Hybrid experimental-numerical strategy for efficiently and accurately identifying post-necking hardening and ductility diagram parameters


High-strength steels and aluminum alloys are widely used in numerous applications such as aviation and automotive owing to their remarkable strength and lightweight. Weight reduction with such materials offers the potential to enhance fuel economy by reducing fuel consumption. However, the practical applications of modern light-weighted and high-strength metals are limited by many challenges. For example, the material formation is significantly affected by the increment in the flow strength while manufacturing-induced crack issues is very complicated and the transition from necking failure to shear fracture also interferes with the sheet metal forming.

Numerical simulation is a powerful tool for understanding the fractural behavior and mechanical properties of high-strength and light-weighted metals. For the simulation of ductile fracture, the fracture criteria, hardening behavior in the post-necking stage are important considerations. Additionally, numerous methods have been developed to identify the post-necking strain hardening behavior, especially for components with large thicknesses. However, most of these methods are not applicable to thin sheet metals due to the difficulty in measuring the deformation of their cross-sectional geometry.

Ductile fracture is mainly attributed to the initiation and propagation of cracks. Many models have been developed to simulate and predict ductile failure in metallic materials. These models are broadly classified into two: coupled and uncoupled models. For coupled models, the damage accumulation deteriorates the mechanical properties of the material, while for uncoupled models, the damage has no influence on the elastic-plastic behavior of the material. Nevertheless, the applications of these models are often difficult or impossible in some circumstances due to the challenges associated with the identification of experimental parameters. Therefore, addressing these issues requires developing accurate, efficient and robust parameter identification strategies.

To this note, researchers at the University of Tokyo: Postdoctoral fellow Dr. Shengwen Tu, Mr. Shota Suzuki, Mr. Zhuocheng Yu and the leader Professor Kazuki Shibanuma developed a new hybrid experimental-numerical approach for efficient and accurate identification of ductility diagram parameters and post-necking hardening behaviors of metallic materials. This procedure required only two types of experiments: a cracking growth test and a conventional tensile test. Numerical optimizations based on load-displacement curves of these tests were employed to identify the parameters for simulating the post-necking strain hardening and the ductile fracture. The proposed strategy was validated by applying it to thin sheets of A2024T3 aluminum alloy with 1.2 mm in thickness. Their work is currently published in the journal, International Journal of Mechanical Sciences.

The research team demonstrated the applicability of the proposed strategy to both thick plates as well as thin sheets, which could not be achieved using conventional methods. The the post-necking hardening behaviors and the ductility diagram parameters were successfully identified via the flat tensile test and the Arcan test. The validation experiments involved tests utilizing two plate specimens with a hole. The results showed good agreements between the numerical prediction and the crack propagation and load-displacement curve histories obtained experimentally. These results indicated the accuracy and feasibility of the proposed strategy.

In summary, the authors developed and successfully validated a simple, efficient and more accurate strategy for identifying post-necking hardening and ductility diagram parameters in both thick plates and thin sheets. Numerical optimizations based on measurable quantities, such as load-displacement curves and engineering stress-strain curves, were employed to accurately obtain all the simulation parameters. Despite being relatively simple and easy to perform than most conventional methods, this strategy is generally effective and practically feasible. In a statement to Advances in Engineering, Professor Kazuki Shibanuma, the corresponding author noted that the proposed strategy would provide a general basis for characterizing the mechanical properties of different metallic materials.

Hybrid experimental-numerical strategy for efficiently and accurately identifying post-necking hardening and ductility diagram parameters - Advances in Engineering

About the author

Dr. Shengwen Tu is currently working as a postdoc in Shibanuma Lab, the department of system innovation, the University of Tokyo, funded by the Japanese Society for the Promotion of Science (JSPS). Before that, he was a project researcher in China University of Petroleum (Beijing), focusing on the buckling behavior of natural gas pipeline subjected to the combination of internal pressure, axial compression and bending. In 2018, he received his Ph.D. in Structural Engineering from the Norwegian University of Science and Technology (NTNU). He has diverse research interest in the mechanical and failure behaviors of metals, covering (i) brittle crack arrest of ultra-thick plates; (ii) ductile fracture of advanced alloys, (iii) structural failure analysis of pipelines in petroleum industries, (iv) finite element modeling, (v)mechanical properties characterization and (vi) experimental mechanics. He has published more than 10 international peer-reviewed journal papers in the field of structural integrity assessment. He is very active in participating academic activities and always open to new challenges in his work.

About the author

Dr Kazuki Shibanuma is an Associate Professor at the Department of Systems Innovation, The University of Tokyo. He obtained his Bachelor’s Degree, Master’s Degree and PhD at Department of Civil and Earth Resources Engineering, Kyoto University, in 2006, 2007 and 2010, respectively. He received The Young Scientists’ Award of The Commendation for Science and Technology from Japanese government in 2021.

The aim of his research is to establish novel strategies for explaining fracture phenomena using a combination of methods spanning theoretical, experimental, computational, and data sciences. His research covers a wide range of fracture phenomena of solids and structures such as fatigue, brittle fracture, ductile fracture and creep. He is an author of over 70 peer-reviewed journal publications at the moment. His latest achievements can be found in his laboratory.


Tu, S., Suzuki, S., Yu, Z., & Shibanuma, K. (2022). Hybrid experimental-numerical strategy for efficiently and accurately identifying post-necking hardening and ductility diagram parametersInternational Journal of Mechanical Sciences, 219, 107074.

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