Gas turbine operating cycles at high temperatures often consist of load reversals mixed with hold times; the latter occurring either as cruise for aero engines or at continuous power output for land based turbines, but also at low frequency loading conditions, e.g. slow “ramp up” of engine thrust. The hold time conditions cause the crack to grow by intergranular fracture due to material damage ...

This paper presents a methodology to quantify the uncertainty in fatigue damage prognosis, applied to structures with complicated geometry and subjected to variable amplitude multi-axial loading. Finite element analysis is used to address the complicated geometry and calculate the stress intensity factors. Multi-modal stress intensity factors due to multi-axial loading are combined to calculate...

The dynamic fracture behavior of layered architectures is experimentally studied. Specifically, crack penetration, trapping, and branching at an interface are examined. A newly introduced optical technique called Digital Gradient Sensing (DGS) that quantifies elasto-optic effects due to a non-uniform state of stress is extended to perform full-field measurements during the fracture event using ...

Polymethylmethacrylate (PMMA) bone cement is a polymeric material that is widely used as a structural orthopedic material. However, it is not an ideal material for bone grafting due to its fragility. Carbon nanotubes (CNTs) have been introduced in order to reinforce PMMA resulting in a composite material which exhibits improved tensile properties, increased fatigue resistance and fracture tough...

using cold working fastener holes is a simple life enhancement procedure that strengthens metallic components by retarding crack growth around a hole. in the present paper, the residual stress field that is induced by the hole expansion process is obtained based on different material models namely elastic perfect plastic, isotropic hardening and kinematic hardening using three-dimensional finit...

The behavior of cleavage crack fronts at grain boundaries in free-standing silicon thin films is investigated through a microtensile experiment. In addition to the crystallographic orientation, the orientation of grain boundary plane also plays a critical role. With respect to the initial crack surface, if the inclination angle is relatively small, the crack tends to penetrate across the bounda...

1 Mines ParisTech, Centre des matériaux, CNRS UMR 7633, BP87 91003 Evry Cedex, France [email protected] Flat to slant crack transition can typically be observed in ductile thin sheet materials. The crack initiates perpendicularly to the loading direction from the notch and then turns to 45° with respect to the loading direction during crack propagation. This phenomenon is, how...

We consider a brittle fracture taking account of self-equilibrated distributed microstresses. To determine how the latter can affect the crack equilibrium and growth, a model of a structured linearly elastic body is introduced consisting of two equal symmetrically arranged layers (or half-planes) connected by an interface as a prospective crack path. The interface is comprised of a discrete set...

Dynamic crack growth is simulated by implementing a cohesive zone model in the generalized interpolation material point (GIMP) method. Multiple velocity fields are used in GIMP to enable handling of discrete discontinuity on either side of the interface. Multilevel refinement is adopted in the region around the crack-tip to resolve higher strain gradients. Numerical simulations of crack growth ...

The role of grain bridging in affecting the initial rising portion of the R-curve and the transient, non-steady-state behavior of short cracks during (cyclic) fatigue-crack propagation has been quantitatively examined in a 99.5% pure alumina. Fatigue-crack growth properties for both long and short ( af < 2 mm) cracks emanating from machined notches (root radius, 15–150 m) were investigated, whe...