STRUCTURAL INTEGRITY AND ANALYSIS
Our experts have more than 20 years of experience in research and innovation in the field of integrity assessment of component and structures. In addition to traditional global approach to fracture, such as that based on fracture mechanics concepts, the company has implemented computational tools based on damage mechanics specifically suited for large scale yielding, ductile tearing and rupture. This approach allowes to accurately predict when and where ductile crack will initiate and how it will propagate into the component according to provided loadas and boundary conditions.
DUCTILE DAMAGE MODEL
The Bonora's damage model (Bonora, Eng. Frac. Mech. 58 (1), pp. 11-28, 1997) is derived in the framework of continuum damage mechanics (CDM). Main features of this model with respect to other similar formulations are:
damage reduces the material stiffness only and not the flow curve. This eliminates problems related to mesh dependency of the solution;
damage accumulates only under tensile (positive stress triaxiality) state of stress. Under reversed plastic flow damage effects are temporarily restored;
damage rate equation is obtained from a general form of the damage dissipation potential;
the model requires the identification of four material parameters only, namely: the threshold strain at which damage processes initiates εth, the failure strain under constant uniaxial constant stress triaxiality εf, the critical damage at rupture Dcr and the shape factor α.
stress triaxiality effect on material dutility is accurately predicted.
This model has been validated for different metals and alloys and can be used to accurately predict: ductile crack initiation and propagation, constraint effect on fracture resistance, fracture under large scale yielding.
The model has been successfully used in a number of applications:
ductile crack initiation and propagation;
low cycle fatigue;
stamping and metalforming;
constraint effect prediction;
high temperature rupture;
Fields of interest:
oil and gas
offshore engineering and technology
The model is avaliable in FEM code MSC MARC r2013. Recently, the damage model has been extended incorporating a stochastic formulation for damage parameters. This feature allows the possibility to account for material statistical variability and to break symmetries.