Search Results (9)

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

The fiber-reinforced composite stringer is commonly used in large civil aircraft wing structures. Under compression loads, it exhibits complex failure modes, with matrix cracking being one of the most common. The quantitative analysis of matrix failure is important and difficult. To address this issue, a multiscale method combining the generalized method of cells (GMC) and macroscopic FEM models is employed to quantitatively predict matrix damage and failure. The extent of matrix damage in the composite structure is represented by the number of failed matrix subcells within the repeating unit cells. The 3D Tsai–Hill failure criterion is established for the matrix phase, and the maximum stress failure criterion is applied to the fiber subcell. Upon meeting the criterion, the stiffnesses of the failed subcells are immediately reduced to a nominal value. In the current study, the ultimate loads, failure modes and load–displacement curves of composite stringers subjected to compressive load are obtained by the experiment approach and the proposed multiscale model. The experimental and simulation results show good agreement, and the multiscale analysis method successfully predicts the extent of matrix damage in the composite stringer under compressive load. The number of failed matrix subcells quantitatively evaluates the damage extent within a 2 × 2 GMC model. The findings reveal that matrix subcell failures primarily occur in the 45° and −45° plies of the middle part of the stringer composite. Full article

A deep understanding of the material parameters and the behavior of sandwich panels, which are used in the construction industry as roof and façade cladding, is important for the design of these construction components. Due to the constant changes in the polyurethane (PU) foams used as a core material, the experimental database for the current foams is small. Nowadays, there is an increasing number of failures of façade and roof panels after installation. This article presents a variety of experimental investigations on sandwich panels from two manufacturers with a core of polyisocyanurate (PIR) rigid foam (density: 40 kg/m³). As part of this study, compression, tension, shear, and bending tests were performed in several spatial directions and over the range required by the standard. The results of the tests showed the orthotropy of the core material and the dependence of the material on the direction and type of load. The stress-strain curves showed linear and non-linear areas. Using the data from this experimental study, a numerical model was implemented which utilized the Hill yield criterion to represent the orthotropy of the core material. The present investigation suggests that the classical von Mises failure criterion, used in many studies, is not suitable for the foam system applied in these sandwich panels. Instead, the Tsai–Wu criterion is more appropriate for defining the failure stresses. 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

Methods to predict the fracture of thin carbon fibre-reinforced polymers (CFRPs) under load are of great interest in the automotive industry. The manufacturing of composites involves a high risk of defect occurrence, and the identification of those that lead to failure increases the functional reliability and decreases costs. The performance of CFRPs can be significantly reduced in assembled structures containing stress concentrators. This paper presents a hybrid experimental–numerical method based on the Tsai–Hill criterion for behavior of thin CFRPs at complex loadings that can emphasize the threshold of stress by tracing the σ-τ envelope. Modified butterfly samples were made for shearing, traction, or shearing-with-traction tests in the weakened section by changing the angle of force application α. ANSYS simulations were used to determine the zones of maximum stress concentration. For thin CFRP samples tested with stacking sequences [0]₈ and [(45/0)₂]_s, the main mechanical characteristics have been determined using a Dynamic Mechanical Analyzer (DMA) and ultrasound tests. A modified Arcan device (AD) was used to generate data in a biaxial stress state, leading to the characterization of the material as a whole. The generated failure envelope allows for the prediction of failure for other combinations of normal and shear stress, depending on the thickness of the laminations, the stacking order, the pretension of the fasteners, and the method used to produce the laminations. The experimental data using AD and the application of the Tsai–Hill criterion serve to the increase the safety of CFRP components. Full article

In composite materials, the use of failure criteria is necessary to determine the failure forces. Various failure criteria are known, from the simplest ones that compare individual stresses with the corresponding strength, to more complex ones that take into account the sign and direction of the stress, as well as mutual interactions of the acting stresses. This study investigates the application of the maximum stress, Tsai-Hill, Tsai-Wu, Puck, Hoffman and Hashin criteria to beech plywood made from a series of plies of differently oriented beech veneers. Specimens were cut from the manufactured boards at various angles and loaded by bending to failure. The mechanical properties of the beech veneer were also determined. The specimens were modelled using the finite element method with a composite modulus and considering the different failure criteria where the failure forces were calculated and compared with the measured values. It was found that the calculated forces based on all failure criteria were lower than those measured experimentally. The forces determined using the maximum stress criterion showed the best agreement between the calculated and measured forces. Full article

Fiber-reinforced polymer (FRP) composite bridges are usually constructed for rapid installation. The durability of the bridge is increased by stiffness, strength to weight ratio, and corrosion resistance. The main factors on which the design of the composite sandwiched bridge considerably depends are ply layers, material system, alignment of ply angles, and thickness of the core. In this work, a parametric design study for a bridge using finite element analysis (FEA) is presented. Two types of composite materials—carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP)—were used as the sandwich structure’s skin, and three different types of woods were used as a core. Different design configurations were acquired based on material and instability constraints by using Euro-codes. Failure criterion of Tsai-Hill, Tsai-Wu, MS, equivalent stress, and maximum shear stress were implemented to analyze the overall failure of the bridge deck under Ultimate Limit State (ULS) conditions. The total deformation was examined under Serviceability Limit State (SLS) conditions, and the results were compared and verified by the previous study. The core was also examined using the core-factor and increasing the thickness of the core through parametric modeling. Full article

The failure types and ultimate loads for eight carbon-epoxy laminate specimens with a central circular hole subjected to tensile load were tested experimentally and simulated using two different progressive failure analysis (PFA) methodologies. The first model used a lamina level modeling based on the Hashin criterion and the Camanho stiffness degradation theory to predict the damage of the fiber and matrix. The second model implemented a micromechanical analysis technique coined the generalized method of cells (GMC), where the 3D Tsai–Hill failure criterion was used to govern matrix failure, and the fiber failure was dictated by the maximum stress criterion. The progressive failure methodology was implemented using the UMAT subroutine within the ABAQUS/implicit solver. Results of load versus displacement and failure types from the two different models were compared against experimental data for the open hole laminates subjected to tensile displacement load. The results obtained from the numerical simulation and experiments showed good agreement. Failure paths and accurate damage contours for the tested specimens were also predicted. Full article

Investigation on the deformation mechanism of sandstone is crucial to understanding the life cycle patterns of pertinent infrastructure systems considering the extensive adoption of sandstone in infrastructure construction of various engineering systems, e.g., agricultural engineering systems. In this study, the state-of-the-art digital image correlation (DIC) method, which uses classical digital photography, is employed to explore the detailed failure course of sandstone with physical uniaxial compression tests. Four typical points are specifically selected to characterize the global strain field by plotting their corresponding strain–time relationship curves. Thus, the targeted failure thresholds are identified. The Hill–Tsai failure criterion and finite element simulation are then used for the cross-check process of DIC predictions. The results show that, though errors exist between the experimental and the theoretical values, overall, they are sufficiently low to be ignored, indicating good agreement. From the results, near-linear relationships between strain and time are detected before failure at the four chosen points and the failure strain thresholds are almost the same; as low as 0.004. Failure thresholds of sandstone are reliably determined according to the strain variation curve, to forecast sandstone damage and failure. Consequently, the proposed technology and associated information generated from this study could be of assistance in the safety and health monitoring processes of relevant infrastructure system applications. Full article