Comparative study of zein- and gluten-based wood adhesives containing cellulose nanofibers and crosslinking agent for improved bond strength

Many of the currently used wood adhesives contain chemicals that are harmful to human health and the environment. Increasing environmental and human health concerns have made the development of safe biobased adhesives a priority. In this study, two plant proteins, i.e., zein and wheat gluten, were used to develop wood adhesives and their performance was compared through simple lap shear tests and plywood flexural/internal bond tests in dry and wet conditions. To increase their bond strength, cellulose nanofibers were added to create nanocomposite adhesives and glutaraldehyde was also used to crosslink the proteins. Single-lap shear test was performed to measure the bond strength of different adhesive formulations and determine the optimal formulations and processing conditions. Fractured bond surfaces were studied using optical observation and scanning electron microscopy to determine bond failure mechanisms. Thermal and chemical properties of the adhesives were evaluated using thermogravimetric analysis and Fourier transform infrared spectroscopy, respectively. The bond strength of both zein and gluten adhesives was significantly increased by the addition of the cellulose nanofibers and/or glutaraldehyde, although the two adhesives responded differently to the two reinforcement materials due to the different solvents used to prepare the adhesives. The bond failure mode changed from cohesive failure of the adhesive to structural failure of the adherent for the gluten adhesive containing CNFs and glutaraldehyde. Potential zein and gluten adhesive formulations were used to produce plywood samples and their performance was assessed under different conditions. The formulations with industrial potential were discovered through this study.     

Non-Hall-Petch hardness dependence in ultrafine fibrous MgAl2O4-MgO eutectic ceramics fabricated by the laser-heated floating zone (LFZ) method

MgAl₂O₄-MgO eutectic ceramics were fabricated by the laser-heated floating zone (LFZ) method with various growth rates to assess its possible beneficial effect on microstructural aspects and mechanical properties. It was determined that the growth rate optimizing the microstructure and mechanical properties is 750 mm/h; below this value, coarsening of the fibrous microstructure takes place with a degradation of these properties. In the extreme case of 50 mm/h growth rate, the presence of undesirable transverse cracks was unavoidable. Thanks to the high growth rate of 750 mm/h, ultra-fine fibrous microstructure MgAl₂O₄-MgO eutectic ceramics can thus be fabricated with greater hardness (15.5 GPa from Vickers indentation and 22 GPa from nanoindentation) and flexural strength (?345 MPa). It is reported that hardness scales with the interfiber spacing λ according to a law of the type lnλ/λ, contrary to the assumed Hall-Petch-like dependence. This proposed law can be explained in terms of dislocation hardening induced by the MgO fibers.     

An investigation of the elastic properties of viscoelastic clusters of particles: A comparison between two methods

Most industrial process lines involve mixing complex dispersions, which can include non-Newtonian liquids and viscoelastic particles. Knowledge of the parameters of these components may provide a key for understanding how dispersions are formed and how equipment should be designed. One parameter is the shear modulus, which describes the ability of particles to resist mechanical stresses. This parameter may play the main role in the mixing process, when a dispersion is formed by the mechanical influence of a rotor (slice or shear in a rotor-stator mixer). In this work, two methods were chosen for measuring the shear modulus: the evaluation method, based on the Warner-Bratzler cut test, and the oscillatory method. Both methods were used for measuring viscoelastic clusters of particles, and the results were adjusted for the purposes of the comparison. The comparison shows that the shear modulus values obtained from Warner-Bratzler are higher than the values obtained from the oscillatory test for the same conditions. This difference can be explained by differences in the mechanical processes during the experiments.     

Hydrogen mixing augmentation mechanism induced by the vortex generator and oblique shock wave in a scramjet engine

The mixing process between the fuel and the incoming air is extremely important for the engineering implementation of the scramjet engine. In the current study, the vortex generator coupled with the oblique shock wave is utilized to promote the hydrogen mixing process in a supersonic crossflow. The configurations of the vortex generator are put into investigation, namely typical ramp, split ramp and ramp vane. Some parameters are provided to evaluate the flow field properties quantitatively. The obtained results predicted by the three-dimensional Reynolds-average Navier-Stokes (RANS) equations show that the method of shock wave/jet shear layer interaction coupled with the vortex generator can effectively improve the mixing efficiency. Different vortex generator structures all have great effect, especially for Case SR (split ramp), with the mixing efficiency raised by 36.27%. The streamwise vorticity plays an important role in the mixing process.     

Predicting shear strength of slender beams without reinforcement using hybrid gradient boosting trees and optimization algorithms

Shear failure of slender reinforced concrete beams without stirrups has surely been a complicated occurrence that has proven challenging to adequately understand. The primary purpose of this work is to develop machine learning models capable of reliably predicting the shear strength of non-shear-reinforced slender beams (SB). A database encompassing 1118 experimental findings from the relevant literature was compiled, containing eight distinct factors. Gradient Boosting (GB) technique was developed and evaluated in combination with three different optimization algorithms, namely Particle Swarm Optimization (PSO), Random Annealing Optimization (RA), and Simulated Annealing Optimization (SA). The findings suggested that GB-SA could deliver strong prediction results and effectively generalizes the connection between the input and output variables. Shap values and two-dimensional PDP analysis were then carried out. Engineers may use the findings in this work to define beam's geometrical components and material used to achieve the desired shear strength of SB without reinforcement.     

基于WEP的横断山垂直带水文过程模拟研究

为了更好模拟横断山在气象、植被、土壤、水分等垂直地带性影响下的水文过程，本文采用分布式流域水文模型 WEP，提出反映空间分异特征的垂直带参数化方案，并选择横断山流域 14 个水文控制断面 1960—2015 年的逐月径流数据进行了模拟验证。结果显示，垂直带参数化方案较好地模拟了横断山区的水循环过程；通过两种对照方案和垂直带参数化方案的对比表明，“垂直带参数化方案”比“普通的参数方案”的 NS 提高 0.03、RE 降低1%，比“均一化参数方案”的 NS 提高 0.3、RE 降低 19.6%。通过考虑参数的垂直变化影响，能够提高模型模拟效果，且可更好地反映气象、植被、土壤、水分等信息的垂直地带性，弥补以往水文模型对参数的垂直变化描述不足的问题。     

Performance Evaluation of Two High‐Shear Impellers in an Unbaffled Stirred Tank

High‐shear impellers (HSIs) are mixers used in industrial stirred tanks to incorporate powders into liquids and break down particle agglomerates. A detailed numerical study of two commercial ring‐style HSIs of laboratory scale was carried out and their performance was compared with the Rushton turbine (RT). It was found that power and pumping numbers or their ratio cannot be simply connected for properly selecting an impeller in applications where highly localized viscous dissipation is desirable. The ratio of the average viscous dissipation in the impeller swept volume to the mean in the entire volume at two constant values of power input turned out to be lower for HSIs compared to that evaluated for RT. However, at higher power input, the dimensionless average viscous dissipation in the blade swept volume was found to be similar for the HSI of two rings and the RT, corroborating the high local viscous dissipation of this HSI when operated at higher speeds.     

Shear Plugging and Frictional Behaviour of Composites and Fabrics Under Quasi‐static Loading

Experimental studies are presented on the shear plugging and frictional behaviour of composites and fabrics under quasi‐static loading. The primary focus is on the effect of specimen thickness on quasi‐static shear plugging behaviour. In the present study, quasi‐static shear plugging and through‐the‐thickness frictional tests are carried out on three types of materials. The materials investigated are 2D plain weave E‐glass/epoxy, 2D plain weave T300 carbon/epoxy and 2D plain weave E‐glass fabric. Typical results on shear plugging strength and frictional behaviour are presented. Effect of specimen thickness on quasi‐static shear plugging behaviour is also investigated.     

T形与L形截面局部设缝短肢剪力墙扭转性能有限元分析

针对T形与L形截面局部设缝短肢剪力墙抗扭性能,分别对墙体底部局部设缝2个T形截面以及2个L形截面短肢剪力墙试件进行扭转性能有限元分析,并与扭转加载试验进行对比,结果表明有限元分析结果与试验基本吻合。     

藏族风情自驾旅游区概念规划——以四川松潘县林坡村为例

四川省甘(孜)—阿(坝)民族地区自然环境优美,民族文化浓郁,旅游资源丰富,近年来吸引了大批自驾游客。甘(孜)—阿(坝)地区松潘县川主寺镇林坡村基于生态和少数民族特色村寨保护的理念,围绕区域"硬资源"(自然景观)和"软资源"(民族特色风情)来构建旅游发展格局,形成了民族特色鲜明、生态可持续发展的体验式自驾旅游区。