Numerical-experimental analysis of laser-welded small energy absorbers with direct impact Hopkinson method

• Published in: Journal of constructional steel research 2024-07, Vol.218, p.108746, Article 108746
• Main Authors: Kucewicz, Michał, Prochenka, Paweł, Janiszewski, Jacek, Małachowski, Jerzy
• Format: Article
• Language: English
• Subjects: Crashworthiness; DIH test; Finite element analysis; High-strength steel; Laser welding; Thin-walled structure
• ISSN: 0143-974X; 1873-5983
• DOI: 10.1016/j.jcsr.2024.108746

This research paper presents a comprehensive numerical-experimental analysis of the phenomena observed during the compression of small energy absorbers (EAs) with dimensions 23 × 23 mm and a thickness of 0.6 mm. This study uses the direct impact Hopkinson (DIH) method. The locus is the detailed prediction of the strength of laser-welded joints in terms of energy absorption under both quasi-static and dynamic loading conditions. Furthermore, the paper explores the potential utility of the described methodology for modeling and predicting the failure mechanisms of small energy absorbers. This investigation delves into key factors that affect the distribution of cracks in deformed energy absorbers. These include: the detail of the reproduction of the absorber geometry, the impact of finite element formulations and modeling method (2D/3D elements) and the complexity of the material model for propagated cracks. Two material models are considered, the simplified Johnson–Cook model and the tabulated Johnson-Cook with Hockett–Shelby extrapolation model, which incorporate linear damage dependent on the stress triaxiality and Lode angle. The study also highlights the advantages and disadvantages of the DIH test method. Some features cannot be effectively observed through experimental testing alone. The experimental procedure involved initial testing and calibration of the material models for both the parent material and the welded joints at three different strain rates. Subsequently, the validated energy absorber models are subjected to static and dynamic crushing. The results are subsequently compared with the virtual results obtained using the gravity hammer method, which is a more readily accessible testing approach. Remarkably, a very high correlation between the numerical simulation and experimental data is observed, providing a comprehensive understanding of the research problem related to laser-welded absorbers. [Display omitted] •A simple constitutive model cannot predict cracking in thin-walled energy absorbers•The fully optimized material model reliably reproduces the HSS failure in a complex state of stress•The strength and ductility increase with a strain rate >1000 s−1 compared to static conditions.•The reduced number of cracks on the folds is observed in the dynamic crushing of energy absorbers.•The sensitivity of the strain rate of material is secondary to the increase of energy absorbed in dynamic crushing.