Polymer Matrix Composite Structures Research Articles

Physicochemical properties of new cellulosic fiber extracted from Carica papaya bark

ABSTRACTThis article presents the characteristics of Carica papaya fibers (CPFs) extracted from the bark of the perennial papaya plant. Detailed chemical compositions of CPFs such as cellulose, lignin, ash, moisture, and wax contents were established and determined by using standard methods. Further, chemical groups, crystalline structure, surface roughness, and thermal stability of CPFs were examined using Fourier transform infrared analysis, X-ray diffraction, atomic force microscope, and thermogravimetric analysis, respectively. The physico-chemical properties of CPFs, crystallinity index (56.34%), cellulose content (38.71 wt. %), hemicellulose (11.8%), and density (943 kg/m3) were compared to those properties of other natural fibers. The results suggest that the biodegradable CPFs can be used as a potential reinforcemnet in the polymer matrix composite structure.

Stationary random response of non-viscously damped polymer matrix composite structure systems

The polymer materials are widely used as the matrix of composite structures in the automobile, aircraft, building, bridge, railway, ship, turbine, and appliance industries. The polymer materials with long-chain molecules exhibit non-viscous damping behaviour. Non-viscous damped composite structure systems in which the damping forces depend on the past history of velocities via convolution integrals over some kernel functions have been raised in many different subjects. The developed analysis methods of dynamic response for such structure systems are almost limited to the deterministic time-history excitation. There is little research report on the random response of such non-viscous damped systems. The author has previously developed the non-viscous damping modelling method for polymer matrix composite structures (Liu, to be published). The goal of this paper is focus on developing two methods, i.e., direct frequency response method and iterative method using real modes, to obtain the power spectral density function (PSDF) of non-viscously damped polymer matrix composite structure systems subjected to stationary stochastic excitation. First, the pseudo excitation method converts the stationary stochastic excitation problem into harmonic excitation problem. Second, the direct frequency response method is derived and proven to get the analytical solution of PSDF. Third, the iterative method using real modes to obtain PSDF matrix is developed based on a harmonic response method. The computational procedure of the iterative method is given in detail. Finally, the random response analyses of two non-viscously damped structure systems, subjected to stationary random excitation, are demonstrated. The results indicate the two methods can achieve the exact solution of PSDF matrix of non-viscously damped structure systems. The iterative method using real modes is more efficient than direct frequency response method.

An anisotropic cyclic plasticity, creep and fatigue predictive tool for unfilled polymers

Resistance to Low Cycle Fatigue (LCF) as well as High Cycle Fatigue (HCF) of polymers and Polymer Matrix Composites (PMC) depends on various loading modes, frequency, temperature, aging, and environmental effects. On the other hand, fatigue, plasticity, and creep deformation mechanisms are history dependent phenomena, and in order to account for their interactions a coupled computational platform is required. Cyclic behavior of polymers and PMCs have been extensively explored experimentally, but a rational fatigue failure model that would be anchored in the microstructure and would allow for coupling between fatigue, creep and plasticity through the lifetime is lacking. This work aims at developing an anisotropic coupled cyclic plasticity, creep and fatigue life predictive technique in which a Continuum Damage Mechanics (CDM) framework is utilized to link microscale LCF and HCF damage mechanisms, i.e. microcracking and microvoiding, to the macroscale fatigue failure. This task is accomplished through a top-down multiscale CDM approach, in which microscale damage laws are calibrated with respect to the macroscale fatigue failure data. Cyclic plasticity and creep models are also incorporated to capture anisotropic inelastic behaviors of Polymer and PMC systems. The developed framework is implemented into a commercial Finite Element Analysis (FEA) code, viz. ABAQUS, through user-defined coding. The FEA model represents an isotropic polymer or homogenized PMC system in which various factors that affect fatigue behavior are studied. A cyclic jump method is also utilized to reduce the computational cost of the proposed coupled computational approach. The performance of the developed computational platform has been examined through numerical studies and comparison to experimental data. The developed fatigue life predictive tool may be utilized by engineers for lifetime prognosis and to improve the performance of Polymer and PMC structures.

Synergistic flame retardancy effect of graphene nanosheets and traditional retardants on epoxy resin

Novel non-toxic halogen-free flame retardants are replacing traditional flame retardants in polymer and polymer matrix composite structures. In this study, graphene nanosheet (GNS) is investigated in combination with traditional layered double hydroxide (LDH), layered rare-earth hydroxide (LRH), and phosphorus-based flame retardant (DOPO) to enhance the flame retardancy of epoxy resin. A synergistic flame retardancy effect is achieved in GNS/LDH and GNS/DOPO systems where combined GNS and LDH increased the viscosity of the epoxy melt, and limited the flame propagation through inhibition of dripping. The limiting oxygen index of epoxy increased from 15.9 to 23.6 with addition of 0.5wt.% each of GNS and LDH. With the addition of 2.5wt.% of both GNS and LDH, the total heat release of epoxy resin also reduced from 33.4MJ/m2 to 24.6MJ/m2. The synergistic effect of GNS and DOPO adopted a different mechanism. The addition of 2.5wt.% of GNS and DOPO reduced the peak heat release rate from 1194kW/m2 to 396kW/m2, and the total heat release rate from 72.5MJ/m2 to 48.1MJ/m2. The synergistic mechanisms of the flame retardants were closely analyzed and correlated with the flame retardant properties.

Polymer-matrix composites carbon fibre characterisation and damage inspection using selectively heating thermography (SeHT) through electromagnetic induction

Polymer-matrix composites (PMCs) such as glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP) are being increasingly used in fields of aerospace, renewable energy, civil and architecture. Damages such as broken fibre, impact and delamination are inevitable during either fabrication or lifetime of PMC structures or components. This work proposed selectively heating thermography (SeHT) through electromagnetic induction and infrared temperature measurement for CFRP characterisation and damage inspection. Broken carbon fibres can be easily identified through SeHT whilst inside delamination is difficult to be inspected due to negative influence of temperature gradient, lateral blur effect, and periodic structures. In order to solve this problem, cross correlation (CC) matched filtering algorithm was proposed to enhance the inspection results. Six CFRP laminate samples with impact damages from 2 to 12J were tested to verify the proposed methods. The experimental studies show that SeHT is capable of characterising fibres and inspecting surface broken area, whilst CC phasegram is capable of inspecting inner delamination due to elimination of non-uniform heating effect and lateral blurring effect. The dependence of damage for CFRP sample on impact energy was also investigated. Through SeHT and CC matched filtering, characterisation and inspection for CFRP can be achieved.

A methodology for the estimation of transverse failure strength of an oxidized lamina from isothermal aging studies

Surface oxidation and ensuing damage substantially decrease the service life of High Temperature Polymer Matrix Composite (HTPMC) structures. Oxidative degradation behavior of composites is strongly dependent on the coupling between chemical and mechanical responses of the material. In a composite lamina, the onset of damage and subsequent coupled acceleration of both damage and oxidation are controlled by the transverse failure strength of the oxidized regions. The direct measurement of this strength from experimentation is challenging and cumbersome. A model-based methodology for estimating the mean transverse failure strength of the oxidized regions of a unidirectional composite is described in this paper. As the strength of the oxidized region is expected to show a high-degree of spatial variability, the estimated mean is shown to be relatively insensitive to the effect of strength variance. The developed methodology is illustrated with isothermal aging data available for a typical high-temperature composite system.

Modeling fatigue damage evolution in polymer matrix composite structures and validation using in-situ digital image correlation

A study is conducted with the aim of developing and implementing a fatigue prediction model for assessing the damage tolerance capabilities of polymer matrix composite structures. The damage mechanics based model uses empirical material parameters to represent orthotropic damage evolution. The model accounts for local multiaxial stresses as well as variable amplitude cyclic loading, which may result from local stress redistributions caused by damage evolution. The numerical results show the capability of the developed model to predict the variation of damage evolution and material property degradation in a triaxially braided carbon fiber polymer matrix component. The predictions are validated by independent experiments on composite components using digital image correlation, which shows a strong correlation between the measured and predicted strain contours at various cyclic intervals. This is a key contribution and a step forward in developing a viable design tool for assessing the integrity and durability of composite structures.

Quasi-Static Tensile Properties and Damage Mechanism of Three-Dimensional Angle-Interlock Woven Composites

The uniaxial tensile properties of three-dimensional angle-interlock woven composites (3DAWCs) under quasi-static loading were investigated in this paper. The samples were manufactured into dog-bone shape and tested on Material Test System 810.23. The strain-stress curves in warp direction indicating the Young’s moduli, maximum stress and maximum strain are achieved from the uniaxial tensile test. The effects of microstructure and damage morphology of 3DAWC under quasi-static tension are discussed. Furthermore, we will focus on the energy absorption mechanism from the view of tensile failure mode. The material parameters of 3DAWC in warp direction can be evaluated for developing quantitative approach to design polymer matrix composite structures.

Influence of thermal distortion to compression failure of polymer matrix composite panels in fire

This paper discusses the influence of thermal distortion to compression failure load of polymer matrix composite panels in fire. The thermal gradient along the thickness of the panel, caused by low thermal conductivity, induces transverse deformation field even without external mechanical loads, known as thermal distortion. The deformation field of thermal distortion obtained from combined thermal–mechanical analysis is presented in terms of non-dimensional parameters that represent thermal and mechanical properties, including those in phase transition at high temperature range, and dimensional lengths. A failure model is proposed to assess the transition from Euler buckling to plastic compression failure under the influence of thermal distortion. For large slenderness ratio, the panel is failed by Euler buckling. For small slenderness ratio, the panel is failed by plastic failure mechanism, where the analysis quantifies the influence of thermal distortion to the reduction of load-bearing capacity. The compression failure mechanism under the influence of thermal distortion is discussed for developing quantitative approach to design polymer matrix composite structures in fire.

Environmental and chemical degradation of carbon/epoxy and structural adhesive for aerospace applications: Fickian and anomalous diffusion, Arrhenius kinetics

Polymer-matrix composite structures in service may be affected by different environmental conditions that modify their mechanical performance, thermal stability, and flammability potential. In this study, epoxy-based structural adhesive and carbon/epoxy specimens were degraded at three conditioning temperatures, by water and commercial fluids typical of aerospace operations: jet fuel, anti-icing additive and hydraulic fluid. Two well-established simple diffusion models (Fickian, Langmuir) were used to interpret the mass uptake data and assess the suitability of such models for these tests. Despite limitations inherent in these models, reasonably good fits were obtained for adhesive and carbon/epoxy specimens immersed in water or anti-icing additive. We report the respective strengths of association of the two models with the individual specimens’ data, and boxplots for the diffusivity changes among the three conditioning temperatures. An Arrhenius trend for the diffusivity of adhesive specimens treated in anti-icing shows that this temperature dependence may not be a good approximation for this problem. The degradation of these materials in hydraulic fluid is very complex, as indicated by the extensive swelling and the color change, and these models could not successfully fit the gravimetric data. These new results could aid researchers in multiphysics modeling of degraded composite structures.

Experimental study of tool–part interaction during autoclave processing of thermoset polymer composite structures

Autoclave manufacturing of thermoset polymer matrix composite structures with high dimensional fidelity requires a good understanding of various parameters affecting process-induced warpage and application of this knowledge to minimize the warpage through appropriate process control. One important contributor is the interaction between a composite part and the tool on which the part is laid and cured. This experimental study quantified the tool–part interaction by measuring the static and dynamic frictional coefficients as a function of process time, using a friction test fixture specially designed to simulate the autoclave environment. Temperature ramp rate was varied to understand the effect of autoclave cure cycle on the friction coefficients. Measured friction coefficients were maximum at the start of the cure cycle and varied as a function of degree of cure ( α) and ramp rate owing to change in the tool–part interface, cure shrinkage, resin/composite properties, residual stress, and mode of interface failure.

Thermal degradation analysis of thermoset resins

AbstractDynamic mechanical analysis, thermogravimetric analysis, and dielectric analysis (DEA) were conducted for three thermoset resin systems: bismaleimide, epoxy, and vinyl ester. The resin samples were subjected to various degrees of thermal exposure (400, 270, and 330°C for 5–150 min). Dielectric constants were measured along with the thermomechanical properties. The glass‐transition temperature, modulus, and weight loss were important parameters for correlating the material property changes with the heat exposure. A linear relation was determined between the thermomechanical properties and the dielectric properties of the resins under the selected exposure conditions. Therefore, DEA can be introduced as a significant technique for evaluating thermally exposed polymer materials. Interestingly, it is a nondestructive evaluation process. In the future, it could be used for onsite health monitoring of thermally exposed polymer matrix composite structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Mechanics of mechanically fastened joints in polymer–matrix composite structures – A review

Abstract As the applications of advanced composite structural materials continue to increase, so does the need to understand the mechanical behavior of mechanically fastened joints in such structures. The most recent and relevant review article on this subject was published more than a decade ago, but it was restricted to stress analysis and strength prediction of mechanically fastened joints in fiber-reinforced plastics. The present article attempts a more comprehensive review of recent literature in the broader area of mechanics of mechanically fastened joints in polymer–matrix composite structures. Since experimental characterization has traditionally played such a fundamental role in such studies, the article begins with a review of relevant mechanical test methods and standards. This is followed by a discussion of the mechanics aspects of design, including joint design methodologies, considerations of the influence of geometric effects, and fastener preload selection. The remaining sections are devoted to failure modes such as bearing failure, failure prediction for both statically and dynamically loaded joints, time-dependent joint preload relaxation, the effects of temperature and moisture on joint strength and failure, and non-destructive evaluation techniques for monitoring the joints. Finally, comments are offered regarding the most important remaining problems in this area, and recommendations for future work.

次世代マグネシウム合金構造部材創製・加工技術開発プロジェクトの概要

The research and development project on advanced composite materials & process development for next generation aircraft structures has been performed since FY2003 under the contract with Ministry of Economy, Trade and Industry (METI) in Japan. This project aims to develop innovative lightweight materials & process technologies for civil aircraft structures and consists of 3 technical areas, radiation-curing technology of polymer matrix composites (PMC) structures, structural health monitoring (SHM) technology of PMC structures, and advanced magnesium alloy technology.In advanced magnesium alloy technology, alloy contents, fabrication process and structure member production technology are being developed about casting alloy technology and powder alloy technology.In this paper, we introduce briefly the activities and typical results up to FY2005 on powder alloy technology of advanced magnesium alloy to be used as structural materials.

Mechanisms generating residual stresses and distortion during manufacture of polymer–matrix composite structures

The mechanisms causing residual stresses and distortions are considered, and the way they develop during the cure discussed. Experimental results are presented through the cure cycle on curvature of unsymmetric laminates, spring-in of curved sections and stresses in flat plates due to tool–part interaction. It is shown that thermal stresses after vitrification are the main cause of distortion of unsymmetric plates, whereas thermal stresses and chemical shrinkage, while the material is in the rubbery state, both contribute to spring-in. Large stresses can develop due to tool–part interaction, even before gelation.

A FINITE ELEMENT COUPLED THERMOVISCOELASTIC CREEP APPROACH FOR HETEROGENEOUS STRUCTURES

Residual stress development in heterogeneous or composite materials is an important problem in manufacture process modeling. Composites possess an intricate microstructure in which the mismatch in thermal expansion coefficients between the fiber and matrix can lead to residual thermal stresses upon part cool-down. It is commonly assumed that prior to cool-down, the entire composite at both micro and macro length scales is at a zero stress temperature. As cool-down initiates, the mismatch in thermostress behavior and the mismatch in viscoelastic time-dependent behavior of the two phases lead to built-in residual stresses in the final product. A novel finite element approach is presented here for the coupled thermovisoelastic analysis of polymer-matrix composite structures containing microscopic heterogeneities. Due to its inherent advantages over other techniques, the asymptotic homogenization approach is employed to obtain the homogenized properties for use in the macroscale problem. For illustration, a simple Kelvin-Voight viscoelastic solid is studied to demonstrate the formulations involved in similar materials for which the time-dependent stress-strain relationship is subsequently homogenized. The formulation accounts for the dissipative corrector behavior for heterogeneous viscoelastic materials. An analytical solution for the degenerative homogeneous viscoelastic material subject to uniform thermal relaxation is employed to verify part of the formulations. Additional examples are shown to further illustrate the approach for more complex scenarios.

A finite element thermo-viscoelastic creep approach for heterogeneous structures with dissipative correctors

A finite element approach is presented for three-dimensional thermo-viscoelastic macro analysis of polymer-matrix composite structures containing micro-level heterogeneities, a two-scale approach. Due to its ability to account for microstructural details, the asymptotic expansion homogenization approach is employed to first, obtain the homogenized properties for use in the macroscale problem, and second, to study the local micro-level stress distributions influenced by macro effects. The theoretical formulations are described and developed for a thermoviscoelastic solid whose time-dependent stress–strain relationship can be homogenized. Arising from homogenization of the constitutive equation in the time domain is a hereditary dissipative corrector term. The dissipative corrector is time-dependent and accounts for heterogeneous behavior across the junction of dissimilar materials at the microstructural level. The additional term is necessary for the governing constitutive equations to satisfy equilibrium at both length scales. The objectives of this paper are three-fold: (1) develop the micro and macro constitutive equations for a thermoviscoelastic Kelvin–Voight material; (2) develop a computational approach for the constitutive equations; and (3) demonstrate and verify illustrative applications using results from the theoretical developments in the literature wherever available for a viscoelastic homogeneous/heterogeneous material.

Progressive fracture of polymer matrix composite structures

An approach independent of stress intensity factors and fracture toughness parameters has been developed and is described for the computational simulation of progressive fracture of polymer matrix composite structures. The damage stages are quantified based on physics via composite mechanics while the degran of the structural behavior is quantified via the finite element method. The approach accounts for all types of composite behavior, structures, load conditions, and fracture processes starting from damage initiation, to unstable propagation and to global structural collapse. Results of structural fracture in composite beams, panels, plates, and shells are presented to demonstrate the effectiveness and versatility of this new approach. Parameters and guidelines are identified which can be used as criteria for structural fracture, inspection intervals and retirement for cause. Generalization to structures made of monolithic metallic materials are outlined and lesson learned in undertaking the development of new approaches, in general, are summarized.

The treatment of fatigue and damage accumulation in composite design

Differences between the treatment of damage, damage accumulation and fatigue for various types of advanced composite systems, for example, polymer matrix composites (PMCs), ceramic matrix composites (CMCs) and metal matrix composites (MMCs) are discussed in general. The approach for PMCs from the aspect of damage mechanics is reviewed next and extended to a discussion of various aerospace certification approaches adopted for PMC structures. Following this an explanation of the theoretical foundations for the ‘wearout philosophy’ in conjunction with related damage and fracture mechanics relationships is provided. This concludes with a survey of flaw, or more precisely, damage growth rate exponents for various matrix and/or interface-dominated failure mechanisms for PMCs and adhesively bonded joints.

Adhesive bonding of polymer composites

AbstractIn structures composed of polymer matrix composite materials, components must be joined such that the overall structure retains its structural integrity while it is performing its, intended function which can include both mechanical loads (static and dynamic) and environmental loads (temperature and humidity). The use of composite materials in complex structures almost always reduces the number of components in the structures compared to the use of metallic alloys for the same structure. Thus, using composite materials not only results in great savings in weight, but also through a reduced number of joining operations, results in significant savings in assembly, inspection, parts storage, and movement, resulting in increased reliability and lower cost. Yet joining is still required. Joining metallic structures is a mature technology involving riveting, bolting, welding, glueing, brazing, soldering, and other methods. However, for most polymer matrix composites only adhesive bonding and mechanical fastening can be utilized. Attention has been given recently, however, to localized welding of thermoplastic polymer matrix composites, and this will be discussed briefly later. Inherently, adhesive bonding is preferable to mechanical fastening because of the continuous connection, whereas in drilling holes for bolts or rivets, fibers or other reinforcements are cut, and large stress concentrations occar at each discrete fastener hole. The following is a review of much of the literature dealing with adhesive bonding of polymer matrix composite structures. It is Intended not only to be a review, but also a background for detailed study of the referenced and other documents, and a catalyst for future research.