low cycle fatigue hysteresis by thermographic and digital image correlation methodologies a first approach

Abstract The energetic behaviour of the material under low-cycle fatigue (LCF) can be controlled by the hysteresis cycle in order to define the variation of the mechanical characteristics and to forecast the fatigue and the failure response. The traditional analysis is performed using the force-displacement signals derived by the testing machine that can be coupled with other measuring methodologies. In the present paper, the authors have used the Digital Image Correlation (D.I.C.) to better define the specimen displacement, avoiding many errors of the displacement measurement chain. The thermographic analysis (T.A.), able to follow quickly and with great accuracy the energetic variations, was combined with the stress-strain measurements, allowing to calculate the damping energy. The results pointed out a similar behaviour between the hysteresis areas defined basing on the D.I.C. displacements and those found by the testing machine outputs, but substantial differences in terms of values. The thermal variations and the areas of the hysteresis loops, both linked to the plastic energy, were compared, showing a reliable agreement

Effect of cyclic torsional preloading on cyclic fatigue resistance of ProTaper Next and Mtwo nickel–titanium instruments

Aim: To evaluate the influence of different torsional preloads on cyclic fatigue resistance of endodontic rotary instruments made by conventional nickel–titanium (NiTi) or M-Wire. Methods: Eighty new Mtwo (#25/0.06) (Sweden & Martina, Due Carrare, Padova, Italy) and ProTaper Next X2 (Dentsply Maillefer, Ballaigues, Switzerland) were used. The Torque and distortion angles at failure of new instruments (n = 10) were measured and 0% (n = 10), 25%, 50%, and 75% (n = 20) of the mean ultimate torsional strength as preloading condition were applied according to ISO 3630-1 for each brand. The twenty files tested for every extent of preload were subjected to 25 or 50 torsional cycles (n = 10). After torsional preloading, the number of cycles to failure was evaluated in a simulated canal with 60° angle of curvature and 5 mm of radius of curvature. Data were analyzed using 2-way analysis of variance. Scanning electron microscope (SEM) was performed to evaluate the fracture surface of each fragment. Results: ProTaper Next X2 reduced their cyclic fatigue after 25 or 50 cycles of every torsional preloading (25%, 50%, and 75%) (P < 0.01). Cyclic fatigue of Mtwo was reduced by 50 cycles of every torsional preloading and only after the 75% of preload for 25 cycles (P < 0.01). Conclusions: Torsional preloads reduced the cyclic fatigue resistance of M-wire and conventional (as ProTaper Next and Mtwo) NiTi rotary instruments except for Mtwo with 25% or 50% of torsional preloading

Cyclic fatigue resistance, torsional resistance, and metallurgical characteristics of M3 Rotary and M3 Pro Gold NiTi files

Objectives: To evaluate the mechanical properties and metallurgical characteristics of the M3 Rotary and M3 Pro Gold files (United Dental). Materials and Methods: One hundred and sixty new M3 Rotary and M3 Pro Gold files (sizes 20/0.04 and 25/0.04) were used. Torque and angle of rotation at failure (n = 20) were measured according to ISO 3630-1. Cyclic fatigue resistance was tested by measuring the number of cycles to failure in an artificial stainless steel canal (60° angle of curvature and a 5-mm radius). The metallurgical characteristics were investigated by differential scanning calorimetry. Data were analyzed using analysis of variance and the Student-Newman-Keuls test. Results: Comparing the same size of the 2 different instruments, cyclic fatigue resistance was significantly higher in the M3 Pro Gold files than in the M3 Rotary files (p < 0.001). No significant difference was observed between the files in the maximum torque load, while a significantly higher angular rotation to fracture was observed for M3 Pro Gold (p < 0.05). In the DSC analysis, the M3 Pro Gold files showed one prominent peak on the heating curve and 2 prominent peaks on the cooling curve. In contrast, the M3 Rotary files showed 1 small peak on the heating curve and 1 small peak on the cooling curve. Conclusions: The M3 Pro Gold files showed greater flexibility and angular rotation than the M3 Rotary files, without decrement of their torque resistance. The superior flexibility of M3 Pro Gold files can be attributed to their martensite phase

Comparison between 3D-reconstruction optical methods applied to bulge-tests through a feed-forward neural network

The mechanical behaviour of rubber-like materials can be investigated through numerous techniques that differ from each other in costs, execution times and parameters described. Bulge test method proved helpful for hyperelastic membranes under plane and equibiaxial stress state. In the present study, bulge tests in force control were carried out on SBR 20% CB-filled specimens. 3D reconstructions of the dome were achieved through two different stereoscopic techniques, the epipolar geometry and the Digital Image Correlation. Through a Feed-Forward Neural Network (FFNN), these reconstructions were compared with the measurements by a laser triangulation sensor taken as reference. 3D-DIC reconstruction was found to be more accurate. Indeed, bias errors of the 3D-DIC and epipolar techniques with respect to the relative reference values, under creep condition, were 0.53 mm and 0.87 mm, respectively.<br /

Poly(ferrocenylsilane) gels and hydrogels with redox-controlled actuation

This concise paper discusses poly(ferrocenylsilane) (PFS)-based organometallic gels and hydrogels as a novel class of redox-responsive materials. First, the use of silicon-bridged spirocyclic [1]ferrocenophane crosslinkers for creating PFS networks swellable in organic solvents is described. Optical properties of PFS composite colloidal crystal films, composed of monodisperse silica spheres embedded in such PFS networks, are shown to be influenced by solvent swelling or redox chemistry, allowing the use of these composites in photonic crystal full-color displays. The synthesis of networks composed of water-soluble PFS polyanions or polycations is discussed. In response to redox stimuli, a polyanionic PFS-hydrogel exerted a pressure, which could render it useful as an actuator

Prognostic Health Management Using IR Thermography: The Case of a Digital Twin of a NiTi Endodontic File

Prognostic and health management technologies are increasingly important in many fields where reducing maintenance costs is critical. Non-destructive testing techniques and the Internet of Things (IoT) can help create accurate, two-sided digital models of specific monitored objects, enabling predictive analysis and avoiding risky situations. This study focuses on a particular application: monitoring an endodontic file during operation to develop a strategy to prevent breakage. To this end, the authors propose an innovative, non-invasive technique for early fault detection based on digital twins and infrared thermography measurements. They developed a digital twin of a NiTi alloy endodontic file that receives measurement data from the real world and generates the expected thermal map of the object under working conditions. By comparing this virtual image with the real one acquired by an IR camera, the authors were able to identify an anomalous trend and avoid breakage. The technique was calibrated and validated using both a professional IR camera and an innovative low-cost IR scanner previously developed by the authors. By using both devices, they could identify a critical condition at least 11 s before the file broke

Digital Modernism Heritage Lexicon

The book investigates the theme of Modernism (1920-1960 and its epigones) as an integral part of tangible and intangible cultural heritage which contains the result of a whole range of disciplines whose aim is to identify, document and preserve the memory of the past and the value of the future. Including several chapters, it contains research results relating to cultural heritage, more specifically Modernism, and current digital technologies. This makes it possible to record and evaluate the changes that both undergo: the first one, from a material point of view, the second one from the research point of view, which integrates the traditional approach with an innovative one. The purpose of the publication is to show the most recent studies on the modernist lexicon 100 years after its birth, moving through different fields of cultural heritage: from different forms of art to architecture, from design to engineering, from literature to history, representation and restoration. The book appeals to scholars and professionals who are involved in the process of understanding, reading and comprehension the transformation that the places have undergone within the period under examination. It will certainly foster the international exchange of knowledge that characterized Modernism