Ductile damage modeling of the machining process
The development of the modeling strategy, for the ductile material and fracture response herein, is embedded in a continuum thermodynamics framework. The Johnson-Cook constitutive model is applied for the eﬀective visco-plastic material response. The ductile fracture behavior, is modelled by a continuum damage enhanced material formulation where an inelastic damage threshold is followed by a damage evolution law. A set of smeared damage evolution models are proposed, which are shown to give mesh independent results for quasi-static and isothermal conditions.
In addition, for more general situations, an alternative continuum progressive ductile damage model coupled to thermodynamics is formulated, where the damage induced fracture area production is based on a progression speed and a length-scale parameter. The damage evolution is then governed by a damage driving energy which, deﬁned from the dissipation rate, consists of both elastic and inelastic contributions. In this way, the model is able to represent the ductile fracture process in a thermodynamically consistent way at high strain-rates and elevated temperatures, while partly preserving the mesh independent response. Moreover, the ability of the model to capture the material and fracture response at various states of stress triaxiality is investigated and results are compared with experiments. The damage model is shown to be able to capture the fracture response with the appropriate formulation of the damage driving energy including at least the inelastic part.
Finally, the continuum progressive ductile damage model is applied in a rigid visco-plastic context for the simulation of the orthogonal machining process. Here, simulation results for the diﬃcult-to-cut material Alloy 718 are compared with experimentally determined forces, tool-chip contact-lengths and chip shapes at varying cutting speeds. Even though the proposed damage model consists of few parameters it is able to represent the cutting parameters considered in good agreement with experiments.
Damage threshold criterion
Damage driving energy
Chalmers, Industri- och materialvetenskap, Material- och beräkningsmekanik
Mesh objective continuum damage models for ductile fracture
International Journal for Numerical Methods in Engineering,; Vol. 106(2016)p. 840-860
Artikel i vetenskaplig tidskrift
S. Razanica, R. Larsson and B. L. Josefson. A ductile fracture model based on continuum thermodynamics and damage.
S. Razanica, B. L. Josefson, R. Larsson and T. Sjögren. Validation of the ductile fracture modeling of CGI at quasi-static loading conditions.
S. Razanica, A. Malakizadi, R. Larsson, S. Cedergren and B. L. Josefson. FE modeling of machining Alloy 718 using a novel ductile damage model.
During a turning operation, the topic of the current thesis, a material portion called “chip” is removed from the workpiece using a cutting tool. A considerable waste of material, up to 10 % of the workpiece material might be removed in order to reach the final geometrical dimensions of the product. Desired product properties are achieved by controlling the processing parameters e.g. cutting forces, chip morphology, temperature and surface roughness which may be a difficult task.
Currently, the manufacturing industry addresses these challenges via simulation tools to increase the knowledge and optimization possibilities of the operation. Hence, in order to accurately simulate the machining processes, it is of utmost importance to accurately represent the behavior of the workpiece material, the interaction at the tool-chip interface and the local fracturing that occur during the chip formation. During this material removal process, regions of the workpiece material are subjected complex phenomena e.g. extremely large deformations, high strains and strain-rates together with elevated temperatures.
Thus, in the current thesis, a modeling framework is presented which accounts for both the material response, tool-chip interaction and fracture in the workpiece during machining. In particular main efforts have been put on the development of a model to represent the onset and evolution of damage followed by subsequent fracture. The modeling framework is implemented in a commercial software to simulate 2D machining (orthogonal cutting). The results obtained are validated against experimentally obtained chip formations, cutting forces and tool-chip contact lengths for machining of the difficult-to-cut material, Alloy 718.
Produktionsteknik, arbetsvetenskap och ergonomi
C3SE (Chalmers Centre for Computational Science and Engineering)
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4565
Chalmers tekniska högskola
Virtual Development Laboratory (VDL)
Opponent: Professor Jörn Mosler, Department of Mechanical Engineering, TU Dortmund, Germany