Papers by Keyword: Shape Memory Materials

Abstract: The latest research directions related to the design of protective clothing concern implementation of smart materials, such as shape memory alloys (SMA), that allow for its functionalization which could not be achieved with traditional materials. As a result of the research project, a thermo-mechanical treatment program of a nickel-titanium alloy has been elaborated. This program allows to obtain active elements in a form of conical springs that are characterized by two-way shape memory effect and predestined for implementation into protective clothing. Textile materials with SMA elements intended for clothing protecting against flame, radiant heat and molten splashes have been developed and manufactured. Laboratory tests aimed at evaluation of the obtained shape change effect were performed according to the specially modified testing methodology. The test results indicated that SMA elements caused an improvement of the protective properties of textile materials due to their increased thickness and creation of an additional air layer. On the basis of the achieved results, it can be also stated that protection performance of clothing according to the EN ISO 11612:2015 can be increased from level 1 to level 2 by means of textile materials with SMA elements.

Abstract: In this contribution, the preparation and characterization of new shape-memory epoxy based nanocomposites filled with modified multiwalled carbon nanotubes are reported. The study has been focused on the optimization of the preparation methodology and on the evaluation of the effect of different contents of surface modified carbon nanotubes on the properties and the microstructure of the obtained materials. In particular, dispersion test, infrared spectroscopy, thermogravimetric analysis and bright field transmission electron microscopy have been carried out to analyze the modified filler. Moreover, the obtained nanocomposites have been characterized by morphological analysis, differential scanning calorimetry, thermomechanical analysis and X-ray analysis in order to clarify the effect of the nanofiller on the structure and shape memory properties of the materials.

Abstract: The dynamic response of structures subjected to high-amplitude vibration is often dangerous and undesirable. Dynamic vibration absorbers (DVA) have received special attention in recent years due to vibration attenuation offered by them. Thus, the present study analyzes the nonlinear dynamics of a system with a dynamic vibration absorber (DVA) using a shape memory material (SMM) whose characteristics are highly dependent upon temperature. The restoring force of the oscillator is provided by a shape-memory device (SMD) described by a thermomechanical model capable to describe the hysteretic behavior via the evolution of a suitable internal variable. Numerical simulations show the effectiveness of using the SMM in reducing oscillations of a harmonic oscillator.

Abstract: Using laser cladding method, the coating of Fe-Mn-Si shape memory materials (SMM) was prepared on the surface of AISI 304 stainless steel. The microstructure and microhardness of SMM laser cladding coating were measured by using a metallographic microscope and a scanning electron microscope, respectively. The phase composition was determined by X-ray diffraction. The wear resistance was evaluated on a high speed reciprocating friction tester. The results show that microhardness of the SMM coating is about Hv263, higher than that of the substrate (Hv225); the SMM coating is composed of ε-martensite and γ-austenite phases; the average friction coefficient of the substrate and SMM coating is about 0.85 and 0.71; the SMM laser cladding coating is of excellent wear resistance validated by friction coefficient, worn-out appearance and wear loss.

Abstract: The shape memory effect is associated to the recovering of a previous memorized shape due to an external action, generally a thermic triggering. In this work, we show the state of the art of shape memory materials and their applications especially as actuators and integrated in more complex machines.

Abstract: Poly (glycerol-sebacate) (PGS) is a recently synthesized elastomer with superior mechanical property, biocompatibility and biodegradation, and serves as soft tissue regeneration and engineering materials or contact guidance materials. The samples for shape memory measurements were prepared by a two steps method. The microstructure and thermal properties of PGS are studied by using Fourier transform infrared (FTIR), differential scanning calorimetry (DSC) and Dynamic-mechanical analysis (DMA) methods. The shape memory effect of PGS is recorded by bending test. It was found that a crosslinked, three-dimensional network of the PGS acting as fixed phase and the amorphous phase of the PGS acting as reversible phase are the two necessary conditions for PGS with shape memory behavior. The response temperature of shape memory is dependent on the glass transition temperature of PGS. The PGS polymer with a high elasticity and a shape-memory ratio of almost 100% showed excellent shape memory effect.

Abstract: NiAl shape memory alloy thin films have been fabricated by a solid-state reaction in Al/Ni bilayer films. Two kinds of synthesis have been used. The first one consists in heating an Al/Ni bilayer film system to temperatures above 480 K. The second one implies the successive deposition of nickel and aluminum films onto a substrate with a temperature above 480 K. Regardless of a kind of the solid-state synthesis, the films obtained reveal a two-way shape memory effect. It is supposed that the solid-state reaction in Al/Ni bilayers starts at a temperature AS of the reverse of the martensitic transition in NiAl alloy. This indicates that the NiAl shape memory alloy thin films can be formed directly during the synthesis without need for lengthy heat treatment.

Abstract: D03-ordered Fe3Al single crystals containing 23, 25 and 28at.%Al were cyclically deformed at [ 49 1 ] loading axis in tension-compression mode. Giant pseudoelasticity took place in Fe-23 and 25at.%Al single crystals at an early stage of cyclic deformation, while a slight strain recovery was observed in Fe-28at.%Al. In Fe-23 and 25at.%Al single crystals, superpartial dislocations with Burgers vector of 1/4[111] moved individually dragging the nearest neighbour anti-phase boundary (NNAPB). The NNAPB pulled back the superpartials during unloading, resulting in giant pseudoelasticity and low residual dislocation density. In contrast, a couplet of the superpartials was observed to bow out leaving two superpartials in Fe-28at.%Al. This means that the dislocation couplet dragged the next-nearest neighbour anti-phase boundary (NNNAPB). The surface tension of NNNAPB is lower than that of NNAPB resulting in a slight strain recovery in Fe-28at%Al. As cyclic deformation proceeded, residual dislocation density increased with an increase in the number of cycles even in Fe-23 and 25at.%Al. In particular, persistent slip bands (PSB) were formed in Fe-23at.%Al single crystals, though PSB is seldom observed in fatigued intermetallic compounds. To-and-fro motion of superpartials during loading and unloading was suppressed by dislocation bundles, resulting in a reduced shape recovery. However, large strain recovery occurred in Fe-25at.%Al single crystals at a strain amplitude of 1.0% even at 20cycles. It was also noted that Fe-23 and 25at.%Al demonstrated tension-compression asymmetry even at [ 49 1 ] orientation; the yield stress in compression was higher than that in tension. This implies that the core structure of <111> screw dislocation played an important role in the deformation behaviour of Fe3Al single crystals.