Figure 1: Dynamic 3-point bending test setup with two high-speed cameras and thermocamera measurement

During this case study, the effectiveness and reliability of FormPlanet novel testing technologies to characterise crash performance of steel grades for automotive parts at laboratory scale have been assessed and compared to classical crash tests done on Omega parts at ArcelorMittal facilities.

The materials used in this case study included three grades for cold forming (DP980 GI – 1.4 mm, Fortiform®1180 Bare – 1.4mm and MS1500 EG – 1.5mm), and two grades for hot forming (Ductibor®1000 AS150 – 1.6mm and Usibor®2000 AS150 – 1.2mm).

Dynamic 3-point bending tests and compression  were performed on omega-profiles. Two-high speed cameras, a thermocamera and a digital image correlation equipment were used to track the sample deformation during testing. Dynamic compression tests were also done on box-beams.

In addition, another FormPlanet Test Bed service was validated in ArcelorMittal case study to evaluate crashworthiness and energy absorption via crashbox testing in a high-speed machine. To achieve typical speeds such as in real crash situations, the crash boxes were compressed in a high-speed machine and two camaras were used to capture the process. By applying a random speckle pattern, the evolution of the deformation process could be measured by Digital Image Correlation (DIC).

The crashbox tests were modelled using the FE-software LS-Dyna. The dynamic tests evaluated with the Stepwise Modelling Method (SMM) were used for material model calibration and GISSMO damage model. High-speed Essential Work of Fracture tests were used for damage model calibration​.

Finally, ArcelorMittal performed two types of crash test in their facilities: the bending impact resistance test, aiming at characterising steel grades for parts dedicated to anti-intrusion (B-pillars, door beam, etc.) and the axial impact resistance test, aiming at characterising steel grades for parts dedicated to energy absorption.

The results of both ArcelorMittal in-house crash tests and Dynamic 3-point bending tests and dynamic compression tests are consistent. Discrepancies were shown only for steel grades not adapted or dedicated to energy absorption.

Figure 2: Setup with two high-speed cameras in the high-speed machine

The crash behaviour of components can be evaluated by two different tests: dynamic 3-point bending tests on omega profiles and dynamic compression tests on box beams.

Dynamic 3-point bending tests are performed on an improved setup of Drop Weight Tower with two high speed cameras (assisted by DIC analysis), application of strain gauges on the component and high-speed thermography. Uniaxial compression tests of crash boxes can be performed, applying 3D DIC for measuring deformations fields around wrinkles and potential cracks.

A small-scale laboratory test using the Essential Work of Fracture (EWF) methodology for the fracture toughness evaluation at high strain rates allows to successfully reproduce real crash conditions, where strain rate abruptly increases. The EWF tests are conducted in a high-speed tensile testing machine, combining Digital Image Correlation (DIC) and high-speed photography for the evaluation of the local deformation in the fracture zone.