Superelastic oxide micropillars enabled by surface tension-modulated 90° domain switching with excellent fatigue resistance.

Superelastic materials capable of recovering large nonlinear strains are ideal for a variety of applications in morphing structures, reconfigurable systems, and robots. However, making oxide materials superelastic has been a long-standing challenge due to their intrinsic brittleness. Here, we fabricate ferroelectric BaTiO3 (BTO) micropillars that not only are superelastic but also possess excellent fatigue resistance, lasting over 1 million cycles without accumulating residual strains or noticeable variation in stress-strain curves. Phase field simulations reveal that the large recoverable strains of BTO micropillars arise from surface tension-modulated 90° domain switching and thus are size dependent, while the small energy barrier and ultralow energy dissipation are responsible for their unprecedented cyclic stability among superelastic materials. This work demonstrates a general strategy to realize superelastic and fatigue-resistant domain switching in ferroelectric oxides for many potential applications.

An Integrated Computational Materials Engineering Framework to Analyze the Failure Behaviors of Carbon Fiber Reinforced Polymer Composites for Lightweight Vehicle Applications.

A bottom-up multi-scale modeling approach is used to develop an Integrated Computational Materials Engineering (ICME) framework for carbon fiber reinforced polymer (CFRP) composites, which has the potential to reduce development to deployment lead time for structural applications in lightweight vehicles. In this work, we develop and integrate computational models comprising of four size scales to fully describe and characterize three types of CFRP composites. In detail, the properties of the interphase region are determined by an analytical gradient model and molecular dynamics analysis at the nano-scale, which is then incorporated into micro-scale unidirectional (UD) representative volume element (RVE) models to characterize the failure strengths and envelopes of UD CFRP composites. Then, the results are leveraged to propose an elasto-plastic-damage constitutive law for UD composites to study the fiber tows of woven composites as well as the chips of sheet molding compound (SMC) composites. Subsequently, the failure mechanisms and failure strengths of woven and SMC composites are predicted by the meso-scale RVE models. Finally, building upon the models and results from lower scales, we show that a homogenized macro-scale model can capture the mechanical performance of a hat-section-shaped part under four-point bending. Along with the model integration, we will also demonstrate that the computational results are in good agreement with experiments conducted at different scales. The present study illustrates the potential and significance of integrated multi-scale computational modeling tools that can virtually evaluate the performance of CFRP composites and provide design guidance for CFRP composites used in structural applications.

A Combined Experimental and Computational Analysis of Failure Mechanisms in Open-Hole Cross-ply Laminates under Flexural Loading.

In this study, integrated experimental tests and computational modeling are proposed to investigate the failure mechanisms of open-hole cross-ply carbon fiber reinforced polymer (CFRP) laminated composites. In particular, we propose two effective methods, which include width-tapered double cantilever beam (WTDCB) and fixed-ratio mixed-mode end load split (FRMMELS) tests, to obtain the experimental data more reliably. We then calibrate the traction-separation laws of cohesive zone model (CZM) used among laminas of the composites by leveraging these two methods. The experimental results of fracture energy, i.e. G Ic and G Tc , obtained from WTDCB and FRMMELS tests are generally insensitive to the crack length thus requiring no effort to accurately measure the crack tip. Moreover, FRMMELS sample contains a fixed mixed-mode ratio of G IIc /G Tc depending on the width taper ratio. Examining comparisons between experimental results of FRMMELS tests and failure surface of B-K failure criterion predicted from a curve fitting, good agreement between the predictions and experimental data has been found, indicating that FRMMELS tests are an effective method to determine mixed-mode fracture criterion. In addition, a coupled experimental-computational modeling of WTDCB, edge notched flexure, and FRMMELS tests are adopted to calibrate and validate the interfacial strengths. Finally, failure mechanisms of open-hole cross-ply CFRP laminates under flexural loading have been studied systematically using experimental and multi-scale computational analyses based on the developed CZM model. The initiation and propagation of delamination, the failure of laminated layers as well as load-displacement curves predicted from computational analyses are in good agreement with what we have observed experimentally.

In-situ Effect in Cross-ply Laminates under Various Loading Conditions Analyzed with Hybrid Macro/Micro-scale Computational Models.

In this work, multi-scale finite element analyses based on three-dimensional (3D) hybrid macro/micro-scale computational models subjected to various loading conditions are carried out to examine the in-situ effect imposed by the neighboring plies on the failure initiation and propagation of cross-ply laminates. A detailed comparative study on crack suppression mechanisms due to the effect of embedded laminar thickness and adjacent ply orientation is presented. Furthermore, we compare the results of in-situ transverse failure strain and strength between the computational models and analytical predictions. Good agreements are generally observed, indicating the constructed computational models are highly accurate to quantify the in-situ effect. Subsequently, empirical formulas for calculating the in-situ strengths as a function of embedded ply thickness and different ply angle between embedded and adjacent plies are developed, during which several material parameters are obtained using a reverse fitting method. Finally, a new set of failure criteria for σ 22-τ 12, σ 22-τ 23, and σ 11-τ 12 accounting for the in-situ strengths are proposed to predict laminated composites failure under multi-axial stress states. This study demonstrates an effective and efficient computational technique towards the accurate prediction of the failure behaviors and strengths of cross-ply laminates by including the in-situ effects.

Experimental and Computational Analysis of Bending Fatigue Failure in Chopped Carbon Fiber Chip Reinforced Composites.

With a better balance among good mechanical performance, high freedom of design, and low material and manufacturing cost, chopped carbon fiber chip reinforced sheet molding compound (SMC) composites show great potential in different engineering applications. In this paper, bending fatigue behaviors of SMC composites considering the heterogeneous fiber orientation distributions have been thoroughly investigated utilizing both experimental and computational methods. First, four-point bending fatigue tests are performed with designed SMC composites, and the local modulus is adopted as a metric to represent the local fiber orientation of two opposing sides. Interestingly, SMC composites with and without large discrepancy in local modulus of opposing sides show different fatigue behaviors. Interrupted tests are conducted to explore the bending fatigue failure mechanism, and the damage processes of valid specimens are also closely examined. We find that the fatigue failure of SMC composites under four-point bending is governed by crack propagation instead of crack initiation. Because of this, the heterogeneous local fiber orientations of both sides of the specimen influence fatigue life. The microstructure of the lower side shows a direct influence while that of the upper side also exhibiting influence which becomes more prominent for high cycle fatigue cases. Furthermore, a hybrid micro-macro computational model is proposed to efficiently study the cyclic bending behavior of SMC composites. The region of interest is reconstructed with a modified random sequential absorption algorithm to conserve all the microstructural details including the heterogeneous fiber orientation, while the rest of the regions are modeled as homogenized macro-scale continua. Combined with a framework to capture the progressive fatigue damage under cyclic bending, the bending fatigue behaviors of SMC composites are accurately captured by the hybrid computational model comparing with our experimental analysis.

Experimental Investigation on the Effects of Fabric Architectures on Mechanical and Damage Behaviors of Carbon/Epoxy Woven Composites.

The mechanical behaviors and damage evolutions of carbon/epoxy woven fabric composites with three different geometries, i.e., one plain weave and two twill weave patterns with different areal densities, are studied under tensile loading. The effects of weave patterns on mechanical properties are investigated by monotonic and cyclic tension tests. Remarkable variations in stress-strain curve, Poisson's ratio, residual strain and strain map exist in the three composites. Crimp ratio is found to be a critical factor to govern the mechanical properties. With smaller crimp ratio, a quasi-linear stress-strain curve with higher elastic modulus and strength is observed. The stress-strain curves of composites with higher crimp ratio contain transition stages with significant tangent modulus degradation. Elastic modulus, strength and damage initiation are all correlated with the crimp ratio linearly regardless of the fabric pattern. Dramatic nonlinear evolution in Poisson's ratio occurs in the composite with higher crimp ratio. Cyclic tension results indicate that the residual strain is a more appropriate damage indicator than the unloading elastic modulus. Microstructure examination shows that damage developments are essentially related to the fabric geometry, and result in various mechanical behaviors. This study provides important insights into the geometry-deformation mechanism-mechanical property relationship of the woven composites.

Contactless treatment for scoliosis by electromagnetically controlled shape-memory alloy rods: a preliminary study in rabbits.

PURPOSE: To evaluate the safety and efficacy of a system aiming to correct scoliosis called "electromagnetically controlled shape-memory alloy rods" (EC-SMAR) used in a rabbit model. METHODS: We heat-treated shape-memory alloy (SMA) rods to achieve a transition temperature between 34 and 47 °C and a C-shape austenite phase. We then developed a water-cooled generator capable of generating an alternating magnetic field (100 kHz) for induction heating. We next studied the efficacy of this system in vitro and determined some parameters prior to proceeding with animal experiments. We then employed a rabbit model, in which we fixed a straight rod along the spinous processes intraoperatively, and conducted induction heating postoperatively every 4 days for 1 month, while performing periodic X-ray assessments. RESULTS: Significant kyphotic deformations with Cobb angles of about 45° (p < 0.01) were created in five rabbits, and no complications occurred throughout the experiment. The rabbits are still very much alive and do not show any signs of discomfort. CONCLUSIONS: This is the first system that can modulate spinal deformation in a gradual, contactless, noninvasive manner through electromagnetic induction heating applied to SMA alloy rods. Although this study dealt with healthy spines, it provides promising evidence that this device also has the capacity to correct human kyphosis and even scoliosis in the future. These slides can be retrieved under Electronic Supplementary Material.

Simulation of Bacillus subtilis biofilm growth on agar plate by diffusion-reaction based continuum model.

Various species of bacteria form highly organized spatially-structured aggregates known as biofilms. To understand how microenvironments impact biofilm growth dynamics, we propose a diffusion-reaction continuum model to simulate the formation of Bacillus subtilis biofilm on an agar plate. The extended finite element method combined with level set method are employed to perform the simulation, numerical results show the quantitative relationship between colony morphologies and nutrient depletion over time. Considering that the production of polysaccharide in wild-type cells may enhance biofilm spreading on the agar plate, we inoculate mutant colony incapable of producing polysaccharide to verify our results. Predictions of the glutamate source biofilm's shape parameters agree with the experimental mutant colony better than that of glycerol source biofilm, suggesting that glutamate is rate limiting nutrient for Bacillus subtilis biofilm growth on agar plate, and the diffusion-limited is a better description to the experiment. In addition, we find that the diffusion time scale is of the same magnitude as growth process, and the common-employed quasi-steady approximation is not applicable here.

Probing phenotypic growth in expanding Bacillus subtilis biofilms.

We develop an optical imaging technique for spatially and temporally tracking biofilm growth and the distribution of the main phenotypes of a Bacillus subtilis strain with a triple-fluorescent reporter for motility, matrix production, and sporulation. We develop a calibration procedure for determining the biofilm thickness from the transmission images, which is based on Beer-Lambert's law and involves cross-sectioning of biofilms. To obtain the phenotype distribution, we assume a linear relationship between the number of cells and their fluorescence and determine the best combination of calibration coefficients that matches the total number of cells for all three phenotypes and with the total number of cells from the transmission images. Based on this analysis, we resolve the composition of the biofilm in terms of motile, matrix-producing, sporulating cells and low-fluorescent materials which includes matrix and cells that are dead or have low fluorescent gene expression. We take advantage of the circular growth to make kymograph plots of all three phenotypes and the dominant phenotype in terms of radial distance and time. To visualize the nonlocal character of biofilm growth, we also make kymographs using the local colonization time. Our technique is suitable for real-time, noninvasive, quantitative studies of the growth and phenotype distribution of biofilms which are either exposed to different conditions such as biocides, nutrient depletion, dehydration, or waste accumulation.

Continuous and efficient elastocaloric air cooling by coil-bending.

Elastocaloric cooling has emerged as an eco-friendly technology capable of eliminating greenhouse-gas refrigerants. However, its development is limited by the large driving force and low efficiency in uniaxial loading modes. Here, we present a low-force and energy-efficient elastocaloric air cooling approach based on coil-bending of NiTi ribbons/wires. Our air cooler achieves continuous cold outlet air with a temperature drop of 10.6 K and a specific cooling power of 2.5 W g-1 at a low specific driving force of 26 N g-1. Notably, the cooler shows a system coefficient of performance of 3.7 (ratio of cooling power to rotational mechanical power). These values are realized by the large specific heat transfer area (12.6 cm2 g-1) and the constant cold zone of NiTi wires. Our coil-bending system exhibits a competitive performance among caloric air coolers.

Phylogenetic genomewide comparisons of the pentatricopeptide repeat gene family in indica and japonica rice.

More than 400 pentatricopeptide repeat (PPR) genes have been found in higher plants, but most of them have not been functionally analyzed and their origins are still obscure. In this study, we performed phylogenetic genomewide comparisons of the PPR gene family in indica and japonica rice to explore the expansion mechanisms of these genes in higher plants. The functions of PPR genes in plant CMS/Rf systems are also discussed. The results indicate that (1) unequal crossing over participated in the expansion of the newly evolved PPR genes in indica and japonica rice genomes, (2) CMS/Rf systems are different in monocots and dicots, (3) the BT-type CMS/Rf system exists in both indica and japonica rice, and (4) both the PPR gene family and the BT-type CMS/Rf system may have existed before the divergence of indica and japonica rice.

Nanocomposite NiTi shape memory alloy with high strength and fatigue resistance.

Many established, but also potential future applications of NiTi-based shape memory alloys (SMA) in biomedical devices and solid-state refrigeration require long fatigue life with 107-109 duty cycles1,2. However, improving the fatigue resistance of NiTi often compromises other mechanical and functional properties3,4. Existing efforts to improve the fatigue resistance of SMA include composition control for coherent phase boundaries5-7 and microstructure control such as precipitation8,9 and grain-size reduction3,4. Here, we extend the strategy to the nanoscale and improve fatigue resistance of NiTi via a hybrid heterogenous nanostructure. We produced a superelastic NiTi nanocomposite with crystalline and amorphous phases via severe plastic deformation and low-temperature annealing. The as-produced nanocomposite possesses a recoverable strain of 4.3% and a yield strength of 2.3 GPa. In cyclic compression experiments, the nanostructured NiTi micropillars endure over 108 reversible-phase-transition cycles under a stress of 1.8 GPa. We attribute the enhanced properties to the mutual strengthening of nanosized amorphous and crystalline phases where the amorphous phase suppresses dislocation slip in the crystalline phase while the crystalline phase hinders shear band propagation in the amorphous phase. The synergy of the properties of crystalline and amorphous phases at the nanoscale could be an effective method to improve fatigue resistance and strength of SMA.

Effects of Zinc Oxide/Zeolite on Intestinal Morphology, Intestinal Microflora, and Diarrhea Rates in Weaned Piglets.

This experiment was conducted to investigate the effects of zinc oxide/zeolite on growth performance, serum biochemistry, intestinal morphology, and microflora of weaned piglets. Two hundred and fifty-six weaned piglets (Duroc × Landrace × Large) at 21 days of age were randomly assigned to 2 groups with 8 replicates and 16 piglets in each pen. The diets of high dose of zinc oxide group (HD-ZnO) supplemented with 1500 mg/kg zinc as zinc oxide, but the diet of experimental group supplemented with 500 mg/kg zinc as zinc oxide that supported on zeolite (SR-ZnO). The experiment was conducted for 2 weeks after weanling. The results showed replacement of high-dosed zinc oxide by SR-ZnO had no significant effects on growth performance and intestinal morphology. However, the dietary supplementation of SR-ZnO reduced the diarrhea rate (P < 0.05), increased the activity of serum alkaline phosphatase (ALP) (P < 0.01), and tended to reduce zinc release in stomach (P = 0.06) and increase serum total protein (TP) (P = 0.07). Although there were no significant effects in ileal microflora on α diversity, the abundance of Campylobacters was found significantly decreased (P < 0.05), whereas the abundance of Clostridium was increased (P < 0.05) after lower-dosed SR-ZnO replacement. It is revealed that replacement of HD-ZnO (1500 mg/kg) by SR-ZnO (500 mg/kg) in creep feed could improve the zinc bioavailability, regulate the intestinal flora, and alleviate the postweaning diarrhea in weaned piglets. Accordingly, the application of SR-ZnO would reduce the zinc in feed and therefore benefits for the ecological environment.

Meso-scale Modeling and Damage Analysis of Carbon/Epoxy Woven Fabric Composite under In-plane Tension and Compression Loadings.

The mechanical properties and damage behaviors of carbon/epoxy woven fabric composite under in-plane tension and compression are studied at the meso-scale level through experiment and simulation. An efficient representative volume element (RVE) modeling method with consistent mesh, high yarn volume fraction and realistic geometry is proposed. The material constitutive laws with plasticity, tension-compression asymmetry and damage evolution are established for the three components - yarn, matrix and interface, respectively. Significantly different mechanical properties and damage evolutions are observed depending on loading conditions and initial geometry characteristics. It shows a non-linear stress-strain curve with clear transition region and intensive damage in tension, while a quasi-linear behavior up to facture is observed in compression with little damage prior to final fracture. Moreover, compared to the constant Poisson's ratio with straining in compression, a dramatic increase in Poisson's ratio appears in tension. Simulation shows damage mechanisms including transverse damage, matrix damage and delamination, which all play critical roles in the property evolution. In particular, the rapid damage accumulation after elastic deformation destroys the strong bonds and causes the easy deformation of transverse yarns which results in the transition region and large Poisson's ratio in tension. All the mechanical behaviors and damage evolutions are well captured and explained with the current RVE model.

Flow cytometric analysis of mitochondrial populations in HL-CMS systems of rice under H2O2 stress.

Cytoplasmic male sterility (CMS) has often been associated with mitochondrial dysfunction. In this report, the heterogeneity of mitochondria was analyzed in both Honglian (HL) CMS (YtA) rice seedlings and those of its corresponding maintainers (YtB) by flow cytometry and staining with rhodamine-123 (Rh-123). Both lines revealed two distinct fluorescence populations: high fluorescence populations (HFP) and light fluorescence populations (LFP), and a somewhat lower LFP/HFP ratio was detected in conjunction with the higher reactive oxygen species (ROS) content in YtA. In addition, use of the specific effector hydrogen peroxide (H2O2) demonstrated a correlation between the LFP/HFP ratio and ROS levels in both lines. Higher ROS content caused a more swift decrease of F(0)F(1)-ATPase activity and ATP contents in YtA than those in YtB, which accompanied with an obvious decline of the LFP/HFP ratio in YtA. Furthermore, a mitochondrial genomic DNA smear was detected by pulsed field gel electrophoresis. Taken together, these results implied that HL-CMS line rice seedlings and those of its corresponding maintainer have different proportion of Rh-123 staining mitochondria populations, which may be accounted for by ROS contents on the basis of ATPase activity and ATP contents.

Quantitative proteomic analysis of CMS-related changes in Honglian CMS rice anther.

Honglian (HL) cytoplasmic male sterility (CMS) is one of the rice CMS types and has been widely used in hybrid rice production in China. The CMS line (Yuetai A, YTA) has a Yuetai B (maintainer line, YTB) nuclear genome, but has a rearranged mitochondrial (mt) genome consisting of Yuetai B. The fertility of hybrid (HL-6) was restored by restorer gene in nuclear genome of restorer line (9311). We used isotope-code affinity tag (ICAT) technology to perform the protein profiling of uninucleate stage rice anther and identify the CMS-HL related proteins. Two separate ICAT analyses were performed in this study: (1) anthers from YTA versus anthers from YTB, and (2) anthers from YTA versus anthers from HL-6. Based on the two analyses, a total of 97 unique proteins were identified and quantified in uninucleate stage rice anther under the error rate of less than 10%, of which eight proteins showed abundance changes of at least twofold between YTA and YTB. Triosephosphate isomerase, fructokinase II, DNA-binding protein GBP16 and ribosomal protein L3B were over-expressed in YTB, while oligopeptide transporter, floral organ regulator 1, kinase and S-adenosyl-L: -methionine synthetase were over-expressed in YTA. Reduction of the proteins associated with energy production and lesser ATP equivalents detected in CMS anther indicated that the low level of energy production played an important role in inducing CMS-HL.