Theoretical analysis for axial crushing behaviour of aluminium foam-filled hat sections

A theoretical analysis was performed to predict the crushing behaviour of aluminium foam-filled single hat and double hat sections subjected to axial compression. The experimental results and superfolding element theory were used to create deformation models for the aluminium foam contained in the hat sections, and several assumptions were made for the theoretical analysis. According to the energy method and superfolding elements theory, the mean crushing force and the interactive effect were theoretically predicted for the axial compression of the aluminium foam-filled hat sections. The final formula specified the relationship between the mechanical characteristics of the aluminum foam and the height of the superfolding element. The mean crush forces and the interactive effect predicted by the theoretical analysis were in good agreement with the experimental results. The theoretical prediction results showed that the interactive effect was mainly from the aluminium foam.     

Validation of constitutive models applicable to aluminium foams

An extensive experimental database has been established for the structural behaviour of aluminium foam and aluminium foam-based components (foam-filled extrusions). The database is divided into three levels, these are: (1) foam material calibration tests, (2) foam material validation tests and finally (3) structural interaction tests where the foam interacts with aluminium extrusions. This division makes it possible to validate constitutive models applicable to aluminium foam for a wide spectrum of loading configurations. Several existing material models for aluminium foam from the literature are discussed and compared. To illustrate the use of the database, four existing material models for foams in the explicit, non-linear finite element code LS-DYNA have been calibrated and evaluated against configurations in the database.     

Optimum design for energy absorption of square aluminium columns with aluminium foam filler

The performance in axial compression of square aluminium columns with aluminium foam filler has been assessed based upon existing design formulas for average crush force, maximum force and effective crushing distance. Using an optimisation algorithm, the combination of (1) foam density, (2) column wall thickness, (3) column width, (4) column material strength and (5) total component length giving the component of minimum mass was determined for specific cases. It was found that optimum foam filled columns compared to the traditionally designed non-filled columns showed smaller cross section dimensions in addition to less weight. As a consequence, mass-, length- and volume reductions are possible by utilising foam filler.     

Dynamic indentation and penetration of aluminium foams

Failure of metal foams caused by dynamic indentation and penetration is very common in practice, such as light-weight structural sandwich panels, packing materials and energy absorbing devices. Rational application of these materials requires a sound understanding of deformation and energy absorption mechanisms of the aluminium foams as well as the effect of impact velocity. In this study, following experimental investigations into compression, tension, sharing and indentation of CYMAT aluminium foams of various densities, a finite element (FE) analysis using ABAQUS is conducted for dynamic indentation process of aluminium foams under a rigid, flat-headed indenter. Two methods of applying impact velocities are considered: the indenter is pushed into the foam at a constant velocity through the whole process or with an initial velocity which then decreases with indentation. Two energy dissipation mechanisms are considered: compression of the foam ahead of the indenter and fracture along the indenter edge. Effect of impact velocity is noted on the size of a localized deformation and the total energy absorbed. A plastic structural shock theory developed by previous researchers is applied to calculate the resistance force with indentation depth during indentation process and fair agreement is obtained between the analytical and numerical results.     

Measurement of strain rate sensitivity of aluminium foams for energy dissipation

In this paper the structural performance of aluminium alloy foams have been investigated under both static and dynamic compression loads. Three foam typologies (M-PORE, CYMAT, SCHUNK) in a wide range of density (from 0.14 to 0.75 g/cm³), made by means of different process-routes (melt gas injection, powder metallurgy, investment casting) have been analysed. Foams microstructural characterization has been carried out through morphometric measurements by means of Scanning Electron Microscopy (SEM) and Computed Tomography (CT) and subsequent digital image processing in order to determine average cells size and cell distributions on different section planes. The experimental study aims to assess the strain rate sensitivity and energy absorption capability of commercially available metal foams and to point out the correlation between the mechanical behaviour and the physical and geometrical properties of the foam. It has been found that the specific energy dissipation of foams with similar density can be quite different: for the same volume of foam, average values of 1770, 1780 and 5590 J/kg at 50% nominal compression have been measured on M-PORE (0.19 g/cm³), CYMAT (0.28 g/cm³) and SCHUNK (0.28 g/cm³) foams, respectively. Impact tests showed that the dependence of the plateau stress on strain rate could be considered negligible for M-PORE and CYMAT foams while it is quite remarkable for SCHUNK foams. Moreover, it was found that the peak stress of CYMAT foams has a quite large sensitivity on the loading rate.     

Quasi-static axial compression of thin-walled circular aluminium tubes

This paper presents further experimental investigations into axial compression of thin-walled circular tubes, a classical problem studied for several decades. A total of 70 quasi-static tests were conducted on circular 6060 aluminium tubes in the T5, as-received condition. The range of D/t considered was expanded over previous studies to D/t=10–450. Collapse modes were observed for L/D10 and a mode classification chart developed. The average crush force, F_AV, was non-dimensionalised and an empirical formula established as F_AV/M_P=72.3(D/t)^0.32. It was found that test results for both axi-symmetric and non-symmetric modes lie on a single curve. Comprehensive comparisons have been made between existing theories and our test results for F_AV. This has revealed some shortcomings, suggesting that further theoretical work may be required. It was found that the ratio of F_MAX/F_AV increased substantially with an increase in the D/t ratio. The effect of filling aluminium tubes with different density polyurethane foam was also briefly examined.     

Frictional seizure of aluminium observed by X-ray imaging

Friction and wear of non-ferrous metals and coatings are of considerable interest in the light of use of the above in tribo-contacts. As most of the mechanisms governing the seizure of materials are concentrated at the center of the contact and are hidden, it is difficult to observe any precipitate changes in the behavior of such materials using conventional tools. In this work, we have used an X-ray microscope for in-situ observation of frictional seizure, wear and interfacial features during the testing of aluminium (AA1100) specimens sliding against Al 6061 disk. This technique enables the observation of interfacial features of the hidden contact despite the small density differences that exist between the sliding pair of materials. Seizure tests were conducted at different sliding speeds of 2 and 4 m/s. Aluminium was found to undergo incipient melting during sliding at a sliding speed of 2 m/s whereas the specimen tested at 4 m/s was found to undergo a severe plastic distortion thus restricting further testing of the same. Frictional heating of concentrated spots resulted in melting wear and diffusion assisted bonding of surface layers. This was later found to develop into a conformal contact following a lumpy transfer of material. The mechanisms of seizure and wear were affected by the sliding speeds during testing. At lower sliding speed (2 m/s) the transfer and bonding of deposits occurred due to direct contact of nascent sliding surfaces.     

Wear of metal stirring rods in molten aluminium and suspensions of alumina particles in molten aluminium

The wear of stainless steel and titanium stirring rods in molten aluminium and a suspension of alumina particles in molten aluminium was studied. The known characteristic of more rapid wear by stainless steel than titanium was confirmed and the suspension of alumina particles was found to accelerate wear of both metals. Examination of worn specimens revealed that the stainless steel rods were separated from the liquid aluminium by a layer of iron, chromium and aluminium. Wear proceeded by the shedding of projections that formed on the layer into the liquid aluminium. Alumina particles accelerated wear by abrasion of the projections. The titanium was surrounded by a much thinner layer of titanium and aluminium mixture with no projections into the molten aluminium. The distribution of wear around the blades was controlled by the flow of liquid metal and of the alumina particles around each blade.     

Wettability improving of 2024 aluminium alloy by oxygen cold plasma treatment

The need to contrast the severe use conditions developing in the aeronautical field requires surface protection of 2024 aluminium alloy structures by a paint coating. Therefore the aluminium alloy, to be suitable for painting, has to be subjected to complex and critical processes involving a cleaning by acid solvent, a chromate plating, a primer and a protective paint application. Oxygen cold plasma treatment represents an efficient, not-polluting and economic alternative to clean and activate aluminium alloy surfaces. It allows simplification of the anticorrosive protection process of aluminium alloy surfaces and, therefore, reduction of their manufacturing costs. The aim of this work has been to improve the wettability and its ageing time of an aluminium alloy surface treated with oxygen cold plasma. A set of process variables has been identified and used to carry out some experimental tests on the basis of design of experiment techniques.     

The effect of aluminium coating on elemental standards in X-ray microanalysis

The standardisation of frozen hydrated bulk biological specimens using gelatin standards is described. The relationship between corrected elemental X-ray counts and ionic concentration was found to be linear, and minimum detectable limits for each element are stated. Variations in uncorrected standard curves were found to be due to changes in aluminium coating thickness. There was an inverse relationship between coating thickness and elemental X-ray counts. The factors causing this are discussed. To avoid errors arising from inconsistent aluminium thickness, experimental material should only be compared with standards of similar aluminium net counts. This can be achieved most easily by mounting and analysing specimen and standard together.     

The wear properties of an SiC-whisker-reinforced aluminium composite

The wear behaviour of an SiC-whisker-reinforced aluminium (SiC_w-Al) composite is studied by comparative testing. The experimental results show that the SiC_w-Al composite exhibits a fairly good wear resistance, especially for higher sliding velocities and/or higher loads in the test. The results are considered to be due to the high hardness of the SiC whiskers, the rotation of the SiC whiskers and the constraint of the SiC whisker in the aluminium matrix. It is also discovered by experiment that during the wear of oxides the wear volume of both the SiC_w-Al composite and the aluminium is small, but the wear volume of the former is a little larger than that of the latter. The reason may be that the compactness of the oxide on the surface of the specimen is damaged because of the existence of the SiC whiskers.     

铝合金变形抗力的实验研究

采用恒应变速率凸轮式形变压缩试验机试验了4种铝合金材料的变形抗力，分析了应变率和应变速率对变形抗力的影响，结果表明随着应变的增加，变形抗力以近似幂函数关系增加，在此基础上建立了简单、适用的变形抗力计算模型。     

High-velocity impact experiment of aluminum foam sample using powder gun

Porous materials such as aluminum foam have been investigated for possible use as impact shock absorbers in transportation aeronautic applications. However, the response of aluminum foam during impacts at high velocities of more than 100 m/s is not yet fully understood. A high-velocity impact experiment was therefore carried out to clarify impact shock absorption properties of aluminum foam. A one-stage powder gun was used to accelerate an aluminum foam sample to impact a rigid wall. Velocity and deformation of the aluminum foam sample during impact was studied using a digital high-speed video camera, while the pressure wave in the aluminum foam sample was measured using a PVDF gauge. The experimental observations revealed uneven collapse of the aluminum foam sample structure during high speed impact with a general stress plateau effect, typical for cellular material structures when subjected to quasi-static loading.     

Energy absorption of aluminum foam filled braided stainless steel tubes under quasi-static tensile loading conditions

A theoretical model to predict the energy absorption capabilities of aluminum foam filled braided stainless steel tubes under tensile loading conditions has been developed and is presented. Experimental testing was completed on braided tubes, with a nominal diameter of 64.5 mm and woven from 304 stainless steel wires with a diameter of 0.51 mm, filled with rectangular prisms of closed cell aluminum foam with densities ranging from 248 to 373 kg/m³. Based upon observations from experimental testing and applying a unit cell concept to the braided tube, a theoretical model which incorporates two stages of deformation was developed. Within the first stage of deformation, which occurs prior to tow lockup of the braided tube, energy absorption is primarily due to compression of the aluminum foam core. After tow lockup has occurred the energy absorption behavior of the assembly is a sole result of the deformation of the braided tube. Comparisons between the energy absorption predictions of the analytical model and experimental observations were found to be in good agreement for assembly lengths of approximately 400 mm. For the tensile loading conditions and geometry of aluminum foam filled braided tubes considered in this research energy absorption ranged from approximately 5.2 to 7.9 kJ with corresponding tube elongations of 400 mm.     

Role of zirconium diboride particles on microstructure and wear behaviour of AA7075 in situ aluminium matrix composites at elevated temperature

ABSTRACT

The present research work examines the impact of temperature on the dry sliding wear behaviour of AA7075 aluminium strengthened zirconium diboride (ZrB₂) particulate composite (0, 3, 6, 9 and 12?wt.%). The dry sliding wear behaviour of the AMCs was inspected utilizing a pin-on-disc machine at differing temperatures (40, 60, 120, 180 and 240°C). The wear resistance of AMCs improved with the increased substance of ZrB₂ particulates at all test temperatures. The worn surface of the AMC pins was described utilizing FESEM. It was found from the SEM micrographs of worn surface, that at different temperatures, adhesion and metal flow were the prime wear process of the AA7075 composites, while for in situ formed AMCs, metal stream and oxidation were the factors affecting the wear process. The worn surface of the AMCs showed that there was a modification in wear component from abrasive wear to metal flow.     

Yield loci of anisotropic aluminium sheets

AA8014 aluminium sheets were tested in uniaxial, equibiaxial (bulge test) and plane-strain tension at an almost constant strain rate of 2 × 10⁻³s⁻¹. The results were compared with predictions at different levels of strain, based on macroscopic and crystallographic theories of yielding. While most of the previous investigations compare the results at a strain level of 0.10, the present comparison was made in early stages of the deformation, which might be considered as the real yielding strain of the material. It was concluded that, at the high strain levels Hosford's method, which is a modification of Hill's “old” criterion, gives a proper fit to the experimental data. However, at the lower strain levels the experimental results were very close to the crystallographic loci.     

Effect of progressive forming process and processing variables on the formability of aluminium bipolar plate with microchannel

A bipolar plate is one of the crucial components that strongly influence the power density of the proton exchange membrane fuel cell stack. Especially, an aluminium bipolar plate not only has better mechanical properties such as density, electrical resistivity and thermal conductivity but also has more corrosion resistance than bipolar plates made of stainless steel and graphite composites. Furthermore, the use of aluminium reduces the cost and weight of the plates, and the plates are easily machinable. This study presents the results of experiments conducted to investigate the feasibility of developing bipolar plates made of aluminium that consist of microchannels. This paper explains experimental investigations performed to investigate the formability of an aluminium sheet. The effects of forming velocity and die temperature on the microchannels in thin sheets of Al5052 having a thickness of 0.3 mm are investigated. The roundness of the core-die channels ranged from 0.3 to 0.1 mm, and the height is 0.6 mm. Formability tests are conducted for forming velocities of 0.1 and 1.0 mm/s and die temperatures in the range from room temperature to 300°C. The experimental results indicate the feasibility of the proposed technique for manufacturing the bipolar plates of aluminium.     

Overlap conduction laser welding of aluminium to steel

In the present study, a continuous wave fibre laser was used in conduction mode to join aluminium alloys to low carbon steel. Two different sets of experiments were performed: with Zn-coated steel and uncoated steel. Welding was carried out in overlap configuration with steel plate on the top aiming to conduct the heat through the steel and melt the aluminium at the interface, wetting the steel substrate. Metallurgical incompatibilities between these two participating alloys originate the formation of intermetallic phases. Therefore, restricting melting of the aluminium would limit the formation and growth of the intermetallic layer (IML). It was shown that the power density of the laser could be used such that, at the interface, aluminium only melts and the steel remains in solid state. The uncoated steel showed a regular pattern of IML formation, while the Zn-coated steel showed a different pattern of IML.     

锻造铝车轮的生产工艺简介及应用现状

锻造铝车轮有着高密度的金属晶体组织和良好的机械性能,重量轻、强度高、表面质量好,其缺点是需要有较大吨位的热模锻设备,工艺复杂、投资大、制造成本高.简要介绍了锻造铝车轮的生产工艺和目前的应用现状,为我国铝车轮制造企业提供参考.     

Viscous pressure bulging of aluminium alloy sheet at warm temperatures

Improving the formability of aluminium alloy sheet metal by using warm or elevated temperature has become a valid approach. In this paper, viscous pressure bulging (VPB) at warm temperature is proposed. The coupled thermo-mechanical finite element method and experimental method were used to investigate the VPB of aluminium alloy AA3003 at warm temperature. The temperature distributions of sheet metal and viscous medium were analyzed for non-isothermal VPB. The influence of forming temperature on thickness distribution, forming load and failure location of sheet metal were investigated. Research results show the temperature gradient field in sheet metal forms when the initial temperature of viscous medium is lower than that of sheet metal. The formability and failure location of sheet metal changes with initial temperature of viscous medium.