Memory Effect Properties Research Articles

Tunable crystallization behavior, memory effect, and thermo-mechanical properties of biobased polyamides PA5X

To reduce carbon dioxide emissions, the development of sustainable bio-based polyamides with performance advantages has become the focus of widespread attention. 1,5-Pentanediamine (PDA) is a renewable monomer produced by decarboxylation of lysine, which can be used as a sustainable alternative to traditional petroleum-based diamines and play a crucial role in the synthesis of bio-based polyamides. Herein, a series of bio-based aliphatic polyamides (PA5X) synthesized from PDA and aliphatic diacids with different methylene groups were successfully prepared via melt polycondensation. Their chemical structures were characterized, and the effects of diacid chain length on crystallization behavior, memory effect, and thermo-mechanical properties were emphatically investigated. The results show that the melting and crystallization temperatures of PA5X decrease with increasing diacid chain length. Meanwhile, the PA5X exhibits high thermal stability, with Td,5 % exceeding 380 °C. Unlike the even-even polyamide, the crystalline form of PA5X is γ-form, and the crystallization behavior and spherulitic morphology change significantly with diacid chain length, which is attributed to the complex entanglement effects. More particularly, the correlation between the diacid chain length and the melt memory effect is explored. PA56 with shorter methylene groups exhibits stronger melt memory effects due to the memory effects being directly affected by segmental chain interactions. Moreover, PA5X exhibits comparable or even superior tensile strength and ductility compared with hexamethylenediamine-based polyamide (PA6X) and reported fully bio-based PA11. This work provides a comprehensive investigation into the structure-property relationship of the bio-based polyamide PA5X, demonstrating great potential for application in high-performance eco-friendly materials.

Application and progress of NiTi alloys in vascular interventional medical devices

Nowadays there has been a substantial escalation in the consumption of the global annual mortality rate due to cardiovascular and cerebrovascular diseases, and the traditional stainless-steel materials used for interventional treatments are sometimes unsuitable for thinner vascular walls. Hence it is imperative to undertake a comprehensive analysis of novel materials in the field of vascular intervention, and NiTi alloys are one of the best materials among them. NiTi alloys are the shape-memory alloys that undergo a phase transformation under certain temperatures and pressures. Owing to its shape memory effect and superelastic properties, it is extensively utilized in the medical filed, representing a future direction for smart materials. As the field of medical intervention evolves, the advantages of NiTi alloys in vascular interventional medical devices are increasingly recognized due to their superior performance, garnering widespread attention. As a result, analyzing their medical applications is required in order to promote interdisciplinary integration. This review summarizes the structural properties, preparation methods, and application areas of NiTi alloys as medical devices for vascular interventions. It also analyzes the properties of NiTi alloys when used as stents or guidewires in specific scenarios, and discusses the current shortcomings, future development directions and application prospects.

Hysteresis gap-shrinking and structural effects of minor Al and Ti modifications on binary CuAl-based high-temperature shape memory alloys

Cu-based shape memory alloys (SMAs), except for exhibiting shape recovery, superelasticity, and high damping, are desirable because these smart materials have higher electrical and thermal conductivity and much lower prices than NiTi SMAs. However, they also have some downsides in mechanical strength and brittleness (mostly stemming from their coarse grain structure) and thermal instability. Therefore, adding some grain refining elements to these SMAs to improve their shape memory effect (SME), and thermal, structural, and mechanical properties is a widespread and simple way that significantly affects their martensitic phase transitions, structure, and mechanical properties. One of these grain-refining elements is titanium. Its thermal conductivity is lower than those of Cu and Al elements and has a low solubility in Cu-matrix. Besides the effects of small Al variations, the use of minor amounts of titanium in binary CuAl-base alloys can show impressive effects on all characteristics of these shape memory alloys, such as shape memory effect properties, martensitic transformation kinetics parameters, and microstructural features. In this research work, CuAlTi ternary high-temperature shape memory alloys (HTSMAs) with new compositions were produced by the arc melting method without a complicating use of Mn or Ni components in usual ternary CuAlMn and CuAlNi shape memory alloys. Thermal analyses of the prepared samples of the alloys were investigated by using differential scanning calorimetry (DSC) and differential thermal analysis (DTA) measurements. In contrast, x-ray diffraction (XRD) test results and optical micrographs were used for analyzing the structure of the alloy samples. The effect of different amounts of low soluble and grain refining Ti element on the binary CuAl alloy system was investigated.

Graphene Oxide-Enhanced and Dynamically Crosslinked Bio-Elastomer for Poly(lactic acid) Modification.

Being a bio-sourced and biodegradable polymer, polylactic acid (PLA) has been considered as one of the most promising substitutes for petroleum-based plastics. However, its wide application is greatly limited by its very poor ductility, which has driven PLA-toughening modifications to be a topic of increasing research interest in the past decade. Toughening enhancement is achieved often at the cost of a large sacrifice in strength, with the toughness-strength trade-off having remained as one of the main bottlenecks of PLA modification. In the present study, a bio-elastomeric material of epoxidized soybean oil (ESO) crosslinked with sebacic acid (SA) and enhanced by graphene oxide (GO) nanoparticles (NPs) was employed to toughen PLA with the purpose of simultaneously preserving strength and achieving additional functions. The even dispersion of GO NPs in ESO was aided by ultrasonication and guaranteed during the following ESO-SA crosslinking with GO participating in the carboxyl-epoxy reaction with both ESO and SA, resulting in a nanoparticle-enhanced and dynamically crosslinked elastomer (GESO) via a β-hydroxy ester. GESO was then melt-blended with PLA, with the interfacial reaction between ESO and PLA offering good compatibility. The blend morphology, and thermal and mechanical properties, etc., were evaluated and GESO was found to significantly toughen PLA while preserving its strength, with the GO loading optimized at ~0.67 wt%, which gave an elongation at break of ~274.5% and impact strength of ~10.2 kJ/m2, being 31 times and 2.5 times higher than pure PLA, respectively. Moreover, thanks to the presence of dynamic crosslinks and GO NPs, the PLA-GESO blends exhibited excellent shape memory effect and antistatic properties.

Effect of Al content on thermal stability, shape memory effect and mechanical properties of Cu–Al–Fe shape memory alloys

Effect of Al content on thermal stability, shape memory effect and mechanical properties of Cu–Al–Fe shape memory alloys

Microstructure and properties of 3D-printed ZrCu–Ti6Al4V laminated composite

The microstructures, shape memory properties, and mechanical properties of 3D-printed ZrCu–Ti6Al4V laminated composites were investigated in this study. The microstructure of the laminated composite effectively combines the characteristics of two alloys. The shape memory effect and mechanical properties of the laminated composite are affected by the thickness of the layer. The results reveal that higher austenite transformation temperature than ZrCu with total recovery strain close to ZrCu, and a compression strain exceeding 21% can be achieved by 3D-printed ZrCu–Ti6Al4V laminated composite with thickness of 0.25 mm. Additionally, the composite with thickness of 0.5 mm demonstrates excellent fracture toughness values of 44.30 MPa⋅m1/2, as well as high yield strength and flow stress values reaching 1818 MPa and 2194 MPa respectively at a strain rate of 3500 s-1. This study highlights that incorporating Ti6Al4V layers into ZrCu through 3D-printing can significantly enhance mechanical properties while maintaining favorable shape memory properties, thus combining the advantages of functional and structural materials.

Effect of Cooling Rate on Microstructure, Shape Memory Effect and Mechanical Properties of Cu–13Al–5Fe High-Temperature Shape Memory Alloy Fabricated by Laser Powder Bed Fusion

Effect of Cooling Rate on Microstructure, Shape Memory Effect and Mechanical Properties of Cu–13Al–5Fe High-Temperature Shape Memory Alloy Fabricated by Laser Powder Bed Fusion

A new modern scheme for solving fractal–fractional differential equations based on deep feedforward neural network with multiple hidden layer

The recent development of knowledge in fractional calculus introduced an advanced superior operator known as fractal–fractional derivative (FFD). This operator combines memory effect and self-similar property that give better accurate representation of real world problems through fractal–fractional differential equations (FFDEs). However, the existence of fresh and modern numerical technique on solving FFDEs is still scarce. Originally invented for machine learning technique, artificial neural network (ANN) is cutting-edge scheme that have shown promising result in solving the fractional differential equations (FDEs). Thus, this research aims to extend the application of ANN to solve FFDE with power law kernel in Caputo sense (FFDEPC) by develop a vectorized algorithm based on deep feedforward neural network that consists of multiple hidden layer (DFNN-2H) with Adam optimization. During the initial stage of the method development, the basic framework on solving FFDEs is designed. To minimize the burden of computational time, the vectorized algorithm is constructed at the next stage for method to be performed efficiently. Several example have been tested to demonstrate the applicability and efficiency of the method. Comparison on exact solutions and some previous published method indicate that the proposed scheme have give good accuracy and low computational time.

Effect of laser power on the microstructure, shape memory effect and mechanical properties of Cu–13Al–5Fe high temperature shape memory alloy by laser powder bed fusion

Effect of laser power on the microstructure, shape memory effect and mechanical properties of Cu–13Al–5Fe high temperature shape memory alloy by laser powder bed fusion

Efficient removal of Cr (VI) from aqueous solution using memory effect property of layered double hydroxide material

Treating wastewater containing pollutants with layered double hydroxide (LDH) material attracts excellent interest. LDH materials are known by the memory effect property, which leads to the reconstruction of the LDH structure after its calcination and rehydration. In this study, LDH material was prepared, calcined, and then rehydrated in an aqueous Cr(VI) solution. XRD, FTIR, and SEM-EDS analysis confirm the successful reconstruction of LDH-loading chromium on its surface and layered space. Response surface methodology (RSM) results showed that LDH mass, contact time, and chromium concentration are the main factors controlling the removal of Cr(VI). The heterogeneous sorption of chromium was described by fitting the equilibrium data to the Freundlich model. Analytical techniques, thermodynamic data, activation, and adsorption energies confirm that the removal process of Cr(VI) is endothermic, spontaneous, and physical nature. LDH exhibits good reusability performance with only a 7% reduction of initial adsorption capacity after five cycles of the calcination-rehydration process. These results show that the memory effect of LDH is helpful for the intercalation and the removal of emergent pollutants, especially for wastewater treatment.

Dissimilar laser welding of NiTi shape memory alloy to NiCr alloy

NiTi shape memory alloy (SMA) offers a wide range of industrial applications due to its shape memory effect and superelastic properties. In this study, a dissimilar joint between NiTi SMA and Ni–20Cr alloy was fabricated, and its microstructural and mechanical properties were analyzed. As a result of the formation of brittle intermetallic compounds (IMC), the tensile characteristics were reduced, and the hardness increased dramatically. Also, the effect of various laser pulse widths on bonding characteristics was examined, and as the pulse width increased, coarser IMCs were formed in the FZ. By performing post-weld heat treatment (PWHT) on the welded samples, the microstructure and mechanical properties of the FZ changed, and the NiTi intermetallic phase was produced. The results revealed that most IMCs generated had the same chemical composition ratio as Ni3Ti and Cr2Ti IMCs. In addition, after PWHT, the plateau region in the stress-strain curves was formed, while in the welded samples without PWHT, the joints failed at low stress and strain before forming the plateau region.

Origin of the Memory Effect in Electrochromic Sputtered WO3 Films: Composition, Structure, or Morphology?

AbstractThe memory effect property, described as a reversible color persistence while the potential is withdrawn, is of particular importance to reaching zero‐energy consumption electrochromic devices. Nevertheless, often observed in organic materials, it is poorly studied in oxides. In this study, electrochromic tungsten oxide thin films are elaborated at different working pressures by radiofrequency magnetron sputtering. The influence of the deposition pressure on the electrochemical properties of WO3 films as well as on their memory effect is investigated. Three kinds of WO3 films can be distinguished: with irreversible blue coloration, with reversible coloration presenting a high memory effect, and with reversible coloration with a low memory effect. The origin of these discrepancies is studied through the composition, the local atomic environment, and the morphology of the WO3 thin films. An increase of transmittance at 550 nm as low as 15.8% in 48 h in air and 5.2% in 24 h in the electrolyte is recorded. This study highlights a better understanding of the memory effect property of electrochromic oxides for low‐consumption energy electrochromic devices, pointing out morphology as a key parameter.

Simultaneously improving memory effect and mechanical properties in Cu-based alloys by α phase spheroidization and Fe alloying: A CuAlMnFe as an example

The spheroidization of lamellar Fe3C in pearlite in steels can significantly increase the plasticity. Inspired by the fact, we proposed that to introduce ductile spherical α phase with precipitates of κ phase by Fe alloying can realize not only better shape memory effect (SME) but also higher mechanical properties than to introduce the blocky α phase does in Cu-based alloys. To confirm our idea, the effects of two annealings in two-phase region were studied on the spheroidization of α phase and precipitation of κ phase and the resultant SME and mechanical properties in a Cu8.5Al9.6Mn3.2Fe alloy. Our results showed that the two annealings could simultaneously spheroidize the α phase and precipitate the κ phase in the alloy. The alloy with the spherical α phase showed ∼1% higher recovery strain and ∼8% higher fracture strain than the alloy with the blocky α phase did. The spheroidization of α phase together with the precipitation of κ phase will be a direction for developing ductile Cu-based alloys with better SME and higher strength.

Adjustable indentation and vibration isolation performances of nacre-like metamaterial

ABSTRACT Along with the living environment, organisms have evolved structures that adapt to specific environments and have better mechanical properties. Bioinspired materials learn from nature and improve their mechanical properties by imitating the structure of living organisms. Based on the 4D printed shape memory polymer and the bioinspired design method, this research proposes a soft and hard phase hybrid bioinspired metamaterial with shape memory effect and programmable mechanical properties. Compared with traditional nacre-like materials, bioinspired materials have adjustable characteristics of mechanical properties, impact resistance, and low-frequency vibration isolation. First, based on the constitutive relation of SMP (Shape memory polymer) material and its numerical simulation, an intelligent bioinspired metamaterial is designed. Subsequently, the mechanical properties and vibration isolation behavior and adjustability performance of multi-scale bioinspired metamaterials are explained by experiments. Finally, the adjustable functional mechanism of the deformation and vibration isolation of the bioinspired metamaterial is described. The research of these bioinspired metamaterials has broad application prospects in the fields of impact protection and low-frequency vibration absorption.

Fabrication of graphene oxide/poly (L-lactide-co-ε-caprolactone) nanocomposite with NIR light-induced shape memory effect and antibacterial properties

Fabrication of graphene oxide/poly (L-lactide-co-ε-caprolactone) nanocomposite with NIR light-induced shape memory effect and antibacterial properties

Game-theoretical problems for fractional-order nonstationary systems

Nonstationary fractional-order systems represent a new class of dynamic systems characterized by time-varying parameters as well as memory effect and hereditary properties. Differential game described by system of linear nonstationary differential equations of fractional order is treated in the paper. The game involves two players, one of which tries to bring the system’s trajectory to a terminal set, whereas the other strives to prevent it. Using the technique of set-valued maps and their selections, sufficient conditions for reaching the terminal set in a finite time are derived. Theoretical results are supported by a model example.

Novel Quaternary CuAlZnMg High Temperature Shape Memory Alloy (HTSMA) Fabricated by Minor Batch of Zn and Mg Additions

Shape memory alloys (SMAs) constitute the second largest commercial smart material class after piezoelectric materials. Different SMA alloy systems or SMAs with miscellaneous functionalities and characteristic properties have been designed for using in different applications until today. High temperature shape memory alloys (HTSMAs) are also widely desired to be used in various smart materials applications. HTSMAs with different functional and characteristic properties are muchly demanded for different tasks to be done by these alloys or devices designed by these alloys. A common and practical way to fabricate SMAs or HTSMAs with different shape memory effect (SME) and other properties is to fabricate them with different alloying compositions and add different additive elements. In this work, a quaternary CuAlZnMg HTSMA with an unprecedented composition consisting minor amount of zinc and magnesium additives was produced by arc melting method. As a result of applying post-homogenization in high β–phase temperature region and immediate quenching, the microstructural mechanism of a SME property was formed in the produced alloy. After then, to examine SME characteristics of the CuAlZnMg alloy some differential thermal analysis (DTA), microstructural (XRD) and magnetization (VSM) characterization tests were carried out. The DTA results showed that the alloy is a HTSMA exhibiting reverse martensitic transformations at temperature range between 167 °C and 489 °C. The XRD pattern obtained at room temperature revealed the martensite phases formed in the alloy, which phases are the base mechanism of the reversible martensitic transformation (the SME property) of the alloy. The VSM test showed that the alloy exhibit a diamagnetic property with a weak ferromagnetic coercivity contribution.

Phase-field method based simulation of martensitic transformation in porous alloys

Porous materials, characterized by the presence of interconnected pores, exhibit the properties different from their bulk counterparts. One of properties of interest is that the pores can influence the martensitic transformation in shape memory alloys (SMAs), which directly affects the material's shape memory effect and mechanical properties. The martensitic transformation is accompanied by the formation of different martensitic variants, which determine the overall morphology, distribution, and self-accommodation effect of the transformed regions. Previous experimental studies have shown that the presence of pores, particularly at the metal-air interface, can significantly affect the martensitic variant structure, leading to its thinning. This thinning effect has been found to be able to improve the damping performance of the alloy. Experimental observations have indicated that no relief of martensitic variants was found around the metal-air interface, but non-transformed regions were observed. These observations suggest that the metal-air interface in porous materials is not a free surface and plays a crucial role in influencing the martensitic transformation. To further investigate the effect of martensitic variant self-accommodation on different constrained interfaces in porous materials, a three-dimensional phase-field model based on the time dependent Ginzburg-Landau (TDGL) function is proposed in this study. The phase-field model can give a comprehensive understanding of the evolution of martensitic variants and their interaction with the constrained interfaces. Remarkably, the simulation results accord well with the experimental findings, demonstrating the presence of fine martensitic variants near the metal-air interface. The simulations under different interface constraint conditions reveal that increasing the specific surface area of porous materials is an effective strategy to obtain a more refined martensitic variant structure. The system’s total energy is minimized by reducing the strain energy, which leads to the formation of a greater number of fine martensitic variants. This finding suggests that controlling the specific surface area of porous materials can be a promising approach to tailoring the mechanical properties of SMAs for specific applications. In conclusion, the presence of metal-air interface in porous material significantly influences the evolution of the martensitic transformation in SMA. Experimental observations show that the introduction of pore can modify the martensitic variant structure, resulting in improved damping performance. The proposed phase-field model successfully captures the behavior of martensitic variants near constrained interface. The simulation results emphasize the importance of specific surface area in obtaining fine martensitic variant structures. These findings contribute to a more in-depth understanding of the role of porous materials in shaping the properties of SMAs and provide a valuable insight into their design and application in various fields.

Characterization of the Commercial Rubber Band as a Shape Memory Smart Material by Swelling Process with Fused Stearic Acid

This study attempted to focus the light on the characterization possibility of the vulcanized, chlorinated, natural rubber products (as the commercial rubber band used in this study) as a shape memory smart material in the case of impregnating it with fused stearic acid by swelling mechanism. Where in this study, the ability of the commercial rubber band on fixing the stretching strain chosen in this study which is of 70% after removing the applied load off the rubber band, was measured after impregnating it with stearic acid (SA) material of weight ratio (30.4%) and swelling time=2hr. At the same time, measuring the ability of that rubber band on rid of this mechanical deformation once it is thermally stimulated and returning to its original shape (before the deformation) by subjugating it to the hot classical shape memory cycle (based on normal cooling at room temperature) with its two stages represented by the shape memory effect (SME) property activation and deactivation stages. Also, the techniques of differential scanning calorimetry (DSC) and x-ray diffraction (XRD) were used to know the agreement between these tests and the SME property test results (thermomechanical cycle test). Through the practical results of all the tests depending on the diagnosis, it was shown that the direct responsibility for the characterization of the commercial rubber band as a shape memory smart material is the stearic acid (SA) material, which acted as a lock in the rubber band structure that can be opened and closed with a temperature change within the melting range of (SA).

Tunable dielectric and memory features of ferroelectric layered perovskite Bi4Ti3O12 nanoparticles doped nematic liquid crystal composite

Herein, we report the synthesis of ferroelectric layered perovskite Bi4Ti3O12 (BT4) nanoparticles (NPs) and the temperature-dependent dielectric and electro-optical (especially memory effect) properties of 4-pentyl-4′-cyanobiphenyl (5CB) nematic liquid crystal (NLC) doped with 1 wt% BT4 NPs (i.e. 5CB-BT4 composite) using polarising optical microscopy and frequency-dependent dielectric spectroscopy techniques. BT4 NPs were synthesised via a microwave-assisted chemical method and characterised using various instrumental techniques, which confirmed the formation of a non-stoichiometric and oxygen-deficient orthorhombic crystal phase. The agglomeration-free and uniform dispersion of BT4 NPs in the 5CB matrix was confirmed by optical textures. The optical memory studied by bias voltage-dependent (ON-OFF) optical textures is decreased by ∼ 2.6 times in the 5CB-BT4 composite compared with 5CB. Moreover, dielectric parameters such as dielectric permittivity, dielectric loss, loss tangent, conductivity, and activation energy of 5CB and composite (5CB-BT4) are estimated using dielectric spectroscopy. The dielectric anisotropy is decreased, whereas no shift in the clearing temperature is observed in the 5CB-BT4 composite compared to the 5CB sample. Also, the DC conductivity of 5CB-BT4 composite is found to be increased by approximately four times compared to the 5CB. Our studies clearly demonstrate the tunability of the dielectric and optical memory features of NLC (5CB) matrix by dopant BT4 NPs, without significantly affecting the molecular alignment of the NLC molecules. Such composites would certainly be useful in the fabrication of NLC based tunable devices such as optical memory and conductivity switches.