F&CP - RESEARCH

Fracture and Crack Propagation

Introduction


In numerical simulations of quasi-static and dynamic ductile fracture, e.g. in analysis of forming processes, crashworthiness and structural impact, many complex and inter­acting phenomena generally occur: large deformations, contact, elastic-plasticity, viscous and thermal effects, damage, localization, fracture, length-scale effects and crack propagation. Solving such problems requires advanced numerical techniques.

Today the finite element method is used in most cases, and ductile fracture and crack propagation are typically solved using uncoupled or coupled damage mechanics and element erosion at a critical value of damage. This approach is deemed to depend on mesh size and mesh orientation, and various regularization techniques (e.g. the non-local approach, gradient theories and viscous regularization) have been proposed to enhance mesh convergence. Two examples of alternative strategies are node splitting coupled with adaptive meshing and extended finite element methods (XFEM). There is a need to evaluate established methods against other possible ­approaches for modelling of ductile fracture and crack propagation, and to make these novel ­procedures available for industrial use.

In the F&CP programme, mathematical models and numerical algorithms for damage, fracture and crack propagation in ductile materials are developed and validated against laboratory tests. The materials considered are rolled, extruded and cast aluminium alloys, high-strength steels and polymers. In 2009, there have been projects running within the following research areas:

  • Numerical aspects of fracture and crack propagation
  • Fracture in cast materials – mechanisms and modelling
  • Fracture in age-hardening aluminium alloys – mechanisms and modelling
  • Plastic instability and localization in ­metals and alloys
  • Optical measuring techniques (PhD ­project Egil Fagerholt)
  • Extended finite element method (XFEM) (PhD project Gaute Gruben)
  • Fundamentals of fracture (PhD project Marion Fourmeau)
  • Material models for the simulation of aluminium die-castings (PhD project Octavian Knoll)