Design Of Composite Structures Research Articles

Mechanical properties of FRP materials at elevated temperature – Definition of a temperature conversion factor for design in service conditions

One of the main concerns about the use of fibre-reinforced polymer (FRP) materials in civil engineering structures is the potential reduction of their stiffness- and strength-related properties when exposed to elevated temperature. This concern, mostly due to the glass transition process underwent by polymeric matrices, needs to be duly reflected in design standards. In the scope of the development of the European Technical Specification CEN/TS 19101: 2022, “Design of Fibre-Polymer Composite Structures”, this paper presents the definition of a temperature conversion factor for in-service conditions to take into account the reduction of FRP mechanical properties with temperature. The first part of the paper briefly describes the basis of design of CEN/TS 19101: 2022 and the framework to consider the effects of environmental conditions on material properties. The second part presents an assessment of recommendations about the reduction of mechanical properties with temperature in existing design guidelines for FRP structures. The third part describes a survey of test data available in the literature concerning mechanical tests at elevated temperature of FRP materials produced with different fibres, resins, shapes and manufacturing methods. The survey shows that the provisions available in existing design guidelines are not always precise and, in some cases, they are non-conservative. Based on this assessment, the fourth and final part of the paper presents the method used to define the values of the temperature conversion factor included in CEN/TS 19101: 2022, which is consistent with the partial factor method of the Eurocodes. The method takes into account (i) the maximum service temperature experienced by the FRP material, (ii) its glass transition temperature, and (iii) the type of mechanical property, namely if it is either fibre- or matrix-dominated. The proposed temperature conversion factor values proved to be adequate considering the test data available in the literature.

Multi-Scale Analysis for Assessing the Impact of Material Composition and Weave on the Ultimate Strength of GFRP Stiffened Panels

A micro-meso-macro analysis framework based on the multi-scale method was employed to analyse the mechanical behaviour of marine GFRP stiffened panels. The study aims to establish a procedure for assessing the impact of material composition and weave on the ultimate strength of GFRP stiffened panels. The ultimate strength assessment was an essential step in the design process, and the investigation of construction materials has a great benefit to the lightweight design of marine composite structures. The micro- and meso-scale RVE models of components used in GFRP materials are established, and their failure criteria and stiffness degradation models are created using the user-defined material subroutine VUMAT in ABAQUS. The equivalent material properties at the micro-scale (meso-scale) obtained by a homogenisation method are used to define the meso-scale (macro-scale) mechanical properties in the finite element analyses. The multi-scale method assesses the macro-mechanics of composites, and it is shown that the ultimate strength of GFRP stiffened panels is mainly determined by the failure of CSM fibre bundles and WR yarns. Parametric study of the meso-mechanics of composite materials can provide an analysis tool to obtain the optimal macro ultimate strength of the composite stiffened panel.

Development and validation of finite element models for buckling of open-hole fiber-reinforced composites at ambient and cryogenic temperatures

Understanding the buckling behavior of fiber-reinforced composites (FRCs) is critical for the design of composite structures. In this study, finite element (FE) models of FRC buckling behaviors were developed and validated. The validated FE models could accurately predict the numerical and experimental observations in the literature. The effect of the specimen geometric imperfections was included in the model to secure a realistic FE model; to this end, linear buckling analyses were employed before beginning the nonlinear buckling analyses. The FRCs’ mechanical properties and buckling behavior of FRCs can be temperature-dependent. Because the presence of a hole in the design of composite structures may be inevitable in a few applications, the temperature-dependent buckling responses of open-hole glass/epoxy, glass/polyester, carbon/epoxy, and carbon/polyester composites were compared with those of the plain specimens. The effects of the fiber and resin types, temperature, and the presence of holes on buckling behavior were investigated and discussed in detail. Five different temperatures, 25, 0, −50, −100, and −180 °C were considered. The cryogenic temperatures raised Young’s moduli and consequently raised the critical buckling loads. The validated models and results on the open-hole composites can be used as benchmarks in composite structure designs involving buckling behavior.

Local buckling resistance of Pultruded FRP columns: Theoretical predictions vs. Experimental study

Fiber-Reinforced Polymer (FRP) in the form of thin-walled plate structures are widely used in different engineering applications due to their outstanding features such as: high strength-to-weight ratio, excellent fatigue and corrosion resistance, etc. Due to the low stiffness, design of FRP material is usually governed by deformations or instabilities, rather than strengths. The development of a technical specification for design of FRP composite structures requires the understanding on buckling behaviour of FRP components. Local buckling of pultruded FRP column is a type of structural instabilities, occurs when the compressive stress reaches to the level that form waves in the flanges or web plates, causing the plastic deformation in the fiber which ultimately reduces its strength and stiffness. This study focuses on the local buckling resistance of pultruded FRP columns by experimental work. The test data were compared to current theoretical and numerical predictions. It is found that the difference of <15% between experiment and predictions can be acceptable. The author recommends that the Kollar’s equations to be used when predicting local buckling of Pultruded FRP column of I or channel shapes.

Optimizing stiffness and lightweight design of composite monocoque sandwich structure for electric heavy quadricycle

Optimizing stiffness and lightweight design of composite monocoque sandwich structure for electric heavy quadricycle

Machine learning-based inverse design methods considering data characteristics and design space size in materials design and manufacturing: a review.

In the last few decades, the influence of machine learning has permeated many areas of science and technology, including the field of materials science. This toolkit of data driven methods accelerated the discovery and production of new materials by accurately predicting the complicated physical processes and mechanisms that are not fully described by existing materials theories. However, the availability of a growing number of increasingly complex machine learning models confronts us with the question of "which machine learning algorithm to employ". In this review, we provide a comprehensive review of common machine learning algorithms used for materials design, as well as a guideline for selecting the most appropriate model considering the nature of the design problem. To this end, we classify the material design problems into four categories of: (i) the training data set being sufficiently large to capture the trend of design space (interpolation problem), (ii) a vast design space that cannot be explored thoroughly with the initial training data set alone (extrapolation problem), (iii) multi-fidelity datasets (small accurate dataset and large approximate dataset), and (iv) only a small dataset available. The most successful machine learning-based surrogate models and design approaches will be discussed for each case along with pertinent literature. This review focuses mostly on the use of ML algorithms for the inverse design of complicated composite structures, a topic that has received a lot of attention recently with the rise of additive manufacturing.

Explicit Dynamics Simulation and Design of Sandwich Composite Structures Reinforced by Multilayer Lattice

Explicit Dynamics Simulation and Design of Sandwich Composite Structures Reinforced by Multilayer Lattice

Vibration analysis of a composite elastic metamaterial plate based on a semi-analytical method

A semi-analytical vibration analyzing process is presented for a kind of finite composite elastic metamaterial plate by combining the effective medium theory and the first-order shear deformation sandwich plate theory, and the natural and steady-state vibration characteristics of such complex composite structure are investigated by means of equivalent analysis. The effectiveness of the semi-analytical analyzing process is demonstrated and some extraordinary vibration behaviors of such composite structure are revealed, such as there is no natural frequency in the bandgap, the modal density consistently increases around the bandgap's starting frequency, and the modes of the appropriate orders before and after the bandgap are consistent at the macroscopic level. The semi-analytical analyzing process and the special vibration behaviors may provide useful reference for relevant investigation and design of composite elastic metamaterial plate structures in the field of vibration control and isolation.

Study of the features of the work of concrete-steel composite beams in buildings with a steel frame

Concrete-steel composite structures are unique structures that combine the advantages of both steel and concrete. Their application is especially relevant in cases where construction objects need to withstand high loads with small cross-sectional dimensions. Thanks to the factory production of most of the elements and easy installation, it is possible to significantly reduce construction times. The main areas of application are high-rise construction, industrial construction, and bridge construction. The main task in the design of concrete-steel composite structures is to take into account the joint work of a reinforced concrete slab and steel beams, i.e. correct modeling of the structure when using calculation systems. This article explores various options for setting the numerical model of a concrete-steel composite beams using the example of one floor of a high-rise building, evaluates their reliability and compliance with the actual behavior of the structure. In conclusion, recommendations are offered on the numerical modeling of concrete-steel composite beams for calculation using the finite element method.

Increasing the strength of the wing structureaircraft based on the use of metal-polymer composite material

In the modern aviation industry, the task of increasing the structural strength of the aircraft wing is being actualize. The author presents an engineering methodology for power calculation and design of composite aircraft structures based on the analysis of strength characteristics of metal and metal-polymer composite materials. The paper uses theoretical and empirical research methods, as well as the results of foreign and domestic scientific materials.

A new design proposal for composite beams with powder actuated shear connectors

This paper introduces a proposal for the SP 266.1325800 code update, which is applied as a national building code for composite structure design in Russian and some CIS countries. The proposal is based on deep codes analyze and comparison and previous authors’ publications. The research is dedicated to nailed shear connectors’ behavior in composite beams with profiled sheeting. The proposal provides a less conservative approach for composite beams with ductile shear connectors and takes into account additional conditions, such as decking geometry and the structure’s performance under fire. The proposed methodology defines the main geometric characteristics of the composite cross-section before determining the shear connector type. If ductile connectors are chosen, it is recommended to use partial design methods for shear connection definition due to the economic benefits of the proposal. The proposal is verified on powder-actuated shear connectors and should be double-checked with other working examples and connector types. The results show that the structure designed according to the new proposal is 13% less utilized with a smaller quantity of shear connectors (22% less) under the same load. It provides benefits from the structure costs and labor time.

Study on the Design of New Connectors for Steel-concrete Composite Beams

Steel-concrete composite beam structure has been widely used in the world because of its own advantages. The key to realize the combination of steel beam and concrete beam is the indirect connection of the contact interface between the two material components. With the diversification of the demand of steel-concrete composite structure and the continuous development of the design scheme, the traditional shear connection structure cannot meet the current composite structure design. Therefore, the research of new type connection gradually becomes the decisive factor of the continuous development of composite beam structure. In this paper, the research and application status and main development trend of steel-concrete composite structure connectors are first discussed. Then, the main development directions of several new connectors are presented. Finally, the relevant cases are analyzed. The results of this paper can provide some effective references for the design of steel-concrete composite structure connectors in the future.

Multi-Objective Multi-Scale Optimization of Composite Structures, Application to an Aircraft Overhead Locker Made with Bio-Composites

The use of composite materials has grown exponentially in transport structures due to their weight reduction advantages, added to their capability to adapt the material properties and internal micro-structure to the requirements of the application. This flexibility allows the design of highly efficient composite structures that can reduce the environmental impact of transport, especially if the used composites are bio-based. In order to design highly efficient structures, the numerical models and tools used to predict the structural and material performance are of great importance. In the present paper, the authors propose a multi-objective, multi-scale optimization procedure aimed to obtain the best possible structure and material design for a given application. The procedure developed is applied to an aircraft secondary structure, an overhead locker, made with a sandwich laminate in which both, the skins and the core, are bio-materials. The structural multi-scale numerical model has been coupled with a Genetic Algorithm to perform the optimization of the structure design. Two optimization cases are presented. The first one consists of a single-objective optimization problem of the fibre alignment to improve the structural stiffness of the structure. The second optimization shows the advantages of using a multi-objective and multi-scale optimization approach. In this last case, the first objective function corresponds to the shelf stiffness, and the second objective function consists of minimizing the number of fibres placed in one of the woven directions, looking for a reduction in the material cost and weight. The obtained results with both optimization cases have proved the capability of the software developed to obtain an optimal design of composite structures, and the need to consider both, the macro-structural and the micro-structural configuration of the composite, in order to obtain the best possible solution. The presented approach allows to perform the optimisation of both the macro-structural and the micro-structural configurations.

Dynamic axial crushing behaviors of circular composite tubes with different reinforcing fibers and triggers

The choice for a proper external trigger and fiber hybridization configuration has a significant impact on the stability of the crushing process and material cost for composite structures in crashworthiness. However, there is still a lack of a thorough understanding of impact characteristics and energy-absorption mechanisms. This study explores the axial crushing responses and crashworthiness characteristics of energy-absorption composite structures by both experiment and finite element analysis. A series of dynamic crushing tests were conducted for three types of composite tubes under the same crushing velocity of 1.944 m/s, including carbon fiber reinforced polymers (CFRP), glass fiber reinforced polymers (GFRP), and CFRP/GFRP inter-layer hybridized composites. The configuration of the composite tubes includes: (i) CFRP composite tubes with a single 45° chamfer trigger (T1), a combined 45 °chamfer and outward-folding crush-cap (T2), and a combined 45 °chamfer and outward-folding crush-cap with a cavity (T3); (ii) GFRP and CFRP/GFRP hybrid composite tube with T2 trigger. A stacked-shell model was developed to investigate the energy-absorption mechanisms. Three distinct failure modes have been found for composite tubes with T1, T2, and T3 triggers, separately, named splaying, outward-folding, and outward-folding with local buckling. The CFRP composite tubes with the T1 trigger exhibited the best crashworthiness performance, while the T2 trigger reduced the friction interaction between the splaying fronds and the platen, causing a 67% reduction of specific energy absorption (SEA)/mean crushing force (MCF). In the meantime, the T3 trigger boosted 101.9% of SEA/MCF from T2. With the same T2 trigger, the GFRP composite tube showed a better crashworthiness performance than the CFRP composite tube: 35.5% reduction of initial peak crushing force (IPCF), 68.6% and 98.5% increment of MCF and SEA respectively. It has been found that the outermost layers dominated the energy absorption behavior, which matches well with the observation that replacing the central CFRP plies with GFRP ones results in similar crashworthiness characteristics between CFRP and CFRP/GFRP hybrid composite tubes. The findings in this study contribute to providing practical guidelines for the crashworthiness design of heavy duty composite structures, such as railway vehicles.

Drop-weight impact responses and energy absorption of lightweight glass fiber reinforced polypropylene composite hierarchical cylindrical structures

A high spike force at the beginning of impact and the load fluctuations caused by unstable plateau deformation are disadvantages to avoid for impact resistance structures. Lightweight glass fiber-reinforced polypropylene composite hierarchical cylindrical structures (namely GFRP-CHCS, with a relative density of less than 0.1) have the potential to achieve low initial force and high crushing force efficiency under dynamic conditions. This work explores the drop-weight impact behaviors and energy absorption capacity of GFRP-CHCS. Deformation modes, failure conditions, and impact load history responses are discussed. Results showed that GFRP-CHCS has no initial load peak and achieves gentle response curves under the low-velocity impact when the load speed is less than 10 m/s. Among the experiments where the impact energy was beyond the range of static energy absorption, more than 94% of the impact energy was absorbed or dissipated when the impact energy ranged from 200 J to 300 J. After unloaded, GFRP-CHCS maintained good integrality and recovered a significant deformation which was over 93% initial structural height. With ideal isotropic material properties, numerical and theoretical predictions were conducted regarding the loading velocity effects on structural deformation mode and mean impact response force. This work utilized a thermoplastic composite consisting of GFRP face sheets and polypropylene core. The results have reference significance for the anti-impact design of thermoplastic composite hierarchical structures.

Reliability-based design shear resistance of headed studs in solid slabs predicted by machine learning models

The economical and reliable design of steel-concrete composite structures relies on accurate predictions of the resistance of headed studs transferring the longitudinal shear forces between the two materials. The existing mechanics-based or empirical design equations do not always produce accurate and safe predictions of the stud shear resistance. This study presents the evaluation of nine machine learning (ML) algorithms and the development of optimized ML models for predicting the stud resistance. The ML models were trained and tested using databases of push-out test results for studs in both normal weight and lightweight concrete. The reliability of ML model predictions was evaluated in accordance with European and US design practices. Reduction coefficients required for the ML models to satisfy the Eurocode reliability requirements for the design shear resistance were determined. Resistance factors used in US design practice were also obtained. The developed ML models were interpreted using the SHapley Additive exPlanations (SHAP) method. Predictions by the ML models were compared with those by the existing descriptive equations, which demonstrated a higher accuracy for the ML models. A web application that conveniently provides predictions of the nominal and design stud shear resistances by the developed ML models in accordance with both European and US design practices was created and deployed to the cloud.

Concurrent Multi-Component Optimization of Stiffened-Plate Yacht Structures

Optimisation has become a necessary tool when designing competitive high-performance composite yachts. The inherently complex material characteristics of composite materials mean there must be careful consideration of laminate and structural design to withstand loading and meet efficiency demands. An optimisation scheme has been developed that allows structural engineers to generate globally optimised yacht structures. This paper investigates a more holistic approach to designing large multi-part composite structures using concurrent genetic algorithm optimisation tools, which will allow designers to understand the effect of optimisation on the decision-making and design processes. Specifically, how can better design decisions be influenced by incorporating tools that augment an experientially based complex composite structural design process? The tool developed concurrently optimises laminate architecture and the arrangement of and number of stiffeners that make up a stiffened-plate geometry such as that seen in a typical yacht structure.

Semi-Active Control of Seismic Response on Prestressed Concrete Continuous Girder Bridges with Corrugated Steel Webs

To improve the seismic capacity of prestressed concrete (PC) continuous girder bridges with corrugated steel webs (CSWs), suitable damping control measures can be used to effectively reduce the seismic response of the bridge. Based on the semi-active control theory, the semi-active control system of a three-span PC continuous girder bridge with CSWs is designed, and the semi-active control system program of the three-span PC continuous girder bridge with CSWs is compiled by MATLAB. The time–history curves of damper energy consumption of active optimal control algorithm and three different semi-active control algorithms are compared and analyzed, as are the time–history curves of main girder displacement, acceleration, and pier internal force with or without semi-active control. The study shows that the rational determination of the weight matrix coefficient can make the active control achieve a better vibration absorption effect and economy. The semi-active control algorithm of Hrovat has the best vibration absorption effect, which is closest to that of the active optimal control algorithm. Under the state of semi-active control, the average vibration absorption rate of displacement and acceleration of the main girder with CSWs are 71% and 20%, respectively. The time–history curve of bending moment and shear force in the pier bottom is similar, and the average vibration absorption rate of bending moment and shear force at the bottom of pier #2 is 70%. At the same time, the average vibration absorption rate of bending moment and shear force at the bottom of pier #3 is between 42% and 48%. The semi-active control measure has a good vibration absorption effect on the overall seismic response of the PC continuous girder bridges with CSWs. This study provides a certain reference for the seismic reduction and isolation design of composite structure bridge with CSWs.

Hysteretic tests of stud connection subjected to combined shear and tension

The hysteretic behaviour of stud connections in the shear direction under the combined action of shear and tension was studied by the push-out test of eight cyclic loading specimens. To compare the difference between cyclic loading and monotonic loading on the shear capacity and the shear–slip curve, eight monotonic loading specimens were designed as reference specimens. The main variables considered in this study were the diameter of the stud, the strength of the concrete, and the magnitude of the tensile force in the stud. Based on the test results, failure modes, shear–slip curves and characteristic points on the curves of all specimens were evaluated. Hysteretic responses such as ductility, strength degradation and energy dissipation of cyclic loading specimens were analysed. The test results show that the diameter of the stud, the strength of concrete and the tensile force of stud connectors have significant effects on the hysteretic performance of stud connections. The stud connection with larger stud diameter and higher concrete grade has higher shear resistance, higher ductility index and higher energy dissipation capacity. In comparison to stud connections under pure shear loading, the hysteretic properties of stud connections with combined action of shear and tension are degraded. The influence of tensile force on the hysteretic performance of stud connections under the combined action of shear and tension would thus need to be taken into consideration in the design of composite structures.

A semi-analytical method for the determination of fracture toughness and bridging law in ELS test

Fracture toughness and bridging law are necessary for characterizing the delamination behavior with the effect of fiber bridging. Accurate determination of them in a simple way is particularly important for the design of composite structures. The end-loaded split (ELS) method, which can obtain stable delamination growth, has been applied in the ISO 15,114 standard to measure the mode II fracture toughness. However, geometric nonlinearity and difficulty on the crack observation are unavoidable. To deal with those problems, a semi-analytical method is proposed in this study for determining the fracture toughness and the bridging law. Predictions from the semi-analytical method are consistent with experimental results of CFRP and GFRP laminates. Furthermore, numerical modelling is performed based on a tri-linear cohesive zone model which integrates the determined bridging law. Numerical load–displacement responses have good agreements with the experimental ones, which illustrates the applicability and accuracy of the proposed method. The proposed method overcomes the problem of real-time monitoring of the crack growth length and the relative sliding displacement at the pre-crack tip, and considers the correction factors to solve the nonlinear problem caused by the large displacement, which is simple and efficient for practical application.