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ABSTRACT: This work comprises the development, implementation and application of methods for the parameter identification of damage mechanical constitutive laws. Ductile damage is described on a continuum mechanical basis by extension of the von Mises yield condition with the Gurson–Tvergaard–Needleman as well as with the Rousselier model. The classical Rousselier model is complemented by accelerated void growth and void nucleation. The non-linear boundary and initial value problem is solved by the finite element system SPC–PMHP, which was developed in the frame of the special research program SFB393 for parallel computers. The material parameters are identified by locally measured displacement fields and measured force–displacement curves. For the material parameter identification a non-linear optimization algorithm is used, which renders the objective function to a minimum by means of a gradient based method. A useful strategy to identify the material parameters was found by careful numerical studies. Finally, using the object grating method the local displacement fields as well as the force–displacement curves are measured at notched flat bar tension specimens made of StE 690 and the parameters of the material are identified.
Archive of Applied Mechanics 04/2012; 75(10):775-797. · 0.95 Impact Factor
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ABSTRACT: In the present contribution numerical stress analyses are presented at static and cyclic loads for the fracture mechanical assessment of railway wheels made of austempered ductile iron (ADI) with graphite nodules. The emphasis is placed on the safe dimensioning of the ADI wheel against fracture and fatigue crack growth. Therefore a linear elastic fracture mechanical analysis is carried out assuming hypothetical crack-like defects at exposed places. The assessment rests on fracture mechanical strength parameters of the ADI material, determined experimentally under static and cyclic loading.
Engineering Fracture Mechanics.
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ABSTRACT: This work is concerned with identification of material parameters for inelastic deformation laws. In this context, non-linear boundary and initial value problems are solved using the developmental finite element code SPC-PMHP for parallel computers. The ductile damage model of Rousselier for large elasto-plastic strains is implemented as a system of non-linear differential and algebraic equations. For solving the inverse problem, the solution of the direct problem is embedded in a gradient based method. This way, material parameters could be identified analysing inhomogeneous two-dimensional displacement fields. Deterministic optimization procedures are used to identify parameters by means of a least-squares functional. A semi-analytical sensitivity analysis was adopted to calculate the gradient of the objective function. Numerical experiments with synthetically generated displacement fields were carried out to check the algorithm. The identification procedure was successful when one material parameter is allowed to vary. Experiments with two or more unknown parameters were less successful, because in some cases only a local minimum was found.
Computational Materials Science.
