Large Strain Response Research Articles

Mechanical Behavior of a Low-Cost Ti–6Al–4V Alloy

Mechanical compression tests were performed on an economical Ti–6Al–4V alloy over a range of strain-rates and temperatures. Low rate experiments (0.001–0.1/s) were performed with a servo-hydraulic load frame and high rate experiments (1000-80,000/s) were performed with the Kolsky bar (Split Hopkinson pressure bar). Emphasis is placed on the large strain, high-rate, and high temperature behavior of the material in an effort to develop a predictive capability for adiabatic shear bands. Quasi-isothermal experiments were performed with the Kolsky bar to determine the large strain response at elevated rates, and bars with small diameters (1.59 mm and 794 µm, instrumented optically) were used to study the response at the higher strain-rates. Experiments were also conducted at temperatures ranging from 81 to 673 K. Two constitutive models are used to represent the data. The first is the Zerilli-Armstrong recovery strain model and the second is a modified Johnson–Cook model which uses the recovery strain term from the Zerilli–Armstrong model. In both cases, the recovery strain feature is critical for capturing the instability that precedes localization.

Large strain response in Li/Nb co-doped Bi0.5(Na0.8K0.2)0.5TiO3 lead-free piezoceramics

A series of (Bi0.5Na0.4K0.1)Ti0.98Nb0.02O3-xLi lead-free ceramics were fabricated using the solid-state reaction technique. The effects of Li/Nb cations on the structural and electrical properties of the ceramics were investigated. All the sintered ceramics exhibited pure perovskite structure and the average grain size increased slightly with increasing the Li content. Shape of the P-E loops illustrated the relaxor characteristic of all the samples. A giant strain of 0.4% was obtained at 60kV/cm at x = 0.01 and the corresponding normalized strain was up to 683pm/V, moreover, the strain exhibits excellent fatigue-resistance behavior. The giant strain can be attributed to the ferroelectric-relaxor phase transition under external driving electric field. These results indicate the sintered Li/Nb co-doped lead-free ceramics can be promising candidate for actuator applications.

Large electric-field-induced strain in B-site complex-ion (Fe0.5Nb0.5)4+-doped Bi1/2 (Na0.82K0.12)1/2TiO3 lead-free piezoceramics

In order to obtain a new system of (Bi1/2Na1/2)TiO3 (BNT) based lead-free incipient piezoceramics with large strain for practical applications of actuators, we investigated the effect of B-site complex-ion (Fe0.5Nb0.5)4+ (FN)-doped Bi1/2 (Na0.82K0.12)1/2TiO3 ceramics on the phase structure, dielectric, ferroelectric, piezoelectric and electric-field-induced strain properties. All samples exhibited single perovskite phase with pseudocubic symmetry. The room temperature electric-field-induced polarization (P-E) and strain (S-E) hysteresis loops indirectly illustrated ferroelectric-to-relaxor (FE-RE) phase transition. The increasing content of FN doping decreased the FE-RE phase transition temperature, TF-R to below room temperature and induced the reversible FE-RE phase transition, giving rise to a large strain of 0.462% with a normalized strain, d*33 of 660pm/V at a critical composition of x = 5. A fluctuation of the dielectric curve for BNKT-5mol% FN ceramics in the spectra around 80°C before and after polarization suggested that the large strain response can be induced via delicate mixing of the FE and RE phase.

Relaxor phase evolution and temperature-insensitive large strain in B-site complex ions modified NBT-based lead-free ceramics

Lead-free Bi0.495(Na0.8K0.2)0.495Sr0.01Ti1−x (Fe0.5Me0.5) x O3 ceramics with x = 0−0.03/0.04 mol (Me = Nb, Sb and Ta, abbreviated as FN0.5–FN4, FS0.5–FS3 and FT0.5–FT3, respectively) were fabricated by a conventional solid-state reaction method. The effects of B-site complex ions content on relaxor phase evolution and electromechanical properties were systematically investigated. Results showed that the modification of FN, FS and FT complex ions can significantly reinforce the B-site compositional disorder, effectively destroy the long-range ferroelectric order and tune the ferroelectric–relaxor transition point (T FR) to around room temperature. The relatively high strain performances (dynamic $$d_{{33}}^{*}$$ values) of 567, 550 and 600 pm/V were obtained in FN2, FS1.5 and FT2 critical compositions, respectively. The large strain responses are closely associated with the reversible relaxor–ferroelectric phase transformation. Furthermore, the electrostrain of FT2 sample presents a temperature-insensitive characteristic with the variation less than 10% up to 120 °C. These findings indicate that the B-site complex ions modified NBT-based ceramics can be considered as promising candidates for lead-free electromechanical actuator applications.

Composition‐induced structural transitions and enhanced strain response in nonstoichiometric NBT‐based ceramics

AbstractIn this work, the nonstoichiometric 0.99Bi0.505(Na0.8K0.2)0.5‐xTiO3‐0.01SrTiO3 (BNKST(0.5‐x)) ceramics with x=0‐0.03 were synthesized by conventional solid‐state reaction method. The composition‐induced structural transitions were investigated by Raman spectra, dielectric analyses, and electrical measurements. It is found that the relaxor phase can be induced through the modulation of the (Na, K) content. The (Na, K) deficiency in BNKST(0.5‐x) ceramics favors a more disordered local structure and can result in the loss of long‐range ferroelectricity. The x=0.015 critical composition possesses relatively high positive strain Spos of 0.42% and large signal piezoelectric constant d33* of 479 pm V−1 at 6 kV mm−1, along with the good temperature (25‐120°C) and frequency (1‐20 Hz) stability. The recoverable large strain responses in nonstoichiometric ceramics can be attributed to the reversible relaxor‐ferroelectric phase transition, which is closely related to the complex defects (, , and ) and the local random fields. This work may be helpful for the exploration of high‐performance NBT‐based lead‐free materials by means of A‐site compositional modification.

Phase transition, switching characteristics of MPB compositions and large strain in lead-free (Bi 0.5 Na 0.5 )TiO 3 -based piezoceramics

Abstract In this study, the switching characteristics of MPB compositions of (1-x-y)(Bi0.5Na0.5)TiO3-xKNbO3-ySrTiO3 (abbreviated as BNT-KN-ST) and temperature- and composition-driven strain behavior, dielectric, ferroelectric (FE), piezoelectric, and pyroelectric properties were systematically explored to achieve lead-free piezoelectric materials with large strain response for practical applications of piezoelectric actuators. The piezoelectric coefficient (d33) declined dramatically and normalized strain Smax/Emax increased markedly as the morphotropic phase boundary (MPB) compositions shifted away from the MPB (I) into the MPB (II) where the ferroelectric rhombohedral and relaxor pseudo-cubic phases coexisted at around critical composition. The critical compositions for the indicated system exhibited enhanced strain response, and at room temperature a high strain of 0.34% with normalized strain Smax/Emax = 486 p.m./V was gained for the critical composition 0.90BNT-0.05KN-0.05ST. The source of the achieved large strain was sought based on the X-ray diffraction (XRD) and Raman-spectra structure analysis, macroscopic properties, thermal depolarization progress, and temperature-dependent correlations of both polarization and strain, and the results indicated that it derived from the phase transformation contribution from ergodic relaxor (ER) to FE phases. Moreover, the present work also established the relationship between the MPB composition and tolerance factor t in BNT-based ceramics, and demonstrated that the t corresponding to the formation of MPB located in a quite narrow range. As a result, we believe that this study will open the door to quickly detect the approximate MPB region for BNT-based solid solutions.

Enhanced electromechanical properties of CaZrO3-modified (K0.5Na0.5)NbO3-based lead-free ceramics

Pairing of large strain response and high d33 with high Tc in (K0.5Na0.5)NbO3-based materials is of high significance in practical applications for piezoelectric actuators. Here, we report remarkable enhancement in the electromechanical properties for (1-x)(K0.52Na0.48) (Nb0.95Sb0.05)O3-xCaZrO3 (KNNS-xCZ) lead-free ceramics through the construction of a rhombohedral (R)-tetragonal (T) phase boundary. We investigated the correlation between the composition-driven phase boundary and resulting ferroelectric, piezoelectric, and strain properties in KNNS-xCZ ceramics. The KNNS-xCZ ceramics with x=0.02 exhibited a large strain response of 0.23% while keeping a relatively large d33 of 237pC/N, which was mainly ascribed to the coexistence of R and T phases confirmed by the XRD and dielectric results. It was found that pairing of large strain response and high d33 in KNN-based materials was achieved. As a consequence, we believe that this study opens the possibility to achieve high-performance lead-free electromechanical compounds for piezoelectric actuators applications.

Impact of Ni dopant on structure and electrical properties of PMN-0.1PT ceramics

The Ni-doped PMN-0.1PT (PMN-0.1PT-xNi) relaxor ferroelectric ceramics were prepared by two-step columbite precursor method, and the effects of Ni dopant on the phase structure, dielectric, ferroelectric and electrostrictive properties were systematically investigated. The introduction of Ni dopant significantly improved the densification and grains size in the ceramics, but also profoundly modified the phase structure. It demonstrated that the substitution of Ni dopant for B-site in PMN-0.1PT lattice could affect electrical properties of PMN-0.1PT binary ceramics. Properly increasing the amount of Ni dopant led to the enhancement of dielectric and ferroelectric and remarkably increased the electrostrictive response. Results in this study indicated that at a composition x of 2.0 mol%, a large strain response could be obtained with maximum strain as high as 0.11% under the low field of 15 kV/mm at room temperature.

Electric-field-temperature phase diagram and electromechanical properties in lead-free (Na0.5Bi0.5)TiO3-based incipient piezoelectric ceramics

In this work, the (1-x)(0.8Na0.5Bi0.5TiO3-0.2K0.5Bi0.5TiO3)-xSrTiO3 (NKBT-xST) incipient piezoelectric ceramics with x=0–0.07 (0ST-7ST) were prepared by the solid-state reaction method and their structural transformation and electromechanical properties were investigated as a function of ST content. As the ST content increases, the long-range ferroelectric order is disrupted, and the ferroelectric-relaxor phase transition temperature (TFR) shifts to around room temperature for NKBT-5ST ceramics, accompanied by a relatively high electrostrain of 0.3% at 6kV/mm. The large strain response associated with the vanished ferroelectric properties around TFR can be attributed to the reversible relaxor-ferroelectric phase transition. The electric-field-temperature (E-T) phase diagrams were established, and the transition between the two field-induced long-range ferroelectric states were found to take place via a two-step switching process through an intermediate relaxor state. The threshold electric field to trigger the conversion between ferroelectric state and relaxor state depends strongly on the dynamics of polarization relaxation, which is influenced by temperature and composition.

Effect of rhombohedral-orthorhombic phase transition on structure and electrical properties of KNN-based lead-free piezoceramics

ABSTRACTLead-free ceramics (1-x)(Na0.7K0.3)0.92Li0.08NbO3-xCaZrO3 (KNNL-xCZ) have been synthesized by the conventional solid-state reaction. X-ray diffraction shows that all ceramics are in pure perovskite phase. The study of their phase transition observed by the temperature-dependent dielectric measurements confirms that the addition of CZ leads to alternation of crystal structure. The KNNL-0.03CZ ceramics exhibit optimum electrical properties and produce large strain response (dS/dE = 193 pm/V). The enhanced properties of the KNNL-xCZ are attributed to the effect of rhombohedral-orthorhombic phase transition in the vicinity of room temperature.

In-situ measurement of the large strain response of the fibrillar debonding region during the steady peeling of pressure sensitive adhesives

The debonding of pressure sensitive adhesives (PSA) is a classical example of the difficult and unsolved issue of fracture in soft viscoelastic confined materials. The presence of a complex debonding region where the adhesive undergoes cavitation and the very large strain of a spontaneously formed fibrillar network has defied many modeling attempts over the past 70 years. We present here a novel technique to provide an accurate measurement of the local large strain response of the fibrillar debonding region during the steady-state peeling of a well known commercial adhesive over a wide range of peeling velocity and angle. The technique is based on high resolution imaging of the debonding region during peeling and is coupled to a cohesive zone modeling of the adhesive interaction between the flexible tape backing and the rigid substrate. The resulting database provides a strong ground for validating and further developing models (Villey et al. in Soft Matter 11:3480–3491, 2015) aiming to capture the effects of both geometry and non-linear adhesive rheology on the exceptional adherence energy of PSAs.

Low electric field-driven giant strain response in 〈001〉 textured BNT-based lead-free piezoelectric materials

The applied electric field to drive intended large strain response in Bi0.5Na0.5TiO3-based piezoelectric ceramics is usually high (mostly with E ≥ 60 kV/cm) and remains a long-standing drawback for actual actuator applications. In this work, we report 〈001〉 oriented (1−x) (0.83Bi0.5Na0.5TiO3–0.17Bi0.5K0.5TiO3)–xBaTiO3 (BNT–BKT–BT) lead-free piezoelectric ceramics using BT as the template particles to tailor the strain behavior under a low driving field. The strain response exhibited an increasing trend with the increasing grain orientation, and remarkably giant S max/E max of 800 pm/V was acquired under a relatively low electric field of 45 kV/cm in the optimized microstructure for textured BNT-BKT–1BT ceramics compared with the reported lead-free Bi-based perovskite ceramics. Furthermore, the achieved textured ceramics showed prominent electric field- and temperature-dependent strain characteristic featured by both a high room-temperature S max/E max of 621 pm/V under a very low driving field of 35 kV/cm and an achievable large S max/E max of 531 pm/V with almost vanished hysteretic behavior at high temperature. Our work may be helpful for designing BNT-based lead-free materials with promising strain response and thus provides a new approach to resolve this drawback of BNT-based lead-free piezoelectric ceramics.

Large strain response in Bi4Ti3O12 modified BNT-BT piezoelectric ceramics

In this paper, a novel system of lead-free piezoelectric ceramics 0.94(Bi0.5Na0.5)TiO3−0.06BaTiO3-xBi4Ti3O12 (abbreviated as BNT-BT-xBiT) were prepared by the solid-state reaction method. The effects of Bi4Ti3O12 dopant on the strain behavior, dielectric, ferroelectric and piezoelectric performance of BNT-BT ceramics were systematically investigated. A optimal strain value of ~0.37% was achieved around the critical composition of x=6 wt% which corresponds to a normalized strain (Smax/Emax) of 465pm/V. The large strain response in this sample is mainly originated from two aspects: one is that BiT addition induced ferroelectric-to-relaxor phase transition evidenced by “pinched” ferroelectric hysteresis loops and vanished negative strain of bipolar strain loops as well as downward shift of TF-R; the other is that the small-sized nanodomains (or polar nanoregions) facilitate the domain switching and domain wall motion with an applied electric field, which lead to large external contribution to strain response. These results indicate that BNT-BT-xBiT piezoelectric ceramics with large strain response may be a promising lead-free material for actuator application.

Enhancement of orbital ordering and spin polarization by controlling the dimensionality of the octahedra network

AbstractTwo-dimensional (2D) systems have been widely investigated with perovskite superlattices because they show excellent epitaxy. A challenging question is naturally raised: whether lower dimensionality, e.g., one dimension (1D) and zero dimension (0D), can be achieved by perovskites? In this work, we propose a way to control the dimensionality of the octahedra network in perovskite superlattices by selecting the substrate orientation and superlattice period. Taking SrTiO3/SrRuO3 as an example, we demonstrate that the 1D structure is in a 1D Ising state, which is paramagnetic, while the 0D structure is ferromagnetic insulator with fully saturated magnetic moment on the Ru sites. New phenomena in the magnetic and electronic properties are observed, including large strain response, half-metallicity, and orbital-selective quantum confinement effects.

Computation of the effective nonlinear mechanical response of lattice materials considering geometrical nonlinearities

The asymptotic homogenization technique is presently developed in the framework of geometrical nonlinearities to derive the large strains effective elastic response of network materials viewed as repetitive beam networks. This works extends the small strains homogenization method developed with special emphasis on textile structures in Goda et al. (J Mech Phys Solids 61(12):2537---2565, 2013). A systematic methodology is established, allowing the prediction of the overall mechanical properties of these structures in the nonlinear regime, reflecting the influence of the geometrical and mechanical micro-parameters of the network structure on the overall response of the chosen equivalent continuum. Internal scale effects of the initially discrete structure are captured by the consideration of a micropolar effective continuum model. Applications to the large strain response of 3D hexagonal lattices and dry textiles exemplify the powerfulness of the proposed method. The effective mechanical responses obtained for different loadings are validated by FE simulations performed over a representative unit cell.

Large strain response in (Mn,Sb)–modified (Bi0.5Na0.5)0.935Ba0.065TiO3 lead–free piezoelectric ceramics

Lead–free piezoelectric ceramics (Bi0.5Na0.5)0.935Ba0.065Ti1–x(Mn0.5Sb0.5)xO3 (BNBT6.5–xMS, x=0.005, 0.010, 0.015, 0.020) were prepared by conventional solid state reaction sintering technique. All ceramics present a pure perovskite phase structure, indicating that (Mn, Sb) has completely diffused into the BNBT6.5 lattice in the studied components. The addition of (Mn, Sb) disrupted the ferroelectric long–range order and promoted the electric field induced strain response. At x=0.015, a large electric field–induced unipolar strain of 0.48% (at an applied electric field of 80kV/cm) with normalized strain d33*(Smax/Emax) of 602pm/V are achieved. Temperature dependent measurements of both polarization and strain from room temperature to 120°C were also studied, and the results suggest that the origin of the large strain is due to a reversible field–induced non–polar relaxor phase to polar ferroelectric phase transformation.

Structure evolution and electrostrictive properties in (Bi0.5Na0.5)0.94Ba0.06TiO3–M2O5 (M = Nb, Ta, Sb) lead-free piezoceramics

The effects of M2O5 (M=Nb, Ta, Sb) addition on the phase transition and electrical properties of 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNBT6) lead-free ceramics were studied. Results showed that M substitution into BNBT6 induced a phase transition from coexistence of ferroelectric tetragonal and rhombohedral to a relaxor pseudocubic with a significant disruption of the long-range ferroelectric order. Accordingly, large strain response of 0.42–0.43% with fatigue-free behavior, which is due to a reversible field-induced ergodic relaxor-to-ferroelectric phase transformation, was obtained at 0.5mol% M content. Furthermore, as the compositions (x≥0.06) lied deep in the pseudocubic region of the phase diagram, a high, purely electrostrictive effect with large electrostrictive coefficient Q33 of 0.020–0.024m4/C2 was achieved. More interestingly, the obtained BNBT6-based electrostrictors showed good resistance to both long-term electric cycling (up to 106 cycles) and thermal influence (20–160°C), rendering them suitable for high-precision positioning devices and other actuators.

Viscoelasticity of the polydomain-monodomain transition in main-chain liquid crystal elastomers

Abstract The goal of this study was to explore the rate-dependent behavior of the stretch-induced polydomain-monodomain (PM) transition of a liquid crystal elastomer (LCE). The main-chain LCE was synthesized and then cross-linked in the nematic polydomain state. The PM transition caused a soft-elastic behavior, which was measured using uniaxial tensile tests at multiple strain rates and temperatures. The main finding was that we were able to apply the temperature-dependent shift factor determined for the small strain behavior and in the frequency domain to create master curves for the large-strain response in the strain rate domain. The soft elasticity phenomenon was absent from the stress-strain curve at equilibrium. The results also suggest that the relaxation mechanisms of the network, and not of the mesogen orientation, dominate the rate-dependent behavior. Finally, we observed a relatively slow recovery behavior, suggesting the presence of an additional slow relaxation mechanism.

Composition, electric-field and temperature induced domain evolution in lead-free Bi0.5Na0.5TiO3-BaTiO3-SrTiO3 solid solutions by piezoresponse force microscopy

In order to clarify the nanoscale mechanism responsible for the large strain response in Bi0.5Na0.5TiO3-BaTiO3-SrTiO3 (BNBST) reported in our previous work, the composition, electric-field and temperature induced domain evolution was investigated. Results indicated the increase of the SrTiO3 concentration led to the evolution from non-ergodic relaxor ferroelectric domain to ergodic relaxor state. The in-situ poling results indicated the transition from the ergodic relaxor to ferroelectric was induced under sufficient high electric field in BNBST with high strain response, which was suggested as the main reason for the large strain level. The temperature-dependent domain evolution was also characterized and discussed.

Temperature-insensitive large strain response with a low hysteresis behavior in BNT-based ceramics

A ternary solid solution Ba(Zr0.05Ti0.95)O3-modified (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3 (BNT–BKT–BZT) was designed and prepared by solid state synthesis. The phase stability and macroscopic electromechanical properties were systematically investigated with an emphasis on the relationship between the structure evolution and strain behavior, and a schematic phase diagram is proposed. Increasing the content of BZT decreased the ferroelectric-to-relaxor phase transition temperature TF-R and induced the reversible transition from the relaxor pseudocubic to ferroelectric rhombohedral phase, giving rise to a promising strain behavior at a critical composition x=0.02 featured by not only high electric-induced normalized strain of Smax/Emax=503pm/V but also a relatively small hysteresis compared with existing BNT-based lead-free ceramics. In particular, by limiting the electric driving field to exclude the contribution from the converse piezoelectric effect, a temperature-insensitive Smax/Emax was obtained in the investigated temperature range from room temperature to 120°C. Furthermore, a high electrostrictive coefficient (Q11) of 0.0237 m4C−2 was achieved at room temperature for the composition with 10mol% BZT, that was highly stable within the investigated temperature and electric field ranges.