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The key component in compliant actuators is the elastic element, typically a spring. Nevertheless, different types of springs have different characteristics in terms of size, weight, maximum allowable force, maximum allowable torque and maximum allowable deflection. It is however very important to compare them on these requirements, since each application has other demands. In this paper, the energy storage capacity of different types of compliant elements are calculated using scaling laws in order to easily derive the maximum achievable energy capacity for a certain arrangement. These scaling laws are given as a function of the structural parameters and are validated with catalog data of spring manufacturers and distributors such as Alcomex, Lesjofors and Century Spring. As such, different types of compliant elements can be compared in an easy way. To fully exploit the capabilities of compliant elements, these scaling laws are used to verify the effect of spring parallelization on mass and/or enclosed volume, which is interesting regarding redundant compliant actuation. From theoretical calculations and a case study, it follows that parallelization is beneficial, especially for mass reduction.

We developed a new actuator, the plus Series-Parallel Elastic Actuator (+SPEA), which is a redundant actuator using brakes. This actuator can achieve additional objectives, other than performing a given task, such as minimum electrical energy consumption. In this paper, we developed a novel control strategy which consists of solving an optimal control problem. Solving this problem allows to use the redundancy of the actuator, as the brakes, in order to achieve lower electrical consumption. The results are then compared to the consumption of an equivalent non-redundant stiff actuator. The results highlight the capability of the actuator to reduce energy consumption in comparison with the latter actuator.

This paper provides a detailed analysis of the power and mechanical/electrical energy consumption of Series Elastic Actuators (SEAs) and Parallel Elastic Actuators (PEAs). The study is done by imposing a sinusoidal motion to a pendulum load, such that the natural dynamics automatically present itself in the power and energy consumption. This allows to link the actuators' dynamics to their loss mechanisms, revealing interesting characteristics of series and parallel elastic elements in actuator designs. Simulations demonstrate that the SEA and PEA allow to decrease both peak power and energy consumption, provided that the stiffness of their elastic element is tuned properly. For the SEA, both are minimized by tuning the elastic element to the antiresonance frequency of the actuator. For the PEA, peak power is minimal at the link's resonance frequency, but the optimal stiffness for minimal electrical energy consumption cannot be determined by a theoretical resonance and needs to be calculated using a complete system model. If these guidelines are followed, both types of elastic actuators can provide significant energetic benefits at high frequencies. This was confirmed by experiments, which demonstrated energy reductions of up to 78% (SEA) and 20% (PEA) compared to rigid actuators.

A hallmark of mature mammalian ventricular myocardium is a positive force-frequency relationship (FFR). Despite evidence of organotypic structural and molecular maturation, a positive FFR has not been observed in mammalian tissue engineered heart muscle. We hypothesized that concurrent mechanical and electrical stimulation at frequencies matching physiological heart rate will result in functional maturation. To this end, we investigated the role of such biomimetic mechanical and electrical stimulation in functional maturation in engineered heart muscle (EHM) comprising collagen type I and neonatal rat heart cells. Following tissue consolidation (8 days), EHM were subjected to electrical field stimulation at 0, 2, 4, or 6 Hz for 5 days, while strained on flexible poles to facilitate auxotonic contractions. EHM stimulated at 2 and 4 Hz displayed a similarly enhanced inotropic reserve, but a clearly diverging FFR. The positive FFR in 4 Hz stimulated EHM was associated with reduced calcium sensitivity, frequency-dependent acceleration of relaxation, and enhanced post-rest potentiation. This was paralleled on the cellular level with improved calcium storage and release capacity of the sarcoplasmic reticulum, increased amounts of SERCA2a and RyR2 protein, and enhanced T-tubulation. We demonstrate that electromechanical stimulation at a frequency matching closely the physiological heart rate supports functional maturation in mammalian EHM. The observed positive FFR in EHM has important implications for the applicability of EHM in cardiovascular research and drug testing.

SANOS technology is the first time accurately analyzed and modeled. Firstly, the retention is studied on capacitors to determine the main retention mechanisms. The electron detrapping in the silicon nitride, followed by tunneling through the aluminum oxide is found to be the dominant mechanism causing the retention loss. The modeling of this effect reproduces the observed temperature, gate work function and window dependency. Secondly, these results are applied to scaled devices where the retention is dominated by the same mechanisms. The difference in the retention loss between capacitors and devices is explained by a different field distribution in the gate dielectric. Thirdly, the issue of lateral redistribution occurring at high temperature in scaled transistors is analyzed by 2D simulations and retention tests in SONOS devices.

The stress and strain partitioning between the different phases of transformation-induced plasticity (TRIP)-aided multiphase steels is evaluated using a mean field homogenization approach. The change of the austenite volume fraction under straining is predicted using a micromechanics-based criterion for the martensitic transformation adapted to the case of small, isolated, transforming austenite grains. The parameters of the model are identified from the mechanical response and transformation kinetics measured under uniaxial tension for two steels differing essentially by the austenite stability. The model is validated by comparing the predictions with tests performed under different loading conditions: pure shear, intermediate biaxial and equibiaxial. An analysis of the effect of the austenite stability on strength and ductility provides guidelines for optimizing properties according to the stress state. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The mechanical behaviour of transformation-induced plasticity (TRIP)-assisted multiphase steels is addressed based on three different microstructures generated from the same steel grade. The mechanisms responsible for the work-hardening capacity and the resulting balance between strength and resistance to plastic localization are investigated at different length scales. The macroscopic mechanical response is determined by simple shear, uniaxial tension, Marciniak and equibiaxial tension supplemented by earlier tensile tests on notched and cracked specimens. It is shown that the transformation rate reaches a maximum for stress states intermediate between uniaxial tension and equibiaxial tension. At an intermediate length scale, the true in situ flow properties of the individual ferrite–bainite and retained austenite phases are determined by combining neutron diffraction and digital image correlation. This combined analysis elucidates the partitioning of stress and strain between the different constitutive phases. Based on these results, supplemented by transmission electron microscopy and electron backscattered diffraction observations, a general overview of the hardening behaviour of TRIP-assisted multiphase steels is depicted.

This paper deals with the DC current sensor with closed loop and high accuracy, and describes the relationship between the latter and the core material magnetic properties. The coercive field H c , which controls strongly the sensor accuracy, may fluctuate heavily with operating temperature and external stresses as shown in the cases of three different FeNi alloys. Non-coated Fe–80%Ni exhibit low H c ( 1 A / m ) : this is kept ( H c ⩽ 1.2 A / m ) under strong external stresses (coating) when a low magnetostriction alloy is used. If coating-induced stresses are avoided, a FeNiCr alloy offers an interesting opportunity to get both good accuracy due to low H c ( ⩽ 2 A / m ) and a cheaper solution.

A physically based model for TRIP carbon steels is developed suitable to predict the macroscopic behaviour of multi-constituent aggregates. It includes the effects of phase composition and morphology on flow stress and strain hardening. In a first part, a detailed description of the stress-assisted and strain-induced martensitic transformation kinetics is given based on a generalised form of the Olson–Cohen model. The appearance of the much harder martensitic phase during plastic straining gives rise to a strong hardening of the retained austenite islands. The matrix behaviour is described using a model previously developed for ferritic–martensitic steels. A quite simple but accurate homogenisation approach is used to determine the TRIP steel behaviour. The predicted evolution of strain-induced martensite volume fraction, flow stress and incremental work hardening is in good agreement with experimental data and illustrates the critical importance of the retained austenite stability on the formability of TRIP steels.

The nanohardness of the phases present in the microstructure of two TRIP (for TRansformation Induced Plasticity)-assisted multiphase steels differing by their silicon content was measured by nanoindentation in an atomic force microscope. It is observed that the softest phase in both steels is the ferritic matrix, followed by bainite, austenite and martensite. It is also shown that the silicon content of the steel grades is responsible for an increase of the hardness of the ferritic matrix due to solid solution strengthening. Finally, the influence of the preparation mode of the surface prior to the nanoindentation measurements has been investigated. An electropolishing stage after mechanical polishing is acceptable to allow valuable nanohardness measurements. (C) 2002 Elsevier Science B.V. All rights reserved.

The damage resistance, fracture toughness and austenite transformation rate in transformation-induced plasticity (TRIP)-assisted multiphase steel sheets were comparatively characterised on two steel grades differing by the volume fractions of the phases (i.e. ferrite, bainite, retained austenite) and by the mechanical stability of retained austenite. The influence of stress triaxiality on austenite transformation kinetics and the coupling between martensitic transformation and damage were investigated using double edge notched (or cracked) plate specimens tested in tension. The map of the distribution of transformation rates measured locally around the notch (or the crack) was compared with the map of the effective plastic strains and stress triaxialities computed by finite element simulations of the tests. The mechanically-activated martensitic transformation was found to progress continuously with plastic straining and to be strongly influenced by stress triaxiality. Fracture resistance was characterised by means of J(R) curves and crack tip opening displacement (CTOD) measurements using DENT specimens. The fracture toughness at cracking initiation was found to be lower for the steel with higher tensile strength and ductility. The contrasted influence of the TRIP effect, which improves formability by delaying plastic localisation but reduces fracture toughness at cracking initiation, is shown to result from parameters such as the volume fraction of non-intercritical ferrite phases or the mechanical properties of martensite. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

This paper deals with the DC current sensor with open loop and high accuracy, and describes the relationship between the latter and the core-material magnetic properties in the case of Fe-50%Ni alloys. It is pointed out that air-gap precision, nonlinearity B – H and hysteresis are the main sources of accuracy; the influences of mechanical stress and temperature on coercive field are quantified and have to be taken into account in the design of the sensor. It is shown by dedicated choice of grades and annealing that Fe-50%Ni alloys may vary their coercive field from 4–6 A/m down to 1.5–4 A/m depending on the final annealing treatment used.

Does the Utilization of a Temporary External Anchoring Suture Increase the Risk of Driveline Infection After Implantation of a Left Ventricular Assist Device M. Fudim,1 C.L. Brown,1 M.E. Davis,2 M. Djunaidi,2 M.R. Danter,3 F.E. Harrell,4 N.A. Haglund,1 S. Maltais .3 1Cardiovascular Medicine, Vanderbilt Univ Med Ctr, Nashville, TN; 2Vanderbilt Univ Med Ctr, Nashville, TN; 3Cardiac Surgery, Vanderbilt Univ Med Ctr, Nashville, TN; 4Biostatistics, Vanderbilt Univ Med Ctr, Nashville, TN.