Large Compressive Strain Research Articles

Heat treatment effects on microstructure and mechanical properties of TiZrNbTa high-entropy alloy

Microstructure and mechanical properties of TiZrNbTa high-entropy alloy (HEA) in the as-cast and annealed states are systematically investigated. The yield strength of TiZrNbTa HEA strongly depends on the heat treatment temperatures. With the increase of heat treatment temperature, the yield strength of TiZrNbTa increases first and then decreases. When the heat treatment temperature reaches 600 ℃, the yield strength and uniform strain of TiZrNbTa HEA are 1583 ± 55 MPa and 20.5% ± 1.8%, respectively. Compared with the as-cast state TiZrNbTa, the yield strength of TiZrNbTa HEA after simple heat treatment, i.e., 600 ℃ for 1 h improves by 47%, which is attributed to the spinodal decomposition strengthening. By comparing the contribution of grain boundary strengthening for the TiZrNbTa HEA before and after annealing, the significant decrease in the yield strength of the TiZrNbTa HEA is not caused by grain coarsening after heat treatment at 800 ℃, but by the formation of a vein-like phase in grain boundaries. The Ti(Zr)-rich and Nb(Ta)-rich phases in TiZrNbTa HEA exhibit different performances in large compressive strain conditions. The Ti(Zr)-rich phase exhibits good compressive plastic deformation ability, and the Nb(Ta)-rich phase has a higher strength. The TiZrNbTa HEA after one-step simple heat treatment displays excellent mechanical properties, which significantly improves the possibility of clinical application as a new orthopedic-implant alloy.

Recyclable shape memory polymers with independent honeycomb crosslinked polymer actuators and temperature response switches inspired by bow principle

AbstractIn order to realize high recovery stress and large recoverable compression strain, by drawing inspiration from the bow‐and‐bowstring principle, we designed the temperature switch and actuator separately to reduce the response temperature when the shape recovers, thereby improving the storage modulus of the actuator and recovery stress. Meanwhile, a self‐template method was used to synthesize shape memory polymer (SMP) which has an actuator with a honeycomb structure to further improve the recovery force. Compared with the loofah‐like interpenetrating network structure SMP (SMP‐L) obtained using the traditional method, the SMP with a honeycomb‐like actuator (SMP‐H) has three times higher recovery stress than SMP‐L. SMP‐H can lift loads more than 400 times its own weight and has three times higher recovery lifting stress than SMP‐L. SMP‐H also has self‐healing, reprocessing, and recyclable properties due to its special honeycomb‐like actuator. This new synthesis strategy could provide opportunities for the wider application of SMPs.

Limitations of the St. Venant–Kirchhoff material model in large strain regimes

The St. Venant–Kirchhoff law is a widely used constitutive relation in engineering applications. However, its limitation to small strains is frequently mentioned in the literature but rarely elaborated on. Therefore, we present a comprehensive study discussing the St. Venant–Kirchhoff law and its shortcomings in large stain regimes, focusing on compressive loading based on one-dimensional stress and strain states. The linear stress–strain relation in combination with the associated Green–Lagrange strain yields a nonphysical structural behavior for large compressive strains, which is reflected in instabilities and nonphysical softening. Common misconceptions concerning the St. Venant–Kirchhoff law and alternative constitutive models are presented and evaluated based on a two-bar snap-through problem.

Mechanically-grown morphogenesis of Voronoi-type materials: Computer design, 3D-printing and experiments

The present work introduces a novel and versatile computer-design and experimental strategy to obtain random Voronoi-type geometries, called M-Voronoi (from mechanically grown), with smooth void shapes and variable intervoid ligament sizes that can reach very low relative densities. This is achieved via a numerical, large strain, nonlinear elastic, void growth mechanical process. Originally small circular voids embedded in a cell of arbitrary shape (triangle, circle, rectangle, trapezoid) grow when subjected to displacement (Dirichlet) boundary conditions. The deformed voids evolve into smooth Voronoi-type geometrical shapes leading to macroscopic isotropy or anisotropy depending on the prescribed boundary conditions. The void growth process is a direct consequence of mass conservation and the incompressibility of the surrounding nonlinear elastic matrix phase and the final achieved relative density may be analytically estimated in terms of the determinant of the applied deformation gradient. In order to study the mechanical properties of the M-Voronoi materials, we focus on two-dimensional porous polymer square representative isotropic and anisotropic geometries in terms of void size and realization, which are 3D-printed and experimentally tested under uniaxial compression. For comparison, we also test random polydisperse porous materials with circular voids, standard eroded Voronoi geometries and hexagonal honeycombs. The first two are also isotropic while the latter are only isotropic in the linear elastic regime. We show that the randomness of the M-Voronoi geometry and their non-uniform intervoid ligament size leads to enhanced mechanical properties at large compressive strains with no apparent peak-stress and strong hardening well before densification. By comparing them with the hexagonal geometries, which tend to exhibit a peak-stress and a plateau-type response, we show that the hardening response of the M-Voronoi is mainly due to their geometrical characteristics and less due to the polymer hardening response. Anisotropic M-Voronoi are also produced and tested indicating that anisotropy only enhances the initial stiffness along the longitudinal direction but instead leads to lower buckling loads and hardening rates than the corresponding isotropic M-Voronoi in the nonlinear regime.

Polymer-Assisted Metal Deposited Wood-Based Composites with Antibacterial and Conductive Properties

Compressible metallic porous materials (CMPMs) have great potential for development in the energy and environmental fields. However, the scale-up preparation of CMPMs with stable metal layers, excellent elasticity, and multifunctionality remains exceedingly challenging. In this study, we designed a novel strategy with the aid of polymer-assisted metal deposition to synthesize metallic porous wood (Ni-PW) with a hierarchical cellular structure and excellent elasticity. Our approach can produce highly compressible MPW using intrinsically porous delignified wood with only 15.16% strain loss under a large compressive strain of 40% after 1000 loading-unloading cycles and 129.4 μm of the average porous size of the Ni-PW measured by mercury injection method. The resulting Ni-PW displays excellent antibacterial properties for Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) and electric conductivity (Resistance < 7 ty), which renders great potential in energy and environmental applications. This research provides a new insight into the fabrication of CMPMs in a cost-effective (~56.5 ¥ m−2) and scalable way.

Rheology of fibrous gels under compression

A number of biological tissues and synthetic gels consist of a fibrous network infused with liquid. There have been a few experimental studies of the rheological properties of such gels under applied compressive strain. Their results suggest that a plot of rheological moduli as a function of applied compressive strain has a long plateau flanked by a steeply increasing curve for large compressive strains and a slowly decreasing curve for small strains. In this paper we explain these trends in rheological properties using a chemo-elastic model characterized by a double-well strain energy function for the underlying fibrous network. The wells correspond to rarefied and densified phases of the fibrous network at low and high strains, respectively. These phases can co-exist across a movable transition front in the gel in order to accommodate overall applied compression. We find that the rheological properties of fibrous gels share similarities with a Kelvin–Voigt visco-elastic solid. The storage modulus has its origins in the elasticity of the fibrous network, while the loss modulus is determined by the dissipation caused by liquid flow through pores. The rheological properties can depend on the number of phase transition fronts present in a compressed sample. Our analysis may explain the dependence of storage and loss moduli of fibrin gels on the loading history. We also point to the need for combining rheological measurements on gels with a microstructural analysis that could shed light on various dissipation mechanisms.

Study on the mechanical properties of CFRP composite auxetic structures consist of corrugated sheets and tubes

In recent years, auxetic (negative Poisson's ratio) structures have attracted great attention because of their non-conventional behaviour. However, auxetic structures are usually characterized by low stiffness, which limits their application. Once, their stiffness can be improved, their application field will be significantly broadened. In addition, most auxetic structures are difficult to be produced due to their complex geometries. To solve these two problems, high-performance carbon fibre reinforced polymer (CFRP) composites are used to manufacture an auxetic structure consist of corrugated sheets and tubes. The mechanical properties of the composite auxetic structure consist of corrugated sheets and tubes (CorTube) are studied by experiments, finite element simulation and theory analysis. The results show that, the composite CorTube structures display obvious negative Poisson's ratio effect in large compression strain range, and the auxetic characteristics of the composite CorTube structures become more notable with the increase of the compression strain. The stiffness of the structure depends on the thickness of the corrugated sheets in small strain stage, while the material parameters of the tubes plays determining role in large strain stage. Finally, the deformation characteristics and failure modes of the CorTube during the compression process are discussed.

Design and mechanical testing of porous lattice structure with independent adjustment of pore size and porosity for bone implant

Porosity is considered to be one of the key factors affecting the structural properties of porous lattices, but in fact, pore size also plays an important role, and it has great potential to adjust pore size and porosity independently to improve structural properties. In this work, by adjusting the sheet thickness of the triply periodic minimal surface (TPMS) lattice structures and adjusting the height of the single row structure according to linear and constant laws, the TPMS lattice structures with given porosity and adjustable pore size are designed, and the mechanical response is investigated. Based on preparing samples by Ti6Al4V laser powder bed fusion, the results of the tests show that the elastic modulus ranges of linear change TPMS (LC-TPMS) and constant TPMS (C-TPMS) lattice structures are 3625.6 MPa–4575.1 MPa and 3820.0 MPa–4509.1 MPa, respectively. In the plateau stage, the LC-TPMS lattice structures have a longer and more stable plateau stage, higher yield stress and better energy absorption capacity than the C-TPMS lattice structures. The maximum energy absorption difference is 62.7 MJ/mm3 and the maximum energy absorption efficiency difference is 0.12. The LC-TPMS lattice structures can also obtain a larger damping ratio under larger compressive strain.

Multifunctional Superelastic Graphene-Based Thermoelectric Sponges for Wearable and Thermal Management Devices.

Power generation through harvesting human thermal energy provides an ideal strategy for self-powered wearable design. However, existing thermoelectric fibers, films, and blocks have small power generation capacity and poor flexibility, which hinders the development of self-powered wearable electronics. Here, we report a multifunctional superelastic graphene-based thermoelectric (TE) sponge for wearable electronics and thermal management. The sponge has a high Seebeck coefficient of 49.2 μV/K and a large compressive strain of 98%. After 10 000 cyclic compressions at 30% strain, the sponge shows excellent mechanical and TE stability. A wearable sponge array TE device was designed to drive medical equipment for monitoring physiological signals by harvesting human thermal energy. Furthermore, a 4 × 4 array TE device placed on the surface of a normal working Central Processing Unit (CPU) can generate a stable voltage and reduce the CPU temperature by 8 K, providing a feasible strategy for simultaneous power generation and thermal management.

Plastic Zr-Al-Ni-Cu-Ag bulk glassy alloys containing quasicrystalline or β-Zr plus ω-Zr phases

Zr70–76Al7–7.5Ni13–15Cu2Ag2–5 glassy alloys were prepared by melt-spinning with Zr contents up to 76 at.%, greatly exceeding the highest Zr content of 70 at.% previously reported for Zr-based glassy alloys exhibiting a calorimetric glass transition. The 70–72Zr and 74Zr alloys were also cast as bulk rods up to 1.5 mm in diameter with glass and [glass + β-Zr + ω-Zr] phases, respectively, by ejection copper-mold casting. The crystallization temperature and Vickers hardness Hv for the glassy ribbons decrease with increasing Zr content from 70 to 76 at.%. The glassy rods show high yield strength (σy) of 1225–1346 MPa, high fracture strength (σf) of 1497–1499 MPa, and large compressive plastic strain (εp) of 9.7–3.2% for the 70–72Zr alloys. Similarly, the 74Zr rod with [glass + β-Zr + ω-Zr] phases shows σy of 1325 MPa, σf of 1472 MPa, εp of 2.4%. The 76Zr thick ribbon with [glass + β-Zr + ω-Zr] phases shows, in tension, high σy of 890 MPa, σf of 988 MPa, and plastic elongation of 0.3%. The Zr-rich glassy ribbons crystallize, showing three exothermic peaks upon heating. The first-stage peak is due to the precipitation of icosahedral quasicrystal (IQ) for the 70–72Zr ribbons, and β-Zr + ω-Zr for the 74–76Zr ribbons. These annealing-induced mixed-phase ribbons with Zr content above 72 at.% exhibit good bending plasticity, even though their HV is about 41% higher than for the as-spun glassy ribbons. Similarly, the 70Zr bulk rod, with [glass + IQ] phases obtained by annealing, shows a distinct increase in σy and σf to 1485 and 1575 MPa, respectively, as well as εp of 0.6%. Thus, the plastic Zr-rich bulk rods with glass, [glass + IQ], and [glass + β-Zr + ω-Zr] phase mixtures are encouraging for the future development of a new type of high-strength structural material.

Elastic response of polymer-nanoparticle composite sponges: Microscopic model for large deformations

We propose a minimalist coarse-grained microscopic model to investigate the mechanical response of ice-templated polymer nanocomposite sponges with large open voids. Earlier experimental work [Rajamanickam et al., Chem. Mater. 26, 5161 (2014)] has demonstrated that such systems show elastic recovery after being subjected to large compressive strains exceeding $80%$, despite being comprised primarily of inorganic nanoparticles. Our model captures the essential features of the nonlinear mechanical response to uniaxial compression up to strain $\ensuremath{\gamma}=0.8$. From our simulation we identify three different regimes for the stress response: (i) the stress increases linearly with strain at low strains up to $\ensuremath{\approx}0.2$; (ii) at intermediate strains, such that $\ensuremath{\gamma}$ is approximately in the range $0.2\ensuremath{-}0.5$, we observe a plateau regime in the stress-strain data; and (iii) finally we see a sharp increase in stress at strains $>0.5$. This agrees with experimental observations. The model helps us establish a correlation between the stress-strain response and the underlying microscopic reorganization of microstructure spanning multiple length scales, which leads to the emergence of the three regimes. The nature of individual void deformations was statistically analysed to demonstrate the progression of void shapes as the sponge is compressed. We also establish that nanoparticles at the interface of voids respond differently to stress as compared to those away from the interface. Our simulation model is versatile and allows us to vary parameters, which correspond to variations in the cross-link density and architecture of nanoparticle connectivity in experiments.

Chirality-Dependent Mechanical Properties of Bundles and Thin Films Composed of Covalently Cross-Linked Carbon Nanotubes.

The effect of nanotube chirality on the mechanical properties of materials composed of single-walled carbon nanotubes (CNTs) is poorly understood since the interfacial load transfer in such materials is strongly dependent on the intertube interaction and structure of the nanotube network. Here, a combined atomistic-mesoscopic study is performed to reveal the effect of CNT diameter on the deformation mechanisms and mechanical properties of CNT bundles and low-density CNT films with covalent cross-links (CLs). First, the pullout of the central nanotube from bundles composed of seven (5,5), (10,10), (20,20), (17,0), and (26,0) CNTs is studied in molecular dynamics simulations based on the ReaxFF force field. The simulations show that the shear modulus and strength increase with decreasing CNT diameter. The results of atomistic simulations are used to parametrize a mesoscopic model of CLs and to perform mesoscopic simulations of in-plane tension and compression of thin films composed of thousands of cross-linked CNTs. The mechanical properties of CNT films are found to be strongly dependent on CNT diameter. The film modulus increases as the CNT diameter increases, while the tensile strength decreases. The in-plane compression is characterized by collective bending of whole films and order-of-magnitude smaller compressive strengths. The films composed of (5,5) CNTs exhibit the ability for large-strain compression without irreversible changes in the material structure. The stretching rigidity of individual nanotubes and volumetric CL density are identified as the key factors that dominate the effect of CNT chirality on the mechanical properties of CNT films. The film modulus is affected by both CL density and stretching rigidity of CNTs, while the tensile strength is dominated by CL density. The obtained results suggest that the on-demand optimization of the mechanical properties of CNT films can be performed by tuning the nanotube chirality distribution.

A novel class of bioinspired composite via ultrasound-assisted directed self-assembly digital light 3D printing

The advent of advanced manufacturing technologies brings about the possibilities of novel materials with potentially unprecedented material properties. Through ultrasound-assisted directed self-assembly digital light processing, we present a novel class of composite – the discontinuous interpenetrating-phase composite (d-IPC) – where the cellular filler phase is based on lines of particle assemblies, as opposed to continuous materials. Through yttria particle doping, we fully illustrate the unique microstructural-specific mechanical properties of the d-IPC. Despite being fully bulk and having a similar density (1.18 g/cm3) and strength (68 MPa) as the matrix polymer, it presents an additional plateau-deformation behaviour under large compressive strains and hence a 218% increase in specific energy absorption up to 37 J/g. The enabling mechanism is derived from the peculiar discontinuous and macroscopically aligned particle-based struts which do not contribute to a notable diminution of strength but can yet modulate high-strain deformation via induction of progressive localized failures. The concept of d-IPC is also extendable to solid fillers of all materials, morphology, and reasonable sizes, allowing the d-IPC to be highly customizable with multifunctional potentials. Through this work, we also aim to demonstrate the potentials of using advanced microstructural-controllable manufacturing techniques to achieve conceptually new and advanced composite materials.

Strong phonon coupling induces low thermal conductivity of one-dimensional carbon boron nanotube

Recently, one-dimensional materials have drawn much attention due to their excellent performance in the field of energy storage and thermal management. As a newly synthesized representative of 1D carbon boron compounds, BC3 nanotube (BC3NT), its thermal conductivity and phonon transport mechanism are urgently required for designing electron-related devices and have been still lacking. Herein, the thermal transport properties of BC3NT are investigated using non-equilibrium molecular dynamic simulations. Compared with the carbon nanotube, the lattice analysis and differential charge density revealed that the much lower thermal conductivity of BC3NT stems from the strong phonon coupling induced by the disorders from atomic mass discrepancy and the polarized covalent bond. Furthermore, the temperature and strain effect of thermal conductivity of BC3NT are explored. Interestingly, it is found that for both CNT and BC3NT, the small tensile strain can enhance the thermal conductivity while the large tensile and compressive strain would impede the phonon transport, indicating that the strain strategy can effectively modulate the thermal conductivity of 1D systems. Our studies not only provide a newly perspective to understand phonon transport of 1D systems and could be helpful to extend phonon coupling mechanism to low-dimensional systems.

Auxetic behavior obtained through the large deformations of variants of the rectangular grid

The deformation behavior of intersecting ligaments forming variants of the square and rectangular grids under mechanical compression was investigated. It was shown that such systems are able to exhibit a negative incremental Poisson’s ratio at relatively large axial compressive strains. Numerical simulations and experimental studies indicated that the extent of auxeticity depends on the relative offset of successive ligaments, the relative lengths of the ligaments as well as on their thickness. It was also shown that there are two distinct modes of deformation, one resembling that of the reentrant hexagonal honeycomb and the other that of the meta-tetrachiral system.

First-principle studies on the metal/semiconductor properties and strain-tuned electronic structures of SnP3 monolayer

Using first-principles calculations, we found several energetically stable structures of monolayer SnP3, which include metal (M−SnP3) and semiconductor (S-SnP3). The structural difference between M−SnP3 and S-SnP3 lies in the buckling angle, which is the reason for the metal–semiconductor transition of SnP3 from bulk to monolayer. When the biaxial strain is applied from −5% to 5%, the buckling decreases and the bond angle increases, leading to the weakened (enhanced) hybridization of the pz (px) orbital and the increase (decrease) of the energy of the corresponding bonding state. Although the biaxial strain of 6% or − 6% does not change the structure of monolayer SnP3 from S-SnP3 to M−SnP3, a large enough compressive strain will close the band gap of semiconductor SnP3. The uniaxial tensile strain has the same effects, but exhibits anisotropic behaviors on the band near the Fermi level. There are similar situations for GeP3 and GeSnP6, which have the same valence electrons. By the investigation of structural characteristics and atomic orbital compositions, this work reveals the mechanism of strain-tuned band structures and metal–semiconductor properties, which is useful for band engineering of two-dimensional materials.

Strain tunable intrinsic ferromagnetic in 2D square CrBr2

Two-dimensional intrinsic magnetic materials with high Curie temperature (Tc) coexisting with 100% spin polarization are highly desirable for realizing promising spintronic devices. In the present work, the intrinsic magnetism of monolayer square CrBr2 is predicted by using first-principles calculations. The monolayer CrBr2 is an intrinsic ferromagnetic half-metal with the half-metallic gap of 1.58 eV. Monte Carlo simulations based on the Heisenberg model estimate Tc as 212 K. Furthermore, the large compressive strain makes CrBr2 undergo ferromagnetic–antiferromagnetic phase transition when the biaxial tensile strain larger than 9.3% leads to the emergence of semiconducting electronic structures. Our results show that the intrinsic half-metal with a high Tc and controllable magnetic properties endow monolayer square CrBr2 as a potential material for spintronic applications.

Doping- and Strain-Dependent Electrolyte-Gate-Induced Perovskite to Brownmillerite Transformation in Epitaxial La1-xSrxCoO3-δ Films.

Much recent attention has focused on the voltage-driven reversible topotactic transformation between the ferromagnetic metallic perovskite (P) SrCoO3-δ and oxygen-vacancy-ordered antiferromagnetic insulating brownmillerite (BM) SrCoO2.5. This is emerging as a paradigmatic example of the power of electrochemical gating (using, e.g., ionic liquids/gels), the wide modulation of electronic, magnetic, and optical properties generating clear application potential. SrCoO3 films are challenging with respect to stability, however, and there has been little exploration of alternate compositions. Here, we present the first study of ion-gel-gating-induced P → BM transformations across almost the entire La1-xSrxCoO3 phase diagram (0 ≤ x ≤ 0.70), under both tensile and compressive epitaxial strain. Electronic transport, magnetometry, and operando synchrotron X-ray diffraction establish that voltage-induced P → BM transformations are possible at essentially all x, including x ≤ 0.50, where both P and BM phases are highly stable. Under small compressive strain, the transformation threshold voltage decreases from approximately +2.7 V at x = 0 to negligible at x = 0.70. Both larger compressive strain and tensile strain induce further threshold voltage lowering, particularly at low x. The P → BM threshold voltage is thus tunable, via both composition and strain. At x = 0.50, voltage-controlled ferromagnetism, transport, and optical transmittance are then demonstrated, achieving Curie temperature and resistivity modulations of ∼220 K and at least 5 orders of magnitude, respectively, and enabling estimation of the voltage-dependent Co valence. The results are analyzed in the context of doping- and strain-dependent oxygen vacancy formation energies and diffusion coefficients, establishing that it is thermodynamic factors, not kinetics, that underpin the decrease in the threshold voltage with x, that is, with increasing formal Co valence. These findings substantially advance the practical and mechanistic understanding of this voltage-driven transformation, with fundamental and technological implications.

Depolarization-mediated monoclinic states in ultrathin [111] PbTiO3 epitaxial films

Stress-depolarization field phase stability map is constructed for ultrathin [111]-PbTiO3 epitaxial films coherently grown on SrTiO3. Despite a large compressive strain imposed by the substrate, rhombohedral to monoclinic transition can be induced so that the polarization vector is confined in a symmetry plane. We investigate competition of phase stability and evolution of monoclinic states by inspecting the flattened energy surface, and show that in the presence of depolarization field the critical stress for inducing low-symmetry states can be remarkably lowered. The influence of vertical stress and depolarization field on polarization, monoclinic shear strain, and volume change of unit cell are calculated for the coherent [111]-PbTiO3, and boundary conditions allowing for considerable enhancement in dielectric and piezoelectric responses are revealed.

Microstructural optimization of FexCrNiAl0.5Ti0.5 high entropy alloys toward high ductility

It remains challenging to develop low-cost body-centered cubic (BCC) high-entropy alloys (HEAs) with superior mechanical properties. In this work, we investigated the microstructure and mechanical properties of BCC FexCrNiAl0.5Ti0.5 HEAs containing L21 nanocrystals. With increasing the Fe content from Fe2 to Fe4 and Fe6, the formation of a big blocky L21 phase and a σ phase can be fully suppressed, and the size and fraction of the L21 crystals also decrease. Fe4 and Fe6 HEAs exhibit an optimized dual-phase microstructure with high-density L21 nanocrystals homogeneously distributed in the BCC matrix. Fe4 and Fe6 HEAs show high strength and do not fracture even at a large compressive strain of 70%, exhibiting the best combination of strength and fracture strain among all the reported BCC HEAs with nanocrystals. The superior mechanical properties of Fe4 and Fe6 HEAs are attributed to the optimized microstructure. These findings promote the development of low-cost HEAs with superior mechanical properties.