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International audience; The aim of this work is to estimate the parameters of elastoplastic and damage laws for nodular graphite cast iron from a cyclic uniaxial test on a dog-bone sample. The paper focuses on the identification of material parameters coupling finite element models and full-field measurements. The gap between the measured and simulated data is used to estimate the quality of the proposed constitutive postulates. Last, a cyclic uniaxial experiment is carried out in a lab tomograph to reveal the damage micro-mechanism. Digital volume correlation is used to measure displacement fields in the bulk of the sample. The correlation residuals are used to detect the damage mechanism occurring in the heterogeneous microstructure of the material.

The effect of sandblasting and sand paper cleaning on the mechanical properties of corroded steel specimens is studied. An experimental assessment of tensile strength of small scale steel corroded specimens is performed. The specimens were cut from a box girder, initially corroded in sea water conditions and later the specimens were subjected to sandblast and sandpaper cleaning. Tension tests are performed to determine the mechanical properties of three groups of specimens, including non-maintained, sandblasted, and sandpaper cleaned, corroded specimen, allowing the estimation of the modulus of elasticity, yield stress, tensile strength, total uniform elongation and n and K strength parameters. Regression equations of the material properties are derived as a function of the degree of corrosion and maintenance actions. It is shown that these two methods of removing corrosion products from the surface of plate specimens have different effects on their mechanical properties and stress-strain relationships. Based on the achieved results a simplified stress-strain curve accounting for the corrosion degradation and maintenance actions is developed, which may be used for structural assessment of ageing marine structures.

The pipes for water and gas distribution are mainly made of polyethylene. An accurate modelling of the nonlinear and time-dependent material responses of such structures represent a key for the prediction of structural integrity and reliability, as well as their design and optimization process. In the present paper the creep fracture mechanisms by slow crack growth in polyethylene PE100 are investigated, both experimentally and numerically. Experimental tests have been performed on the standard specimen type 1BA and axisymmetrically cracked specimen denoted as a full-notched crack tensile (FNCT) specimen [1]. Based on the experimental results, the primary/secondary creep constitutive model is proposed. It is shown that the crucial fracture mechanics parameter for determination of the lifetime of a PE100 material is steady-state creep C*-integral [2]. In addition, the Failure Assessment Diagram in the form of C*–integral versus time to failure is proposed [1]. Computational algorithm for the integration of the primary/secondary creep constitutive law is derived [3] and implemented at the material point level in the finite element code ABAQUS by using the user subroutine CREEP [4]. In order to check the accuracy of the derived algorithm, the creep simulation on a FNCT specimen is performed. Furthermore, the detailed finite element solutions for the C*-integral values are obtained for a thick-walled polyethylene gas pipe with an external axial surface crack.

International audience; In this paper the nonlinear behavior of nodular graphite cast iron is investigated under in-plane biaxial loading regimes. Multiaxial experiments enable a wide variety of loading paths to be investigated. In the presented study two loading histories are proposed, namely, equibiaxial and " snail " loading paths corresponding to proportional and nonproportional regimes. The center gauge zone of the testing cruciform specimen is observed. Mean strain fluctuations are measured and presented in order to determine the material response for the prescribed biaxial loading paths. For the equibiaxial and snail loading histories finite element model updating will couple 2D-DIC measurements with 3D-FE analyses to calibrate material parameters describing elasticity, isotropic or kinematic hardening.

This paper investigates the behaviour of a receding contact when a cylindrical indenter presses an unbonded layer resting on a substrate. The problem is analysed by using FEM within the scope of the linear theory of elasticity and under the assumption of plane strain. This paper presents new and original results in the analysis of influence of load intensity and indenter geometry on the contact parameters. In addition, in the investigation into material properties a reference analysis was carried out for the case of material similarity between all three bodies, and material properties were subsequently varied for each body. This class of problems shows nonlinear behaviour, with both contact pressure distributions and contact half-widths found to depend nonlinearly on the applied load. The experimental analysis was carried out by employing the digital image correlation method and the ARAMIS 4M system was used. The obtained measurement results show good agreement with the numerical results.

An experimental and numerical study of the cyclic deformation and low-cycle fatigue behaviour of the aluminium alloy AlCu5BiPb–T8 is presented. The experimental program included monotonic tensile tests, symmetric and unsymmetric strain-controlled fatigue tests, fracture toughness tests, as well as fatigue crack initiation and propagation tests. Within the framework of numerical investigations an efficient algorithm for modelling of cyclic plasticity is proposed. This algorithm is implemented into the finite element program ABAQUS and applied to the analysis of a crack growth near the notch. The accuracy of the computational procedure is tested by comparing the computed results with the real experimental data.

The present paper evaluates the fatigue life of ductile nodular cast iron EN-GJS-400-18LT with four different microstructures. Characterisation of the graphite morphology and the matrix microstructure is performed on 50 samples for every material type. Tensile stress–strain curves, symmetrical and unsymmetrical stress–strain hysteresis loops, cyclic stress–strain curves, crack resistance curves and fatigue life curves of these four microstructures are obtained. Experimental results show that size, shape and distribution of the graphite nodules has no significant influence on cyclic hardening of the material but they play a great role in the crack initiation and propagation process. It is shown that the larger irregularly shaped nodules reduce fracture toughness and fatigue strength. Furthermore, the results demonstrated that pearlitic phase does not strongly affect fatigue life if its proportion does not exceed 10%. The monitoring of crack length during the tests is performed by an optical method developed in the present work.

This paper presents an experimental and numerical study on two different types of the nodular cast iron EN-GJS-400-18-LT. The experimental procedure includes symmetrical and unsymmetrical strain controlled tests on the cylindrical specimens as well as crack initiation and propagation tests on the compact tension and single edged notched specimens. Different loading regimes are applied, and monitoring of the crack length during the tests is performed by an optical system. Within the framework of numerical investigations an efficient algorithm for modelling of cyclic plasticity is examined. Experimental results show that two material types have significantly different the crack behaviour.

The effects of smoothing non-smooth function on estimation of dynamical stability of the periodic response determined in the frequency domain are considered in this paper. For that purpose, a simple single-degree-of-freedom system with piecewise-linear force-displacement relationship subjected to a harmonic force excitation is analyzed. Stability of the periodic response obtained in the frequency domain by the incremental harmonic balance method is determined by using the Floquet-Liapounov theorem. Results obtained are verified in the time domain by the method of piecing the exact solutions and Runge-Kutta integration routine.