Search Results (14)

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

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

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

The present study provides a thorough analysis of the influence of filament orientation on the tensile stiffness of 3D-printed structures. This exploration employs a combination of numerical simulations and experimental trials, providing an extensive understanding of additive manufacturing, particularly 3D printing. This process involves layer-by-layer material deposition to produce three-dimensional objects. The examination specifically targets PLA-based 3D printed structures created using Fused Filament Fabrication (FFF) technology and subjects them to rigorous evaluations using a universal tensile testing machine. Additionally, this approach combines Representative Volume Element (RVE) and Classical Lamination Theory (CLT) techniques to extrapolate the mechanical properties of the test material. Although the initial methodology faces challenges in determining the shear modulus with precision, an in-depth investigation results in enhanced accuracy. Furthermore, this study introduces a parametric RVE numerical method, demonstrating its resilience in handling sensitivity to shear modulus. A comparative study of results derived from both the analytical methods and experimental trials involving five series of samples with varied layups reveals that the newly proposed numerical method shows a stronger correlation with the experimental outcomes, delivering a relative error margin of up to 8%. Full article

In recent years, there has been an increasing interest in open-hole and filled-hole laminate failure analysis. The open and filled-hole laminate failure analysis is used in several important areas, especially in designing mechanically fastened composite joints. Various analytical, empirical, and numerical methods are available for the design of mechanically fastened composite joints. The large number of material and geometrical design variables at the preliminary design stage makes the empirical and numerical methods effortful, expensive, and time-consuming. Therefore, analytical methods are recommended over numerical and empirical methods at the preliminary design stage merely because of their simplification in calculations, making them computationally efficient. Taking this into consideration, current research presents an improvement to the analysis capabilities of the previously introduced analytical method, i.e., the coupled approach of Classical laminate theory (CLT) and Lekhnitskii solutions. These improvements include the development of failure envelops for the open-hole and filled-hole laminates, estimation of optimized filling material for attaining maximum load-bearing capacity of filled-hole laminates, and optimization of stacking sequence for maximum load-bearing capacity of open-hole and filled-hole laminates. From the failure envelop results, it was found that failure envelopes of filled-hole laminates are bigger than open-hole laminates. Furthermore, it was found that the stiffness of the filling material should be equal to the stiffness of the laminate to achieve maximum bearing strength of the filled-hole laminate. It was also demonstrated that the coupled approach of CLT and Lekhnitskii solutions may provide carpet plots that can be utilized to optimize the stacking sequence for open-hole and filled-hole laminates. Full article

Analytical calculations were performed on carbon fiber-reinforced polymer (CFRP) laminates in an asymmetrical configuration. The asymmetric configuration of composites was investigated, where extension–twisting and extension–bending couplings were used to obtain the elastic element. Analysis of the presence of elastic couplings was conducted according to Classical Laminate Theory (CLT). Components of matrices A, B, and D, as well as the parameters D_c and B_t, were obtained using the MATLAB software environment. The results show that couplings between the extension and bending, as well as between the extension and twisting, were strongly dependent on specimen plies’ orientation. Moreover, additional analysis was performed on the influence of layer angle on the terms which are components of the B_t and D_c coefficients. The results indicate that the angle of laying fibers around 45–50° significantly amplifies the effects of elastic couplings. Full article

Experimental and numerical investigations are presented for a theory-guided machine learning (ML) model that combines the Hashin failure theory (HFT) and the classical lamination theory (CLT) to optimize and accelerate the design of composite laminates. A finite element simulation with the incorporation of the HFT and CLT were used to generate the training dataset. Instead of directly mapping the relationship between the ply angles of the laminate and its strength and stiffness, a multi-layer interconnected neural network (NN) system was built following the logical sequence of composite theories. With the forward prediction by the NN system and the inverse optimization by genetic algorithm (GA), a benchmark case of designing a composite tube subjected to the combined loads of bending and torsion was studied. The ML models successfully provided the optimal layup sequences and the required fiber modulus according to the preset design targets. Additionally, it shows that the machine learning models, with the guidance of composite theories, realize a faster optimization process and requires less training data than models with direct simple NNs. Such results imply the importance of domain knowledge in helping improve the ML applications in engineering problems. Full article

Car clutch facings are complex fiber-reinforced composites. The coefficient of thermal expansion (CTE) of the composite is one of the main thermal properties, which affects dry clutch engagement process due to heat associated with friction. In the case of clutch facing, which only exists in its final form as a non-planar annular disc, it is difficult to define an elementary representative volume. The objective of this work was to develop a method for identifying the CTE distributions on the entire part. A device allowing measuring the strain fields by digital image correlation (DIC) under homogeneous thermal loading (up to 300 °C) was developed. The experimental results highlight the heterogeneity and the orthotropic nature of the material behavior and the influence of the angle between the fibers on the CTE. To take into account that the measured strain fields are related to the CTE, but also to the shape of the part, different approaches to identify the CTE were considered: direct measurements, classical laminate theory (CLT) and finite element method updating (FEMU). Only the FEMU allows an accurate identification of the CTE distributions. Nevertheless, the CLT respects the orders of magnitude and remains a useful tool for the design of clutches. Full article

In this paper, the modal and linear buckling analysis of a laminated composite drive shaft reinforced by 11 multi-walled carbon nanotubes (MWCNTs) was carried out using an analytical approach, as well as the finite element method (FEM). The theoretical model is based on classical laminated theory (CLT). The fundamental frequency and the critical buckling torque were determined for different fiber orientation angles. The Halpin–Tsai model was employed to calculate the elastic modulus of composites having randomly oriented nanotubes. The effect of various carbon nanotube (CNT) volume fractions in the epoxy resin matrix on the material properties of unidirectional composite laminas was also analyzed. The fundamental frequency and the critical buckling torque obtained by the finite element analysis and the analytical method for different fiber orientation angles were in good agreement with each other. The results were verified with data available in the open literature, where possible. For the first time in the literature, the influence of CNT fillers on various composite drive shaft design parameters such as the fundamental frequency, critical speed, and critical buckling torque of a hybrid fiber-reinforced composite drive shaft is finally predicted. Full article

Currently, the photovoltaic (PV) panels widely manufactured on market are composed of stiff front and back layers and the solar cells embedded in a soft polymeric interlayer. The wind and snow pressure are the usual loads to which working PV panels need to face, and it needs the panels keep undamaged under those pressure when they generate electricity. Therefore, an accurate and systematic research on bending behavior of PV panels is important and necessary. In this paper, classical lamination theory (CLT) considering soft interlayer is applied to build governing equations of the solar panel. A Rayleigh–Rita method is modified to solve the governing equations and calculate the static deformation of the PV panel. Different from many previous researches only analyzing simply supported boundary condition for four edges, a special boundary condition which consists of two opposite edges simply supported and the others two free is studied in this paper. A closed form solution is derived out and used to do the numerical calculation. The corresponding bending experiments of PV panels are completed. Comparing the numerical results with experiment results, the accuracy of the analytical solutions are verified. Full article

In recent years, sites with low annual average wind speeds have begun to be considered for the development of new wind farms. The majority of design methods for a wind turbine operating at low wind speed is to increase the blade length or hub height compared to a wind turbine operating in high wind speed sites. The cost of the rotor and the tower is a considerable portion of the overall wind turbine cost. This study investigates a method to trade-off the blade length and hub height during the wind turbine optimization at low wind speeds. A cost and scaling model is implemented to evaluate the cost of energy. The procedure optimizes the blades’ aero-structural performance considering blade length and the hub height simultaneously. The blade element momentum (BEM) code is used to evaluate blade aerodynamic performance and classical laminate theory (CLT) is applied to estimate the stiffness and mass per unit length of each blade section. The particle swarm optimization (PSO) algorithm is applied to determine the optimal wind turbine with the minimum cost of energy (COE). The results show that increasing rotor diameter is less efficient than increasing the hub height for a low wind speed turbine and the COE reduces 16.14% and 17.54% under two design schemes through the optimization. Full article

This paper uses classical laminate theory (CLT) and experimental methods to predict the longitudinal specific modulus of braided high modulus polyethylene (HMPE) rope without a matrix. When applying conventional CLT, the modulus, braided angle of strand, and packing factor (PF), i.e., the cross-sectional area ratio of the strand to the rope, are required. Because the void (space between strands) and PF of braided rope without a matrix readily change during the application of load, and given the difficulty measuring PF experimentally, it is difficult to predict the modulus by conventional CLT. This paper proposes the use of the unit of N/tex in place of conventional MPa for CLT. This study demonstrates that changes in PF due to void changes can be neglected when using the N/tex unit. The predicted longitudinal specific modulus of the rope using N/tex unit was found to be in qualitatively agreement with the longitudinal modulus measured experimentally. Full article

In the present study, the mesostructure of a fused deposition modeling (FDM) processed part is considered for the investigation of its mechanical behavior. The layers of FDM printed part behave as a unidirectional fiber reinforced laminae, which are treated as an orthotropic material. The finite element (FE) procedure to find elastic moduli of a layer of the FDM processed part is presented. The mesostructure of the part that would be obtained from the process is replicated in FE models in order to find stiffness matrix of a layer. Two distinctive architectures of mesostructure are considered in the study to predict the mechanical behavior of the parts. Also, influences of layer thickness, road shape and air gap on the elastic properties of a material are investigated. Further, the parts fabricated with FDM process are treated as laminate structures. From the numerical results, it is seen that the elastic moduli are governed by mesostructures. Our laminate results are validated with experimental to demonstrate the use of classical laminate theory (CLT) for FDM parts. The elastic moduli (E₁, E₂, G₁₂, ν₁₂) of a layer used in the analysis are calculated from FE simulations. This study establishes relationship between mesostructure and macro mechanical properties of the part. Full article