Abstract: The objective of this work was the development of a processing methodology for embedding NiTi fibers into a polymer-based composite plate. A carbon fiber reinforced polymer (CFRP) prepreg and NiTi thin wires were used. A uniaxial hot press was prepared to be used in the composite processing. Two prototypes were fabricated to provide fiber alignment and fixation fixture. A CFRP composite plate without fiber and another with NiTi fibers were processed. Micrometers and a universal materials testing machine were used to measure the plate thickness and Young's modulus. It was possible to develop a processing methodology for embedding NiTi fibers into a polymer-based composite plate. The CFRP plate without fiber presented almost no variation in plate thickness and Young's modulus measurement thus enabling the CFRP manufacture by the hot uniaxial press. The fiber fixation fixture developed was able to produce CFRP-NiTi fiber hybrid composites with different number of fibers embedded, the spacing distance between fibers was at least 1 mm and the fiber alignment was achieved.
Abstract: Shape memory alloys (SMA) are thermo-responsive materials where deformation can be induced and recovered through temperature changes. Therefore, SMA are considered smart materials. In this work, an epoxy beam reinforced by NiTi SMA wires was developed. This active composite contains five pre-trained NiTi SMA wire actuators, evenly distributed along the neutral plane of the epoxy beam, which can be activated by resistive heating. The results of different ways for electrical activation of the smart composite in a simply clamped mode are discussed. It was possible to demonstrate the viability of this concept for attenuation of mechanical vibrations by controlled electrical heating of the NiTi wire actuators.
Abstract: The rocket propellant ignition system uses electro-explosive device actuated by wire electrode. Those wires are usually made by Fe-Ni based alloy with controlled thermal expansion inserted into a ceramic feed-through and are connected to thin resistive wire which is heated through the passage of an electrical current for propellant ignition. The contact between ceramic feed-through and wires should be reliable since sometimes it could fail. A novel alternative process is to use SMA wires taking into account the shape recovery effect constraining the wire inside the feed-through. The recovery stress of 326 MPa for 4% pre-strain should be enough to constrain the wire inside the feed-trough avoiding the gas leakage.
Abstract: The possibility of uniting two or more different materials to obtain structures capable to feel and adapt to environmental alterations and operational conditions, has been leading to the development of active composites with functional properties that makes possible the control of shape, vibration, rigidity and/or structural integrity monitoring. These characteristics are very well accepted in modern technological applications. In this context, active composites were manufactured using pre-impregnated (Pre-Pregs) of carbon fiber reinforced polymer (CFRP) and NiTi shape memory alloy (SMA) thin wires in different conditions. The functional capacity of the obtained CFRP-NiTi smart composites was verified through detection of buckling and thermal contraction/expansion effects by electrical heating of the NiTi wires inside the CFRP matrix. Although the NiTi wires represent a minimum volumetric fraction in the CFRP-NiTi produced systems, its influence was evidenced.
Abstract: The relevant and unique thermomechanical properties of shape memory alloys (SMA) have motivated researches for applications in several fields of engineering. The pseudoelasticity and shape memory effect (SME) are some behaviors displayed by these functional materials. The aim of the current work is the manufacture, physical characterization and investigation of electro-thermomechanical response of a SMA copper-based cylindrical element aiming the development of a smart electrical connector. The cylindrical element was manufactured by plasma melting and injection molding of a CuAlNi based SMA. During thermal activation, the SMA cylindrical element presented satisfactory movement of closure through the recovery of its shape, demonstrating a strong potential to generate normal contact forces useful for electrical connections.
Abstract: Shape Memory Alloys (SMA) are smart materials that have attracted increasing attention due to their superior damping properties when compared to conventional structural materials. These functional materials exhibit high damping capacity during phase transformation as well as in the low temperature martensitic state. In this work NiTi SMA, commercial aluminum, stainless steel and brass were submitted to dynamic mechanical analysis (DMA) in a single cantilever mode. Small beam specimens were manufactured to accomplish the DMA tests. The studied NiTi presented a damping capacity peak during phase transformation, being much higher than damping of conventional materials. NiTi SMA also showed an increase of storage modulus after conversion of low temperature phase to high temperature phase while an almost linear decrease is observed for the conventional materials studied.
Abstract: Most of the applications of NiTi SMA are as a wire form. In this sense it is important to know the effects of thermo-mechanical processing such as reduction per pass and intermediate annealing on the wire drawing process. For this work they were produced wire by cold drawing using 15 % area reduction per pass with and without intermediate annealing. The starting ingot was produced by VIM process. The influence of thermo-mechanical processing will be related to the martensitic transformation temperatures.
Abstract: The use of smart material such as Ti-Ni in actuators application requires an intense mechanical and metallurgical investigation to understand its behavior. This paper studies martensitic transformation using DSC and X-ray diffraction techniques to compare shape memory parameters in Ti-50.2%Ni (A1) and equiatomic Ti-50.0%Ni (A2) Alloys. The as as-received samples were submitted to annealing at 400°C and 500°C for 24 hours then quenched in at 25°C. The influence of heat treatment on martensitic transformations temperatures and the appearance of R-phase were analyzed using DSC and X-ray diffraction.
Abstract: Earlier works showed that NiTi shape memory alloy production by electron beam melting (EBM) is a viable process in which its main characteristic is the low contamination by impurities such as carbon and oxygen. Some difficulties arise when compared to conventional vacuum induction melting (VIM) process such as composition control and complex machine operation. This work focus on the production of ever made large scale 150mm in diameter NiTi ingot produced by EBM showing its viability. The carbon contamination was only 0.016wt% compared to usual 0.05wt% of VIM process. The ingot radial composition homogeneity was proved by small variation presented by direct and reverse peak martensitic transformations temperatures which was around 2°C.