Amount Of Shape Recovery Research Articles

3D and 4D Printing of PETG-ABS-Fe3O4 Nanocomposites with Supreme Remotely Driven Magneto-Thermal Shape-Memory Performance.

This study introduces novel PETG-ABS-Fe3O4 nanocomposites that offer impressive 3D- and 4D-printing capabilities. These nanocomposites can be remotely stimulated through the application of a temperature-induced magnetic field. A direct granule-based FDM printer equipped with a pneumatic system to control the output melt flow is utilized to print the composites. This addresses challenges associated with using a high weight percentage of nanoparticles and the lack of control over geometry when producing precise and continuous filaments. SEM results showed that the interface of the matrix was smooth and uniform, and the increase in nanoparticles weakened the interface of the printed layers. The ultimate tensile strength (UTS) increased from 25.98 MPa for the pure PETG-ABS sample to 26.3 MPa and 27.05 MPa for the 10% and 15% Fe3O4 nanocomposites, respectively. This increase in tensile strength was accompanied by a decrease in elongation from 15.15% to 13.94% and 12.78%. The results of the shape-memory performance reveal that adding iron oxide not only enables indirect and remote recovery but also improves the shape-memory effect. Improving heat transfer and strengthening the elastic component can increase the rate and amount of shape recovery. Nanocomposites containing 20% iron oxide demonstrate superior shape-memory performance when subjected to direct heat stimulation and a magnetic field, despite exhibiting low print quality and poor tensile strength. Smart nanocomposites with magnetic remote-control capabilities provide opportunities for 4D printing in diverse industries, particularly in medicine, where rapid speed and remote control are essential for minimally invasive procedures.

Elementary molecular processes that govern the chemical stimulation of a polyurethane-based shape memory polymer

After programming, polyurethanes like ESTANE ETE 75DT3 (SMP-E) show chemically triggered one-way shape memory effect (1WE). When small molecules enter the polymer, weakening the hydrogen bonds between the SMP-E macromolecules and reducing TSWITCH below the environmental temperature. Herein, we investigate how three alcohols—methanol, ethanol and 1-propanol—perform in chemically actuating the 1WE in SMP-E. Weight gain studies show that a smaller size molecule more rapidly saturates SMP-E. The results from mechanical spectroscopy show that TSWITCH decreases with increasing alcohol molecular concentrations, independent of their chemical nature. In line with these findings, all three alcohols show the same amount of shape recovery, which is the fastest when using the smallest methanol molecule for chemical actuation. Infrared spectroscopy helps to identify the mechanism responsible for the decrease in TSWITCH during chemical exposure. Small alcohol molecules interrupt hydrogen bonds between macromolecular chains attaching to C=O groups and creating free NH groups.

Fabrication and characterization of nanostructured Fe–28Mn–6Si–5Cr shape memory alloy

Mechanical alloying and consequent sintering techniques were used to create a bulk alloy of Fe–28Mn–6Si–5Cr from elemental powder. The microstructure and shape memory behavior due to bending deformation were investigated. The majority of α phases that existed at the start of the mechanical alloying process were changed into γ phases by the end of the 40-hour process. The γ phase was essential to achieving shape recovery behavior, which was boosted by mechanical alloying. A stress-induced γ to ε phase transformation occurred at the end of the bending deformation process. Shape recovery was observed after the subsequent heat treatment process due to reverse martensitic ε to γ phase transformation. After mechanical alloying, a grain size of 9.5 nm was attained and a considerable amount of shape recovery was achieved at the end of the recovery heat-treatment process. As a result, we came to the conclusion that combining mechanical alloying with powder metallurgy and then sintering has the potential to synthesize Fe-Mn-Si-Cr shape memory alloy.

The Influence of Alloy Composition and Heat-Treatments on the Shape Memory Properties in a Cu-Sn-X Alloy

We have focused on shape-memory properties of Cu-Sn based ternary alloys in this study. We have attempted to suppress degradation at room temperature aging and to improve the amount of shape recovery by adding the third element to a binary Cu-Sn alloy. The attempt has successfully conducted in Cu-Sn-Mn alloy, the degradation due to aging at room temperature was suppressed and the thermal stability was improved. Furthermore, the present study revealed that Cu-Sn-Mn alloy exhibited a large super elastic recovery in three point bending tests. We have also investigated the shape-memory properties of Cu-Sn-Si alloys and revealed that the ternary alloy has achieved super-elastic recovery better than the Cu-Sn-Mn alloy in the three-point bending tests.

J0410103 Fe-Mn-Si系形状記憶合金におけるシュミット因子によるvariant選択性

The shape memory effect (SME) in Fe-Mn-Si based alloy is associated with γ&elarr;ε martensitic transformation which is caused by motion of the Shockley partial dislocation. The variants in Fe-Mn-Si based alloy could appear the four orientations according to Shouji-Nishiyama (S-N) relation in the austenite phase (A-phase) to the martensitic phase (M-phase). It was reported that the variant formed the single orientation under stress induced transformation and that is the advantage for SME in the variant selection behavior. In this study, the variant selection of Fe-Mn-Si based alloy under stress applied is investigated on the basis of crystallography in the SME with Electron Backscatter Diffraction (EBSD). The amount of shape recovery was quantified by means of bending test and the best recovery ratio was revealed about 83% for the specimen annealed 600[℃]. The SME in improved by not only the increase of A-phase but also the promotion of the single orientation under stress induced transformation. Most of A-phase formed the single orientation with Schmid's factor during the stress-induced martensitic transformation.

Coarse-grained simulation of molecular mechanisms of recovery in thermally activated shape-memory polymers

Thermally actuated shape-memory polymers (SMPs) are capable of being programmed into a temporary shape and then recovering their permanent reference shape upon exposure to heat, which facilitates a phase transition that allows dramatic increase in molecular mobility. Experimental, analytical, and computational studies have established empirical relations of the thermomechanical behavior of SMPs that have been instrumental in device design. However, the underlying mechanisms of the recovery behavior and dependence on polymer microstructure remain to be fully understood for copolymer systems. This presents an opportunity for bottom-up studies through molecular modeling; however, the limited time-scales of atomistic simulations prohibit the study of key performance metrics pertaining to recovery. In order to elucidate the effects of phase fraction, recovery temperature, and deformation temperature on shape recovery, here we investigate the shape-memory behavior in a copolymer model with coarse-grained potentials using a two-phase molecular model that reproduces physical crosslinking. Our simulation protocol allows observation of upwards of 90% strain recovery in some cases, at time-scales that are on the order of the timescale of the relevant relaxation mechanism (stress relaxation in the unentangled soft-phase). Partial disintegration of the glassy phase during mechanical deformation is found to contribute to irrecoverable strain. Temperature dependence of the recovery indicates nearly full elastic recovery above the trigger temperature, which is near the glass-transition temperature of the rubbery switching matrix. We find that the trigger temperature is also directly correlated with the deformation temperature, indicating that deformation temperature influences the recovery temperatures required to obtain a given amount of shape recovery, until the plateau regions overlap above the transition region. Increasing the fraction of glassy phase results in higher strain recovery at low to intermediate temperatures, a widening of the transition region, and an eventual crossover at high temperatures. Our results corroborate experimental findings on shape-memory behavior and provide new insight into factors governing deformation recovery that can be leveraged in biomaterials design. The established computational methodology can be extended in straightforward ways to investigate the effects of monomer chemistry, low-molecular-weight solvents, physical and chemical crosslinking, different phase-separation morphologies, and more complicated mechanical deformation toward predictive modeling capabilities for stimuli-responsive polymers.

Role of Si in Improving the Shape Recovery of FeMnSiCrNi Shape Memory Alloys

The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The microstructural observations revealed that in these alloys the microstructure remains single-phase austenite (γ) up to 6 pct Si and, beyond that, becomes two-phase γ + δ ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing in the microstructure after 7 pct Si and makes these alloys brittle. Silicon addition does not affect the transformation temperature and mechanical properties of the γ phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct Si show poor recovery due to the formation of δ-ferrite. The shape memory effect (SME) in these alloys is essentially due to the γ to stress-induced e martensite transformation, and the extent of recovery is proportional to the amount of stress-induced e martensite. Alloys containing less than 4 pct and more than 6 pct Si exhibit poor recovery due to the formation of stress-induced α′ martensite through γ-e-α′ transformation and the large volume fraction of δ-ferrite, respectively. Silicon addition decreases the stacking fault energy (SFE) and the shear modulus of these alloys and results in easy nucleation of stress-induced e martensite; consequently, the amount of shape recovery is enhanced. The amount of athermal e martensite formed during cooling is also observed to decrease with the increase in Si.

Effect of Al concentration on pseudoelasticity in Fe 3Al single crystals

Pseudoelasticity in Fe 3Al single crystals with different Al contents was investigated focusing on the dislocation configuration and the ordered domain structure. Giant pseudoelasticity only appeared in the D0 3-ordered Fe 3Al single crystals, while the B2-ordered crystals and those with the disordered α phase exhibited small strain recovery. The amount of shape recovery in the D0 3-ordered crystals showed a maximum near 23.0at.%Al and decreased with increasing deviation from this Al concentration. In the D0 3 phase at 22.0–25.0at.%Al, 1/4[1 1 1] superpartial dislocations moved individually dragging the nearest-neighbour antiphase boundaries (NNAPB), while couplets of the superpartials were observed to bow out, dragging the next-nearest-neighbour antiphase boundaries (NNNAPB) in Fe–28.0at.%Al. In Fe–22.0–25.0at.%Al single crystals, the NNAPB pulled back the superpartials to decrease its energy during unloading, resulting in the giant pseudoelasticity. In contrast, the surface tension of the NNNAPB was lower than that of the NNAPB, leading to the small strain recovery in Fe–28.0at.%Al.

Effect of Alloying Elements (Ga, Ge, Si) on Pseudoelasticity in Fe3Al Single Crystals

ABSTRACTPseudoelasticity in Fe3Al single crystals doped with a small amount of Ga, Ge and Si was investigated focusing on the antiphase boundary (APB) energy and the ordered domain structure. Single crystals of Fe-23at%Al and Fe-21at%Al-2at%X (X=Ga, Ge, Si) were grown by a floating zone method. In Fe-23at%Al single crystals, superpartial dislocations with Burgers vector (b) of 1/4<111> moved dragging APB during loading, while APB pulled back the superpartials during unloading. This resulted in giant pseudoelasticity regardless of martensitic transformation and the recoverable strain was about 5%. Ga addition was found to be effective in increasing the recovery strain compared with Fe-23at%Al crystals. In contrast, both Ge and Si additions decreased the amount of shape recovery. Stress at which the shape recovery started, was increased by Ga, Ge and Si additions. This means the APB energy increased by the additions, since the surface tension of APB pulling back the superpartials increases with increasing the energy. On the other hand, the frictional stress of the superpartials with b=1/4<111> increased significantly by Ge or Si doping due to solid solution hardening, though the stress of Ga-doped crystals was almost the same as that of the binary crystals. Higher frictional stress of Ge- and Si-doped crystals made the reversible motion of the superpartials difficult, resulting in the small recovery ratio. Ordered domains with displacement vector (R) of 1/4<111> in Fe-23at%Al and Fe-Al-Ga alloys were observed to be small, less than 100nm. In contrast, Ge and Si additions increased the domain size to more than 500nm. Since the domain boundaries with R=1/4<111> played an important role in the individual motion of the superpartials with b=1/4<111>, the fine domain structure was found to be favorable for giant pseudoelasticity in Fe3Al single crystals. Ga addition increased the APB energy following the superpartials and kept the domain size small, resulting in the increase in recovery strain.

Fundamental Study on Cavitation Erosion Using a NiTi Shape Memory Alloy.

In order to clarify the role of slip deformation on cavitation erosion, vibratory cavitation tests were carried out for a NiTi shape memory alloy in martensitic phase and austenitic phase. This alloy deforms plastically by the combination of slip and twinning deformation, and the erosion resistance of NiTi shape memory alloy is 500 to 1000 times higher than that of SUS316 stainless steel. The erosion resistance of austenitic phase is superior to martensitic phase, because the accumulation of slip in the austenitic phase is slower due to the superelasticity than that in the martensitic phase. The martensitic phase test with intermittent shape recovery shows a better resistance without the shape recovery, since the deformation twins produced by cavitation erosion test are eliminated by shape recovery, resulting in the delay of slip accumulation. However, the amount of shape recovery was decreased with test duration. The decreasing rate of shape recovery has a good linear relationship with the volume loss rate. It was concluded that the accumulation of slip deformation corresponds well with the volume loss rate.

In-(13−<I>X</I>) at%Pb-<I>X</I> at%Sn擬2元系合金のマルテンサイト変態

Changes in both crystal structure and surface relief during the phase transformation in Indium-(13−X) at%Pb-X at%Sn pseudobinary alloys have been studied by means of metallurgical techniques. Lattice parameters at each temperature during the phase transformation show that the alloys undergo two kinds of phase transformation: fct(c⁄a<1)↔fco phase transformation in the alloys containing (0-9) at%Sn and fct(c⁄a<1)↔fct(c⁄a>1) one in the alloys containing (11-13) at%Sn. The characteristic feature of phase transformation becomes more recognizable first-order gradually with increasing tin content. The appearance of a banded surface relief in a low-temperature phase concludes that these phase transformations are martensitic ones taking place by the cooperative movement of atoms. The change in surface relief is reversible in the alloys containing (0-7) at%Sn, but not in others. Corresponding to this, the amount of shape recovery in the former alloys is nearly constant, and the latter alloys show a decrease in shape recovery with increasing tin content. The characteristic features of shape recovery associated with phase transformation on heating is discussed in terms of the crystallographic reversibility in each phase transformation. Furthermore, the fct(c⁄a<1)↔fco phase transformation is analyzed phenomenologically on the basis of the Landau theory, and some physical quantities such as the change in entropy and the elastic constant C′ are calculated. The temperature dependence of the stress-strain relation is also discussed in terms of ferro- and super-elasticity. The analyzed results suggest that the characteristic behavior of the fct(c⁄a<1)↔fco phase transformation depends upon the average atomic size as well as the valence electron concentration.

Observations of aging effects in a Cu-Sn shape memory alloy

A Cu-15.0 at. pct Sn alloy has been chosen as a model alloy for the study of aging effects in copper-based shape memory alloys. Different thermal aging treatments were carried out to determine the effects of both parent phase and martensite aging on the amount of shape recovery and the characteristic transformation temperaturesMs,As, andAf. Aging of the martensite reduces both the amount of shape recovery and the extent of the reverse martensite → parent transformation. High martensite heating rates promote complete shape recovery and reverse transformation while the aging occurring during slow heating can inhibit or prohibit both. But irrespective of the martensite heating rate the transformation temperature hysteresis as given by (Ms -As) is large for the Cu-15 pct Sn alloy compared to other shape memory alloys exhibiting thermoelastic behavior. On the other hand, some beneficial effects were noted when the Cu-15 pct Sn alloy was aged in the parent phase condition prior to subsequent transformation to martensite. TheMs,As, andAf were lowered following prior parent phase aging, possibly because of a change in long range order, but prior parent phase aging was found to diminish the deleterious effect of martensite aging. Both shape recovery and the extent of the reverse martensite → parent transformation are enhanced by prior parent phase aging. The enhancement is greater the higher the aging temperature or the longer the aging time at a given temperature.