Quasi-static Measurements Research Articles

Biomechanics of the human lens and accommodative system: Functional relevance to physiological states.

The ability of the human lens to accommodate is mediated by the ciliary muscle and zonule; the manifest optical power changes depend on the shape and material properties of the lens. The latter are difficult to measure with accuracy and, given the dynamic aspects of accommodation and the ageing of cells and tissues, the biomechanics of the lens is neither fixed nor constant. A range of techniques have been developed to measure both ageing trends and spatial variations in the mechanical properties and these have yielded a diverse array of findings and respective conclusions. The majority of quasi-static measurements, where the observation time is in minutes or hours, indicate that the stiffness of the lens increases with age at a faster rate in the lens centre than in the periphery. Dynamic measurements show that lens material properties are dependent on the loading frequency. Recent in vivo analyses suggest that, along the optic axis, profiles of elastic moduli are very similar to profiles of refractive index. This review assesses the advantages and limitations of different measurement techniques and consequent variations in elastic moduli that have been found. Consideration is given to the role of computational modelling and the various modelling methods that have been applied. The changes in mechanical properties of the lens associated with ageing and pathology and future implications for implant design are discussed.

Field-Driven Hopping Transport of Oxygen Vacancies in Memristive Oxide Switches with Interface-Mediated Resistive Switching

The dynamics of mobile oxygen vacancies depend on electric field and temperature, and this is key to controlling interfacial resistive switching in BiFeO${}_{3}$ memristive devices, which are interesting especially for neuromorphic computing. The authors use impedance spectroscopy and quasistatic state measurements to reveal the dynamics of resistance changes in such devices, and relate these changes to the redistribution of oxygen vacancies via modeling. This work will also impact the use of other oxides with mobile oxygen vacancies in similar devices.

Microscopic characterization of structural relaxation and cryogenic rejuvenation in metallic glasses

Plasticity improvement in metallic glasses resulting from cycling treatment between room and liquid nitrogen temperature has been reported and attributed to rejuvenation due to a non-uniform thermal expansion coefficient. However, the detailed microscopic effect is still unclear. The present study focuses on the microscopic effect of room-temperature ageing and cryogenic cycling. La70Cu15Al15 and La70Ni15Al15 metallic glasses were subjected to varying ageing times, after which some were also cryogenically cycled. Quasi-static anelastic relaxation measurements were then employed to characterize the time-constant spectra over seven orders of magnitude. The overall anelastic strain decreases with increasing ageing time, but is not noticeably affected by cryogenic cycling. On the other hand, while ageing also causes an increase in characteristic time constants, cycling reverses this effect. The new details shed light on the effect of structural relaxation and rejuvenation on the properties of shear transformation zones.

Assessing bone quality through mechanical properties in postmenopausal trabecular bone

BackgroundThe inner structure of trabecular bone is a result of structural optimization provided by remodeling processes. Changes in hormonal status related to menopause cause bone tissue loss and micro-architectural deterioration with a consequent susceptibility to fracture. Accumulation of micro-damage in bone, as a function of the rate of production and rate of repair, underlies the development of stress fractures, increasing fragility associated to age and osteoporosis, especially in transmenopausal women. Patients and MethodsQuasi-static and nano-dynamic mechanical characterization were undertaken in trabecular bone from femoral neck biopsies of postmenopausal women. AFM (Atomic Force Microscopy) complementary studies were performed to determine nano-roughness (SRa) and the fibrils width of collagen. Nanoindentations were used to quantify transmenopausal changes in intrinsic mechanical properties of trabecular bone: hardness (Hi), modulus of Young (Ei), complex modulus (E*), tan delta (δ), storage modulus (E') and loss modulus (E"). ResultsAs result of the quasi-static measurements, 0.149 (0.036) GPa and 2.95 (0.73) GPa of Hi and Ei were obtained, respectively. As result of the nano-dynamic measurements, 17.94 (3.15), 0.62 (0.10), 13.79 (3.21 and 6.39 (1.28) GPa of E*, tan (δ), E' and E" were achieved, respectively. 101.07 SRa and 831.28 nm of fibrils width were additionally obtained. ConclusionsThis study poses a first approach to the measurement of bone quality in postmenopausal trabecular bone by combining quasi-static, nano-DMA analysis and tribology of dentin surface through AFM characterization.

Quantitative correlation between Flash and equivalent transistor for endurance electrical parameters extraction

Nowadays, the study of physical mechanisms that occur during Flash memory cell life is mandatory when reaching the 40 nm and beyond nodes in terms of reliability. In this paper we carry out a complete experimental method to extract the floating gate potential evolution during the cell aging. The dynamic current consumption during a Channel Hot Electron operation for a NOR Flash is a proper quantitative marker of the cell degradation. Here both drain and bulk currents are measured and monitored throughout the endurance tests. We coupled these characteristics with quasi-static measurements to correlate the cell degradation with an equivalent transistor. The final goal is to be able to split the physical effects of repetitive hot carrier and Fowler-Nordheim operations, typical of Flash memories, to extract the electrical parameters evolution on a simple equivalent transistor.

Dynamic OFF-State Current (Dynamic ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ ) in ${p}$ -GaN Gate HEMTs With an Ohmic Gate Contact

The OFF-state drain leakage characteristics in 600-V p-GaN HEMTs with an ohmic gate contact are investigated under dynamic switching conditions instead of commonly used quasi-static measurement setup. It is found that fast dynamic OFF-state leakage current (dynamic ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ ) is substantially higher than the slow-ramping quasi-static ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ due to the weaker trapping effect in the buffer layer. With sufficiently large positive ON-state gate bias, further increase in dynamic ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ is observed and is attributed to ON-state hole injection that leads to energy band lowering in the buffer. The underlying physical processes are explained by the dynamic behavior of the traps in the buffer layer. This letter indicates that the ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ under practical switching operations is much higher than the static measurement results and should be used to evaluate dynamic OFF-state power consumption in the p-GaN HEMTs with an ohmic gate contact.

Development of a scanning electron microscopy with polarization analysis system for magnetic imaging with ns time resolution and phase-sensitive detection.

Scanning electron microscopy with polarization analysis is a powerful lab-based magnetic imaging technique offering simultaneous imaging of multiple magnetization components and a very high spatial resolution. However, one drawback of the technique is the long required acquisition time resulting from the low inherent efficiency of spin detection, which has limited the applicability of the technique to certain quasi-static measurement schemes and materials with high magnetic contrast. Here we demonstrate the ability to improve the signal-to-noise ratio for particular classes of measurements involving periodic excitation of the magnetic structure via the implementation of a digital phase-sensitive detection scheme facilitated by the integration of a time-to-digital converter to the system. The modified setup provides dynamic imaging capabilities using selected time windows and finally full time-resolved imaging with a demonstrated time resolution of better than 2 ns.

Frequency Measurement of Dynamic Stress in Polarization Maintaining Fibers

Up to now, the distributed polarization coupling (DPC) measurement system based on white light interferometry (WLI) has been mainly studied for static and quasi-static measurement. In this paper, we developed the DPC system to measure the instantaneous frequency of dynamic stress. First, we set up a model of transversal stress on the panda polarization maintaining fiber (PMF) and simulated the interferograms of dynamic coupling points when the PMF is subjected to stress of cosine wave, sawtooth wave and square wave. Then, we did groups of experiments to measure the interferograms of dynamic coupling points, including cosinoidal coupling point, sawtooth wave coupling point, square wave coupling point, and two cosinoidal coupling points. By applying wavelet transform to the envelops of interferograms, we can obtain the time-frequency distribution images and demodulate the instantaneous frequency of external stress. The absolute error of experiments is less than 1.84 Hz. Finally, we deduced the upper and lower limits for frequency measurement and discussed the methods of enlarging the frequency range in detail. The method introduced in this paper has potential application in fiber sensing of dynamic stress.

Fast-Convergent Expression for the Barrel-Plate Capacitance in the Physics-Based Via Circuit Model

The widely used analytical formula for the barrel-plate capacitance in the physics-based via circuit model involves an infinite summation, which requires a truncation during practical computations. Such a truncation is problem-dependent and prone to either underestimate the capacitance value or ruin the computation when truncating too late. This letter proposes a fast-convergent expression of the barrel-plate capacitance based on a convergence study of the original formula. The proposed expression comprises a well truncated and a closed-form part, whose computation is more efficient and free of truncation error. It is validated against quasi-static solutions and measurement.

Studies on transient characteristics of unipolar resistive switching processes in TiO2 thin film grown by atomic layer deposition

The transient characteristics of resistive switching processes have been investigated in TiO2 thin films grown by atomic layer deposition (ALD) to study the temporal evolution of the switching processes and measure the switching times. The reset and set switching times of unipolar Au/TiO2/Pt devices were found to be ~250 µs and 180 ns, respectively in the voltage windows of 0.5–0.9 V for reset and 1.9–4.8 V for set switching processes, obtained from quasi-static measurements. The reset switching time decreased exponentially with increasing amplitude of applied reset voltage pulse, while the set switching time remained insensitive to the amplitude of the set voltage pulse. A fast reset process with a switching time of ~400 ns was achieved by applying a reset voltage of ~1.8 V, higher than that of the quasi-static reset voltage window but below the set voltage window. The sluggish reset process in TiO2 thin film and the dependence of the reset switching time on the amplitude of the applied voltage pulse was understood on the basis of a self-accelerated thermal dissolution model of conducting filaments (CFs), where a higher temperature of the CFs owing to enhanced Joule heating at a higher applied voltage imposes faster diffusion of oxygen vacancies, resulting in a shorter reset switching time. Our results clearly indicate that fast resistive switching with switching times in hundreds of nanoseconds can be achieved in ALD-grown TiO2 thin films. This may find applications in fast non-volatile unipolar resistive switching memories.

Strain Rate Effect on Tensile Flow Behavior and Anisotropy of a Medium-Manganese TRIP Steel

The dependence of the plastic anisotropy on the nominal strain rate for a medium-manganese (10 wt.% Mn) transformation-induced plasticity (TRIP) steel with initial austenite volume fraction of 66% (balance ferrite) has been investigated. The material exhibited yield point elongation, propagative instabilities during hardening, and austenite transformation to α′-martensite either directly or through e-martensite. Uniaxial strain rates within the range of 0.005–500 s−1 along the 0°, 45°, and 90° orientations were selected based upon their relevance to automotive applications. The plastic anisotropy (r) and normal anisotropy (rn) indices corresponding to each direction and strain rate were determined using strain fields obtained from stereo digital image correlation systems that enabled both quasistatic and dynamic measurements. The results provide evidence of significant, orientation-dependent strain rate effects on both the flow stress and the evolution of r and rn with strain. This has implications not only for material performance during forming but also for the development of future strain-rate-dependent anisotropic yield criteria. Since tensile data alone for the subject medium-manganese TRIP steel do not satisfactorily determine the microstructural mechanisms responsible for the macroscopic-scale behavior observed on tensile testing, additional tests that must supplement the mechanical test results presented herein are discussed.

Indentation size effects of ferritic/martensitic steels: A comparative experimental and modelling study

The paper presents a comparative study of different nanoindentation methods as applied to the ferritic/martensitic steels T91 and Eurofer97, here investigated in the non-irradiated reference state, but envisaged as structural materials for nuclear fission and fusion applications, respectively. Depth-controlled single cycle measurements at various indentation depths, force-controlled single cycle, force-controlled progressive multi-cycle measurements, and continuous stiffness measurements (CSM) using a Berkovich tip at room temperature have been combined to determine the indentation hardness and the elastic modulus, and to assess the robustness of the different methods in capturing the indentation size effects (ISE) of those steels. The Nix−Gao model is found inappropriate because it does not account for the breakdown of the scaling regime at small indentation depths that is linked to the extremely high density of dislocations associated with martensitic lath boundary misorientation. A generalization of the Nix–Gao model is therefore developed which allows the prediction of the dislocation densities in the lath structure in accordance with neutron diffraction results. Amplitude and frequency of the CSM oscillations influence the ISE observed. Differences of the microstructure-based parameters describing the ISE of quasi-static and dynamic measurements on T91 and Eurofer97 may reflect differences in the associated deformation mechanisms and histories.

Formation and characterization of intermetallic compounds in electroplated cobalt–tin multilayers

Intermetallic compounds (IMC) form during the metallurgical bonding processes when the interfaces involve solid metal and molten solder. Cobalt (Co) is a promising candidate to be used as under bump metallization (UBM) material, tin (Sn)-based solder alloying element, and transient liquid phase bonding base metal. This work aims at studying the intermixing reaction in Co–Sn system from electroplated Co and Sn multilayers. Co–Sn couples were sequentially electroplated and reflowed at 400 °C for 1 and 4 h. The microstructure and composition of the phases formed at different reflow duration were characterized by field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Mechanical properties of the IMC layers formed in the samples were characterized using the nanoindentation technique under quasi-static and continuous measurement modes. FESEM/EDX and XRD analysis showed a mixture of CoSn+CoSn2 phases was formed in the 1 h reflow sample. As reflow time was increased to 4 h, only CoSn phase was found. Pure CoSn phase exhibits high nanohardness of 9.51 GPa while the region with CoSn+CoSn2 phases gives nanohardness value of 6.83 GPa.

Mechanical Properties of Uranium Silicides by Nanoindentation and Finite Elements Modeling

Three methods were used to measure the mechanical properties of $${\text{U}}_{3}{\text{Si}}$$ , $${\text{U}}_3{\text{Si}}_{2}$$ , and USi. Quasi-static and continuous stiffness measurement nanoindentation were used to determine hardness and Young’s modulus, and microindentation was used to evaluate the bulk hardness. Hardness and Young’s modulus of the three U-Si compounds were both observed to increase with Si content. Finally, finite elements modelling was used to validate the nanoindentation data calculated for $${\text{U}}_{3}{\text{Si}}_{2}$$ and estimate its yield strength.

High Temperature Dynamic Response of a Ti-6Al-4V Alloy: A Modified Constitutive Model for Gradual Phase Transformation

Dynamic deformation behavior of a commercial Ti-6Al-4V alloy is measured between room temperature and beyond the β-transus temperature with high thermal resolution using a rapid-heating Kolsky bar technique. The high thermal resolution allows for a thorough investigation of the dynamic thermal softening behavior of this alloy including effects related to the transformation from the initial hcp α/bcc β dual phase structure to a full β structure for improved modeling of high temperature dynamic manufacturing processes such as high-speed machining. Data are obtained at an average strain rate of 1800 s−1 from room temperature to 1177 °C, with total heating times limited to 3.5 s for all tests. Short heating times prevent thermal distortion of the Kolsky bar loading waves and can allow an investigation of non-equilibrium mechanical behavior, although no such behavior was identified in this study. Between 800 °C and 1000 °C, a progressive change in the thermal softening rate was observed that corresponded well with the equilibrium phase diagram for this alloy. The dynamic thermal softening behavior in the transformation region is incorporated via a new modification of the Johnson–Cook (J–C) viscoplastic constitutive equation. Rate sensitivity is determined at room temperature by combining Kolsky bar data with quasi-static measurements at strain rates from 7.5 × 10−5 s−1 to 0.16 s−1 and the data are fit using multi-parameter optimization to arrive at a full modified J–C model for Ti-6Al-4V to nearly 1200 °C. In its generic form, the modification factor we propose, G(T), is applicable to any material system undergoing gradual phase transformation over a range of temperatures.

Growth-Induced In-Plane Uniaxial Anisotropy in V2O3/Ni Films

We report on a strain-induced and temperature dependent uniaxial anisotropy in V2O3/Ni hybrid thin films, manifested through the interfacial strain and sample microstructure, and its consequences on the angular dependent magnetization reversal. X-ray diffraction and reciprocal space maps identify the in-plane crystalline axes of the V2O3; atomic force and scanning electron microscopy reveal oriented rips in the film microstructure. Quasi-static magnetometry and dynamic ferromagnetic resonance measurements identify a uniaxial magnetic easy axis along the rips. Comparison with films grown on sapphire without rips shows a combined contribution from strain and microstructure in the V2O3/Ni films. Magnetization reversal characteristics captured by angular-dependent first order reversal curve measurements indicate a strong domain wall pinning along the direction orthogonal to the rips, inducing an angular-dependent change in the reversal mechanism. The resultant anisotropy is tunable with temperature and is most pronounced at room temperature, which is beneficial for potential device applications.

Data-driven approaches for measurement interpretation: analysing integrated thermal and vehicular response in bridge structural health monitoring

A comprehensive evaluation of a structure’s performance based on quasi-static measurements requires consideration of the response due to all applied loads. For the majority of short- and medium-span bridges, temperature and vehicular loads are the main drivers of structural deformations. This paper therefore evaluates the following two hypotheses: (i) knowledge of loads and their positions, and temperature distributions can be used to accurately predict structural response, and (ii) the difference between predicted and measured response at various sensor locations can form the basis of anomaly detection techniques. It introduces a measurement interpretation approach that merges the regression-based thermal response prediction methodology that was proposed previously by the authors with a novel methodology for predicting traffic-induced response. The approach first removes both environmentally (temperature) and operationally (traffic) induced trends from measurement time series of structural response. The resulting time series is then analysed using anomaly detection techniques. Experimental data collected from a laboratory truss is used for the evaluation of this approach. Results show that (i) traffic-induced response is recognized once thermal effects are removed, and (ii) information of the location and weight of a vehicle can be used to generate regression models that predict traffic-induced response. Asa whole, the approach is shown to be capable of detecting damage by analysing measurements that include both vehicular and thermal response.

Dynamic magnetic permeability of the heterogeneous nanosystems based on (Co41Fe39B20) x (SiO2)100 – x composites

Thin films of (Co41Fe39B20) x (SiO2)100 – x nanocomposites and hybrid nanocomposite–semiconductor [(Co41Fe39B20) x (SiO2)100 – x /C]50 multilayers are synthesized by ion-beam deposition at various contents x of ferromagnetic metallic Co41Fe39B2O nanogranules in an SiO2 matrix and at various carbon layer thicknesses h < 2 nm. Their magnetic and electrical properties, high-frequency magnetic permeability, magnetooptical spectra, and FMR spectra are studied. It is found that both the single-layer nanocomposites and the multilayers with carbon interlayers are superparamagnetic at x < x per, where x per is the electric conduction percolation threshold: a hysteresis at room temperature is absent, and the blocking temperature determined in quasi-static measurements does not exceed 20–30 K and weakly depends on the carbon layer thickness. At a carbon layer thickness h = 1.2–1.8 nm, the real and imaginary parts of complex magnetic permeability at 50 MHz and room temperature are substantially higher than those of the nanocomposites without carbon layers: their values are typical of ferromagnets. This dependence points to an exchange interaction between nanogranules in layers through a carbon interlayer. The influence of a conducting layer on the static and dynamic magnetic properties of a system of interacting superparamagnetic particles is discussed.

Imaging ferroelectric domains via charge gradient microscopy enhanced by principal component analysis

Local domain structures of ferroelectrics have been studied extensively using various modes of scanning probes at the nanoscale, including piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM), though none of these techniques measure the polarization directly, and the fast formation kinetics of domains and screening charges cannot be captured by these quasi-static measurements. In this study, we used charge gradient microscopy (CGM) to image ferroelectric domains of lithium niobate based on current measured during fast scanning, and applied principal component analysis (PCA) to enhance the signal-to-noise ratio of noisy raw data. We found that the CGM signal increases linearly with the scan speed while decreases with the temperature under power-law, consistent with proposed imaging mechanisms of scraping and refilling of surface charges within domains, and polarization change across domain wall. We then, based on CGM mappings, estimated the spontaneous polarization and the density of surface charges with order of magnitude agreement with literature data. The study demonstrates that PCA is a powerful method in imaging analysis of scanning probe microscopy (SPM), with which quantitative analysis of noisy raw data becomes possible.

Research of the Load Bearing Capacity of Shape-Optimized Metal Inserts Embedded in CFRP under Different Types of Stresses

An efficient implementation of lightweight design is the use of continuous carbon fiber reinforced plastics (CFRP) due to their outstanding specific mechanical properties. Embedded metal elements, so-called inserts, can be used to join metal-based attachments to structural CFRP parts in the context of multi-material design. They differ from other mechanical fasteners and have distinctive benefits. In particular, drilling of the components to be joined can be avoided and, depending on the preforming, fiber continuity can be maintained using such elements. Thus, no local bearing stress is anticipated. Previous work published by the authors [1] dealt with a systematic research of the influence of different types of stresses on the load bearing capacity of welded inserts. This contribution aims at the investigation of the performance of shape-optimized inserts under the same types of loading to compare with the results of the welded inserts serving as a reference. For that purpose, the respective load bearing capacities were evaluated after preinduced damages from impact tests and thermal cycling. In addition, dynamic high-speed tensile tests (pull-out) were conducted under different loading velocities. It is shown that the load bearing capacities increased up to 19% for high velocities (250 mm/s) in comparison to quasi-static loading conditions (1.5 mm/min) showing an obvious strain rate dependency of the CFRP. Quasi-static residual strength measurements under tensile loading identified the influence of the respective preinduced damages of the insert. Influence of the thermal loading condition was evaluated by placing the specimens in a climate chamber and exposing it to various numbers of temperature cycles from-40 °C to +80 °C with a duration time of 1.5 hours each. Here, it turned out that already 10 temperature cycles decreased the quasi-static load bearing capacity up to 31%. According to DIN EN 6038 the specimens were loaded with different impact energies and the residual strength were measured carrying out pull-out tests. It could be shown that the damage tolerance is significantly lower for the shape-optimized insert due to failure-critical delamination. The optimized insert also endured lower impact energies and the influence on the performance was higher.