Creep Behavior Of Composites Research Articles

Analysis of contact creep behaviour of nanofilled composites

An effective modelling method for analysing the contact creep behaviour of composite materials with different nanofillers was proposed. Considering both the contact and creep material nonlinearities, an augmented Lagrangian algorithm was used to treat the unilateral contact constraints, and a time-hardening creep constitutive equation was adopted to describe the deformation characteristics of the nanocomposites. The constitutive parameters were extracted through a series of linear fittings based on the multiaxial creep theory and creep test curves, and the accuracy of the constitutive equation was validated. The applications of the proposed modelling method were demonstrated using a rope-wheel contact system (RWCS), in which the wheels were made of polystyrene (PS) with carbon black (CB), multi-walled carbon nanotubes (MWCNT), or chemically reduced graphene oxide (CRGO). The results indicated that the addition of nanofillers significantly reduced the creep deformation of the contact zone. The CRGO exhibited a better anti-creep performance than that of CB and MWCNT. Compared with pure PS, the maximum deformation on the contact path of the nanocomposite wheel with 5.0 wt% CRGO sheets at 1500 s and 104 s was reduced by approximately 22 % and 52 %, respectively. The coefficient of friction μ had a strong influence on the contact creep deformation when μ < 0.3. Additionally, the anti-creep capability of the added nanofillers became more evident as the loading time increased. The contact creep deformation of the CRGO composite was less than one-tenth that of the matrix material after 30 d.

Evaluation of room temperature creep deformation of in situ Fe-based bulk metallic glass nanocomposites by instrumented indentation

In the present work, Fe57Cr9Mo5B16P7C6 (at. %) in situ bulk metallic glass nanocomposites of varying crystallinity, i.e. 0 to 80 vol. %, were synthesized by spark plasma sintering. Room temperature indentation creep behaviour of these composites was evaluated with nanoindentation technique. Effect of crystalline phase content on overall creep behaviour of the BMG composites was evaluated. Creep resistance of the BMG composites was improved with increase in the amount of crystalline phases up to 40 vol. %. Improved creep resistance is attributed to the presence of nanocrystalline phases in amorphous matrix and lower defect concentration in the BMG composite samples. However, excess crystallinity imparted brittleness and resulted in poor creep performance of the BMG composites. Derived stress exponent values are significantly lesser for the BMG composite sample in comparison to the amorphous compact indicating the transition in the mode of plastic deformation from inhomogeneous to nearly homogeneous. Loading rate has more pronounced influence on final creep displacement of fully amorphous sample in comparison to that of BMG composite.

Assessment and simulation of the thermomechanical tensile and creep behavior of C/PEKK composites for aircraft applications above the glass transition temperature

The present work focuses on the assessment and the simulation of the thermomechanical tensile and creep behavior of Poly Ether Ketone Ketone 7002/carbon fibers composites behavior under tensile and creep solicitation between the glass transition temperature and 200 °C, via a multiscale approach starting from the behavior of the PEKK 7002 neat polymer.Tensile and creep polymer and composite experimental curves are employed to develop and validate generalized Semi – Analytical Homogenization / Localization Method for the simulation of the thermomechanical tensile and creep behavior of composite laminates. Through the employment of the model, a similarity of behavior between polymer and composites is demonstrated.The proposed algorithm capabilities of simulating the thermomechanical tensile and creep behavior of composites with different ply orientations and stacking sequences are then presented.

Creep behaviour of ozone treated jute fabric/epoxy composites filled with ozonized and pulverized corn husk particles

In present work, the creep performance of ozone treated jute fabric/epoxy composites was studied at different environment temperatures after incorporation of 1, 3 and 5 wt % of ozonized and pulverized corn husk particles. The ozone treatment of jute fabric as well as corn husk fibres was found successful in removal of non-cellulosic contents. Furthermore, the ozone treatment of corn husk fibres was observed beneficial during ball milling as it easily pulverized them into particles due to decrease in strength. When the creep behaviour of composites was investigated using several creep models (i.e., Findley's power law model, Burger's model, and Coupling Model), the incorporation 3 wt % corn husk particles was found to reduce the creep deformation and strain rate of composites to greater extent especially at higher temperatures. The 3 wt % corn husk particles were found to restrict the segmental mobility of epoxy matrix in extended temperature range of 100 °C–140 °C. Nevertheless, the microbead pull out and nanoindentation tests indicated that the interfacial shear strength properties of composites increased after the incorporation of 5 wt % of corn husk particles. Among various creep models, the coupling model predicted the creep behaviour of composites more accurately in addition to explanation on the creep mechanism.

Experimental analysis of time dependent phenomena and temperature effects on macro-synthetic fibre reinforced concretes in different loading conditions

Fibre reinforced concretes (FRCs) are composite materials now largely adopted in structural applications given their mechanical properties in terms of the residual tensile strength, almost absent for plain concrete. The short-term mechanical behaviour of these material has been deeply studied, while their time-dependent deformations have received less attention from the scientific community. The present paper presents the experimental characterization of the creep deformations of a concrete reinforced with polypropylene fibers by means of different types of tests, together with an analysis of the temperature effect. Innovative test set-ups are used to this aim. The paper presents the results of shrinkage, compression creep, uniaxial tension and flexural creep tests and discusses the contribution of the different components of the FRC to the composite creep behavior.

Transverse creep induced by interfacial diffusion in fiber-reinforced composites: A micromechanics model and computational validation

Interface diffusion is an important weakening mechanism in the creep behavior of metal matrix composites at high temperatures. The increase in the creep strength of composite materials caused by stress transfer from matrix to rigid reinforcements may be totally offset by rapid interface diffusion. However, in-depth understanding of the complex multi-field coupling process of interface diffusion remains lacking. Here, we present a theoretical method in the framework of micromechanics theory based on Eshelby's solution to solve this problem. The misfit deformation and stress redistribution caused by mass diffusion are taken into account by introducing a time-evolving eigenstrain into reinforcements. Mass conservation in the diffusion process, is guaranteed by keeping the volume constant, leading to incompressibility of creep strains. In this work, the creep behavior of composites induced by interface diffusion is systematically studied, including macroscopic creep strain and stress relaxation. Closed-form solutions are obtained and verified by finite element simulation with a built-in time-step algorithm. This methodology can be conveniently applied to account for plasticity and creep of matrix, interface debonding, microcracks, etc., paving the way for the study of the complex behavior of composite materials at high temperatures.

Time-temperature superposition of flexural creep response of carbon fiber PEKK composites manufactured using different prepreg stacking sequence

In this work, the long-term creep response of high-performance carbon fiber PEKK (CF/PEKK) composites was evaluated by performing extrapolated short-term flexural creep tests at various temperatures. The time-temperature superposition principle (TTSP) with vertical as well as horizontal shifting was used to generate master curves at reference temperatures of 120°C. Satin weave-based CF/PEKK prepregs were used to manufacture eight-layer composites via compression molding, with three different stacking sequences: (a) zero-direction [0]8 (b) cross-ply [0, 90]4 and (c) quasi-isotropic [90, −45, 45, 0]2 s. The flexural properties under three-point bending arrangement in a universal testing machine were also evaluated. A dynamic mechanical thermal analyzer (DMTA) in three-point bending mode was used to evaluate the temperature-dependent viscoelastic properties of the three types of composites. The creep and creep-recovery behavior was evaluated at 40°C, 80°C, 120°C, 160°C and 200°C. To construct a master curve, extrapolated short-term isothermal creep tests were performed from 120°C to 180°C at the intervals of 10°C. The predicted master curve represents the creep behavior of composites over more than 10 years. It was shown that the quasi-isotropic CF/PEKK composites exhibited 27% and 12% higher creep resistance at 120°C as compared to zero-direction and cross-ply laminates, respectively. Higher flexural modulus (23%) and flexural strengths (33%) were also exhibited by the quasi-isotropic CF/PEKK composites. The final thickness of quasi-isotropic laminates was 8% lower than the 0o laminates. After analyzing the cross-sections of the composites, it was proposed that the superior mechanical properties of the quasi-isotropic laminates could be due to enhanced nesting between neighboring prepreg layers during the compression molding process, which resulted in closer packing of the fibers. It has been shown that the prepreg stacking sequence could affect the creep behavior and flexural properties of the compression-molded CF/PEKK composites.

The relation of porosity and creep behavior of glass fiber/epoxy composite: Design of experiments approach

AbstractThis work aimed to analyze the influence of voids content, morphology (size and shape), and position on the creep behavior of glass/epoxy composites with a reduced number of experiments, applying the design of experiments statistical approach to describe the creep behavior. For this purpose, a three‐dimensional microstructure of the materials is created from the images of X‐ray microtomography. Analysis of variance shows that the temperature contributes 90% to the initial and final creep deformation; meanwhile, stress and porosity act as secondary factors. Void content is responsible for 15% of the composite creep behavior; meantime, the increase of elliptical and irregular porosity decreases creep resistance. The Weibull analytical model combined with surface response methodology (Taguchi approach) proves to be feasible to predict the creep deformation curve with low error.

Upper and lower bounds on the creep strain and stress relaxation induced by interface diffusion in metal-matrix particulate composites

In this study, we developed a micromechanics scheme to predict the upper and lower bounds on the creep strain and stress relaxation induced by interface diffusion in metal-matrix particulate composites. The normal stress acting on the matrix-inclusion interface, which is the driving force for interface diffusion, is estimated by using the Hashin-Shtrikman bounds and mean-field micromechanics theory. Analytical solutions of upper and lower bounds on the creep strain under constant stress and the relaxed stress at fixed strain are obtained. Results of this work show that the ultimate creep strain and relaxed stress are only related to the material properties and the percentage of each component, such as volume fraction of inclusion and elastic modulus ratio of inclusion to matrix. The parameters of interface diffusion only influence the rate of creep strain. It is found that the creep deformation and stress relaxation of composites are more sensitive to the volume fraction of inclusion than the elastic modulus ratio. The methodology of this study also applies to analysis of creep deformation of composites where both the matrix creep and interface diffusional creep need to be considered. The present study offers new perspectives for in-depth understanding of creep behavior of composites driven by mass diffusion along inclusion-matrix interface.

Ceramic-Reinforced γ-TiAl-Based Composites: Synthesis, Structure, and Properties.

In this study, new multilayer TiAl-based composites were developed and characterized. The materials were produced by spark plasma sintering (SPS) of elemental Ti and Al foils and ceramic particles (TiB2 and TiC) at 1250 °C. The matrix of the composites consisted of α2-TiAl and γ-TiAl lamellas and reinforcing ceramic layers. Formation of the α2 + γ structure, which occurred via a number of solid–liquid and solid–solid reactions and intermediate phases, was characterized by in situ synchrotron X-ray diffraction analysis. The combination of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis revealed that an interaction of TiC with Ti and Al led to the formation of a Ti2AlC Mn+1AXn (MAX) phase. No chemical reactions between TiB2 and the matrix elements were observed. The microhardness, compressive strength, and creep behavior of the composites were measured to estimate their mechanical properties. The orientation of the layers with respect to the direction of the load affected the compressive strength and creep behavior of TiC-reinforced composites. The compressive strength of samples loaded in the perpendicular direction to layers was higher; however, the creep resistance was better for composites loaded in the longitudinal direction. The microhardness of the composites correlated with the microhardness of reinforcing components.

Interface-controlled creep in metallic glass composites

In this work we present molecular dynamics simulations on the creep behavior of Cu64Zr36 metallic glass composites. Our results reveal that all composites exhibit much higher creep rates than the homogeneous glass. This is because the glass–crystal interface acts like a weak interphase, where the activation of shear transformation zones is easier than in the surrounding glass. We observe that the creep behavior of the composites does not only depend on the interface area but also on the orientation of the interface with respect to the loading axis. We propose an explanation in terms of different mean Schmid factors of the interfaces, with the amorphous interface regions acting as preferential slip sites.

Effects of aging on water and lubricating oil on the creep behavior of a GFRP matrix composite

The creep behavior of an E-glass-polyester matrix composite was evaluated as a function of time of immersion in water and lubricant oil. The effect of the test temperature was also evaluated. It was observed that, after 6 and 14months of exposure to the aging fluids, the Young’s modulus of the composite was reduced by 20% regardless the aging fluid when the test was performed at room temperature. For the tests performed at 60°C, the effects of immersion in lubricant oil were more severe than those after immersion in water. Variation of the creep behavior due to exposure to water was associated only to physical aging, because the properties’ variation was correlated to the amount of absorbed water, decreasing only while the amount of water increased. The test temperature was shown to be the main parameter influencing the creep behavior of the composite. The action of the plasticizing effect of water and reduction of oil viscosity with temperature influenced the results of the steady creep rate when the tests were performed at 60°C. Micromechanics approach was used to qualitatively explain the experimental results obtained.

Flexural creep behaviour of jute polypropylene composites

Present study is about the flexural creep behaviour of jute fabric reinforced polypropylene (Jute-PP) composites. The PP sheet and alkali treated jute fabric is stacked alternately and hot pressed in compression molding machine to get Jute-PP composite laminate. The flexural creep study is carried out on dynamic mechanical analyzer. The creep behaviour of the composite is modeled using four-parameter Burgers model. Short-term accelerated creep testing is conducted which is later used to predict long term creep behaviour. The feasibility of the construction of a master curve using the time-temperature superposition (TTS) principle to predict long term creep behavior of unreinforced PP and Jute-PP composite is investigated.

Effect of boron carbide particle size and volume fraction of TiB–TiC reinforcement on steady state creep behaviour of PM processed titanium matrix composites

TiB–TiC reinforced titanium matrix composites (TMCs) were synthesised through pressureless sintering of titanium and boron carbide (B4C) powder compacts. Effect of boron carbide (B4C) particle size and volume fraction of TiB–TiC reinforcement on steady state compression creep behaviour of composites was investigated in the temperature range of 773–873 K. The creep rates of composites are found to be about two orders of magnitude lower than those of unreinforced titanium. The creep rates further lowered with decrease in size of B4C particles (from 16 to 3 μm) used in preparation of composites as well as with increase in volume fraction of the TiB–TiC reinforcement from 10 to 30 vol.%. By using the concept of effective stress as well as incorporation of load transfer and substructural strengthening effect produced by the reinforcement into analysis, the entire creep data of Ti and the composites can be made to merge on to a single line within a scatter band of factor of 2–3 and can be represented by a unified power-law equation.

Flexural Creep Behavior of Composites from Polypropylene and Rubberwood Flour

The effects of plastic grades and composition contents on creep behavior of extruded composites from polypropylene and rubberwood flour were investigated. Virgin polypropylene gave lower creep strain than recycled polypropylene, both in composites and as unfilled plastic. An increase of rubberwood flour content reduced the creep deformation of the composites, both virgin and recycled plastics. Maleic anhydride-grafted polypropylene as a coupling, 5 wt% addition increased the creep strain of the composite materials. Likewise, an addition of 1 wt% ultraviolet (UV) stabilizer content significantly enhanced the creep deformation. The results recommend that the amount of UV stabilizer should be as small as possible to limit its negative effects. Four-element Burger model offered a good fitting on the creep behavior of each composite formulation.

Effect of boron carbide particle size and volume fraction of TiB–TiC reinforcement on steady state creep behaviour of PM processed titanium matrix composites

AbstractTiB–TiC reinforced titanium matrix composites (TMCs) were synthesised through pressureless sintering of titanium and boron carbide (B4C) powder compacts. Effect of boron carbide (B4C) particle size and volume fraction of TiB–TiC reinforcement on steady state compression creep behaviour of composites was investigated in the temperature range of 773–873 K. The creep rates of composites are found to be about two orders of magnitude lower than those of unreinforced titanium. The creep rates further lowered with decrease in size of B4C particles (from 16 to 3 μm) used in preparation of composites as well as with increase in volume fraction of the TiB–TiC reinforcement from 10 to 30 vol.%. By using the concept of effective stress as well as incorporation of load transfer and substructural strengthening effect produced by the reinforcement into analysis, the entire creep data of Ti and the composites can be made to merge on to a single line within a scatter band of factor of 2–3 and can be represented by...

High-temperature mechanical characteristics of NiO/3YTZP composites

NiO/3YTZP (3mol% Y2O3-stabilized tetragonal ZrO2) composites with 40mol% NiO (26vol% NiO) have been fabricated by mechanical mixing of NiO and 3YTZP powders and sintering at 1500°C for 10h in air. The resulting microstructures have been characterized by electron microscopy. Compressive mechanical tests at constant strain rate were conducted on these materials at temperatures between 1150 and 1350°C in air. The σ–ɛ curves display extended secondary creep regimes without signals of macroscopic failure. The composite creep behavior is characterized by a stress exponent n=2 and an activation energy for flow Q=490kJ/mol. The overall creep behavior of the composites is essentially controlled by the zirconia matrix, due to the softness of the NiO phase in the experimental conditions used in this study.

Threshold stress and load partitioning during creep of metal matrix composites

The threshold stress, σ o, included in the creep equation to explain the high-temperature behavior of discontinuously reinforced metal matrix composites (MMCs) is criticized on the basis of microstructural considerations and a new creep data analysis. An alternative interpretation, based on changes in the composite matrix microstructure and, in particular, a load transfer mechanism, is proposed. The resulting creep equation is similar to that in which σ o is used: in essence, σ o is simply replaced by the stress carried by the reinforcement (referred to as σ T). New creep data on 6061Al–15 vol.% SiC w composite and the corresponding unreinforced alloy, allowing direct experimental assessment of composite creep strengthening, Δ σ, are analyzed. The linear dependence found of Δ σ with the applied stress, σ, Δ σ( σ), correlates reasonably well with shear-lag and Eshelby model predictions of σ T, transferred during composite creep deformation. The possible occurrence of damage mechanisms and the complexity of modeling these mechanisms to predict the overall composite creep behavior are also discussed.

Nonlinear Viscoelastic Creep Prediction of HDPE-Agro-fiber Composites

Agro-based plastic composites are being used as deck boards and other load-bearing materials. In these composites, both fibers and plastics contribute to creep when they carry loads. However, the existing literature concentrates on creep prediction and characterization of composites as a single-phase material. In our study, an attempt is made to develop a generic creep prediction model that describes the creep behavior of composites with the constituents’ creep behavior. The ‘theory of mixture’ for composites is extended to describe the creep behavior of this material, which is two phase. This model is validated for HDPE-rice husk composites with power-law-Boltzmann’s superposition principles. The model works well not only to describe creep, but also its nonlinearity. The model is generic enough for extending it to incorporate varying environmental conditions, such as time and temperature. This is the first model to describe creep for a two-phase bio-based composite. This study is a vanguard in correlating Schapery’s ‘single-phase’ model with a ‘two-phase’ model, where the same is validated for step-loading situations.

Analysis of the creep behavior of polypropylene‐woodflour composites

AbstractThe creep behavior of composites prepared from woodflour and polypropylene has been analyzed. The woodflour content was varied from 0% to 60%. The compatibility between filler and matrix was varied by adding a non‐commercial polypropylene‐maleic anhydride copolymer (PPMAN) to the mixture. Short‐term and long‐term creep tests of woodflour/polypropylene composites at different temperatures were carried out. The effects of filler content, addition of compatibilizing agent and temperature were discussed. The creep deformation was generally reduced with woodflour addition, except at very high filler concentrations because of filler‐wetting and dispersion problems. Low temperatures and addition of PPMAN also reduced the creep deformation. The creep compliance was modeled using the Bürgers model and a power law equation. The parameters were found from the best fitting of experimental data using an optimization method. The Bürgers model was found to provide a good description of the linear viscoelastic behavior. The mathematical description obtained from the short‐term creep was utilized to predict the dynamic mechanical behavior of the composites with very good agreement between experimental and calculated values. Attempts to use the time‐temperature‐superposition principle to predict long‐term creep from high temperature results were not successful because of the aging of the samples during creep at low temperatures. However, there was a good superposition of the short‐term and long‐term data at temperatures close to 70°C–80°C. The reason for this behavior is a relaxation of the PP matrix that takes place in that temperature range and erases any previous aging of the material. Polym. Eng. Sci. 44:1594–1603, 2004. © 2004 Society of Plastics Engineers.