Composite Structural Components Research Articles

Unstable Delamination Growth in Stiffened Composite Panels Under Cyclic Loading Conditions.

Aeronautical structures can be damaged by objects during operation and maintenance. Indeed, foreign object impacts (FOIs) affect the overall performance of composite structural components. Delamination is the most critical damage mechanism as it is undetectable and develops silently. This phenomenon can be worsened by cyclic loading, as residual strength and stiffness can decrease rapidly, potentially leading to collapse. Unstable delamination growth is critical because it can occur without an increase in the applied load, threatening the integrity of the structure. Predicting this behaviour under fatigue loading is challenging for standard non-linear finite element methods (FEMs), which often face convergence problems when simulating the dynamic nature of delamination growth. This paper presents an efficient alternative methodology for analysing the propagation of delamination under cyclic loading in composite structures, with non-linear static analyses. This new methodology has been shown to be able to correctly account for the decrease in load carrying capacity during growth by performing ad hoc iterations with alternating force and displacement-controlled FEM simulations. To achieve this objective, the Paris law approach has been implemented in the ANSYS FEM code together with an enhanced virtual crack closure technique (VCCT)-based method. The model correctly predicted delamination growth in stiffened aeronautical panels with artificial delaminations subjected to cyclic compression loading.

Comprehensive analysis of thermal performance and low-grade energy charging efficiency of pipe-embedded building envelopes enhanced with single-level tree-shaped fin structures

Pipe-embedded walls (CnPWs) are structural and energy composite building components that can resist external disturbances by forming stealth thermal shielding layers. To tackle the mismatch between the heat charging rate and heat diffusion rate during energy charging processes, as well as the unsatisfactory robustness of stealth thermal shielding layers, the single-level tree-shaped metal finnd pipe-embedded walls (TfPWs) are proposed. To verify the effectiveness of TfPWs and obtain dynamic performances, a simulation study is conducted on 8 risk variables in 4 pairs through the validated numerical model. Results showed that the improved design was effective in obtaining more robust thermal shielding layers in auxiliary energy supply mode, the effect gained prominence as both the injection temperature and pipe spacing were augmented. In room heat load reduction mode, favorable benefits arise when pipe spacing exceeds 400 mm. The maximum increase rate of total injected energy under different reduction ratios of external insulation layer was 11.83%–31.91 %, while the maximum extra total heat loss was 5.33 %. Secondly, the trunk fins and branch fins played different roles in minimizing the excessive heat accumulation surrounding pipes, and the vertical and horizontal sizes of heat accumulation region mainly increased with the increase in trunk fin size and branch fin size respectively. Meanwhile, the utilization efficiency of fin material was higher when trunk fin size was smaller, and parameter combinations with trunk fin size of 0.2b and branch fin size of 0.4a/0.6a could achieve a better balance between material input and performance increase. Thirdly, the improvement effect of single left branch fin schemes was close to that of double branch fin schemes and significantly better than that of single right branch fin schemes. It was recommended to use single left branch fin schemes with an inclination angle of 60°. Finally, even if the reduction ratio of external insulation layer in different cities increased to 80 %, the inside surface temperature of TfPWs was still greater than room air. Taking CnPWs with standard external insulation layer as references, the TfPWs applied in Harbin, Beijing, and Shanghai could achieve similar or better results even when the reduction ratio of external insulation layer increased to 60 %, while TfPWs applied in Guangzhou could exhibit better performance even when the reduction ratio of external insulation layer increases to 80 %.

Study on the critical conditions for ductile-brittle transition in ultrasonic-assisted grinding of SiC particle-reinforced Al-MMCs

High volume fraction (45 %) silicon carbide particle-reinforced aluminum matrix composites (SiCp/Al-MMCs) play a significant role in various engineering fields due to their outstanding performance. However, damages characterized by SiC particle fracture during machining lead to poor surface integrity, which severely affects the fatigue performance of SiCp/Al composite structural components. Ultrasonic-assisted grinding (UAG) is acknowledged as beneficial for promoting ductile grinding in hard and brittle materials. This study focuses on the critical conditions for ductile-brittle transition in ultrasonic-assisted grinding of SiCp/Al composites and develops a mechanism and data driven model of critical undeformed chip thickness (UCT) for ductile grinding to accurately predict the material removal mode. The model thoroughly integrates considerations of chip morphology, removal mode transition mechanism, and grinding surface damage characteristics. Response surface methodology (RSM) and genetic algorithms (GA) were utilized to correct the impact of processing parameters on the removal regime. Experiments on ultrasonic-assisted side and end grinding were conducted to thoroughly discuss the effects of different undeformed chip thicknesses, grinding speeds and ultrasonic vibration amplitude on surface damage and the critical conditions for the ductile-brittle transition. The findings corroborate the experimental data with the predicted values. Ultrasonic vibration can effectively reduce the brittle fracture of SiC particles in SiCp/Al composites. Appropriately increasing the grinding speed and reducing the chip thickness can enhance the critical chip thickness for ductile grinding and decrease the proportion of brittle surfaces, thereby achieving a balance between surface integrity and grinding efficiency. This research provides guidance for high-performance machining of SiCp/Al composites.

Predicting the fatigue life of T800 carbon fiber composite structural component based on fatigue experiments of unidirectional laminates

This study is based on the fatigue experiment results of unidirectional laminates and investigates the fatigue performance of T800 carbon fiber/epoxy resin composite structural components through experimental and numerical analysis. Fatigue experiments were performed on [0]16, [90]16, and [±45]8 laminates individually, obtaining the fundamental fatigue parameters necessary for modeling. The fatigue life model for T800 carbon fiber/epoxy resin unidirectional laminates was refined, and fatigue degradation rules were provided for the fatigue progressive damage model. A fatigue progressive damage analysis model for T800 laminates was established based on the 3D Hashin criterion, predicting the fatigue life and fatigue damage failure process of the laminates. A fatigue life prediction model was developed for T800 carbon fiber composite I-beam structural components, which can predict the primary types of fatigue failure, fatigue life and the location of fatigue failure occurrence. The predicted fatigue life of structural components shows good consistency with the experimental results. This method can calculate structural components including ply angles of 0°, 45°, and 90° and obtain the fatigue life contour.

Modified honeycomb cores for enhancing the durability of sandwich structures under low-velocity impact

Honeycomb cores are essential components of composite sandwich structures, and enhancing their ability to withstand out-of-plane loads can improve the resilience of sandwich structures under low-velocity transverse impacts. Therefore, this study computationally investigates the potential for improving the out-of-plane strength of honeycomb cores by superposing periodic sinusoidal perturbations to their cell walls. Such perturbations have been used to enhance the acoustic properties of honeycomb cores. Results demonstrated that introducing these perturbations can improve the strength of honeycomb cores under localized out-of-plane loadings resembling colliding with small objects at low impact speeds. Superposed perturbations increased the out-of-plane strength by a maximum of 28.5 % and eliminated the post-buckling softening behavior. Moreover, they increased the toughness, represented by the area under the force-displacement curve, under localized out-of-plane loads by a maximum of 56.7%. The perturbed honeycomb cores showed more sensitivity to the frequency of the superposed perturbations than their magnitude.

Thermal/photothermal-induced flexible folding and rapid soft-to-rigid transition in dark fiber composite structural components

Foldable and deployable structures find extensive applications in space deployment equipment, yet dark fiber composites (DFCs) utilized for crafting these structures still grapple with the trade-offs among resin flow, curing speed, and degree of cure. To address these issues, a novel thermal/photothermal (TPT) system was developed, leveraging two-stage and photo-induced photothermal synergistic techniques. The first stage involves a room-temperature click reaction, producing a gel intermediate state with an impressive fracture elongation rate of up to 123.15 %, allowing for arbitrary flexible folding and deployment. The second stage involves photo-induced photothermal curing, where the heat generated during the curing process (reaching temperatures up to 131.5 °C) can trigger thermal curing. The second-stage sample can achieve a Young's modulus up to 22,000 times that of the first stage. When applied in the fabrication of DFCs, the TPT system significantly enhances the curing degree of the resin on the backside of the DFCs, achieving a rapid soft-to-rigid transformation within 1 min. This represents a significant improvement over thermal curing in terms of speed and energy consumption. The use of DFCs in structural components has demonstrated their capability for flexible folding and rapid soft-to-rigid transformation.

Experimental investigation of the behavior of UHPCFST under repeated axial tension

A ultra-high performance concrete filled steel tube (UHPCFST) is a composite structural component that extends the performance of both steel and concrete. It is a promising component to be used in a diagrid structure to further reduce self-weight. Compared with the research on compressive performance of UHPCFST, there is a lack of knowledge on the mechanical behavior of UHPCFST under axial tension. This paper fills this knowledge gap by carrying out experiments on UHPCFST subjected to monotonic and repeated tension. The test parameters are steel tube thickness and volume fraction of ultra-high performance concrete (UHPC). The failure modes, load-strain curves, tensile strength and tensile stiffness are studied in detail. Stiffness degradation is also studied. The test results show that: (1) under axial tension load, a UHPCFST typically experiences fracture failure of the outer steel tube, followed by section fracture of the UHPC, and notable deformation before a final ductile failure; (2) tensile strength increases with the increase of the thickness of the steel tube, while it is less obvious in a UHPCFST with a higher steel ratio; (3) the force-strain curve of a UHPCFST under monotonical axial tension is close to that of the UHPCFST under repeated axial tension, suggesting that the accumulated damage during unloading and reloading is limited. An exponential decay formula is proposed to predict stiffness degradation observed in the repeated axial tensile tests. It is found that the design codes from Europe, USA, and China underestimate tensile strength and stiffness of UHPCFST. Finally, a three-phase empirical model is proposed for the load-strain curve of UHPCFST under tension.

Image driven deep learning method with FFT solver for predicting the microscale full field stress of stochastic boundary composites

AbstractA novel image‐driven deep learning approach embedded with model‐data‐knowledge information can directly predict the full field stress distribution and mechanical properties of composites solely based on initial scanning geometry images. The fiber spatial distribution and morphological features are identified by Scanning Electron Microscopy (SEM) initially. An effective random fiber generation algorithm is further utilized to generate images database comprising equivalent geometric models of various microstructures. Subsequently, the geometry model images database is analyzed by fast Fourier transform (FFT) to produce the database including the elastic modulus parameters and full field stress distributions of composites with distinct microstructures. Finally, an innovative image‐learning comprehensive paradigm uniting convolutional neural networks and convolutional autoencoders is elaborated systematically to learn the inherent laws of geometry images and field images. The results show that the proposed method have capacity to effectively and accurately predict the elastic modulus and full field stress distributions combined with error analysis even for stochastic boundary composites. The proposed methodology is a symbiosis of cutting‐edge image learning and non‐destructive testing techniques for composites, which can directly use the local non‐destructive or scanning images of composite structural components to quickly obtain field information and further predict damage evolution online.Highlights Proposing a novel deep learning approach combined with FFT directly to predict stress distribution of stochastic boundary composites solely based on micro‐images. Adopting equivalent geometric models dispersed by higher pixels mesh density considering extreme thin interface. Incorporate adaptive algorithms for streamlined training optimization. An innovative integration of deep learning and non‐destructive testing technology for the stress distribution and properties prediction online.

Improving the impact performance of natural fiber reinforced laminate through hybridization and layup design

There is growing interest in Natural Fiber Reinforced Polymer (NFRP) composites for structural components despite their lower mechanical performance than synthetic composites such as Glass Fiber Reinforced Polymer (GFRP) composite. This study demonstrates significant improvement in impact resistance of NFRP-GFRP hybrid laminates can be achieved through the integration of laminate layup design with interlaminar hybridization. By placing more GFRP plies near the top and bottom of the hybrid laminate while reducing the occurrence of neighbouring GFRP-GFRP plies and neighbouring NFRP-NFRP plies around the centre of the laminate, the impact resistance of the hybrid laminate can be significantly improved and even surpass GFRP laminates. On top of stacking sequence of plies, the impact resistance of the hybrid laminates can be further improved by introducing a bio-inspired helicoidal layup. The result shows that with 30 wt% GFRP plies and 70 wt% NFRP plies, the perforation energy of NFRP-GFRP hybrid helicoidal laminate outperforms both the plain GFRP and plain NFRP laminates by 11.7% and 143.8%, respectively, whereas the peak load of the hybrid helicoidal laminate subjected to impact is also comparable to the plain GFRP laminate.

Enhanced Cathode Performance in Pr0.5Sr0.5FeO3-δ of Perovskite Catalytic Materials via Doping with VB Subgroup Elements (V, Nb, and Ta).

Perovskite-style materials are cathode systems known for their stability in solid oxide fuel cells (SOFCs). Pr0.5Sr0.5FeO3-δ (PSF) exhibits excellent electrode performance in perovskite cathode systems at high temperatures. Via VB subgroup metals (V, Nb, and Ta) modifying the B-site, the oxidation and spin states of iron elements can be adjusted, thereby ultimately adjusting the cathode's physicochemical properties. Theoretical predictions indicate that PSF has poor stability, but the relative arrangement of the three elements on the B-site can significantly improve this material's properties. The modification of Nb has a large effect on the stability of PSF cathode materials, reaching a level of -2.746 eV. The surface structure of PSF becomes slightly more stable with an increase in the percentage of oxygen vacancy structures, but the structural instability persists. Furthermore, the differential charge density distribution and adsorption state density of the three modified cathode materials validate our adsorption energy prediction results. The initial and final states of the VB subgroup metal-doped PSF indicate that PSFN is more likely to complete the cathode surface adsorption reaction. Interestingly, XRD and EDX characterization are performed on the synthesized pure and Nb-doped PSF material, which show the orthorhombic crystal system of the composite theoretical model structure and subsequent experimental components. Although PSF exhibits strong catalytic activity, it is highly prone to decomposition and instability at high temperatures. Furthermore, PSFN, with the introduction of Nb, shows greater stability and can maintain its activity for the ORR. EIS testing clearly indicates that Nb most significantly improves the cathode. The consistency between the theoretical predictions and experimental validations indicates that Nb-doped PSF is a stable and highly active cathode electrode material with excellent catalytic activity.

Ultrasonic Nondestructive Evaluation of Composite Bond Strength: Quantification through Bond Quality Index (BQI)

This article presents a concept, materials, and methods to devise a Bond Quality Index (BQI) for assessing composite bond quality, approximately correlating to the respective bond strength. Interface bonding is the common mechanism to join two composite structural components. Ensuring the health and quality of the bond line between two load-bearing composite structures is crucial. The article presents the classification and data-driven distinction between two types of bond lines between similar structural components. The interface bonds in composite plates were prepared using polyester peel ply and TX-1040 nylon peel ply. For all the plates, ultrasonic inspection through scanning acoustic microscopy (SAM) (>10 MHz) was performed before and after localized failure of the plate by impinging energy. Energy was impinged 0–10 J/cm2 of in the 16-ply plates, and 0–25 J/cm2 were impinged in 40-ply plates. Followed by bond failure and SAM, a new parameter called the Bond Quality Index (BQI) was formulated using ultrasonic scan data and energy data. The BQI was found to be 0.55 and 0.45, respectively, in plates with polyester peel ply and TX-1040 nylon peel ply bonds. Further, in 40-ply plates with polyester peel ply resulted in a BQI equivalent to 3.49 compared to 0.75 in plates with a TX-1040 nylon peel ply bond. Currently, the BQI is not normalized; however, this study could be used for AI-driven normalized BQIs for all types of bonds in the future.

Assessing critical fracture energy in mode I for bonded composite joints: A numerical–experimental approach with uncertainty analysis

The manufacturing process of composite structural components involves the assembly of composite parts using adhesives, which introduces variations in the geometrical and mechanical properties of bonded joints. The fracture energy under mode-I loading ( G I c) is a parameter used to predict crack propagation and evaluate the residual strength of the joint. This work proposes a numerical-experimental procedure to determine G I c in mode I, while considering the uncertainties inherent in the manufacturing process of bonded joints. The proposed procedure employs a three-dimensional finite element model to simulate a double cantilever beam test, using finite element commercial software. The cohesive zone model is applied to simulate the mechanical behavior of the adhesive, and experimental data are used to feed the computational model. A Plackett-Burman design is performed to reduce the number of experiments and evaluate the effect of the main influence parameters. Force-displacement curves are obtained, the compliance-based beam method is applied to determine G I c in mode I, employing both trapezoidal and triangular traction-separation laws. The results are thoroughly examined, taking into account the potential strengths and limitations of the proposed procedure, particularly in its application to predicting the behavior of bonded composite joints under mode I loading conditions. The proposed approach can help to understand the uncertainties effect related to the manufacturing process of bonded joints on G I c values, and improve the reliability of predicting crack propagation and residual strength assessment in bonded joints.

Havacılık Kompozit Malzemelerinde Mikroskobik Teknikler Kullanılarak Yapısal Sağlık İzleme Uygulamaları

Structural Health Monitoring (SHM) is a process that involves the observation and analysis of a system over time using periodically sampled response measurements to monitor changes to the material and geometric properties of engineering structures such as bridges, buildings, and aerospace composite structures. The goal of SHM is to detect changes in the structural behavior or condition that may indicate damage or degradation before a catastrophic failure occurs. SHM involves the implementation of damage detection strategies for structures of high importance. It is commonly used in civil engineering, aerospace engineering, and mechanical engineering applications to ensure the safety and reliability of structures. It improves the safety of aerospace composite structures by detecting damage at an early stage, preventing damage from occurring, improving reliability, and extending the life of the structure. SHM applications enable aircraft to spend less time on the ground and carry more passengers and cargo, thereby reducing operational costs. It can be utilized in various fields such as monitoring the health condition of aircraft tail and wing areas in the aviation industry, preventing damage and deterioration of car parts and components under operating conditions in the automotive sector, monitoring the health condition of bridges and tunnels in the transportation sector, and monitoring the health condition of wind turbines and other structures in the energy sector. Aerospace composite structures can suffer from several complex nonlinear damage modes, including impact damage, delamination, matrix cracking, fiber breakage, and voids. This study provides general and useful information on how structural health applications of aviation composites can be supported by microscopic techniques. In order to better understand the subject, an example aircraft composite structural component containing impact damage, which was mentioned above, was examined using microscopic techniques. In this investigation conducted using Stereo and Scanning Electron Microscopes (SEM), the identification of potential damage sources and the assessment of damage severity are explained in detail.

Graphite Nanoplatelets Nanostructured Films as Multifunctional Protective Layer in Kevlar/Nomex Sandwich Composites

In the aerospace sector, structural and non-structural composite components are usually subjected to a wide range of environmental conditions. Among all, moisture can seriously damage these materials’ performance, reducing their mechanical, thermal, electrical, and physical properties as well as their service time. Lightweight protective barrier coatings capable of reducing the diffusion of gases and/or liquids in a material can improve the material’s resistance in humid environments. In this work, nanolamellar nanocomposites characterized by a high in-plane orientation of nanoplatelets have been employed as protective coatings for Kevlar sandwich panels, reproducing the construction of a nacelle engine. The effectiveness of the protection against water uptake of nanocomposites reinforced with graphite nanoplatelets (GNPs) at high filler contents (70, 80 and 90 wt%) has been investigated using moisture uptake and Ground-Air-Ground (GAG) tests in an environmental chamber. GNP coatings effectively work as barrier by generating highly tortuous paths for molecule diffusion. Results showed a dependence of the absorption on the coating composition and inner structure. Films @70 wt% GNPs showed the best protection against moisture uptake by delaying the phenomenon and reducing the absorption by −80% after 3 days and −35% after 41 days.

Cognizant Fiber-Reinforced Polymer Composites Incorporating Seamlessly Integrated Sensing and Computing Circuitry.

Structural fiber-reinforced polymer (FRP) composite materials consisting of a polymer matrix reinforced with layers of high-strength fibers are used in numerous applications, including but not limited to spacecraft, vehicles, buildings, and bridges. Researchers in the past few decades have suggested the necessary integration of sensors (e.g., fiber optic sensors) in polymer composites to enable health monitoring of composites' performance over their service lives. This work introduces an innovative cognizant composite that can self-sense, compute, and implement decisions based on sensed values. It is a critical step towards smart, resilient infrastructure. We describe a method to fabricate textile sensors with flexible circuitry and a microcontroller within the polymer composite, enabling computational operations to take place in the composite without impacting its integrity. A microstructural investigation of the sensors showed that the amount of oxidative agent and soaking time of the fabric play a major role in the adsorption of polypyrrole (PPy) on fiberglass (FG). XPS results showed that the 10 g ferric chloride solution with 6 h of soaking time had the highest degree of protonation (28%) and, therefore, higher adsorption of PPy on FG. A strain range of 30% was achieved by examining different circuitry and sensor designs for their resistance and strain resolution under mechanical loading. A microcontroller was added to the circuit and then embedded within a composite material. This composite system was tested under flexural loading to demonstrate its self-sensing, computing, and actuation capabilities. The resulting cognizant composite demonstrated the ability to read resistance values and measure strain using the embedded microcontroller and autonomously actuate an LED light when the strain exceeds a predefined limit of 2000 µε. The application of the proposed FRP system would provide in situ monitoring of structural composite components with autonomous response capabilities, as well as reduce manufacturing, production, and maintenance costs.

Manufacture and characterisation of a structural supercapacitor demonstrator

Structural power composites, a class of multifunctional materials, may facilitate lightweighting and accelerate widespread electrification of sustainable transportation. In the example considered in this paper, structural power composite fuselage components could provide power to open aircraft doors in an emergency and thus reduce or eliminate the mass and volume needed for supercapacitors currently mounted on the doors. To demonstrate this concept, an 80 cm long multifunctional composite C-section beam was designed and manufactured, which powered the opening and closing of a desktop-scale composite aircraft door. Twelve structural supercapacitor cells were made, each 30 cm × 15 cm × 0.5 mm, and two stacks of four cells were integrated into the web of the beam by interleaving and encasing them with low-temperature-cure woven carbon fibre/epoxy prepreg. This article culminates by considering the engineering challenges that need to be addressed to realise structural power composite components, particularly in an aerospace context.

Investigation of Ti alloying for microstructural evolution and strengthening mechanism: Avoiding Al4C3 formation in SiCp/Al composites via laser directed energy deposition

The near-net-shape characteristics of Additive Manufacturing offer significant advantages in fabricating SiCp/Al composite components. However, the high-temperature melt pool during the deposition process promotes an interface reaction between SiC and Al, forming Al4C3. Al4C3 shortens the service life of SiCp/Al composite structural components, so it is critical to avoid its formation when preparing SiCp/Al composites via laser-directed energy deposition. This study prepared SiCp/Al composite components through coincident wire powder laser-directed energy deposition with Ti alloying, effectively preventing the formation of Al4C3 in AMC. Furthermore, it investigated the effect of Ti atoms on the microstructural evolution and strengthening mechanism. The results showed that the formation of large flake-like Al4C3 was avoided without generating excess Al3Ti only when using an appropriate amount of Ti (Ti: SiC = 3: 10). After introducing Ti, Ti atoms in the melt pool migrated towards the SiC surface and reacted with C atoms (from the dissolution of SiC) and formed TiC. The resulting TiC enclosed the SiC particles in a thin film, preventing the further dissolution of SiC and inhibiting the generation of Al4C3. Additionally, some TiC nanoparticles dispersed within the matrix, serving as heterogeneous nucleation sites for Al, reducing the average equivalent circular grain radius from 38.10 µm to 7.20 µm. After Ti alloying, the average modulus and yield strength of AMC both increased. This increase was attributed to the load transfer energy of SiC particles, grain refinement of the matrix, and the dispersion-strengthening effect of TiC nanoparticles. An intrinsic relationship between the SiC-Al-Ti interfacial reaction and the mechanical properties of SiCp/Al composites has been established to provide theoretical guidance for eliminating Al4C3 phases in SiCp/Al composites prepared by laser-directed energy deposition, ensuring performance comparable to traditionally fabricated products.

Numerical Analysis of Flexural Performances of Composite Steel-Timber Beams under Fire Conditions

Recently, a novel type of composite structure, composite steel-timber (CST) structure, has attracted much attention by combining steel and timber in an effective way to form composite structural components, which unitises the advantages of high strength and excellent ductility of steel and decent sustainability and fire resistance of timber. However, the existing research is lacking, especially in structural fire design and analysis. In this study, based on the sequentially coupled method, the commercial finite element software ABAQUS was used to numerically simulate the dynamic performances in the temperature field and the flexural behaviours in the displacement field for a typical CST beam with a steel element embedded within the Glulam and connected by adhesives and bolts under standard fire for two hours. In the numerical simulations, the temperature distributions within the CST beam were explored, and the flexural performances of the beam in the displacement field were examined. Through the comparative analysis, the temperature distributions in the embedded steel beam and the surrounding Glulam beam under one-hour standard fire verified the advantages of this type of CST beam in structural fire design. Specifically, under a 2-hour standard fire, the surrounding Glulam could still protect the embedded steel beam from sustaining too high temperatures, so as to retain most of its material properties and help maintain the bearing capacity of the whole structure and improve the refractory limit. Parametric studies on the fire resistance of the CST beam were also conducted by adjusting the bolt spacing and the protection thickness of the Glulam. The obtained results indicated that reducing the bolt spacing and the thickness of the Glulam protection layer would have an adverse effect on the temperature distributions in the embedded steel element to a large extent, and would eventually lead to its rapid heating and strength loss and the final failure of the whole CST structure.

Numerical prediction of thermoacoustic responses of CNT reinforced natural (luffa) fibre/epoxy hybrid composite and experimental verification

This research reported the thermoacoustic radiation characteristics of luffa fibre/epoxy hybridised with MW-CNT (multi-walled carbon nanotube) composite flat panel structures. The acoustic responses are evaluated under harmonic excitation and uniform thermal environments. The panel model is derived from a coupled scheme by merging two different computational techniques, i.e., finite element method, FEM (structural modelling) and boundary element method, BEM (fluid part), via higher-order deformation kinematics. Additionally, the higher-order panel model utilises an equivalent single-layer theory for computational purposes. The responses are obtained through MATLAB computer code from the derived mathematical formulation by customising the parameters (geometry and material). A few frequency responses with and without environmental effects are compared with experimental data from home-grown experimentation facilities. The impact of individual parameters is thoroughly analysed, and highlighted their significance in controlling the panel’s acoustic radiation behaviour. The findings of this study contribute to the understanding of the acoustic radiation properties of luffa fibre/epoxy hybridised with MW-CNT composite flat panels. The higher-order coupled FEM-BEM scheme-based tailored MATLAB code also provides a reliable computational tool for analysing various composite structural components for futuristic design. This research would be a valuable reference for optimising composite flat panel structural design and performance in engineering applications requiring enhanced vibroacoustic control.

Composite component incremental consolidation for fiber waviness inhibition and its effect on damage progression of curved beams

AbstractSevere fiber waviness defect often occurs during the consolidation process of fiber reinforced polymer composite component, which arises from that multiple interactional plies start to slide simultaneously and out‐of‐control under sufficient pressure. In this study, based on the significant in‐plane tension gradient along thickness of viscoelastic composite, a concept of incremental consolidation was proposed to actively inhibit fiber waviness in prepreg‐based composite component. Via applying a series of tiny step pressures continuously, plies were triggered to slide and consolidate layer by layer from top to bottom with a just‐right in‐plane tension and concurrent stresses relaxation. Incremental consolidation avoided the complex interaction among plies and allowed in‐plane tension to be significantly reduced by 165 times compared with autoclave processing with a constant pressure. The fiber waviness defects in a typical wing spar were successfully inhibited by the proposed method. The failure load of the component increased by 1.5 times and curved beam strength increased by 1.1 times while elastic displacement increased by 75%. The inhibition method was highly effective, easy to implement and affordable, which showed considerable promise to improve the manufacturability of the primary structural composite components.