Guidelines for Applying Cohesive Models to the Damage Behaviour of Engineering Materials and Structures

This brief provides guidance for the application of cohesive models to determine damage and fracture in materials and structural components. This can be done for configurations with or without a pre-existing crack. Although the brief addresses structural behaviour, the methods described herein may also be applied to any deformation induced material damage and failure, e.g. those occurring during manufacturing processes. The methods described are applicable to the behaviour of ductile metallic materials and structural components made thereof. Hints are also given for applying the cohesive model to other materials

Numerical prediction of the stress-strain response of a lamellar gamma-TiAl polycrystal using a two-scale modelling approach

An advanced model incorporating a two-scale structural description with integrated constitutive formulations of crystal plasticity was adopted to describe the mechanical behaviour of a gamma-TiAl polycrystal with grains of staggered (gamma/alpha_2)-phase lamellae. The numerical model assembles a polycrystalline compound of 64 lamellar grains generated from periodic unit cells (PUC) taking relevant phase configurations. The representative parameter set for the crystal plasticity are estimated by modelling the lamellar deformation and fitting the compression and tension test results in two steps: firstly, the fundamental parameters were identified for a poly-synthetically twinned single crystal (PST) under compression, and secondly, these PST parameters were adjusted to the gamma-TiAl polycrystal consisting of fully lamellar grains. Numerical results show that the compression-tension anomaly in the stress-strain curves can be successfully described by a ‘high-grade’ PUC model including six domain variants of the gamma-phase occurring in the lamellae. Using a PUC model with simplified mapping of lamellar microstructure, the prediction quality remains unsatisfactory with respect to the observed compression and tension anomaly and the crystal parameters are found to be inconsistent. Differently aligned lamellar grains in polycrystalline cubic model are predicted, which showed that the global stress-strain curves are weakly affected by different local alignments (or textures) of the grains, whereas, the single grain analyses show strong variations in local stress-strain curves. The simulated nature of local variations in grain scale stress-strain behaviour accords with the independent results from instrumented indentation testing of the same lamellar polycrystal

Use of spherical indentation technique for measurement of property variations of gamma-TiAl

Novel lightweight intermetallic titanium aluminides, so-called gamma-TiAl, provide good strength and creep resistance up to 700 °C. Their stress–strain behavior at room temperature is however strongly confined in elongation due to their low ductility. For studying the stress–strain behavior of gamma-TiAl, the viscoplastic mechanical properties are determined using spherical indentation testing. The identification problem is solved on the continuum level by neural network analysis, which is based on a unified viscoplasticity model. The identified material parameters are validated by comparing the predicted stress–strain behavior with conventional compression tests at different deformation velocities. It was found that the average response of the indentation tests is in good agreement with the compression tests of round bars. Using a spherical indenter tip of R=0.2 mm, a small volume is tested, offering possibilities for investigation of local property variations due to processing. The experimental indentation curves exhibited wide hysteresis loops, revealing the existence of pure kinematic hardening. Since tensile fracture strength for gamma-TiAl is very low, microcracking occurred during loading as well as during unloading, significantly contributing to the unloading compliance

Guidelines for Applying Cohesive Models to the Damage Behaviour of Engineering Materials and Structures

XII, 89 p. 70 illus., 5 illus. in color.online re

Fracture in Natural and Engineered Systems

IASS-IACM 2008 Session: Fracture in Natural and Engineered Systems -- Session Organizers: Robert HABER (UIUC), Anthony INGRAFFEA (Cornell Univ.) -- Keynote Lecture: "Assessment of stiffened shell structures using advanced fracture and damage mechanics methods" by Karl-Heinz SCHWALBE , Wolfgang BROCKS, Alfred CORNEC, Wernfried Schonfeld, Ingo SCHEIDER, Uwe ZERBST (GKSS Research Centre) -- "Residual strength characterization of integrally-stiffened structures utilizing novel manufacturing technologies" by B. R. SESHADRI, S. W. SMITH , W. M. JOHNSTON, JR. (NASA Langley Research Center) -- "Towards modeling of fragmentation and dynamic delamination interactions in CFRP composites" by Jean-Mathieu GUIMARD , Oliver ALLIX (ENS Cachan), Nicolas PECHNIK (AIRBUS France), Pascal THEVENET (EADS France) -- "A damage-based cohesive model in an adaptive spacetime discontinuous Galerkin method" by Reza ABEDI, Robert B. HABER (University of Illinois at Urbana-Champaign) -- "A unified potential-based cohesive model of mixed-mode fracture" by Glaucio H. PAULINO , Kyoungsoo PARK, Jeffrey ROESLER (The University of Illinois at Urbana-Champaign) -- "Surface and embedded cracks in offshore pipelines subjected to plastic strains" by Espen BERG , Bjorn SKALLERUD, Kjell HOLTHE (Norwegian University of Science and Technology) -- "Automated finite element based predictions of simultaneous crack growth and delamination growth in multi-layers in advanced metallic hybrid stiffened panels using the Alcoa ASPAN-FP tool" by Henry SKLYUT , Michael KULAK, Marcus HEINIMANN, Mark JAMES (Alcoa Technical Center), Olexander V. GONDLIAKH, Roman PASHINSKIJ (KPI, Kiev, Ukraine) -- "Crack trajectory prediction in thin shells using finite element analysis" by Jake D. HOCHHALTER , Ashley D. SPEAR, Anthony R. INGRAFFEA (Cornell University) -- "Analysis of localized failure in metal beams and plates" by Jaka DUJC, Bostjan BRANK (University of Ljubljana), Adnan IBRAHIMBEGOVIC (ENS Cachan

HIGH BARTONELLA SEROPREVALENCE IN PROTEINASE 3-ANTI-NEUTROPHIL CYTOPLASMIC ANTIBODY-ASSOCIATED VASCULITIS

18th International Vasculitis and ANCA Workshop, Univ Tokyo, Tokyo, JAPAN, MAR 25-28, 2017International audienceno abstrac