Aase Gavina Roberg Reyes

Crashworthiness of aluminum extrusions subjected to oblique loading: experiments and numerical analyses

Oblique loading was studied through quasi-static experiments and numerical simulations. The behavior of square aluminum columns in alloy AA6060 subjected to quasi-static oblique loading was investigated experimentally for three different load angles. The square columns were clamped at one end and oblique load conditions were realized by applying a force with different angles to the centerline of the column. These tests were used to validate a numerical model. Numerical studies of oblique impact were carried out using the validated model, and the mean crush load was investigated through factorial analysis with parameters as load angle, thickness, length, and heat treatment of the alloy and impact velocity.

Square aluminum tubes subjected to oblique loading

The behavior and energy-absorbing capability of obliquely loaded square thin-walled aluminum columns in alloy AA6060 were studied through quasi-static experiments and FEM-analyses with LS-DYNA. The specimens were clamped at one end and oblique loading conditions were realized by applying a force with different angles to the centerline of the column. The primary variables were load angle, wall thickness and heat treatment of the alloy. The experimental results were compared with the numerical results, and the capacity was compared with Eurocode 9. LS-DYNA was able to predict peak loads with very good accuracy, while the mean loads were conservative compared to the experimental results. Furthermore, the study showed that Eurocode 9 is conservative, and that the moment capacity can be increased for temper T4 and cross-section class 1 and 2. The initial and subsequent failure loci are constructed from experimental and numerical results, and the failure loci shrink for increasing additional rotation from the initial position.

Empty and foam-filled circular aluminium tubes subjected to axial and oblique quasi- static loading

Tests on tubular columns made of the aluminium alloy 6060-T4 under axial and oblique, quasi-static loading have been performed. The columns were fixed at one extremity, while a concentrated force was applied at the other through a rigid collar. Empty and foam-filled columns were tested for load angles equal to 0, 5, 15 and 30 degrees with respect to the longitudinal direction of the column. The columns outer diameter was 80 mm and the thickness was 1.5 mm, while the distance from the point of load application to the fixed support was 245 mm. The aluminium foam density was about 0.3 g/cm 3 . The response parameters were the peak force, the absorbed energy and the mean crush force, in addition to visual observations of the deformation mode and fracture. Furthermore, LS-DYNA simulations of the experiments were performed. The columns were modelled with shell elements, while brick elements were used to model the aluminium foam core. The aluminium alloy was modelled using an isotropic elastoplastic model with isotropic strain hardening. Fracture in the aluminium column was not considered in the simulations. The aluminium foam was modelled using the Deshpande-Fleck model. In selected simulations, fracture was assumed to occur at a critical value of the plastic volumetric strain. The agreement between the experimental and predicted results was in general good.

Design and finite element simulations of aluminium foam-filled thin-walled tubes

This paper presents experiences gained at SIMLab in modelling and design of aluminium-foam-filled tubes for structural applications. The main challenges for robust finite element simulations using explicit codes are outlined and references to previous studies are used for illustration. Any details whatsoever may be found in the original papers referenced in the text.

Determination of forming limit strains using Marciniak-Kuczynski tests and automated digital image correlation procedures

Forming limit strains are used to construct a forming limit diagram (FLD), which is a diagram in the principal strain space, traditionally used for designing forming operations of sheet metals. A line indicating the boundary between safe and unsafe strains is often called the forming limit curve (FLC). FLDs are also used to evaluate results from finite element simulations. Therefore consistency and reproducibility are important. This paper deals with the experimental determination of forming limit strains from Marciniak-Kuczynski (MK) tests. The material tested is AA6016 aluminum alloy in three different conditions: virgin material and material subjected to 5% and 8% deformation by rolling. Strains were measured by the use of digital image correlation (DIC) technique. Forming limit strains were determined by the use of two automated methods. The results from the two methods are compared and evaluated regarding their applicability to the Marciniak-Kuczynski test and ability to capture actual forming limit strains.

Experimental Detection of the Onset of Local Necking in an Aluminium Sheet

Forming limit diagrams (FLDs) are widely used to assess metal sheet formability. Experimental FLDs are obtained by performing formability tests and determining failure strains. The standard method for detection of forming limits is based on the spatial distribution of the strains and requires formation of a single local neck. Some aluminium alloys, such as AA6016, have a tendency to form multiple strain localizations in formability tests, which can be interpreted as multiple local necks. Thus, use of the standard method is questionable for these aluminium alloys. The present paper presents an alternative, digital-image-correlation-based method for experimental detection of the onset of local necking in an aluminium sheet. The method is based on monitoring the sheet-thickness evolution, and is developed to be user independent and resistant to noise in the measurements. The method can be used in combination with different types of formability tests. The main requirement is that digital image correlation is used for strain measurements. Here, the method is initially tested on uniaxial tension tests of AA6016 aluminium alloy sheets and then extended to formability tests.

Crash behavior of obliquely loaded aluminum extrusions

The energy absorbing capability of obliquely loaded aluminum extrusions was studied through quasi-static experiments. Square aluminum columns in alloy AA6060 were clamped at one end and oblique load conditions were realized by applying a force with different angles to the centerline of the column. The primary variables were load angle, wall thickness and heat treatment of alloy. In addition, numerical simulations were performed and comparisons with the experimental results were satisfactory. Numerical simulations with other load angles than in the experiments were also carried out to supplement the experimental results.