3D crack identification using the Nelder-Mead Simplex algorithm combined with a random generation of crack positions

In this paper, we present a scheme for cracks identification in three-dimensional linear elastic mechanical components. The scheme uses a boundary element method for solving the forward problem and the Nelder-Mead simplex numerical optimization algorithm coupled with a low discrepancy sequence in order to identify an embedded crack. The crack detection process is achieved through minimizing an objective function defined as the difference between measured strains and computed ones, at some specific sensors on the domain boundaries. Through the optimization procedure, the crack surface is modelled by geometrical parameters, which serve as identity variables. Numerical simulations are conducted to determine the identity parameters of an embedded elliptical crack, with measures randomly perturbed and the residual norm regularized in order to provide an efficient and numerically stable solution to measurement noise. The accuracy of this method is investigated in the identification of cracks over two examples. Through the treated examples, we showed that the method exhibits good stability with respect to measurement noise and convergent results could be achieved without restrictions on the selected initial values of the crack parameters

Enhancing mechanical properties and crack resistance of earth-sand building materials through alfa fiber reinforcement: An experimental investigation

This paper investigates enhancing the mechanical properties and crack resistance of earth-sand building materials by incorporating Alfa fibers, derived from the Alfa plant. Earth-based construction materials, known for their sustainability, face challenges in mechanical performance and cracking. The study explores a composite of earth (60 wt%) and sand (40 wt%) reinforced with Alfa fibers of varying lengths and rates. Tensile strength and water absorption of the fibers were assessed, and prismatic specimens (40x40x160 mm3 ) with different cutting lengths were tested. Results inform the potential of Alfa fibers for improving earth-based material performance. Incorporating 2% wt of Alfa fibers reduced the unit weight of the composite from 1849 kg/m3 to 1632 kg/m3 , resulting in a slight material weight decrease. Compared to unreinforced adobe specimens, fibrous samples exhibited lower linear shrinkage rates and improved mechanical behavior, with 2% wt of 3 cm fibers showing optimal performance. The fibers effectively impeded crack propagation, with both length and content influencing crack attenuation. However, microstructural observation revealed poor fiber/matrix adhesion, negatively impacting adobe specimen compactness despite enhanced mechanical properties

Simulation de Ia propagation de fissures dans les solides elastiques en modes mixtes par Ia methode des equations integrales duales

International audienceThe present paper is concerned with the effective numerical implementation of the two dimensional Dual Boundary element method to analyse the mixed-mode crack growth All the boundaries are discretized with discontinuous quadratic boundary elements and the crack-tip is modeled by singular elements that exactly represent the strain field singularity $1/\sqrt{r}$. The Stress lntensity Factors can be computed very accurately from the crack opening dis placement at collocation points extremely close to the crack tip The algorithm is applied to severa[ two dimensional examples and the results obtained are in very good agreement with experimental results.Nous présentons dans cet article une démarche numérique basée sur la méthode des éléments de frontière permettant de résoudre différents problèmes complexes de propagation de fissures dans les solides élastiques en modes mixtes Le contour de la structure est discrétisé par des éléments quadratiques, sauf en fond de fissure que nous représentons par des éléments singuliers permettant d'y reproduire la singularité des déformations. Les facteurs d'intensité de contraintes sont évalués à partir des déplacements des nœuds de l'élément singulier. Une comparaison est effectuée avec des résultats expérimentaux de la littérature

Crack identification in plates-type structures using natural frequencies coupled with successful history-based adaptive differential evolution algorithm

In this study, a new approach, for identification and characterization of straight cracks in plates-like structures, is presented. The finite element method using a commercial software (Abaqus)is coupled with successful history-based adaptive differential evolution algorithm (SHADE) which, ensures the minimization of the objective function based on the mean relative error, that is defined as the difference between the measured (experimental) frequencies of a plate with an unknown crack identity and numerical frequencies of a cracked plate given by the approach Shade/FEM. This method will be applied on a steel thin plate to find the identity of the crack given by length, orientation and centre coordinates. Two strategies are applied to validate the effectiveness of the proposed approach. The first one, is based on the inverse problem using natural frequencies of a plate withknown crack identity obtained by a modal simulation on Abaqus. In the second, the experimental frequencies of a cracked plate were used. With just a population size of 25 and 150 iterations, the results show a good accuracy of the proposed approach with a relative error of the objective function less than 0.8%

Crack identification in plates-type structures using natural frequencies coupled with successful history-based adaptive differential evolution algorithm

In this study, a new approach, for identification and characterization of straight cracks in plates-like structures, is presented. The finite element method using a commercial software (Abaqus)is coupled with successful history-based adaptive differential evolution algorithm (SHADE) which, ensures the minimization of the objective function based on the mean relative error, that is defined as the difference between the measured (experimental) frequencies of a plate with an unknown crack identity and numerical frequencies of a cracked plate given by the approach Shade/FEM. This method will be applied on a steel thin plate to find the identity of the crack given by length, orientation and centre coordinates. Two strategies are applied to validate the effectiveness of the proposed approach. The first one, is based on the inverse problem using natural frequencies of a plate withknown crack identity obtained by a modal simulation on Abaqus. In the second, the experimental frequencies of a cracked plate were used. With just a population size of 25 and 150 iterations, the results show a good accuracy of the proposed approach with a relative error of the objective function less than 0.8%

Identification et caractérisation des défauts en milieux axisymétriques par la méthode des équations intégrales duales

COMPIEGNE-BU (601592101) / SudocSudocFranceF

Simulation du contact dans les assemblages boulonnés fissurés

La modélisation d’un assemblage fissuré nécessite d’avoir une méthode de représentation des fixations adaptée aux exigences voulues. En effet, il est parfois suffisant de respecter le taux d’effort transféré par la fixation. Dans d’autre cas, c’est la contrainte locale au bord du trou de l’une des plaques que l’on désire connaître. Dans ce dernier cas, il est nécessaire de tenir compte du contact entre le boulon et les plaques ainsi que du contact des plaques entre elles. Le problème du contact dans les assemblages boulonnés fissurés est un problème tridimensionnel complexe (contact boulon - plaque, contact latéral plaque - plaque, flexion du boulon, serrage du boulon...). On présente dans cet article une approche bidimensionnelle pour la résolution de ce genre de problème tout en répondant aux exigences voulues (respecter le taux d’effort transféré par la fixation et obtention du champ de contraintes autour du trou). Les résultats de simulation de la propagation de fissures par la méthode des équations intégrales couplée à la procédure itérative de contact sont comparés avec des résultats expérimentau

Numerical method coupling finite elements and boundary elements to model forming process tools

Nowadays, the simulation of forming process is rather well integrated in the industrial numerical codes. However, in order to take into account the possible modifications of the tool during rates of working, a dedicated numerical software is currently developed within the laboratory Roberval, this software allows to simulate forming process. The tool is discretized by boundary elements and the product, which is subjected to non-linearities, is discretized by finite elements. For the product, an isotrope law of behaviour is integrated, and the damage is taken into account by the uncoupled Rice and Tracey model. This paper deals with a contact algorithm, coupling boundary elements and finite elements, programmed in the software KSP. For that, friction is described by the Coulomb law and the resolution of contact problems is done by the penalty method. An adaptive step has been developed in order to increase the robustness of the contact algorith

Conception d'outil par couplage des éléments de domaine et de contour

À l'heure actuelle, la conception des procédés de mise en forme s'appuie grandement sur la simulation numérique via l'utilisation de codes industriels. Ces simulations portent souvent sur la déformation des pièces et rarement sur la durée de vie des outils. Afin de prendre en compte les éventuelles modifications de l'outil au cours des cadences de mise en forme, nous développons un outil numérique dédié. Cet outil numérique permettra plus particulièrement l'identification des critères de fatigue de l'outil. Il sera alors possible de concevoir des formes optimales d'outils permettant d'augmenter leur durée de vie tout en assurant la qualité exigée sur les pièces ainsi fabriquées. Ce dernier utilise un couplage en contact avec frottement de la méthode des éléments-finis – pour modéliser la pièce – et de la méthode des éléments de frontière – pour modéliser l'outil. Dans cet article, nous traiterons un exemple de cisaillement