The fatigue crack growth-rate test of rail head, waist, and bottom material for U71Mn welded was carried out. Digital image correlation (DIC) used to capture the full-field displacement. crack-tip position accurately obtained based on displacement data, an accurate opening (CTOD) measurement point found. CTOD values head under overloaded unloaded condition were extracted, area size elastic plas...

The dislocation shielding field at a crack tip was experimentally proven at the atomic scale by measuring the local strain in front of the crack tip using high-resolution transmission electron microscopy (HRTEM) and geometric phase analysis (GPA). Single crystalline (110) silicon wafers were employed. Cracks were introduced using a Vickers indenter at room temperature. The crack tip region was ...

Using molecular dynamics with an accurate many-body potential for metallic Tantalum, we studied crack propagation in a pre-notched nano-slab under uniaxial strain in a [100] direction. We study dislocation emission from the crack tip for various strain rate and temperatures and focus on the inuence of the local temperature at the crack tip on the nature of the crack propagation We nd a close co...

Crack tip shielding phenomena, whereby the "effective crack-driving force" actually experienced at the crack tip is locally reduced, are examined with reference to fatigue crack propagation behavior in metals, composites and ceramics. Sources of shielding are briefly described in terms of mechanisms relying on the production of elastically constrained zones which envelop the crack (zone shieldi...

Evidence has accumulated recently that a crack can propagate on an interface between dissimilar solids at speeds between the smallest and the largest sonic speeds of the constituent solids. Such an intersonic crack has posed several challenges to the existing theory. Assuming that the crack tip is a structureless point, and the solids are linearly elastic all the way to the crack tip, the theor...

ANALYSIS of the deformation field consistent with a Prandtl stress distribution travelling with an advancing plane-strain crack reveals the functional form of the near tip crack profile in an elastic-plastic solid. The crack opening 6 is shown to have the form 6 N r In (const./r) at a distance r from the tip. This observation coupled with data generated from finite element investigations of gro...

Continuum models, based upon both the Volterra and the Peierls descriptions of a screw dislocation ahead of a mode III crack, are used to evaluate the critical loading for dislocation nucleation at the tip of a ® nite pre-blunted crack. Results are presented for various crack tip root radii, for several crack lengths. Moreover, the e€ ect of ledge formation at the crack tip is evaluated. It is ...

A comparative study of fracture in Al is carried out by using quantum mechanical and empirical atomistic description of atomic interaction at crack tip. The former is accomplished with the density functional theory (DFT) based Quasicontinuum method (QCDFT) and the latter with the original Quasicontinuum method (EAM-QC). Aside from quantitative differences, the two descriptions also yield qualit...

As a first step towards a new crack healing methodology for cyclic loading, this paper examines two promising crack-tip shielding mechanisms during fatigue of a microcapsule toughened epoxy. Artificial crack closure is achieved by injecting precatalyzed monomer into the crack plane to form a polymer wedge at the crack tip. The effect of wedge geometry is also considered, as dictated by crack lo...

A HALF-PLANE CRACK propagates dynamically, nominally in the x direction. along the plane _V = 0 in an unbounded solid subjected to remote loading equivalent to a static stress intensity factor K*. The crack front at time t lies along the arc x = c,,t+a_/‘(z, t) where a,) is a constant velocity, J’(z, t) is an arbitrary function, and E is a small parameter. The crack front speed thus varies alon...