Fatigue and its effect on the piezopotential properties of gallium nitride nanowires

2021 ◽  
Author(s):  
Jin Zhang ◽  
Yao Du
Keyword(s):  
Gallium Nitride ◽  
Fatigue Loading ◽  
Md Simulations ◽  
Dielectric Constants ◽  
Molecular Structures ◽  
Defect Concentration ◽  
Dynamic Reliability ◽  
Material Parameters ◽  
Fatigue Process ◽  
Final Failure

Abstract The gallium nitride (GaN) nanowires (NWs) in piezotronic applications are usually under cyclic loading, which thus may inevitably suffer the mechanical fatigue. In this paper, the fatigue behaviours of defective GaN NWs are investigated by using molecular dynamics (MD) simulations. Our results show no significant changes in the molecular structures of GaN NWs until their final failure during the fatigue process. The final fracture occurring in the GaN NWs under fatigue loading is triggered by the crack that unusually initiates from the NW surface. The GaN NW with a smaller defect concentration or under the fatigue load with a smaller amplitude is found to possess a longer fatigue life. In addition, the ultimate fatigue strain of GaN NWs can be significantly increased by reducing the defect concentration of NWs. The material parameters including elastic constants, piezoelectric coefficients, and dielectric constants of GaN NWs in the fatigue test are evaluated through MD simulations, all of which are found to keep almost unchanged during the fatigue process. These material parameters together with the band gaps of GaN NWs extracted from first-principles calculations are employed in finite element calculations to investigate the piezopotential properties of GaN NWs under fatigue loading. No significant changes are found in the piezopotential properties of GaN NWs during the fatigue process, which indicates the long-term dynamic reliability of GaN NWs in piezotronic applications.

scholarly journals Modeling of Bimodular Bone Specimen under Four-Point Bending Fatigue Loading

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 474
Author(s):  
Yufan Yan ◽  
Xianjia Meng ◽  
Chuanyong Qu
Keyword(s):  
Compressive Strain ◽  
Fatigue Loading ◽  
Degradation Process ◽  
Neutral Axis ◽  
Image Correlation ◽  
Bending Test ◽  
Correlation Technique ◽  
Fatigue Process ◽  
Four Point Bending ◽  
Bone Properties

The fatigue damage behavior of bone has attracted significant attention in both the mechanical and orthopedic fields. However, due to the complex and hierarchical structure of bone, describing the damage process quantitively or qualitatively is still a significant challenge for researchers in this area. In this study, a nonlinear bi-modulus gradient model was proposed to quantify the neutral axis skewing under fatigue load in a four-point bending test. The digital image correlation technique was used to analyze the tensile and compressive strains during the fatigue process. The results showed that the compressive strain demonstrated an obvious two-stage ascending behavior, whereas the tensile strain revealed a slow upward progression during the fatigue process. Subsequently, a theoretical model was proposed to describe the degradation process of the elastic modulus and the movement of the neutral axis. The changes in the bone properties were determined using the FEM method based on the newly developed model. The results obtained from two different methods exhibited a good degree of consistency. The results obtained in this study are of help in terms of effectively exploring the damage evolution of the bone materials.

scholarly journals Analysis of Damage Evolution in Concrete under Fatigue Loading by Acoustic Emission and Ultrasonic Testing

Materials ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 341
Author(s):  
Marc Thiele ◽  
Stephan Pirskawetz
Keyword(s):  
Acoustic Emission ◽  
Elastic Modulus ◽  
Cyclic Loading ◽  
Fatigue Damage ◽  
Fatigue Loading ◽  
Measurement Methods ◽  
Material Structure ◽  
Fatigue Process ◽  
Acoustic Methods ◽  
Normal Strength

The fatigue process of concrete under compressive cyclic loading is still not completely explored. The corresponding damage processes within the material structure are especially not entirely investigated. The application of acoustic measurement methods enables a better insight into the processes of the fatigue in concrete. Normal strength concrete was investigated under compressive cyclic loading with regard to the fatigue process by using acoustic methods in combination with other nondestructive measurement methods. Acoustic emission and ultrasonic signal measurements were applied together with measurements of strains, elastic modulus, and static strength. It was possible to determine the anisotropic character of the fatigue damage caused by uniaxial loading based on the ultrasonic measurements. Furthermore, it was observed that the fatigue damage seems to consist not exclusively of load parallel oriented crack structures. Rather, crack structures perpendicular to the load as well as local compacting are likely components of the fatigue damage. Additionally, the ultrasonic velocity appears to be a good indicator for fatigue damage beside the elastic modulus. It can be concluded that acoustic methods allow an observation of the fatigue process in concrete and a better understanding, especially in combination with further measurement methods.

scholarly journals Application of Life-Dependent Material Parameters to Fatigue Life Prediction under Multiaxial and Non-Zero Mean Loading

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1587 ◽  
Author(s):  
Krzysztof Kluger ◽  
Aleksander Karolczuk ◽  
Szymon Derda
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Fatigue Loading ◽  
Mean Value ◽  
Multiaxial Fatigue ◽  
Fatigue Life Prediction ◽  
Test Results ◽  
Material Parameters ◽  
Fixed Material ◽  
Stress Ratios

This study presents the life-dependent material parameters concept as applied to several well-known fatigue models for the purpose of life prediction under multiaxial and non-zero mean loading. The necessity of replacing the fixed material parameters with life-dependent parameters is demonstrated. The aim of the research here is verification of the life-dependent material parameters concept when applied to multiaxial fatigue loading with non-zero mean stress. The verification is performed with new experimental fatigue test results on a 7075-T651 aluminium alloy and S355 steel subjected to multiaxial cyclic bending and torsion loading under stress ratios equal to R = −0.5 and 0.0, respectively. The received results exhibit the significant effect of the non-zero mean value of shear stress on the fatigue life of S355 steel. The prediction of fatigue life was improved when using the life-dependent material parameters compared to the fixed material parameters.

Study of Initial Stages of Fatigue Process Using Non-Destructive Testing Methods

2013 ◽  
Vol 592-593 ◽  
pp. 553-556
Author(s):  
František Vlasic ◽  
Josef Volák ◽  
Libor Nohál ◽  
Pavel Mazal ◽  
Filip Hort
Keyword(s):  
Acoustic Emission ◽  
Crack Nucleation ◽  
Electrical Potential ◽  
Fatigue Loading ◽  
Non Destructive Testing ◽  
Testing Methods ◽  
Destructive Testing ◽  
Fatigue Process ◽  
Cyclic Damage ◽  
Non Destructive

This paper deals with the basic research of cyclic damage during the initial stages of fatigue process using the non-destructive testing methods. The acoustic emission method was used for monitoring of the microstructure changes during fatigue loading. The electrical potential measurements of specimen and microscopic observation were used mainly to detect the first short cracks and their propagation. The fatigue tests at room temperature were conducted on titanium alloy and creep-resistant steel specimens under bending and tension loading. The aim of the study was to compare the acoustic emission signal at different types of loading until fracture and to analyze in detail the signal changes in initial stages of fatigue process. This analysis was primarily based on the waveform similarity and division into classes. The results show the high sensitivity of the acoustic emission technology in the transition from the stage of surface relief evolution to the stage of crack nucleation and propagation.

scholarly journals Polydopamine and eumelanin molecular structures investigated with ab initio calculations

2017 ◽  
Vol 8 (2) ◽  
pp. 1631-1641 ◽  
Author(s):  
Chun-Teh Chen ◽  
Francisco J. Martin-Martinez ◽  
Gang Seob Jung ◽  
Markus J. Buehler
Keyword(s):  
Molecular Dynamics ◽  
Density Functional Theory ◽  
Dft Calculations ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Density Functional ◽  
Md Simulations ◽  
Molecular Structures ◽  
Brute Force ◽  
Functional Theory

A set of computational methods that contains a brute-force algorithmic generation of chemical isomers, molecular dynamics (MD) simulations, and density functional theory (DFT) calculations is reported and applied to investigate nearly 3000 probable molecular structures of polydopamine (PDA) and eumelanin.

Diffusion of Epoxy Molecules on the Chemically Modified Graphene: A Molecular Dynamics Simulation Study

2015 ◽  
Vol 817 ◽  
pp. 803-808 ◽  
Author(s):  
Jian Wei Zhang ◽  
Cai Jiang ◽  
Gang Shi ◽  
Da Zhi Jiang
Keyword(s):  
Molecular Dynamics ◽  
Polymer Composites ◽  
Functional Groups ◽  
Md Simulations ◽  
Molecular Structures ◽  
Dynamics Simulation ◽  
Graphene Layers ◽  
Wall Structures ◽  
Modified Graphene ◽  
Main Factor

Buckypaper based polymer composites provides a new technical approach toward realizing conductive/structural multifunctional composites. Resin infiltration in the buckypaper is critical for the fabrication of buckypaper/polymer composites. To investigate the micro-infusion process of the polymer inside the paper, molecular dynamics (MD) simulations are conducted to study the diffusion behavior of epoxy molecules on the modified graphene and between graphene layers. The graphene molecular structures are constructed to represent the wall structures of the carbon nanotubes. Diffusion coefficients of the epoxy molecules on the graphene modified with different functionalization densities and interlayer distances are calculated. The results indicate that the functional groups increase the interfacial interactions between the epoxy molecules and graphene, however, largely decrease the diffusion speeds of the epoxy molecule. The simulations on the graphene layer systems indicate that, the viscous resistance of the resin is the main factor for retarding the diffusion of the epoxy molecules for the unmodified graphene layers; while for the modified graphene layers, functional groups are the main factor for retarding the resin diffusion

scholarly journals Multiscale Modeling of Amyloid Fibrils Formed by Aggregating Peptides Derived from the Amyloidogenic Fragment of the A-Chain of Insulin

2021 ◽  
Vol 22 (22) ◽  
pp. 12325
Author(s):  
Michał Koliński ◽  
Robert Dec ◽  
Wojciech Dzwolak
Keyword(s):  
Structure Prediction ◽  
Amyloid Fibrils ◽  
Md Simulations ◽  
Molecular Structures ◽  
Coarse Grained ◽  
Multi Scale ◽  
Modeling Procedure ◽  
Scale Modeling ◽  
Multi Scale Modeling ◽  
A Chain

Computational prediction of molecular structures of amyloid fibrils remains an exceedingly challenging task. In this work, we propose a multi-scale modeling procedure for the structure prediction of amyloid fibrils formed by the association of ACC1-13 aggregation-prone peptides derived from the N-terminal region of insulin’s A-chain. First, a large number of protofilament models composed of five copies of interacting ACC1-13 peptides were predicted by application of CABS-dock coarse-grained (CG) docking simulations. Next, the models were reconstructed to all-atom (AA) representations and refined during molecular dynamics (MD) simulations in explicit solvent. The top-scored protofilament models, selected using symmetry criteria, were used for the assembly of long fibril structures. Finally, the amyloid fibril models resulting from the AA MD simulations were compared with atomic force microscopy (AFM) imaging experimental data. The obtained results indicate that the proposed multi-scale modeling procedure is capable of predicting protofilaments with high accuracy and may be applied for structure prediction and analysis of other amyloid fibrils.

Optical Reflectance Studies of Stage 1-6 Graphite-Fecl3 Intercalation Compounds

1982 ◽  
Vol 20 ◽  
Author(s):  
D. S. Smith ◽  
P. C. Eklund
Keyword(s):  
Free Carrier ◽  
Dielectric Constants ◽  
Intercalation Compounds ◽  
Interband Absorption ◽  
Optical Reflectance ◽  
Material Parameters ◽  
Important Material ◽  
Stage 1 ◽  
Reflectance Measurements ◽  
Frequency Dependences

ABSTRACTResults of Optical Reflectance measurements on stage 1-6 graphite-FeCl3 intercalation compounds are reported. The frequency dependences of the dielectric constants(∊1, ∊2) are determined. The contributions from free carrier and interband absorption are separated to determine important material parameters.

The Stochastic Dynamic Reliability Research on Nonlinear Pile-Soil-Structure Interaction System with Uncertain Parameters

2011 ◽  
Vol 243-249 ◽  
pp. 5764-5767
Author(s):  
Ai Hong Zhou ◽  
Ying Yuan ◽  
Bai Qing Xu
Keyword(s):  
Pile Foundation ◽  
Soil Structure ◽  
Soil Structure Interaction ◽  
Stochastic Dynamic ◽  
Uncertain Parameters ◽  
Soil Material ◽  
Dynamic Reliability ◽  
Structure Interaction ◽  
Material Parameters ◽  
Interaction System

According to the damage characteristics of pile-soil-structure interaction system subjected to the earthquake, the seismic design method of using the dual design guideline of strength and deformation and taking the same reliability for both pile foundation and superstructure was put forward. The stochastic dynamic reliability of pile-soil-structure interaction system with uncertain parameters was studied on the basis of the randomness of earthquake, the nonlinearity of soil material parameters, and especailly the variability of soil material parameters. The results show that the control indexes of pile foundation and superstructure decreases with the increases of failure probability and the variation of material parameters will make the pile foundation structure partial unsafe.

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