Modeling and simulation of the effect of fiber breakage on creep behavior of fiber-reinforced metal matrix composites

A theoretical model and computer simulation methodology was developed to predict the effect of fiber fracture on creep behavior of continuous fiber-reinforced metal matrix composites. Initially, a single fiber model was developed based upon the fiber statistical characteristics and a shear-lag analysis to establish the computation simulation route. Then, the methodology was extended to predict the creep behavior of a multiple fiber composite. A failure criterion was also incorporated in the model to predict the rupture life of the composite. A parametric study was also conducted to investigate the effects of properties of the constituents on the longitudinal creep behavior of the SCS-6/Ti composite.     

Effect of elastic–plastic matrix on thermo-mechanical response of continuous anisotropic fiber-reinforced composites

Based on a concentric cylinder model, the analytical elastic–plastic solution of deformations and stresses for the composites reinforced with transversely isotropic, circumferentially orthotropic and radially orthotropic fibers subjected to axisymmetric thermo-mechanical loading is developed. How the plasticity, volume fraction, physical and mechanical properties of the matrix affect the elastic–plastic thermo-mechanical response of the composites is investigated. The plasticity of the matrix decreases greatly the axial compressive stress in the matrix, but more noticeably increases the axial compressive stress in the fiber. For the composites reinforced with transversely isotropic, circumferentially orthotropic and radially orthotropic fibers, decreasing the volume fraction, thermal expansion coefficient and Young's modulus, and increasing the yield stress and hardening parameter of the matrix can lower the maximum equivalent stress of the fiber. However, increasing the yield stress and hardening parameter of the matrix raises the maximum equivalent stress of the matrix.     

High-temperature oxidation behavior of SiC-coated carbon fiber-reinforced carbon matrix composites

The high-temperature oxidation behavior of bare and SiC-coated carbon fiber-reinforced carbon matrix (C/C) composites was examined in the temperature range 900–3000 K. In the course of the measurements, the main focus was placed upon the effect of oxygen partial pressure on the oxidation behavior and the transition temperature between the passive and active oxidation regimes. To understand the oxidation behavior of SiC-coated C/C composites quantitatively, a morphological characterization of coating cracks was carried out, and then, in the oxygen diffusion controlling temperature range, an analytical model was developed for the prediction of weight loss due to oxidation of SiC-coated C/C composites. The oxidation rates derived from this model were in fairly good agreement with the experiment results.     

The beneficial influence of matrix anisotropy in fiber composites

Summary It has been recently shown [1] that the stress concentrations in anisotropic materials with distinct complex or imaginary roots of the respective characteristic function are much higher than in materials with equal roots. It was further shown [2] that anisotropic materials with equal roots behave like quasi-isotropic materials. Modern carbon-carbon and metal-ceramic composites are intuitively using these facts to create much stronger materials by reinforcing the matrix properties.A theory is presented in this paper where the coupling of strongly anisotropic fibers along their axis with strongly anisotropic matrices along either the fiber direction or the transverse plane to the direction of the fibers, either deteriorates, or improves perceptibly the mechanical behavior of the composites. It was shown that anisotropy of the matrix, increasing its mechanical properties on the transverse isotropic plane of the composite, increased the transverse Poisson's ratio, whereas decreased the longitudinal shear modulusG _LC . This resulted in values of the eigenangle _c receding from the corresponding value _ic for the respective isotropic, case. This resulted in a deterioration of the mechanical performance of the composite since the material now has the tendency to develop higher stress concentrations for equivalent loadings.On the contrary, a strong anisotropic matrix along the direction of the fibers yielded the inverse results for the various moduli of the anisotropic composite. The most important result is the increase of the longitudinal shear modulusG _L , so that the ratioE _L /2G _L is consistently decreasing, thus yielding values of the eigenangle _c tending to approach the critical value _c for the isotropic material. This decrease of _c indicates the improvement of the quality of the composite, which develops relatively lower stress concentration factors approaching their respective isotropic values.This fact makes the anisotropic composite material to approach an equivalent state of quasi-isotropy and thus to improve the strength of the material by reducing considerably the eventual, anisotropic stress concentration factors of the respective structural elements.Examples with T300/N5208 Graphite-Epoxy composites and Borsic-1100 Aluminum metal-metal composites indicate clearly the beneficial effect of the anisotropy of their matrices.     

Micromechanical analysis of fiber-reinforced composites on account of influence of fiber coatings

The new asymptotic method for the analysis of inhomogeneous composite materials on account of the micromechanical influence of fiber coatings is proposed in the present paper. The problem of longitudinal shear of the fiber-reinforced composites with the square and hexagonal lattices of periodically distributed parallel cylindrical fibers is examined. The asymptotic homogenization method is applied and the relevant unit cell problem is solved with the aid of the method of perturbation of boundary shape. The asymptotic analytical solutions are found for the effective longitudinal shear moduli and for the local stresses occurring in the composites on the microlevel. Local shear stresses along the fiber-coating and the matrix-coating interfaces are calculated. The influence of properties of coatings on the maximum local shear stresses on the interfaces of constituents is analysed. The obtained results are suitable for any values of stiffness and volume fractions of constituents, including the limiting case of absolutely rigid fibers converging to contact.     

Effect of fiber coating on the longitudinal damping capacity of fiber-reinforced metal matrix composites

A novel model for calculating the damping capacity of continuous fiber-reinforced metal matrix composites (FMMCs) is proposed based on the viewpoint of energy loss. Finite element method (FEM) has been employed to investigate the effect of fiber coating on the longitudinal damping capacity of a composite by varying the thickness and the material properties of the coating. The results show that the damping of a composite containing the elastic coating increases with a decrease in the elastic modulus of the coating, while for the case of plastic coating, the weak coating or the high elastic modulus coating may help in improving the overall damping of composite.     

Flexural creep of long fiber-reinforced thermoplastic composites: Effect of processing-dependent fiber variables on creep response

Flexural creep properties were studied as a function of fiber weight fraction and processing-induced fiber alignment in extrusion/compression-molded, long fiber-reinforced thermoplastic (LFT) nylon 6/6, polypropylene, and high-density polyethylene and their 10 wt.% and 40 wt.% E-glass fiber reinforced LFT composites. The residual fiber lengths and probability distribution parameters were near-equal, regardless of the initial fiber length and processing. Creep compliances decreased with increasing fiber weight fraction, and clear influence of fiber alignment was found in model parameters. Processing-induced fiber alignment imaged using X-ray radiography, was correlated with the creep compliances of strategically sectioned specimens, and tested as per ASTM D-2990. Longitudinal fibers aided in lowering the creep compliance, and the range in compliance decreased with lower preferential fiber alignment. Creep compliances from flexural creep tests and dynamic mechanical analysis/static creep tests were combined using time–temperature–stress superposition (TTSSP) to construct long-term master curves that correlated closely with long-term tests.     

Quasi-static penetration resistance behavior of glass fiber reinforced thermoplastic composites

Quasi-static penetration resistance of a composite structure represents the energy dissipating capacity of the structure under transverse loading without dynamic and rate effects. In this paper, a comparative study of the quasi-static penetration resistance behavior of S-2 Glass/SC-15, S-2 Glass/HDPE and E-Glass/HDPE composite systems with varying thicknesses, i.e., 1.4–8.4-mm, is presented using the Quasi-Static Punch Shear Test (QS-PST) methodology developed earlier. The penetration resistance behavior is usually presented by a series of force–displacement graphs at different support conditions, the integral of which is the energy dissipated by the composite during the quasi-static penetration at corresponding support conditions. The penetration energy varies with the diameter of the support span which is usually higher than the punch diameter, and also with the thickness of the composite laminate. During QS-PST experiments, a flat punch of diameter 7.6-mm with a range of support spans 8.89–50.8-mm has been used to obtain varying support span to punch diameter ratios (i.e., SPR = D_S/D_P = 1.16, 1.33, 1.67, 2.00, 2.33, 2.67, etc.). In order to compare the penetration resistance behavior of three different material systems, the S-2 Glass/SC-15, S-2 Glass/HDPE and E-Glass/HDPE composites of identical layer counts are used and the S-2 Glass/SC15 composite system is considered as the baseline. Composite plate specimens are sectioned after the test and then dipped into an ink–alcohol solution to study the damage mechanisms at different SPRs. Non-linear penetration stiffness and an average penetration resistance force are defined to quantify the average penetration resistance of each material. S-2 Glass and E-Glass reinforced HDPE composite material showed lower stiffness, lower peak force, higher deflection, lower damage area, and lower energy dissipation as compared to the baseline. A detailed comparison of results is presented.     

Fique fiber-reinforced polyester composites: Effects of fiber surface treatments on mechanical behavior

Composites consisting of fique fibers (Colombian fibers) and unsaturated polyester (UP) matrix have been investigated. Fique fiber bundles were subjected to alkalization and/or treated with different chemical agents such as maleic anhydride, acrylic acid and a silane to provide increased compatibility between fiber and resin. The mechanical behavior of the composite materials was analyzed by flexural tests. Maximum mechanical properties were observed for composites with fibers subjected to alkalization and also when it was applied as previous process for the other treatments. Aspects of composite materials such as fiber bundle length, fiber content as well as two ways of preparing the material, lamination and BMC, have been evaluated. The influence of surface treatment of fiber on curing of the polyester resin was analyzed by differential scanning calorimetry (DSC). Dynamic mechanical properties were also evaluated to establish the influence of the interfacial interactions on the mechanical behavior of the laminates.     

连续纤维增强NiAl基复合材料研究进展

连续纤维增强NiAl基复合材料是一类极具应用前景的高温结构材料.本文对Al2O3(f)/NiAl复合材料的工艺、界面结合状况、改善措施及Al2O3纤维的拉伸性能进行了评述.在已开发的最具代表性的各种工艺(扩散结合法,压力铸造,定向/悬浮区域熔炼)中,扩散结合法中的磁控溅射法对Al2O3纤维的损伤最少.在不同工艺过程中引入杂质使Al2O3(f)/NiAl复合材料的界面变得复杂,以及NiAl与Al2O3纤维的热膨胀系数(CTE)不匹配(NiAl CTE=16 ×10-5 ℃-1,Al2O3 fiberCTE=9.4×10-6 ℃-1),要求对复合材料的界面进行改性,而BN涂层对界面改性十分有效.关于Al2O3(f)/NiAl复合材料的力学性能,大多数的研究集中在Al2O3纤维的拉伸强度以及复合材料制备过程中Al2O3纤维强度的退化.对Al2O3(f)/NiAl复合材料的发展方向及前景进行了展望.     

Fabrication of fiber-reinforced celsian matrix composites

A method has been developed for the fabrication of small diameter, multifilament tow, fiber-reinforced ceramic matrix composites. Its application has been successfully demonstrated for the Hi-Nicalon/celsian system. Strong and tough celsian matrix composites, reinforced with BN/SiC-coated Hi-Nicalon fibers, have been fabricated by infiltrating the fiber tows with the matrix slurry, winding the tows on a drum, cutting and stacking of the prepreg tapes in the desired orientation, and hot pressing. The monoclinic celsian phase in the matrix was produced in situ, during hot pressing, from the 0.75BaO–0.25SrO–Al₂O₃–2SiO₂ mixed precursor synthesized by solid state reaction from metal oxides. Hot pressing resulted in almost fully dense fiber-reinforced composites. The unidirectional composites having ∼42 vol.% of fibers exhibited graceful failure with extensive fiber pullout in three-point bend tests at room temperature. Values of yield stress and strain were 435±35 MPa and 0.27±0.01%, respectively, and ultimate strengths of 900±60 MPa were observed. Young's modulus of the composites was measured to be 165±5 GPa.     

Microstructural efficiency and fracture toughness of short fiber/thermoplastic matrix composites

This paper outlines the fracture behavior of composites with thermoplastic matrices of different fracture toughness K_cm (increasing in the order PPS → PET (I) → PET (II) → ETFE → PC). In particular, the way in which the fracture toughness of these composite systems, K_cc, is affected by the volume fraction, orientation and distribution of short glass fibers across the plaque thickness (fiber length ≈ 200 μm, fiber diameter ≈ 10 μm), and by the quality of their interfacial bonding to the matrix is discussed. SEM studies were carried out to define the microstructural details and the dominant mechanisms of energy adsorption during breakdown of the composites.In general, an increase in composite toughness can be expected with increasing extent of reinforcement if the matrix is in a brittle condition (here also verified by K_c-tests at lower temperatures) and if the fibers are well bonded and mostly oriented perpendicular to the crack front. An opposite tendency may occur for matrices which behave in a highly ductile manner even in the presence of fibers. The probability of this behavior is favored in poorly bonded systems. The results are discussed in terms of a ‘microstructural efficiency factor’ M, which mainly considers the relative contributions of fiber and matrix related mechanisms to energy dissipation during breakdown of a composite (‘energy absorption ratio’ n) as well as the reinforcement content and its arrangement in the matrix (‘reinforcing effectiveness parameter’ R).     

On the mechanical behavior of fiber-reinforced composites

In this paper, the derivation of the state potential is presented to model the mechanical behavior of fiber-reinforced composites. It allows matrixcracking, interfacial debonding and sliding to be accounted for in the framework of Continuum Damage Mechanics. An application is performed on a unidirectional SiC/SiC composite.     

Effective behavior of inelastic fiber-reinforced composites

The average behavior of unidirectional fiber-reinforced composites, whose constituents are anisotropic in the elastic region and isotropic viscoplastic in the inelastic region, is determined. In the special case of perfectly elastic phases, effective moduli of the composite are obtained. Extensive comparisons between the effective behavior of the composite, as predicted by the present theory and by other theoretical, numerical and experimental approaches, are given.     

连续纤维增强热塑性树脂基复合材料自动铺放原位成型技术的航空发展现状

基于自动铺丝手段,连续纤维增强热塑性树脂基复合材料可实现原位成型效果,即铺贴同时完成零件制造。该技术可降低复合材料成本达到50%以上,由于其高效低耗的技术特点,该技术被认为在航空领域具有广泛的应用前景。文章调研了热塑性复合材料原位成型技术在国内外航空领域相关的研究和应用工作。结合典型的技术开发案例,重点分析了目前原位成型技术在应用材料、装备及工艺控制技术等方面的水平现状,并阐述了原位成型技术的最新发展趋势。      

Reactive processing of textile fiber-reinforced thermoplastic composites – An overview

Thermoplastic composites offer some interesting advantages over their thermoset counterparts like a higher toughness, faster manufacturing and their recyclable nature. Traditional melt processing, however, limits thermoplastic composite parts in size and thickness. As an alternative, reactive processing of textile fiber-reinforced thermoplastics is discussed in this paper: a low viscosity mono- or oligomeric precursor is used to impregnate the fibers, followed by in situ polymerization. Processes that are currently associated to manufacturing of thermoset composites like resin transfer molding, vacuum infusion and resin film infusion, might be used for manufacturing of thermoplastic composite parts in near future. This paper gives an overview of engineering and high-performance plastic materials that are suitable for reactive processing and discusses fundamental differences between reactive processing of thermoplastic and thermoset resins.     

Characterization of fatigue behavior of long fiber reinforced thermoplastic (LFT) composites

Fatigue behavior of long fiber reinforced thermoplastic composites (polypropylene/20 vol.% E-glass fiber) is presented in terms of stress – number of cycles to failure curves. Samples tested along longitudinal direction showed a higher fatigue life than the transverse samples which can be explained by the preferential orientation of the fibers along the longitudinal direction developed during the processing. Fatigue life decreased with increase in frequency. Hysteretic loss and temperature rise were measured; they depended on the stress amplitude as well as the cyclic frequency. Long fiber reinforced thermoplastic composite showed a lower temperature rise compared to unreinforced PP because long fiber reinforced thermoplastic has higher thermal conductivity than unreinforced PP and thus faster heat dissipation to the surroundings occur. The hysteretic heating also led to decrease in the modulus of long fiber reinforced thermoplastic as a function of number of cycles due to the softening of the matrix during fatigue cycling and depended on stress amplitude and frequency of the test.     

Micro-crack behavior of carbon fiber reinforced thermoplastic modified epoxy composites for cryogenic applications

Three different types of thermoplastics, poly(ether imide) (PEI), polycarbonate (PC), and poly(butylene terephthalate) (PBT) were used to modify epoxy for cryogenic applications. Carbon fiber reinforced thermoplastic modified epoxy composites were also prepared through vacuum-assisted resin transfer molding (RTM). Dynamic mechanical analysis (DMA) shows that the storage moduli of PEI, PC, and PBT modified epoxies are 30%, 21%, and 17% higher than that of the neat epoxy respectively. The impact strength of the modified epoxies at cryogenic temperature increases with increasing thermoplastic content up to 1.5 wt.% and then decreases for further loading (2.0 wt.%). The coefficient of thermal expansion (CTE) values of the PBT, PEI, and PC modified epoxies also decreased by 17.76%, 25.42%, and 30.15%, respectively, as compared with that of the neat epoxy. Optical microscopy image analysis suggests that the presence of PEI and PC in the carbon fiber reinforced epoxy composites can prevent the formation of micro-cracks. Therefore, both the PEI and PC were very effective in preventing micro-crack formation in the composites during thermal cycles at cryogenic condition due to their low CTE values and high impact strength.