Creep Of Composites Research Articles

The Possible Detriment of Oxygen in Creep of Alumina and Zirconia Ceramic Composites Reinforced with Graphene.

This paper aims to give an answer to the following question: is the oxidation of graphene a critical issue for high-temperature plasticity in graphene-reinforced ceramics? To give a convincing reply, we will focus on two very different graphene-based ceramic composites: reduced graphene oxide (rGO)-reinforced alumina (α-Al2O3) and reduced graphene oxide (rGO)-reinforced yttria tetragonal zirconia (t-ZrO2). The processing of the powders has been made using a colloidal route, and after that, a spark plasma sintering process was performed in order to densify the samples. Creep tests were performed at temperatures between 1200–1250 °C in an argon atmosphere. The microstructure obtained by SEM of the sintered and tested specimens was characterized quantitatively to elucidate the deformation mechanism. Raman spectroscopy was carried out to check the integrity of the graphene. The average grain size was in the order of 1 µm and the shape factor was 0.7 for all the studied materials. The integrity of the graphene was checked before and after the creep experiments. The careful analysis of the creep tests shows that graphene oxide or its reduced version are not efficient phases for creep resistance improvement in general, contrary to what is reported elsewhere. However, the results permit the suggestion of a creep improvement in nanocomposites at a very high temperature regime due to an enhanced reactivity of oxygen between carbon and alumina interfaces. In the case of zirconia, the results give us the conclusion that the oxidation of graphene is a highly detrimental issue regarding the improvement of high-temperature plasticity.

Research on Creep Constitutive and Numerical Simulation of Composite Solid Propellant

Through the composite creep solid propellant creep experiment, the composite solid propellant curve is obtained. The power rate constitutive model, linear viscoelastic model and Schapery nonlinear constitutive model are used to describe the creep process. The study shows that Schapery modified nonlinear constitutive model can better describe the creep properties of composite solid propellants. Through the ABAQUS user subroutine, the finite element application of Schapery’s creep-type nonlinear constitutive model is studied. The research results in this paper can provide a reference for the analysis of the creep effect of the grain during the vertical storage of the solid rocket motor.

Multiscale characterization and representation of variability in ceramic matrix composites

Low density, high strength, and high creep and oxidation resistance properties of ceramic matrix composites (CMCs) make them an ideal choice for use in extreme environments in space and military applications. This paper presents a detailed characterization study of structural and manufacturing flaws in Carbon fiber Silicon-Carbide-Nitride matrix (C/SiNC) CMCs at different length-scales. Energy-dispersive spectroscopy (EDS) is used for the chemical characterization of the material’s elemental constituents. High-resolution multiscale graphs obtained from scanning electron microscope (SEM) and confocal laser scanning microscope (LSM) are used to characterize the distribution and morphology of defects at different length scales. This is followed by the classification and quantification of the common manufacturing defects. An image processing algorithm based on the image segmentation process is developed to quantify the variability of various scale-dependent architectural parameters. Finally, a three-dimensional stochastic representative volume element (SRVE) generation algorithm is developed to provide precise representations of material textures at multiple length scales. The developed algorithm accurately accounts for material features and flaws based on a range of multiscale structural and defects characterization results.

Creep deformation of poly(methyl methacrylate)-multiwalled carbon nanotube composites

Considering the long-term structural stability of polymer-nanotube composites under different service conditions, we investigate the tensile creep of polymer-nanotube composites consisting of poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotubes (MWCNTs). The PMMA is pre-irradiated by ultraviolet light with different doses to change the molecular weight. The creep deformation of the PMMA-MWCNT composites with the weight fraction of MWCNTs in a range of 0 to 0.7 wt.% in a temperature range of 50 to 80 °C is well described by a Maxwell standard model with parallel connection between a spring, E1, and a Maxwell element (a dashpot, η, in the series connection with a spring, E2). The value of E1 is a linear function of the inverse of the normalized weight fraction with the average values of the coefficients/constants for the linear relation being increasing functions of the weight fraction of MWCNTs. The value of η is a power function of the molecular weight with a power index of ~3.3. The activation energy for the creep deformation of the PMMA-MWCNT composites increases with the increase of the weight fraction of MWCNTs.

Stress relaxation, creep, and recovery of carbon fiber non-crimp fabric composites

Considering that structural composites are typically composed of off-axis plies, i.e. quasi-isotropic stacking sequence, their strength and stiffness are time-dependent due to the viscoelastic character of polymer matrices. This work consists of determining creep, recovery, and stress relaxation of carbon fiber-reinforced polymer (CFRP) composites. Long-term experimental analyses are conducted via dynamic mechanical analysis under several temperatures and stress levels. From the experimental observations, the changes in the relaxation mechanisms are predicted using Fancey's latch model. The rate of relaxation at different temperatures is also covered. Since at certain strain levels the viscoelastic behavior cannot be properly determined, the stress-relaxation is determined using the time-temperature superposition (TTS) principle, considering nine temperatures at three strain levels in order to cover the three main regions of the composite system (glassy, glass transition and rubbery regions). The models and experiments herein presented can be extended to any polymeric system.

Creep and relaxation of polyester acrylate composites

It is shown that creep and relaxation are the most important properties for structural materials. This research presents the results of a study of filled polyester acrylate composites’ creep and relaxation. The comparison of mechanical indicators with similar for unfilled materials is shown in this work. Investigation of mechanical properties of the samples was carried out on a universal testing machine Shimadzu Autograph AG-X Series at room temperature. It was revealed that the intensity of stress and creep relaxation in the composite is much weaker than in pure resin. It was found that composites are characterized by a logarithmic time dependence of stress relaxation and creep. Logarithmic dependences for the studied parameters are of the same nature. Changes in indicators are mainly due to the properties of the binder.

Experimental test and curve fitting of creep recovery characteristics of modified graphene oxide natural rubber and its relationship with temperature

The creep recovery properties of different graphene-doped rubber and the effect of temperature on them were studied. Doping graphene, especially with the surface functional group or surface microstructure, can significantly improve the creep resistance of natural rubber (NR). The permanent creep of each composite tested under the same conditions for 20 min. Graphene oxide, hydrazine hydrate reduced graphene oxide, and 3-aminopropyltriethoxysilane (APTS) grafted graphene oxide was 33%, 16%, and 51% lower than those filled with carbon black respectively. Four parameter model and Weibull distribution function used to analyze and evaluate the creep and recovery test results of composite rubber. These curve fitting results can adequately describe the influence of different types of nanofillers on the creep and recovery properties of composite rubber. The long-term creep of composites forecasted by the time-temperature superposition principle (TTSP). The results show that graphene doping can improve the creep resistance of the rubber. Besides, graphene oxide and surface-modified graphene oxide had better creep resistance than reduced graphene oxide filled natural rubber. It can see that the interfacial properties between the graphene sheet and the natural rubber matrix play an essential role in the creep and recovery properties of graphene/natural rubber composites.

Performance Analysis of Silicon Carbide Composite Clad Uranium Carbide Fuel for a Long-Life Gas-Cooled Fast Reactor Under Normal Operation—Part II: Modeling and Simulation

Fuel performance analysis was conducted for silicon carbide (SiC) composite clad uranium carbide (UC) fuel of a 500-MW(thermal) gas-cooled fast reactor, specifically the energy multiplier module (EM2) under normal operation. The analysis consists of two parts: Part I includes a description of design bases and criteria, fuel element design specifications, and material properties and models, while Part II (this paper) includes the fuel modeling approach, computer code, and the fuel design evaluation. In Part II, the FRAPCON-4.0 code was updated to include material properties and models of UC fuel, SiC composite cladding, and helium coolant, and named FRAPCON-4.0GA. The analysis was performed using the hot rod power envelope and burnup history. The results show that the present design of the EM2 fuel element has ample margin to melting owing to the high thermal conductivity of the UC fuel and annular pellet configuration. The operating temperature of the fuel element also minimizes the radiation-induced deformation of the SiC composite cladding. The simulation results show that the hoop stress of the cladding is below its tensile stress limit, i.e., one-third of ultimate tensile stress, while the cladding hoop strain limit is reached at 22.5 year, which is less than its design life of 32 years. However, sensitivity calculations of the swelling rate and design parameters indicate that it is feasible to reduce the cladding hoop strain by accommodating the fuel swelling into the open pore. Considering uncertainties associated with the material properties and models, it is highly recommended to experimentally verify the UC swelling and SiC composite creep, which are critical properties in analyzing the long-life fuel behavior.

Rheological parameters, thixotropy and creep of 3D-printed calcium sulfoaluminate cement composites modified by bentonite

The structural instability and poor thixotropy of three-dimensional (3D) printing of calcium sulfoaluminate (CSA) cement composites hinder their applicability in the construction field. In this study, the rheological parameters, thixotropy and creep of 3D-printed CSA cement composites containing bentonite are investigated based on shear-rate- and shear-stress-controlled protocols to achieve a stable three-dimensional structure and excellent thixotropy. Experimental results show that a stable 3D structure with excellent thixotropy can be achieved when the content of bentonite is 2%. In this case, the plastic viscosity and dynamic yield stress are lower than 2.50 Pa s and 645.54 Pa, respectively. The correlation between the rheological parameters and thixotropy of 3D-printed CSA cement composites suggests that the actual thixotropy can be predicted by the yield stress. Furthermore, the shear-stress-controlled protocol was implemented to simulate the effect of gravity and test different creep periods of 3D-printed CSA cement composites with bentonite. The improved static yield stress exhibited better effectiveness in resisting structural deformation over time.

Cantilever creep method for testing ceramic composites and a case study for chemically bonded phosphate ceramic composites reinforced with glass, carbon and basalt fibers, including both experiments and simulations

This paper presented the cantilever beam experiments and the method for creep in chemically bonded ceramics reinforced with glass, carbon, and basalt unidirectional fibers. The ceramic composite samples were fabricated by mixing wollastonite powder and phosphoric acid, through the resonant acoustic mixing technique. The reinforced fibers were added via pultrusion process. The manufactured materials were exposed to high temperature creep tests at 600, 800 and 1000℃, with an annealing time of 1 h, all in air environment. Some examples of real large-scale structures made manually by a company were also included. In order to understand the microstructure, X-ray diffraction and scanning electron microscopy analysis were included. The presented method is simple and can be used in any inorganic ceramic slurry types, such as geopolymers, phosphate cements, clay-based materials, or Portland cement composites. The sample response in high temperature creep experiments was analyzed with a new but very simple technique, and modeled using finite element analysis over all compositions. Results revealed that fibers have a significant effect on the composite creep when compared to the ceramic without reinforcement, and particularly carbon fibers showed a quite interested effect in reducing the creep effects. Results show the limit of the materials under conditions typically found in fires and other extreme environments.

Review: creep of fibre-reinforced ceramic matrix composites

ABSTRACTThe content of the review covers, first, generalities on creep. Then, the creep of ceramics and fibres, that are key constituents of fibre-reinforced ceramic matrix composites (CMCs) are addressed. The general features of ceramic matrix composites that may influence the creep behaviour and creep rupture are discussed. Emphasis is placed on microstructure–property relationships and load sharing between fibres and matrix that are critical for CMCs. Then, creep tests and the creep behaviour of various types of fibre-reinforced composites are presented. Mechanisms and models are discussed. The influence of various factors including composite structure, constituent properties (matrix and fibres), interfacial properties and environmental conditions are examined. The paper focuses on non-oxide composites like SiC/SiC that received much attention during the last three decades. Creep of oxide ceramics, fibres and composites are addressed more briefly.

Research on preload relaxation for composite pre-tightened tooth connections

Abstract Preload is the primary reason why pre-tightened tooth connections (PTTC) can transfer relatively large loads. However, creep of the composite would cause the preload relaxation, resulting in reducing bearing capacity of the connection. To study the preload relaxation of PTTC caused by the creep of composites, a prediction formula is deduced by converting the viscoelastic problem to an elastic problem using Laplace transform. Meanwhile, long-term experimental research on the preload relaxation of composite pre-tightened tooth connection with different initial preloads and different geometry sizes was made. The theoretical results are compared with experimental data obtained by long-term experiment, and the results indicate that the calculation formula can predict the preload relaxation well in linear viscoelastic state. The preload relaxation mainly occurs at the beginning of loading and it tends to be steady in the middle and later periods.

Creep Properties of Squeeze-Infiltrated Carbon Nanotube and Aluminum Borate Whisker Reinforced AS52 Mg Metal Matrix Composites

The effects of carbon nanotubes (CNTs) and aluminum borate whisker (ABw) on the creep and tensile properties of an AS52 alloy matrix composites were investigated. A hybrid 5 vol% CNT + 20 vol% ABw/AS52 Mg MMC and a single 25 vol% ABw/AS52 Mg MMC were fabricated by preform fabrication and squeeze infiltration. Creep tests were carried out at temperatures of 150–250 °C under stresses of 50 and 70 MPa. The tensile property was evaluated at room temperature and 150 °C. The minimum creep rate decreased in the order AS52 > single MMC > hybrid MMC. The creep activation energy of the hybrid MMC was 182.9 kJ/mol which was 28% and 83% higher than those of the single MMC and the AS52, respectively. The room-temperature and high-temperature tensile strengths of the hybrid MMC showed the highest values. Creep properties of the hybrid MMC improved on addition of CNTs, which prevented creep void initiation and crack propagation along the ABw interface.

Creep and thermal behavior of quarry dust-silicon carbide hybrid particles reinforced ZA-27 alloy composites using stir casting technique

In this research, creep and thermal behavior of stir cast ZA-27 alloy-based hybrid composites modified with quarry dust (QD) and silicon carbide (SiCp) particles was investigated. ZA-27 hybrid composite samples reinforced with 10 wt% QD-SiCp particles containing varied weight percentage 0, 25, 50, 75, and 100% quarry dust was developed using stir casting technique. Dimensional stability (creep) evaluation and thermal behavior were performed to assess the performance of the produced modified composites. Thermal behavior was carried out using DSC thermal analyzer at operating temperatures of 0–500 °C to determine the behavior of the composites relative to temperatures, while the creep behavior (dimensional stability) was conducted using Dynamic Mechanical Analyzer (DMA 242E) at elevated temperature of 100 °C under a load of 3 N for 70 min. The results show that hybrid composites with designation B2 (50% SiCp:50%QD) and B3 (25% SiCp:75% QD) displayed superior creep resistance without dimensional instability; the highest dimensional change of 0.11 pct was observed in Bo (100% SiCp), while dimensional changes of < 0.05 pct was observed for unmodified alloy, B1 (75% SiCp:25% QD) and B4 (100% QD), respectively. However, superior elevated temperature was observed in sample designations Bo and B2, respectively, when compared with unmodified (unreinforced) alloy.

Effect of Nonlinear Functions on Prediction of the Creep Behavior in Fibrous Composites Theoretically

This paper presents the analysis of the creep behavior for safe designing the fibrous composite devices. Special theoretical method is presented for analyzing the second stage creep of the short fiber composites subjected to axial load using nonlinear displacement functions. Behavior of creeping matrix is described by an exponential creep law, whilst the fibers behave elastically in general. The major plan of the present research work is prediction of the creep behavior in the fibrous composites for preventing unwanted events, over and above, controlling the creep deformation rate theoretically and numerically. Finally, good compatibilities are seen between finite element method and present theoretical method results. As an important result and finding, in general, the mentioned behaviors are ascending along with soft gradients, and so they are controllable and desired.DOI: http://dx.doi.org/10.5755/j01.mech.24.2.19535

Rheological behavior of composites made from linear medium-density polyethylene and hemp fibers treated by surface-initiated catalytic polymerization

This work presents different rheological methods to determine the effect of fiber surface treatment on their interaction with a polymer matrix. In particular, surface-initiated catalytic polymerization was investigated on hemp fibers to improve their adhesion with linear medium-density polyethylene (LMDPE). The selected rheological tests (creep-recovery (solid state), small and large amplitude oscillation shear, and transient rheology (melt state)) were used to compare the treated and untreated fiber composites with the neat matrix. The results showed a significant improvement of the treated hemp composite (LPHC) creep modulus with respect to its untreated counterpart (LNHC) leading to a reduction of the creep strain, especially as temperature increases. The transient viscosity was modeled using a modified Kohlrausch-Williams-Watt (KWW) equation showing an increase in the transient viscosity ( $$ {\eta}_0^{+} $$ ) and relaxation time (τ) with fiber addition and surface treatment. These results were confirmed by large amplitude oscillatory shear (LAOS) through the reduction of the relative third harmonic (I3/1), intrinsic nonlinearity parameter (Q0), and nonlinear viscoelastic ratio (NRL). The results clearly show that catalytic polymerization is a good surface modification technique to increase the compatibility between natural fibers and polymer matrices as to improve all their final properties.

Finite-volume homogenization of elastic/viscoelastic periodic materials

In this contribution, the three-dimensional (3D) finite-volume direct averaging micromechanics (FVDAM) is reconstructed by incorporating parametric mapping capability into the theory’s analytical framework, which allows using arbitrarily shaped and oriented hexahedral subvolumes in the material microstructure discretization. The technique is then further extended to include linear viscoelastic capability to investigate the creep and relaxation behavior of polymeric matrix composites and stress field evolution with either continuous or discontinuous reinforcements. Elastic-viscoelastic correspondence principle is employed in the unit cell solution to relate the governing relations between time domain and Laplace-Carson domain. After establishing the homogenized constitutive equations and solving the boundary value problems in Laplace-Carson domain, Zakian inversion scheme is used to invert the inexplicit homogenization functions to obtain both relaxation moduli and stress distributions during a relaxation history in real space. The FVDAM theory via correspondence principle is validated extensively by comparing with Mori-Tanaka, finite-element, locally exact solutions and experimental data. Good agreement between the present theory and other methods, along with a few numerical investigations, explains not only the accuracy of the 3D parametric FVDAM but also the validity and efficiency of the correspondence principle and Zakian inversion technique.

The Mechanical Properties and Modeling of Creep Behavior of UHMWPE/Nano-HA Composites

Composites with different levels of hydroxyapatite (HA) content and ultra-high molecular weight polyethylene (UHMWPE) were prepared in this work. Mechanical properties of the composites were examined here, and to evaluate the effect of HA particles on the time-dependent behavior of the pure matrix, the creep and recovery performance of composites at various stress levels were also researched. As expected, the addition of HA influenced the time-dependent response of the UHMWPE and the effect had a strong dependence on the HA content. The creep and recovery strain of the composites significantly decreased with increasing HA content, and tensile properties were also impaired, which was due to the concentration of HA fillers. The mechanism and effect of HA dispersed into the UHMWPE matrix were examined by scanning electron microscopy. Additionally, since variations in the adjusted parameters revealed the impact of HA on the creep behavior of the UHMWPE matrix, Findley’s model was employed. The results indicated that the analytical model was accurate for the prediction of creep of the pure matrix and its composites.

Numerical analysis and investigation of short- and long-term behavior of unidirectional composites

This study gives a detailed analysis on estimating the ultimate tensile strength of unidirectional fiber reinforced composites and its creep behavior under sustained tension load. We develop two different micromechanical models that allow us to estimate the longitudinal tensile strength and the evolution with time of fiber and matrix stresses around arbitrary array of fiber breaks. The first model is based on the shear-lag theory while the second one is developed using the software Abaqus. The comparison of the above models allowed to validate the fundamental assumptions of the shear-lag theory (first model) as well as several numerical issues related to time integration and spatial discretization. The Monte–Carlo method was used in order to account for the stochastic fiber strength and its impact on the ultimate tensile strength (short-term) and creep (long-term behavior) of unidirectional composites. Finally, a parametric investigation on the fiber type and the load level on the long-term behavior of unidirectional composites was performed showing an accelerating creep effect for fibers of inferior quality such as glass fibers compared to carbon fibers.

High-temperature creep of carbon nanofiber-reinforced and graphene oxide-reinforced alumina composites sintered by spark plasma sintering

Alumina (Al2O3) ceramic composites reinforced with either graphene oxide (GO) or carbon nanofibers (CNFs) were prepared using Spark Plasma Sintering. The effects of GO and CNFs on the microstructure and in consequence on their mechanical properties were investigated. The microstructure of the sintered materials have been characterized quantitatively prior to and after the creep experiments in order to discover the deformation mechanism. Graphene-oxide reinforced alumina composites were found to be more creep resistant than carbon nanofibers-reinforced alumina ones or monolithic alumina with the same grain size distribution. In all the cases, grain boundary sliding was identified as the deformation mechanism.