A multiscale homogenization procedure to predict the elasto-viscoplastic behavior of polymer-based nanocomposites

2021 ◽  
pp. 096739112110233
Author(s):  
Mohammad Hassan Shojaeefard ◽  
Abolfazl Khalkhali ◽  
Sharif Khakshournia
Keyword(s):  
Design Procedure ◽  
Polymeric Matrix ◽  
Elastic Behavior ◽  
Algorithm Optimization ◽  
Multiphase Materials ◽  
Rate Dependent ◽  
Main Challenge ◽  
Compressive Loads ◽  
Structural Parts ◽  
The Impact

It has been demonstrated that adding a few percent of nanoscale reinforcements, leads to remarkable improvement in mechanical properties of the polymers such as stiffness, damping, and energy absorption. These lightweight materials are attractive substitutes for the heavy metallic structural parts in the automotive, military, aerospace and many other industries. However, due to complexity of these multiphase materials, accurate modeling of their behavior in real loading cases is still ambiguous. The impact simulation is a vital step in design procedure of a vehicle, where a strain rate-dependent model of its components is required. In this paper, an elasto-viscoplastic modeling procedure of the polymer-based nanocomposites, assuming the elastic behavior of the nano-phase is presented; whereas the polymeric matrix deformation is dependent to the loading rate and is characterized by the method of Genetic algorithm optimization-based fitting to the experimental observations. By introducing a modified Halpin-Tsai method, the nanocomposite is then modeled as a homogenized material where the modification algorithm is the main challenge. A combination of approaches including parametric analysis, central composite design of experiments and response surface method is proposed to modify the tangent modulus of the polymeric matrix to be passed as the input to the Halpin-Tsai equations. Finally, the procedure is implemented to a set of epoxy-GNP nanocomposites under unidirectional compressive loads with different rates and the stress-strain curves are predicted with a decent precision.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

scholarly journals Geoinformation Technologies in Support of Environmental Hazards Monitoring under Climate Change: An Extensive Review

2021 ◽  
Vol 10 (2) ◽  
pp. 94
Author(s):  
Andreas Tsatsaris ◽  
Kleomenis Kalogeropoulos ◽  
Nikolaos Stathopoulos ◽  
Panagiota Louka ◽  
Konstantinos Tsanakas ◽  
...  
Keyword(s):  
Climate Change ◽  
Environmental Monitoring ◽  
Environmental Hazards ◽  
Geographic Information ◽  
Added Value ◽  
Spatial Data Analysis ◽  
Anthropogenic Factors ◽  
Geospatial Technologies ◽  
Main Challenge ◽  
The Impact

Human activities and climate change constitute the contemporary catalyst for natural processes and their impacts, i.e., geo-environmental hazards. Globally, natural catastrophic phenomena and hazards, such as drought, soil erosion, quantitative and qualitative degradation of groundwater, frost, flooding, sea level rise, etc., are intensified by anthropogenic factors. Thus, they present rapid increase in intensity, frequency of occurrence, spatial density, and significant spread of the areas of occurrence. The impact of these phenomena is devastating to human life and to global economies, private holdings, infrastructure, etc., while in a wider context it has a very negative effect on the social, environmental, and economic status of the affected region. Geospatial technologies including Geographic Information Systems, Remote Sensing—Earth Observation as well as related spatial data analysis tools, models, databases, contribute nowadays significantly in predicting, preventing, researching, addressing, rehabilitating, and managing these phenomena and their effects. This review attempts to mark the most devastating geo-hazards from the view of environmental monitoring, covering the state of the art in the use of geospatial technologies in that respect. It also defines the main challenge of this new era which is nothing more than the fictitious exploitation of the information produced by the environmental monitoring so that the necessary policies are taken in the direction of a sustainable future. The review highlights the potential and increasing added value of geographic information as a means to support environmental monitoring in the face of climate change. The growth in geographic information seems to be rapidly accelerated due to the technological and scientific developments that will continue with exponential progress in the years to come. Nonetheless, as it is also highlighted in this review continuous monitoring of the environment is subject to an interdisciplinary approach and contains an amount of actions that cover both the development of natural phenomena and their catastrophic effects mostly due to climate change.

Influence of Human Error on Structural Reliability

2017 ◽  
Author(s):  
Eric Brehm ◽  
Robert Hertle ◽  
Markus Wetzel
Keyword(s):  
Human Error ◽  
Structural Reliability ◽  
Failure Modes ◽  
Structural Model ◽  
Limit State ◽  
Design Procedure ◽  
Material Strength ◽  
Limit States ◽  
The Impact

In common structural design, random variables, such as material strength or loads, are represented by fixed numbers defined in design codes. This is also referred to as deterministic design. Addressing the random character of these variables directly, the probabilistic design procedure allows the determination of the probability of exceeding a defined limit state. This probability is referred to as failure probability. From there, the structural reliability, representing the survival probability, can be determined. Structural reliability thus is a property of a structure or structural member, depending on the relevant limit states, failure modes and basic variables. This is the basis for the determination of partial safety factors which are, for sake of a simpler design, applied within deterministic design procedures. In addition to the basic variables in terms of material and loads, further basic variables representing the structural model have to be considered. These depend strongly on the experience of the design engineer and the level of detailing of the model. However, in the clear majority of cases [1] failure does not occur due to unexpectedly high or low values of loads or material strength. The most common reasons for failure are human errors in design and execution. This paper will provide practical examples of original designs affected by human error and will assess the impact on structural reliability.

Impact of a Fixed-Length Rigid Cylinder on an Elastic-Plastic Homogeneous Body

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Raja R. Katta ◽  
Andreas A. Polycarpou
Keyword(s):  
Impact Damage ◽  
Element Model ◽  
Elastic Behavior ◽  
Magnetic Storage ◽  
Practical Case ◽  
Homogeneous Body ◽  
Rigid Cylinder ◽  
Elastic Plastic ◽  
Fixed Length ◽  
The Impact

A contact mechanics (CM) based model of a fixed-length rigid cylinder impacting a homogeneous elastic-plastic homogeneous body was developed and includes an improved method of estimating the residual depth after impact. The nonlinear elastic behavior during unloading was accounted for to develop an improved coefficient of restitution model. The impact model was applied to study a practical case of a cylindrical feature on the slider of a magnetic storage hard disk drive impacting the disk to predict various critical impact contact parameters. The CM model was validated using a plane strain finite element model and it was found that a cylindrical feature with a longer length results in a substantial alleviation of impact damage.

scholarly journals Sensitivity of Supersonic ORC Turbine Injector Designs to Fluctuating Operating Conditions

2015 ◽  
Author(s):  
Elio A. Bufi ◽  
Paola Cinnella ◽  
Xavier Merle
Keyword(s):  
Method Of Characteristics ◽  
Organic Rankine Cycle ◽  
Design Procedure ◽  
Rankine Cycle ◽  
Operating Conditions ◽  
Real Gas ◽  
Real Gas Effects ◽  
Nozzle Shape ◽  
Turbine Design ◽  
The Impact

The design of an efficient organic rankine cycle (ORC) expander needs to take properly into account strong real gas effects that may occur in given ranges of operating conditions, which can also be highly variable. In this work, we first design ORC turbine geometries by means of a fast 2-D design procedure based on the method of characteristics (MOC) for supersonic nozzles characterized by strong real gas effects. Thanks to a geometric post-processing procedure, the resulting nozzle shape is then adapted to generate an axial ORC blade vane geometry. Subsequently, the impact of uncertain operating conditions on turbine design is investigated by coupling the MOC algorithm with a Probabilistic Collocation Method (PCM) algorithm. Besides, the injector geometry generated at nominal operating conditions is simulated by means of an in-house CFD solver. The code is coupled to the PCM algorithm and a performance sensitivity analysis, in terms of adiabatic efficiency and power output, to variations of the operating conditions is carried out.

Aerodynamic and structural design for the development of a MALE UAV

2018 ◽  
Vol 90 (7) ◽  
pp. 1077-1087 ◽  
Author(s):  
Pericles Panagiotou ◽  
Efstratios Giannakis ◽  
Georgios Savaidis ◽  
Kyros Yakinthos
Keyword(s):  
Structural Design ◽  
Design Procedure ◽  
Unmanned Aircraft ◽  
Content Type ◽  
Parameterized Design ◽  
Detail Design ◽  
Aerial Vehicle ◽  
Structural Parts ◽  
Long Endurance ◽  
Structural Aspects

Purpose The purpose of this paper is to present the preliminary design of a medium altitude long endurance (MALE) unmanned aerial vehicle (UAV), focusing on the interaction between the aerodynamic and the structural design studies. Design/methodology/approach The classic layout theory was used, adjusted for the needs of unmanned aircraft, including aerodynamic calculations, presizing methods and CFD, to estimate key aerodynamic and stability coefficients. Considering the structural aspects, a combination of layout, finite element methods and custom parameterized design tools were used, allowing automatic reshapes of the skin and the internal structural parts, which are mainly made of composite materials. Interaction loops were defined between the aforementioned studies to optimize the performance of the aerial vehicle, maximize the aerodynamic efficiency and reduce the structural weight. Findings The complete design procedure of a UAV is shown, starting from the final stages of conceptual design, up to the point where the detail design and mechanical drawings initiated. Practical implications This paper presents a complete view of a design study of a MALE UAV, which was successfully constructed and flight-tested. Originality/value This study presents a complete, synergetic approach between the configuration layout, aerodynamic and structural aspects of a MALE UAV.

Green Infrastructure Development in Sustainable Water Resources Management System

2015 ◽  
Vol 747 ◽  
pp. 127-131
Author(s):  
Quintarina Uniaty
Keyword(s):  
Water Management ◽  
Green Infrastructure ◽  
Management System ◽  
Urban Systems ◽  
Difficult Situation ◽  
Sustainable Water Resources Management ◽  
Main Challenge ◽  
The Impact ◽  
Green City

The main challenge in the twenty-first century is to work towards a more resilient urban world and sustainable. In the context of a global urban strategy, endurance is the attention to the capacity of urban systems, including the natural environment, the built environment, social and economic elements; to be able to manage change, to learn from a difficult situation and be in a position to rise from urban problems. Globally, the townsfolk face a water crisis within the next ten years, as the impact of climate change in exhaust emissions will affect the quality of air, land and water; which will ultimately reduce the quality of the environment. Sustainability questioned whether certain aspects of the day-to-day activities, and the systems of community life, can be ongoing into the futureonce again from the standpoint of social, economic and environmental. Eco city is a phrase that is often used in ecological issues raised in the concept of sustainable urban planning and green city embodiment of the challenges ahead in sustainable economic development, and the future development of smart green city. The convergence of technology and environmental issues has changed the world economy that offers a green city promising future - a city that appreciates natural heritage and offer all parties involved. This paper will discuss green infrastructure as water management control system in urban development concepts that contribute to build a sustainable green city management.Key words : green infrastructure, water management system.

scholarly journals Analysis of isothermal and cooling rate dependent immersion freezing by a unifying stochastic ice nucleation model

2015 ◽  
Vol 15 (9) ◽  
pp. 13109-13166
Author(s):  
P. A. Alpert ◽  
D. A. Knopf
Keyword(s):  
Cooling Rate ◽  
Surface Area ◽  
Ice Nucleation ◽  
Rate Dependence ◽  
Nucleation Theory ◽  
Freezing Process ◽  
Nucleation Kinetics ◽  
Rate Dependent ◽  
Immersion Freezing ◽  
The Impact

Abstract. Immersion freezing is an important ice nucleation pathway involved in the formation of cirrus and mixed-phase clouds. Laboratory immersion freezing experiments are necessary to determine the range in temperature (T) and relative humidity (RH) at which ice nucleation occurs and to quantify the associated nucleation kinetics. Typically, isothermal (applying a constant temperature) and cooling rate dependent immersion freezing experiments are conducted. In these experiments it is usually assumed that the droplets containing ice nuclei (IN) all have the same IN surface area (ISA), however the validity of this assumption or the impact it may have on analysis and interpretation of the experimental data is rarely questioned. A stochastic immersion freezing model based on first principles of statistics is presented, which accounts for variable ISA per droplet and uses physically observable parameters including the total number of droplets (Ntot) and the heterogeneous ice nucleation rate coefficient, Jhet(T). This model is applied to address if (i) a time and ISA dependent stochastic immersion freezing process can explain laboratory immersion freezing data for different experimental methods and (ii) the assumption that all droplets contain identical ISA is a valid conjecture with subsequent consequences for analysis and interpretation of immersion freezing. The simple stochastic model can reproduce the observed time and surface area dependence in immersion freezing experiments for a variety of methods such as: droplets on a cold-stage exposed to air or surrounded by an oil matrix, wind and acoustically levitated droplets, droplets in a continuous flow diffusion chamber (CFDC), the Leipzig aerosol cloud interaction simulator (LACIS), and the aerosol interaction and dynamics in the atmosphere (AIDA) cloud chamber. Observed time dependent isothermal frozen fractions exhibiting non-exponential behavior with time can be readily explained by this model considering varying ISA. An apparent cooling rate dependence ofJhet is explained by assuming identical ISA in each droplet. When accounting for ISA variability, the cooling rate dependence of ice nucleation kinetics vanishes as expected from classical nucleation theory. The model simulations allow for a quantitative experimental uncertainty analysis for parameters Ntot, T, RH, and the ISA variability. In an idealized cloud parcel model applying variability in ISAs for each droplet, the model predicts enhanced immersion freezing temperatures and greater ice crystal production compared to a case when ISAs are uniform in each droplet. The implications of our results for experimental analysis and interpretation of the immersion freezing process are discussed.

scholarly journals Analysis of a risk prevention document using depend ability techniques: a first step towards an effectiveness model

2017 ◽  
Author(s):  
Laetitia Ferrer ◽  
Corinne Curt ◽  
Jean-Marc Tacnet
Keyword(s):  
Failure Modes ◽  
Communication Effectiveness ◽  
Decision Support Model ◽  
Analytical Methodology ◽  
Regulatory Constraints ◽  
Effectiveness Model ◽  
Main Challenge ◽  
Technical Functions ◽  
The Impact ◽  
The Way

Abstract. Major hazard prevention is a main challenge given than it's particularly based on information communicated to the general public. In France, preventive information is provided by the way of a regulatory document named DICRIM (In French Document d'Information Communal sur les Risques Majeurs that means in English Municipal Information Document on Major Risks). It is made by mayors and addressed to the public in order to provide information on major hazards affecting their municipalities. Unfortunately, the law imposes only few specifications concerning its content therefore one can question the impact on the general population relative to the way it is concretely realized. Ergo, the purpose of our work is to propose an analytical methodology to evaluate preventive risk communication effectiveness and apply it to the DICRIM. The methodology is based on dependability approaches. EFA (External Functional Analysis) permits the identification of (i) the service and technical functions involved, and (ii) the form, content and regulatory constraints of a DICRIM. FMEA (Failure Modes and Effects Analysis) is used to define the dysfunctions and detection elements are then listed to evaluate conformity with the 3 types of constraint. The outputs are validated by experts from the different fields investigated. Those results are obtained in order to build in future works a decision support model for the municipality (or specialized consulting firms) in charge of drawing up documents. The method is applied to a database of 30 DICRIMs. This analysis leads to a discussion on points such as usefulness of the elements missing.

scholarly journals Atomic-scale viscoplasticity mechanisms revealed in high ductility metallic glass films

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Hosni Idrissi ◽  
Matteo Ghidelli ◽  
Armand Béché ◽  
Stuart Turner ◽  
Sébastien Gravier ◽  
...  
Keyword(s):  
Metallic Glass ◽  
Metallic Glasses ◽  
Shear Banding ◽  
Atomic Scale ◽  
Microscopy Imaging ◽  
Rate Dependent ◽  
Imaging And Spectroscopy ◽  
Shear Transformation Zones ◽  
The Impact ◽  
Glass Films

Abstract The fundamental plasticity mechanisms in thin freestanding Zr65Ni35 metallic glass films are investigated in order to unravel the origin of an outstanding strength/ductility balance. The deformation process is homogenous until fracture with no evidence of catastrophic shear banding. The creep/relaxation behaviour of the films was characterized by on-chip tensile testing, revealing an activation volume in the range 100–200 Å3. Advanced high-resolution transmission electron microscopy imaging and spectroscopy exhibit a very fine glassy nanostructure with well-defined dense Ni-rich clusters embedded in Zr-rich clusters of lower atomic density and a ~2–3 nm characteristic length scale. Nanobeam electron diffraction analysis reveals that the accumulation of plastic deformation at room-temperature correlates with monotonously increasing disruption of the local atomic order. These results provide experimental evidences of the dynamics of shear transformation zones activation in metallic glasses. The impact of the nanoscale structural heterogeneities on the mechanical properties including the rate dependent behaviour is discussed, shedding new light on the governing plasticity mechanisms in metallic glasses with initially heterogeneous atomic arrangement.

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