Post-fire mechanical properties of sandwich composite structures

Applications of sandwich composites are increasing as they continue to develop. The reason for the growth in development and the rising demand for sandwich composites in numerous industries is due to its ability to achieve high stiffness and strength, while simultaneously being lightweight in comparison to traditional materials. 3D printed plastic hollow core sandwich composites were focused on in this study where a bioplastic, Polylactic Acid (PLA), was compared to a conventional plastic, Polypropylene (PP). The study investigated the effects of varying core and face sheet parameters on the mechanical properties of 3D printed plastic core sandwich composites to obtain the optimum sandwich composite structure. A finite element model was developed in ANSYS Workbench to conduct the study. Numerical results were compared with experimental results, and both results revealed that the mechanical properties of sandwich composite structures are certainly influenced by the core and face sheet parameters. An optimum sandwich composite structure cannot be defined for a general case, as it depends on the application for which it is being designed. Hence, different optimum structures were determined for different desired mechanical properties.

Composite honeycomb sandwich structures are being widely used in the aerospace industry as a light weight structural design. However, the residual strength (damage tolerance) analysis required to address the vulnerability of such structures after the impact damage has proven difficult to perform with confidence. An integrated progressive failure analysis method is developed herein that simulates the progressive intra/inter laminar failure mechanisms observed in composite honeycomb sandwich structures. This method adopts a continuum damage mechanics approach and modifies the stiffness degradation scheme to enable prediction of the intralaminar matrix cracking and fiber fracturing. It also applies integrated VCCT/Cohesive method to allow the explicit modeling of interlaminar failure – the debond/delamination growth from the structural flaw, as well as the formation of the secondary debond/delamination that eventually merges with the primary damage to precipitate the ultimate failure of certain composite honeycomb sandwich structures. The formulation of the method are derived rigorously and summarized in this paper. The analysis predictions are correlated against existing test data for various honeycomb sandwich structures with an embedded flaw that fails in different failure modes.

Although much effort has been made to explore the characteristics of composite lattice truss core sandwich structures, little work has been undertaken into non-destructive evaluation (NDE) and structure health monitoring (SHM). This paper presents a baseline-free NDE method to determine the debonding of truss bar in composite lattice truss core sandwich structures. The method is proposed based on the uniform load surface (ULS) curvature and developed according to the combination of gapped smoothing method (GSM) and Teager energy operator (TEO), which is denoted as GSM-TEO method. The effects of truss bar on the vibration and wave motion characteristics of composite lattice truss core sandwich structures are firstly investigated, and then, experiment and numerical simulation are conducted to assess the performance of the proposed method. Results verify the method is reliable and applicable for damage localization in composite lattice truss core sandwich structures. doi: 10.12783/SHM2015/74

Experimental study of the influence of preliminary complex mechanical loads on the deformation and strength properties of polymer composites

Strength, stiffness, and panel peeling strength of carbon fiber-reinforced composite sandwich structures with aluminum honeycomb cores for vehicle body

When exposed to fire, load-bearing mass timber structures, such as cross-laminated timber (CLT), soften and decompose, which causes significant deformation and weakening, ultimately leading to failure. A combined experimental and modeling analysis is presented to predict the postfire residual compression properties of CLT. Multiple experimental fire exposure and postfire mechanical tests were performed under identical conditions to respectively characterize the internal and external thermal response of the CLT and assess the residual postfire compression properties. An analytical modeling strategy based on the measured through-the-thickness temperature profile during fire exposure is presented to predict the residual postfire compression properties of the CLT. X-ray computed tomography analysis revealed the charring rate to be nonconstant, which is in line with current research findings but not in line with Eurocode design suggestions. The analytical analysis revealed the transverse (cross) lamina to provide minor contribution to the axial compression properties but critically to the thermal protection and structural integrity of longitudinal (load-aligned) laminae during fire exposure.

Mechanical and oxidation properties of C/SiC corrugated lattice core composite sandwich panels

The existing studies indicate polymers will present obviously different properties in tension and compression (bimodular effect) which is generally ignored because of the complexity of the analysis. In this study, a functionally graded piezoelectric cantilever beam with bimodular effect was investigated via analytical and numerical methods, respectively, in which a one-dimensional theoretical solution was derived by neglecting some unimportant factors and a two-dimensional numerical simulation was performed based on the model of tension-compression subarea. A full comparison was made to show the rationality of one-dimensional theoretical solution and two-dimensional numerical simulation. The result indicates that the layered model of tension-compression subarea also makes it possible to use numerical technique to simulate the problem of functionally graded piezoelectric cantilever beam with bimodular effect. Besides, the modulus of elasticity E* and the bending stiffness D* proposed in the one-dimensional problem may succinctly describe the piezoelectric effect on the classical mechanical problem without electromechanical coupling, which shows the advantages of one-dimensional solution in engineering applications, especially in the analysis and design of energy harvesting/sensing/actuating devices made of piezoelectric polymers whose bimodular effect is relatively obvious.

Preparation of lightweight glass microsphere/Al sandwich composites with high compressive properties

Compression, bending, energy absorption properties, and failure modes of composite Kagome honeycomb sandwich structure reinforced by PMI foams

Composite honeycomb sandwich structure is widely used in aircraft wing leading edge, rudder surface, engine fairing, etc. It is susceptible to strong aerodynamic noise and impact loads from birds, hails, and stones. Therefore, it is essential to evaluate the life of structure with sound and collision load. In this paper, an acoustic fatigue life evaluation method based on vibro-acoustic coupling with impact damage is proposed. A representative composite honeycomb sandwich structure is built up to implement the proposed method. Firstly, the low-velocity impact process is simulated by the finite element (FE) method. This analysis case is used to get the structure with damage and material degradation. Secondly, the FE model is linked with the acoustic indirect boundary element (BE) model. A white Gaussian noise load is applied to the coupled FE/indirect BE model, and the power spectral density (PSD) curve of the structural dangerous point is obtained by modal-based vibro-acoustic coupling response case and random post-processing analysis case. At last, the fatigue life of the honeycomb structure is computed by the PSD theory. The result shows that with the increase of the impact energy, the structural life under the same acoustic load decreases. This method reveals high computational efficiency and excellent feasibility. The analytical result has reference value for the acoustic and mechanical properties design of composite honeycomb sandwich structure.

Nonlinear post-fire simulation of concentrically loaded rectangular thin-walled concrete-filled steel tubular short columns accounting for progressive local buckling

Integrating scrap rubber particles as fillers into polymer matrix composites offers a cost effective and environmentally sustainable pathway to manage tyre waste through the creation of value-added products. This research explores the low-velocity impact (LVI) response and compression after impact (CAI) properties of rubberised foam-core glass fibre-reinforced epoxy (GFRE) sandwich composites. Syntactic foam cores integrated with rubber particles were manufactured using vacuum-assisted resin transfer moulding (VARTM). The compression properties of rubberised foam core, vital for resisting impact damage during LVI, were examined. Results show more than 40% reduction in compression strength and modulus of the syntactic foam upon the inclusion of 33 wt.% rubber particles. The LVI response and residual compression properties of rubberised foam-core composites were also evaluated. Rubberised foam cores caused a marginal reduction in the peak impact force and led to approximately 60% reduction in the delamination area. The pre-impact compression strength was unaffected by rubber particles within the core as the GFRE face sheets carried most of the compression load. Post-impact compression strength was slightly higher in rubberised foam-core composites due to reduced delamination. Digital Image Correlation (DIC) analysis tracking of the strain evolution during CAI experiments revealed the stress-raising effect of the impact damaged region. This study showcases sustainable scrap tyre management through the inclusion of rubber particles into foam-core composites without substantially reducing in-plane compression properties before or after low-velocity impact.

ABSTRACTIn this study, a novel electromagnetic (EM) wave absorbing composite sandwich structure and its application process are proposed. The composite sandwich can be applied to the outer part of structures as a final surface treatment through a secondary bonding process, and this covers all the surface components that illuminate the incident EM waves. This process improves the structural material properties of the original components and their durability against the environment in contrast to EM wave absorbing paint or patch. With the help of EM wave absorbing characteristics and continuous impedance of the composite sandwich structures, the EM signals from reflection, diffraction, and scatter decrease effectively. The outer skin of the composite sandwich includes a resistive periodic patterned sheet prepared using printed electronics, and a low-dielectric foam is adopted as the core material. This composite is designed based on the equivalent circuit theory and is subsequently fabricated. The EM characteristics are tested after application on an aircraft skin structure through a secondary bonding process. The measurement of reflection loss and image processing of the reflected signal show that this composite and application process decrease the EM wave reflections from the original structure significantly.

Compact bone fatigue damage—I. Residual strength and stiffness