Performance Problems and Structural Retrofit Analysis of Existing BCTs

Automobile accident reports and full-scale crash tests of existing breakaway cable terminals (BCTs) indicated their poor performance during end-on impacts. This paper presents results of a feasibility study, which was conducted to identify problems with existing BCTs. The nonlinear, explicit, dynamic finite-element code LS-DYNA was used in the investigation of BCT design problems. Several problems were identified in the past during the full-scale crash tests. These problems became clearly visible when computational mechanics analyses were used. In addition to severe vehicle damage, vehicular impact induced dangerous, large deceleration peaks and uncontrolled vehicle trajectories. Analysis of actual crash tests and LS-DYNA data led to the conclusion that the terminal is too stiff along its longitudinal direction and fails to smoothly control dissipation of the vehicle kinetic energy. Therefore, the major objective of the research was to soften the existing system by weakening the rail in strategically located areas. The paper describes the design retrofit process, which was continuously guided by computational mechanics analyses. Specific retrofit recommendations emerged at the end of this process and they are described in the paper. Full-scale crash tests are recommended to confirm expected benefits of the proposed retrofit.     

Metallic nanobowls by galvanic replacement reaction on heterodimeric nanoparticles

Well-defined metallic nanobowls can be prepared by extending the concept of a protecting group to colloidal synthesis. Magnetic nanoparticles are employed as "protecting groups" during the galvanic replacement of silver with gold. The replacement reaction is accompanied by spontantous dissociation of the protecting groups, leaving behind metallic nanobowls.     

Tuning and implementation variants of discrete-time ADRC

Practical implementations of active disturbance rejection control (ADRC) will almost always take place in discretized form. Since applications may have quite different needs regarding their discrete-time controllers, this article summarizes and extends the available set of ADRC implementations to provide a suitable variant for as many as possible use cases. In doing so, the gap between quasi-continuous and discrete-time controller tuning is closed for applications with low sampling frequencies. The main contribution of this article is the derivation of three different discrete-time implementations of error-based ADRC. It is shown that these are almost one-to-one counterparts of existing output-based implementations, to the point where transfer functions and coefficients can be reused in unaltered form. In this way, error-based implementations become firmly rooted in the established landscape of discrete-time ADRC. Furthermore, it becomes possible to equip error-based variants with windup protection abilities known from output-based ADRC.     

In Situ Observation of Point-Defect-Induced Unit-Cell-Wise Energy Storage Pathway in Antiferroelectric PbZrO3

Phase transition is established to govern electrostatic energy storage for antiferroelectric (AFE)-type dielectric capacitors. However, the source of inducing the phase transition and the pathway of storing the energy remains elusive so far given the ultrafast charging/discharging process under normal working conditions. Here, by slowing down the phase-transition speed using electron-beam irradiation as an external stimulus, the in situ dynamic energy-storage process in AFE PbZrO₃ is captured by using atomic-resolution transmission electron microscopy. Specifically, it is found that oxygen-lead-vacancy-induced defect core acts as a seed to initiate the antiferrodistortive-to-ferrodistortive transition in antiparallel-Pb-based structural frames. Associated with polarity evolution of the compressively strained defect core, the ferroelectric (FE)–ferrodistortive state expands bilaterally along the b-axis direction and then develops into charged domain configurations during the energy-storage process, which is further evidenced by observations at the ordinary FE states. With filling the gap of perception, the findings here provide a straightforward approach of unveiling the unit-cell-wise energy storage pathway in chemical defect-engineered dielectric ceramics.     

Wetting,reactivity, and phase formation at interfaces between Ni–Al melts and TiB2 ultrahigh‐temperature ceramic

The wetting, reactivity, and phase formation at the liquid Ni–Al/TiB₂ ceramic interfaces have been investigated at the temperatures close to the Ni–Al liquidus line. The wetting kinetics has been studied by the sessile drop technique utilizing liquid drop dispension and high‐speed high‐resolution video imaging. It is established that the wetting behavior changes from a nonreactive for the Al‐rich melts to a dissolution‐reactive for the Ni‐rich melts. For the Ni concentration ≥40 at.%, TiB₂ precipitates are found in the solidified Ni–Al droplets after the high‐temperature interaction of the melts with TiB₂ substrates. Besides, new (Al,Ti)Ni₃ and (Al,Ti)₂Ni₂₁B₆ phases are formed due to dissolution of TiB₂ ceramic in Ni‐rich melts and subsequent solidification.     

Anomalous Resistance Hysteresis in Oxide ReRAM: Oxygen Evolution and Reincorporation Revealed by In Situ TEM

The control and rational design of redox‐based memristive devices, which are highly attractive candidates for next‐generation nonvolatile memory and logic applications, is complicated by competing and poorly understood switching mechanisms, which can result in two coexisting resistance hystereses that have opposite voltage polarity. These competing processes can be defined as regular and anomalous resistive switching. Despite significant characterization efforts, the complex nanoscale redox processes that drive anomalous resistive switching and their implications for current transport remain poorly understood. Here, lateral and vertical mapping of O vacancy concentrations is used during the operation of such devices in situ in an aberration corrected transmission electron microscope to explain the anomalous switching mechanism. It is found that an increase (decrease) in the overall O vacancy concentration within the device after positive (negative) biasing of the Schottky‐type electrode is associated with the electrocatalytic release and reincorporation of oxygen at the electrode/oxide interface and is responsible for the resistance change. This fundamental insight presents a novel perspective on resistive switching processes and opens up new technological opportunities for the implementation of memristive devices, as anomalous switching can now be suppressed selectively or used deliberately to achieve the desirable so‐called deep Reset.     

Locally resolved hysteresis measurement of advanced glass-mat thermoplastic composites

With hysteresis measurement stiffness, creep and damping can be recorded at cyclic loading. Using a laser extensometer a locally resolved hysteresis measurement was formerly developed. It allows to observe several hysteresis-loops simultaneously. Local hysteresis measurement is suitable for fatigue tests of inhomogeneous materials or materials which have inhomogeneous damage process.Locally resolved hysteresis measurement was demonstrated for textile-reinforced advanced glass-mat thermoplastic composites which are interesting for structural components in automotive applications. Cyclic tension tests show stiffness degradation, creep and increasing damping especially for the fracture zones. In cyclic compression loading, the change of the material properties is less pronounced.A component test at a U-profile shows a good agreement between hysteresis measurement and major strain in the fracture zone of the U-profile recorded with digital image correlation.For the interpretation of creep and stiffness degradation at cyclic tension loading, strain oriented considerations were made. It can be shown that for the longitudinal and transversal samples a similar location of the trend-line in a total strain Wöhler-diagram can be found, therefore a total strain dominated failure behavior seems obvious. For further analysis a relative consideration concerning the development of strain amplitude and mid-strain is made. For each single test the ratio between the development of the strain amplitude and the development of the strain middle is calculated. A significant tendency of the above mentioned quotient concerning the stress amplitude can be observed.     

Modelling and experimental study of multi‐pass wire drawing of hypo‐eutectoid steels

The paper presents the results of extensive experimental research focused on the analysis of deformation conditions in multi‐pass drawing process. The wire rod of medium and high‐carbon steel manufactured with application of controlled cooling rate after hot rolling was chosen as the material to be drawn. Suitability of the wire rod for the multi‐pass drawing process was assessed by means of detailed analysis of mechanical properties of a material before drawing, after each pass as well as of the final product. The drawing process was realised without intermediate heat treatment, assuming maximum possible reduction to be attained. The effect of history of deformation (distribution and number of unit reductions, die geometry) on the mechanical properties of drawn wires was analysed. The force parameters of the drawing process were also evaluated in detail, which allowed for an attempt to determine the optimum drawing conditions. The separate part of work was the upper‐bound process modelling which included calculations of the components of power of deformation as well as the analysis of state of strain by means of strain redundancy factor evaluation. Finally, conclusions were formulated concerning suitability of the investigated wire rod for deep cold working as well as the influence of history of deformation on the product quality.     

Atomic ordering and magnetism in L10 ordered FePd alloys

Intermetallic compounds due to their promising corrosion resistance and high-temperature mechanical strength give hope for their application as high-temperature structural materials. Inter-metallics of L1₀ type structure in recent years in addition have attracted great interest as potential recording media. These alloys are ferromagnetic and display marked mechanical and magnetic anisotropy with the tetragonal c-axis of the ordered domains as the “easy axis” of magnetization High-density magnetic recording may be achieved by a preferential domain orientation with the c-axis perpendicular to the surface, if these materials can be stabilized as low-dimensional magnetic structures. Knowledge of kinetic parameters, that determine alloy stability is essential for alloy design. technical application, and performance of materials. We used FePd as a model system for this class of L1₀-ordered intermetallics and have studied the changes of long-range order during heat treatments in the bulk and in thin films produced by different techniques. Results of X-ray diffraction (XRD). resistivity measurement. Mößbauer spectroscopy, and measurement of magnetization in both geometries are compared.     

Real-time guidewire simulation in complex vascular models

The base of all training in interventional radiology aims at the development of the core skills in manipulating the instruments. Computer simulators are emerging to help in this task. This paper extends our previous framework with more realistic instrument behaviour and more complex vascular models. The instrument is modelled as a hybrid mass–spring particle system while the vasculature is a triangulated surface mesh segmented from patient data sets. A specially designed commercial haptic device allows the trainee to use real instruments to guide the simulation through the vasculature selected from a database of 23 different patients. A new collision detection algorithm allows an efficient computation of the contacts, therefore leaving more time to deal with the collision response for a realistic simulation in real time. The behaviour of our simulated instruments has been visually compared with the real ones and assessed by experienced interventional radiologists. Preliminary results show close correlations and a realistic behaviour.