Abstract
Fracture toughness determination of dual-phase DP450 steel using the essential work of fracture (EWF) methodology is the major focus of this research work. The EWF method is used for the determination of fracture toughness of thin sheets in a plane stress dominant condition. The EWF method is discussed in detail with the help of DP450 steel experimental results. Double edge notched tension (DENT) specimens with fatigue pre-crack and without fatigue crack (notched) have been used for testing. Specific essential work of fracture (we), crack tip opening displacement (δce) and crack tip opening angle (ψe) parameters were used for the comparative analysis. High-intensity laser beam cutting technology was used for the preparation of notches. Fracture toughness values of fatigue pre-cracked and notched samples were compared. The effect of notch tip radius and fatigue crack on the fracture toughness values were analysed. Digital image correlation (DIC) technology was used for the identification of local strain distribution and validation of the methodology. Fractured surfaces were examined by a scanning electron microscope (SEM) to analyse the fracture morphology and stress state.
Highlights
The automotive industry is under constant pressure to increase the efficiency of vehicles, reduce emissions and get better crashworthiness
The local strain distribution, displacements and necking of the specimen were evaluated variation of stress for all ligament lengths is in the earlier-specified range, which is an empirical indication of similar stress states in all samples
A series of images were taken with the help of two cameras in the digital image correlation technology (DIC) system
Summary
The automotive industry is under constant pressure to increase the efficiency of vehicles, reduce emissions and get better crashworthiness. Cotterell and Reddel used the Broberg concept of energy consumed in the independent autonomous end region (FPZ) as material property for the sheet thickness. Marchal and Delannay observed better linearity in specific essential work of fracture for different ligament lengths but expressed their concern on the hypothesis of EWF about zone separation (FPZ and outer plastic zone). The primary focus of the EWF test is to find the specific essential work of fracture (we ) Cotterell proposed parameters, such as crack tip opening displacement (δec or CTOD) and crack tip opening angle (ψe or CTOA), based on the elongation data during EWF test [27]. To determine the effect of notch tip radius on specific essential work of fracture, a notch tip radius of 55 μm was selected and the results are compared with fatigue cracked samples. The yield strength is replaced by the ultimate strength to verify the plane stress state in the ligament length [14]
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