Search Results (61)

The LaRC02 criterion is a classical criterion for determining fiber kinking failure of UD laminates under longitudinal compression (LC), but its basis for determining matrix cracking in a fiber kinking coordinate system is based on stress-invariant theory rather than on a physical mechanism. Herein, three Puck-like physical-mechanism-based inter-fiber failure criteria are extended to LC failure of UD composites, and thus three failure criteria (denoted as LC-Guo, LC-Li, and LC-Puck failure criteria) are constructed for fiber kinking failure determination. The stresses in the global coordinate system are transformed to the fiber kinking coordinate system by a three-level coordinate system transformation, and then the failure determination is performed using the three Puck-like criteria. The results show that the overall accuracy of the three proposed criteria is higher than that of the LaRC02 criterion, especially the LC-Guo criterion. Additionally, an analysis of the influence of material properties shows that the failure envelope curves tend to be conservative, and the predicted off-axial compression strength decreases as the transverse compression strength and in-plane shear strength increase and the transverse tensile strength decreases. This work proposes a more reasonable assessment methodology for the determination of LC failure of UD composites, which has important theoretical significance and engineering value. Full article

The use of veneer composites as structural components in engineering requires special design. The dimensioning of laminated wood can be optimized by varying the wood species, veneer thickness, orientation, arrangement, number of single layers, and other factors. Composite properties can be calculated using suitable model approaches, such as the classical laminate theory. Thus, an optimization can be achieved. The present study verified the adaptability of the classical laminate theory for veneer composites. Native veneer, adhesive-coated veneer, and solid wood were investigated as raw materials for the plywood layers. Mechanical properties were determined using tensile and shear tests and used as parameters to calculate the composite properties of the plywood. The adhesive coating results in an increase in stiffness and strength compared with the native veneer parameters, which is greater perpendicular to the fiber than in the fiber direction. The increase due to the adhesive decreases with increasing veneer thickness. The plywood was bending tested. The measured Young’s modulus was in the range of 8000–10,700 MPa, the shear modulus was in the range of 500–1100 MPa, and the strength was in the range of 70–100 MPa. The values obtained were compared to the calculations. The best prediction of the plywood properties is obtained by using the properties of the adhesive-coated veneer as a single layer. Full article

This paper introduces a methodology for structural mass optimization of High-Altitude Long Endurance (HALE) aircraft across a complete mission profile, tailored for use in preliminary design. A conceptual HALE vehicle and its mission profile are assumed for this study, which also evaluates the impact of risk-based design decisions on optimized mass. The research incorporates a coupled aeroelastic solver and a mass optimization algorithm based on classical laminate theory to construct a geometrically accurate spar model. A novel approach is proposed to minimize the spar mass of the aircraft throughout the mission profile. This algorithm is applied to a representative T-Tail HALE model to compare optimized mass between two mission profiles differing in turbulence exceedance levels during the ascent and descent mission stages, while maintaining the same design robustness for on-station operation. Sample numerical results reveal a 10.9% reduction in structural mass for the mission profile with lower turbulence robustness design criteria applied for ascent and descent mission phases. The significant mass savings revealed in the optimization framework allow for a trade-off analysis between robustness to turbulence impacts and critical HALE platform parameters such as empty weight. The reduced empty vehicle weight, while beneficial to vehicle performance metrics, may be realized but comes with the added safety of flight risk unless turbulent conditions can be avoided during ascent and descent through risk mitigation strategies employed by operators. The optimization framework developed can be incorporated into system engineering tools that evaluate mission effectiveness, vehicle performance, vehicle risk of loss, and system availability over a desired operating area subject to environmental conditions. Full article

Additive manufacturing (AM) is an emerging technology with the greatest potential impact on many engineering applications. Among the AM technologies, material extrusion is particularly interesting for plastic components due to its versatility and cost-effectiveness. There is, however, a limited knowledge of design methods to predict the mechanical strength of parts built by material extrusion. The materials are polymers, sometimes also reinforced, and deposited in layers like in laminated composites. Therefore, the mechanical behavior and strength can be characterized and modeled with methods already known for composite materials. Such tools are the classical lamination theory (CLT) and the failure criteria for composites. This paper addresses an analysis of a composite material made of long-fiber glass in a polyamide matrix built by additive manufacturing; in this relatively new technique, a continuous fiber is inserted between layers of polyamide deposited from a wire with a fused filament fabrication (FFF) 3D printer. The mechanical behavior was studied from tensile tests that were carried out to demonstrate the feasibility of modeling with the mentioned tools, and the material properties for predicting the stiffness and strength of components built with that technique were identified. The results show that the classical models for the mechanical behavior of composite materials are well-suited for this material to predict the influence of the main building parameters. Full article

This paper investigates the dynamic behavior of shell structures presenting variable-angle tow laminations. The choice of placing fibers along curvilinear patterns allows for a broader structural design space, which is advantageous in several engineering contexts, provided that more complex numerical analyses are managed. In this regard, Carrera’s unified formulation has been widely used for studying variable-angle tow plates and shells. This article aims to expand this formulation through the derivation of the complete formulation for a generic shell reference surface. The principle of virtual displacements is used as a variational statement for obtaining, in a weak sense, the stiffness and mass matrices within the finite element solution method. The free vibration problem of singly and doubly curved variable-angle tow shells is then addressed. The proposed approach is compared to Abaqus three-dimensional reference solutions and classical theories to investigate the effectiveness of the developed models in predicting the vibrational frequencies and modes. The results demonstrate a good agreement between the proposed approach and reference solutions. Full article

Fibre-reinforced polymers based on natural fibers, such as flax fibers, exhibit pronounced nonlinear orthotropic material behavior. This presents a significant challenge in finite element analysis (FEA) simulations, as the nonlinear constitutive models available in commercial FEA tools are difficult to apply and fail to capture all the material’s specific characteristics. Relying on initial or reduced secant moduli in linear quasi-static analyses of deformations or stress states can result in inaccurate outcomes and overly optimistic strength predictions, particularly in compression-dominated cases. However, with appropriate modifications, classical laminate theory (CLT) can be adapted for nonlinear analysis. This involves iteratively updating the components of the stiffness matrix for the unidirectional (UD) ply during the calculation process based on the current strain state and stress interactions. This study presents and discusses a computational algorithm for the FEA software ABAQUS/CAE 2019, which incorporates material-related orthotropic nonlinearities and stress-dependent interactions within the CLT framework. The algorithm represents a single-scale material model at the meso level (UD ply) and is based on the concept of orthotropic elasto-damage within the framework of continuum damage mechanics (CDM) theory. Numerical implementation is achieved through a user-defined field (USDFLD) subroutine, accompanied by a pre-processing Python script for managing experimental data, computing data fields, and calculating parameters. As shown below, this type of implementation appears justified compared to a user material subroutine (UMAT) subroutine in terms of computational efficiency and practicality. Full article

Physics-Informed Neural Networks (PINNs) integrate physics principles with machine learning, offering innovative solutions for complex modeling challenges. Laminated composites, characterized by their anisotropic behavior, multi-layered structures, and intricate interlayer interactions, pose significant challenges for traditional computational methods. PINNs address these issues by embedding governing physical laws directly into neural network architectures, enabling efficient and accurate modeling. This review provides a comprehensive overview of PINNs applied to laminated composites, highlighting advanced methodologies such as hybrid PINNs, k-space PINNs, Theory-Constrained PINNs, optimal PINNs, and disjointed PINNs. Key applications, including structural health monitoring (SHM), structural analysis, stress-strain and failure analysis, and multi-scale modeling, are explored to illustrate how PINNs optimize material configurations and enhance structural reliability. Additionally, this review examines the challenges associated with deploying PINNs and identifies future directions to further advance their capabilities. By bridging the gap between classical physics-based models and data-driven techniques, this review advances the understanding of PINN methodologies for laminated composites and underscores their transformative role in addressing modeling complexities and solving real-world problems. Full article

Due to their improved recyclability, thermoplastic composites (TPCs) are increasing their application across industries. The current work deals with the dimensioning, manufacturing, and characterisation of vacuum-infused TPCs cured at RT and made of non-crimp glass fabric and the liquid acrylic-based resin Elium©. Laminates with 10 and 12 layers achieved a fibre weight content of 73% measured by the burn-off process, which corresponds to a fibre volume content of 55%. Three-point bending tests revealed a bending strength of 636.17 ± 25.70 MPa and a bending modulus of 24,600 ± 400 MPa for the 12 layer laminate. Using micro-mechanical models, unidirectional elastic constants are calculated and applied in classical laminate theory (CLT) for optimising composite lay-ups by maximising bending stiffness, whilst yielding a laminate thickness prediction error of −0.18% and a bending modulus prediction error of −1.99%. Additionally, FEA simulations predicted the bending modulus with a −4.47% error and illustrated, with the aid of the Tsai–Hill criterion, the relationship between the onset of layer failure and discrepancies between experimental results and simulations. This investigation demonstrates the effective application of analytical and numerical methods in the dimensioning and performance prediction of TPCs. Full article

This article presents the concept, research, and modeling of a sandwich composite made from ULTEM 9085 and polycarbonate (PC). ULTEM 9085 is relatively expensive compared to polycarbonate, and the composite structure made of these two materials allows for maintaining the physical properties of ULTEM while reducing the overall costs. The composite consisted of outer layers made of ULTEM 9085 and a core made of polycarbonate. Each layer was 3D-printed using the fused filament fabrication (FFF) technology, which enables nearly unlimited design flexibility. The geometry of the test specimens corresponds to the ISO 527-4 standard. Tensile and three-point bending tests were conducted. The structure was modeled in a simplified manner using averaged stiffness values, and with the classical laminate theory (CLT). The models were calibrated through tensile and bending tests on ULTEM and polycarbonate prints. The simulation results were compared with experimental data, demonstrating good accuracy. The 3D-printed ULTEM-PC-ULTEM composite exhibits favorable mechanical properties, making it a promising material for cost-effective engineering applications. Full article

This study focused on evaluating the sensitivity and limitations of the simplified equipment used in the Digital Image Correlation (DIC) technique, comparing them with the analog extensometer, based on the mechanical property data of a composite made of fiberglass and epoxy resin. The objectives included establishing a methodology based on the literature, fabricating samples through manual lamination, conducting mechanical tests according to the ASTM D3039 and D3518 standards, comparing DIC with the analog extensometer of the testing machine, and contrasting the experimental results with classical laminate theory. Three composite plates with specific stacking sequences (${\left[0\right]}_3$, ${\left[90\right]}_4$, and ${[\pm 45]}_3$) were fabricated, and samples were extracted for testing to determine tensile strength, modulus of elasticity, and other properties. DIC was used to capture deformation fields during testing. Comparisons between data obtained from the analog extensometer and DIC revealed differences of 11.1% for the longitudinal modulus of elasticity $E_1$ and 5.6% for $E_2$. Under low deformation conditions, DIC showed lower efficiency due to equipment limitations. Finally, a theoretical analysis based on classical laminate theory, conducted using a Python script, estimated the longitudinal modulus of elasticity $E_x$ and the shear strength of the ${[\pm 45]}_3$ laminate, highlighting a relative difference of 31.2% between the theoretical value of 7136 MPa and the experimental value of 5208 MPa for $E_x$. Full article

The structural design of a composite bracket applied to an aircraft propulsion system was carried out in this study. Aircraft engine intakes are fitted with various components in order for the engine to operate. The thickness of the composite laminate was determined through classical laminate theory. The mechanical properties of the manufactured specimen were analyzed and reflected in the conceptual design. The material for the design and analysis was a composite material consisting of carbon fiber and epoxy resin. The results of the designed composite structures were compared with those of aluminum alloy structures, and the structural integrity was investigated via the structural analysis of the designed bracket. The commercial FEM code Nastran 2022 and ANSYS 2023 software were used for numerical analysis. A stress and deformation analysis was carried out, and the buckling stability was also evaluated due to the characteristics of the composite structure. The bracket was shown to be sufficiently safe through structural analysis. Full article

The main goal of this work is to combine the usage of the numerical homogenization technique for determining the effective properties of representative volume elements with artificial neural networks. The effective properties are defined according to the classical laminate theory. The purpose is to create and train a rapid surrogate model for the quick calculation of the mechanical properties of hollow concrete slabs. First, the homogenization algorithm was implemented, which determines membrane, bending and transverse shearing properties of a given parametrized hollow-core precast slab reinforced with steel bars. The algorithm uses the finite element mesh but does not require a formal solution of the finite element method problem. Second, the learning and training artificial intelligence framework was created and fed with a dataset obtained by optimal Latin hypercube sampling. In the study, a multilayer perceptron type of artificial neural network was used. This allows for obtaining rapid calculations of the effective properties of a particular hollow-core precast slab by using a surrogate model. In the paper, it has been proven that such a model, obtained via complex numerical calculations, gives a very accurate estimation of the properties and can be used in many practical tasks, such as optimization problems or computer-aided design decisions. Above all, the efficient setup of the artificial neural network has been sought and presented. Full article

Even though the influence of the printing direction on the mechanical properties of 3D-printed samples by fused filament fabrication is established in the literature, very little is known about mechanical and electrical coupling. In this study, electrically conductive polylactic acid filled with carbon black particles undergoes monotonic and repeated progressive tensile loading to better understand the influence of the printing direction on the electro-mechanical properties of three-dimensional-printed samples. The objective is to analyse the electro-mechanical behaviour of this composite for its potential application as an actuator. The classical laminate theory is also applied to evaluate the relevance of this theory in predicting the mechanical characteristics of this material. In addition, a comprehensive damage analysis is performed using acoustic emission, infrared thermography, scanning electron microscopy, and X-ray microcomputed tomography imaging. Results show that the degradation of the mechanical and electrical properties is highly influenced by the printing direction. The appearance and development of crazes in 0° filaments are highlighted and quantified. The conclusions drawn by this study underline the interest in using longitudinal and unidirectional printing directions to improve the conductive path within the samples. Furthermore, the evolution of the resistance throughout the experiments emphasizes the need to control the implemented voltage in the design of future electro-thermally triggered actuators. Full article

This paper provides a brief review on modeling of composite structures. Composite structures in this paper refer to any structure featuring anisotropy and heterogeneity, including but not limited to their traditional meaning of composite laminates made of unidirectional fiber-reinforced composites. Common methods used in modeling of composite structures, including the axiomatic method, the formal asymptotic method, and the variational asymptotic method, are illustrated in deriving the classical lamination theory for the composite laminated plates. Future research directions for modeling composite structures are also pointed out. Full article

The purpose of this work is to theoretically and experimentally investigate the applicability of the Tsai–Hill failure criterion and classical laminate theory for predicting the strength and stiffness of 3D-printed polylactide laminate composites with various raster angles in mechanical tests for uniaxial tension and compression. According to the results of tensile and compression tests, the stiffness matrix components of the orthotropic individual lamina and strength were determined. The Poisson’s ratio was determined using the digital image correlation method. It was found that the Tsai–Hill criterion is applicable for predicting the tensile strength and yield strength of laminate polymer composite materials manufactured via fused deposition modeling 3D printing. The calculated values of the elastic moduli for specimens with various raster angles correlate well with the values obtained experimentally. In tensile tests, the error for the laminate with a constant raster angle was 3.3%, for a composite laminate it was 4.4, in compression tests it was 11.9% and 9%, respectively. Full article