Ultrahigh Strain Research Articles

Concurrent anomalies in electric field-temperature dependence of direct/converse piezoelectric response in Bi0.5Na0.5TiO3-BaTiO3

Doping in bismuth sodium titanate (BNT)-based ceramic is often intended to realize excellent direct piezoelectric responses mainly through A-site substitution and generate ultrahigh strain behaviors mainly by B-site doping, which indicate the different effects of the doping on direct and converse piezoelectricity. Here, we reported simultaneous occurrences of anomalies in electric field and temperature dependence of direct/converse piezoelectric responses of 0.94Bi0.5Na0.5TiO3-0.06BaTiO3(BNT-BT6) ceramics by detailed analyses of the weak-field piezoelectric coefficient d33, high-field piezoelectric coefficient d33∗, and small signal bias-field piezoelectric coefficient d33∗(E = 0). The multiple piezoelectric responses presented similar anomalies at critical field Ep = 20 kV/cm and critical temperature Tf = 120 °C. The analogous changes in direct/converse piezoelectric behaviors are highly related to the electric-field/temperature-driven phase transformation, which could boost polarization reorientation and domain switching to a lager extent. Particularly, the phase transition resulted in an obvious increase in high-field piezoelectric coefficient d33∗, and so offer a potential strategy for further development of high-performance lead-free piezoelectric materials.

Flexural Behavior of Cracked RC Beams Retrofitted with Strain Hardening Cementitious Composites

In the present research, the efficiency and the effectiveness of different Ultra High Performance Strain Hardening Cementitious Composites (UHP-SHCC) schemes for flexure retrofitting of a cracked RC beams were investigated experimentally, numerically and analytically. The experimental program consisted of six RC beams. The control specimen was loaded until failure. The middle third part of the control specimen was replaced with UHP-SHCC, then, it was loaded again until failure. The other five beams were loaded until 52% of the failure load of the control beam, then they were retrofitted with a layer of UHP-SHCC casted at tension side. The main parameters were thickness and the reinforcement ratio of UHP-SHCC layer with two different lengths of UHP-SHCC layer. The test results showed that using UHP-SHCC layer is a highly effective technique to increase the flexural capacity and the ductility of RC beams. As the reinforcement ratio of the layer increased, the flexural capacity increased. The flexural capacity of the beams with a layer length of 75% beam span was less than the capacity of the beams having a layer length equal to the beam span. Analytical and numerical results agreed with the experimental results.

Solvent-assisted electrospun fibers with ultrahigh stretchability and strain sensing capabilities

Large strain flexible strain sensors have recently been the focus of many studies due to their wide range of applications in wearable technologies. However, development of a thin, conformable, and flexible strain sensor with a high maximum stretchability and a high gauge factor has still remained a challenge. In resistive-type sensors specifically, there is a trade-off between these two competing factors which has left a gap in development of large strain flexible strain sensors. To increase the sensitivity of the sensor, tuning the microstructure of the sensor through introducing a larger surface area is suggested. Using a solvent-assisted electrospinning technique and a highly stretchable copolymer of styrenebutadiene-styrene, super elastic mats composed of microfibers with a large surface area are obtained. Coating the fibers with different conductive materials and coating methods, a flexible strain sensor able to detect up to 1000% strain is fabricated. The sensors also show low hysteresis under cyclic-induced applied loadings.

Abnormal twin-twin interaction in an Mg-3Al-1Zn magnesium alloy processed by laser shock peening

Twin-twin interaction in an Mg-3Al-Zn1 magnesium alloy subjected to ultra-high strain rate deformation (~106/s) was investigated. The material was processed by laser shock peening and the microstructure at various depths was characterized by electron backscattered diffraction. The results show that different 101¯2 twin variants were activated in individual parent grains, and the interfaces between these twin variants present very abnormal morphologies. One variant can be totally surrounded by the other, forming isolated or disconnected islands which have the same crystallographic orientation. A mechanism was proposed to account for the abnormal twin-twin interaction.

Sonication induced amorphisation in Ag nanowires

It has long been conjectured that pure-element face-centred cubic (fcc) metals can be transformed into a glassy state by deformation at ultra-high strain rates. However, when an impact force is applied at the nanoscale, deformation-induced melting prevents observations of fcc metal amorphisation. Here we propose a sonication treatment of Ag nanowires (fcc) and confirmed amorphisation induced by high strain rates at bent areas of the Ag nanowires. Owing to the mismatch of the deformation modes between the core and the surface, we observed a diameter related increase of the ductility of Ag nanowires under deformation at ultra-high strain rates generated by sonication. The sonication-prepared amorphous Ag was stable at room temperature. Amorphous Ag at the bent areas was highly reactive and was readily recrystallized under light illumination or vulcanised. Our study verifies the occurrence of high strain rate induced amorphisation in pure fcc MGs and provides a powerful tool for mechanical studies on metal nanomaterials under extremely high strain rates and forces.

Performance of polyimide film under hypervelocity impact of micro flyer: Experiments and simulations

The characteristics of polyimide film hypervelocity impacted (HVI) by micro flyer are investigated though experimental and numerical methods. Using the laser driven flyer (LDF) method combined with the technique of scanning electron microscopy (SEM) and explicit dynamics numerical algorithm, the fracture morphology and detailed mechanical responses of polyimide film, both in the impact and non–impact zones, are captured; and a dynamic fracture strain criteria, combing temperature and strain rate, is presented. A parametric study on the performance of polyimide film is implemented and the influence of the factors, including the impact velocity, film thickness, strain rate constant and pre–stress, are assessed. The research reveals that polyimide film exits two failure modes, i.e. ductile punching and brittle cracks. Polyimide materials in the impact zone have experienced a high temperature (>Tg = 685 K), ultrahigh strain rate (108∼109) and plastic state; while in the non–impact zone, it is normal temperature (293–295 K), high strain rate (105∼106) and elastic state.

A Study on the Measurement Method of Transient Temperature in Materials at Ultra-High Strain Rate by Using the PIR Fiber

A Study on the Measurement Method of Transient Temperature in Materials at Ultra-High Strain Rate by Using the PIR Fiber

Microstructural evolution of aluminum alloy during friction stir welding under different tool rotation rates and cooling conditions

The microstructural evolution during friction stir welding (FSW) has long been studied only using one single welding parameter. Conclusions were usually made based on the final microstructure observation and hence were one-sided. In this study, we used the “take-action” technique to freeze the microstructure of an Al-Mg-Si alloy during FSW, and then systematically investigated the microstructures along the material flow path under different tool rotation rates and cooling conditions. A universal characteristic of the microstructural evolution including four stages was identified, i.e. dynamic recovery (DRV), dislocation multiplication, new grain formation and grain growth. However, the dynamic recrystallization (DRX) mechanisms in FSW depended on the welding condition. For the air cooling condition, the DRX mechanisms were related to continuous DRX associated with subgrain rotation and geometric DRX at high and low rotation rates, respectively. Under the water cooling condition, we found a new DRX mechanism associated with the progressive lattice rotation resulting from the pinning of the second-phase particles. Based on the analyses of the influencing factors of grain refinement, it was clearly demonstrated that the delay of DRV and DRX was the efficient method to refine the grains during FSW. Besides, ultra-high strain rate and a short duration at high temperatures were the key factors to produce an ultrafine-grained material.

Highly stretchable nanofiber-coated hybrid yarn with wavy structure fabricated by novel airflow-electrospinning method

Nanofiber-coated hybrid yarn not only exhibited the performance advantages of coating nanofiber-layer, but also possessed the structural feature of core layer, which could endow it excellent application prospect. Previous studies for fabricating nanofiber-coated hybrid yarn had limitations of poor yarn structure and discontinuity, and obtained hybrid yarns with a small strain. Herein, a novel stepped airflow-electrospinning method, in which stepped airflow field could effectively control the movement of nanofibers, was proposed to spin continuous nanofiber-coated hybrid yarn. Interestingly, a highly stretchable nanofiber-coated hybrid yarn with uniform wavy structure was obtained by our designed method, achieving an ultra-high strain of 531.98%.

Strain sensing behaviors of stretchable conductive polymer composites loaded with different dimensional conductive fillers

Herein, we investigate the dependence of the strain sensing behaviors of isoprene rubber (IR) based conductive composites on filler dimensionality. It is found that carbon black (CB)/IR composites display ultrahigh strain sensitivity and good recoverability since CB-networks are easily broken under stretching and fast rebuilt under releasing. However, the drawback of CB/IR composites is the high electrical percolation threshold (8.01 phr), leading to the complex processing, poor mechanical properties, and high cost. In contrast, carbon nanotubes (CNTs)/IR composites possess low percolation threshold (1.44 phr) but also low sensitivity and poor recoverability because CNT-networks are more stable under strain. Interestingly, it is observed that combining zero-dimensional CB and one-dimensional CNTs to construct the hybrid CNT-CB networks is an effective route to overcome the drawbacks of CB-networks and CNT-networks, which endows the stretchable CNTs/CB/IR composites with low percolation threshold, high strain sensitivity and good recoverability. Moreover, the demonstration experiments show that the stretchable CNTs/CB/IR composites could be used to detect human motions and emotional expressions. This study provides a deeper understanding of the strain sensing behaviors of the stretchable conductive polymer composites loaded with different dimensional conductive fillers, which helps to design strain sensing materials.

Large-Scale Production of Highly Stretchable CNT/Cotton/Spandex Composite Yarn for Wearable Applications.

Incorporation of carbon nanotubes (CNTs) into textiles without sacrificing their intrinsic properties provides a promising platform in exploring wearable technology. However, manufacture of flexible, durable, and stretchable CNT/textile composites on an industrial scale is still a great challenge. We hereby report a facile way of incorporating CNTs into the traditional yarn manufacturing process by dipping and drying CNTs into cotton rovings followed by fabricating CNT/cotton/spandex composite yarn (CCSCY) in sirofil spinning. The existence of CNTs in CCSCY brings electrical conductivity to CCSCY while the mechanical properties and stretchability are preserved. We demonstrate that the CCSCY can be used as wearable strain sensors, exhibiting ultrahigh strain sensing range, excellent stability, and good washing durability. Furthermore, CCSCY can be used to accurately monitor the real-time human motions, such as leg bending, walking, finger bending, wrist activity, clenching fist, bending down, and pronouncing words. We also demonstrate that the CCSCY can be assembled into knitted fabrics as the conductors with electric heating performance. The reported manufacturing technology of CCSCY could lead to an industrial-scale development of e-textiles for wearable applications.

Size distribution of pores in metal melts at non-equilibrium cavitation and further stretching, and similarity with the spall fracture of solids

Non-equilibrium cavitation in liquids is similar in many aspects to the spall fracture of solids. The dynamics of cavitation and further evolution of melt with cavities are determined by the processes of nucleation and size variation in the ensemble of pores. Exploration of the statistical distribution of the pore sizes and its evolution in the course of the melt stretching is important for in-deep understanding of the spall fracture of melts and formulation of adequate models. Size distributions of pores in pure Al, Ni, Cu, Ti and Fe melts under stretching with ultra-high strain rates are investigated with the help of molecular dynamics simulations and analysis of the obtained atomic configurations by an algorithm of pore searching. The size distribution of pores fits well to exponential one at the stage of active homogeneous nucleation of pores in all considered cases. This form of distribution is explained by the exponential growth of the nucleation rate together with the decrease in the size of critical pores at the decrease in pressure. A transition from the exponential distribution to normal one in the course of stretching is found out for melts of most metals except Fe at the strain rates above 30/ns. The transition to the normal distribution is explained by depopulation in the area of small pores due to their collapse in conditions of the increase in pressure. The transition occurs near the pore number maximum, because the reaching the maximum indicates that the collapse becomes predominant over the nucleation. The collapse of small pores is accompanied by enlargement of the largest pores and rapid widening of the size distribution with increase in the mean pore size. This is a mediated mechanism of the volume redistribution from the small pores to the largest ones; this mechanism is the most pronounced in Al melt and the most suppressed in Fe melt. In most cases, it is accompanied by direct merging of pores that is, vice versa, the most active in Fe and the most delayed in Al. The merging knocks out pores from the distribution depending on both the pore size and the mutual position of pores; therefore, predominant depopulation of the area of small pores does not happens at merging. The prevalence of merging over the collapse in Fe melt at the strain rates above 30/ns prevents the transition to the normal distribution in this melt, and the size distribution remains exponential after the stopping of nucleation. The merging also leads to corruption of the size distribution at the late stages of stretching for all melts. Time evolution of the distribution parameters reflects the distribution widening and shows the beginning of the distribution corruption. It is shown for the case of Al melt that the general behavior of the size distribution of pores remains the same within the range of strain rates from 100/ns down to 1/ns. In the case of Fe melt, the transition to the normal size distribution arises for the strain rates below 10/ns because of the delaying of merging. Additional simulations for solid Ni and Al at room temperature show that the statistical behavior of the pore ensemble in solid metals at high-rate stretching is very similar to that is observed in the case of metal melts.

Effects of service temperature on tensile properties and microstructural evolution of CP titanium subjected to laser shock peening

Effects of service temperature on the tensile properties and microstructural evolution of tensile specimens manufactured by commercial pure (CP) titanium subjected to laser shock peening (LSP) were investigated. Special attention was paid to the microstructural features at the top surface close to the fracture zone of the failed LSPed specimens at 20 °C, 150 °C, 250 °C, and 350 °C by means of transmission electron microscopy (TEM) observations. Results indicated that the ultimate tensile strength (UTS) of LSPed specimens gradually decreased, but the area reduction and elongation of LSPed specimens increased with the increment of service temperature. Furthermore, the influence mechanism of service temperature on the microstructural evolution of the LSPed CP titanium consisted of two modes: (a) ultra-high strain rate inhibited the dislocation motion at a lower temperature which was more prone to the occurrence of deformation twinning, and (b) ultra-high strain rate was easier to activate dislocation motion at a higher temperature, making deformation twinning disappear in the plastic deformation layer of CP titanium.

Surface gradient microstructural characteristics and evolution mechanism of 2195 aluminum lithium alloy induced by laser shock peening

The peak-aged 2195 aluminum lithium alloy was treated by laser shock peening (LSP). The surface gradient microstructural characteristics of this alloy induced by ultrahigh strain rate deformation during LSP were systemically examined with transmission electron microscope (TEM), the observed results suggested that the grains refined and precipitates partially dissolved in the surface after LSP. The original coarse grains with average size of about 16 μm in length and 5 μm in width were refined instantly to equiaxed grains with size of about 91 nm at the top surface after LSP. The quantitative calculation of recrystallization kinetics proved that the grain refinement was the result of rotation dynamic recrystallization (RDR). The adiabatic temperature increase, the generation of high-density dislocations around the precipitates, and the increase of grain boundary area caused by grain refinement provided the thermodynamics and kinetics conditions for partial dissolution of precipitates. The microhardness tested results showed gradient distribution characteristics of microhardness values after LSP, and the maximum of microhardness was at the top surface of this alloy. The refined grains and deformed substructures played important roles on the enhancement of surface microhardness.

Micro-structured fiber distributed acoustic sensing system for borehole seismic survey

Distributed fiber optic sensing is increasingly recognized as a viable alternative to geophone arrays for the acquisition of borehole seismic data. The ability to acquire borehole seismic data in a producing well without the need to disrupt production also offers significant benefits to the operator. A novel fiber distributed acoustic sensor (DAS) with ultra-high sensitivity is presented. Through designing and fabricating the distributed micro-structured optical fiber (DMOF) with successive longitudinal microstructures to enhance the signal-to-noise ratio (SNR) of the backscattered light, and employing the coherent optical time domain reflectometer technique (C-OTDR), the sensing performance of acoustic signal can be greatly improved. Wide frequency band from 0.1Hz to 45 kHz along the 500m long sensing fiber with ultra-high strain resolution of 0.16nε is experimentally demonstrated on the ground surface and in a shallow borehole.

Investigation on mechanical properties and microstructural evolution of TC6 titanium alloy subjected to laser peening at cryogenic temperature

The aim of this study was to investigate the influence of the synergistic function of cryogenic temperature and ultrahigh strain rate deformation during the process of Cryogenic Laser Peening (CLP) on the mechanical properties and microstructural evolution of TC6 titanium alloy. The measurements of tensile properties at room and elevated temperatures, as well as micro-hardness on the cross-sectional direction were carried out. Meanwhile, the microstructural evolution was characterizated by Electron Backscattered Diffraction (EBSD) analysis and Transmission Electron Microscopy (TEM) observation. The experimental results demonstrated that cryogenic laser peening could significantly improve the strength and ductility, as well as the stability at elevated temperature condition of TC6 titanium alloy. At the same time, cryogenic laser peening could provide higher surface micro-hardness than room temperature laser peening (RT-LP), the surface micro-hardness of the specimen subjected to cryogenic laser peening increased by 4.86% than that of the specimen treated by room temperature laser peening. Additionally, cryogenic laser peening could generate finer grains and higher-density of dislocation structures, while large numbers of sub-grains and mechanical twins were also observed in the surface layer. Finally, the microscopic strengthening mechanism of cryogenic laser peening for better mechanical properties on TC6 titanium alloy was also analyzed in detail.

(Invited) Battery Safety across Different Use-Cases

Battery Safety has been discussed at length in the literature. Recently, the use of mathematical models to describe failure mechanisms and propagation modes within battery modules and packs has become more prevalent. Detailed models that represent thermal events from ohmic heating [1] to component-wise reaction heats, [2] gradual degradation of cell components, [3] plating of lithium leading to internal short circuits,[4] failure of welded joints,[5] venting of the cell via the crimp or the can walls,[6] mechanical deformation have been developed.[7] This presentation will highlight the utility of physics-based models to discuss a few practical questions posed during the design process. We begin by attempting to present an electrochemical definition of a short circuit that is consistent across different failure modes. This section of the presentation will explore in detail the origin of failure within a cell. With our mathematical derivation, we identify parameters that govern the evolution of failure under a few key scenario, including an internal-short and mechanical crush. Next, we discuss different experimental approaches to measure these parameters and issues associated with the different measurement techniques. The second part of the presentation will cover modeling tools for propagation of failure across a module. We will discuss the influence of different trigger mechanisms and compare the amounts of heat released across the different modes. The set of case-studies presented include gradual degradation of the interface, to ultra-high strain rate deformation scenario. We will present a methodology to distinguish between gradual deformation across prolonged periods of time and severe degradation across fewer use-cycles. These results are particularly relevant in designing duty cycles for different applications and to monitor how safety evolves as a function of the aging profile of the battery. Finally we conclude with a generic map (Fig. 1) of the heat evolution versus dissipation rates that summarizes the various case-studies discussed in the presentation. This approach enables us to compare different cell designs for a given module requirement, determine packaging and/or spacing requirements as well as design of cooling loads that help mitigate the risk of failure propagation for a given design.

Nanoclay Reinforced Self‐Cross‐Linking Poly(N‐Hydroxyethyl Acrylamide) Hydrogels with Integrated High Performances

AbstractDespite recent significant progress in fabricating tough hydrogels, it is still a challenge to realize high strength, large stretchability, high toughness, rapid recoverability, and good self‐healing simultaneously in a single hydrogel. Herein, Laponite reinforced self‐cross‐linking poly(N‐hydroxyethyl acrylamide) (PHEAA) hydrogels (i.e., PHEAA/Laponite nanocomposite [NC] gels) with dual physically cross‐linked network structures, where PHEAA chains can be self‐cross‐linked by themselves and also cross‐linked by Laponite nanoplatelets, demonstrate integrated high performances. At optimal conditions, PHEAA/Laponite NC gels exhibit high tensile strength of 1.31 MPa, ultrahigh tensile strain of 52.23 mm mm−1, high toughness of 2238 J m−2, rapid self‐recoverability (toughness recovery of 79% and stiffness recovery of 74% at room temperature for 2 min recovery without any external stimuli), and good self‐healing properties (strain healing efficiency of 42%). The work provides a promising and simple strategy for the fabrication of dual physically cross‐linked NC gels with integrated high performances, and helps to expand the fundamentals and applications of NC gels.

Ultra-high sensitivity strain sensor based on piezotronic bipolar transistor

Due to the coupling of piezoelectric and semiconductor properties, the wurtzite structure semiconductors have been used for fabricating high performance piezotronic devices. The carrier transport behavior can be effectively controlled by the polarized charges induced by applied strain. High-sensitive piezotronic strain sensors have potential application in next generation self-powered, flexible electronics and wearable systems. In this study, a piezotronic bipolar transistor has been studied through theoretical calculation and numerical simulation. The output current, gauge factor and carrier concentration have been simulated under the influence of different strains. The piezotronic bipolar transistor based strain sensor has ultrahigh sensitivity and the gauge factor can reach over 104. This investigation not only provides a theoretical insight into the piezotronic effect on bipolar transistor, but also presents a new approach to design ultra-high sensitivity strain sensor.

The research of micro pattern transferring on metallic foil via micro-energy ultraviolet pulse laser shock

A micro-energy high frequency ultraviolet pulse laser was introduced for fabricating the micro pattern on pure aluminum foil by laser shock transferring. The copper mesh mold (mesh size: 400# and 1000#) and pure aluminum foil were used to investigate the effect of laser pulse energy and overlap ratio on micro pattern transferring. A FEM model was adopted to simulate the aluminum foil deformation and plastic strain in laser shock process. To investigate the micro forming mechanism of laser shock transferring, the micro morphology of significant area on processed micro pattern was observed by atomic force microscope (AFM). The experimental results revealed that the depth of transferred micro pattern increased with the increasing of single pulse energy and overlap ratio within certain range. The forming depth of aluminum foil imprinted from 400# mold was larger than that of 1000#, and more sensitive to pulse energy and overlap ratio. The aluminum foil on mold bars was smoother than that of on mold holes. The study demonstrated that the micro-energy ultraviolet pulse laser shock can realize the precise, controllable, fast and ultrahigh strain rate fabrication of surface microstructure.