Ductile Fracture Behavior of Mild and High-Tensile Strength Shipbuilding Steels

Abstract

A comparison is made of the ductility limits of one mild (normal) and two high-tensile strength shipbuilding steels with an emphasis on stress state and loading path dependency. To describe the ductile fracture behavior of the considered steels accurately, an alternative form of ductile fracture prediction model is presented and calibrated. The present fracture model combines the normalized Cockcroft–Latham and maximum shear stress criterion, and is dependent on both stress triaxiality and Lode angle parameter. The calibrations indicate that, depending on the hardening characteristics of the steels, ductile fracture behavior differs considerably with stress state. It is demonstrated that the adopted fracture model is able to predict the ductile fracture initiation in various test specimens with good accuracy and is flexible in addressing the observed differences in the ductile fracture behavior of the considered steel grades.

Revisiting the fracture forming limits of bulk forming under biaxial tension

“…A recent work of Cerik and Choung (2020) focused on the development of a criterion that works for the entire range of stress-triaxiality values suggests the combination of the integrands τitalicmax/trueσ¯ and σ1/trueσ¯ of the normalized maximum shear and Cockcroft-Latham criteria, as follows, where Ci are parameters to be experimentally determined and trueθ¯ is the normalized Lode angle.…”

“…Under these circumstances, the authors recovered the idea of Cerik and Choung (2020) of combining integrands from different fracture criteria to setup a new criterion for bulk metal forming that can successfully predict the experimental values of effective strain at fracture trueε¯f for the entire stress-triaxiality range. But, instead of using the integrands of two shear-based criteria, they made use of the integrands σ1/trueσ¯ and η of the normalized Cockcroft-Latham and McClintock criteria, which are directly related to crack opening by out-of-plane shear and tension, respectively.…”

Fracture Estimation in Ship Collision Analysis—Strain Rate and Thermal Softening Effects

“…Figure 7 presents plots of the flow stress at different strain rates. In the adiabatic domain, the thermal softening effect becomes dominant at considerable strain, which is typically observed for steels used in ship construction [37,38]. Figure 8 presents the ductile fracture and localized necking loci under proportional loading paths for the same strain rates, where the former and latter are plotted using the continuous lines and dashed lines, respectively.…”

“…The struck ship was made of high-tensile strength steel. The assumed material parameters under quasi-static conditions were obtained from reference [37]. The additional parameters related to the rate-dependency were assumed to be similar to those reported The struck ship was made of high-tensile strength steel.…”

“…The additional parameters related to the rate-dependency were assumed to be similar to those reported The struck ship was made of high-tensile strength steel. The assumed material parameters under quasi-static conditions were obtained from reference [37]. The additional parameters related to the rate-dependency were assumed to be similar to those reported by Roth and Mohr [21] for DP590 grade high-tensile strength steel.…”