搅拌摩擦加工制备具有单一和混合表面的Al5083/CeO_2/SiC复合材料的显微组织和磨损行为（英文）

利用搅拌摩擦加工(FSP),将纳米尺寸的氧化铈(CeO_2)和碳化硅(SiC)颗粒以单独和混合形式嵌入Al5083合金基体,制备表面复合材料,并研究这些增强相对合成的表面复合层显微组织和耐磨性能的作用。在室温下用销-盘式磨损试验机检测合成的单独和混合表面复合层的磨损特性。用光学显微镜和扫描电镜观察FSPed区和磨损表面的显微组织。在熔核区可观察到显著的晶粒细化和均匀分布的增强颗粒。与基体金属相比,所有复合材料都具有更高的硬度和更好的耐磨性。其中,混合复合材料Al5083/CeO_2/SiC的耐磨性能最好,摩擦因数最低,而Al5083/SiC的硬度最高,是Al5083基体合金硬度的1.5倍。混合复合材料表面耐磨性能的提高是由于CeO_2颗粒的固体润滑效果。非复合材料中主要的磨损机制是严重的粘着磨损,当存在增强颗粒时转变为磨粒磨损和分层。     

Microstructure and wear performance of Al5083/CeO2/SiC mono and hybrid surface composites fabricated by friction stir processing

Friction stir processing (FSP) was utilized to produce surface composites by incorporating nano-sized cerium oxide (CeO₂) and silicon carbide (SiC) particles individually and in combined form into the Al5083 alloy matrix. The study signified the role of these reinforcements on microstructure and wear behavior of the resultant surface composite layers. The wear characteristics of the resultant mono and hybrid surface composite layers were investigated using a pin-on-disc wear tester at room temperature. The microstructural observations of FSPed regions and the worn out surfaces were performed by optical and scanning electron microscopy. Considerable grain refinement and uniform distribution of reinforcement particles were achieved inside the nugget zone. All the composite samples showed higher hardness and wear resistance compared to the base metal. Among the composite samples, the hybrid composite (Al5083/CeO₂/SiC) revealed the highest wear resistance and the lowest friction coefficient, whereas the Al5083/SiC composite exhibited the highest hardness, i.e., 1.5 times as hard as that of the Al5083 base metal. The enhancement in wear behavior of the hybrid composites was attributed to the solid lubrication effect provided by CeO₂ particles. The predominant wear mechanism was identified as severe adhesive in non-composite samples, which changed to abrasive wear and delamination in the presence of reinforcing particles.     

Consideration of concurrent transverse cracking and induced delamination propagation using a generalized micro‐meso approach and experimental validation

The aim of this study is to investigate the applicability and more verification of recently developed new micro‐meso approach by the authors. Defining the damage evolution law in traditional classic mesomechanics approaches needs multifarious standard and non‐standard lay‐up tests. By combining the micromechanics and mesomechanics approaches, a relatively new micro‐meso model is proposed to overcome the major disadvantage of traditional meso‐scale modelling. In this study, standard tests are firstly performed to obtain the stress‐strain behaviour of various laminates and then the effects of transverse cracking and induced delamination on laminates responses are examined under uniaxial loading. Furthermore, the recently developed new micro‐meso approach is employed to predict the damage growth and stress‐strain response of examined composite specimens in the experimental study. The experimental results are used to verify this micro‐meso approach and discuss the differences. It is shown that the predicted stress‐strain behaviours using the developed method are in good agreement with the experimental results for various laminates with different lay‐up configurations.     

Progressive damage analyses of angle‐ply laminates exhibiting free edge effects using continuum damage mechanics with layer‐wise finite element method

Capability of continuum damage mechanics (CDM) to predict the damage mechanism evolution of composite laminates has rarely been carried out, and most of the previous CDM works mainly focused on the overall response of the laminates. In this paper, progressive damage and overall response of the composite laminates under quasi‐static, monotonic increasing loading are investigated using three‐dimensional (3D) CDM implementation in a finite element method that is based on the layer‐wise laminate plate theory. In the damage formulation, each composite ply is treated as a homogeneous orthotropic material exhibiting orthotropic damage in the form of distributed microscopic cracks that are normal to the three principal material directions. The progressive damage of different angle‐ply composite laminates under quasi‐static loading that exhibit free edge effects is investigated. It is shown that using CDM global behaviour and various damage mechanisms affected by the complex nature of free edges can be qualitatively well predicted.     

A generalized set of correlations for plus fraction characterization

The importance of accurate determination of the critical properties of plus fractions in prediction of phase behaviour of hydrocarbon mixtures by equations of state is well known in the petroleum industry. It has been stated in various papers (Elsharkawy, 2001) that using the plus fraction as a single group in equation of state calculations reduces the accuracy of the results. However in this work it has been shown that using the proper values of critical temperature and pressure for the plus fraction group can estimate the properties of hydrocarbon mixtures, and they are accurate enough to be used in reservoir engineering and enhanced oil recovery calculations. In this paper, a new method is proposed for calculating the critical properties of plus fractions of petroleum fluids. One can use this method either in predicting critical pressure and temperature of single carbon numbers (SCNs) after the splitting process or in predicting critical pressure and temperature of the plus fraction as a single group. A comparison study is performed against Riazi-Daubert correlation (Riazi and Daubert, 1987) and Sancet correlations (Sancet, 2007) for 25 oil samples taken from 14 fields from southwest Iran. The results indicate the superiority of the proposed method to the Riazi-Daubert and Sancet correlations.     

GENERATION OF BIOLUMINESCENT MORGANELLA MORGANII AND ITS POTENTIAL USAGE IN DETERMINATION OF GROWTH LIMITS AND HISTAMINE PRODUCTION

A mini-Tn5 promoter probe carrying the intact lux operon of Photorhabdus luminescens (pUT mini-Tn5 luxCDABE ) which allowed measurement of light output without the addition of exogenous substrate was constructed. It was used to create a pool of chromosomally lux -marked strains of Morganella morganii. Also plasmid-mediated expression of bioluminescence in M. morganii was assessed using plasmid pT7-3 luxCDABE. No significant differences in growth and histamine formation characteristics of the lux -marked strains and wild type M. morganii strain were observed. Luminescent strain of M. morganii was used in experiments in which the correlation between light output, viable cell count and histamine formation was assessed. During the exponential growth phase, a positive linear correlation was observed between these three parameters in trypticase soy broth-histidine medium at 37C. It was demonstrated that expression of bioluminescence had not had a significant effect upon both growth rate and histamine production. Thus, the measurement of bioluminescence was found to be a simple, fast and reliable method for determination of viable cell count and histamine content.

PRACTICAL APPLICATIONS

Constructing predictive models in microbiology requires a large number of data on desired factors. Commonly used traditional methods of counting viable cells and measuring histamine, e.g., to model the growth limits of M. morganii as a function of different intrinsic and extrinsic factors, are time consuming and laborious, and require a lot of laboratory space and materials. According to the results of this research, measurement of bioluminescence is a simple, fast and reliable method for the determination of viable cell count and histamine content during the exponential growth phase. Thus, it can be used as a labor- and material-saving selective data capture method for constructing predictive models in many different areas.