High strain rate response of real-size S690QL and S960QL steel specimens

This study presents a comprehensive experimental investigation into the high strain rate tensile behaviour of real-scale specimens of high-strength steel S690QL and very high-strength steel S960QL. Using the unique HopLab facility at JRC-Ispra, dynamic tensile tests were conducted on large dog-bone specimens, having a rectangular cross-section 24 mm × 12 mm and 30 mm gauge length, under strain rates ranging from 30 to 250 s −1 and compared with quasi-static tests. Advanced diagnostics, including Digital Image Correlation (DIC), thermography, and Scanning Electron Microscopy (SEM), were employed to analyse deformation, temperature evolution, and fracture mechanisms. The objective of this study is to evaluate the strain-rate sensitivity of real-size specimens and to compare their behaviour with that of individual layers possessing distinct microstructures, thereby elucidating the influence of dynamic loading on the structural performance of real-size components. The results reveal significant strain rate sensitivity in both materials, particularly in the ultimate tensile strength, with a concurrent reduction in ductility at higher rates. The investigation further underscores the impact of specimen size and geometry on mechanical behaviour, reinforcing the applicability of homogenization models, including the Tamura-Tomota-Ozawa approach. This methodology effectively links the behaviour observed in previously studied small samples of microstructural layers (outer-inner-outer section) with that of real-scale specimens. Homogenised Johnson-Cook parameters were derived, enabling accurate numerical modelling. These findings provide critical insights for the design and simulation of steel structures subjected to dynamic loading conditions. • Full-size S690QL and S960QL steel specimens were tested under high strain rates (30–230 s −1 ) using the 200 m HopLab facility, enabling accurate assessment of structural steel behaviour under extreme loading. • Digital Image Correlation (DIC), thermography, and SEM analyses revealed strain localization, thermal effects, and fracture mechanisms, supporting the calibration of Johnson–Cook models. • The study confirms strain-rate sensitivity and scale effects in high-strength steels, providing validated data for structural applications like bridges and offshore platforms under dynamic loads.