Composite Structural Components Research Articles

Semi-active Damage Identification for a Composite Structural Missile Component using Minimal Passive Sensing with Data-driven Models

Cost, complexity, and weight restrictions often constrain industrial structural health monitoring (SHM) systems to the use of one sensor. Often, this one sensor is passive, i.e., it only measures the structural response. Therefore, new SHM techniques that utilize only one passive sensor along with advanced data interrogation methods are needed. A semi-active damage detection technique is described in this study that utilizes passively estimated forces and response measurements to update data-driven frequency-response-function (FRF) models of a filament-wound missile casing that is used as a test structure. During a damaging impact, the structural response is influenced by both the healthy and damaged structure properties. As a result, the magnitudes of the estimated FRFs can exhibit a splitting phenomenon at the natural frequencies of the healthy and damaged structure, and this phenomenon is evident in the experimental data. The updated FRFs are used with an active damage detection technique to quantify the damage. The normalized differences in the damaged and healthy FRFs and the shift of the natural frequencies of the structure quantify damage in this study. The shift of the natural frequencies more accurately quantifies the damage caused by four experimental impacts than the normalized differences in the FRFs.

Optimization of a satellite with composite materials

The design of complex flexible multibody systems for industrial applications requires not only the use of powerful methodologies for the system analysis, but also the ability to analyze potential designs and to decide on the merits of each one of them. This paper presents a methodology using optimization procedures to find the optimal layouts of fiber composite structure components in multibody systems. The goal of the optimization process is to minimize structural deformation and to fulfill a set of multidisciplinary constraints. These methodologies rely on the efficient and accurate calculation of the system sensitivities to support the optimization algorithms. In this work a general formulation for the computation of the first order analytic sensitivities based on the direct differentiation method is used. The direct method for sensitivity calculation is obtained by direct differentiation of the equations defining the response of the structure with respect to the design variables. The equations of motion and the sensitivities of the flexible multibody system are solved simultaneously and, therefore, the accelerations and velocities of the system, and the sensitivities of the accelerations and velocities, are integrated in time using a multistep multiorder integration algorithm. Different models for the flexible components of the system, using beam and plate elements, are also considered. Finally, the methodology proposed here is applied to the optimization of the unfolding of a complex satellite made of composite plates and beams. The ply orientations of lamination are the continuous design variables. The potential difficulties in the optimization of composite flexible multibody systems are highlighted in the discussion of the results obtained.

Hemp yarn reinforced composites – II. Tensile properties

Whereas the first paper is addressing the characteristics of textile hemp yarn, this second paper is addressing the tensile properties of aligned hemp yarn composites under influence of a number of experimental variables: hemp yarn type, fibre volume fraction, thermoplastic matrix type, process temperature, conditioning humidity, and loading direction relative to the fibre direction. Altogether, the results show that aligned hemp yarn composites demonstrate the good potential of plant fibres as reinforcement in composites for structural components. The tensile performance of the hemp yarn composites is excellent. As an example, a fibre volume fraction of 0.48 results in a stiffness of 28 GPa and an ultimate stress of 280 MPa. It is demonstrated that the influence of experimental variables is well understood and can be quantitatively described.

Autonomous Impact Damage Monitoring in a Stiffened Composite Panel

This study is concerned with the detection and characterization of impact damage in a stiffened woven composite structure using high frequency Lamb waves and low frequency modal vibrations. The geometric and material complexities of the structure present practical difficulties in the direct analysis of both wave propagation and modal vibration data using theoretical constructs. Improved ultrasonic and vibration test setups consisting of distributed, high fidelity, and surface mounted sensor arrays are used here to determine changes in the dynamical properties of the composite structural components in the presence of damage. The sensors are assumed to provide both the low frequency global response (i.e., modal frequencies and mode shapes) of the structure to external loads and the (local) high frequency signals due to wave propagation effects in either passive or active mode of the ultrasonic array. A damage index, comparing the measured dynamical response of two successive states of the structure is introduced as a determinant of structural damage. The method relies on the fact that the dynamical properties of a structure change with the initiation or growth of damage. A diagnostic imaging tool is used for the interpretation and graphical representation of the indices to enable automated monitoring of the changes in the indices at a given instant of time. The value of the index at a given sensor increases with the proximity of the damage to the sensor. A sensitivity analysis is carried out in an effort to determine a threshold value of the index below which no reliable information about the state of health of the structure can be estimated. It is shown that the automated procedure is able to identify a defect right from its appearance, with some degree of confidence. The feasibility of developing a practical intelligent structural health monitoring system (ISHMS), based on the concept of `a structure requesting service when needed,' is discussed.

Jointing of high-loaded composite structural components. Part 3. An experimental study of strength of joints with transverse fastening microelements

A system of comprehensive experimental support for strength analysis and design of joints has been developed. It involves an experimental procedure, special specimen designs and test setups. For joints with transverse fastening microelements, we summarize some results of experimental determination of (i) compliance coefficients, (ii) degree of strength degradation in embedment zones of cylindrical pins (0.8, 1.0, 1.5, and 2.0 mm in diameter) and pyramidal (milled) pins in variously structured carbon-reinforced plastic, (iii) bearing strength anisotropy of carbon-, glass-, and organic-reinforced plastics depending on the composite material structure, force direction, dimensions of fastening elements and methods of their installation (mold-embedment in a stack of prepreg plies or insertion into drilled holes in the composite material after polymerization).

Cure shrinkage characterization and modeling of a polyester resin containing low profile additives

Resin Transfer Moulding (RTM) has great potential as an efficient and economical process for fabricating large and complicated composite structural components. The low capital investment cost required and process versatility in component integration and assembly make RTM very attractive for high volume automotive applications. One of the challenges facing the automotive field is the resulting surface finish of manufactured components. The shrinkage associated with the curing of thermoset resins contributes to the poor surface quality. Low profile additives (LPA) are added to the resin to compensate for the cure shrinkage; however their effects on the thermal, rheological and morphological properties of polyester resins are not well understood. In this paper, the effect of LPA on cure kinetics, cure shrinkage and viscosity of a polyester resin is studied through differential scanning calorimetry (DSC) and special rheological techniques. Models are developed to predict cure shrinkage, LPA expansion, cure kinetics and viscosity variations of the resin as a function of processing temperature. Finally, morphological changes in the resin with and without LPA, during isothermal cure, are studied with hot stage optical microscopy. The results show that the LPA content in the range tested had no significant effect on the cure kinetics. However, higher LPA content reduced cure rate and cure shrinkage. A minimum of 10% LPA was required to compensate for cure shrinkage. Shrinkage behavior of all formulations was similar until a degree-of-cure of 0.5. However, resin formulations with higher LPA content showed expansion at later stages during curing.

Jointing of high-loaded composite structural components. Part 2. Modeling of stress-strain state

Based on the study of interactions between elements of proposed design and engineering solutions, a unified technique is proposed for analyzing the stress-strain state in joints with a continuous, discontinuous, or a combined bonding layer in components with longitudinally variable geometrical and rigidity parameters, under arbitrary thermomechanical loading. Resolving systems of linear equations are derived, an extent of sufficient discretization of s structure is assessed, and some numerical results are provided. The paper gives recommendations of how to use this technique and demonstrates that it can be efficiently applied to the majority of joint types.

Multi-scale modeling, stress and failure analyses of 3-D woven composites

The very complex, multi-level hierarchical construction of textile composites and their structural components commonly manifests via significant property variation even at the macro-level. The concept of a “meso-volume” (introduced by this author in early 1990s) is consistently applied in this work to 3-D stress/strain and failure analyses of 3-D woven composites at several levels of structural hierarchy. The meso-volume is defined as homogeneous, anisotropic block of composite material with effective elastic properties determined through volumetrically averaged 3-D stress and strain fields computed at a lower (“finer”) level of structural hierarchy and application of generalized Hooke’s law to the averaged fields. The meso-volume can represent a relatively large, homogenized section of a composite structural component, a lamina in laminated composite structure, a homogenized assembly of several textile composite unit cells, a single homogenized unit cell, a resin-impregnated yarn, a single carbon fiber, even a carbon nanotube assembly. When composed together, distinct meso-volumes constitute a 3-D Mosaic model at the respective hierarchy level. A multi-scale methodology presented in this paper first illustrates 3-D stress/strain analysis of the Mosaic unidirectional composite, computation of its effective elastic properties and their further use in 3-D stress/strain analysis of the Mosaic model of 3-D woven composite Unit Cell. The obtained 3-D stress/strain fields are then volumetrically averaged within the Unit Cell, and its effective elastic properties are computed. The predicted effective elastic properties of 3-D woven composite are compared with experimental data and show very good agreement. Further, those effective elastic properties are used in 3-D simulations of three-point bending tests of 3-D woven composite; theoretical predictions for central deflection show excellent agreement with experimental data. Finally, a 3-D progressive failure analysis of generic 3-D Mosaic structure is developed using ultimate strain criterion and illustrated on the 3-D woven composite Unit Cell. The predicted strength values are compared to experimental results. The presented comparisons of theoretical and experimental results validate the adequacy and accuracy of the developed material models, mathematical algorithms, and computational tools.

Jointing of high-loaded composite structural components. Part 1. Design and engineering solutions and performance assessment

The author presents and discusses the results of investigation to verify the design principles for jointing composite components. Based on the findings, novel design and engineering solutions for metal-composite joints are put forward. To ensure an effective transition from a composite material to a metal butt-joint fitting, new jointing techniques have been developed involving the use of embedded longitudinal and transverse fastening microelements in a composite material, which are molded into or mounted on a metal component. A modification of half-stitch jointing is proposed which enables the joint to work in compression and reduces the pressing stresses in the winding zone. Based on the study of force transfer conditions in the proposed joint design and the jointing solutions, the author defines the main lines of theoretical and experimental investigations to support the engineering and stress analysis activities. The experimental static strength assessment demonstrates effectiveness of the proposed solutions.

Estimation of degraded composite laminate properties using acoustic wave propagation model and a reduction‐prediction network

PurposeTo develop a new method for estimation of damage configuration in composite laminate structure using acoustic wave propagation signal and a reduction‐prediction neural network to deal with high dimensional spectral data.Design/methodology/approachA reduction‐prediction network, which is a combination of an independent component analysis (ICA) and a multi‐layer perceptron (MLP) neural network, is proposed to quantify the damage state related to transverse matrix cracking in composite laminates using acoustic wave propagation model. Given the Fourier spectral response of the damaged structure under frequency band‐selective excitation, the problem is posed as a parameter estimation problem. The parameters are the stiffness degradation factors, location and approximate size of the stiffness‐degraded zone. A micro‐mechanics model based on damage evolution criteria is incorporated in a spectral finite element model (SFEM) for beam type structure to study the effect of transverse matrix crack density on the acoustic wave response. Spectral data generated by using this model is used in training and testing the network. The ICA network called as the reduction network, reduces the dimensionality of the broad‐band spectral data for training and testing and sends its output as input to the MLP network. The MLP network, in turn, predicts the damage parameters.FindingsNumerical demonstration shows that the developed network can efficiently handle high dimensional spectral data and estimate the damage state, damage location and size accurately.Research limitations/implicationsOnly numerical validation based on a damage model is reported in absence of experimental data. Uncertainties during actual online health monitoring may produce errors in the network output. Fault‐tolerance issues are not attempted. The method needs to be tested using measured spectral data using multiple sensors and wide variety of damages.Practical implicationsThe developed network and estimation methodology can be employed in practical structural monitoring system, such as for monitoring critical composite structure components in aircrafts, spacecrafts and marine vehicles.Originality/valueA new method is reported in the paper, which employs the previous works of the authors on SFEM and neural network. The paper addresses the important problem of high data dimensionality, which is of significant importance from practical engineering application viewpoint.

Polymer composites in fire

This paper reviews the state of the art with regard to the numerical modelling of the performance of polymer composite structural members and components at elevated temperature. The methods available for thermal modelling, i.e. the prediction of temperature distributions, within polymer composites acting alone and also when they act in conjunction with fire protection materials are considered first. Consideration is given to the basic differential equations and their numerical solution and also to the more difficult problem of the thermal and transport properties of the materials. The review then moves to thermo-mechanical modelling and considers the mechanical properties of polymer composites at elevated temperature. Numerical and test results are compared for the performance of columns and wall panel assemblies.

Simulating in‐plane fatigue damage in woven glass fibre‐reinforced composites subject to fully reversed cyclic loading

ABSTRACTThe interest in using fibre‐reinforced composites in structural components is increasing. Some of these structural composites, such as wind turbine blades, aircraft components and torsion shafts are subject to fatigue loadings. It is widely accepted that fully reversed cyclic loading is the most adverse loading for fibre‐reinforced composites, but the modelling of the material behaviour under this loading condition is very difficult. In this paper, a damage model is presented for woven glass fibre‐reinforced composites subject to fully reversed cyclic loading. First fatigue experiments have been conducted in displacement‐controlled fully reversed bending and the stiffness degradation and damage patterns have been observed. Based on these experimental data, a damage model has been developed, which includes the in‐plane stress components and the degradation of the in‐plane elastic properties. The model has been implemented in a commercial finite‐element code and simulation of the successive stages in the fatigue life has been performed. The model has been validated for a plain woven glass fabric reinforced composite and simulated stiffness degradation, damage growth and damage distribution have been compared with experimental data.

Hot-Wet Property Characterisation of a High-Temperature Cured Glass–Epoxy Composite in Immersion Environment

The hygrothermal diffusion and degradation behavior of a high-temperature cured glass–epoxy (Epoxy Novolac – EPN) composite system was studied under two environmental conditions (i.e. 323 K and 343 K immersion in distilled water). Samples immersed at 343 K showed higher diffusivity (Dc) value and lower saturation time (tm) than those of 323 K immersion while the maximum moisture content (Mm) remained the same, good Fickian correlation were observed for the composite system. As regards the degradative effects, the glass transition temperature (Tg) of the composite decreased with increased moisture content showing a maximum drop of 30 C at full saturation, while the mechanical properties (ILSS and IPS) of saturated specimens degraded upto 26 and 33% respectively. Further these mechanical properties obtained at 70 C/85%RH test condition showed good correlations with those predicted by a theoretical equation (Chamis et al. An Intergrated Theory for Predicting the Hydrothermo Mechanical Response of Advanced Composite Structural Components, Lewis Research Center, Cleveland, Ohio, NASA Technical Memorandum 73812).

Composite structural panels subjected to explosive loading

Details of an extensive large-scale test programme on a series of composite structural components subjected to explosive loading are presented in this paper. The test components include conventional reinforced concrete slabs, steel fibre reinforced concrete slabs, profiled steel sheeting reinforced concrete slabs, steel–air–steel sandwich panels and steel–concrete–steel sandwich panels. A total of seventy four specimens were tested using seventeen detonation phases; with charge weight ranging between 8 and 100 kg of bare high explosives and each at stand-off distance of 5 m. The main parameters observed in the tests were the generic construction form of the materials and slab thickness. Air-blast overpressure and accelerations of the specimens were captured. A modified plasticine displacement gauge was used to measure the maximum displacement. Failure modes of each type of specimens were recorded and are presented in the paper. Major conclusions relating to structural safety are summarised.

Progressive crushing of fiber-reinforced composite structural components of a Formula One racing car

The present paper describes an experimental and numerical investigation on energy absorbers for Formula One side impact and steering column impact. The crash tests are performed measuring the load-shortening diagram and the energy absorbed by the structure. A finite element model is then developed using the non-linear, explicit dynamic code LS-DYNA. To set up the numerical model, tubes crushing testing are conducted to determine the material failure modes and to characterise them with LS-DYNA. The results presented in this study show that the composite structural components of the investigated Formula One racing car possess high value of specific absorbed energy and crash load efficiency around 1.1. The finite element simulations accurately predict the overall shape, magnitude and pulse duration in all the types of impact as well as the deformation and failure of the structures. Comparing the numerical data of the specific absorbed energy to the experimental results, the differences are around 10%.

Thermal and Geometrically Nonlinear Stress Analyses of an Adhesively Bonded Composite Tee Joint with Double Support

Carbon fiber reinforced plastics (CFRP) can be successfully joined to metal or composite structural components using the adhesive bonding technique [Semerdjiev, S. (1970). Metal to Metal Adhesive Bonding, Business Books Ltd., London.]. The stress and deformation fields occurring in the adhesive joints due to the thermal loads as well as the structural loads play an important role on the joint strength since the thermal and mechanical properties of the adhesive and adherends are different. Previous thermal stress analyses of the adhesive single-lap joints with simple geometries assumed a uniform temperature distribution through the adhesive joint, consequently predicted uniform thermal strain and stress distributions. In this study, the thermal stress analysis of an adhesively bonded tee joint with double support made of unidirectional CFRP was carried out for variable thermal loading conditions along its outer boundaries and different plate edge conditions. The large displacement and rotation effects were considered using the small strain-large displacement theory. The stress fields in the adhesive layer and the composite members of two tee joints bonded to a rigid base and a flexible plate were investigated. In the thermal analysis, a reference uniform temperature was attributed to all joint members for its stress free state, and air streams with different temperature and velocity were specified along the outer surfaces of the adhesive joint. In addition, the air streams were specified in the vertical or horizontal directions to the composite plates and adhesive layer. The consideration of convective and conductive heat transfer showed that nonuniform temperature distributions occurred in the adhesive tee joints. High heat fluxes took place along the free surfaces of the adhesive fillets at the free ends of the adhesive layers. Geometrical nonlinear stress analyses of two tee joints were carried out using the calculated temperature fields for two different plate edge conditions. Since the adhesive joints consist of materials with different thermal and structural properties, the thermal strains become incompatible along the adhesive layer–plate interfaces. Consequently, the stress concentrations occurred inside the adhesive fillets around the adhesive free ends, and in the regions near the adhesive layer–composite plate interfaces. The adhesive fillets, middle region of the horizontal plate, the elbow sections of the left and right supports appeared as most critical regions of the tee joints. In addition, the support length did not have similar effect of reducing the normal and shear stresses at these critical adhesive and adherend locations.

Shape optimization of bonded patch to cylindrical shell structures

AbstractAdhesive bonding has been widely used to join or repair metallic and composite structural components to achieve or restore their designated structural stiffness and strengths. However, current analysis methods and empirical databases for composite bonded patch repairs or joints are limited to flat structures, and there exists a very limited knowledge on the effect of curvature on the performance and durability of composite bonded joints and repairs. Recently, a novel finite element formulation was presented for developing adhesive elements for conducting 2.5‐D simplified stress analysis of bonded repairs to curved structures. This paper presents the work on optimal shape design of a bonded curved composite patch using the newly developed adhesive element. The Sequential Linear Programming (SLP) method is employed as the optimization algorithm in conjunction with a fully implemented mesh generation algorithm into which new features have been incorporated. The objective of shape optimization is to minimize the maximum stress in the entire adhesive layer to ensure that the bonded patch effectively works together with the parent structure in service. Several different objective functions, related to possible failure mechanisms of the adhesive layer, are proposed to optimize the shape of a bonded patch. Copyright © 2003 John Wiley & Sons, Ltd.

Nonlinear stress analysis for bonded patch to curved thin-walled structures

Adhesive bonding has been widely used to join or repair metallic and composite structural components to achieve or restore their designated structural stiffness and strengths. However, current analysis methods and empirical databases for composite bonded joint design and composite bonded patch repair are limited to flat plate and/or flat laminate geometries, and the effects of curvature on the performance and durability of composite bonded joints and repairs is not known. This paper presents a novel finite element formulation for developing adhesive elements and conducting 2.5-D simplified stress analysis of bonded repairs to curved structures. Both large deflections of the parent structures and nonlinear adhesive behavior are incorporated in the formulation. An in-house software called BPATCH has also been developed. A variety of numerical examples are presented to illustrate the effects of curvature, moderately large deflection and adhesive nonlinear behavior on stresses in the adhesive layer. Illustrative examples also indicate the effect of patch location, i.e., internal and external patches, patch size and patch thickness.

Characterization and analysis of delamination fracture in composites: An overview of developments from 1990 to 2001

Delamination is a major failure mode in laminated composites and has received much research attention. A huge amount of literature has been published on this subject, resulting in considerable improvement in our understanding of delamination behavior. A rather comprehensive review paper was published by Garg in 1988. That paper contains 136 references from 1971 to 1988, a period spanning roughly two decades. A more recent survey by Pagano and Schoeppner contains critical reviews of many selected papers, especially the pioneering works on delamination research. An overview of Russian and Soviet literature on this subject is also given by Bolotin. The present paper aims to review major developments in the analysis and characterization of buckling driven delamination from 1990 to the present. Its abridged version was presented in a plenary lecture at the 13th International Conference on Composite Materials, Beijing. Particular emphasis is placed on the application of fracture mechanics methods in the analysis of delamination. The question of the extent of fracture mechanics’ success in characterizing delamination, both in laboratory-based specimens and in more realistic structural composite components, is discussed. Some recent numerical formulations for efficient computational modeling and analysis of delaminations are also reviewed. This review lists 270 major works covering a period of about a decade, indicating that there is still considerable research interest and activity in this field.

Composite Structural Components Under Blast Loading

An extensive large-scale test programme was conducted for a series of composite structural components under blast loading, which includes normal reinforced concrete (RC), profiled steel sheeting RC (PSSRC), steel-air-steel sandwich (SASS) and steel-concrete-steel sandwich (SCSS) slabs. Twenty-four specimens were tested in eight detonation phases; each comprising 100 kg of TNT at a standoff distance of five metres. The main parameters of the tests were the type of materials and the slab thickness. During testing, the air-blast pressures on the specimens and the accelerations of the specimens were captured by appropriate instrumentation. The maximum and permanent displacements were measured by a specially designed plasticize displacement gauge, Failure modes of each type of specimens were carefully observed and examined with different parameters. Major conclusions are summarised at the end of this paper.