Analysis of Composite Structures

State of the art of composite structures in non-deterministic framework: A review

A mechanics-based modeling approach is developed to rapidly predict damage in polymer matrix composites resulting from a low velocity impact event. The approach is incorporated into a computer code that provides an efficient means to assess the damage resistance for a range of material systems, layup configurations, and impact scenarios. It is envisioned that the developed approach will aid in early design and analysis of composite structures where sizing and layup decisions must be made, and evaluating the feasibility of a large number of laminate configurations using numerical approaches such as finite element analysis (FEA) is prohibitively expensive. Therefore, the goal of the modeling approach is to predict the impact damage size given the laminate configuration and impact scenario. This information can then be used to determine the residual strength of the material. To be useful in such a context, the tool is designed to run quickly (<2 minutes) to allow a large number of design cases to be investigated. The results presented demonstrate that the model is capable of efficiently predicting low velocity impact damage size, shape, and location within an acceptable accuracy suitable for preliminary design and analysis of composite structures.

The paper presents a theoretical and experimental study of the influence of damage accumulation in composite material on the elastic fourth-rank tensor and on the strength under quasi-static, cyclic and dynamic loads. Layered polymer composites (glass or carbon fiber-reinforced plastic) are considered. This work aims to develop a mathematical model that accounts for the impact of damage in the composite material on the fourth-rank tensor of elastic properties. The constitutive relations for an orthotropic composite material are proposed, taking into account the accumulation of damage during tensile or shear loading. A numerical simulation using the finite element method is done for a periodicity cell for composite variants (unidirectional, layered, etc.) to determine the effective elastic properties. Quasi-static loading experiments were conducted on composite samples (carbon plastic) to validate the model and the degradation of elastic properties was determined by measuring the longitudinal sound speed. The full-scale experiments confirmed that damage accumulation in carbon fiber-reinforced plastic leads to the degradation of its effective elastic properties. In this connection, a technique was developed to take into account irreversible damage in an orthotropic composite material through the components of the ductility tensor, which may be helpful for the design and analysis of composite structures. The findings of the study could help with the creation of new materials with enhanced mechanical characteristics, as well as with raising the quality of already-existing materials. The developed mathematical model of orthotropic composite material can be used to enhance the structural strength properties and boost the application safety in a variety of industry.

Model materials for photo-orthotropic-elasticity

Finite element analysis of composite structures

Nonlinear vibrations of orthotropic thick annular plates using higher order shear deformation theory

Extended multiscale finite element method for large deflection analysis of thin-walled composite structures with complicated microstructure characteristics

The article presents a finite element based study of linear and geometrically non-linear progressive failure analysis of thin walled composite aerospace structures subjected to combined in-plane and out-of-plane loading which are typically encountered in thin walled aerospace structures. Different ply and constituent based failure criteria and material property degradation schemes have been coded into a PCL code in Nastran. As case studies, progressive failure analyses of sample composite laminates with cut-outs under combined loading are executed to study the effect of geometric non-linearity on the first ply failure and progression of failure. Different ply and constituent based failure criteria and different material property degradation schemes are also compared in terms of predicting the first ply failure and failure progression. For mode independent failure criteria, a method is proposed for the determination of separate degradation factors for fiber and matrix failures which are assumed to occur simultaneously. The results of the present study, show that under combined out-of-plane and in-plane loading, depending on the load case linear analysis can significantly underestimate or overestimate the failure progression compared to geometrically non-linear analysis even at low levels of out-of-plane loading.

This paper proposes a new approach for the FE analysis of composite structures by means of 1D refined models that have been derived in the framework of the Carrera Unified Formulation (CUF). CUF provides hierarchical higher-order structural models with arbitrary expansion orders. Taylorand Lagrange-type polynomials were used to interpolate the displacement field over the element cross-section. The proposed new approach, referred to as Composite-Wise (CW), is able to provide stress and strain fields with solid-like accuracy and very low computational cost. Within the CW approach, different scale components (fiber, matrix, laminae and laminates) can be simultaneously considered in the same structural model. Failure analyses are conducted by implementing well-known failure criteria. Furthermore, an integral evaluation of failure parameters is introduced to determine critical portion of the structure where failure could take place. Results are provided to show the enhaced capability of the present formulation in the failure analysis of fiber-reinforced composite structures by the detection of detailed displacement/stress fields with reduced computational cost.

Locking-free curved elements with refined kinematics for the analysis of composite structures

Composite structure often shows undesirably significant uncertainty in its mechanical properties, which may consequently result into large stochastic variation of its natural frequency. This study provides stochastic natural frequency analysis of typical composite structures based on micro-scale (constituent-scale) and meso-scale (ply-scale) uncertainty. Uncertainty propagation across micro-scale and meso-scale is investigated. Response surface method (RSM) based on finite element modeling is employed to obtain approximate natural frequency of structures with complex shape or boundary conditions, and mean value and standard deviation of natural frequency of composite plate and cylindrical shell are derived. Differences in natural frequency statistics of composite plates and cylindrical shells derived by considering uncertainty at different scales are quantified and discussed. Significant statistical correlation between ply elastic properties and ply density is observed, and the statistical correlation is demonstrated to lay great influence on the statistics of structure natural frequency.

Finite element analysis of composite structures with smart constrained layer damping

The characteristics of composite materials are of high importance to engineering applications; therefore the increasing use as a substitute for conventional materials, especially in the field of aircraft and space industries. It is a known fact that researchers use finite element programs for the design and analysis of composite structures, use of symmetrical conditions especially in complicated structures, in the modeling and analysis phase of the design, to reduce processing time, memory size required, and simplifying complicated calculations, as well as considering the response of composite structures to different loading conditions to be identical to that of metallic structures. Finite element methods are a popular method used to analyze composite laminate structures. The design of laminated composite structures includes phases that do not exist in the design of traditional metallic structures, for instance, the choice of possible material combinations is huge and the mechanical properties of a composite structure, which are anisotropic by nature, are created in the design phase with the choice of the appropriate fiber orientations and stacking sequence. The use of finite element programs (conventional analysis usually applied in the case of orthotropic materials) to analysis composite structures especially those manufactured using angle ply laminate techniques or a combination of cross and angle ply techniques, as well considering the loading response of the composite structure to be identical to that of structures made of traditional materials, has made the use of, and the results obtained by using such analysis techniques and conditions questionable. Hence, the main objective of this paper is to highlight and present the results obtained when analyzing and modeling symmetrical conditions as applied to commercial materials and that applied to composite laminates. A comparison case study is carried out using cross-ply and angle-ply laminates which concluded that, if the composition of laminate structure is pure cross-ply, the FEA is well suited for predicting the mechanical response of composite structure using principle of symmetry condition. On the other hand that is not the case for angle-ply or mixed-ply laminate structure.

Hygrothermal Effects on the Linear and Nonlinear Analysis of Composite Plates

This paper focuses on investigating the mechanical buckling behavior of composite and orthotropic classical rectangular plates using the Galerkin theory. By utilizing the classical plate theory of elasticity, the governing equations for the functionally graded plate material subjected to a uniaxially distributed load along the x and y axes are derived based on the principle of work energy. Consequently, the displacement function is determined as the solution to a differential equation that satisfies specific boundary conditions. The equilibrium expression derived from the work‐energy equation is then minimized and analytically solved to determine the stresses and critical buckling loads of an orthotropic composite rectangular plate. The critical buckling loads of all edges, including clamped and simply supported orthotropic and isotropic thin rectangular plates with aspect ratios ranging from 0.1 to 3, are calculated and compared with existing literature to assess the stiffness of isotropic and orthotropic plates. The findings reveal that the critical buckling load of a clamped plate decreases as the aspect ratio increases from 0.1 to 1 but increases for aspect ratios between 1 and 3. The average percentage variation of critical buckling load values obtained from previous studies using orthotropic and isotropic (classical lamination plate theory [CLPT]) materials is found to be 1.93% and 3.65%, respectively. Additionally, it is observed that the critical buckling load of clamped edges in isotropic plates is lower than that of orthotropic plates at lower aspect ratios (0.4–1.0) but higher at higher aspect ratios (above 1.0). The results indicate that plates with all‐round clamped boundaries exhibit higher buckling loads due to their effective fixation at all boundaries, which provides greater resistance to deformation and buckling compared to plates with all edges simply supported, where there is more flexibility for deformation under loads. This highlights the influence of boundary conditions on the critical buckling load of the plate. Furthermore, a significant percentage difference is noted when comparing approximate solutions, while a low percentage difference of 0.43% with the author’s derived displacement function indicates close agreement, demonstrating the high level of accuracy and reliability of the proposed model in predicting buckling load of plates. Hence, it can be recommended for stability analysis, especially where the material properties need to be controlled in a specific direction to optimize performance.