Forest diversity and community dynamics along an altitudinal gradient of Ailaoshan Mountain (Yuanyang, Yunnan Province, China)

In order to evaluate forest community diversity, the quantity of forest community succession along an altitudinal gradient from 1690 to 2016 m above sea level, the understanding of relationships between diversity and community dynamics, and data from sampling plots of forest communities were studied. Forest communities were mid-mountain moist evergreen broad-leaved forests on the southern slope of the Ailaoshan Mountain in Yuanyang County (near the Hani terraces) in Yunnan Province, China. The results showed that (1) the mean species richness, ecological dominance, and evenness (E) were 9.16, 0.31, and 0.27, respectively. The mean Shannon-Wiener Index and Coverage Weighted Foliage-Height Diversity Index were 0.84 and 0.41, respectively. (2) The mean live aboveground biomass (AGS) was 99.23 Mg/ha and the mean Composition Index (CI) was 182.17. Species diversity (including E, richness, and Shannon-Wiener Index), live AGS, and CI could be predicted by the mid-domain effect (MDE), which displayed a unimodal pattern against elevation. (3) Richness, E, Shannon-Wiener Index, and Coverage Weighted Foliage-Height Diversity Index increased with CI. Ecological dominance decreased with increased CI, following a quadratic relationship. Whittaker Index decreased with both increased CI and AGS, with a quadratic relationship. Much forest diversity could be explained by the MDE. However, forest dynamics were seriously disturbed by human activities. More attention should focus on increasing forest diversity in order to prevent the degradation of forest ecological functions thus resulting in threats to the sustainable development of the local ecological systems

Liquid Phase Assisted Superplastic Deformation of TiO2-Doped ZTA Ceramics

In this study, the compressive deformation of zirconia toughened alumina (ZTA) ceramics doped with different amounts of TiO2 dopants were investigated in the temperature range of 1300–1400 °C to evaluate the stress exponent (n value) and apparent deformation activation energy (Q value). With 0–8 wt.% TiO2 dopants, the n values and Q values of the TiO2-doped ZTA ceramics were calculated as 2–3 and 605–749 kJ/mol, respectively. Moreover, three grain boundary features were observed in these deformed materials, named the clean grain boundary, thin liquid phase grain boundary, and thick liquid phase grain boundary. Based on the deformation behavior and microstructure evolution, it was found that the lower apparent activation energy and higher strain rate of TiO2-doped ZTA ceramics are intensively related to the grain boundary feature

Influence of blank holder-die gap on micro-deep drawing of SUS304 cups

Micro-deep drawing (MDD) is a promising micro-manufacturing technology. Size effects complicate and signify the influence of the blank holder-die gap on MDD, which was investigated in this study. Annealing of SUS304 foils of 50 µm thick was conducted to obtain various grain sizes. Micro-tensile testing was carried out to acquire the stress-strain curves of the foils, followed by MDD experiments. Advanced FE models were developed to simulate the MDD process taking into account material inhomogeneity and surface morphology of the foils at micro-scale. Bending dominates the early stage of MDD. A combination of proper gap size and punch/die corner radius may incur in-process springback before the occurrence of the maximum drawing force, benefiting the MDD process. A relatively small gap is favourable to a uniform distribution of wall thickness without obviously increasing the risk of fracture. It also improves the overall shape accuracy of outer surface whilst may result in the inner surface distortion. The complex development of the shape accuracy in three defined areas on the drawn cup can be attributed to the integrated effect of the gap size, material inhomogeneity and surface morphology of the foil. The combined design and multi-object optimisation of the gap size and the corner radii of punch and die should be conducted for improving the MDD process

Effect of Temperature and Strain Rate on the Hot Deformation Behaviour of Ferritic Stainless Steel

The flow behaviour and microstructure characteristics of a ferritic stainless steel were investigated using plain strain compression test on a Gleeble 3500 thermo-mechanical test simulator with a hydrawedge system in the temperature range of 850-1100 °C and strain rate range of 0.1-50 s−1. The phenomenological constitutive model and the relationship between the Zener-Hollomon (Z) parameter and flow stress were established. The results reveal that the flow softening phenomenon occurs at high strain rate, which is caused by the coupling effect of the adiabatic heating and dynamic recrystallisation (DRX). New grains nucleate preferentially at the original grain boundaries by strain-induced grain boundary migration. With an increase of temperature or strain rate, a part of new grains form in the interior of deformed grains. The DRX grain size and fraction increase with the increase of temperature, however, exhibit a non-linear relationship with strain rate

Superflexible Multifunctional Polyvinylpolydimethylsiloxane-Based Aerogels as Efficient Absorbents, Thermal Superinsulators, and Strain Sensors

Aerogels are porous materials but show poor mechanical properties and limited functionality, which significantly restrict their practical applications. Preparation of highly bendable and processable aerogels with multifunctionality remains a challenge. Herein we report unprecedented superflexible aerogels based on polyvinylpolydimethylsiloxane (PVPDMS) networks, PVPDMS/polyvinylpolymethylsiloxane (PVPMS) copolymer networks, and PVPDMS/PVPMS/graphene nanocomposites by a facile radical polymerization/hydrolytic polycondensation strategy and ambient pressure drying or freeze drying. The aerogels have a doubly cross‐linked organic–inorganic network structure consisting of flexible polydimethylsiloxanes and hydrocarbon chains with tunable cross‐linking density, tunable pore size and bulk density. They have a high hydrophobicity and superflexibility and combine selective absorption, efficient separation of oil and water, thermal superinsulation, and strain sensing

Bioinspired gradient stretchable aerogels for ultrabroad-response-range wearable pressure sensors

With the increasing demand for electronic skin, health management, and extreme pressure monitoring, development of broad-response-range flexible pressure sensors is in urgent need. However, the reported flexible pressure sensors usually show a narrow detection range. It’s a great challenge to achieve a broad detection range of 1 Pa-10 MPa for a flexible pressure sensor. Herein, unprecedented bioinspired wearable pressure sensors based on highly stretchable reduced graphene oxide/polyurethane foam composite aerogels with modulus-gradient porous structures have been reported. A hot pressing method is applied to increase the modulus and compressive strength of the high-modulus layer of the aerogel, which ensures their compressibility at high pressures and significantly enhances the upper detection limit. Benefiting from their unique superelastic (90-99% reversible strain) and gradient structures with the gradient modulus spanning from 5.4 kPa to 430 kPa and gradient compressive stress (at 90% strain) spanning from 25 kPa to 37 MPa, the resulting pressure sensors exhibit a record-breaking detection range of 1 Pa-12.6 MPa. In addition, the pressure sensors can withstand 10000 cycles at a high pressure of 1 MPa, which can’t be achieved by traditional flexible pressure sensors. This work provides a versatile and powerful strategy towards next-generation high-performance broad-response-range flexible electronics

Flow behaviour and constitutive modelling of a ferritic stainless steel at elevated temperatures

The flow behaviour of a ferritic stainless steel (FSS) was investigated by a Gleeble 3500 thermal-mechanical test simulator over the temperature range of 900-1100 °C and strain rate range of 1-50 s−1. Empirical and phenomenological constitutive models were established, and a comparative study was made on the predictability of them. The results indicate that the flow stress decreases with increasing the temperature and decreasing the strain rate. High strain rate may cause a drop in flow stress after a peak value due to the adiabatic heating. The Zener-Hollomon parameter depends linearly on the flow stress, and decreases with raising the temperature and reducing the strain rate. Significant deviations occur in the prediction of flow stress by the Johnson-Cook (JC) model, indicating that the JC model cannot accurately track the flow behaviour of the FSS during hot deformation. Both the multiple-linear and the Arrhenius-type models can track the flow behaviour very well under the whole hot working conditions, and have much higher accuracy in predicting the flow behaviour than that of the JC model. The multiple-linear model is recommended in the current work due to its simpler structure and less time needed for solving the equations relative to the Arrhenius-type model

Analysis of the microstructure, texture and magnetic properties of strip casting 4.5wt.% Si non-oriented electrical steel

The microstructure, texture and magnetic properties of 4.5wt.% Si electrical steel fabricated by the processes of twin-roll casting, warm-rolling and final annealing were systematically investigated with the aim of introducing a remarkable and promising electrical steel with extensive potential applications. The results show that unusually sharp {411} texture is obtained in addition to common Cube, rotated Cube, Goss and {111} orientation after final annealing. Excellent magnetic inductions of 1.518T (B8) and 1.703T (B50), and iron losses of 24.92W/kg (W10/400) and 24.47W/kg (W5/1000) have been achieved

Bioinspired Gradient Poly(ionic liquid) Ionogels for Ionic Skins with an Ultrawide Pressure Detection Range

Recently, with the increasing demand for artificial skins and human bodily motion/physical signals monitoring, flexible pressure sensors with a wide detection range are urgently needed. Transparent and stretchable gels with ionic conductivities are considered to be ideal candidates for flexible pressure sensors. However, the gel-based pressure sensors usually show a relatively narrow detection range, which significantly limits their practical applications. Herein, we report an unprecedented bioinspired highly flexible modulus/conductivity-dual-gradient poly(ionic liquid) (PIL) ionogel, which is achieved by constructing three layers of PIL ionogels with different monomer concentrations via a layer-by-layer gelation method. The flexible pressure sensor based on the gradient PIL ionogel exhibits an ultrabroad detection range of 10 Pa-1 MPa. This wearable pressure sensor is highly stable in environments and able to monitor both the tiny pressures as low as 10-100 Pa and the high pressures up to 0.1-1 MPa during human body movements. This work provides a powerful strategy for the preparation of flexible gradient materials that are promising for wearable electronics with a wide pressure detection range