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Reinforcement in composite and notched structures has long been the objective of many researchers. One of the commonly used solutions is hybrid composite. Other recently reemerged solutions are graded materials. These respond, according to their modes of solicitation, to the targeted resistance objectives. However, composites with UD (unidirectional) fiber quality limit the choice of structural grading solely based on their thickness. Using the finite element method and the ABAQUS calculation code, this work presents the embodiment through numerical prediction of an idea based on the concept of material grading by FGM function. The objective of this approach is to introduce the volumetric fraction of the FGM concept into the Fiber-Matrix mixing laws in UD composite. Thickness-graded composites are subjected to a volumetric fraction function raised to the power of a parameter called volumetric fraction index (n). These structures, according to the proposed concepts, are analyzed under thermomechanical loading. The proposed grading of these composites is based on the presence of fibers in the matrix, where the fiber is denser on one side, called the simple concept C-S. The other two symmetrical concepts, named C-2 and C-3, present denser fibers in the middle and on both sides of the plate, respectively. These proposed concepts aim to observe how damage is caused by different responses and levels. The results under the different analyzed parameters are evaluated and compared to the results of the two other non-graded composites, thus showing the limits of those that are graded in terms of properties. According to the thermomechanical loading, the proposed graded composite has demonstrated a resistance overcapacity by the grading index (n) or their locations by concept C1- and C-2 of fibers have played a role in optimizing this capacity. The results also show that damage is caused by deformation overcapacity. [ABSTRACT FROM AUTHOR]

AbstractElbow joints in pressurized tubular structures experience biaxial stress due to their geometry. Under cyclic flexural loading, cross-sectional ovalization is the primary damage mechanism. This study employs finite element analysis using ABAQUS to investigate damage caused by cyclic flexural loading. The research aims to analyze the mixed hardening behavior of pressurized elbows under combined and oriented bending moments, both in-plane (closure) and out-of-plane (opening). Steel hardening behavior is modeled using a combined approach: the Ohno-Wang model for kinematic hardening and an isotropic model, both implemented in ABAQUS with parameters calibrated to experimental data. This strain-rate-independent plasticity model follows the Von Mises equivalent stress flow theory. Cyclic behavior results are presented through hysteresis curves of bending moment versus angular displacement, up to a critical moment indicating structural failure. Damage analysis due to crack propagation under cyclic loading utilizes the eXtended Finite Element Method (XFEM). The study reveals a strong correlation between elbow resistance and the orientation of combined cyclic loading relative to the bending moment planes. This finding highlights the importance of considering load orientation in the design and assessment of pressurized pipe elbows. [ABSTRACT FROM AUTHOR]

Given the various loading cases possible in tubular structures, cyclic bending moment is one of the frequent cases presented in bent structures attached by straight tubular parts, as in straight tubular structures or a connecting tubular element; their loading is under various cyclic modalities; analyzing these pressurized tubular structures or unlocking the difficulties of numerically predicting or approximating to possible and actual fatigue behavior is of interest to several researchers, this work opts to use 316LN stainless steel, also known as Z2CND18.12 N of an elbow attached by straight parts, the study of the cyclic response up to the damage of the pressurized bend is aimed at evaluating the behavior under the effects of the parameters analyzed, namely the amplitude and the pattern of the cyclic bending moment, The fatigue behavior of the steel is formulated as a combined isotropic and kinematic Ohno-Wang model introduced into the ABAQUS calculation code by parameters calibrated to the experimental, using the finite element method. The damage to the structure under a high cyclic bending moment is introduced into the structure mesh. Of the cyclic accumulation of stress, the damage will occur in the structure by crack initiation and propagation, hence using the XFEM technique. The non-linear behavior, independent of the strain rate, is based on the Von Mises equivalent stress flow theory by mode effect at high cyclic bending moment; the results presented by moment-rotation curves show a significant effect on the response, as well as the level of damage. That damage by crack initiation and propagation precedes excessive ovalization at the level of the elbow cross-section. The approach followed in this analysis and the reliability of the results obtained were previously based on a validation of experimental results, which showed good agreement with the numerical model used. [ABSTRACT FROM AUTHOR]

Given their many advantages, composite materials have always proven their effectiveness. As in aeronautical structures where reinforcement techniques are used, their application is widened in various fields. Analyzing these composite structures or proposing new concepts for reinforcements remains an interest of several researchers. This work opts for the use of a hybrid composite of a tubular structure of an elbow attached by straight parts. The structural composite is twill. The aim of the elbow damage study is to evaluate the proposed reinforcement concept. The stiffness and damage parameters of the plies are introduced at the size of the fiber and according to the thickness per row of finite elements, hence the use of an adequate meshing technique. The linear behavior follows the equivalent stress flow theory of Von Mises. The results presented as moment-rotation curves were evaluated under design effect and bending moment mode. Depending on the loading conditions, the proposed concept of the hybrid composite showed an overcapacity of resistance where the location of the fiber qualities played the optimization of this capacity. The structure has shown even more resistance for certain locations of the folds which are reinforced in thickness. Depending on the bending moment mode applied, the results show that the damage is caused at very low deformations by ovalization of the elbow and in fiber tension. [ABSTRACT FROM AUTHOR]

This study examines the mechanical behavior of notched materials under severe uniaxial monotonic loading until failure. Instead of focusing on the structural damages caused by notches, this study explores the complex loading experienced by notches. Finite element analysis of notched specimens is performed using ABAQUS-explicit. It is based on Von Mises' flow theory and the Gurson–Tvergaard–Needleman damage model for void growth and coalescence. Functionally graded materials are strategically applied around the notches to enhance structural integrity. Concept-1 is proposed near the notch for maximum reinforcement, while Concept-2 is proposed in the central graded area for the optimal transition between the two concepts. A volumetric fraction index is an essential tool for enhancing gradation design robustness. As a result, the model can accurately predict ductile ruptures and void evolutions, proving that gradation concepts play a pivotal role in the behavior of structures. As a result of analyzing structures subjected to severe loads in real-world environments within industries such as aerospace, automotive, and construction, this groundbreaking work contributes to the fundamental understanding of the mechanical behavior of materials under extreme loading conditions. [ABSTRACT FROM AUTHOR]

AbstractThe elbow is presented in pressurized tubular structures as a connecting element, generally subjected to bending moments either out-of-plane or in-plane, in closure or opening. Another mode of bending moment that can also occur in these tubular structures is the combined bending moment between out-of-plane and in-plane in closure, or out-of-plane and in-plane in opening. In this work, to better present the potential severity caused by this loading mode, an elbow structure attached by straight tubular sections made of X60 steel is analyzed and its damage under this combined bending moment with orientations between the plane and out-of-plane of the structure is discussed. A reinforcement proposal will be made in the second part of this work. Indeed, the structure is pretreated thermally at the elbow, resulting in a graded structure along the thickness with two different material constituents: the base metal and the thermally affected zone (HAZ). Based on the concept of Functionally Graded Materials (FGM), the gradation is by volume fraction between the base metal and the HAZ, following a power law function of a volume fraction index (n). This graded property is introduced along the thickness by finite element layers. The elastic-plastic behavior of the HAZ-base metal mixture is modeled using the Voce model and the Von Mises equivalent stress flow theory. Using the XFEM technique(extended finite element method), the damage of the pressurized and thermally treated structure under a combined out-of-plane bending moment shows that these parameters condition the response and the level of damage. [ABSTRACT FROM AUTHOR]

AbstractAccording to cyclic loading modes, highly pressurized tubular elements, such as those in elbows, differ from other straight tubular structures in their modes of stress and damage. This work aims to perform a numerical prediction of a tubular structure. It consists of an X52 steel elbow welded to X65 grade ends by straight tubular sections. This pressurized structure is subjected to strong cyclic loading in bending moment applied until damage occurs. The bending moment is combined with different orientations between the closing or opening moment and the out-of-plane moment, presenting a possible but rarely analyzed situation. This cyclic loading mode is taken as an evaluative parameter in its various amplitudes, orientations, and patterns. The cyclic hardening of the elbow and straight tubular sections, including those of the welded joints, are all formulated by the combined isotropic and kinematic model introduced in the ABAQUS calculation code with parameters calibrated according to the Voce model and experimental results, using plasticity by the Von Mises equivalent stress flow theory. The appropriate XFEM (Extended Finite Element Method) technique is used in conjunction with the hardening model to overcome numerical calculation difficulties and predict damage in traction laws, separation by crack initiation and propagation. The results, in the form of hysteresis curves in cyclic bending moment and angular displacement, have shown a strong dependency that conditions the structure’s response as well as the level of its damage. [ABSTRACT FROM AUTHOR]