Nonlinear Fracture Mechanics Models
Invited Lecturers
- Gabriella Bolzon (Politecnico di Milano, Milano, Italy)
- 6 lectures on: The predictive capabilities of fracture models rely on the accurate calibration of parameters (e.g., specific fracture energy, tensile strength). This calibration may consist of inverse analysis based on experimental information and mimimization of the discrepancy from corresponding data provided by test simulation. Various techniques for fracture parameter identification by deterministic and stochastic approaches will be presented with reference to laboratory and in situ experiments.
- Wolfgang Brocks (GKSS Forschungszentrum, Geesthacht, Germany)
- 6 lectures on: Thin-section lightweight structures make different demands on integrity assessment methods with respect to heavy-section constructions as they do not meet the size requirements of the conventional test standards. Two models for the numerical simulation of ductile crack extension in panels and shells are presented and compared. They are based on the crack tip opening angle (CTOA) and on a cohesive surface approach, respectively. An introduction to the fundamentals of both models is given. They are applied to various specimen configurations and structural components, like aircraft fuselages.
- Alberto Carpinteri (Politecnico di Torino, Torino, Italy)
- 5 lectures on: The so-called Size or Scale Effect will be explained in detail. It represents the strong variation in structural response due to a variation in the specimen dimensions. As small specimens are relatively ductile, so large specimens made of the same material are relatively brittle. The cohesive zone models are able to capture this transition very accurately, with a clear prevalence of the catastrophical behaviour (snap-back) when a nondimensional number, which is a function of all the most relevant mechanical and geometrical parameters, is below a certain threshold value.
- Bhushan L. Karihaloo (Cardiff University, Cardiff, Wales, Great Britain)
- 6 lectures on: The trajectory of a growing crack depends on the asymptotic stress field ahead of the tip via a growth criterion, e.g. the criterion of maximum hoop stress. In quasi-brittle materials, such as concrete, ceramics, etc., such fields were not known until very recently. Universal asymptotic expansions, analogous to Williams expansions at a traction-free crack tip are obtained for frictional and frictionless cohesive cracks. The derivation of the asymptotic fields and their implementation in the extended finite element methodology will be fully discussed.
- Alan Needleman (Brown University, Providence, Rhode I., USA)
- 6 lectures on: Damage and cohesive models of fracture will be discussed. In damage-type models the creation of a new free surface is incorporated directly into the material constitutive relation whereas in cohesive models deformation and fracture constitutive relations are specified separately. Attention will be focused on ductile fracture and, for damage modeling, on the Gurson constitutive framework. The circumstances under which initial/boundary value problems are well-posed together with the numerical implementation issues will be discussed.
- Thomas Siegmund (Purdue University, West Lafayette, Indiana, USA)
- 6 lectures on: The cohesive zone model approach for fatigue loading will be discussed. First, a phenomenological fatigue cohesive zone model is described where an endurance limit and a cyclic cohesive zone length are introduced. The application of the model to crack growth in elastic and elastic-plastic solids is described with special focus on structures with bi-material interfaces and on size effects. Finally, a model with damage evolution based on dislocation activity is introduced with specific focus on problems in metal fatigue.