R. Narasimhan

Experimental and numerical investigations of mixed mode crack growth resistance of a ductile adhesive joint

Polymeric adhesive joints are extensively employed in various industrial and technological applications. It has been observed that in ductile adhesive joints, interface fracture is a common mode of failure which may involve stable crack propagation followed by catastrophic growth. The objectives of this paper are to investigate the effects of bondline thickness and mode mixity on the steady state energy release rate

An Experimental Investigation Of Constraint Effects On Mixed Mode Fracture Initiation In A Ductile Aluminium Alloy

J_{ss}

A finite element analysis of mixed-mode fracture initiation by ductile failure mechanisms

of such a joint. To this end, a combined experimental and numerical investigation of interfacial crack growth is carried out using a modified compact tension shear specimen involving two aluminium plates bonded by a thin ductile adhesive layer. A cohesive zone model along with a simple traction versus separation law is employed in the finite element simulations of crack growth. It is observed that

A numerical fracture analysis of indentation into thin hard films on soft substrates

J_{ss}

Fracture in metallic glasses: mechanics and mechanisms

increases strongly as mode II loading is approached. Also, it enhances with bondline thickness in the above limit. These trends are rationalized by examining the plastic zones obtained from the numerical simulations. The numerically generated

A numerical study of T-stress in dynamically loaded fracture specimens

J_{ss}

A finite element analysis of quasistatic crack growth in a pressure sensitive constrained ductile layer

values are found to agree well with the corresponding experimental results.

A cohesive finite element formulation for modelling fracture and delamination in solids

The effect of constraint on ductile fracture initiation from a notch tip under mode I and mixed mode (involving modes I and II) loading is investigated. To this end, mixed mode fracture experiments are performed with Compact Tension Shear (or CTS) specimen of a ductile 2014-O aluminium alloy. The constraint effects are investigated by considering specimens with two crack length to width ratios. The effect of crack tip constraint on the relationship between the critical value of the J-integral at fracture initiation (J c ) and M p is examined. Further, the micromechanics of mixed mode ductile fracture initiation is investigated by performing fractographic studies and metallographic examination of the mid-plane region of the specimen near the notch tip.

J-Dominance in mixed mode ductile fracture specimens

Ductile crack initiation from a notch under mixed-mode loading involving Modes I and II is studied within the context of plane strain, small-scale yielding conditions. A finite element procedure is employed along with the finite strain version of the Gurson constitutive model that accounts for the ductile failure mechanisms of micro-void nucleation. growth and coalescence. Attention is focused on two issues. Firstly, the competition between two different failure mechanisms, involving micro-void coalescence and localized plastic deformation in the form of an intense band, which are simultaneously operating near the notch under mixed-mode loading, is examined. Secondly. the effect of mixed-mode loading on the critical value of the J-integral at incipient material failure is investigated. The results show that for Mode I predominant loading micro-void coalescence near the blunted portion of the notch is clearly the preponderant failure mechanism. On the other hand, for mixed-mode loading with a high Mode II component, a band of intense plastic strain concentration begins to form near the sharpened part of the notch before failure by micro- void coalescence can occur. Also it is found that the critical value of J decreases as the loading changes from Mode I to Mode II. A local fracture parameter based on notch tip deformation is identified for characterizing mixed-mode failure due to micro-void coalescence.

Numerical Simulations of Hole Growth and Ductile Fracture Initiation Under Mixed-Mode Loading

In this paper, finite element simulations of spherical indentation of a thin hard film deposited on a soft substrate are carried out. The primary objective of this work is to understand the mechanics of fracture of the film due to formation of cylindrical or circumferential cracks extending inwards from the film surface. Also, the role of plastic yielding in the substrate on the above mechanics is studied. To this end, the plastic zone development in the substrate and its influence on the load versus indentation depth characteristics and the stress distribution in the film are first examined. Next, the energy release rate J associated with cylindrical cracks is computed. The variation of J with indentation depth and crack length is investigated. The results show that for cracks located near the indenter axis and at small indentation depth, J decreases over a range of crack lengths, which implies stability of crack growth. This regime vanishes as the location of the crack from the axis increases, particularly for a substrate with low yield strength. Finally, a method for combining experimental load versus indentation depth data with simulation results in order to obtain the fracture energy of the film is proposed.