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.     

Static crushing of square aluminium extrusions with aluminium foam filler

An experimental investigation was carried out to study the behaviour of square aluminium extrusions filled with aluminium foam under quasi-static loading conditions. Based on the experimental work, simple relations between dimensionless numbers governing the influence of the foam on the characteristics of the crush problem were identified. Furthermore, a simplified set of equations applicable for design of foam-filled components was proposed.     

铝合金型材与其在电子设备上的应用

从工业用铝合金型材的材料性能、应用特点出发，通过与普通钢件的机械性能、加工工艺进行比较，显示出铝合金型材自身的优越性，并举例说明了其在电子设备上的应用。     

The plastic collapse of sandwich beams with a metallic foam core

Plastic collapse modes of sandwich beams have been investigated experimentally and theoretically for the case of an aluminium alloy foam with cold-worked aluminium face sheets. Plastic collapse is by three competing mechanisms: face yield, indentation and core shear, with the active mechanism depending upon the choice of geometry and material properties. The collapse loads, as predicted by simple upper bound solutions for a rigid, ideally plastic beam, and by more refined finite element calculations are generally in good agreement with the measured strengths. However, a thickness effect of the foam core on the collapse strength is observed for collapse by core shear: the shear strength of the core increases with diminishing core thickness in relation to the cell size. Limit load solutions are used to construct collapse maps, with the beam geometrical parameters as axes. Upon displaying the collapse load for each collapse mechanism, the regimes of dominance of each mechanism and the associate mass of the beam are determined. The map is then used in optimal design by minimising the beam weight for a given structural load index.     

泡沫铝填充帽型结构轴向冲击吸能特性的试验研究

利用冲击试验系统,通过试验方法研究了泡沫铝填充帽型结构在轴向冲击工况下的吸能特性。首先进行了泡沫铝、空心帽型结构以及泡沫铝填充帽型结构的轴向冲击试验;然后根据试验结果,对泡沫铝填充帽型结构轴向冲击工况下的吸能特性进行了分析,评估了填充泡沫铝以及应变率对帽型结构吸能特性的影响。试验结果表明, 与空心结构相比,填充泡沫铝之后帽型结构的轴向压缩稳定性和吸能特性有明显的改善;由于材料对应变率敏感, 与准静态压缩相比,结构的吸能特性有一定的提高。     

铝合金AA6082(T5)挤压型材基本力学性能试验和成形极限图的建立

对铝合金6082(T5)矩形中空截面挤压型材的基本力学性能进行了实验研究，获得了真实应力应变关系曲线和厚向异性指数rc、r45和r90。采用带缺口的单拉试样，建立了铝合金挤压型材拉弯成形极限图，为拉弯成形破裂现象的研究提供了有效判据。     

Cross-sectional deformations of rectangular hollow sections in bending: Part I — experiments

This investigation deals with deformations of individual cross-sectional members as flanges and webs in bending of rectangular hollow sections. Part I describes the experimental work, while analytical models developed to predict pre- and post-buckling deformations are presented in a paper to follow (Part II). The experimental program involved rectangular single- and double-chamber aluminium alloy AA6060 extrusions with three different wall thicknesses. The profiles were given two distinct heat treatments to obtain different hardening characteristics. Multiaxial tests were performed to determine the mechanical properties of the materials. The profiles were then bent into a number of different bend radii. Measurements of strains, curvatures, deflections and bending forces were taken. The results show that cross-sectional distortions take place from the very beginning of bending; at first in the form of a uniform sagging-like deformation along the entire length of both sides of the bend until the inner (compressive) flange buckles into several half-waves, superimposing the pre-deformation modes. The instant at which buckling occurs is found to be mainly associated with the width-to-thickness ratio of the flange and the strain hardening characteristic of the material. The magnitude of pre- and post-deformations, however, appears to be more directly related to the actual width of the flange than to its slenderness. The material stress–strain curve is shown to have an increasingly effect on the distortions of members directly sustained to buckling as bending proceeds beyond the onset of buckling, leading to severely concentrated deformations for sections made of low hardening materials. The material has less impact on sagging of the outer (tensile) flange.     

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.     

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.     

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.     

High temperature tribological behaviour of tool steels during sliding against aluminium

Soldering and abrasive wear of die-casting tools are some of the biggest problems facing the aluminium die-casting industry. The understanding of the tribological behaviour is crucial to design new tool steels and tool steel-coating systems. The present study aims at investigating aluminium adhesion of aluminium/tool steel pair, performing sliding tests at high temperature with ball-on-disc configuration to reproduce solid/solid interaction. Different test conditions have been conducted in order to select the optimal test parameters to obtain aluminium adhesion on disc surface. Once the lab test has been designed, the high temperature tribological performance of different hot work tool steels (uncoated and coated by PVD) sliding against aluminium has been studied to allow proper die material design and selection.     

MODELLING THE BASIC CUTTING ACTION AND MACHINING PERFORMANCE OF SINTERED METALLIC MATERIALS

Extensive ‘classical’ orthogonal cutting tests have been run to study and model the basic cutting action and machining performance of a popular sintered metallic material widely used in structural automotive components. These tests were also run to assess whether the ‘Unified-Generalised Mechanics of Cutting Approach’ to force and power prediction in practical machining operations such as turning and drilling is likely to be applicable to sintered materials. The orthogonal cutting tests have shown that the modified mechanics of cutting analysis, incorporating the edge force, was equally applicable to sintered metallic materials while comprehensive drilling and turning tests over a wide range of operation variables have shown good qualitative and quantitative correlation between predicted and measured forces and torques thus confirming the validity of the predictive force models for machining sintered materials. This investigation has provided further evidence of the generic nature of the predictive machining performance modelling approach developed at the University of Melbourne and its applicability to both conventionally produced and sintered metallic materials for structural components.

It has also been shown that the chip formation, cutting characteristics and mechanics of cutting analyses for the sintered metallic material for structural components, with its relatively high density and low porosity, are qualitatively similar to those for conventionally produced metallic materials. Quantitatively, however, the basic cutting quantities for use in the predictive force models are different and have to be established for each tool-workpiece material combination irrespective of whether the metallic material is a conventionally produced material or a sintered P/M material.     

On the tearing energy of a ductile thin plate

The tearing energy of a ductile thin plate has long been considered as a material constant. This concept of energy is regarded useful for design of energy absorption components. However, it has been noticed that various existing test data for the tearing energy are not consistent. This indicates that the tearing energy may not be a constant determined by material only. Other factors, such as loading mechanisms and geometry may be influential. In the present study, we propose a “mode” concept for in-plane tearing tests by introducing a mixity parameter γ, for in-plane tearing. Through the finite element modelling, the mixity parameter is calculated from the principal stresses in front of tear tips. Laboratory tests were also conducted on samples with two different geometric configurations. The first set of the tests, conducted on the double-notch-tensile specimen, provided the tearing energy, while the second set of tests on the unnotched uni-axial tensile specimen served the purpose of verification.     

聚氨酯泡沫填充的碳纤维增强复合材料锥管吸能性能数值模拟及试验验证

提出了一种新型的碳纤维增强复合材料（CFRP）填充聚氨酯（PU）泡沫的汽车前部吸能结构，通过材料性能试验获得了PU泡沫、CFRP复合材料的力学性能参数及PU泡沫填充的CFRP锥管的准静态压缩吸能结果。应用LS-DYNA进行复合材料准静态压溃仿真分析，仿真结果与试验结果吻合较好，验证了复合材料填充结构有限元模型和材料模型的正确性，并且发现泡沫填充的CFRP锥管具有良好的吸能性能，填充结构比吸能高于两种材料单独使用时的比吸能之和。     

Friction in aluminium extrusion—Part 1: A review of friction testing techniques for aluminium extrusion

In the aluminium extrusion process, the friction at the workpiece/tooling interface is a highly complex phenomenon, affected by local temperature, relative velocity, contact pressure, geometry and tooling surface roughness, etc. Despite of this understanding, general rules for the selection of friction testing techniques have not been established yet. This paper summarises the recent development of the friction testing techniques for aluminium extrusion processes and detailed comparisons of these techniques are presented. Of the existing friction testing techniques, the combination of extrusion friction tests and short sliding distance ball-on-disc tests is recommended.     

激光辐照对 LY12CZ 铝合金试样及构件疲劳寿命的影响

介绍了激光辐照强化处理ＬＹ１２ＣＺ铝合金及其构件的研究概况，在材料性能研究的基础上进行了模拟件试验，研究了辐照处理对疲劳寿命的影响。试验结果表明，激光辐照强化处理能显著提高飞机构件的疲劳寿命     

镁合金在现代铁道车辆上的应用

与铝合金材料相比,镁合金材料具有质量轻、环保性能好和电磁屏蔽性能好等多方面的优点;因此,逐步被定位成新型的铁道车辆应用材料,其在铁道车辆上的应用已得到有关部门的重视。本文在结合镁合金特点的基础上,分析了其在铁路车辆上的适用情况与当前主要存在的问题,并对镁合金材料在现代铁道车辆上的应用前景进行了展望,提出了具有建设性意义的建议。     

Characteristics of the Friction Between Aluminium and Steel at Elevated Temperatures During Ball-on-Disc Tests

Appropriate specification of the frictional boundary condition for the finite-element (FE) simulation of metal-forming processes is of great importance to the trustworthiness of the results. The research reported in this communication aimed at understanding the interfacial contact between aluminium and steel at elevated temperatures and determining friction coefficients at this material mating. A series of high-temperature ball-on-disc tests were carried out with the AA7475 aluminium alloy as the material of disc and the hardened H11 steel as the material of ball. A mathematical model developed in the preceding research was employed to account for the evolution of the contact interface during ball-on-disc tests. Friction coefficients at different temperatures and over a number of laps were determined. The shear friction stresses and mean contact pressures along with the progress of the tests at 350–500 °C were calculated. It was found that the friction coefficients obtained from ball-on-disc tests alone were insufficient to represent the frictional interaction between deforming aluminium and steel at elevated temperatures. The evolution of the contact interface with increasing sliding distance must be taken into consideration and the friction behaviour can be reasonably characterized by using friction stress.     

粉煤灰漂珠/聚氨酯复合泡沫铝材料压缩性能与本构关系研究

采用压力渗透法制备出了铝基复合泡沫材料,填充材料是以粉煤灰漂珠为主要组分、硬质聚氨酯泡沫为粘结剂的复合泡沫材料.通过准静态实验和分离式霍普金森压杆(Split Hopkinson pressure bar,SHPB)动态压缩的方法研究了复合泡沫铝的压缩力学响应,然后建立了动态本构关系.研究表明,复合泡沫铝的压缩应力-应变曲线与其它泡沫材料的应力-应变曲线类似,文中的两种铝基复合泡沫具有应变率效应,复合泡沫铝较密度相近未填充前的泡沫铝基具有更高的压缩强度与能量吸收能力.但由于漂珠尺寸的不同,导致两种复合泡沫铝的动态压缩结果不尽相同,且小颗粒复合泡沫铝在动态冲击下吸能效果最好.在本研究实验的应变率和密度范围内,本文建立的本构模型曲线与实验曲线吻合较好.     

粉煤灰漂珠/聚氨酯复合泡沫铝材料压缩性能与本构关系研究

采用压力渗透法制备出了铝基复合泡沫材料,填充材料是以粉煤灰漂珠为主要组分、硬质聚氨酯泡沫为粘结剂的复合泡沫材料.通过准静态实验和分离式霍普金森压杆(Split Hopkinson pressure bar,SHPB)动态压缩的方法研究了复合泡沫铝的压缩力学响应,然后建立了动态本构关系.研究表明,复合泡沫铝的压缩应力-应变曲线与其它泡沫材料的应力-应变曲线类似,文中的两种铝基复合泡沫具有应变率效应,复合泡沫铝较密度相近未填充前的泡沫铝基具有更高的压缩强度与能量吸收能力.但由于漂珠尺寸的不同,导致两种复合泡沫铝的动态压缩结果不尽相同,且小颗粒复合泡沫铝在动态冲击下吸能效果最好.在本研究实验的应变率和密度范围内,本文建立的本构模型曲线与实验曲线吻合较好.