Charpy Impact Testing and Mechanical Characterization of TMT Fe 500 Reinforcement

Abstract

In the design and performance of contemporary civil engineering structures, the strength and toughness of reinforcement steel is very important, particularly when the structure is located in a region that is prone to seismic or impact loading. This work examines the impact behavior of Thermo-Mechanically Treated (TMT) Fe 500 Steel Bars, using the Charpy Impact Test as specified in IS:1757 (Part-2):2020, compatible with ISO 148 series. Two samples of 12 mm diameter were tested at room temperature (27°C) and resulted in absorbed energies of 180 J and 162 J, respectively, for an average absorbed energy of 171 J. These test results provide evidence of the high toughness and ductility of Fe 500 Bars as reinforcement, indicating the material can be maintained in an elastic state during sudden dynamic load and that it would not fail through \'brittle fracture.\' When compared to earlier works, it has been established that TMT bars (including those tested) can be regarded as consistently better in their performance than characteristic mild steel at low temperatures or during impact testing related to seismic loading, to a substantial degree because of the improved microstructure and dual-phase nature of the reinforcement when the TMT process is adopted. The output findings indicate the suitability of Fe 500 to be used as a reliable Steel bar material for use as reinforcement in earthquake resistant, high-rise and long-span structures. In summary, this work provides a report of experimental validation of Steel bar material behavior, but is enhanced with comparative literature review discussions, ultimately validating the role of Charpy toughness in the selection of material for infrastructure sustainability.

Introduction

The mechanical reliability of reinforced concrete structures largely depends on the quality and properties of embedded steel reinforcement. Thermo-Mechanically Treated (TMT) steel bars, particularly the Fe 500 grade, are widely used due to their high yield strength (500 N/mm²) and ductility, making them suitable for high-rise buildings, bridges, and seismic-resistant structures. The toughness of steel, or its ability to absorb energy during fracture, is a key property for resisting dynamic or impact loads, commonly assessed via the Charpy Impact Test.

Fe 500 TMT bars have a dual-phase microstructure, with a hard martensitic outer layer and a ductile ferrite-pearlite core, providing both tensile strength and energy absorption capacity. Research indicates that TMT bars outperform conventional mild steel, offering higher impact strength and ductility, making them particularly suitable for seismic zones and long-span structures.

In the present study, 12 mm Fe 500 TMT bars were tested at room temperature using a pendulum-type Charpy Impact Testing Machine. Two samples absorbed energies of 180 J and 162 J, averaging 171 J, with ductile fracture surfaces observed. This impact strength is significantly higher than conventional mild steel (80–120 J), confirming superior toughness. These findings align with prior literature, reinforcing the suitability of Fe 500 TMT bars for structures subjected to dynamic and seismic loads.

The high toughness is attributed to the dual-phase microstructure: the martensitic shell provides hardness, while the ductile core absorbs energy, preventing brittle failure. Practical implications include their use in earthquake-resistant buildings, bridges, highways, and high-rise constructions, supporting the mechanical and safety requirements of modern sustainable infrastructure.

Conclusion

In the present study, the Charpy Impact toughness of Fe 500 TMT Steel Bars was evaluated according to an impact testing procedure, yielding an average absorbed energy of 171 J at room temperature. The mechanical test results show the Fe 500 Bars have a higher toughness, and energy absorption, than baseline normal mild steel, which is relatively consistent with an impact toughness of 80–120 J. The enhanced impact resistance of the Fe 500 Bars was attributed to the thermo-mechanical treatment processes, which induce a dual-phase microstructure (a hard martensitic shell surrounding a ductile ferrite-pearlite core). The ability to enhance both yield strength and ductility of the Bars with this dual-phase structure protects the Bars against brittle fracture with sudden loading. The results resemble the literature in that TMT bars nearly always have higher impact strength and toughness than standard steel reinforcement. As shape once again emphasizes that Fe 500 Bars may provide a safe/sustainable option for reinforcement within high-rise built form as well as bridges and structures designed to withstand seismic events. In summary, Fe 500 TMT Bars can be fully endorsed as a superior alternative for modern day built infrastructure projects where safety/durability are metric factors and determinants. Future work should examine variations of TMT reinforcement including grades Fe 415, Fe 550, Fe 600 as well as studies of durability at elevated temperatures and or long duration cyclic loading conditions.

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Copyright

Copyright © 2025 Sardar Shakti Singh, Rohit Srivastava, Anurag Shrivastava. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.