Elastic Impact Research Articles

Investigating the hydrolytic degradation of PLA/PCL/ZnO nanocomposites by using viscoelastic models

AbstractIn this research, the degradation of a polymer blend in the presence of nanoparticles by considering the effect of nanoparticles on the degradation was investigated using emulsion models and fractional Zener model for the first time. Poly(lactic acid)/poly(caprolactone)/zinc oxide nanocomposite blends were prepared using the melt mixing method. Interface complex shear modulus for the neat polymer blend and its nanocomposites were calculated using emulsion models in a range of frequencies. All competing factors imposing elasticity on the systems, including the solid‐like behavior and degradation catalytic activity of ZnO nanoparticles in the presence of polyesters, were considered. After comparing the interface complex shear modulus of samples, it was revealed that the negative elastic impact of ZnO (degradation role) governs the viscoelastic behavior of these systems. Accordingly, the samples containing ZnO nanoparticles exhibited low elasticity, which was attributed to overcoming the degradation role of ZnO compared with the hydrodynamic interaction of ZnO nanoparticles. Additionally, the results obtained from the fractional Zener model were in good harmony with the emulsion model analysis.

Hygrothermal aging effect on the properties of PMMA nanocomposites reinforced by ceramic nanoparticles

This paper aimed to evaluate hygrothermal aging effects on polymethyl methacrylate modified with TiO2, SiO2, and Al2O3 nanoparticles in 0.5, 1, and 2% weight fractions. The distribution of nanoparticles was characterized by the scanning electron microscopy (SEM) method. Moisture absorption behavior and mechanical properties of samples in terms of elastic modulus, tensile strength, impact strength, and hardness were investigated. Furthermore, the coefficient of hygrothermal expansion (CHE) for each sample was calculated thanks to experimental data. Finally, by applying the multi-criteria decision making (MCDM) technique, the optimum composition for superior performance was obtained in 0.5 wt% of nanoparticles, more specifically for SiO2.

Experimental and Numerical Simulation of Coal Rock Impact Energy Index Based on Peridynamics

In response to the increasing severity of the rock burst phenomenon and its relatively difficult prediction, peridynamics and indoor uniaxial compression experiments were used to calculate the changes of the internal elastic energy (t) and impact energy (c) for different rock masses during a loading process from an energy perspective. Two traditional indices for judging rock burst tendency—the rock elastic deformation energy index (WET) and the rock impact energy index (WCF)—were combined to define a new actual impact energy index (W) to more accurately determine the occurrence tendency of rock bursts. The LAMMPS software was used to simulate the internal energy changes of rock materials under pressure, and the results were compared with experimental results for verification. The results were as follows: (1) in the uniaxial compression experiments of different specimens, fine sandstone had the strongest impact resistance, followed by coarse sandstone, mudstone, bottom coal seam, and top coal seam, and the obtained material properties provide a reference for predicting the rock bursts of various rock types in practical engineering. (2) The values calculated using the actual impact energy index (W) and the simulation value were 1.75 and 1.77, respectively, which corresponded to a lower error than when the rock impact energy index (WCF) and the rock elastic deformation energy index (WET) were used individually. Thus, this index can better predict the rock burst. (3) The simulated specimen was subjected to a gradual increase in the internal stored elastic energy during compression, which gradually decreased after the ultimate compressive strength was exceeded. The degree of impact damage formed after macroscopic crushing occurred depended on its residual energy.

Measuring the effect of trade liberalisation on the consumption of non-renewable energy sources in Latin America & the Caribbean Countries

This article investigates the impact of trade openness on the consumption of fossil fuels for a panel of fourteen LAC countries over the period from 1990 to 2014. To this end, a PARDL model in unrestricted error-correction form is estimated. The results of the model regression point indicate that the impact of economic growth and elasticity of trade openness are statistically significant at the 1% level and contribute to increased consumption of fossil fuels in the LAC countries. However, the impact and elasticity of consumption of renewable energy are statistically significant at 1% and 5% levels and thus contribute to decreasing consumption of fossil fuels.

Influence of the Cellulose and Soft Wood Fibres on the Impact and Tensile Properties in Polypropylene Bio Composites

Investigation presents an experimental study of mechanical properties of hybrid bio-composites made from man-made cellulose fibres and soft wood microfiller embedded into polypropylene homopolymer matrix at different weight contents. Mechanical properties such as elastic modulus, tensile strength, and impact resistance of the reinforced composites determined for various total weight contents of both biobased fillers were used as the design parameters. The problem was solved by planning the experiments and response surfaces method. The results demonstrate that using the both filler types enhance the mechanical properties. The tensile modulus increases by ~115%. The bio-composite with the highest weight content of man-made cellulose fibres and the lowest content of soft wood microfibers possesses maximum tensile strength (more 66 MPa). Addition of man-made cellulose fibres demonstrate a significant influence on the impact resistance of the investigated composites.

Energy dissipation study in impact: From elastic and elastoplastic analysis in peridynamics

Contact models employed in the available peridynamic studies are generally based on the short-range repulsive force model. In this paper, we implement a Hertz model in the peridynamic model and analyze energy dissipation from normal elastic impact at low and high impact speeds. We also introduce a new model for elastoplastic contact in peridynamics and compare its results in terms of hysteresis in the load-displacement curves with corresponding Finite Element Method results. The results show that while the short-range repulsive force model in peridynamics gives results that are close to those from an elastic (Hertz) contact peridynamic model, in elastoplastic impact problems, however, it underestimates the plastic energy dissipation. The proposed elastoplastic contact model in peridynamics is more suitable for modeling impact problems in which plastic dissipation is significant.

Near-fiber nanomechanical mapping and impact failure mechanism of 3D braided composites subjected to thermo-oxidative environment

The macroscopic mechanical behaviors generally correlate with nanomechanical properties, especially elastic modulus. This paper presents the thermo-oxidative ageing effects on nanoscale elastic modulus and impact failure mechanism of 3D braided composites at micro and macro levels using PeakForce Quantitative Nano-Mechanics (PF-QNM) and digital image correlation (DIC) technologies. The values of nanoscale elastic modulus of near-fiber resin pocket were about three times than that of global modulus in neat resin under low-velocity impact compression (LVIC) loading. However, the modulus retention rates were consistent which was ∼88% after ageing for 16 days at 180 °C. The decline of them has provided a direct evidence for resin degradation after ageing. In addition, the in-plane impact failure mechanism of braided composites mainly contained five modes, i.e., matrix cracking, interface cracking, matrix fracture and peeling off, fiber buckling and slipping, and fiber breakage. Thermo-oxidative ageing only changed the crack propagation path but not the damage modes.

Investigation the effect of geometry and position of polymeric heart valves on hemodynamic with fluid-structure interaction numerical method

Computational modeling and numerical simulation of heart valve dynamics incorporating both fluid dynamics and valve structural replications has been challenging. In this study, we developed a double-coupled fluid-structure interaction (FSI) model using arbitrary lagrangian eulerian(ALE) and steered adaptive mesh(SAM). So we were looking to simulate transcatheter aortic valve (TAV) hemodynamic performance throughout entire cardiac cycles [1]. To reach this object, semi-real geometry of aorta and aortic polymeric valves has been created. At model inlet, left ventricular pressure and at the model outlet the elastic porous tube have been considered. Nonlinear finite element way and Sparse solver was utilized to couple fluid and solid equation. Consequently, extensive and comparative simulation were performed to investigate the impact of valve elasticity and valve positions on hemodynamics and solid parameters. Effective Orifice Area(EOA) also has been calculated [1]. The simulation results indicated that the lower of the elastic modulus cause to increase the EOA. Furthermore, the result of valve position showed, whenever the valve is closer to sinuses, a greater EOA and lower stresses impose on the leaflet are achievable.

Discontinuous dynamics of an asymmetric 2-DOF friction oscillator with elastic and rigid impacts

• An asymmetric 2 DOF oscillator with elastic and rigid impacts is investigated. • Negative feedback forces and nonlinear spring of cubic term are considered. • Switching conditions of motion at separation boundaries are explored. • Several typical motions are simulated numerically by MATLAB software. In this paper, by using flow switching theory of discontinuous dynamical systems , the discontinuous dynamic behavior of a 2-DOF (two-degree-of-freedom) friction oscillator with elastic impact and rigid impact on different sides is investigated. For the 2-DOF friction oscillator, when the direction of object’s velocity changes, the negative feedback works and the inequality of maximum static friction force and kinetic friction force leads to the existence of flow barriers. In addition, the elastic impact and rigid impact can change motion states of object, resulting in the discontinuity of this 2-DOF system. Considering the multiple motion states of object and better analyzing the equation of object’s motion, the phase space of each object is divided into different motion domains and boundaries in relative and absolute coordinates by means of the discontinuities resulted from the friction and impact. Moreover, because the elastic impact exists in a time period, there will be a variety of motion behaviors coexisting, such as elastic and rigid impacts occur simultaneously. With that in mind, in absolute coordinate system, the phase space of the system is divided in six cases according to whether there are stick motion and stuck motion. Based on flow switching theory, the switching conditions at discontinuous boundaries for all possible motions are given by using G-functions, and it should be noted that the vanishing conditions of the sliding motion become more complicated due to the existence of flow barriers at speed boundaries. Through defining the switching sets on separation boundaries, the mapping structures are further introduced to demonstrate the global dynamic behavior and periodic motions. For a better understanding of the object’s motion and the switching criteria at separation boundaries, the numerical simulation method is used to demonstrate several typical motions such as passable motion, sliding motion, grazing motion, stick motion (elastic impact), rigid impact and periodic motions etc. The results obtained have reference value for the optimization design and noise control of mechanical systems with gap couplings and negative feedbacks.

Dissipative joints under impact loadings

AbstractUnforeseen and unpredictable exceptional events can lead to abnormal loading distribution in the structures; however, in such situation, structures have to withstand additional loadings to avoid disproportionate damage and progressive collapse. Impact loadings are among the exceptional events that a structure can experience during its lifetime. In order to give a contribution to the research on impulsive loading on structural joints, this work focuses on the behavior of slide hinge joints (SHJ) with a Symmetric Friction Damper (SFD) under drop weight impact tests. Six drop weight impact tests on a double‐sided beam‐to‐column joints were performed and a 3D finite element model was created and validated in ABAQUS/CAE Explicit. The model includes the calibration of material damage, correlating the equivalent plastic strain to the stress triaxiality, damping of the system, calibrated on elastic impact tests using Rayleigh's classical damping and strain rate sensitivity through the Johnson Cook model. Furthermore, a parametric analysis was performed in order to investigate the influence of three parameters on the joint behavior: the impact velocity, the impact mass and the impact energy. The energy is used to estimate the dissipation rate of the joint, which can be considered as a reliable parameter to quantify the joint behavior under drop weight impact.

The Minkowski overlap and the energy‐conserving contact model for discrete element modeling of convex nonspherical particles

AbstractA unified contact overlap, termed the Minkowski overlap, between any two shapes is proposed in this article. This overlap is based on the concept of the Minkowski difference of two shapes, and particularly on the equivalence between the contact state of the two shapes and the location of the origin relative to their Minkowski difference. The Minkowski contact features of a contact, including the overlap, normal direction, and contact points, are also defined for convex shapes. In particular, an important property of the Minkowski overlap is introduced which lays the solid theoretical foundation for proposing a Minkowski overlap based energy‐conserving contact model in the current work. The energy‐conserving property for cases where the contact normal direction and point may be subject to discrete changes is also rigorously proved. For convex particles, the computational procedures combining both GJK and EPA algorithms are outlined, and uniqueness and ambiguity issues associated with some special cases are clarified and resolved. The elastic energy conservation of the proposed contact model for convex shapes in elastic impact is further verified using two numerical examples, and two more examples involving more convex particles with different sizes and shapes are also conducted to demonstrate the robustness and applicability of the proposed Minkowski overlap contact model and the computational procedures.

Elastic impact of sphere on large plate

Different from the Hertz impact, a sphere impacting on a plate has an extra dissipation by the flexural wave propagating on the plate. This wave dissipation has been noticed by Zener (1941), who introduced this dissipation term into the governing equation. Because of this extra dissipation term by the flexural wave, the Zener equation cannot be treated as the same way as in the Hertz impact problem. As a result, in the past 80 years, except few numerical tries for Zener equation, no analytical solution has been provided for the evolution of compressive displacement or contact force during the Zener impact. In this paper, by using homotopy analysis method, we analytically solved the Zener impact problem. After constructing an auxiliary linear operator, we derived an analytical solution for the evolution of contact force up to the first order of the embedding homotopy parameter. Present model can take full account of the elongation of contact time by plate compliance, which is impossible by using Hertz impact model. Comparisons with finite element simulation show that the prediction of the contact force history is of high accuracy. With the solution of force history, we derived an explicit expression for the energy loss of Zener type, this Zener loss has a different dependence on the impact velocity as the Hunter loss does. Also, both the motions of the sphere and the plate are able to be predicted with high accuracy. In addition, with the zeroth-order solution, we derived explicit expressions for both the coefficient of restitution and the contact duration.

A Viscoelastic Contact Analysis of the Ground Reaction Force Differentiation in Walking and Running Gaits Realized in the Simplified Horse Leg Model Focusing on the Hoof—Ground Interaction

In the present study, the systematic method for the forward dynamics associated with the ground contact model was introduced to be able to consider the viscoelastic effect when contacting with the ground. In particular, we focused on the hoof-ground interaction in the simplified horse leg model because walking and running gaits are known to be different in trajectories; however, the force analysis still remains as unsolved issues. The computational experiments in Matlab, elastic and inelastic impact with the ground was resolved by using the dissipative contact force model proposed by Lankarani and Nikravesh and the ground reaction force was clearly examined in four different conditions from the combination of walking/running and elastic/inelastic contact. As result, two peaks during the stance phase in the walking condition were realized as well as the human gait and a single peak was newly observed in running with a time gap in elastic and inelastic condition. The proposed method contributes to the establishment of the detail time course analysis of the ground reaction force for animal and human gaits in a consistent manner.

Bi-level pricing and inventory strategies for perishable products in a competitive supply chain

This paper aims to develop a new bi-level game model for joint pricing and inventory decisions in a competitive supply chain consisting of a dominant manufacturer, who produces single perishable product from deteriorating raw materials, and two follower retailers who face nonlinear price-dependent demand and operate under Cournot assumptions. Three levels of warehousing including raw material warehouse, final product warehouse, and retail warehouses with exponential deterioration rates are considered to explore the joint impact of deterioration rate and price elasticity on the equilibrium inventory decisions. A Stackelberg–Nash–Cournot model is developed to seek the equilibrium prices, quantities, and replenishment cycles and is solved through an exact methodology. A numerical example is presented to validate the proposed model and comprehensive sensitivity analyses are carried out to measure the impact of the model’s key parameters including the deterioration rate in the producer’s and the retailers’ warehouses, the retail and competitor price elasticity, and the market scale on the equilibrium.

Peak states of molybdenum single crystals shock compressed to high stresses

To determine crystal anisotropy effects at high stresses, peak states behind the plastic shock waves were examined in BCC single crystals. Using plate impact experiments, molybdenum (Mo) single crystals were shock compressed up to 190 GPa elastic impact stress along [100], [110], and [111] orientations. Laser interferometry was used to measure wave velocities and particle velocity profiles at the Mo–LiF window interface. These data were analyzed to obtain in-material quantities in the peak states. The Hugoniots for [100] and [110] orientations were comparable, but the Hugoniot for the [111] orientation was different from the other two orientations. Also, these Mo single crystal Hugoniots display differences from the polycrystalline Mo Hugoniots. Although none of the differences can be considered large, the present results demonstrate that, unlike FCC metal single crystals (Cu, Al), some anisotropy is preserved in Mo single crystal Hugoniots even at high stresses.

Impact of capacity mechanisms and demand elasticity on generation adequacy with risk-averse generation companies

While on-going and future developments will likely increase the short-term elasticity of the electricity demand, capacity markets are often put forward as a possible remedy to ensure generation adequacy. In this paper, we provide a model formulation of a stochastic non-cooperative capacity planning problem reflecting short-term elastic energy demand, risk-averse investors, and a capacity market. The Conditional-Value-At-Risk is used as a coherent risk-measure. For solving the model, we deploy an Alternating Direction Method of Multipliers. We analyze the impact of short-term demand elasticity on the social welfare, agents’ surpluses, and Loss-of-Load-Expectation of an energy-only market and a market complemented by a capacity market. Moreover, we consider the impact of set capacity targets. For the energy-only market, we show that short-term demand elasticity even amplifies the negative effect of risk aversion on social welfare. A capacity market can be used to hedge against the negative effects of risk aversion, even if the capacity target is not set ideally. Furthermore, we show that a capacity market can be used to mitigate welfare transfer to investors and lower the loss-of-load-expectation induced by scarcity times.

Country competitiveness and investment allocation in the mining industry: A survey of the literature and new empirical evidence

Mining exploration investment is the primary driver of future mining production. Without exploration investment, it is not possible to sustain metal production. Countries with higher mining competitiveness will tend to attract larger amounts of exploration investments. According to the so-called “traditional” view, a country's geological potential is a crucial determinant of its mining competitiveness. This proposition implies that the geological potential would be the primary driver for allocating exploration investments worldwide. Recently, an “alternative” view of mining competitiveness emerged. According to this hypothesis, a country's investment climate is the primary determinant of its mining competitiveness. However, the empirical evidence supporting the “alternative” view is still scarce.This article aims to analyze the validity of these two competing views. First, we survey the literature on the subject to identify the main determinants of total mining exploration expenditure, which is the leading indicator of mining competitiveness identified in the literature. Second, to analyze the total mining exploration expenditure's determinants, we develop an exponential mean model to test the “alternative” view. We use the Poisson Pseudo-Maximum Likelihood (PPML) method to obtain the parameter estimates, considering our dependent variable's non-linear and skewed nature.Working with a cross-sectional dataset of 72 countries for 2014, we find strong empirical support for the “alternative” view of mining competitiveness. Total budgeted mining exploration expenditure is positively determined by two location factors: countries' geological potential and investment climate. Besides, we analyze the impact of two additional drivers on mining competitiveness: social conflicts and population density. These variables have a statistically significant negative effect on mining competitiveness. Likewise, we estimate regional average elasticities to measure the drivers’ impact on mining competitiveness in North America, Oceania, Europe, Latin America, Asia, and Africa. The effects of these drivers vary enormously across world regions. Finally, we show that the investment climate has a strong elastic impact on attracting mining exploration investments in all the distribution deciles through a quintile analysis. Simultaneously, the geological potential triggers a relevant but still inelastic effect starting in the sixth decile. Our findings can help policymakers and business people to develop strategic plans to attract mining investments and promote economic growth in different jurisdictions.

Modelling utility-aggregator-customer interactions in interruptible load programmes using non-cooperative game theory

Aggregator-activated demand response (DR) is widely recognised as a viable means for increasing the flexibility of renewable and sustainable energy systems (RSESs) necessary to accommodate a high penetration of variable renewables. To this end, by acting as DR aggregators and offering energy trading capabilities to smaller customers, energy retailers unlock additional sources of demand-side flexibility to ensure the cost-optimal operation of RSESs. Accordingly, a growing body of literature has highlighted the ways in which non-cooperative game theory could be used to reduce the gaps between modelled and real-world results for aggregator-mediated DR schemes. This paper aims to contribute to the trends of giving a realistic grounding to research on distributed DR-integrated energy scheduling by using insights from non-cooperative game theory to determine: (1) the optimal trade-off between importing electricity and utilising DR capacity in grid-tied RSESs, (2) the impact of the price elasticity of DR supply of different customer classes – especially, new sources of electricity demand, such as e-mobility – on the system-level dispatch of DR resources, and (3) the financial implications of harnessing the flexibility potential of a large number of end-consumers across different sectors. Accordingly, the principal goal of the paper is to develop an operational planning optimisation model that can be directly applied to real-world aggregator-mediated, market-based demand-side flexibility provisioning domains. To this end, this paper presents the first DR elasticity-aware, non-cooperative game-theoretic DR scheduling model that: (1) yields the best compromise solution between imported power and dispatched DR resources from the utility’s perspective, (2) characterises the utility-aggregator-customer interactions during the market-based DR trade process with several customer categories involved, and (3) disaggregates the total sectoral load on the system to individual end-consumers, which has potential implications for pre-feasibility and business case assessments. The application of the model to a conceptual micro-grid for the town of Ohakune, in New Zealand, demonstrates its effectiveness in reducing the daily system operational cost (over the critical peak hours) by ~66% and ~47% on a representative summer and winter day, respectively. Importantly, the paper provides statistically significant evidence supporting that activating the flexibility potential of small- to medium-scale end-consumers through specifically defined third-party aggregators in a market-based approach – that is aware of strategic interactions among instrumentally rational economic agents involved in the dispatch and delivery of DR resources – plays a significant role in the cost-optimal transition to 100%-renewable electricity generation systems within the smart grid paradigm.

Experimental study on mechanical properties of polypropylene nanocomposites reinforced with a hybrid graphene/PP-g-MA/kenaf fiber by response surface methodology

In this study, the mechanical properties of polypropylene (PP)-based nanocomposites reinforced with graphene nanosheets, kenaf fiber, and polypropylene-grafted maleic anhydride (PP-g-MA) were investigated. Response surface methodology (RSM) based on Box–Behnken design (BBD) was used as the experimental design. The blends fabricated in three levels of parameters include 0, 0.75, and 1.5 wt% graphene nanosheets, 0, 7.5, and 15 wt% kenaf fiber, and 0, 3, and 6 wt% PP-g-MA, prepared by an internal mixer and a hot press machine. The fiber length was 5 mm and was being constant for all samples. Tensile, flexural, and impact tests were conducted to determine the blend properties. The purpose of this research is to achieve the highest mechanical properties of the considered nanocomposite blend. The addition of graphene nanosheets to 1 wt% increased the tensile, flexural, and impact strengths by 16%, 24%, and 19%, respectively, and an addition up to 1.5 wt% reduced them. With further addition of graphene nanosheets until 1.5 wt%, the elastic modulus was increased by 70%. Adding the kenaf fiber up to 15 wt% increased the elastic modulus, tensile, flexural, and impact strength by 24%, 84%, 18%, and 11%, respectively. The addition of PP-g-MA has increased the adhesion, dispersion and compatibility of graphene nanosheets and kenaf fibers with matrix. With 6 wt% PP-g-MA, the tensile strength and elastic modulus were increased by 18% and 75%, respectively. The addition of PP-g-MA to 5 wt% increased the flexural and impact strengths by 10% and 5%, respectively. From the entire experimental data, the optimum values for elastic modulus, as well as, tensile, flexural, and impact strengths in the blends were obtained to be 4 GPa, 33.7896 MPa, 57.6306 MPa, and 100.1421 J/m, respectively. Finally, samples were studied by FE-SEM to check the dispersion of graphene nanosheets, PP-g-MA and kenaf fibers in the polymeric matrix.

Wind turbines in atmospheric flow: fluid–structure interaction simulations with hybrid turbulence modeling

Abstract. In order to design future large wind turbines, knowledge is needed about the impact of aero-elasticity on the rotor loads and performance and about the physics of the atmospheric flow surrounding the turbines. The objective of the present work is to study both effects by means of high-fidelity rotor-resolved numerical simulations. In particular, unsteady computational fluid dynamics (CFD) simulations of a 2.3 MW wind turbine are conducted, this rotor being the largest design with relevant experimental data available to the authors. Turbulence is modeled with two different approaches. On one hand, a model using the well-established technique of improved delayed detached eddy simulation (IDDES) is employed. An additional set of simulations relies on a novel hybrid turbulence model, developed within the framework of the present work. It consists of a blend of a large-eddy simulation (LES) model by Deardorff for atmospheric flow and an IDDES model for the separated flow near the rotor geometry. In the same way, the assessment of the influence of the blade flexibility is performed by comparing two different sets of computations. The first group accounts for a structural multi-body dynamics (MBD) model of the blades. The MBD solver was coupled to the CFD solver during run time with a staggered fluid–structure interaction (FSI) scheme. The second set of simulations uses the original rotor geometry, without accounting for any structural deflection. The results of the present work show no significant difference between the IDDES and the hybrid turbulence model. In a similar manner, and due to the fact that the considered rotor was relatively stiff, the loading variation introduced by the blade flexibility was found to be negligible when compared to the influence of inflow turbulence. The simulation method validated here is considered highly relevant for future turbine designs, where the impact of blade elasticity will be significant and the detailed structure of the atmospheric inflow will be important.