Material Characterization of High-Toughness Steel

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Designers have long recognized the inherent structural efficiency and economy associated with non-redundant bridge systems. Presently, steel bridge structures with non-redundant tension members, labeled as fracture critical members (FCMs), are subjected to more stringent design, material, fabrication, and inspection requirements. FCM requirements are contained in the AASHTO/AWS Fracture Control Plan (FCP) and Code of Federal Regulations (CFRs). The consequence of the requirements, in particular as related to the associated in-service inspection costs, is a higher life-cycle cost when compared to redundant steel bridge structures. However, significant advances have been made over the past 40 years since the original AASHTO/AWS FCP was introduced. Advances in the understanding of fracture mechanics, material and structural behavior, and fatigue crack initiation and growthas well as advancements in fabrication and inspection technologies have allowed other industries to address fracture in a more integrated manner. One-step toward an integrated FCP is to take advantage of the superior fracture toughness of modern steels. While increased fracture toughness is a performance benefit often highlighted for modern steels, there is a lack of fundamental test data and material characterizationstudies. A large test program was conducted focused on the use of high-toughness steels routinely used in bridge fabrication to establish rational inspection intervals for members traditionally classified as fracture critical. The project was comprised of small-scale material testing, full-scale fracture testing of steel bridge axial and bending members, three-dimensional finite element modeling, and an analytical parametric study. Material characterization results, which included tensile testing, chemistry, Charpy v-notch (CVN) impact testing, percent shear measurement, reference temperature determination, and ductile tearing initiation testing, are presented. Test results showed some of the steels tested demonstrated larger than expected CVN scatter in the transition region. Most importantly, the research revealed for the steels tested the master curve created using Charpy-sized SE(B) specimens resulted in an overestimate of fracture toughness compared to 1 T SE(B) specimens.


High performance steel; Toughness; Fracture; Material characterization; CVN


Structural Engineering



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