5 - Experimental characterization and modeling of metallic materials with hexagonal closed-packed structure

Non-proportionally multiaxial cyclic deformation of AZ31 magnesium alloy: Experimental observations

Bridge load testing can answer a variety of questions about bridge behavior that cannot be answered otherwise. The current governing codes and guidelines for bridge load testing in the United States are the 1998 NCHRP Manual for Bridge Rating through Load Testing and Chapter 8 of the AASHTO Manual for Bridge Evaluation. Over the last two decades, the practice of load testing has evolved, and its intersections with other fields have expanded. The outcomes of load tests have been used to keep bridges open cost-effectively without unnecessarily restricting legal loads, when theoretical analyses cannot yield insights representative of in-service performance. Load testing data can be further used to develop field-verified finite-element models of tested bridges to understand these structures better. In addition, structural reliability concepts can be used to estimate the probability of failure based on the results of load tests, and noncontact measurement techniques capturing large surfaces of bridges allow for better monitoring of structural responses. Given these developments, a new Transportation Research Board (TRB) Circular, Primer on Bridge Load Testing, has been developed. This document contains new proposals for interpreting the results of diagnostic load tests, loading protocols, and the determination of bridge load ratings based on the results of proof load tests. In addition, included provisions provide an estimation of the resulting reliability index and the remaining service life of a bridge based on load testing results. The benefit of load testing is illustrated based on a cost-benefit analysis. The current state-of-The-practice has demonstrated that load testing is an effective means for answering many important questions regarding bridge behavior that are critical to decisions on bridge maintenance or replacement. Load testing has evolved over its history, and the newly developed TRB Circular reflects this evolution in a practical way.

Noble-metal nanoboxes offer an attractive form of nanomaterials for catalytic applications owing to their open structure and highly efficient use of atoms. Herein, we report the facile synthesis of Ag-Ru core-shell nanocubes and then Ru nanoboxes with a hexagonal close-packed (hcp) structure, as well as evaluation of their catalytic activity toward a model hydrogenation reaction. By adding a solution of Ru(acac)3 in ethylene glycol (EG) dropwise to a suspension of silver nanocubes in EG at 170 °C, Ru atoms are generated and deposited onto the entire surface of a nanocube. As the volume of the RuIII precursor is increased, Ru atoms are also produced through a galvanic replacement reaction, generating Ag-Ru nanocubes with a hollow interior. The released Ag+ ions are then reduced by EG and deposited back onto the nanocubes. By selectively etching away the remaining Ag with aqueous HNO3 , the as-obtained Ag-Ru nanocubes are transformed into Ru nanoboxes, whose walls are characterized by an hcp structure and an ultrathin thickness of a few nanometers. Finally, we evaluated the catalytic properties of the Ru nanoboxes with two different wall thicknesses by using a model hydrogenation reaction; both samples showed excellent performance.

The forming limit diagram (FLD) is an important tool to be used when characterizing the formability of metallic sheets used in metal forming processes. Experimental measurement and determination of the FLD is time-consuming and therefore the analytical prediction based on theory of plasticity and instability criteria allows a direct and efficient methodology to obtain critical values at different loading paths, thus carrying significant practical importance. However, the accuracy of the plastic instability prediction is strongly dependent on the choice of the material constitutive model [1–3]. Particularly for materials with hexagonal close packed (HCP) crystallographic structure, they have a very limited number of active slip systems at room temperature and demonstrate a strong asymmetry between yielding in tension and compression [4, 5]. Not only the magnitude of the yield locus changes, but also the shape of the yield surface is evolving during the plastic deformation [4]. Conventional phenomenological constitutive models of plasticity fail to capture this unconventional mechanical behavior [4, 6]. Cazacu and Plunkett [6] have proposed generic yield criteria, by using the transformed principal stress, to account for the initial plastic anisotropy and strength differential (SD) effect simultaneously. In this contribution, a generic FLD MATLAB script was developed based on Marciniak–Kuczynski analytical theory and applied to predict the localized necking. The influence of asymmetrical effect on the FLD was evaluated. Several yield functions such as von Mises, Hill, Barlat89, and Cazacu06 were incorporated into analysis. The paper also presents and discusses the influence of different hardening laws on the formability of materials with HCP crystal structures. The findings indicate that the plastic instability theory coupled with Cazacu model can adequately predict the onset of localized necking for HCP materials under different strain paths.

Microstructural and mechanical characterization of an equiatomic YGdTbDyHo high entropy alloy with hexagonal close-packed structure

31 - Residual stress development in curing processes: Material characterization and modeling

Epitaxial growth of Ag in the hexagonal structure

In the Ural Federal University, samples are obtained by the method of 3D-printing based on the agglomeration of Zr or Ti powders under the preclinical study of osseointegration with the use of an innovative implant. This paper presents a comparison of elastic properties of materials with a close-packed hexagonal structure exemplified by vectorial models characterizing the dependence of Young's modulus on direction and crystalline texture.

Large-scale software systems like Amazon and healthcare.gov are used by thousands or millions of people every day. To ensure the quality of these systems, load testing is a required testing procedure in addition to the conventional functional testing techniques like unit and system integration testing. One of the important requirements of load testing is to create a field-like test environment. Unfortunately, this task is often very challenging due to reasons like security and rapid field updates. In this paper, we have conducted an exploratory study on the impact of environment variations on the results of load tests. We have run over 110 hours load tests, which examine the system's behavior under load with various changes (e.g., installing an anti-virus program) to the targeted deployment environment. We call such load tests as environment-variation-based load tests. Case studies in three open source systems have shown that there is a clear performance impact on the system's performance due to these environment changes. Different scenarios react differently to the changes in the underlying computing resources. When predicting the performance of the system under environment changes that are not previously load tested, our ensemble models out-perform (24% - 94% better) the baseline models.

Interpenetrating polymer network–reinforced acrylic elastomers used for dielectric elastomer actuators are made by introducing a curable and cross-linkable liquid additive into a highly prestretched acrylic elastomer membrane. After curing the additive, force equilibrium between the polymeric networks preserves part of the prestretch, after the external forces are removed. This leads to a material system with promising properties for applications as dielectric elastomer transducers. This work presents an experimental electromechanical characterization of circular actuators made of interpenetrating polymer network–reinforced acrylic elastomers. The relative dielectric permittivity and passive mechanical response of interpenetrating polymer network membranes with different material compositions were characterized. Circular actuators were tested leading to 70 measured responses of 8 interpenetrating polymer network membranes at different voltage levels. The active deformation at a given voltage was found to increase with the amount of secondary network. This effect is mainly attributed to the decreasing membrane thickness. The actuation performance and variability of the active response can be evaluated based on these observations. Furthermore, the present data can be used to develop and validate models of interpenetrating polymer network actuators. All experiments were compared with corresponding finite element simulations using membrane-specific model equations.

The growing demands of the IoT market call for novel ultra-low-cost RF semiconductor devices. Using GHz-frequency Schottky diodes fabricated on a wafer-scale, low-cost natively flexible rectennas and RF energy harvesters can be realized. This paper will present, for the first time, the non-linear model followed by antenna-circuit co-design for solution-processed Zinc-Oxide (ZnO) Schottky diodes. The diode's equiv-alent circuit model is extracted and compared to experimental on-wafer characterization showing very good agreement up to 40 GHz. Using a complex-impedance source emulating a printable rectenna, the designed voltage doubler rectifier shows a power conversion efficiency up to 70% in the UHF RFID band (0.915 GHz). The optimum source and load impedance parameters for a single-series and voltage-doubler rectifier are finally presented, showing that ZnO nano-gap diodes can be adopted in future rectenna designs.

This article focuses on evaluating the influence that the addition of carbonyl iron micro-particles (CIPs) and its alignment have on the mechanical and rheological properties for magnetorheological elastomers (MREs) fabricated using polydimethylsiloxane (PDMS) elastomer, and 24 wt % of silicone oil (SO). A solenoid device was designed and built to fabricate the corresponding composite magnetorheological material and to perform uniaxial cyclic tests under uniform magnetic flux density. Furthermore, a constitutive material model that considers both elastic and magnetic effects was introduced to predict stress-softening and permanent set effects experienced by the MRE samples during cyclic loading tests. Moreover, experimental characterizations via Fourier transform infrared (FTIR), X-ray diffraction (XRD), tensile mechanical testing, and rheological tests were performed on the produced MRE samples in order to assess mechanical and rheological material properties such as mechanical strength, material stiffness, Mullins and permanent set effects, damping ratio, stiffness magnetorheological effect (SMR), and relative magnetorheological storage and loss moduli effects. Experimental results and theoretical predictions confirmed that for a CIPs concentration of 70 wt %, the material samples exhibit the highest shear modulus, stress-softening effects, and engineering stress values when the samples are subject to a maximum stretch value of 1.64 and a uniform magnetic flux density of 52.2 mT.

The results of an experimental programme aimed at studying the undrained behaviour of Hostun sand are presented in this paper. Specific conditions concerning the initial relative density (medium loose arrangements) and the loading paths (compression and extension under monotonic and cyclic loadings) were considered in the test programme. Monotonic tests carried out in both drained and undrained conditions show a significant difference in behaviour between compression and extension. It is observed that, in undrained conditions, Hostun sand is weaker in extension than in compression. In compression, the material is stable (dilatant) and the phase-transformation state controls the mechanical behaviour. In extension, the experimental results show an unstable behaviour (contractant), with monotonic, liquefaction-induced instability in undrained conditions. The results of cyclic tests, carried out with one- and two-way stress reversals, show a good correlation with the results of monotonic tests. The loading path strongly influences the undrained mechanical behaviour of the sand, mainly by inducing liquefaction in extension. This situation suggests that differences in soil fabric, caused by the sample preparation technique (air pluviation), can influence the sand behaviour by inducing a significant contraction in extension. By further analysing the cyclic results, it is shown that, during unloading, the stress paths reflect the transverse isotropy (orthotropy) of the sand, with stiffer elastic characteristics in the vertical direction than in the horizontal direction.Key words: liquefaction, cyclic mobility, sands, triaxial test, anisotropy, loading path.

ABSTRACTThis research proposes a sensitivity‐based framework for selecting the optimal prescribed loading path for a biaxial cruciform specimen. Optimality here is determined by the direction and magnitude of the prescribed displacement that minimizes the influence of random noise on the material model parameter identification. Using simulated experimental data based on finite element simulation, in this work, we identify the material model parameters of a Ludwik hardening model and plane stress implementation of the Hill‐48 yield criterion using finite element model updating (FEMU). Our analysis reveals that the identification (or estimator) uncertainty of model parameters depends on the displacement boundary conditions (i.e., loading sequence) and the ground‐truth value of the individual parameters. Optimal experimental design (OED) criteria based on the Fisher information matrix were investigated to mitigate indecision in the choice of optimal load path when the identification uncertainty of different material model parameters optimized at different load paths. The determinant of the Fisher information matrix was chosen here as the more useful metric due to its ability to capture uncertainty of the most influential material model parameters. The proposed framework demonstrates potential for real‐time automated load step selection using scalar criteria derived prior to mechanical loading. The framework can be generalized to other geometries, boundary conditions and material models, allowing this procedure to be utilized for different experimental configurations and materials.

Materials for solid-state batteries often exhibit complex chemical compositions, defects, and disorder, making both experimental characterization and direct modeling with first principles methods challenging. Machine learning (ML) has proven versatile for accelerating or circumventing first-principles calculations, thereby facilitating the modeling of materials properties that are otherwise hard to access. ML potentials trained on accurate first principles data enable computationally efficient linear-scaling atomistic simulations with an accuracy close to the reference method. ML-based property-prediction and inverse design techniques are powerful for the computational search for new materials. Here, we give an overview of recent methodological advancements of ML techniques for atomic-scale modeling and materials design. We review applications to materials for solid-state batteries, including electrodes, solid electrolytes, coatings, and the complex interfaces involved.