Porous Shape Memory Alloy Research Articles

Synergetic enhancement of ultimate strength and damping properties by pore structure in novel porous Cu-Al-Mn shape memory alloy

To meet the higher device vibration reduction requirements, novel porous Cu71Al18Mn11 shape memory alloys (SMAs) with controllable porosity were prepared using Cu, Al, and Mn elemental powders as raw materials. To further enhance the strength and damping performance of SMAs, a low-temperature reactive synthesis combined with spark plasma sintering (LTRS+SPS) process was used. In this paper, the effects of LTRS+SPS process on pore structure and texture, compressive strength, and damping properties of porous Cu71Al18Mn11 alloy were studied. The outcomes indicated that LTRS+SPS process can effectively improve both compressive strength and damping properties. The associated closed pore structure caused by this process and the second phase γ2 phase formed by element diffusion result in a variety in compressive strength from 324.6 MPa to 617.9 MPa, which were 3.9 times that of the comparable porosity alloy with alloy powder as raw material by vacuum sintering. Meanwhile, the damping value changed from 0.27 to 0.10, which was 4.5 times that of the homogeneous dense alloy. The increase in damping property is caused by the increase of motionable interfaces in the matrix for the introduction of pores, which leads to the increase of energy dissipation. Besides. the interaction between the second phase γ2 and dislocation contributes to the improvement of damping, as well as the compressive strength. These findings in this paper provide new insights and references for the structural design and microstructure design of high-performance Cu-based alloys.

A low-density polymer/CrMnFeCoNi composite with high strength and high damping capacity

A novel damping composite was successfully prepared by taking a porous CrMnFeCoNi high-entropy shape memory alloy as the skeleton and filling its pores with the composite composed of carbon nanotubes and polyurethane/epoxy interpenetrating polymer networks. When the porosity, pore size and CNT loading are 80 %, 1.2 mm and 2 wt%, respectively, the compressive strength, elastic modulus and energy absorption capacity of the composite are 35.7 MPa, 1.31 GPa and 23.1 MJ/m3 (ε = 65 %), respectively. Furthermore, it has a mere density of 2.525 g/cm3. Its loss factor is greater than 0.093 and can reach a maximum of 0.145 within the temperature and frequency range of 20 ∼ 150 ℃ and 0.1 ∼ 200 Hz. A triple-phase micromechanical model was utilized to explore the damping mechanism of composites. Results indicate the coupling of multiple damping mechanisms is the reason for the high ground-state damping of composites, and interface damping is the primary damping mechanism. The superposition of the ε → γ reverse martensite transformation peak of the CrMnFeCoNi HESMA skeleton and the glass transition peak of the CNTs/polymer composite matrix realizes the wide damping temperature range of the composite.

Mechanical and Magnetic Properties of Porous Ni50Mn28Ga22 Shape Memory Alloy

A porous Ni50Mn28Ga22 alloy was produced using powder metallurgy, with NaCl serving as the pore-forming agent. The phase structure, mechanical properties, and magnetic properties of annealed bulk alloys and porous alloys with different pore sizes were analyzed. Vacuum sintering for mixed green billets in a tube furnace was employed, which facilitated the direct evaporation of NaCl, resulting in the formation of porous alloys characterized by a complete sinter neck, uniform pore distribution, and consistent pore size. The study found that porous alloys within this size range exhibit a recoverable shape memory performance of 3.5%, as well as a notable decrease in the critical stress required for martensitic twin shear when compared to that of bulk alloys. Additionally, porous alloys demonstrated a 2% superelastic strain when exposed to 353 K. Notably, under a 1.5 T magnetic field, the porous Ni50Mn28Ga22 alloy with a pore size ranging from 20 to 30 μm exhibited a peak saturation magnetization of 62.60 emu/g and a maximum magnetic entropy of 1.93 J/kg·K.

An Explicit Modeling for the Pseudoelastic Response of Porous SMA Thick-Walled Cylinders under Internal and External Pressure

Shape-memory alloy (SMA) structures, either dense or porous, are widely used because of their functional characteristics arising from shape-memory effect and pseudoelasticity. Hence, the precise modeling of these materials is essential due to design issues. In this study, the solution algorithm based on an explicit phenomenological constitutive model is investigated to analyze pressurized cylinders. The proposed method is extracted following return mapping scheme to find the evolution of phase transformation in these structures. The formulation is validated by comparing uniaxial tension–compression curves during loading, unloading and thermal actuation against published literature. By the aid of this model, assuming elastic and phase transformation strains, a comprehensive study is presented to inspect stress, strain and displacement fields along the thickness of internally and externally pressurized thick-walled cylinders. To this end, the governing nonlinear equation in elastic–inelastic zones is discretized by the efficient method of generalized differential quadrature (GDQ) and the resultant relations are solved numerically. The influences of internal and external pressure on stress distribution along the cylinder wall during loading–unloading for different temperatures including phase transformation and saturation states are discussed. Also, the closed-form solution for critical pressure at the onset of the phase transformation is studied.

Superelastic properties of biomedical Ti–Zr–Nb–Sn highly porous shape memory alloys prepared by fiber metallurgy

Artificial bone substitutes to satisfy the specific properties of cancellous bone for the repair of bone defects are highly desirable. In this study, combining the unique superelasticity and high porosity, biomedical Ti–Zr–Nb–Sn highly porous shape memory alloys (HPSMAs) were prepared by fiber metallurgy for the potential repair of damaged cancellous bone. Three-dimensional and open porous networks constructed by fiber-fiber bonds were obtained in the HPSMAs with a porosity of 79.5%. The recovery strain at room temperature was improved from 2.3% in the as-sintered specimen to 3.8% in the 700 °C solution-treated one by adjusting the transformation temperature. The mechanical performances in the Ti–Zr–Nb–Sn HPSMAs were similar to those of cancellous bone. Stable superelastic behaviors with a recovery strain of 4% were achieved at room temperature after cycle training. The Ti–Zr–Nb–Sn HPSMAs satisfy those specific properties of cancellous bone and show great potential in the repair of cancellous bone defects.

Phase Field Simulations of Microstructures in Porous Ferromagnetic Shape Memory Alloy Ni2MnGa

The magnetic domain structures and martensite microstructures of porous Ni2MnGa Heusler alloys with various circle-shaped and ellipse-shaped pores were systematically studied by the phase field method. The magnetization curves and magnetic field-induced strains (MFIS) at the external field were determined. A mesoscopic mechanism was proposed for simulation to reveal the influence of the pores on the microstructures and the MFIS of porous magnetic shape memory alloy. The stress concentration effect and the recovery strain of the porous alloy are studied. The results indicate the MFIS value increases when ellipse-shaped pores elongate along the twin boundary. The effects of porosity and pore size on MFIS for porous Ni-Mn-Ga alloys with randomly distributed pores were also explored. The present study is of guiding significance for understanding the role played by pores on the MFIS and may provide a possible way to adjust the functional properties of ferromagnetic shape memory alloys.

Specific mechanical properties of highly porous Ti-Zr-Mo-Sn shape memory alloy for biomedical applications

Porous Ti-5Zr-3Mo-6.5Sn (at.%) shape memory alloy scaffolds were fabricated by fiber-sintering. Microstructural morphology of the scaffolds showed high density of three dimensional and interconnected pores ranging from 100 to 500 μm in diameter. β →α" martensitic transformation, which is induced by the applied stress, occurs at human body temperature. The porous shape memory alloy scaffold has excellent superelasticity and then exhibited the strain recovery ratio of 90%. An elastic modulus of the Ni-free shape memory alloy scaffold, which was prepared by fiber-sintering, was as low as 19 GPa due to the high density of pores. These mechanical properties of low elastic modulus and superelasticity matched well with those of human bone. Considering the specific mechanical properties, structural morphology and biocompatibility, the fiber-sintered Ni-free shape memory alloy scaffolds satisfy the major requirements of bone substitutes for damaged or diseased bones.

A micromechanical constitutive model for porous ferromagnetic shape memory alloys under magneto-mechanical coupling

A micromechanical constitutive model for porous ferromagnetic shape memory alloys under magneto-mechanical coupling

Design of Porous Shape Memory Alloys with Small Mechanical Hysteresis

The mechanical hysteresis loop behavior always limits the applicability of shape memory alloys (SMAs) in mechanical devices requiring high sensitivity, durability and energy conversion efficiency. In this study, through experiments and finite element simulations, we systematically investigated the effects of porosity and pore distribution on the mechanical hysteresis behavior of porous Ti49.2Ni50.8 SMAs. Inspired by atomic crystal structures, some porous SMAs with ordered void distributions were investigated to compare them with SMAs with random pore distributions. Our results show that the hysteresis reduces with increasing porosity in porous SMAs. The designed BCC-type ordered porous SMAs possess a narrower hysteresis loop with less energy dissipation at the same porosity. The gradual and homogenous martensitic-phase transformations are responsible for this characteristic. The present work provides an effective way to design porous SMAs with narrow hysteresis, which is promising in applications for mechanical sensors or actuators.

A Poromechanics-Based Phenomenological Model for Porous Shape Memory Alloys

A Poromechanics-Based Phenomenological Model for Porous Shape Memory Alloys

A micromechanical constitutive model for porous ferromagnetic shape memory alloys considering magneto-thermo-mechanical coupling

In this work, a three-phase constitutive model describing the magneto-thermo-mechanical behaviors of porous Ferromagnetic Shape Memory Alloys (FSMAs) is established through a combination of micromechanical and thermodynamic theories. The kinetic equation is obtained in accordance with the thermodynamic driving force caused by the reduction of Gibb’s free energy of porous FSMAs. The thermodynamic driving force in combination with the corresponding resistance is used to establish the balance equation for calculating the volume fractions of martensitic variants under the action of different given magnetic fields, stresses and temperatures. Good agreement between the theoretical prediction of dense FSMA models and published experimental data is observed. The mechanical behaviors of porous FSMAs under magneto-thermo-mechanical coupling with different porosities and initial conditions are then discussed, which will provide a reliable theoretical basis for the future research of these functional materials as sensors or actuators.

Concept of Elastocaloric Granular Material Made from SMA Wires in Bending

Shape memory alloys (SMAs) are promising materials for the creation of heating or cooling systems due to their elastocaloric character. The paper proposes a concept of elastocaloric “porous” SMA beam working in bending. The beam was made with superelastic nickel-titanium SMA wires of different diameters placed in a flexible tube. While water was flowing through the tube, bending was manually applied using 3D printed wavy profiles with portions of arcs with constant curvatures. Preliminary results showed an oscillation of the fluid temperature at the outlet of the flexible tube (containing the SMA wires) at the same frequency as the mechanical loading, validating therefore the concept of elastocaloric porous SMA beam operating in bending.

Effect of Pore Shape on Mechanical Properties of Porous Shape Memory Alloy

Porous shape memory alloys (SMAs) have been widely used in the aerospace, military, medical, and health fields due to its unique mechanical properties such as superelasticity, biocompatibility, and shape memory effect. In this work, the pore shape was considered in the constitutive model of the porous SMAs by respectively introducing the parameter of aspect ratio and for different pore shapes including oblate, sphere, and prolate shapes, so the expression of Young’s modulus for the porous SMA can be derived. Then, the constitutive model for such a porous shape memory alloy was established. When the porosity was zero, the model can be degenerated to the dense case. The stress–strain curves for the porous SMA with a porosity of 13% with different aspect ratio are then given. Numerical results showed good agreement with the published experimental data that proved the validation of the model. Based on the proven constitutive model, the properties of porous SMA with different porosity and pore shapes are discussed. The results showed that the pore shapes and the porosities had a big effect on the stress–strain curves for the porous shape memory, while with the increasing porosities, the Young’s modulus and the hysteresis both decreased. With the same porosities, the Young’s modulus and hysteresis loop of SMA with round pores were the largest, while the Young’s modulus and hysteresis loop were the smallest when , and they were greater when than when . It can be seen that the closer to the circle, the better the performance of the material.

Improving the mechanical and damping properties of polymer/memory alloy composite by introducing nanotubes covered with nano-scale Ni particles

Ni@CNT reinforced polymer/memory alloy damping composites were successfully fabricated by filling a porous CuAlMn shape memory alloy skeleton structure using polyurethane/epoxy interpenetrating network matrix. As 4 wt% Ni@CNT is dispersed in the polymer matrix, the loss factor (ratio of loss modulus to storage modulus) of the composite is above 0.09, and the maximum value can reach 0.156, at the whole test frequency (0.1 ∼ 200 Hz) and temperature (-10 ∼ 100 ℃) range. Meanwhile, its elastic modulus can reach 1137.9 MPa and the density is only 2.04 g/cm3. Compared with polymer/memory alloy composite, the average loss factor and elastic modulus of the prepared composite increased by 40.1% and 33.4%, respectively. A triphase damping model and a mechanical model were used to investigate the damping mechanism and elastic properties of composites, respectively. Calculation and simulation results indicated that the damping capacity of the Ni@CNT/polymer/memory alloy composite is basically related to interfacial dissipation, which is significantly enhanced via introducing nanotubes covered with nano-scale Ni particles. Due to the light weight, certain strength, good deformation resistance and excellent damping performance, this nanocomposite has potential applications in the damping field of aerospace.

Development of a torsional theory for radially functionally graded porous shape memory alloy circular bars

This work develops a novel torsional theory for a radially functionally graded (FG) porous shape memory alloy (SMA) circular bar. Prior to the theoretical development, the effective three-dimensional (3D) phenomenological constitutive model for SMAs with high porosity is proposed. To help derive successfully the theory, the pure shear-driven material parameters in the effective model are expressed in the cubic polynomial. Subsequently, the torsional theory for radially FG porous SMA circular bar is derived considering the evolution of effective phase evolution in the bar. This phase evolution consideration guarantees the accuracy of the developed theory. Indeed, the soundness of effective constitutive model is confirmed by 3D finite element method (FEM) simulation of porous SMA structure in Abaqus using the well-established ZM’s model for dense SMAs. Specifically, the simulating results in terms of the shear stress-shear strain response obtained from two prediction methods considering a variation of SMA volume fraction and temperature are in good agreement. Furthermore, accuracy of torsional theory is validated by 3D FEM simulation using the 3D effective constitutive model with a good agreement observed. It is found that the superelasticity of the bar can be enhanced by increasing the gradient index and decreasing the temperature and wall thickness.

Bending model for functionally graded porous shape memory alloy/poroelastic composite cantilever beams

A new model is developed for bending of functionally graded (FG) porous shape memory alloy (SMA)/poroelastic composite cantilever beams. The model generalizes the ZM model for dense SMAs to cases involving potentially high degrees of porosity. The accuracy of the proposed model is verified against experimental data as well as simulations involving finite element analysis (FEA) of porous architected SMAs with fully detailed geometries. Using the new model, a bending theory is derived for a porous composite cantilever beam reinforced with a FG porous (FGP) SMA layer. The derivation involves expressing the effective material parameters of the porous SMA as polynomial functions of porosity, which facilitates analytical treatment of the bending theory. Moreover, the theory accounts for the distribution of solid phases within a beam cross section as a function of applied load during a complete loading cycle. Results such as the load-deflection behavior of the beam, as well as the location of the neutral axis and distribution of axial stress as a function of the applied load are validated against FEA data. The validated theory is further utilized to investigate the influence of several parameters on the behavior of the composite beam, including the index gradient, temperature, and thickness of the SMA layer.

Correction to: Modeling of Superelastic–plastic Behavior of Porous Shape Memory Alloys Incorporating Void Shape Effects

Correction to: Modeling of Superelastic–plastic Behavior of Porous Shape Memory Alloys Incorporating Void Shape Effects

Modeling of Superelastic–plastic Behavior of Porous Shape Memory Alloys Incorporating Void Shape Effects

A new constitutive model for describing the superelastic–plastic behavior of porous shape memory alloys (SMAs) is proposed. The model incorporates the influences of void shape and hydrostatic pressure as well as the elastic modulus mismatch between austenite and martensite. In addition, the interactions between plastic strain and transformation strain are considered via the plastic back stress. The porous SMAs are considered as two-phase composites with the dense SMA matrix and the second phase representing ellipsoidal voids. Based on Gurson’s formulation, the transformation and plastic flow potentials accounting for the transformation–plasticity coupling are developed. The numerical results present good agreement with available experimental data for various levels of porosity, which proves that the model is capable of capturing stress-induced phase transformation and plastic deformation of porous SMAs. Using the proposed model, the influence of plastic strain on reverse transformation and the effects of porosity and void shape on the pseudoelastic and plastic behavior of porous SMAs are investigated.

A thermomechanical constitutive model for porous SMAs accounting for the influence of void evolution

A new thermomechanical constitutive model is proposed for shape memory alloys (SMAs) with randomly distributed microscopic porosity. The influence of the microscopic voids on SMA behavior is accounted for by means of two scalar variables representing damage due to porosity and inelastic dilatation due to the expansion or shrinking of voids. Starting with a newly formulated expression of the Helmholtz free energy density, a general stress-strain relation is derived for porous SMAs. The relation features internal dissipative variables for which thermodynamically consistent flow rules are proposed. In particular, loading functions are obtained for variables representing the volume fraction of martensite, inelastic strain due to martensite detwinning and reorientation, as well as damage and inelastic dilatation caused by the presence and evolution of voids. Appropriate loading conditions and flow rules are then introduced in a way that satisfies the principles of thermodynamics. The model is numerically integrated using a multi-surface return mapping algorithm implemented in a finite element software. The integration procedure, including the formulation of the required time-discrete equations and the derivation of the material Jacobian are presented in detail. The developed model is validated by two sets of experimental results and one modeling work to good agreement. The model is then used for simulating reference stress-strain data taken from the literature, in addition to test cases showcasing the ability of the model to simulate complex structures in presence of non-proportional loading and strong stress gradients.

Free and forced vibration analysis of a sandwich beam considering porous core and SMA hybrid composite face layers on Vlasov’s foundation

This paper aims to investigate the free and forced vibration behavior of a sandwich beam with functionally graded porous core and composite face layers embedded with shape memory alloy (SMA). Three different porosity patterns are assumed through the thickness direction of the core, and composite face layers are reinforced with carbon nanotubes (CNT). The sandwich beam is resting on an elastic foundation which is simulated by Vlasov’s model. By using Hamilton’s principle and first-order shear deformation theory, the governing equations of motion are derived. The analytical solution is presented to solve the equations of motion using Navier’s solution. Results are verified with corresponding literatures. Finally, the effects of important parameters such as temperature, volume fraction of SMA, porosity distribution, weight fraction of CNT, and geometric parameters are explored in detail.