Behavior Of Fiber-reinforced Composites Research Articles

A Review of Experimentation Numerical Simulation of Low-Velocity Impact Performances and Damages of Fiber-Reinforced Composites

Fiber-reinforced composites (FRCs) are extensively utilized in various industries due to their lightweight and high-strength properties, making the understanding of their response to low-velocity impact (LVI) crucial for ensuring structural integrity, performance and invisible internal damages that can compromise performance and safety. This paper critically examines the current state of research on the low-velocity impact behavior of FRCs, focusing on both experimental and numerical simulation approaches. The review comprehensively surveys on characterizing and modeling the response of FRCs to low-velocity impacts leading to damages. The effects of parameters including composites preparation; impact mechanics; testing methods; induced damages including assessment methods; different performance parameters including impact energy, force, load, impact resistance; post-impact damages and their resistance; performance and damage affecting different factors; numerical and simulation modeling are discussed. Current challenges and future prospects regarding the subject matter is highlighted. The comprehensive analysis presented in this review goals to consolidate current knowledge, identify research gaps, and guide future endeavors in enhancing the understanding of low-velocity impact (LVI) behavior in fiber-reinforced composites (FRCs).

A phase-field fracture model for fatigue behavior in fiber-reinforced composites

A new framework based on the phase field method is developed to model the fatigue fracture behavior of fiber-reinforced composite laminates. The growth path of matrix cracks can be simulated more accurately compared to the classical model. Further, anisotropic fatigue accumulation effects are considered in this model. Comparisons between simulations by the phase field model with uniform fatigue accumulation effects and the proposed method are encouraging. The new framework proposed can more naturally capture different types of crack growth in fiber- reinforced composites. The reliability and potential of this framework to model fatigue behavior for fiber-reinforced composite laminates are demonstrated by investigating several numerical examples. Moreover, the finite element implementation utilizes a simpler and robust approach via the ABAQUS user-defined subroutine UMAT and UMATHT, including the so called AT1, AT2 and PF-CZM models and two solution strategies.

Computational modeling of micro curing residual stress evolution and out-of-plane tensile damage behavior in fiber-reinforced composites

This paper focuses on revealing the evolution mechanism of micro curing residual stress and its impacts on the mechanical responses of medium-temperature cured composites (T700/7901) under out-of-plane tension. An integrated multi-scale framework is established, the macro-scale thermal-chemical and micro-scale stress–strain models are set up to predict the development of the micro residual stress during curing, and the obtained stress field is further employed as the initial boundary conditions in the micromechanical analysis to explore its effect qualitatively and quantitatively. Experimental and analytical methods are taken to verify and validate the current model. Besides, the impacts of different curing cycles on the micro residual stress and out-of-plane tensile strength are also discussed. The evolution of the micro curing residual stress in T700/7901 composites is intuitively revealed, and the results of the micromechanical model show that the out-of-plane tensile strength increases by nearly 14.4% due to the occurrence of the process-induced stress. Both the interfacial damage and matrix plastic deformation are delayed owing to the residual stress. The work builds the connection between the curing process and mechanical responses of unidirectional composites and demonstrates the necessity of considering curing residual stress in designing and evaluating composites.

Multi-Parameter Layup Optimization and the Effect of Layup Homogenization on the Bending Compliance Matrix of Coupled Composites

The behaviour of fibre-reinforced composites greatly depends on their layup structures. Through a full-field layup optimization study based on multiple parameters, this paper investigates how different properties change with the layup. The aim was to maximize the extension-twist coupling performance while ensuring adequate bending stiffness and low thermal warpage to make the laminate suitable for shape-adaptive helicopter rotor blade application. The Classical Laminate Theory-based calculations revealed that satisfying the bending compliance and thermal warpage criteria significantly limited the achievable extension-twist performance. The warpage limit affected the desired coupling behaviour more because both properties are driven by terms in the extensional-bending compliance matrix, unlike bending compliance. Symmetric laminates do not have an intrinsic extension-twist capability, but some asymmetric laminates demonstrated significant coupling performance while being practically warpage-free (based on the ISO2768 standard). The results prove that the advantages of asymmetric laminates can outweigh their sometimes negligible disadvantages. The paper also investigates if there is a universal tendency in how layup homogenization affects the terms of the bending compliance matrix of composites. Through analytical calculations, we showed that depending on the layup of the sub-laminate, homogenization can increase or reduce the value of any term in the bending compliance matrix; therefore, there is no universal tendency. Based on these results, layup homogenization cannot only be exploited for its most general purpose – warpage mitigation – but also for improving other characteristics of the laminate (e.g. reducing the bending compliance for increased bending stiffness or increasing the bend-twist compliance for improved coupling performance).

Constitutive Modelling for Anisotropic Damage in Woven E-Glass Reinforcements

It is easy for composite laminates to be damaged by relative lower velocity impact which could give rise to internal delamination that will strongly weaken the compressive strength of laminates. In order to predict the occurrence of matrix failure, the elastic-brittle behaviors of fiber-reinforced composites were modeled constitutively by an anisotropic damage model. The dynamic tensile testing was performed at a constant velocity of 2 mm/min until the sample broke to achieve the mechanical parameters of E-glass reinforcements. The elastic constitutive equation and the constitutive damage model were obtained on basis of the fundamental theory of mechanics about the orthotropic constitutive of reinforcements. The methodology for this constitutive model which is developed by Hashin considered both the effect of fiber and matrix failure. Then, the developed constitutive equations were incorporated into the FE (finite element) codes, ABAQUS, through the user subroutine module to simulate the process of projectile impacting GFRP composite laminates. The results show that the material deformation reaches a maximum at 24 μs, then occurs rebound with the increase of the time. The stress of reinforcements traverse section linearly increases outward from 0 MPa to 509.8 MPa. Material damage area increases with the prolonging of time, and for a fixed time, material damage gradually increases from the edges to the center and reaches a constant value of 1, which means the rupture of the damage process.

Stress-Strain Characterization in Fiber-Reinforced Composites by Digital Image Correlation

Composite materials are widely used in structural mechanics as they can withstand high loads; although after a while, they can present relative strain due to these loadings. In the present work, it is implemented digital image correlation using one laser-beam and the speckles created by its reflection to describe the mechanical behavior of fiber-reinforced composites submitted under compression test. Composites were tested in two set of arrays: the first was done with fibers orientated parallel to the load and the second was done with fibers randomly orientated, as it is known that the stress-strain evolution change according to the orientation of the fibers. Our method allows us to evaluate the heterogeneous strain evolution observed during the tests. Validity of optical strain-measurements is assessed against the results of an universal testing machine, a good correlation was found by comparing the results.

Micromechanical analysis of transverse damage of fibre-reinforced composites

The mechanical behaviour of fibre-reinforced composites under transverse tension, compression and shear is studied using computational micromechanics. The representative volume element is constructed for fibre’s random distribution. The Drucker–Prager model and cohesive zone model are used to simulate the matrix damage and interfacial debonding, respectively. The stress distribution along the interface is studied using the model with only one fibre embedded in the matrix. It is found that the interface tensile failure at the equators of fibre firstly occurs under transverse tension; the interface shear failure firstly occurs under transverse compression; both the interface tensile failure and shear failure occur under transverse shear. The direction of fracture plane is perpendicular to the loading direction under transverse tension, 52.5° with the perpendicular direction under compression and 7.5° with the perpendicular or vertical direction under shear, respectively.

Effects of Dimension on Dynamic Behaviors of Fiber-Reinforced Composites

For analyzing the effects of specimen-dimension on dynamic behaviors of fiber-reinforced composites, 4 kinds of CFRP specimens for different dimension were designed and made. The compressive loading tests were conducted by Ф 37mm split Hopkinson pressure bar (SHPB) system. The results show that the dynamic compression effects of specimen-dimension were exposed. An amount of Fiber-reinforced units inside the compressed area of the fiber-reinforced composites, then the experimental data are veracious for the material.

Scaling Effects on the Tensile Strength of Fibrous Composites

The primary objective of this paper is to illustrate the effects of weak-link scaling on the tensile behaviour of fiber-reinforced composites. The proposed model takes into account the random nature of fiber strength, which is given by a two-parameter Weibull distribution function. Several hundred Monte-Carlo replications are executed to simulate the statistical strength distributions of the composites. It is shown that probabilistic tensile strength distributions and size scaling is dependent on both the stress redistribution and the fiber strength statistics.

Stress-strain behavior of carbon filament yarns under high strain rates

Fiber-reinforced composites used in numerous technical applications have to meet the ever increasing safety requirements. Resistance to extreme stress under high velocity impact loads assumes even greater significance. Previous studies on the behavior of fiber-reinforced composites under impact loads provide little insight about the properties of filament yarns, a basis for many composite applications. Hence this paper focuses on the development of a suitable test method for performing high speed tensile tests on all filament yarn types, and the acquisition and analysis of the test results. This will enable the derivation of material models for their usage in the field of composites applications. Initially, the widely used carbon fiber filament yarns have been tested. The conclusive test results with a reduced yarn clamp mass and high stiffness of the test apparatus indicate that tensile strength and modulus of elasticity of carbon filament yarns increase with higher strain rates.

Role of Pyrolysis Conditions on Fracture Behaviour of Fibre Reinforced Composites

Fracture response of matrix prepared by pyrolysis of polysiloxane resin used for composite reinforced by long fibres was the main goal of this contribution. A set of composites with matrix prepared by partial pyrolysis of polysiloxane resin was studied. An effect of pyrolysis temperature on the composite behaviour and fracture resistance was monitored. An optimal procedure of pyrolysis was established. Heat treatment at 1550°C in air atmosphere was conducted on fully pyrolysed matrix to explore its high temperature potential. Determination of reliable parameters characterising microstructural changes in the matrix by instrumented indentation technique was used. Both optical and scanning electron microscopy was employed in microstructural observations and fracture mechanism qualification. Observation of indents and associated cracking caused by microstructural changes as well as 3D surface reconstruction using confocal microscopy was employed.

Modeling of multi-inclusion composites with interfacial imperfections: Micromechanical and numerical simulations

A micromechanical approach based on a two-layer built-in model and a numerical simulation based on boundary element method are proposed to predict the effective properties of the multi-inclusion composite with imperfect interfaces. The spring model is introduced to simulate the interface imperfection. These two methods are compared with each other, and good agreement is achieved. The effects of interface spring stiffness, volume ratio and stiffness of inclusions on the micro- and macro-mechanical behaviors of fiber-reinforced composites are investigated. It is shown that the developed micromechanical method is very comprehensive and efficient for fast prediction of effective properties of composites, while the numerical method is very accurate in detailed modeling of the mechanical behavior of composites with multiple inclusions.

On the use of the geometric mean approximation in estimating the effective hygro-elastic behavior of fiber-reinforced composites

A geometric averaging is employed in a scale transition model dedicated to determining the effective hygro-elastic macroscopic properties of a fiber-reinforced composites from the properties of its constituents (i.e., the fiber and the matrix), for the first time. Calculations of macroscopic and local stresses due to hygroscopic loads are also carried out. Numerical computations performed according to the geometric mean are compared to the corresponding predictions given by the arithmetic average, classically used in the field of micro-mechanical modeling.

Influence of adding poly(vinyl alcohol) fibres to poly(methyl methacrylate) matrix on the fracture behaviour of fibrereinforced composites

AbstractThis paper reports on the relationship between structure and mechanical properties of poly(methyl methacrylate) (PMMA) reinforced with randomly oriented short poly(vinyl alcohol) (PVA) fibres. Special focus was on the effect of fibre content on the impact resistance of PMMA/PVA composites. Instrumented Charpy impact tests were carried out to characterize the impact resistance of PMMA/PVA composites. Linear elastics fracture mechanics was used to determine the dynamic critical strain energy release rate (GId) and the critical stress intensity factor (KId). Fracture surfaces were observed using scanning electron microscopy (SEM). Dynamic mechanical analysis was carried out to describe the viscoelastic response of the material. Finally, the behaviour of PMMA/PVA composites was interpreted using current short-fibre composite models. It was shown that a small amount of added PVA fibres (0.42 - 1.68 vol.-%) led to an increase of elastic modulus and yield stress under impact conditions. GId was also slightly increased, but KId remained unchanged. Good agreement was found between SEM observations and fracture toughness measured under impact loading.

Percolation study of orientated short-fiber composites by a continuum model

We present a percolation study of a two-dimensional crossbar networks and investigate the percolation behavior in fiber-reinforced composites. A modified model of sticks with a finite width is proposed for predicting percolation threshold of volume fraction of the fiber-reinforced composites. Based on the presented model and Monte Carlo simulations, the influences of fiber aspect ratio and orientation on the percolation behavior were investigated. It was found that the percolation threshold had a linear dependence with aspect ratio more than 40 in double-logarithmic plot. The percolation threshold had larger dependence on the orientation angle less than 30 ∘ . In terms of a model considering the tunneling effect, furthermore, the composite system filled with carbon nanotubes predicted to obtain lower percolation threshold. For lower fiber aspect ratios, fiber ends strongly affected the connection of crossbar networks.

섬유 보강 복합재료의 미시역학적 거동 해석

The investigation, which includes the material homogenization and the calculation of local stress concentration of long-fibrous composites in a microscopic level, has been performed to analyze the behavior of fiber-reinforced composites by using finite element method. In order to carry out this study, the finite element models of composites have been generated by the idealized arrays as square and hexagonal-packed type. In the FE analysis, the boundary conditions of micromechanical finite element method(MFEM) have been defined and verified by comparing with the results from multi-cells, and the effective material properties of composites composed of graphite/epoxy have been also evaluated by rules of mixture. For acquiring the relation between the global and local behaviors of composites, the magnifications of strain, stress, and interfacial stress of composites subjected to a longitudinal and transverse loading respectively have been calculated. And the magnifications have been proposed as the stress concentration in the microscopic level at composite material.

A mechanical model for fiber reinforced composite materials with elasto-plastic matrix and interface debonding

The behaviour of fiber-reinforced composites is examined through the formulation of a non-linear constitutive law obtained through a physical-based approach. The elasto-plastic macro constitutive equations for such a class of materials, composed by a matrix phase with elasto-plastic behaviour and several fiber-reinforcing phases, is obtained by considering an imperfect bounds between the matrix and the fibers, i.e. a certain amount of sliding is assumed to be present at the matrix–fiber interface. The fibers are assumed to have only axial stiffness with negligible relative matrix–fiber displacements orthogonal to the fiber's axis. The amount of sliding has been determined through energetic considerations by taking into account the evolution of the shear stress distribution along a single fiber during an increasing load history applied to the composite. The mechanical constitutive law has been implemented in a F.E. code and some numerical simulation have been performed in order to assess the reliability of the proposed model.

Numerical modelling of the fatigue behavior of fibre-reinforced composites

The behavior of fibre-reinforced composites is examined through the formulation of a micromechanical-based model. The elasto-plastic macro constitutive equations for such a class of materials, composed by a matrix phase with elasto-plastic behavior and a fibre-reinforcing phase, is firstly obtained considering an imperfect bond between the matrix and the fibres; a two-parameters model, obtained from energetic considerations and by considering the evolution of the shear stress distribution along a single fibre during the loading process, is formulated to determine the entity of the debonding. Moreover, the progressive damage which occurs in the case of repeated loading is considered to account for the degraded properties of the matrix and of the interface due to fatigue. The proposed model is implemented in a FE code and some numerical simulations are performed in order to assess its reliability.

Hydrostatic Pressure Effect on the Fracture Toughness of Unidirectional (0-deg) Graphite/Epoxy Laminated Composites

Previous studies show that hydrostatic pressure affects elastic modulus, strength, and strain of fiber-reinforced composites. However, no work has been done to understand the compressive fracture behavior of laminated composites under hydrostatic pressure. This work is an experimental study of the hydrostatic pressure effects on the compressive fracture behavior of fiber-reinforced composites. Compressive fracture tests were conducted under various hydrostatic pressures from 0.1 MN/m2 (atmospheric pressure) to 200 MN/mi2 (2 Kbar). Test specimens used were unidirectional (0-deg) graphite/epoxy laminated composites with a single delamination at the center of specimen. First, compression load-displacement curves were determined as a function of hydrostatic pressure and delamination length. Second, the compressive fracture toughness was determined from the compliance method based on the load-displacement curves as a function of hydrostatic pressure. The results showed that compliance, fracture load, and fracture toughness were significantly influenced by hydrostatic pressure. The fracture load increases as hydrostatic pressure increases. The compliance decreases linearly with increasing pressure. Particularly, fracture toughness increased from 3.45 N-mm/mm2 to 4.53 N-mm/mm2 (32% increase) as hydrostatic pressure increased from 0.1 MN/mm2 to 200 MN/mm2. Apparently the increase of fracture toughness is due to the suppression of local delamination with increasing hydrostatic pressure.

Internal stress superplasticity in directionally solidified Al–Al 3Ni eutectic composite

Thermal cycling creep behavior in fiber-reinforced composites was investigated using a directionally solidified Al–Al 3Ni eutectic composite. A superplastic elongation of 120% was obtained during a thermal cycling tensile creep test. Compression creep tests were performed under an external stress applied either parallel or perpendicular to the growth direction. The average strain rates for the two directions exhibited the characteristics of internal stress superplasticity: those at low stresses were much higher than the corresponding isothermal creep rates and were proportional to the applied stress. In the case of transverse loading, the thermal cycling creep rate was explained quantitatively using the previously reported internal stress superplasticity model for particle-dispersed composite. In the case of longitudinal loading, it was much lower than that predicted using the model because of the difference in the stress state and the relaxation process. However, thermal cycling creep had very low activation energy, which is a unique characteristic of internal stress superplasticity.