Large inelastic response of unbonded metallic foam and honeycomb core sandwich panels to blast loading

Sandwich panels constructed from metallic face sheets with the core composed of an energy absorbing material, have shown potential as an effective blast resistant structure. In the present study, air-blast tests are conducted on sandwich panels composed steel face sheets with unbonded aluminium foam (Alporas, Cymat) or hexagonal honeycomb cores. Honeycomb cores with small and large aspect ratios are investigated. For all core materials, tests are conducted using two different face sheet thicknesses. The results show that face sheet thickness has a significant effect on the performance of the panels relative to an equivalent monolithic plate. The Alporas and honeycomb cores are found to give higher relative performance with a thicker face sheet. Under the majority of the loading conditions investigated, the thick core honeycomb panels show the greatest increase in blast resistance of the core materials. The Cymat core panels do not show any significant increase in performance over monolithic plates.     

The effect of core thickness on the flexural behaviour of aluminium foam sandwich structures

The effect of core thickness on the deformation mechanism of an aluminium foam core/thermoplastic composite facing sandwich structure under 4-point bending was investigated. Full field strain analysis and visual observations show a number of failure mechanisms between the different core thicknesses. High strain concentrations were observed in each sample thickness corresponding to the particular region of failure. The thinner samples exhibited skin wrinkling and fracture, and some core cracking and crushing while the thicker samples failed due to core indentation. Increasing the skin thickness eliminated the incidence of core indentation. Instead, significant core shear cracking was observed.     

Ballistic impact experiments of metallic sandwich panels with aluminium foam core

Metallic sandwich structures with aluminium foam core are good energy absorbers for impact protection. To study their ballistic performance, quasi-static and impact perforation tests were carried out and the results are reported and analysed in this paper. In the experiments, effects of several key parameters, i.e. impact velocity, skin thickness, thickness and density of foam core and projectile shapes, on the ballistic limit and energy absorption of the panels during perforation are identified and discussed in detail.     

Aluminium foam sandwiches collapse modes under static and dynamic three-point bending

Static and dynamic three-point bending tests were carried out in order to investigate the structural response (collapse modes, energy dissipation, strain rate sensitivity) of two different typologies of aluminium foam sandwich (AFS) panels, consisting of a closed-cell aluminium foam core with either two integral (Schunk) or two glued (Alulight) faces. Impact measurements were performed by a bi-pendulum testing machine designed by the authors. It was found that different collapse modes can be obtained for samples with identical nominal dimensions, depending on the support span distance and on the own AFS properties. Simplified theoretical collapse models were introduced to explain the observed experimental behaviour, showing good agreement between predicted and experimental limit loads. As far as energy dissipation is concerned, no strain rate sensitivity was found for initial impact velocity up to about 1.2 m/s.     

Finite element modelling of core thickness effects in aluminium foam/composite sandwich structures under flexural loading

This paper models the flexural behaviour of a composite sandwich structure with an aluminium foam core using the finite element (FE) code LS-DYNA. Two core thicknesses, 5 and 20 mm, were investigated. The FE results were compared with results from previous experimental work that measured full-field strain directly from the sample during testing. The deformation and failure behaviour predicted by the FE model compared well with the behaviour observed experimentally. The strain predicted by the FE model also agreed reasonably well with the distribution and magnitude of strain obtained experimentally. However, the FE model predicted lower peak load, which is most likely due to a size effect exhibited by aluminium foam. A simple modification of the FE model input parameters for the foam core subsequently produced good agreement between the model and experimental results.     

Factors associated with the likelihood of injury resulting from collisions between four-wheel drive vehicles and passenger cars

The specific effects of vehicular type on the likelihood of an injury occurring are relatively unexplored. This study sought to assess the relative risk of injury to occupants of four-wheel drive vehicles and their counterparts in passenger cars.Data for 1143 occupants from all of the 454 crashes in Oklahoma, in 1995 that involved a four-wheel drive vehicle were used. Multiple logistic regression analysis determined the association between potential predictive factors and vehicular injury. Odds ratios revealed occupancy in a passenger car to be a major predictor of the likelihood of injury. Other factors include the driver being female, driving too fast, travel on curved or level roadways, and being hit laterally or from the rear.     

A model for process-based crash simulation

Manufacturing of a bumper system from aluminium extrusions often involves series of forming operations performed in the soft W-temper condition, and then artificially age-hardening of the components to the material's peak hardness T6 condition. It is probable that proper finite element (FE) modelling of the crash performance of the resulting systems must rely upon a geometry obtained from an FE model following the process route, i.e., including simulation of all major forming operations. The forming operations also result in an inhomogeneous evolution of some internal variables (among others the effective plastic strain) within the shaped components. Results from tensile tests reveal that plastic straining in W-temper leads to a significant change of the T6 work-hardening curves. In addition, the tests show that the plastic pre-deformation causes a reduction of the elongation of the T6 specimens. In the present work, these process effects have been included in a user-defined elastoplastic constitutive model in LS-DYNA incorporating a state-of-the-art anisotropic yield criterion, the associated flow rule and a non-linear isotropic work hardening rule as well as some ductile fracture criteria. A first demonstration and assessment of the modelling methodology is shown by ‘through-process analysis’ of two uniaxial tensile test series. The industrial use and relevance of the modelling technique is subsequently demonstrated by a case study on an industrial bumper beam system.     

Structure and Mechanical Properties of AFS Sandwiches Studied by in‐situ Compression Tests in X‐ray Microtomography

Al foam core / Al alloy skins sandwiches have potential for application in light weight structures. Recently, the foaming processes have improved and large, thick and 3D‐shape panels can be produced using the precursor technology. The microstructure of an AFS sandwich is analysed in this paper at a microscale and a mesoscale using X‐ray tomography and conventional SEM analysis. The main deformation mechanism of the core under compression is also studied thanks to in situ test. It is shown that the foam first present plastic buckling and then walls rupture. This is well correlated to the microstructure of the constitutive material of the core.     

Compressive behaviour of aluminium foams at low and medium strain rates

Compressive behaviour of CYMAT aluminium foams with relative densities ranged from 5% to 20% has been studied experimentally in this paper. An MTS machine is employed to apply a compressive load at strain rates of 10⁻³–10⁺¹ s⁻¹ to these closed-cell aluminium foams. It has been found that the plateau stress is insensitive to the strain rate and is related to the relative density by a power law. Deformation is not uniform over the whole sample: it first occurs in the weakest band, followed by the next weakest bands after the first one has been completely crushed.     

镁的添加对制备泡沫铝夹芯板泡孔稳定性的影响

通过粉末-铝板复合轧制方法制备出一种界面为冶金结合的泡沫铝夹芯板.分别采用对发泡剂的处理和添加Mg元素的方法来提高芯材泡沫的稳定性.研究发现只有同时对发泡剂处理以及添加Mg元素才能够提高泡沫的稳定性.研究了此种方法中重要的泡沫稳定机制,Mg元素的添加改善了铝硅合金粉末原料生产过程中产生的氧化物颗粒在孔壁上的润湿性,使氧化物颗粒嵌入孔壁中,阻碍了孔壁上金属排液现象的产生,有效的起到稳定泡孔的作用.     

Characteristics of traffic crashes in Maryland (1996-1998): differences among the youngest drivers

Motor vehicle crashes (MVCs) are the leading cause of death among teenagers in the US. The present study examines how crash rates and crash characteristics differed among drivers aged 16-21 in the state of Maryland from 1996 to 1998. The results show that, based on police reports. the youngest drivers have the highest rate of MVCs per licensed driver and per annual miles driven. Furthermore, crash characteristics suggest that inexperience rather than risky driving may account for the differing rates. Drivers closer to the age of 16 had their crashes under the safest conditions: during the day in clear weather while drinking less.