Identification and Frequency Dependence of Viscoelastic Parameters during Dynamic Creep Tests on Selected Pome Fruits

In this paper, a novel control-loop concept is presented to investigate the viscoelastic properties of different pome fruits. Repeated mechanical effects are one of the most important risk factors during the postharvest procedures, so our work aimed to expand knowledge in the field. The actual investigations involved Golden Delicious apples and Packham pears. The developed model is based on the Poynting–Thomson body and, during the validating dynamic creep tests, different repeated compressive loads were applied. The examined frequencies were chosen from the most common components of the frequency distribution during the transportation process; the given range is responsible for the highest volume of fruit damage and the most extensive losses. The identified mathematical system determines the viscoelastic model parameters with the best fit to the measured creep data. The model properties of the tested fruit textures are compared in six different frequency setups, with the inspected pome species showing different elastic and viscous responses for the adjusted load conditions. The custom testing device with variable load functions and the proposed solution allow system identification with a wide range of setup possibilities. The resulted viscoelastic parameters can be used for further failure analysis and for the comparison of different pome fruit materials.

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Creep Modelling of Rootstock during Holding in Watermelon Grafting

Agriculture ◽

10.3390/agriculture11121266 ◽

2021 ◽

Vol 11 (12) ◽

pp. 1266

Author(s):

Kang Wu ◽

Jianzhong Lou ◽

Chen Li ◽

Wei Luo ◽

Congcong Li ◽

...

Keyword(s):

Creep Deformation ◽

Viscoelastic Model ◽

Mechanical Damage ◽

Viscoelastic Behavior ◽

Damage Mechanism ◽

Deformation Characteristics ◽

Mechanical Compression ◽

Creep Tests ◽

Viscoelastic Parameters ◽

Test Velocity

The fragile structure of a rootstock predisposes the stem to mechanical damage during grafting. Thus, it is necessary to take into account the rootstock’s rheological properties under mechanical compression when designing a clamping mechanism. This study focused on cucurbit, a typical rootstock for watermelon grafting. Firstly, we adopted a four-element Burgers model to analyze viscoelastic behavior and deformation characteristics of the rootstock, then conducted creep tests to obtain the parameters of the viscoelastic model. Next, we developed a model for the rootstock during holding based on viscoelastic parameters, loading force and contact time. Moreover, we evaluated the effect of various loading forces and test velocities on creep deformation to reveal the least damage on the rootstock. Results showed that the influence of loading force on the creep deformation was greater than test velocity. Finally, the holding test indicated that the clamping mechanism with silicone rubber can effectively prevent the damage to the stem. Specifically, the loading force should be controlled below 4 N to reduce the associated damage. Taken together, our findings provide a theoretical basis for analyzing the holding damage mechanism during watermelon grafting.

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Influence of Aging on Viscoelastic Response of Asphalt Mixture

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.255-260.3350 ◽

2011 ◽

Vol 255-260 ◽

pp. 3350-3353

Author(s):

Pei Long Li ◽

Zhan Ding ◽

Zheng Qi Zhang

Keyword(s):

Viscoelastic Model ◽

Asphalt Mixture ◽

Aging Effect ◽

Asphalt Mixtures ◽

Model Parameters ◽

Viscoelastic Response ◽

Short Term ◽

Viscoelastic Parameters ◽

Static Creep

Two gradations of asphalt mixtures were conducted to short term and long term aging tests. And then, static creep test was implemented on the samples of mixture. According to creep compliance curves from the stress-strain relations, Burgers viscoelastic model parameters were got to analyze the influences of aging effect on the viscoelastic response of asphalt mixture. The results and analysis indicated that aging is an important reason introducing viscoelasticity changes of asphalt mixture. For aged asphalt mixtures, the stiffness increases, the flexibility declines, the instantaneous elastic and the viscous compliance decrease. But short-term aging and long-term aging have different effects. And the viscoelastic parameters of the asphalt mixture with large voids vary more significantly, so aging process is much faster.

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Mechanical Behavior of Liquid Nitrile Rubber-Modified Epoxy Resin under Static and Dynamic Loadings: Experimental and Constitutive Analysis

Materials ◽

10.3390/ma11091565 ◽

2018 ◽

Vol 11 (9) ◽

pp. 1565 ◽

Cited By ~ 2

Author(s):

Xiao Xu ◽

Shiqiao Gao ◽

Zhuocheng Ou ◽

Haifu Ye

Keyword(s):

Epoxy Resin ◽

Dynamic Compression ◽

Viscoelastic Model ◽

Nitrile Rubber ◽

Elastic Behavior ◽

Model Parameters ◽

Strain Rates ◽

Nonlinear Viscoelastic ◽

Wide Range ◽

Nonlinear Viscoelastic Model

Quasi-static and dynamic compression experiments were performed to study the influence of liquid nitrile rubber (LNBR) on the mechanical properties of epoxy resin. The quasi-static experiments were conducted by an electronic universal machine under strain rates of 0.0001/s and 0.001/s, while a Split Hopkinson Pressure Bar (SHPB) system was adopted to perform the dynamic tests for strain rates up to 5600/s. The standard Zhu-Wang-Tang (ZWT) nonlinear viscoelastic model was chosen to predict the elastic behavior of LNBR/epoxy composites under a wide range of strain rates. After some necessary derivation and data fitting, a set of model parameters for the tested materials were finally obtained. Meanwhile, the incremented form of the ZWT nonlinear viscoelastic model were deduced and implemented into the user material program of LS-DYNA. A simulation-test contrast had been performed to verify the validity and feasibility of the algorithm. The results showed that the viscoelastic behavior of epoxy resin can be effectively simulated.

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Inferring Linkage Disequilibrium Between a Polymorphic Marker Locus and a Trait Locus in Natural Populations

Genetics ◽

10.1093/genetics/156.1.457 ◽

2000 ◽

Vol 156 (1) ◽

pp. 457-467 ◽

Cited By ~ 1

Author(s):

Z W Luo ◽

S H Tao ◽

Z-B Zeng

Keyword(s):

Linkage Disequilibrium ◽

Allele Frequency ◽

Random Mating ◽

Natural Populations ◽

Polymorphic Marker ◽

Marker Locus ◽

Model Parameters ◽

Phenotypic Variance ◽

Wide Range ◽

Trait Locus

Abstract Three approaches are proposed in this study for detecting or estimating linkage disequilibrium between a polymorphic marker locus and a locus affecting quantitative genetic variation using the sample from random mating populations. It is shown that the disequilibrium over a wide range of circumstances may be detected with a power of 80% by using phenotypic records and marker genotypes of a few hundred individuals. Comparison of ANOVA and regression methods in this article to the transmission disequilibrium test (TDT) shows that, given the genetic variance explained by the trait locus, the power of TDT depends on the trait allele frequency, whereas the power of ANOVA and regression analyses is relatively independent from the allelic frequency. The TDT method is more powerful when the trait allele frequency is low, but much less powerful when it is high. The likelihood analysis provides reliable estimation of the model parameters when the QTL variance is at least 10% of the phenotypic variance and the sample size of a few hundred is used. Potential use of these estimates in mapping the trait locus is also discussed.

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Antifungal Activity of Propyl Disulfide from Neem (Azadirachta indica) in Vapor and Agar Diffusion Assays against Anthracnose Pathogens (Colletotrichum gloeosporioides and Colletotrichum acutatum) in Mango Fruit

Microorganisms ◽

10.3390/microorganisms9040839 ◽

2021 ◽

Vol 9 (4) ◽

pp. 839

Author(s):

Muhammad Rafiullah Khan ◽

Vanee Chonhenchob ◽

Chongxing Huang ◽

Panitee Suwanamornlert

Keyword(s):

Antifungal Activity ◽

Mycelial Growth ◽

Colletotrichum Gloeosporioides ◽

Colletotrichum Acutatum ◽

Model Parameters ◽

Pathogenicity Test ◽

Agar Diffusion ◽

Wide Range ◽

Significant Difference ◽

Diffusion Assay

Microorganisms causing anthracnose diseases have a medium to a high level of resistance to the existing fungicides. This study aimed to investigate neem plant extract (propyl disulfide, PD) as an alternative to the current fungicides against mango’s anthracnose. Microorganisms were isolated from decayed mango and identified as Colletotrichum gloeosporioides and Colletotrichum acutatum. Next, a pathogenicity test was conducted and after fulfilling Koch’s postulates, fungi were reisolated from these symptomatic fruits and we thus obtained pure cultures. Then, different concentrations of PD were used against these fungi in vapor and agar diffusion assays. Ethanol and distilled water were served as control treatments. PD significantly (p ≤ 0.05) inhibited more of the mycelial growth of these fungi than both controls. The antifungal activity of PD increased with increasing concentrations. The vapor diffusion assay was more effective in inhibiting the mycelial growth of these fungi than the agar diffusion assay. A good fit (R2, 0.950) of the experimental data in the Gompertz growth model and a significant difference in the model parameters, i.e., lag phase (λ), stationary phase (A) and mycelial growth rate, further showed the antifungal efficacy of PD. Therefore, PD could be the best antimicrobial compound against a wide range of microorganisms.

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A Reinforcement Learning Framework for Spiking Networks with Dynamic Synapses

Computational Intelligence and Neuroscience ◽

10.1155/2011/869348 ◽

2011 ◽

Vol 2011 ◽

pp. 1-12 ◽

Cited By ~ 3

Author(s):

Karim El-Laithy ◽

Martin Bogdan

Keyword(s):

Reinforcement Learning ◽

Spike Timing ◽

Neural Representation ◽

Model Parameters ◽

Learning Framework ◽

Reference Target ◽

Wide Range ◽

Spiking Network ◽

Dynamic Synapses ◽

Exclusive Or

An integration of both the Hebbian-based and reinforcement learning (RL) rules is presented for dynamic synapses. The proposed framework permits the Hebbian rule to update the hidden synaptic model parameters regulating the synaptic response rather than the synaptic weights. This is performed using both the value and the sign of the temporal difference in the reward signal after each trial. Applying this framework, a spiking network with spike-timing-dependent synapses is tested to learn the exclusive-OR computation on a temporally coded basis. Reward values are calculated with the distance between the output spike train of the network and a reference target one. Results show that the network is able to capture the required dynamics and that the proposed framework can reveal indeed an integrated version of Hebbian and RL. The proposed framework is tractable and less computationally expensive. The framework is applicable to a wide class of synaptic models and is not restricted to the used neural representation. This generality, along with the reported results, supports adopting the introduced approach to benefit from the biologically plausible synaptic models in a wide range of intuitive signal processing.

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Modelling the Inflation and Elastic Instabilities of Rubber-Like Spherical and Cylindrical Shells Using a New Generalised Neo-Hookean Strain Energy Function

Journal of Elasticity ◽

10.1007/s10659-021-09823-x ◽

2021 ◽

Author(s):

Afshin Anssari-Benam ◽

Andrea Bucchi ◽

Giuseppe Saccomandi

Keyword(s):

Experimental Data ◽

Energy Function ◽

Limit Point ◽

Strain Energy ◽

Cylindrical Shells ◽

Strain Energy Function ◽

Model Parameters ◽

Wide Range ◽

Cylindrical Tubes ◽

Gent Model

AbstractThe application of a newly proposed generalised neo-Hookean strain energy function to the inflation of incompressible rubber-like spherical and cylindrical shells is demonstrated in this paper. The pressure ($P$ P ) – inflation ($\lambda $ λ or $v$ v ) relationships are derived and presented for four shells: thin- and thick-walled spherical balloons, and thin- and thick-walled cylindrical tubes. Characteristics of the inflation curves predicted by the model for the four considered shells are analysed and the critical values of the model parameters for exhibiting the limit-point instability are established. The application of the model to extant experimental datasets procured from studies across 19th to 21st century will be demonstrated, showing favourable agreement between the model and the experimental data. The capability of the model to capture the two characteristic instability phenomena in the inflation of rubber-like materials, namely the limit-point and inflation-jump instabilities, will be made evident from both the theoretical analysis and curve-fitting approaches presented in this study. A comparison with the predictions of the Gent model for the considered data is also demonstrated and is shown that our presented model provides improved fits. Given the simplicity of the model, its ability to fit a wide range of experimental data and capture both limit-point and inflation-jump instabilities, we propose the application of our model to the inflation of rubber-like materials.

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Study on Friction in Automotive Shock Absorbers Part 1: Friction Simulation Using a Dynamic Friction Model in the Contact Zone of an FEM Model

Vehicles ◽

10.3390/vehicles3020014 ◽

2021 ◽

Vol 3 (2) ◽

pp. 212-232

Author(s):

Ludwig Herzog ◽

Klaus Augsburg

Keyword(s):

Ride Comfort ◽

Viscous Friction ◽

Simulation Method ◽

Friction Model ◽

Model Parameters ◽

Dynamic Friction ◽

Friction Modeling ◽

Shock Absorbers ◽

Operation Conditions ◽

Wide Range

The important change in the transition from partial to high automation is that a vehicle can drive autonomously, without active human involvement. This fact increases the current requirements regarding ride comfort and dictates new challenges for automotive shock absorbers. There exist two common types of automotive shock absorber with two friction types: The intended viscous friction dissipates the chassis vibrations, while the unwanted solid body friction is generated by the rubbing of the damper’s seals and guides during actuation. The latter so-called static friction impairs ride comfort and demands appropriate friction modeling for the control of adaptive or active suspension systems. In this article, a simulation approach is introduced to model damper friction based on the most friction-relevant parameters. Since damper friction is highly dependent on geometry, which can vary widely, three-dimensional (3D) structural FEM is used to determine the deformations of the damper parts resulting from mounting and varying operation conditions. In the respective contact zones, a dynamic friction model is applied and parameterized based on the single friction point measurements. Subsequent to the parameterization of the overall friction model with geometry data, operation conditions, material properties and friction model parameters, single friction point simulations are performed, analyzed and validated against single friction point measurements. It is shown that this simulation method allows for friction prediction with high accuracy. Consequently, its application enables a wide range of parameters relevant to damper friction to be investigated with significantly increased development efficiency.

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Free volume based nonlinear viscoelastic model for polyurea over a wide range of strain rates and temperatures

Mechanics of Materials ◽

10.1016/j.mechmat.2020.103650 ◽

2021 ◽

Vol 152 ◽

pp. 103650

Author(s):

Chencheng Gong ◽

Yan Chen ◽

Ting Li ◽

Zhanli Liu ◽

Zhuo Zhuang ◽

...

Keyword(s):

Free Volume ◽

Viscoelastic Model ◽

Strain Rates ◽

Nonlinear Viscoelastic ◽

Wide Range ◽

Nonlinear Viscoelastic Model

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Identification of Nonlinear Viscoelastic Models of Flexible Polyurethane Foam From Uniaxial Compression Data

Journal of Engineering Materials and Technology ◽

10.1115/1.4032169 ◽

2016 ◽

Vol 138 (2) ◽

Cited By ~ 5

Author(s):

Yousof Azizi ◽

Patricia Davies ◽

Anil K. Bajaj

Keyword(s):

Uniaxial Compression ◽

Viscoelastic Model ◽

Viscoelastic Behavior ◽

Model Parameters ◽

Viscoelastic Models ◽

Nonlinear Viscoelastic ◽

Compression Data ◽

Computationally Intensive ◽

Nonlinear Viscoelastic Model ◽

Flexible Polyurethane

Flexible polyethylene foam is used in many engineering applications. It exhibits nonlinear and viscoelastic behavior which makes it difficult to model. To date, several models have been developed to characterize the complex behavior of foams. These attempts include the computationally intensive microstructural models to continuum models that capture the macroscale behavior of the foam materials. In this research, a nonlinear viscoelastic model, which is an extension to previously developed models, is proposed and its ability to capture foam response in uniaxial compression is investigated. It is hypothesized that total stress can be decomposed into the sum of a nonlinear elastic component, modeled by a higher-order polynomial, and a nonlinear hereditary type viscoelastic component. System identification procedures were developed to estimate the model parameters using uniaxial cyclic compression data from experiments conducted at six different rates. The estimated model parameters for individual tests were used to develop a model with parameters that are a function of strain rates. The parameter estimation technique was modified to also develop a comprehensive model which captures the uniaxial behavior of all six tests. The performance of this model was compared to that of other nonlinear viscoelastic models.

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