A constitutive model that incorporates material dilation and the concept of continuum damage mechanics is developed to predict ductile fracture of steel under monotonic quasi-static loading. In this model, damage is assumed to be isotropic and is a function of the state of stress and the plastic strain increment. Material dilation is assumed to vary with the state of damage. Fracture occurs when the damage limit is reached. The constitutive model is implemented in a finite element program. Parameters used in the analyses are calibrated using data obtained from tension coupon tests. The constitutive model and the process used to determine its parameters are described.

An experimental program with rounded steel coupons was conducted to acquire test data to verify the model. A total of sixteen specimens with three different heat treatments and different geometry were tested. Each specimen was tested until fracture with regular stoppages during the test for taking the static readings and the digital photographs of the deformed shape. All specimens were monotonically loaded with the exception of two specimens, which were unloaded and reloaded intermittently during the test. The ductility of the specimen decreases as the gage length or the transition radius or both are reduced. The model is able to give a good prediction of the specimen load-deformation behaviour, the deformed shape, and the instant fracture occurs. It also captures the decrease in ductility associated with a higher hydrostatic tension stress, as occurs in the case of a shorter gage length or a smaller transition radius.

To illustrate the application of the material model, numerical simulations are carried out for some practical cases such as predicting the capacity and the failure of a steel structure connection or a corroded pipe. Existing test data for slotted tubular tension members are used in comparison. The numerical solution closely matches the measured load-deformation response, the location of fracture and the moment fracture occurs.