Study on Mechanical Properties of Nanocrystal Surface Layer of an Aluminum Alloy

The nanocrystal surface layer of an aluminum alloy induced by High Speed Shot Peening (HSSP) was investigated in this paper. The results of nanoindentation experiment show that the elastic modulus and the hardness of nanocrystal surface layer increased,by 8% and 20%, respectively. The elastic modulus and the hardness appear to be independent of the distance from nanocrystalized surface and the process time.

Experimental investigation of the shear strength of a unidirectional carbon/aluminum composite under dynamic torsional loading

In this paper, the dynamic shear strength of a unidirectional C/A356.0 composite and A356.0 alloy, respectively, are measured with a split Hopkinson torsional bar (SHTB) technique. The results indicate that the carbon fibers make very little contribution to the enhancement of the shear strength of the matrix material. The microscopic inspections on the fracture surface of the composite show a multi-scale zigzag feature. This implies that there is a complicated shear failure mechanism in the unidirectional carbon/aluminum composite.

Nano-Tribological Study on a Super-Hydrophobic Film Formed on Rough Aluminum

A novel super-hydrophobic stearic acid (STA) film with a water contact angle of 166° was prepared by chemical adsorption on aluminum wafer coated with polyethyleneimine (PEI) film. The micro-tribological behavior of the super-hydrophobic STA monolayer was compared with that of the polished and PEI-coated Al surfaces. The effect of relative humidity on the adhesion and friction was investigated as well. It was found that the STA monolayer showed decreased friction, while the adhesive force was greatly decreased by increasing the surface roughness of the Al wafer to reduce the contact area between the atomic force microscope (AFM) tip and the sample surface to be tested. Thus the friction and adhesion of the Al wafer was effectively decreased by generating the STA monolayer, which indicated that it could be feasible and rational to prepare a surface with good adhesion resistance and lubricity by properly controlling the surface morphology and the chemical composition. Both the adhesion and friction decreased as the relative humidity was lowered from 65% to 10%, though the decrease extent became insignificant for the STA monolayer.

Theermal Stress and Fracture in Transparent Optical Materials due to Laser Energy-Absorption by a Defect

利用热弹性理论分析了在光学材料中由于缺陷吸收激光能量引起的温度和热应力分布,并且针对一个简单的裂纹模型分析了热应力产生的应力强度因子,给出了一些主要参数对于应力强度因子的影响的规律。

Amorphous Coatings Deposited on Aluminum Alloy by Plasma Electrolytic Oxidation

Amorphous [Al-Si-O] coatings were deposited on aluminum alloy by plasma electrolytic oxidation (PEO). The process parameters, composition, micrograph, and mechanical property of PEO amorphous coatings were investigated. It is found that the growth rate of PEO coatings reaches 4.44 mu m/min if the current density is 0.9 mA/mm(2). XRD results show that the PEO coatings are amorphous in the current density range of 0.3-0.9 mA/mm(2). EDS results show that the coatings are composed of O, Si and At elements. SEM results show that the coatings are porous. Nano indentation results show that the hardness of the coatings is about 3 - 4 times of that of the substrate, while the elastic modulus is about the same with the substrate. Furthermore, a formation mechanism of amorphous PEO coatings was proposed.

The Evolution of Fatigue bocks in Aluminum Alloy LY-12 under Shock beading

对LY12铝合金在低周疲劳条件下的裂纹情况和随后进行的动态拉伸条件下裂纹的发展给予了观察和统计分析。发现裂纹的累积数密度分布在损伤演化过程中保持指数形式,用NAG模型对实验结果进行分析,得出该材料裂纹演化发展方程的各种参数。

The plastic collapse and energy absorption capacity of egg-box panels

The plastic collapse response of aluminium egg-box panels subjected to out-of-plane compression has been measured and modelled. It is observed that the collapse strength and energy absorption are sensitive to the level of in-plane constraint, with collapse dictated either by plastic buckling or by a travelling plastic knuckle mechanism. Drop weight tests have been performed at speeds of up to 6 m s-1, and an elevation in strength with impact velocity is noted. A 3D finite element shell model is needed in order to reproduce the observed behaviours. Additional calculations using an axisymmetric finite element model give the correct collapse modes but are less accurate than the more sophisticated 3D model. The finite element simulations suggest that the observed velocity dependence of strength is primarily due to strain-rate sensitivity of the aluminium sheet, with material inertia playing a negligible role. Finally, it is shown that the energy absorption capacity of the egg-box material is comparable to that of metallic foams. © 2003 Elsevier Ltd. All rights reserved.

Constant volume combustion of aluminum and cornstarch dust in microgravity

The subject of the present work is to report an experimental comparative study of the effect of dispersion-induced turbulence on dust combustion in constant volume vessel, carried out both in normal gravity and in microgravity environment. Dispersion system with small scale of turbulence, creating uniform homogeneous mixture, was used in experiments. To improve reproducibility of the explosion data an ignitor of small energy, with local soft ignition was developed. Both factors contributed to acquisition of more reproducible experimental data. In experiments under microgravity conditions a dust suspension during combustion remains constant. This makes possible to study dust explosion under stationary dust suspension without influence of turbulence.

The mechanical properties of an aluminum alloy by plasma-based ion implantation and solution-aging treatment

The age-strengthening 2024 aluminum alloy was modified by a combination of plasma-based ion implantation (PBII) and solution-aging treatments. The depth profiles of the implanted layer were investigated by X-ray photoelectron spectroscopy (XPS). The structure was studied by glancing angle X-ray diffraction (GXRD). The variation of microhardness with the indenting depth was measured by a nanoindenter. The wear test was carried on with a pin-on-disk wear tester. The results revealed that when the aluminum alloys were implanted with nitrogen at the solution temperature, then quenched in the vacuum chamber followed by an artificial aging treatment for an appropriate time, the amount of AIN precipitates by the combined treatment were more than that of the specimen implanted at ambient temperature. Optimum surface mechanical properties were obtained. The surface hardness was increased and the weight loss in a wear test decreased too.

Comparative study of the slurry erosion and free-fall particle erosion of aluminum

A study has been performed of the erosion of aluminium by silica sand particles at a velocity of 4.5 m s-1, both air-borne and in the form of a water-borne slurry. Measurements made under similar experimental conditions show that slurry erosion proceeds at a rate several times that of air-borne erosion, the ratio of the two rates depending strongly on the angle of impact. Sand particles become embedded into the metal surface during air-borne particle erosion, forming a composite layer of metal and silica, and provide the major cause of the difference in wear rate. The embedded particles giving rise to surface hardening and a significant reduction in the erosion rate. Embedment of erodent particles was not observed during slurry erosion. Lubrication of the impacting interfaces by water appears to have minimal effect on the wear of aluminium by slurry erosion.