Effects of geometric nonlinearities on damage propagation in patched beam-plates subjected to pressure loading
by Carabetta, P. M.; Bottega, W. J.
The problem of edge debonding of patched beam-plates subjected to transverse pressure is examined using two related mathematical models; one which incorporates geometric nonlinearities and the other which neglects them. The models, developed in a prior study, present the energy release rates in self-consistent functional form and yield closed form analytical solutions for the specific problem of interest. Results of numerical simulations based on each model are presented in the form of debond growth paths and compared. The growth paths are subsequently presented with corresponding pre-growth load-deflection paths to further examine the differences resulting from each model. It is seen that significant discrepancies occur between the behaviors predicted by the two
Fatigue fracture of SnAgCu solder joints by microstructural modeling
by Erinc, M.; Assman, T. M.; Schreurs, P. J. G.; Geers, M. G. D.
The ongoing miniaturization trend in the microelectronic industry enforces component sizes to approach the micron, or even the nano scale. At these scales, the underlying microstructural sizes and the geometrical dimensions are comparable. The increasing influence of microscopic entities on the overall mechanical properties makes conventional continuum material models more and more questionable. In this study, the thermomechanical reliability of lead-free BGA solder balls is investigated by microstructural modeling. Microstructural input is provided by orientation imaging microscopy (OIM), converted into a finite element framework. Blowholes in BGA solder balls are examined by optical microscopy and a statistical analysis on their size, position and frequency
Plastic notch stress intensity factors for pointed V-notches under antiplane shear loading
by Lazzarin, P.; Zappalorto, M.
The paper deals with a work-hardening, elastic–plastic, stress analysis of pointed V-notches under antiplane shear deformation loading both under small and large scale yielding. Stress and strain field intensities are expressed in terms of plastic Notch Stress Intensity Factors, which are analytically linked to the corresponding linear elastic ones under small scale yielding. The near tip stress and strain fields are then used to give closed-form expressions for the Strain Energy Density over a circular sector surrounding the notch tip, and for the J-integral parameter, both as a function of the relevant plastic NSIFs, these expressions being valid both under small and large scale yielding.
DOI: 10.1007/s10704-008-9260-0
Online Date: 10/16/2008
A model on twinning-induced crack kinking out of a metal-ceramics interface
by Zhang, Xi
A continuum model is proposed to study the effects of deformation twinning on interface crack kinking in metal/ceramics layered materials. At the final stage of material failure, plastic work hardening exhausts and lattice rotation becomes main mechanism after competing with dislocation gliding. The crack-tip plasticity is established in terms of the second gradient of microrotation due to the coupling effect of the twins. The formed twinning structures not only shield the crack tip, but inhibit further dislocation emission by increasing the near-tip stress levels. A Dislocation-Free Zone (DFZ) can exist in the immediate vicinity of the tip. The model is based on the equivalence of the stresses derived from twin-based crack-tip plasticity, macroscopic plasticity and
Line creep in paper peeling
by Rosti, Jari; Koivisto, Juha; Traversa, Paola; Illa, Xavier; Grasso, Jean-Robert; Alava, Mikko J.
The dynamics of a “peeling front” or an elastic line is studied under creep (constant load) conditions. Our experiments show in most cases an exponential dependence of the creep velocity on the inverse force (mass) applied. In particular, the dynamical correlations of the avalanche activity are discussed here. We compare various avalanche statistics to those of a line with non-local elasticity, and study various measures of the experimental avalanche-avalanche and temporal correlations such as the autocorrelation function of the released energy and aftershock activity. From all these we conclude, that internal avalanche dynamics seems to follow “line depinning”-like behavior, in rough agreement with the
SEM in-situ investigation on failure of nanometallic film/substrate structures under three-point bending loading
by Wang, Xi-Shu; Yan, Cheng-Kun; Li, Ying; Xue, Yibin; Meng, Xiang-Kang; Wu, Bi-Sheng
Three-point bending tests on nanocrystalline Cu or Cu/Ni-film/Cu-substrate samples were conducted in-situ with scanning electron microscopy (SEM) observations. The SEM in-situ observations show undulation deformation of the surface of thin film, as the thin film fractures easily at the concave–convex points of deformation and multi-cracks appear on the surface of the thin film in a periodic fashion. The critical wavelength of undulation is calculated based on experimental observations, which are comparable with the theoretical predictions. For the Cu/Ni multi-layered films/substrate structures, the micro-cracking pattern depends on the interfacial strength between the film and the substrate, rather than the interfacial strength between the layers of films.
Effects of microstructure on flexural strength of biomorphic C/SiC composites
by Park, Hee S.; Jang, Jong J.; Lee, Kyong H.; Lim, Kwang H.; Park, Sang B.; Kim, Yun C.; Hong, Soon H.
Biomorphic C/SiC composites were fabricated from different kinds of wood by liquid silicon infiltration (LSI) following a two-step process. In the first-step, the wood is converted into carbon preforms by pyrolysis in a nitrogen atmosphere. The carbon preforms are then infiltrated by silicon melt at 1,560°C under vacuum to fabricate C/SiC composites. The mechanical properties of the C/SiC composites were characterized by flexural tests at ambient temperature, 1,000, and 1,300°C, and the relationship between mechanical properties and microstructure was analyzed. The flexural strength of the biomorphic composites was strongly dependent on the properties of the carbon
Competition between deflection and penetration at an interface in the vicinity of a main crack
by Martin, E.; Poitou, B.; Leguillon, D.; Gatt, J. M.
The mechanisms which govern crack deflection and crack penetration at interfaces must be understood in order to design composites and layered materials. Experimental observations have shown that a realistic description of crack deflection must take into account the initiation of fracture mechanisms by the stress field of an approaching matrix crack. Fracture mechanisms which include interfacial debonding and penetration are thus analysed in the vicinity of a main crack. For this purpose, a unit cell consisting of a single fibre surrounded by a cylindrical tube of matrix is studied with the help of a finite element model. Initiation stress and nucleation length are determined for both mechanisms by
Effect of thickness on fracture criterion in general yielding fracture mechanics
by Kulkarni, D. M.; Chaudhari, Vikas; Prakash, Ravi; Kumar, A. N.
In this research work, the effect of thickness on fracture criterion is studied for extra deep drawn (EDD) steel sheets. Experimental results are generated on fracture toughness of EDD steel sheets using compact tension specimens and a ‘maximum load’ as a fracture criterion. Critical crack tip opening displacement (CTOD) is found with the help of three methods: plastic hinge model (PHM), crack flank opening angle (CFOA) and finite element model (FEM). The fracture toughness is found to increase with increase in thickness of specimens. The fracture behaviour exhibited characteristics of general yielding fracture mechanics.
DOI: 10.1007/s10704-008-9253-z
Online Date: 8/19/2008
Print publication date: 6/1/2008
Effect of acetic acids on the corrosion crack growth of 3.5NiCrMoV steels in high temperature water: synergistic interaction between stress corrosion and corrosion fatigue
by Maeng, Wan Young
Stress Corrosion Cracking (SCC) tests (pH: 3 ~ 5) and Corrosion Fatigue (CF) tests (R = 0.2, 0.1 Hz) were conducted to evaluate the effect of acetic acid on the corrosion crack growth behavior in high temperature water at 150°C. Acetic acid significantly influenced the corrosion fatigue cracking behavior of turbine disc steels in high temperature water. The CF crack growth rates of turbine disc steels increase until the organic acid concentration reaches a critical saturation value (between pH 4 and pH 3) because of the crack tip sharpening. Below the critical value of pH, the CF crack growth rates decreases because of the crack tip blunting. The corrosion fatigue crack growth rate is accelerated by the interaction of
RSS
