Critical Analysis of “Maximum Stress Failure Criterion” for Composite Materials

The paper deals with critical considerations upon different points of view that were enounced by some authors referring to Maximum Stress Failure Criterion for composite materials. The considerations stem both from a comparative analysis of the mentioned theories and from the results of theoretical and numerical tests performed by the authors

INCAS BULLETIN, Volume 15, Issue 3/ 2023, pp. 31 – 46 (P) ISSN 2066-8201, (E) ISSN 2247-4528 Off-axis response and shear characterization of unidirectional ply-level hybrid carbon-fiber-reinforced polymer materials

Composite materials, among them Carbon Fiber Reinforced Polymers (CFRP), have become a key material in structural applications for lightweight structures such as spacecraft and aircraft. CFRP can be found under various quality grades and their mechanical performances increase with their cost and quality grade. In order to limit the costs of the material without degrading technical performances, hybridization could be of interest. However, assessing the conservation of quality standards of hybridized CFRP is crucial. This paper investigates the off-axis mechanical response of ply-level hybrid carbon composites, with varying thickness and material quality. Two types of carbon fiber prepregs were combined in the same laminate using symmetric and asymmetric stacking sequences. Monotonic quasi-static off-axis tests were performed to evaluate the non-linear stress-strain behavior of the laminates, with Digital Image Correlation used to measure strain. The apparent elastic modulus and the in-plane shear modulus were evaluated from the tensile tests at three off-axis angles. The results indicate that the hybrid laminates exhibit higher failure stress levels compared to simple laminates, with an intermediate failure strain. Overall, this study provides insights into the off-axis mechanical behavior of ply-level hybrid carbon fiber composites, with potential applications in the design of composite structures

Strain resolving method of composite plane plates

The paper deals with the extension of isotropic plates problem to the case of composite plates. In order to perform it, the Kirchhoff-Love hypotheses were “softened” by some additional ones. Considering the constitutive laws for composite materials the stress functions were eliminated by using Cauchy equations. As a result a partial derivative equation in displacements was obtained. Finally the boundary condition formulation was extended for the case of complex composite plates

Attitude Dynamics of a Spinning Rocket with Internal Fluid Whirling Motion

This paper evaluates the impact that helical motion of fluid products of combustion within the combustion chamber of a rocket can have on the attitude dynamics of rocket systems. By developing the study presented by Sookgaew (2004), we determined the configuration of the Coriolis moment components, which catch the impact of the combustion product’s whirling motion, for the radial and centripetal propellant burn pattern specific to S-5M and S-5K solid rocket motors. We continue the investigation of the effects of internal whirling motion of fluid products of combustion on the attitude behavior of variable mass systems of the rocket type by examining the spin motion and transverse attitude motion of such systems. The results obtained show that internal fluid whirling motion can cause appreciable deviations in spin rate predictions, and also affects the frequencies of the transverse angular velocity components

Modélisation 2D de l impact d une structure sur l eau (Initiation de l endommagement)

Le travail réalisé au cours de cette thèse a porté sur la modélisation de impact d un corps 2D sur une surface fluide, ainsi que l apparition de son endommagement (au sens rupture macroscopique) associé. Une des applications visées est la modélisation des efforts de tossage (slamming) s exerçant sur la partie avant d un bâtiment de surface sous conditions de mer sévéres. Les contraintes et déformations fluctuantes, engendrées sur la carène du navire, peuvent provoquer une dégradation mécanique prématurée par fatigue. Les travaux principaux ont consisté à développer puis valider un outil numérique (lmpact++ ABAQUS) permettant l étude de l interaction fluide-structure lors du contact violent entre un corps à géométrie simple (structures 2D planes et axisymétriques à section simple [diédre et cône] ou complexe [géométrie variable de la génératrice- cylindre, sphère, paraboloïde de révolution, ellipsoïde de révolution, etc]) et une surface libre d eau. Cette approche a pris en compte les déformations de la structure lors de la détermination de l écoulement du fluide et réciproquement. Au final, notre outil numérique s appuie sur le code éléments finis industriel ABAQUS et permet de calculer les états de contraintes, de déformations, les énergies et les efforts globaux pour une structure solide 2D impactant un fluide. Le second objectif de l étude était, en vue d un dimensionnement des coques navales, d apporter une représentation quantitative et qualitative de l amorçage du dommage d une structure métallique, et plus précisément de pouvoir prédire, lors de ces impacts répétés avec l eau, l instant et l endroit d apparition de l endommagement microscopique (au sens rupture). Nous avons choisi de représenter ces phénomènes par des conditions de perte d unicité de la solution en vitesse (bifurcation) dans léquilibre mécanique du solide déformable.The research work in this thesis covers the modeling of the impact of a 2D body with water and the subsequent appearance of macroscopic fractures. The main application is the modeling of the slamming forces acting on the ship structure in severe sea conditions. The time-dependent stresses and strains on a ship hull can provoke a premature mechanical failure due to fatigue. The main work consists in the development and validation of a numerical tool (lmpact++ ABAQUS) simulating the fluid-structure interaction during the violent impact of a body of a simple geometry (wedge, cone, cylinder, sphere, axisymmetric parabolic body, ellipsoid, etc) on a free water surface. This approach considers the effect of the deformation of the structure on the flow and vive versa. The numerical tool is based on the commercial finite element code ASAQUS and permits to calculate thee stresses and deformations, energies and the global forces for a 2D solid structure inipacting a fluid. In view of the long-term goal of aiding structural design of ships, the second objective was to bring a quantitative and qualitative representation of the beginning of the damage of a metallic structure impacting water, namely to predict the time and location of fracture initiation due to repeated slamming impacts. These phenomena are modeled here by a bifurcation of the solution for the velocity in the mechanical equilibrium equation for the deformable body.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF

Damage assessment through cyclic load-unload tensile tests for ply-level hybrid carbon fiber composites

International audienceComposite materials are of increasing interest in aircraft and spacecraft structures, and carbon fiber reinforced polymers (CFRP) have emerged as materials meeting quality standards for structural applications in the aircraft industry. Despite their high mechanical properties, CFRPs are associated with high production costs. Building on recent research by the authors, this paper investigates the use of ply-level hybridization to reduce manufacturing costs while maintaining the mechanical performance of the manufactured material. Focusing on the causes of nonlinear response under off-axis tensile loading, the paper involves cyclic load-unload (LU) tensile tests conducted at off-axis angles of 15°, 30°, and 45° to predict mechanical characteristics and damage evolution. Residual strains are directly extracted from load-unload stress-strain re-sponses. Three distinct methods for estimating cycle modulus are employed and compared for damage variable formulation. The research findings reveal dependencies of both the damage variable and residual strains on the off-axis angle. Furthermore, the method used to assess the modulus during cycling loading significantly influences the damage variable estimation. En-couragingly, the hybrid laminates exhibit reduced internal damage and matrix plasticity compared to reference counterparts, indicating a positive effect on the mechanical performances of hybridized CFRPs in addition to the cost reduction

Experimental Characterization of Internal Structure and Physical Properties of Unidirectional Ply‐Level Hybrid Carbon Composite Material

International audienceThe complexities associated with the response of carbon fiber composites to different loading cases and methods of improving it without increasing their cost are still being researched. Herein, by an experimental approach, the ply-level hybridization technique for tailoring the composite response is explored, and two different types of unidirectional prepregs with the same fiber type but different quality and prices are mixed. The purpose of this study is to analyze the influence of this type of hybridization on the structure and mechanical response of carbon fiber composites and to assess the compromise between manufacturing cost reduction and mechanical response. Hybridization is obtained in both layer thickness and material quality and reference materials are also manufactured. The properties of the unidirectional hybrid and nonhybrid composites are evaluated by density and fiber volume fraction measurements. The in-plane mechanical properties are determined using quasistatic tensile tests, in 0° and 90° directions. No thickness effects are noticed on the stress–strain response under both longitudinal and transverse directions and hybrid composites exhibit an improved 0° failure stress