Stress concentration

About: Stress concentration is a research topic. Over the lifetime, 23250 publications have been published within this topic receiving 422911 citations.

Fracture in mechanism-based strain gradient plasticity

Abstract: In a remarkable series of experiments, Elssner, Korn and Ruehle (Scripta Metall. Mater. 31 (1994) 1037) observed cleavage fracture in ductile materials, a phenomenon that cannot be explained by classical plasticity theories. In this paper we present a study of fracture by the theory of mechanism-based strain gradient (MSG) plasticity (Gao et al., J. Mech. Phys. Solids 47 (1999b) 1239); Huang et al., J. Mech. Phys. Solids 48 (2000a) 99). It is established that, at a distance much larger than the dislocation spacing such that continuum plasticity is applicable, the stress level in MSG plasticity is significantly higher than that in classical plasticity near the crack tip. The numerical results also show that the crack tip stress singularity in MSG plasticity is higher than that in the HRR field, and it exceeds or equals to the square-root singularity. This study provides a means to explain the observed cleavage fracture in ductile material.

High‐Temperature Failure of an Alumina‐Silicon Carbide Composite under Cyclic loads: Mechanisms of Fatigue Crack‐Tip Damage

Abstract: Experimental results are presented on the mechanisms of tensile cyclic fatigue crack growth in an A1203-33-vol%-SiC-whisker composite at 1400°C. The ceramic composite exhibits subcritical fatigue crack propagation at stress-intensity-fator values far below the fracture toughness. The fatigue characterized by the stressintensity-factor range, ΔK, and crack propagation rates are found to be strongly sensitive to the mean stress (load ratio) and the frequency of the fatigue cycle. Detailed transmission electron microscopy of the fatigue crack-tip region, in conjunction with optical microscopy, reveals that the principal mechanism of permanent damage ahead of the advancing crack is the nucleation and growth of interfacial flaws. The oxidation of Sic whiskers in the crack-tip region leads to the formation of a silica-glass phase in the 1400°C air environment. The viscous flow of glass causes debonding of the whisker-matrix interface; the nucleation, growth, and coalescence of interfacial cavities aids in developing a diffuse microcrack zone at the fatigue crack tip. The shielding effect and periodic crack branching promoted by the microcracks result in an apparently benefcial fatigue crack-growth resistance in the A1203—SiC composite, as compared with the unreinforced alumina with a comparable grain size. A comparison of static and cyclic load crack velocities is provided to gain insight into the mechanisms of elevated temperature fatigue in ceramic composites.

Initiation of fracture at the interface corner of bi-material joints

Abstract: Within the context of linear elasticity, a stress singularity of the form Hr λ −1 may exist at the interface corner of a bi-material joint, where r is the radial distance from the corner, H is the stress intensity factor and λ −1 is the order of the singularity. Recent experimental results in the literature support the use of a critical value of the intensity factor H = H c as a fracture initiation criterion at the interface corner. In this paper, we examine the validity and limitations of this criterion for predicting the onset of fracture in a butt joint consisting of a thin layer of an elastic–plastic adhesive layer sandwiched between two elastic adherends. The evolution of plastic deformation at the corner is determined theoretically and by the finite element method, and the solution is compared with the extent of the elastic singular field. It is shown that H c is a valid fracture parameter if h > B ( H c / σ Y ) 1/(1− λ ) where the non-dimensional constant B =100 for β =0 and B =13 for β = α /4. Here, h is the thickness of the adhesive layer, σ Y is the uniaxial yield stress of the bulk adhesive and ( α , β ) are Dundurs’ parameters (Dundurs, J., J. Appl. Mech. 36 (1969) 650). Experimental results for aluminium/epoxy/aluminium and brass/solder/brass sandwiched joints are used to assess the role of plastic deformation on the validity of the failure criterion.