Comment on 'Temperature dependence of the energy dissipation in dynamic force microscopy'

A recent article in this journal by Roll et al (2008 Nanotechnology 19 045703) presents experimental results of the temperature dependence of dissipation in dynamic force microscopy which they use to elucidate the mechanisms of such a dissipation signal in the PTCDA on KBr system. We argue here that dissipation results are often highly dependent upon the tip structure, and urge caution in the interpretation of single sets of experimental data.     

Fatigue Hysteresis Behavior of Unidirectional SiC/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Composite at Elevated Temperature under Tension-Tension Loading

In this paper, the fatigue hysteresis behavior of unidirectional SiC/Si₃N₄ ceramic-matrix composite at elevated temperature has been investigated. The hysteresis loops models considering interface friction between fibers and the matrix have been developed to establish the relationships between the fatigue hysteresis loops, fatigue hysteresis dissipated energy and the interface frictional coefficient. Using the experimental fatigue hysteresis dissipated energy, the interface frictional coefficient of SiC/Si₃N₄ composite at 1000 °C were obtained for different cycle numbers and fatigue peak stresses. The effects of fatigue peak stress, test temperature and cycle number on the evolution of fatigue hysteresis dissipated energy and interface frictional coefficient have been analyzed. It was found that the fatigue hysteresis dissipated energy can be used to monitor the interface debonding and damage evolution inside of the composite.     

How localized are energy dissipation processes in nanoscale interactions?

We describe fundamental energy dissipation in dynamic nanoscale processes in terms of the localization of the interactions. In this respect, the areal density of the energy dissipated per cycle and the effective area of interaction in which each process occurs are calculated for four elementary dissipative processes. It is the ratio between these two, which we term M, that provides information about how localized the interactions are. While our results are general, we use concepts from dynamic atomic force microscopy to describe the physical phenomenon. We show that neither the phase lag, nor the magnitude of the energy dissipated alone provide information about how dissipative processes are localized. Instead, M has to be considered.     

PTCDA molecules on a KBr/InSb system: a low temperature STM study

We have used scanning tunnelling microscopy (STM) at 77?K to investigate 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) molecules adsorbed on an ultrathin (1-2?monolayer (ML)) film of KBr grown on a c(8 × 2)InSb(001) substrate. The molecules are stabilized both at the KBr steps and on the terraces. On the 1?ML film the PTCDA molecules appear predominantly as single entities, whereas on the 2?ML film formation of molecular clusters is preferred. Differences in the adsorption configurations indicate that the interaction between the molecules and the surface differs significantly for the cases of 1 and 2?ML films. We present images of the molecules obtained with sub-molecular resolution for both filled and empty state sampling modes. We argue that the highest occupied molecular orbital (the lowest unoccupied molecular orbital) is responsible for intramolecular contrast in filled (empty) state images of the molecules, even though they are deformed due to strong interaction with the substrate.     

Relationship Between Hysteresis Dissipated Energy and Temperature Rising in Fiber-Reinforced Ceramic-Matrix Composites Under Cyclic Loading

In this paper, the relationship between hysteresis dissipated energy and temperature rising of the external surface in fiber-reinforced ceramic-matrix composites (CMCs) during the application of cyclic loading has been analyzed. The temperature rise, which is caused by frictional slip of fibers within the composite, is related to the hysteresis dissipated energy. Based on the fatigue hysteresis theories considering fibers failure, the hysteresis dissipated energy and a hysteresis dissipated energy-based damage parameter changing with the increase of cycle number have been investigated. The relationship between the hysteresis dissipated energy, a hysteresis dissipated energy-based damage parameter and a temperature rise-based damage parameter have been established. The experimental temperature rise-based damage parameter of unidirectional, cross-ply and 2D woven CMCs corresponding to different fatigue peak stresses and cycle numbers have been predicted. It was found that the temperature rise-based parameter can be used to monitor the fatigue damage evolution and predict the fatigue life of fiber-reinforced CMCs.     

基于迟滞耗散能的纤维增强陶瓷基复合材料疲劳寿命预测方法

纤维增强陶瓷基复合材料(CMCs)在疲劳载荷作用下,纤维相对基体在界面脱粘区往复滑移导致其出现疲劳迟滞现象,迟滞回线包围的面积,即迟滞耗散能,可用于监测纤维增强CMCs疲劳损伤演化过程。提出了一种基于迟滞耗散能的纤维增强CMCs疲劳寿命预测方法及考虑纤维失效的迟滞回线模型,建立了迟滞耗散能、基于迟滞耗散能的损伤参数、应力-应变迟滞回线与疲劳损伤机制(多基体开裂、纤维/基体界面脱粘、界面磨损与纤维失效)之间的关系。分析了疲劳峰值应力、疲劳应力比与纤维体积分数对纤维增强CMCs疲劳寿命S-N曲线、迟滞耗散能和基于迟滞耗散能的损伤参数随循环次数变化的影响。疲劳寿命随疲劳峰值应力增加而减小,随纤维体积含量增加而增加;迟滞耗散能随疲劳峰值应力增加而增加,随应力比和纤维体积分数增加而减小;基于迟滞耗散能的损伤参数随纤维体积分数增加而减小。      

High resolution LT-STM imaging of PTCDA molecules assembled on an InSb(001) c(8 × 2) surface

The self-assembling of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) molecules deposited on an InSb(001) c(8 × 2) surface at sub-monolayer quantities has been investigated at low temperature (77?K) using scanning tunnelling microscopy. Sub-molecular resolution was obtained on PTCDA molecules. The results reveal that individual PTCDA molecules are arranged on the substrate in chains parallel to the [110] crystallographic direction, correlated with characteristic features of the low temperature InSb(001) c(8 × 2) surface electronic structure. A?structural model for PTCDA molecules adsorbed on InSb is proposed.     

The role of the tip in non-contact atomic force microscopy dissipation images of ionic surfaces

In this paper we use simulations to investigate the role of the tip in nc-AFM measurements of dissipated energy. Using a virtual AFM we simulate the experiment focusing on the atomic scale energy dissipation on an NaCl(100) flat surface. The non-conservative interaction was treated with the theory of dynamic response and all the calculations were carried out using an atomistic model; several sets of tips were tested using ionic crystals (NaCl, KBr, MgO), each in different configurations (ideal, vacant, divacant, doped). Using an MgO-doped tip we were able to calculate a dissipation signal comparable to what is typically measured in experiments. It was not possible to see any dissipation with ideal tips, although they still have a significant interaction with the surface and give atomic contrast in the frequency shift signal. The effect of the scanning speed on measured frequency shift and dissipation is also calculated and discussed.     

Energy dissipation under thermomechanical fatigue loading

The paper presents a numerical approach to compute the total amount of dissipated energy under arbitrary rate independent uniaxial thermomechanical fatigue (TMF) loading. Such an approach is based on the stress controlled Prandtl type operator enabling continuous energy dissipation calculation. It focuses on non-isothermal stress–strain conditions of a spring–slider segment, and relates slider movements to irreversible energy dissipation. The correct amount of dissipated energy is computed at any moment (online), without the need of ‘waiting’ the cycle to finish. The operator approach guaranties monotonically increasing progress of energy dissipation, which is within the framework of thermodynamics. It is also shown that the operator approach results in the same dissipated energy after closed isothermal cycle as the traditional integration approach.     

Energy dissipation under multiaxial thermomechanical fatigue loading

The paper presents an approach to the energy dissipation calculation under arbitrary multiaxial thermomechanical fatigue (TMF) loading. In such an approach the total area of plastic hysteresis loops is taken as a measure of dissipated energy. The calculation is based on the concept of the developed temperature dependent Prandtl type operator. Energy dissipation is associated to irreversible dislocation movements represented by slider shifts of three independent operators. The dissipated energy is then obtained continuously at any time by collecting dissipated energy increments of each operator. It is shown that the multiaxial operator approach gives us the same total energy of plastic deformation as compared to the classical integration approach. Furthermore, the presented approach enables to automatically split the obtained dissipated energy between the “true” dissipated energy and the elastically “stored” energy. In order to satisfy the request for a minimum number of dedicated material tests, the approach assumes fixed principal directions. Therefore, the proportional as well as non-proportional loading conditions are addressed in the same manner, which is currently the main deficiency of the approach.     

Conductance and polarisability of C60 films

Thin films of C60 deposited in vacuum are studied using current-voltage (I-V) measurements and atomic force microscopy (AFM). In situ electrical measurements give an average resistivity of ca. 30 Mn cm for the as-deposited films at room temperature. The I-V dependences are found to correspond to ohmic behaviour but they have a hysteresis shape attributed to remnant polarisation due to the domain structure of the films. AFM images show a grainy surface morphology for the deposited C60. Temperature dependent measurements in the range 290-365 K provide evidence for a variable range hopping mechanism of conductance with an activation energy of 0.8-1.0 eV. With further temperature increase the C60 films restructure leading to an increase in grain size and a change of the electrical properties with I-V dependences showing Schottky barrier formation. The effect of oxygen on the conductance of the C60 films under their exposure to an ambient atmosphere is considered and discussed.     

Synergistic Effects of Frequency and Temperature on Damage Evolution and Life Prediction of Cross-Ply Ceramic Matrix Composites under Tension-Tension Fatigue Loading

In this paper, the synergistic effects of loading frequency and testing temperature on the fatigue damage evolution and life prediction of cross-ply SiC/MAS ceramic-matrix composite have been investigated. The damage parameters of the fatigue hysteresis modulus, fatigue hysteresis dissipated energy and the interface shear stress were used to monitor the damage evolution inside of SiC/MAS composite. The evolution of fatigue hysteresis dissipated energy, the interface shear stress and broken fibers fraction versus cycle number, and the fatigue life S–N curves of SiC/MAS composite under the loading frequency of 1 and 10 Hz at 566 °C and 1093 °C in air condition have been predicted. The synergistic effects of the loading frequency and testing temperature on the degradation rate of fatigue hysteresis dissipated energy and the interface shear stress have been analyzed.     

Long Jumps of an Organic Molecule Induced by Atomic Force Microscopy Manipulation

Non‐contact atomic force microscopy at cryogenic temperatures is used for the controlled lateral manipulation of individual 3,4,9,10‐perylene‐tetracarboxylicacid‐dianhydride (PTCDA) molecules on the Ag(111) surface. The molecules are moved along the [‐110] direction of the Ag lattice in the regime of repulsive tip‐molecule forces performing discrete jumps that span distances from single to multiple lattice spacings. The analysis of the two‐dimensional force field measured before and during the manipulation reveals that the displacement beyond nearest neighbor sites cannot be explained by long range tip‐molecule forces but instead has to involve an energy transfer to translational modes of the molecule. Combined with the results of the simultaneous measurement of the energy dissipation, these findings allow to identify a likely manipulation mechanism and provide insight into the process of energy transfer between excited large molecules and metal surfaces. Furthermore, implications for the theoretical treatment of NC‐AFM based molecule manipulation are discussed.     

组合式双圆锥耗能器的设计与性能模拟分析

设计了组合式双圆锥耗能器,阐述了其构造和耗能原理,采用有限元软件对18个不同尺寸的双圆锥耗能元件和3个不同组装方式的双圆锥耗能器进行了数值仿真分析,研究了不同设计参数对双圆锥耗能器的滞回性能和应力分布的影响。研究结果表明：对于双圆锥耗能元件,当其总高H一定时,其初始刚度和屈服位移取决于两个锥体中较大锥体的高度大小;屈服位移可设置在1mm以内,耗能系数值可达2.5。双圆锥耗能元件通过不同的方式组合成双圆锥耗能器时,双圆锥耗能器的滞回性能取决于所选用的双圆锥耗能元件和其上、下连接板的刚度,当连接板刚度较大时,双圆锥耗能元件的滞回性能与其组装后的双圆锥耗能器的相关滞回性能满足叠加关系,双圆锥耗能器的相关滞回性能可由所选用的双圆锥耗能元件的相关参数(初始刚度、屈服位移和耗能系数等)来确定。     

Energy-based prediction of low-cycle fatigue life of BS 460B and BS B500B steel bars

This paper develops energy-based models for predicting low-cycle fatigue life of BS 460B and BS B500B steel reinforcing bars. The models are based on energy dissipated in the first cycle, in average cycles and in total energy dissipated to failure for strain ratios R = −1, −0.5, and 0. Upon prediction of the low-cycle fatigue life, the total energy dissipated during the entire fatigue life of steel reinforcing bars can also be predicted based on the predicted fatigue life. The results indicated that the hysteresis plastic strain energy dissipated during fatigue loading is an important and accurate parameter for predicting the fatigue life of steel reinforcing bars and that the predictions based on energy dissipated on average cycles are more accurate than those based on energy dissipated in the first cycle. It is concluded that the strain ratio R has a clear effect on the energy dissipation for both materials where BS B500B dissipated more energy than BS 460B for R = −0.5 and 0 and about the same energy for R = −1 for certain range of fatigue life. Other conclusions and observations were also drawn based on the experimental results.     

Simulation of Adhesive–Dissipative Behavior of a Microparticle Under the Oblique Impact

The adhesive–dissipative behavior of a microparticle under the oblique impact is investigated numerically and the new discrete element method (DEM)-compatible interaction model is elaborated. The modeling approach is based on the Derjaguin–Muller–Toporov model of normal interaction for the adhesive elastic contact. Adhesion hysteresis is specified by the loss of the kinetic energy governed by the fixed amount of the adhesion work, required to separate two adhesive contacting surfaces. This effect is captured in the new interaction model by adding an additional dissipative force component to normal contact during unloading and detachment. The essential feature of this approach, differing from that of the viscous damping model, is that, according to the proposed method, the amount of the dissipated energy is not influenced by the actual initial velocity during the entire contact. The influence of adhesion on slip friction is reflected by considering the adhesive normal force components in the Coulomb's law of friction. The contribution of the adhesion-related dissipation is illustrated by a comparison of the behavior of the attractive–dissipative and attractive–non-dissipative models. The oblique impact of a microparticle on the plane surface at the intermediate impact angle is also investigated numerically. The link between adhesion and friction is supported by the numerical results.     

Synergistic Effects of Temperature,Oxidation and Multicracking Modes on Damage Evolution and Life Prediction of 2D Woven Ceramic-Matrix Composites under Tension-Tension Fatigue Loading

In this paper, the synergistic effects of temperature, oxidation and multicracking modes on damage evolution and life prediction in 2D woven ceramic-matrix composites (CMCs) have been investigated. The damage parameter of fatigue hysteresis dissipated energy and the interface shear stress were used to monitor the damage evolution inside of CMCs. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface/fiber oxidation model, interface wear model and fibers statistical failure model at elevated temperature, based on the assumption that the fiber strength is subjected to two-parameter Weibull distribution and the load carried by broken and intact fibers satisfy the Global Load Sharing (GLS) criterion. When the broken fibers fraction approaches to the critical value, the composite fatigue fractures. The evolution of fatigue hysteresis dissipated energy, the interface shear stress and broken fibers fraction versus cycle number, and the fatigue life S–N curves of SiC/SiC at 1000, 1200 and 1300 °C in air and steam condition have been predicted. The synergistic effects of temperature, oxidation, fatigue peak stress, and multicracking modes on the evolution of interface shear stress and fatigue hysteresis dissipated energy versus cycle numbers curves have been analyzed.     

Optical properties of Tl2InGaS4 layered single crystal

The temperature dependence of the optical band gap of Tl₂InGaS₄ single crystal in the temperature region of 300–500 K and the room temperature refractive index, n(λ), have been investigated. The absorption coefficient, which was calculated from the transmittance and reflectance spectra in the incident photon energy range of 2.28–2.48 eV, increased with increasing temperature. Consistently, the absorption edge shifts to lower energy values as temperature increases. The fundamental absorption edge corresponds to an indirect allowed transitions energy gap (2.35 eV) that exhibits a temperature coefficient of −4.03 × 10⁻⁴ eV/K. The room temperature n(λ), calculated from the reflectance and transmittance data, allowed the identification of the oscillator strength and energy, static and lattice dielectric constants, and static refractive index as 16.78 eV and 3.38 eV, 5.96 and 11.77, and 2.43, respectively.     

基于形状记忆合金的X形板阻尼器的力学模型

根据超弹性形状记忆合金（SMA）的分段线性化本构关系,建立了X形SMA板式阻尼器的力学模型;通过MATLAB程序进行数值模拟,绘制了X形SMA板的阻尼力滞回曲线,并研究了位移幅值、温度、形状尺寸对阻尼器基本特征参数（等效割线刚度、单位循环消耗的能量、等效阻尼比）的影响。结果表明：X形SMA板式阻尼器具有“旗帜”形的滞回曲线,耗能较小,但复位能力好;随位移幅值增加,耗能力和等效阻尼比增加,等效割线刚度降低,温度的影响与此相反;阻尼器的特征参数随板高增加均呈降低趋势;增加板宽,单位循环耗能与等效割线刚度增加,而等效阻尼比不变。研究结果为X形SMA板式阻尼器的设计和工程应用提供了理论依据。     

Study on energy properties and failure behaviors of heat-treated granite under static and dynamic compression

Abstract

The material testing machine and the split Hopkinson pressure bar (SHPB) were adopted, respectively, to conduct the static and dynamic compression tests on granite specimens heat treated by different temperatures. The effects of strain rate and heat-treatment temperature on the mechanism of energy evolution of the specimen during deformation and failure process were studied. The results show a significant strain rate effect on the granite, with the energy dissipation density increasing with increasing impact velocity (or strain rate), regardless of the treatment temperature. The specimens heat treated at 300?°C and 700?°C have the minimum and maximum energy dissipation densities, respectively. The specimen in the SHPB tests easily broke into pieces or even powder; while under static compression, only macroscopic fracture surfaces and spalling phenomenon on the specimen were detected. The energy dissipation density is inversely proportional to the compressive strength of the specimen. The rate of energy dissipation change is defined, which can be used to identify the stages in the deformation process of rock and to determine the position of the failure point in the stress-strain curve. For both the dynamic and static compression tests, the value of energy utilization ratio is relatively low, with a maximum value of about 35%.