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 sVoronoid 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 demonstr...

The relationships between a resistance curve (R-curve), the corresponding fracture process zone length, the shape of the traction/displacement softening law, and the propagation of fracture are examined in the context of the through-the-thickness fracture of composite laminates. A procedure that accounts for R-curve toughening mechanisms by superposing bilinear cohesive elements is proposed. Si...

An anisotropic cohesive model of fracture is applied to the numerical simulation of Coker and Rosakis experiments (2001). In these experiments, a unidirectional graphite–epoxy composites plate was impacted with a projectile, resulting in an intersonic shear-dominated crack growth. The simulations account for explicit crack nucleation––through a selfadaptive remeshing procedure––crack closure an...

Recent estimates of fracture energy G' in earthquakes show a power-law dependence with slip u which can be summarized as G' ∝ ua where a is a positive real slightly larger than one. For cracks with sliding friction, fracture energy can be equated to Gf : the post-failure integral of the dynamic weakening curve. If the dominant dissipative process in earthquakes is friction, G' and Gf should be ...

Presented is a concise summary of recent Northwestern University studies of six new problems. First, the decrease of fracture energy during crack propagation through a boundary layer, documented by Hu and Wittmann, is shown to be captured by a cohesive crack model in which the softening tail slope depends on the distance from boundary (which causes an apparent size effect on fracture energy and...

The primary objective of this work was to analyse the adequacy of the Double Cantilever Beam (DCB) test in determining fracture toughness under pure mode I loading of cortical bone tissue. A new data reduction scheme based on specimen compliance and the crack equivalent concept was used to overcome the difficulties inherent in crack monitoring during its growth. It provides a complete resistanc...

Fatigue and fracture mechanisms have been studied in a steel-based metal matrix composite (MMC), comprising a 316L austenitic matrix reinforced with 25 wt% particulate titanium diboride (TiB2). The fracture toughness was determined in the as-HIPped condition as being slightly below 30 MPa√m. Fatigue crack growth rates have been determined, and corrected for the effects of crack closure. The fra...

Crack growth along an interface joining an elastic-plastic solid to a solid that does not yield plastically is studied numerically, accounting for mixed mode loading under conditions of small scale yielding. The fracture process is represented in terms of a cohesive zone model, for which the work of separation per unit area and the peak stress required for separation are basic parameters; but w...

For composite structure, fracture toughness is a dominant parameter when using cohesive laws to predict the nominal strength. In the present study the compact tension test is performed on composites structures and is simulated using FEM. The process of fracture takes places in two sequential stages, crack initiation and crack propagation. The critical energy release rate is determined using the...

INTRODUCTION CAD/CAM (computer-aided design and computer-aided manufacturing) systems have refreshed the idea of chair-side production of restorations, but the fracture of ceramic veneers remains a problem. Cementation with glass fibers may improve the fracture strengths and affect the failure modes of CAD/CAM-generated ceramic veneers. Therefore, this study compared the fracture strengths of c...