Outcomes from elective colorectal cancer surgery during the SARS-CoV-2 pandemic

This study aimed to describe the change in surgical practice and the impact of SARS-CoV-2 on mortality after surgical resection of colorectal cancer during the initial phases of the SARS-CoV-2 pandemic

Microstructural and Thermo-Mechanical Characterization of Cast NiTiCu20 Shape Memory Alloy

Among NiTi-based alloys, one of the most promising and exploited alloys is NiTiCu, since the addition of Cu in substitution of Ni in the binary equiatomic NiTi has a significant influence on the martensitic transformation and the thermomechanical properties of the system. A high content of Cu improves the damping properties at the expense of phase homogeneity and workability. The present study focuses on an alloy with a high copper content, i.e., 20 at.%. For this specific composition, the correlation between the thermal treatments, microstructure, formation of secondary phases, and damping properties are investigated by several analyses. The microscopic observation, together with the compositional analysis, allowed the determination of four different phases in the alloy. Both the calorimetry and dynamic thermo mechanical measurements, which confirmed the high damping ability of the alloy, provided a characterization of the martensitic transition. Finally, the electron backscatter diffraction (EBSD) analysis detected the different crystallographic structures (i.e., cubic austenite, orthorhombic martensite, and cubic (face-centered) NiTi2) and their orientation in the different phases. Therefore, the present work aims to improve the knowledge of the role of secondary phases in the optimization of the NiTiCu20 alloy as a valuable alternative to typical alloys used for damping purposes

A Study on Damping Property of NiTi Elements Produced by Selective Laser‐Beam Melting

The damping properties of NiTi elements produced through selective laser melting are investigated by tuning the process parameters. To this end, twelve parameters’ sets are selected to fabricate fully-dense NiTi specimens. Damping is evaluated through loss factor index, mechanical loading cycles (up to 104 cycles), solicitation frequency and strain amplitude. Results confirm that NiTi fabricated through selective laser-beam melting is an excellent candidate to substitute conventional materials when used in the martensite phase. Furthermore, the selected process parameters enable specific damping performances that can be collected in damping maps which turn out to be practical tools for the fabrication of NiTi parts with tunable damping response

Study of pseudoelastic systems for the design of complex passive dampers: Static analysis and modeling

This work presents an experimental and numerical analysis of several parallel systems of NiTi pseudoelastic wires. Standard tensile tests were accomplished to evaluate the global damping capacity, the energy dissipated per cycle and the maximum attenuated force in a static condition. Besides, a numerical model was implemented to predict the damping response of more complex pseudoelastic arrangements. It was found a damping capacity upper limit of 0.09 regardless the number and the length of the NiTi components. In addition, it was found that the energy dissipated per cycle is related to the strain and to the number of the NiTi components; furthermore, the system composed of NiTi wires with different length allows for an elastic region that is related to the numbers of wires and that presents a modulation of the stiffness. Finally, the proposed numerical model allows a precise design of complex pseudoelastic combinations as it is able to represent the rhombohedral characteristic

Towards an understanding of the functional properties of NiTi produced by powder bed fusion

In this work, near fully dense NiTi components have been fabricated using a 55.2Ni-Ti (wt.%) powder through selective laser beam melting. The effect of the manufacturing process on mechanical and functional properties of the selected NiTi alloy has been systematically investigated by tuning the hatching distance, h, and the scanning speed, v, in order to define a set of 12 NiTi families. The as-built NiTi parts present phase transformation temperatures higher than those of the feedstock, ascribed to the depletion of Ni during the process. Pseudoelasticity and shape memory responses have been evaluated through uniaxial compression and bending measurements, respectively. Both quasi-static and dynamic analyses have been considered. It is shown that the resulting material may exhibit distinct damping and strain recovery responses depending on the used process parameters

Investigation of microstructural influence on entropy change in magnetocaloric polycrystalline samples of NiMnGaCu ferromagnetic shape memory alloy

Among NiMnGa-based quaternary systems, NiMnGaCu exhibits an interesting giant magnetocaloric effect thanks to the temperature overlapping of magnetic transition and thermoelastic martensitic transformation (TMT), in particular for compositions with ≈6 at% Cu content. In the present work polycrystalline alloy samples with Ni50Mn18.5Cu6.5Ga25 chemical composition were prepared. We present an extensive calorimetric and structural characterization to explore the correlation between microstructural properties and magnetocaloric response induced by means of selected thermal treatments, likely driven by the contribution of TMT to the magnetocaloric effect. Our results give important hints on how the efficiency of the martensitic transition and its modulation in temperature has a final effect on the total ΔS change. Keywords: Magnetic Shape Memory Alloys, Calorimetric investigation, Thermoelastic martensitic transition, Magnetocaloric effect, Thermal treatment, NiMnGaC

A Study of a Cryogenic CuAlMn Shape Memory Alloy

In extreme temperature environments, a newly emerging engineering application involves both the active and passive control of structures using cryogenic shape memory alloys, which are smart materials able to recover high deformation below the freezing point. With the objective of carrying out new advances in this area, the present work aims to investigate the Cu-7.5Al-13.5Mn (wt.%) shape memory alloy. Thermal, microstructural, and thermomechanical analyses of as-cast and hot-rolled specimens were performed, taking into account the effects of annealing and solubilization. It was observed that the phase transition occurs at temperatures below 120 K and changes according to the thermo-mechanical path. Specifically, hot-rolling lowers the phase transition temperature range with respect to the as-cast condition–from 34 K to 23 K for Mf, and from 89 K to 80 K for Af. Additionally, when the annealing temperature rises, the phase transformation temperature increases as well, and the alloy loses its cryogenic features when heat treated above 473 K. Finally, loss factors of 0.06 and 0.088, which were respectively found in dynamic and static settings, validate the material’s good damping response