Functional fatigue of NiTi Shape Memory wires for a range of end loadings and constraints

The availability of engineering strength data on shape memory alloys (SMAs) under cyclic thermalactivation (functional fatigue) is central to the rational design of smart actuators based on these materials. Testresults on SMAs under functional fatigue are scarce in the technical literature and the few data available aremainly limited to constant-stress loading. Since the SMA elements used within actuators are normally biased byelastic springs or by another SMA element, their stress state is far from constant in operation. The mismatchbetween actual working conditions and laboratory arrangements leads to suboptimal designs and underminesthe prediction of the actuator lifetime. This paper aims at bridging the gap between experiment and reality. Fourtest procedures are planned, covering most of the typical situations occurring in practice: constant-stress,constant-strain, constant-stress with limited maximum strain and linear stress-strain variation with limitedmaximum strain. The paper describes the experimental apparatus specifically designed to implement the fourloading conditions and presents fatigue results obtained from commercial NiTi wires tested under all thoseprotocols

Functional fatigue of shape memory wires under constant-stress and constant-strain loading conditions

Abstract Shape memory alloys (SMAs) are increasingly used for the construction of simple solid-state actuators characterized by outstanding power density. The rational design of these actuators requires reliable data on the fatigue strength of the alloy under cyclic thermal activation (functional fatigue). The technical literature shows scanty test results for SMAs under functional fatigue. Furthermore, the few data available are mainly limited to the condition of constant stress applied to the material. Sincethe SMA elements used within actuators are normally biased by conventional springs or by another SMA element, their stress condition is far from constant in operation. The disagreement between actual working conditions and laboratory conditions leadsto suboptimal designs and undermines the prediction of the life of the actuator. This paper aims at bridging the gap between experiment and reality. Four characteristic test conditions are envisioned, covering most of the actual situations occurring inpractice: constant-stress, constant-strain, constant-stress with controlled maximum strain and cyclic-stress with controlled maximum strain. The paper presents the experimental apparatus specifically designed to implement the four test conditions. Fatigue results on a commercial NiTi wire (0.15 mm diameter) tested under constant-stress and constant-strain loading are also presented and discussed

Optimum Mechanical Design of Binary Actuators Based on Shape Memory Alloys

This chapter describes the optimum mechanical design of shape memory based actuators. The authors show how to exploit the Shape Memory Alloy (SMA) to design silent, compact and light binary actuators. Two simple mechanical models are considered to describe the SMA behaviour and design equations are provided for two classes of actuators. First SMA actuators are analyzed and designed on the basis of the backup element needed to recover the stroke. Second SMA actuators are improved by adding a compensator system to enhance the output mechanical response, especially in terms of available stroke. Useful design procedures are provided to help the engineer in the synthesis of SMA actuators. Starting from the design specifications, a step by step procedure is built to define the mechanical dimension of the SMA active elements, of the backup system and of the compensator

AFLATOXIN B1 IN CORN: DIRECT VERIFICATION OF CONTAMINATION THROUGH AN AUTOMATIC COMPUTERIZED SYSTEM BASED ON THE FLUORESCENCE

"Aflaflesh" is a computer based instrument, designed combining a visual data acquisition system with a sophisticated software of acquisition and analysis of images. This system allows you to check on a representative sample (5/10 kg) contamination of corn by AFB1, using fluorescence under UV light when the grain is contaminated. To optimize the use of this control equipment were analyzed in two phases, a total of 80 samples comparing the results obtained by chemical analysis (Hplc) to those obtained using "Aflaflesh". Initially the study was set to correlate the number of contaminated grains to the ppb read by the official method, Hplc; the second step was to correlate ppb values to the number of pixel of contaminated surface of the grains read by the "Aflaflesh" instrument. The apparatus was then calibrated through a statistical analysis of the results obtained, to allow a direct reading of the AFB1 concentrations in a short period of time (15 min) without the assistance of specialized personnel

Achieving DFT accuracy with a machine-learning interatomic potential: Thermomechanics and defects in bcc ferromagnetic iron

We show that the Gaussian Approximation Potential machine learning framework can describe complex magnetic potential energy surfaces, taking ferromagnetic iron as a paradigmatic challenging case. The training database includes total energies, forces, and stresses obtained from density-functional theory in the generalized-gradient approximation, and comprises approximately 150,000 local atomic environments, ranging from pristine and defected bulk configurations to surfaces and generalized stacking faults with different crystallographic orientations. We find the structural, vibrational and thermodynamic properties of the GAP model to be in excellent agreement with those obtained directly from first-principles electronic-structure calculations. There is good transferability to quantities, such as Peierls energy barriers, which are determined to a large extent by atomic configurations that were not part of the training set. We observe the benefit and the need of using highly converged electronic-structure calculations to sample a target potential energy surface. The end result is a systematically improvable potential that can achieve the same accuracy of density-functional theory calculations, but at a fraction of the computational cost

A Conceptual Representation of Documents and Queries for Information Retrieval Systems by Using Light Ontologies

International audienceThis article presents a vector space model approach to representing documents and queries, based on concepts instead of terms and using WordNet as a light ontology. Such representation reduces information overlap with respect to classic semantic expansion techniques. Experiments carried out on the MuchMore benchmark and on the TREC-7 and TREC-8 Ad-hoc collections demonstrate the effectiveness of the proposed approach

Model-Based Analysis of Flow-Mediated Dilation and Intima-Media Thickness

We present an end-to-end system for the automatic measurement of flow-mediated dilation (FMD) and intima-media thickness (IMT) for the assessment of the arterial function. The video sequences are acquired from a B-mode echographic scanner. A spline model (deformable template) is fitted to the data to detect the artery boundaries and track them all along the video sequence. The a priori knowledge about the image features and its content is exploited. Preprocessing is performed to improve both the visual quality of video frames for visual inspection and the performance of the segmentation algorithm without affecting the accuracy of the measurements. The system allows real-time processing as well as a high level of interactivity with the user. This is obtained by a graphical user interface (GUI) enabling the cardiologist to supervise the whole process and to eventually reset the contour extraction at any point in time. The system was validated and the accuracy, reproducibility, and repeatability of the measurements were assessed with extensive in vivo experiments. Jointly with the user friendliness, low cost, and robustness, this makes the system suitable for both research and daily clinical use

DevOps and its Philosophy : Education Matters!

DevOps processes comply with principles and offer practices with main objective to support efficiently the evolution of IT systems. To be efficient a DevOps process relies on a set of integrated tools. DevOps is among the first competencies together with Agile method required by the industry. As a new approach it is necessary to develop and offer to the academy and to the industry training programs to prepare our engineers in the best possible way. In this chapter we present the main aspects of the educational effort made in the recent years to educate to the concepts and values of the DevOps philosophy. This includes principles, practices, tools and architectures, primarily the microservices architectural style, which shares many aspects of DevOps approaches especially the modularity and flexibility which enables continuous change and delivery. Two experiences have been made, one at academic level as a master program course and the other, as an industrial training. Based on those two experiences, we provide a comparative analysis and some proposals in order to develop and improve DevOps education for the future

An MRI volumetric study for leg muscles in congenital clubfoot

PURPOSE: To investigate both volume and length of the three muscle compartments of the normal and the affected leg in unilateral congenital clubfoot. METHODS: Volumetric magnetic resonance imaging (VMRI) of the anterior, lateral and postero-medial muscular compartments of both the normal and the clubfoot leg was obtained in three groups of seven patients each, whose mean age was, respectively, 4.8 months, 11.1 months and 4.7 years. At diagnosis, all the unilateral congenital clubfeet had a Pirani score ranging from 4.5 to 5.5 points, and all of them had been treated according to a strict Ponseti protocol. All the feet had percutaneous lengthening of the Achilles tendon. RESULTS: A mean difference in both volume and length was found between the three muscular compartments of the leg, with the muscles of the clubfoot side being thinner and shorter than those of the normal side. The distal tendon of the tibialis anterior, peroneus longus and triceps surae (Achilles tendon) were longer than normal on the clubfoot side. CONCLUSIONS: Our study shows that the three muscle compartments of the clubfoot leg are thinner and shorter than normal in the patients of the three groups. The difference in the musculature volume of the postero-medial compartment between the normal and the affected side increased nine-fold from age group 2 to 3, while the difference in length increased by 20 %, thus, showing that the muscles of the postero-medial compartment tend to grow in both thickness and length much less than the muscles of the other leg compartments