An irregular lattice model is proposed for simulating quasistatic fracture in softening materials. Lattice elements are defined on the edges of a Delaunay tessellation of the medium. The dual (Voronoi) tessellation is used to scale the elemental stiffness terms in a manner that renders the lattice elastically homogeneous. This property enables the accurate modeling of heterogeneity, as demonstrated through the elastic stress analyses of fiber composites. A cohesive description of fracture is used to model crack initiation and propagation. Numerical simulations, which demonstrate energy-conserving and grid-insensitive descriptions of cracking, are presented. The model provides a framework for the failure analysis of quasibrittle materials and fiber-reinforced brittle-matrix composites.

Seismic protection systems include the use of special passive devices to introduce supplemental damping into the structure. In building applications, passive devices are normally used in brace configurations and activated by a component of the structural drift. However, in applications where small elastic interstory displacements are expected, the conventional usage of such devices may not be suitable. Lever mechanisms, which amplify the displacements and velocities affecting the damping device, can be employed to overcome this deficiency. This work describes a displacement amplification device (DAD) based on a gear-type mechanism and connected in series with a fluid viscous damper (FVD). Laboratory test results are given here for a small-scale version of the DAD-FVD system. Potential implementations of this amplification system in civil structures are briefly described.