In this page you will be able to find the scientific publications related to ToughSteel project published by partners:
Toughness properties influence on the automotive stamped components
La Metallurgia Italiana
by Michele Maria Tedesco and David Frómeta
The CO2 emissions of passengers cars and commercial vehicles are becoming more and more important year by year because they have a direct effect on climate change. For this reason, the main OEMs are increasing the usage of Advance High Strength Steel (AHSS) to replace the common low carbon steels (mild steel) in order to reduce the vehicle weight and so in parallel reduce the CO2 emissions in compliance with the international requirements that are becoming more restrictive than the past.
AHSSs forming operations are complicated due to their lower formability (global and local). , Therefore, it is crucial to be able to predict and select the best material for the components based on their shape and mechanical properties. This is the reason why CRF and Eurecat are working on several projects together, such as ToughSteel, to implement new fracture criteria for edge cracking sensitivity prediction in order to prevent and/or solve potential problems during forming.
In this paper, case study in which the Essential Work of Fracture (EWF) measurement was essential to define failure’sroot cause during the forming operation will be presented.
Optimization of Thick 22MnB5 Sheet Steel Part Performance through Laser Tempering
by Eduard Garcia-Llamas; Jaume Pujante; David Frómeta; David Corón; Laura Galceran; Stefan Golling; Carlos Seijas; Daniel Casellas
Press Hardening offers the possibility to obtain a wide range of mechanical properties through microstructural tailoring. This strategy has been successfully applied in thin sheet components, for instance, through differential cooling strategies. The application of these added value features to truck components implies adapting the process to the manufacture of thick sheet metal. This introduces an additional layer of complexity, but also opportunity, in a process where the final microstructure and, thus the mechanical performance is generated in the press shop. This work presents a study on optimizing the crash worthiness and impact energy absorption on a press hardened thick 22MnB5 steel sheet. Different microstructure design strategies have been studied, including ferrite-Pearlite (representative of a differential heating and austenitization strategy), in-die generated Bainite (representative of differential cooling) and Tempered Martensite (generated through laser tempering), keeping a fully hardened martensite as a reference condition. The material performance has been compared in terms of the monotonic properties, useful for anti-intrusion performance, and Essential Work of Fracture, a well-suited parameter to predict the crash failure behavior of high strength steels. The results show that laser tempering offers properties similar to Bainite-based microstructures and can be a successful replacement in components where the sheet thickness does not allow for the fine control of the in-die thermomechanical evolution.
Optimization of the essential work of fracture method for characterization of the fracture resistance of metallic sheets
Engineering Fracture Mechanics, 2022
by A. Hilhorst; P.J. Jacques; T. Pardoen
The essential work of fracture (EWF) method is a powerful approach to characterize the fracture resistance of thin ductile sheets based on a principle of separation of energy contributions. A major drawback of the method is an extensive use of material, requiring a series of double-edge notched tensile (DENT) specimens with several ligament lengths to extract the EWF. This can be a serious limitation when the material is difficult to process and/or expensive. Here, we propose an improved methodology to reduce the amount of material as much as possible while keeping the same statistical level of accuracy for the estimated EWF. We show that the width and height of the DENT specimens can be adapted as a function of the ligament length. A statistical model has been developed to determine the distribution of ligament lengths minimizing the total amount of material. This new approach is validated both numerically with Monte Carlo simulations and experimentally. In the experiments, the strain fields in the ligament were quantified by digital image correlation to ensure that the validity criteria were met for each specimen, as well as to provide an in-depth analysis of the plastic zone development. From these results, guidelines are provided to optimally rationalize EWF experimental data.
Assessing the effect of the experimental parameters in the evaluation of the essential work of fracture in high-strength thin sheets
Engineering Fracture Mechanics, 2022
by Ilef Tarhouni; David Frómeta; Daniel Casellas; J. Costa; P. Maimi
The essential work of fracture methodology (EWF) has been successfully adopted to evaluate the fracture toughness of various metals and polymers. However, some aspects of the methodology are still far less understood, such as the influence of the experimental parameters on EWF measurement in thin metal sheets. In the present paper, the ligament range criterion of the EWF approach was revised for several advanced high-strength steels (AHSS). The validity of the upper and lower ligament length limits given by the ESIS protocol is redefined and rationalized according to the necking capability and the plasticity behaviour of the different AHSS grades. The work provides a new criterion to define the minimum ligament length to be tested, based on the minimum distance required by the crack to fully develop the necking capability of the material. The width constraint is too restrictive and has no effect on the deviation from linearity in the upper range. On the other hand, the maximum ligament length is proven to be controlled by the size of the plastic zone as proposed by the ESIS protocol.