Dr Leon Mishnaevsky from the University of Stuttgart in Germany gave a lecture on “Computational Mesomechanics of Materials: Effect of Microstructure on Damage and Fracture of Materials”. Leon is an Heisenberg Fellow of the German Research Council and leader of a new research group on Strength of Materials. He shares his time between Stuttgart and the Technical University of Darmstadt.

In addition to the distinguished Heisenberg award, he received Fellowships of the Japanese Society for the Promotion of Science; the Japanese Science and Technology Agency; and the German Engineering and Humbolt Foundations. He has held Visiting appointments at the Science University of Tokyo, Rutgers University and the Ecole National Superieure d’Arts et

Matiers. Among other recognition, he has been a Visiting Scholar at the Department of Material Sciences and Engineering of MIT.

During the lecture, Leon discussed advanced finite element techniques for the simulation of material behaviour under mechanical loading advantages, limitations and perspective of different approaches being applied for the simulation of deformations, damage and fracture of materials, taking into consideration their micro- and meso-structure. Development of simulation methods for different aspects of material behaviour (such as unit cell approach, real structure simulation, cohesive zone model, etc) were described including simplified versions of the methods as well as advanced, highly efficient models. The use of finite element models to develop new materials were analysed.

The lecture also presented some experimental tests carried out to determine how micromechanics control the deformation and damage of materials. Three dimensional cases of numerical testing of microstructures were discussed with special emphasis on the strength and damage resistance of light-weight computers for aerospace applications. The effect of particle size variation in damage evaluation was also investigated.

Failure stress of components increases in the following order clustered < regular < random<graded microstructure. Variations of particle size led to the quicker failure of composites.

The study was extended to crack propagation in microstructures, using numerical testing.

Leon presented the following conclusions:

  • Strength and damage resistance of materials can be improved by varying microstructures of the materials
  • The optimum microstructure of materials can be determined by using numerical experiments
  • A number of new numerical tools for the microstructural computational testing of materials have been developed.
  • It was shown that graded microstructures of composites with round particles of constant radius or platelets oriented normal to the loading direction ensure the maximum damage resistance.

The lecture was followed with great interest by the participants and ended with a lively discussion.