Finite element analysis of rebar cutting using hydraulic system

Abstract

The present thesis investigates the cutting process of reinforcing steel bars (rebars) using hydraulic systems, with a focus on developing a reliable and validated finite element analysis (FEA) framework. Rebars, as essential elements in reinforced concrete structures, provide tensile strength and significantly contribute to the overall stability of buildings and infrastructure. The efficiency and precision of rebar cutting operations are therefore critical not only to ensure dimensional accuracy but also to guarantee safety, structural performance, and economic sustainability in construction projects. Although hydraulic rebar cutters are widely adopted in practice due to their ability to generate large forces with high reliability, the detailed mechanical behavior of rebar cutting—including stress distribution, deformation, and fracture mechanisms—remains insufficiently understood. This research addresses these limitations by combining computational simulation and experimental validation in a comprehensive study. A three-dimensional geometric model of the hydraulic cutting system was first developed using SolidWorks. The model consists of a 10 mm diameter AISI 1045 rebar and two blades manufactured from SPK 1.2080 tool steel: a fixed cylindrical blade and a moving blade with a U-shaped notch attached to the piston rod of a hydraulic cylinder. The numerical analysis was carried out using ANSYS Explicit Dynamics (2025 R1), selected for its robustness in handling large plastic deformations, severe nonlinear contact, fracture initiation, and transient dynamics. The Johnson–Cook constitutive and fracture models were applied to represent the elastoplastic and failure behavior of the rebar under high localized stresses, incorporating strain-rate effects and damage evolution. Nonlinear contact conditions were defined at the blade–rebar interfaces, with frictional interactions explicitly modeled to reflect realistic cutting conditions. Mesh refinement was applied selectively in the contact regions to capture local stress gradients, while convergence tests were performed to ensure the reliability of the results. The findings showed strong agreement between simulation and experiment, with differences below 6%. Force–time diagrams indicated three distinct stages: an initial elastic–plastic increase, a nonlinear strain-hardening region, and a final peak force followed by a rapid drop during fracture. Maximum cutting force was obtained for the 90° blade, while significantly lower values were recorded for the 88° and 86° blades. Stress distribution analysis revealed critical zones near blade–rebar contact, particularly at sharp blade edges where localized stresses were concentrated. The combined experimental and numerical analyses highlight the dual role of blade geometry: while smaller edge angles enhance cutting efficiency by reducing the required force, they also compromise tool durability by increasing localized stress levels. These insights underscore the importance of selecting an optimal blade geometry that balances cutting performance with tool life. Furthermore, the validated FEA framework developed in this thesis provides a reliable predictive tool for evaluating cutting performance under various material and process conditions. The contributions of this research are threefold. First, it establishes a validated numerical model of hydraulic rebar cutting, integrating advanced constitutive modeling, nonlinear contact mechanics, and mesh optimization techniques. Second, it provides quantitative insights into the relationship between blade geometry, cutting force, and stress distribution, contributing directly to the optimization of hydraulic cutter design. Third, it demonstrates a practical methodology for linking simulation results with experimental validation, offering a pathway for future studies on fatigue, wear, and thermal effects in industrial cutting systems. In conclusion, this study enhances the understanding of material behavior and tool performance in hydraulic rebar cutting and delivers practical guidelines for the design and operation of cutting tools. The developed methodology can be extended to different rebar diameters, alternative tool materials, and more complex blade geometries.