Response of high performance concrete plates to impact of non-deforming projectiles

The relatively recent technology, which enables the production of high strength concrete (HSC), makes HSC a prospective material for the construction of impact-resisting barriers. However, current penetration formulae are based on test data of normal strength concrete (NSC) and their extrapolation to higher concrete strengths is unsafe. The response of 80×80 cm high performance concrete (HPC) plate specimens to an impact of non-deforming steel projectiles was examined in an experimental study. The tests were planned with an aim to observe the influence of the concrete mix ingredients and amount and type of reinforcement on the performance of HSC under this type of loading. The variants that were examined were the aggregates (different types and maximum size), addition of micro-silica (MS) and steel fibers, and reinforcement details. The main findings show that design of HPC barriers to withstand impact loads involves several aspects. These are aimed at achieving enhanced properties of the structural element, where only one of which is the concrete's compressive strength.     

Book Reviews

The results of astudy of the multi-axial creep rupture of thick-walled tubes at 600°C are presented here as asequel to aprevious report on the characteristic creep behaviour of the same type 316austenitic steel under purely tensile stress conditions.

It is demonstrated that simply devised and inexpensive direct double-shear creep rupture tests can be used to identify the correct creep rupture multi-axial stress criterion appropriate to pure shear-dominated conditions for the steel being studied. It is also shown that the introduction of this criterion into the reference stress method of creep analysis enables acceptable predictions of the creep lifetimes of thick-walled tubes under torsional stress to be made.

In addition, anumber of preliminary supporting test results on thick-walled tubes under internal pressure and under pure bending are briefly reported and the results discussed with respect to the central theme of the study.     

Normal perforation of reinforced concrete target by rigid projectile

An analytical model on the normal perforation of reinforced concrete slabs is constructed in the present paper. The effect of reinforcing bars is further hybridized in a general three-stage model consisting of initial crater, tunnelling and shear plugging. Besides three dimensionless numbers, i.e., the impact function I, the geometry function of projectile N and the dimensionless thickness of concrete target χ, which are employed to predict the ballistic performance of perforation of concrete slabs, the reinforcement ratio ρ_s of concrete (or area density) and the tensile strength f_s of reinforcing bars are considered as the other main factors influencing the perforation process. Simpler solutions of ballistic performances of normal perforation of reinforced concrete slabs are formulated in the present paper. Theoretical predictions agree well with individual published experimental data and have a higher degree of accuracy than the model suggested by Dancygier [Effect of reinforcement ratio on the resistance of reinforced concrete to hard projectile impact. Nucl Eng Des 1997;172:233–45].     

Comparative analysis of perforation models of metallic plates by rigid sharp-nosed projectiles

Based on the mode of ductile hole enlargement, the present paper compares the models of a rigid sharp-nosed projectile perforating the ductile metallic target plate, given by Chen and Li [1] and Forrestal and Warren [2], respectively. It indicates that the formulae of ballistic limit and residual velocity of these two perforation models are consistent in form but with different applicable range, which due to them employing the spherical cavity expansion theory and cylindrical cavity expansion theory, alternately. Further analyses are conducted to discuss the effects of target material and plate thickness on the terminal ballistic performance with referring the experimental results of aluminum alloy and Weldox E steel plates. It is confirmed that the perforation mechanisms may transform with increasing the plate thickness and the strength of target material.     

全铝车身的发展与探索

本文从全铝车身使用材料的强化及性能特点入手,通过与铜构车身的对比,分析了其优缺点,研究了目前消费现状,指出了发展趋势,做出了市场前景分析。     

Perforation of metallic plates struck by a blunt projectile with a soft nose

The present paper constructs a rigid–plastic model to assess the effect of a soft nose on the perforation of metallic plates struck by a stubby projectile. A low-density nose-cabin-column, i.e., an assembly of seeker and guidance/control unit, is installed in the front of a real missile. It usually acts as an energy absorber and buffer in the perforation of metallic plates and notably affects the terminal results of projectile. The problem is equivalent to a blunt rigid projectile with a soft nose perforating a circular metallic plate. Effects of transverse shear, bending and membrane deformations on the perforation process are included in a rigid–plastic analysis. Especially the effect of an ahead structural response, induced by the soft nose impacting the target plate, is considered in the model. Analytical formulae for the ballistic performance are obtained for a range of plate thicknesses, which agree well with available experimental results.     

Perforation equations for conical and ogival nose rigid projectiles into aluminum target plates

We developed closed-form perforation equations for rigid, conical and ogival nose projectiles that perforate aluminum target plates at normal impact. An existing cylindrical, cavity-expansion model that was experimentally verified with perforation data into 5083-H131 aluminum armor plates was used as the starting point for the development of the perforation equations. We identified a small parameter in those perforation equations, performed power-series expansions, and obtained closed-form, accurate perforation equations for the ballistic-limit and residual velocities. The closed-form, perforation equations are shown to be very accurate when compared with existing data for 6061-T651 and 5083-H131 aluminum target plates. Our perforation equations display clearly the dominant problem parameters.     

Dissimilar friction welding of 6061-T6 aluminum and AISI 1018 steel: Properties and microstructural characterization

Joining of dissimilar materials is of increasing interest for a wide range of industrial applications. The automotive industry, in particular, views dissimilar materials joining as a gateway for the implementation of lightweight materials. Specifically, the introduction of aluminum alloy parts into a steel car body requires the development of reliable, efficient and economic joining processes. Since aluminum and steel demonstrate different physical, mechanical and metallurgical properties, identification of proper welding processes and practices can be problematic. In this work, inertia friction welding has been used to create joints between a 6061-T6 aluminum alloy and a AISI 1018 steel using various parameters. The joints were evaluated by mechanical testing and metallurgical analysis. Microstructural analyses were done using metallography, microhardness testing, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray elemental mapping, focused ion beam (FIB) with ultra high resolution SEM and transmission electron microscopy (TEM) in TEM and STEM modes. Results of these analysis first suggested that joint strengths on the order of 250 MPa could be achieved. In addition, failures were seen in the plasticized layer on the aluminum side of the joint. Further, bond lines were characterized by a thin layer of formed Al–Fe intermetallic. This intermetallic layer averaged roughly 250 nm thick and compositionally appears related to the FeAl and Fe₂Al₅ phases.     

A comparative study of energy absorption characteristics of foam-filled and multi-cell square columns

A comparative study of energy absorption characteristics between foam-filled square columns and multi-cell square columns was conducted by using nonlinear finite element codes LS-DYNA. The columns and the foam were made of the same material aluminum and the thickness of all sidewalls of columns was kept 1.5 mm. Numerical results compared well with theoretical predictions and showed that the energy absorption efficiency of multi-cell columns was about 50–100% higher than that of foam-filled columns. It means that multi-cell columns were more attractive than foam-filled columns and the reason for this was analyzed by a comparison of the collapse modes. Furthermore, a type of pre-crushed trigger was introduced and modeled for multi-cell columns. This type of trigger was found to be effective to eliminate the initial peak force and improve the efficiency of a multi-cell column as an energy absorber.     

A numerical study on the quasi-static axial crush characteristics of square aluminum–composite hybrid tubes

In this paper, we describe a numerical investigation on the quasi-static axial crush performance of aluminum–composite hybrid tubes containing a filament-wound E-glass fiber-reinforced epoxy over-wrap around square aluminum tubes. The fiber orientation angle in the overwrap was varied between [±30°] and [90°] with respect to the tube’s axis. The quasi-static axial crush resistance of the hybrid tubes are compared in terms of the maximum load, mean crush load, crush energy and specific energy absorption. The deformation modes of these tubes are also described. An empirical equation is proposed for predicting the mean crush force of hybrid tubes.     

Thermal fatigue behavior of squeeze cast, discontinuous alumina-silicate fiber-reinforced aluminum alloy (A356) composite

Microstructural damage mechanisms owing to thermal cycling and isothermal exposure at elevated temperature are studied for a short alumina-silicate fiber-reinforced aluminum alloy (A356) composite produced by pressure casting. The tensile strength of the metal matrix composite is found to degrade considerably in each case. An X-ray double-crystal diffraction method is employed to study the mechanisms of recovery in the matrix. The fractal dimension of the X-ray “rocking curves” for individual grains in the composite reflects the substructure formation owing to the rearrangement of dislocations into subdomain walls. Recovery by polygonization is more pronounced in the case of thermal cycling than for equivalent isothermal exposure. The residual stresses in the matrix that provide the fiber clamping force undergo more relaxation in the case of isothermal exposure. The two competing damage mechanisms, thermally activated recovery by polygonization and relaxation of clamping stresses in the matrix, result in identical strength degradation (25%) for both thermal cycling and isothermal exposure.     

铝合金功能薄膜与溅射靶材

近年来 ,铝合金广泛用于生产多种功能薄膜。作为制备高性能溅射薄膜用的铝合金靶材也得到了相应的应用。本文重点介绍应用于不同领域的几种铝合金功能薄膜 ,简述了铝合金薄膜与溅射靶材的制备工艺、铝合金靶材的显微结构及其对溅射薄膜性能的影响 ,最后指出了铝合金薄膜及溅射靶材的发展趋势     

铝及铝合金阳极氧化膜的绿色封闭工艺研究进展

本文概述了铝及铝合金阳极氧化膜的新型封闭方法,着重介绍了稀土盐封闭、溶胶封闭和微波水合封闭三种新型绿色封闭的工艺及发展,并对其封闭机理作了简要概述,指出更多绿色、高效且易于工业化生产的铝及其合金阳极氧化膜封闭工艺将被开发.     

铜及铜合金与钢连接技术的研究进展

本文综述了铜及铜合金与钢连接技术的国内外研究发展动态。简述了铜钢固相连接和熔化焊接领域国内外研究者已取得的部分研究成果，指出熔钎焊接工艺的发展推动了铜钢熔化焊接的应用。在工程中，须根据实际铜钢结构型式和使用条件来选择合适的焊接方法。     

3D numerical study on wrinkling characteristics in NC bending of aluminum alloy thin-walled tubes with large diameters under multi-die constraints

With an increase in the diameters of aluminum alloy thin-walled tubes (AATTs) and a decrease in their bending radii, wrinkling characteristics and its prediction under multi-die constraints have become a key problem urgently to be solved for improving the forming quality in numerical control (NC) bending of AATTs with large diameters. Thus in this paper, considering the characteristics of the bending processes, based on the ABAQUS software environment, a 3D elastic–plastic finite element model and a wrinkling energy prediction model under multi-die constraints are established and their reliabilities are validated, respectively, in which, the appropriate choosing of forming parameters is achieved to guarantee no excessive thinning and flattening in the processes even if wrinkling borders on occurring. By combining the two models, variation relationships of the maximum wrinkling factor with different compressed deformation zones and forming ratios, and effects of clearances and friction between different dies and tubes on the maximum wrinkling factor are obtained, and then an investigation into the wrinkling characteristics is carried out for the processes. It is found that the larger the diameters of AATTs, the larger the wrinkling sensitive zones (WSZs), and there is a larger possibility of wrinkling in the bending segments of WSZs than in the straight ones; the larger the effects of clearances and friction between different dies and tubes on wrinkling.