by Stec, Mateusz; Faleskog, Jonas

In ferritic steels a propagating cleavage microcrack changes its propagation direction as it advances from grain to grain. This is due to differences in the orientation of the cleavage planes of two neighboring grains. In order to reach a cleavage plane in a new grain, a microcrack must first penetrate the grain boundary. Grain boundaries therefore act as natural barriers in cleavage fracture. The influence of a grain boundary and the associated misorientation in cleavage planes on crack arrest is here examined using a 3D finite element model with axisymmetric periodicity, representing two grains whose cleavage planes are tilted and twisted relative to each other. The temperature dependent mechanical properties of ferrite are

by Astafurova, E. G.; Chumlyakov, Yu. I.; Maier, H. J.

The ductile-to-brittle transition (DBT) in Fe-13Mn-1.3C (Hadfield steel, I) and Fe-13Mn-2.7 Al-1.3C (Hadfield steel, II) (wt.%) single crystals oriented along $${[011], [{\bar{{1}}}44]}$$, and [$${\bar{{1}}11}$$] directions was investigated under tension in the temperature interval of 77 to 673 K. The DBT temperature interval was found to be independent of single crystal orientation. The DBT temperatures were estimated (1) as the mean value between the temperature corresponding to the minimum crystal ductility and the one coinciding with the onset of the plateau of the $${\varepsilon}$$(T)-dependence (TDBT1); and (2) as the temperature where the volume fraction of brittle failure on the fracture surfaces was 50% (TDBT2). The DBT temperatures estimated this

by Armero, Francisco; Linder, Christian

This paper presents the extension of some finite elements with embedded strong discontinuities to the fully transient range with the focus on dynamic fracture. Cracks and shear bands are modeled in this setting as discontinuities of the displacement field, the so-called strong discontinuities, propagating through the continuum. These discontinuities are embedded into the finite elements through the proper enhancement of the discrete strain field of the element. General elements, like displacement or assumed strain based elements, can be considered in this framework, capturing sharply the kinematics of the discontinuity for all these cases. The local character of the enhancement (local in the sense of defined at the element level, independently for each element)

by Häusler, C.; Jelitto, H.; Neumeister, P.; Balke, H.; Schneider, G. A.

The fracture behaviour of metal-piezoceramic interfaces under mechanical and electrical loading is examined by four point bending using commercial multilayer actuators. The experiments are performed under stable crack growth in a custom made very stiff testing machine. Besides mechanical loading, a constant electric field was methodically switched on in longitudinal specimen direction. Both poled and unpoled actuators were tested. The crack morphology and the fracture toughness depend on the type of the metal-ceramic interfaces. Assuming different electrical crack boundary conditions of a permeable and an impermeable crack, the field intensity factors K

by Zhang, X. B.; Li, J.; Boukha, S. E.

In order to better understand the failure behaviour of brittle or quasi-brittle materials, we developed a numerical model to analyse the creation of a main macro-crack from a large number of micro-cracks. The boundary element method is used to simulate numerically the formation of a main macro-crack by the growth and the coalescence of the micro-cracks. Different two-dimensional panels in PMMA with initial micro-cracks are studied. The macroscopic responses of the panels are observed by simulating the damage process induced by the growth of micro-cracks. The ultimate tensile stress of the material can be then determined. The material toughness heterogeneity is taken into account in the developed model. The

by Guimard, Jean-Mathieu; Allix, Olivier; Pechnik, Nicolas; Thévenet, Pascal

This paper addresses the question of rate effects in the propagation of delamination cracks in Composite Fiber-Reinforced Plastics (CFRPs). In order to make use of a simple loading device, a mode-II case is used as the basis of the experimental study. The position of the crack is recorded quantitatively by means of a high-speed camera and dedicated image processing techniques. The delamination process is modeled by means of an interfacial Continuum Damage Model (CDM), similar to Cohesive Zone Model (CZM) approaches. In order to make suitable comparison between test and explicit finite element simulation of the test, criterai of proper temporal and spatial discretization have been derived. They ensure

by Ervin, John; Sevostianov, Igor

The paper provides statistical analysis on the effect of mutual positions of individual contacts on the overall resistance and incremental elastic stiffness of a cluster of contacts. We consider an example of a cluster with 76 contact spots of the same radii. The regular lattice of the contacts is compared with the perturbed ones (random clusters). The constriction resistance is determined as a sum of self resistance of the individual contacts and interactions between them. It is shown that the effect of perturbations is very small and, therefore, the mean distance between the centers of individual contacts can be used to estimate the overall cluster resistance. Using elasticity-conductivity cross-property connections, this result is