-7 Chapter 6 - Tsunami Effects and Loads suggest conservative estimations of the debris spatial spreading based on limited sets of field data to assess debris impact potential (Chock et al., 2012; Naito et al., 2014). The primary objective of this study was to investigate the spatial and temporal displacement of floating debris due to rapid coastal flooding in a built-in port environment using two novel different measuring techniques: (1) high-accuracy video debris detection and tracking system and (2) a real-time locating “smart” sensor-tracking system. Results are compared with prescriptions of the ASCE7 Chapter 6 pertaining to debris motion.

On the Microstructural Characteristics of UFG Microalloyed Steel Influencing the Mechanical Behavior under Dynamic Loading

This paper presents a summary of a preliminary research aimed at producing ultrafine-grained (UFG) and heterogeneous microstructure in microalloyed steel and testing these materials under dynamic loading conditions (strain rates 800 s-1 and 1800s-1). The UFG and bimodal-structures, due to grain size, structural composition or morphology of structural components, were produced by an advanced thermomechanical processing, namely rolling in: hot, two-phase and cold-hot combined conditions. The advantage of bimodal microstructures is their maximization of mechanical behavior under extreme loading conditions due to promoted accumulation and interactions of geometrically necessary dislocations. The dynamic work-hardening behavior has been studied as a function of solute atoms and fine-scale, second-phase particles in the UFG and bimodal-structures. The substantial complexity of the phenomena, which occur through the evolution of microstructure and texture in response to dynamic loading, presents formidable challenges to theoretical model development of plastic deformation of UFG and bimodal-structures. Such an extraordinary work hardening provides an attractive strategy to develop optimal combination of mechanical properties i.e. strength/ductility ratio. A multi-scale analysis capable of including material behavior in different scales should be applied to discuss mechanical response of mentioned above microstructures and to help to analyze their influence on mechanical behavior under dynamic loading. The investigation was performed for a material of common application: high strength microalloyed steel X70. The experimental results show that strain rate sensitivity of the heterogeneous microstructures obtained by various thermomechanical rolling routes are significant, but not by a similar magnitude with the microstructure compositions and increasing strain rate.

Mechanism for improvement of friction/wear by using Al2O3 and SiO2/Gear oil nanolubricants

Gear oil of heavy mining machineries are designed to provide anti-wear and anti-friction protection under extreme load condition. In present study thermophysical and tribological properties of industrial gear oil with nanoparticles additives (Al2O3 and SiO2) has been experimentally evaluated. Morphology of dry nanoparticles under FE-SEM shows that both nanoparticles are spherical. DLS test shows the presence of mild-agglomeration of nanoparticles in the dispersion. Density and viscosity of nanolubricants is tested with varying temperature and particle volume fraction. Measured viscosity results for Al2O3/gear oil nanolubricants follow the existing empirical model and new model has been proposed for SiO2/gear oil nanolubricants. Anti-friction and anti-wear properties of nanolubricants are tested on pin-on-disc test apparatus. FE-SEM and energy dispersive spectroscopy (EDS) analysis of wear scar (pin SS-304), evident the occurrence of ball bearing and surface polishing effects, which may be responsible for advanced tribological properties of the oil. Test results reveals that ball bearing have dominating effect in enhancement of tribological performance.

Seismic assessment of small modular reactors: NuScale case study for the 8.8 Mw earthquake in Chile

Abstract Reducing greenhouse gas emissions and improving energy production sustainability is a paramount of Chile’s 2050 energy policy. This though, is difficult to achieve without some degree of nuclear power involvement, given that the geography of the country consists of many areas that are practically off-grid, whereas cannot be developed and financially exploited due to the lack of basic commodities such as water and electricity. Recently small modular reactors (SMRs) have gained lots of attention by both researchers and world policy makers for their promised capabilities of enhanced safety systems, affordable costs and competitive scalability. SMRs can be located in remote areas and at this time are being actively developed in Argentina, USA, Brazil, Russia, China, South Korea, Japan, India and South Africa. Chile’s 2010 earthquake and Fukushima’s 2011 nuclear disaster have increased significantly both the population’s fear and opposition to Nuclear Power Energy for the possible consequences of radiation on the lives of people. This paper aims to study the seismic resistance of a typical nuclear structure, being at time proposed in Small Modular Reactors, by using earthquake conditions typically seen in Chile. Since many designs are under study, a NuScale reactor from USA is analyzed under these extreme loading conditions. The major advantages of the NuScale reactor are in the power scalability (it can go from 1 to 12 reactor cores producing from 60 to 720 MWe), limited nuclear fuel concentration, modules allocated below grade and high strength steel containments fully immersed in water. The cooling effect beyond Design Basis Accident is ensured indefinitely, which induces a significant safety factor in the case of an accident. For the purpose of this study a detailed 3D detailed structural model was developed, reproducing the NuScale reactor’s reinforced concrete framing system, where nonlinear analyses was performed to assess the overall mechanical response of the structure. The framing system has been tested under high seismic excitations typically seen in Chile (Mw > 8.0), showing high resistance and capability to cope with the developed forces due to its design. Based on a Soil-Structure Interaction analysis, it was also found that the NuScale framing system manages to maintain a low-stress level at the interaction surface between the foundation and the soil, where the structural system was found to be able to withstand significant earthquake loads. Finally, further investigation is deemed necessary in order to study the potential damages of the structure in the case of other hazards such as tsunami events, blast loads, etc.

Extreme static compression of carbon to terapascal pressures

Recent reports of record-setting ultrahigh static pressures achieved in diamond anvil cells (DACs, 495 GPa) and double-stage DACs (ds-DACs, 1 TPa) raise fundamental questions about mechanical response of diamond and related carbon structures under extreme compression. Here we present results from a combined first-principles calculation and finite-element analysis that unveil the mechanisms responsible for the greatly enhanced compressive strengths of these carbon structures by lateral confining stresses concentrated near anvil tips, stemming from structural deformations in compressed DACs and further strengthened by additional confining pressures in ds-DACs. Our results indicate that diamond anvils oriented in the [001] direction with a flat culet diameter of 20 μm can sustain peak pressures above 500 GPa, vastly exceeding its pure compressive strength of about 200 GPa. Among nano-carbon structures with enhanced shear strengths by nano- or grain-boundaries, we find that nano-twinned diamond possesses the highest compressive strength, reaching 1 TPa in ds-DAC settings, in agreement with experimental observations. The present findings establish key benchmarks and expand the realm of understanding of diamond and related carbon structures under extreme loading conditions; these results offer crucial insights for rational design of advanced and novel DAC devices.

Progressive structural capacity loss assessment-A framework for modern reinforced concrete buildings.

By the virtue of burgeoning terrorism, the exponential growth of advanced weaponry, and allied aids for explosions, it is quite evident that infrastructural facilities in the world have increasingly become more susceptible to sabotaging activities. The ever enhancing employment of reinforced concrete (RC) in the construction industry around the globe, the progressive collapse mechanisms, and respective mitigation strategies in the context of terrorism have garnered quite an attraction by the structural engineering community. The proficiency to envisage the complete collapse under the chain reaction of structural failures, partial collapse of key structural members, or the strength degradation of fundamental structural elements under the blast or impact loading can deliver significant information to cope with partial or complete structural failure. It is quite convenient to say that during the service life, a structure may experience extreme loading conditions. The current study has proposed a new methodology to cover the effect of uncertainty involved in loading on key structural elements of new and complex structures by emphasizing a very realistic structural capacity loss mechanism that allows the incremental reduction in the structural capacities of pivotal structural elements against any sort of impact loading instead of their complete annihilation. To demonstrate the application of the proposed methodology, a 13-story complex structure was selected that was comprised of a diverse structural configuration. The outcomes and results ensured the structural integrity against the applied loadings, as well as the effectiveness of the proposed methodology.

Simulation of Kinetics of Crack Development in Surface Layers of Material

Methods and results of physical and mathematical simulation of fracture processes at various scale-structural levels and under various (including extreme) loading conditions are given. The kinetics of cracks and their trajectories in the surface layers of material under conditions of cyclic loading, friction of rolling and sliding, indentation, and shearing of the sample edge are analyzed. The prospects of combined experimental and numerical simulation methods in the study of fracture processes are shown. A criterion for averaged stresses at the crack tip is proposed for predicting the trajectory of a crack under mixed loading conditions.

Computationally Efficient and Robust Nonlinear 3D Cyclic Modeling of RC Structures Through a Hybrid Finite Element Model (HYMOD)

A computationally efficient and robust simulation method is presented in this work, for the cyclic modeling of reinforced concrete (RC) structures. The proposed hybrid modeling (HYMOD) approach alleviates numerical limitations regarding the excessive computational cost during the cyclic analysis and provides a tool for the detailed simulation of the 3D cyclic nonlinear behavior of full-scale RC structures. The simplified HYMOD approach is integrated in this work with a computationally efficient cyclic concrete material model so as to investigate its numerical performance under extreme cyclic loading conditions. The proposed approach adopts a hybrid modeling concept that combines hexahedral and beam-column finite elements (FEs), in which the coupling between them is achieved through the implementation of kinematic constraints. A parametric investigation is performed through the use of the Del Toro Rivera frame joint and two RC frames with a shear wall. The proposed modeling method managed to decrease the computational cost in all numerical tests performed in this work, while it induced additional numerical stability during the cyclic analysis, in which the required number of internal iterations per displacement increment was found to be always smaller compared with the unreduced (hexahedral) model. The HYMOD provides for the first time with the required 3D detailed FE solution tools in order to simulate the nonlinear cyclic response of full-scale RC structures without hindering the numerical accuracy of the derived model nor the need of developing computationally expensive models that practically cannot be solved through the use of standard computer systems.

Experimental study on impact behaviour of stud shear connectors in composite beams with profiled steel sheeting

This paper deals with the shear behaviour of steel stud connectors in composite beams with profiled steel sheeting under static and impact loads. An experimental program including five static and ten impact push-out tests is firstly carried out, and the failure modes, the time history of impact load and slippage displacement, as well as the shear capacity of stud connectors are presented and discussed. Based on the dynamic responses, the influence of the arrangement form of profiled steel sheeting on the shear mechanism of steel stud connectors under impact loading is examined. Moreover, a design proposal developed previously by the authors is verified to reasonably predict the shear capacity of stud connectors with profiled steel sheeting parallel to the steel beam under impact loading. However, it is unsafe to predict the dynamic shear capacity of stud connectors with profiled steel sheeting transverse to the steel beam when the strain rate effect is considered. Additionally, the failure mode of shear connectors with solid slab in this paper is different from that of the previous work, which lead to the lower dynamic shear capacity of the connectors with the solid slab, and some further discussion is also carried out. The testing results can provide an essential data for future analytical and design-oriented study of composite beam with shear stud connectors with profiled steel sheeting under extreme loading conditions.

Evaluation of dynamic increase factor models for steel fibre reinforced concrete

The use of steel fibre reinforced concrete (SFRC) in protective structures against extreme loading conditions (e.g. high-velocity impact and blast) has gained worldwide interest in recent years, which is attributed to its advantages of higher tensile strength and better energy absorption capability compared to normal concrete. This paper presents a comprehensive review of the dynamic increase factors (DIF) for both compressive strength and tensile strength of SFRC reported in the literature. In particular, the influences of matrix strength, fibre shape and fibre volume fraction on the rate sensitivity of SFRC are investigated. A versatile DIF formula is then proposed based on the reported data for describing the dynamic material strength of SFRC, which considers the effects of various parameters in one unified formulation for the first time. To demonstrate the effectiveness and feasibility of the proposed DIF formula, a 3D finite element model is established, and the proposed DIF formula is employed to simulate the dynamic responses of SFRC plates under impact. The developed finite element model is validated by comparing the predicted results with experimental data.