Mechanics of Crystalline Nanowires

MRS Bulletin ◽  
2009 ◽  
Vol 34 (3) ◽  
pp. 178-183 ◽  
Author(s):  
Harold S. Park ◽  
Wei Cai ◽  
Horacio D. Espinosa ◽  
Hanchen Huang
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Chemical Composition ◽  
Shape Memory ◽  
Volume Ratio ◽  
Building Blocks ◽  
Elastic Stiffness ◽  
Atomistic Simulations ◽  
One Dimensional ◽  
Future Challenges

AbstractNanowires are among the most exciting one-dimensional nanomaterials because of their unique properties, which result primarily from their chemical composition and large surface area to volume ratio. These properties make them ideal building blocks for the development of next generation electronics, opto-electronics, and sensor systems. In this article, we focus on the unique mechanical properties of nanowires, which emerge from surface atoms having different electron densities and fewer bonding neighbors than atoms lying within the nanowire bulk. In this respect, atomistic simulations have revealed a plethora of novel surface-driven mechanical behavior and properties, including both increases and decreases in elastic stiffness, phase transformations, shape memory, and pseudoelastic effects. This article reviews such atomistic simulations, as well as experimental data of these phenomena, while assessing future challenges and directions.

Shape memory alloy–actuated prestressed composites with application to morphing automotive fender skirts

2018 ◽  
Vol 30 (3) ◽  
pp. 479-494 ◽  
Author(s):  
Venkata Siva C Chillara ◽  
Leon M Headings ◽  
Ryohei Tsuruta ◽  
Eiji Itakura ◽  
Umesh Gandhi ◽  
...  
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Smart Materials ◽  
Design Procedure ◽  
Building Blocks ◽  
Smart Composite ◽  
Thermally Induced ◽  
One Dimensional ◽  
Flat Shape

This work presents smart laminated composites that enable morphing vehicle structures. Morphing panels can be effective for drag reduction, for example, adaptive fender skirts. Mechanical prestress provides tailored curvature in composites without the drawbacks of thermally induced residual stress. When driven by smart materials such as shape memory alloys, mechanically-prestressed composites can serve as building blocks for morphing structures. An analytical energy-based model is presented to calculate the curved shape of a composite as a function of force applied by an embedded actuator. Shape transition is modeled by providing the actuation force as an input to a one-dimensional thermomechanical constitutive model of a shape memory alloy wire. A design procedure, based on the analytical model, is presented for morphing fender skirts comprising radially configured smart composite elements. A half-scale fender skirt for a compact passenger car is designed, fabricated, and tested. The demonstrator has a domed unactuated shape and morphs to a flat shape when actuated using shape memory alloys. Rapid actuation is demonstrated by coupling shape memory alloys with integrated quick-release latches; the latches reduce actuation time by 95%. The demonstrator is 62% lighter than an equivalent dome-shaped steel fender skirt.

Conceptual Approach to Development, Structure Formation and Hardening Micro-Alloyed by Steels for the Metallurgical Tool

2020 ◽  
Vol 299 ◽  
pp. 658-663
Author(s):  
S.E. Krylova ◽  
Sergey V. Gladkovskii ◽  
E.V. Romashkov
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Chemical Composition ◽  
Structure Formation ◽  
Structural Parameters ◽  
Structural Transformations ◽  
Conceptual Approach ◽  
Phase And Structural Transformations ◽  
Technological Cycle ◽  
Development Structure

The scientific bases for the development of rational compositions and methods for hardening a large-sized metallurgical tool from micro-alloyed steels are stated. Based on the generalization of the experimental data, the regularities of phase and structural transformations at various stages of the technological cycle are revealed; the relationships between structural parameters, chemical composition and mechanical properties have been studied and described.

Computation of HAZ Hardness for Low Alloyed Welded Steels Using Five-Parameter Logistic Function

2014 ◽  
Vol 216 ◽  
pp. 103-109
Author(s):  
Marius Bodea ◽  
Radu Mureşan
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Chemical Composition ◽  
Heat Flow ◽  
Welding Process ◽  
Logistic Function ◽  
Steel Plates ◽  
Maximum Hardness ◽  
Welded Structures ◽  
Asymmetric Data

The mechanical properties of the welded structures are directly related to the weldability of the steels, thus the estimation of the microstructural constituents in the weld and maximum hardness in the HAZ according to the welding process parameters represent a problem of great interest. The microstructural changes in the HAZ are estimated using a five-parameter logistic function (5PL), which is very accurate in the fitting highly asymmetric data. Also, the same 5PL function can be used in order to predict hardness and toughness in the HAZ based on the heat flow, cooling rates between 800-500 oC and chemical composition of the material. A discussion about the parameters of the 5PL function and fitting experimental data is presented and a studied case for welding S355J2 steel plates is also analyzed.

scholarly journals Non-Reciprocal Wave Transmission in a Bilinear Spring-Mass System

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Zhaocheng Lu ◽  
Andrew N. Norris
Keyword(s):  
Wave Motion ◽  
Building Blocks ◽  
Elastic Stiffness ◽  
Spring Stiffness ◽  
Mass System ◽  
One Dimensional ◽  
Transmitted Pulse ◽  
Higher Dimensional ◽  
Significant Difference ◽  
Spatial Modulations

Abstract Significant amplitude-independent and passive non-reciprocal wave motion can be achieved in a one-dimensional (1D) discrete chain of masses and springs with bilinear elastic stiffness. Some fundamental asymmetric spatial modulations of the bilinear spring stiffness are first examined for their non-reciprocal properties. These are combined as building blocks into more complex configurations with the objective of maximizing non-reciprocal wave behavior. The non-reciprocal property is demonstrated by the significant difference between the transmitted pulse displacement amplitudes and energies for incidence from opposite directions. Extreme non-reciprocity is realized when almost-zero transmission is achieved for the propagation from one direction with a noticeable transmitted pulse for incidence from the other. These models provide the basis for a class of simple 1D non-reciprocal designs and can serve as the building blocks for more complex and higher dimensional non-reciprocal wave systems.

Constitutive Modeling of SMA in Constrained Recovery Mode

Aerospace ◽  
2006 ◽  
Author(s):  
Federica Daghia ◽  
Erasmo Viola ◽  
Thomas M. Seigler ◽  
Daniel J. Inman
Keyword(s):  
Experimental Data ◽  
Residual Stress ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Phenomenological Model ◽  
Constitutive Modeling ◽  
Low Temperatures ◽  
One Dimensional ◽  
Cooling Temperature ◽  
Loading Paths

Shape memory alloys (SMA) can develop large stresses in the constrained recovery mode. Heating generates tension in the material, depending upon the cooling temperature some residual stress may remain after actuation. Brinson's one dimensional phenomenological model can be used to predict the stress/temperature loading paths in constrained recovery; however the model shows some discrepancies with experimental data when the SMA is cooled at low temperatures. This paper examines this behavior and proposes a modification to the Brinson model that better represents constrained recovery at low temperatures.

UNCERTAINTY ANALYSIS OF A ONE-DIMENSIONAL CONSTITUTIVE MODEL FOR SHAPE MEMORY ALLOY THERMOMECHANICAL DESCRIPTION

2014 ◽  
Vol 06 (06) ◽  
pp. 1450067 ◽  
Author(s):  
SERGIO A. OLIVEIRA ◽  
MARCELO A. SAVI ◽  
ILMAR F. SANTOS
Keyword(s):  
Experimental Data ◽  
Shape Memory Alloy ◽  
Constitutive Model ◽  
Uncertainty Analysis ◽  
Numerical Simulations ◽  
Shape Memory ◽  
Tensile Tests ◽  
One Dimensional ◽  
Uncertainty Range ◽  
Constitutive Parameters

The use of shape memory alloys (SMAs) in engineering applications has increased the interest of the accuracy analysis of their thermomechanical description. This work presents an uncertainty analysis related to experimental tensile tests conducted with shape memory alloy wires. Experimental data are compared with numerical simulations obtained from a constitutive model with internal constraints employed to describe the thermomechanical behavior of SMAs. The idea is to evaluate if the numerical simulations are within the uncertainty range of the experimental data. Parametric analysis is also developed showing the most sensitive constitutive parameters that contribute to the uncertainty. This analysis provides the contribution of each parameter establishing the accuracy of the constitutive equations.

AN ALTERNATIVE TO PERIODIC HOMOGENIZATION FOR DENTIN ELASTIC STIFFNESS

2020 ◽  
Vol 20 (02) ◽  
pp. 1950081
Author(s):  
CHLOE ARSON ◽  
YANNICK YASOTHAN ◽  
ROMAIN JEANNERET ◽  
AURELIE BENOIT ◽  
NICOLAS ROUBIER ◽  
...  
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Environmental Scanning Electron Microscopy ◽  
Elastic Stiffness ◽  
Image Correlation ◽  
Testing Procedures ◽  
Order Of Magnitude ◽  
Transverse Isotropic ◽  
Homogenization Scheme ◽  
Resonant Ultrasound

Dentin, the main tissue of the tooth, is made of tubules surrounded by peri-tubular dentin (PTD), embedded in a matrix of inter-tubular dentin (ITD). The PTD and the ITD have different relative fractions of collagen and hydroxyapatite crystals. The ITD is typically less rigid than the PTD, which can be seen as a set of parallel hollow cylindrical reinforcements in the ITD matrix. In this paper, we extend Hashin and Rozen’s homogenization scheme to a nonuniform distribution of hollow PTD cylinders, determined from image analysis. We relate the transverse isotropic elastic coefficients of a Representative Elementary Volume (REV) of dentin to the elastic and topological properties of PTD and ITD. The model is calibrated against experimental data. Each sample tested is consistently characterized by Environmental Scanning Electron Microscopy (ESEM), nanoindentation and Resonant Ultrasound Spectroscopy (RUS), which ensures that macroscopic mechanical properties measured are correlated with microstructure observations. Despite the high variability of microstructure descriptors and mechanical properties, statistical analyses show that Hashin’s bounds converge and that the proposed model can be used for back-calculating the microscopic Poisson’s ratios of dentin constituents. Three-point bending tests conducted in the laboratory were simulated with the Finite Element Method (FEM). Elements were assigned transverse isotropic elastic parameters calculated by homogenization. The tubule orientation and the pdf of the ratio inner/outer tubule radius were determined in several zones of the beams before testing. The remainder of the micro-mechanical parameters were taken equal to those calibrated by RUS. The horizontal strains found experimentally by Digital Image Correlation (DIC) were compared to those found by FEM. The DIC and FEM horizontal strain fields showed a very good agreement in trend and order of magnitude, which verifies the calibration of the homogenization model. By contrast with previous studies of dentin, we fully calibrated a closed form mechanical model against experimental data and we explained the testing procedures. In elastic conditions, the proposed homogenization scheme gives a better account of microstructure variability than micro–macro dentin models with periodic microstructure.

Study of the character and causes of destruction of the cardan shaft of the propeller engine

2019 ◽  
Vol 85 (12) ◽  
pp. 43-50
Author(s):  
D. A. Movenko ◽  
L. V. Morozova ◽  
S. V. Shurtakov
Keyword(s):  
Mechanical Properties ◽  
Chemical Composition ◽  
Yield Point ◽  
Protective Coating ◽  
Fracture Pattern ◽  
Corrosion Cracking ◽  
Tempered Martensite ◽  
Neck Formation ◽  
Static Mechanism ◽  
Shaft Surface

The results of studying operational destruction of a high-loaded cardan shaft of the propeller engine made of steel 38KhN3MFA are presented to elucidate the cause of damage and develop a set of recommendations and measures aimed at elimination of adverse factors. Methods of scanning electron and optical microscopy, as well as X-ray spectral microanalysis are used to determine the mechanical properties, chemical composition, microstructure, and fracture pattern of cardan shaft fragments. It is shown that the mechanical properties and chemical composition of the material correspond to the requirements of the regulatory documentation, defects of metallurgical origin both in the shaft metal and in the fractures are absent. The microstructure of the studied shaft fragments is tempered martensite. Fractographic analysis revealed that the destruction of cardan shaft occurred by a static mechanism. The fracture surface is coated with corrosion products. The revealed cracks developed by the mechanism of corrosion cracking due to violation of the protective coating on the shaft. The results of the study showed that the destruction of the cardan shaft of a propeller engine made of steel 38Kh3MFA occurred due to formation and development of spiral cracks by the mechanism of stress corrosion cracking under loads below the yield point of steel. The reason for «neck» formation upon destruction of the shaft fragment is attributed to the yield point of steel attained during operation. Regular preventive inspections are recommended to assess the safety of the protective coating on the shaft surface to exclude formation and development of corrosion cracks.

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