Design Of Composite Structures Research Articles

On Crashworthiness and Energy-Absorbing Mechanisms of Thick CFRP Structures for Railway Vehicles.

This study aims to provide important guidelines for the crashworthiness design of composite energy-absorbing structures, especially railway vehicles. An experimental and numerical investigation was carried out to explore the crushing response of circular composite tubes reinforced with plain woven carbon fiber-reinforced polymers (CFRP). Quasi-static and dynamic axial crushing tests were performed on CFRP tubes with an inner diameter of 100 mm and a nominal wall thickness of 12 mm. Experimental results showed that increasing loading velocity led to a 21.8% reduction in specific energy absorption (from 99.7 kJ/kg to 78.7 kJ/kg) but had negligible influence on failure modes. Finite element models were also established and validated against the experimental results using ABAQUS/Explicit software. The effects of several different parameters such as the number of shell layers, friction coefficient, and interface properties on the simulated results, were also investigated and analyzed. A small variation in these parameters could change the total energy absorption of CFRP tubes. The comparisons between the predicted and experimental results indicated that a finite element model with 10 shell layers could effectively replicate the crushing response. In addition, the simulated results indicated that the damage of tubal wall materials dominated the major energy-absorbing mechanisms of CFRP tubes under quasi-static loads, which was 69.1% of the total energy. The energy dissipated by friction effects between the loading platen and the crushed fronds was 24.1% of the total energy. The increase in the loading velocity led to a decrease in the composite damage energy except for friction energy, resulting in a decrease in the total energy absorption.

Composite structure design of a broadband metamaterial absorber based on magnetic composites

The requirements for electromagnetic wave absorbing materials are increasing as modern technology advances. However, traditional absorbing materials have limitations due to their thickness and incompatibility with high and low frequencies, and metamaterial absorbers have limitations due to their narrow effective absorption bandwidth. This paper overcomes these problems and designs and prepares a broadband, thin and light metamaterial absorber. The effective absorption bandwidth of the composite structure metamaterial absorber (CSMMA) with a thickness d1 of 3 mm reaches 11.55 GHz with the addition of FeSiBPCuY5p/paraffin magnetic composite into the metamaterial absorber and the optimization of the structural parameters. The composite structure design greatly improves the absorption performance of the metamaterial absorber. The advantages of the tunable frequency absorption characteristics of the metamaterial absorber and the high-frequency broadband absorption performance of the magnetic wave absorbing materials are fully exploited in the design of the absorber. Which is of great significance for the development of broadband and thin-absorbing materials. This absorber can be adapted to meet the needs of practical applications by adjusting its structural design, expanding its range of applications and having a substantial influence on the use of wave absorbing materials.

Large amplitude vibration and bistable jump of functionally graded graphene-platelet reinforced porous composite plates

Using high-performance lightweight functionally graded graphene-platelet reinforced (FG-GPLR) porous composite plates opens up an avenue for a new generation of structural and material designs, which could be tailored to the need of specific applications. Consider the von Karman plate model with geometrical nonlinearity, the equation of motion can be formulated. The Halpin − Tsai model is employed to predict the elastic properties of FG-GPLR porous composite plates. The moving Kriging interpolation mesh-free computational framework, which is confirmed to have high computing performance in terms of accuracy, convergence and robustness, is used to discretize the nonlinear vibration equation. Then, the linearized updated mode (LUM) method is used to obtain iterative solutions. An intensive work, investigating the influence of boundary constraints, porosity distributions, graphene platelets (GPLs), and vibration amplitudes, is conducted. It is found that a continuous increase in the amplitude parameter ultimately yields an abrupt change of the fundamental frequency, inducing a bistable vibration mode jump phenomenon. The present results can provide useful guidelines for the application design of nano-reinforced composite structures.

The design of blended laminates regardless of the stack: The search propagation direction

Handling blending constraint, a fundamental manufacturing requirement for the design of composite structures made of laminates with different thickness, is a hard task. A rigorous methodology to construct blended laminates regardless of the orientation value and of the position of the dropped plies within the laminates is presented and justified from a mathematical perspective in this work. The concept at the basis of the methodology is referred to as search propagation direction. It allows for a net simplification of the stack recovery phase. Since blending is automatically satisfied between adjacent laminates, the problem is reduced to determine orientation values, in analogy to the stack recovery problem for a single laminate.

Fusion-bonding performance of short and continuous carbon fiber synergistic reinforced composites using fused filament fabrication

In this work, short and short continuous fiber synergistic reinforced composites (S-CFRPCs) were successfully fabricated by fused filament fabrication. The influences of short fiber content on the filament bonding properties were evaluated through short beam shear (SBS) and in-plane tensile shear tests. The data showed an increasing and then decreasing trends of interlaminar shear strength (ILSS) and in-plane shear strengths of S-CFRPCs specimens as short fiber content rose from 0 wt% to 10 wt%. Specimens with a short fiber content of 5% displayed higher load carrying capacities and significant fusion-bonding performances, with approximately 41% and 80% increase in ILSS and in-plane shear strength when compared to 0% specimen, respectively. The fracture surfaces of tested S-CFRPCs specimens indicated fiber pull-out and resin fracture as dominant bonding failure models. The use of proper amounts of short fibers effectively improved the fusion-bonding of S-CFRPCs. In sum, these findings look promising for future design of strong and tough composite structures.

Deep learning approach for delamination identification using animation of Lamb waves

The complex design of composite structures makes it very difficult for conventional visual inspection techniques to detect defects in these materials. Therefore, numerous types of nondestructive testing and structural health monitoring techniques have been developed for damage identification in composite structures, among which ultrasonic guided waves, particularly Lamb waves, have gained much popularity. In recent years, apart from piezoelectric pointwise measurements, laser Doppler vibrometry has been used for full wavefield measurements of propagating Lamb waves. Damage imaging can be done with animations of Lamb waves interacting with defects. In this work, two end-to-end deep learning-based models of many-to-one sequence prediction were developed to perform pixel-wise image segmentation. A large dataset of full wavefield images resulting from the interaction with delamination of random size, shape, and location was utilised to train the proposed deep learning models. The main goal of this work is to investigate the feasibility of implementing deep learning methods for delamination identification in composite laminates by only utilising the animations of Lamb waves. The elaborated models worked well on the numerically generated test data and have also shown good performance on the real-world experimental data. These methods can enable the automation of delamination identification and to create damage maps without the intervention of the user.

Multi-Objective Optimization for Curvilinearly Stiffened Porous Sandwich Plates Reinforced with Graphene Nanoplatelets

With the development of innovative manufacturing technology, multi-objective optimization algorithms for optimal design of advanced composite structures have gained increasing attention. An effective and high-accurate prediction on the mechanical behavior of structures is the basic core of optimization algorithms. Thus, a novel refined sinusoidal higher-order theory (NRSHT) combined with isogeometric analysis (IGA) is developed as the high-precision solver. A novel curvilinearly stiffened porous sandwich plate reinforced with graphene nanoplatelets (CSP-GPL) is proposed as the research object. Compared with previous higher-order theories, the proposed NRSHT can more accurately forecast the natural frequencies of CSP-GPL through several numerical and experimental tests. Subsequently, the shape and material distribution design of CSP-GPL are studied with multi-objective optimization. The random forest regression (RFR) is utilized as the high-fidelity surrogate model to construct the objective function in the improved Nondominated Sorting Genetic Algorithm (NSGA-II), which can significantly accelerate the integration of NRSHT-IGA and NSGA-II. Finally, the Pareto-optimal solutions, optimizing for fundamental frequency and total mass of CSP-GPL, are obtained from the present platform, which can give effective suggestions for the future designer to meet specific requirements.

Composite structure in the Kutus-kutus factory building, Gianyar, Bali

This study focuses on the design implementation and performance analysis of concrete-steel composite structure of a four-story Kutus-Kutus Factory, a facility for the production of herbal oils, built in the seismically active Gianyar district of Bali. In order to create an efficient, fully composite cross section, the design process uses an analytical approach that emphasizes the relationship between the concrete slab and steel beams as well as the design of each of these components. The structure was designed and assessed in accordance with Indonesia Building Standard guidelines for minimum load, earthquake-resistant, and concrete and steel based material requirements. The final results of the design confirmed that the composite performance is strong enough to withstand enormous loads combined in industrial buildings, particularly in seismically active areas, and can operate within the recommended safety margins and restrictions. This paper ends with a call for more research on the real application of composite structure design in Indonesia, which can then assist the rapidly expanding Indonesian construction industry in maximizing the advantages of using composite construction techniques.

Multiscale topology optimization of biodegradable metal matrix composite structures for additive manufacturing

Recent advances in biomedical engineering have promoted the development of innovative metal implants that have integrated mechanical and biodegradable properties. Most of the existing implant designs were created by using a trial-and-error approach, which depends on the designer's experience. Alternatively, inverse design approaches, such as topology optimization, have evolved into an efficient design solution to optimize the structural and material layout within a given design domain. Here we introduce a novel topology optimization scheme to support the microstructural design of biodegradable metal matrix composite structures (BM−MCS). The effect of material degradation on the mechanical performance of the structure is considered by integrating a degradation simulation algorithm into the structural finite element (FE) analysis. The objective function is to minimize the structural compliance at macroscale in a certain number of time steps to realize sufficient structural integrity in the initial bone healing stage, and the different stiffness reduction properties can be adjusted by changing the volume ratio of the two base constitutive biodegradable materials. The sensitivity of the above objective function concerning design variables was derived with considering the time-dependent degradation of the biodegradable material. Several numerical design examples were presented and benchmarked with classical designs. Finally, several prototypes were fabricated by integrating additive manufacturing with casting technology. Collectively, this demonstrates the feasibility and effectiveness of the proposed inverse design method for additive manufacturing.

Experimental characterization and numerical modelling of the translaminar fracture of woven-ply hybrid fibers reinforced thermoplastic laminates

The understanding of fracture mechanisms and the assessment of fracture toughness are key factors to the design of high-performance composite structures to be used in aeronautics. Thus, this work addresses the influence of initial notch orientation on the translaminar fracture of woven-ply hybrid fibers reinforced thermoplastic polyether ether ketone (PEEK) laminates. The translaminar fracture of Single-edge-notch bending (SENB) specimens is experimentally characterized depending on two initial notches (0° and 45°). Such geometry results in a complex stress state within the laminates plies as well as simultaneous tension/compression failures. A full-field measurement technique has been implemented to monitor the crack initiation and growth on the specimen surface during mechanical loading. To better understand the role played by the initial notch orientation as well as the plies orientation contribution to fracture behavior, a specific Finite Element mesoscale model was built to account for the deformation mechanisms (namely local plasticity) and the different damage behaviours (fiber breakage in tension and compression, kinking/crushing in compression, delamination) occurring within the plies of quasi-isotropic laminates. Linear elastic fracture mechanics concepts have been applied to quantify the critical translaminar fracture toughness (about 40 kJ/m2 in both cases). Finally, this study provides useful information on the fracture toughness values for engineers willing to design thermoplastic-based composite parts with stress concentrators.

Investigation of Biaxial Properties of CFRP with the Novel-Designed Cruciform Specimens.

The biaxial loading properties of carbon-fiber-reinforced polymer (CFRP) are critical for evaluating the performance of composite structures under the complex stress state. There are currently no standardized specimens for the CFRP biaxial experiments. This work developed a new design criterion for the cruciform specimen coupled with the Hashin criterion. The finite element analysis was conducted to investigate the effect of geometric parameters on the stress distribution in the test area. The embedded continuous laying method (ECLM) was proposed to achieve the thinning of the center of the test region without introducing defects. The manufacturing quality of the cruciform specimens was verified by the ultrasonic C-scanning test. The biaxial test platform consisting of the biaxial loading system, digital image correlation (DIC) system, strain electrical measurement system, and acoustic emission detection system was constructed. The biaxial tensile tests under different biaxial loading ratios were conducted. The results showed that the biaxial failure efficiently occurred in the test area of the cruciform specimens designed and manufactured in this paper. The failure modes and morphology were characterized using macro/microscopic experimental techniques. The biaxial failure envelope was obtained. The results can be used to guide the design of composite structures under biaxial stress.

Dynamic characteristics of composite damping sandwich open conical shell

In this work, the dynamic characteristics of composite damping sandwich open conical shells are investigated. Considering the superposition effect of rotational inertia and shear deformation during structural vibration, the expressions of kinetic energy and strain energy of composite damping sandwich open conical shell (CDSOCS) are derived based on the first-order shear deformation theory. The Rayleigh-Ritz method is used to establish the free vibration equations for thin and medium-thickness shells. According to the simply supported boundary conditions, the Navier double series method is used to solve the vibration equation. The theoretical solution is compared with the previous results and ANSYS finite element simulation results, and the rationality and effectiveness of the theoretical calculation model are verified. The influence of the thickness change of the sandwich layer under different laying angles and the position change of the sandwich layer under different thickness-diameter ratios on the dynamic characteristics of the CDSOCS is discussed, which provides a reference for the design of orthotropic composite damping sandwich complex structures.

A comprehensive investigation on bending stiffness of composite grid-stiffened and functional foams sandwich beam

This paper investigates the bending stiffness of composite grid-reinforced sandwich beams with functional foam cores by a combination of analysis, simulation, and experiment. First, the sandwich layer composed of stiffeners and foam cores is homogenized, and the equivalent mechanical parameters of the sandwich layer are proposed. Then, based on the first-order shear deformation theory, the three-point bending deflection of the beam is derived and verified by tests and simulations. Finally, the factors affecting the bending stiffness are investigated, such as the elastic modulus of the foam cores, the thickness of the stiffeners, the longitudinal and transverse spacing of the stiffeners, and the fiber lay-up angle of the stiffeners. The results of this paper are of great significance to the stiffness design and parameter optimization of composite grid-stiffened sandwich structures with foams for underwater vibration and noise reduction.

Optimal Desing of Composite Box-Type Structures

The present paper considers the optimization methods of box-type thin-wall structures both in terms of materials and in terms of calculation methods. These structures are widely used in transport, construction and other areas. The example of such structures are bodies of buses, trolleybuses, trams, camper vans, train carriages, emergency vehicles, mobile workshops, accommodation facilities and others. At first global and later local optimization for the preset exposure by system analysis, mathematical modelling and IT-technologies were performed. Determination of global target function and optimization criteria, global and local limitations is shown during optimization. Development of a box-type composite thin-wall structure project was suggested including geometric simulation, selection of material components and whin-wall elements composition. For the purpose of comparison application of nature biological organism for combination of composite panel by separation of principal organ systems providing its vital activity: a locomotive, circulatory, inspiratory and etc., was described. It was shown that similarly to an organism a vehicle (non-uniform system) can provide general and local strength and rigidity of structural elements. When composing a thin-wall element, each variant of a panel is considered as a module with its physical and mechanical characteristics. Methods that can be applied to nonuniform structure analysis and formulae to determine the given flexural rigidity of plate and shell elements of “equivalent” uniform material are described further. An example of box-type thin-wall composite structure optimal design was shown. The conclusion with regard to the proposed method of optimal analysis and design of composite thin-wall structures is made by means of system approach.

Impact simulation of composite panels for aerospace applications

The aerospace research community has been working towards the development of a comprehensive framework for the design of composite structures at the component, subassembly, assembly, and system levels. Such a framework requires accurate, efficient and easy-to-use mathematical and computational models that are in sync with physical reality. The research work in this paper is designed to help an aerospace structural engineer move towards this goal by simulating dynamic impact to composite panels. First, the existing orthotropic visco-elastic visco-plastic material model in LS-DYNA commercial finite element program, MAT_COMPOSITE_TABULATED_PLASTICITY_DAMAGE (MAT_213) is enhanced with the development and use of rate-dependent damage data. Using state-of-the-art experimental procedures, impact validation test data are created. Second, the versatility of the constitutive model is examined by its ability to simulate a low velocity (27 ft/s, 8 m/s) impact test, and two high velocity impact tests (385–417 ft/s, 117–127 m/s) that straddle the ballistic limit of the projectile and the composite panels. Third, these impact events are modeled using three different finite element types – under-integrated and fully-integrated solid elements, and fully-integrated thin shell elements. Insight into accuracy versus numerical efficiency is gained by comparing the performance of solid versus thin shell elements. The numerical results show that accurate predictions of these impact events can be obtained with reasonable effort and care.

Optimal design of broadband radar-absorbing composite structures based on different compositions, processing, and geometric parameters

The main challenge in the design of radar-absorbing composite structures (RASs) is that there is a variety of different parameters affecting the absorbing performance. In this study, these parameters are categorized into: (1) reinforcing materials including fabric types (i.e., glass fabric, carbon fabric, and 3D fabric) and filler types (i.e., carbon black, carbonyl iron, and polyaniline); (2) geometric parameters including layer thickness and stacking sequences; and (3) manufacturing methods. Up to now, the effect of all these parameters has not been simultaneously investigated and optimized on the X-band radar-absorbing feature of composite structures. Therefore, the influence of all these parameters is first experimentally investigated using waveguide tests; then, a new multi-objective optimization algorithm based on NSGA II technique is developed to simultaneously optimize the effective parameters for high-performance RAS with maximum average reflection loss and minimum weight, while considering structural limitations. Finally, the proposed algorithm is evaluated by experimental results.

Potential Benefit of Structural Health Monitoring System on Civil Jet Aircraft.

Structural health monitoring represents an interesting enabling technology towards increasing aviation safety and reducing operating costs by unlocking novel maintenance approaches and procedures. However, the benefits of such a technology are limited to maintenance costs reductions by cutting or even eliminating some maintenance scheduled checks. The key limitation to move a step further in exploiting structural health monitoring technology is represented by the regulation imposed in sizing aircraft composite structures. A safety margin of 2.0 is usually applied to estimate the ultimate loading that composite structures must withstand. This limitation is imposed since physical nondestructive inspection of composite structures is really challenging or even impossible in some cases. However, a structural health monitoring system represents a viable way for a real time check for the health status of a composite structure. Thus, the introduction of structural health monitoring should help into reducing the stringent safety margin imposed by aviation regulation for a safe design of composite structures. By assuming a safety margin reduction from 2.0 to 1.75 thanks to the installation of permanently attached sensors for structural health diagnostics, this paper assesses the potential fuel savings and direct operating costs through a multidisciplinary analysis on a A220-like aircraft. According to the foreseen level of technology, addressed through the number of sensors per square meter, a DOC saving from 2% up to 5% is achievable preserving, at the same time, all the key aircraft performance.

An aeroelastic optimisation framework for manufacturable variable stiffness composite wings including critical gust loads

This work presents a new aeroelastic optimisation framework for the preliminary design of variable stiffness composite wing structures. The framework is constructed by sequentially and iteratively solving two sub-problems: aeroelastic tailoring and lay-up retrieval, using gradient-based algorithms with full-analytical sensitivities provided. During aeroelastic tailoring, the wing mass is minimised by optimising the lamination parameters and thickness of wing laminates together with wing jig twist distribution. The load cases cover not only static loads, but also the critical gust loads that are identified across the entire flight envelop at every iteration of optimisation. Further, a cruise shape constraint is included in addition to other aerostructural constraints, so that the optimal aircraft performance can be ensured. During lay-up retrieval, the manufacturable stacking sequence is retrieved according to the optimal lamination parameters with the consideration of minimal steering radius constraint. Moreover, to fix the possible constraint violations caused by lay-up retrieval, a correction strategy is incorporated to tighten the violated constraints for repeating aeroelastic tailoring. Finally, several case studies on the design of NASA common research model wing are carried out and investigated. The results indicate that the critical gust loads and cruise shape constraint have a large influence on the design of tow-steered composite wing structures, which therefore demonstrate the usefulness and benefits of the proposed optimisation framework.

Design and Analysis of Composite Structure for Industrial Platforms

Design and Analysis of Composite Structure for Industrial Platforms

Parametric Influences of Geometric Dimensions on High Temperature Mechanical Behaviors and Damage Mechanisms of Ceramic Matrix Composite and Superalloy Double Bolted Joints

Given multiple material performance advantages, ceramic matrix composite (CMC) material has become one of the most promising hot structural materials used for thermal protection system in hypersonic vehicles. Under harsh thermal exposure of vehicles in flight, the design of connection structure would be a critical issue in improving load-carrying efficiency and ensuring service safety of aircraft structures in service environments. However, little attention was paid on mechanical behavior and its factors affecting the mechanical property of CMC joining at elevated temperature. To address this concern, a 3D finite element model coupled with progressive damage analysis is carried out to predict high temperature tensile properties and failure behavior of single-lap, double-bolt CMC/superalloy joints assembled by two serial protruding-head bolts. In the implementation of progressive damage analysis of 2D plain-woven C/SiC composites, a user-defined subroutine UMAT including a nonlinear constitutive model, 3D Alvaro failure criterion and Tan’s material degradation rule were embedded into the general package ABAQUS® through Fortran program interface. A parametric study considering geometries of joints was performed to evaluate their resultant influence on high temperature tensile behavior and the associated damage mechanisms for the CMC/superalloy double-bolt joint. New findings were provided for full exploitation of high performance through geometric design of ceramic matrix composite hot structure for hypersonic aircraft.