Failure Process Of Composites Research Articles

Effect of Mechanical Properties on Fibre Addition of Flax and Graphene-Based Bionanocomposites

Natural fibre-based polymer nanocomposites have played an essential role in many industry domains for four to five years because of their strong mechanical and physical qualities. The primary goal of this research is to establish the mechanical and morphological properties of nanocomposite materials in natural environments. Flax fibre was employed as a reinforcement, nanographene powder was used as a filler, and epoxy resin was used as a matrix material to achieve the goals above, keeping the following restrictions in mind: (i) fibre length (15, 30 and 45 mm), (ii) fibre content (10, 15 and 20 mm), and (iii) wt.% of nanofiller (2.5, 5 and 7.5 wt.%). The composite materials were laminated using the compression moulding process per the Taguchi L9 design. The mechanical characteristics of the material, such as flexural, tensile, and impact properties, were examined according to ASTM standards. The mechanical characteristics of combinations A2, B2, and C2 are the best when compared to other combinations. The graphene-based nanocomposites revealed that 2.5 wt.% graphene contributes 33.08% of mechanical properties, the 5 wt.% graphene contributes 36.4%, and the 7.5 wt.% graphene contributes 30.53%. Including 5 wt.% graphene content provides the highest mean values of mechanical strength like 36.59 MPa tensile, 40.25 MPa flexural, and 31.68 kg/m2 of impact. Scanning electron microscopy (SEM) images of the cracked specimens were used better to understand the failure process of composites during mechanical testing.

Water Retention Behaviour and Fracture Toughness of Coir/Pineapple Leaf Fibre with Addition of Al2O3 Hybrid Composites under Ambient Conditions

Due to their high mechanical and physical properties, natural fibre-based composite materials have been important in many fields of application for four to five years. The chief intention of the current study is to determine the mechanical and water retention features of composite materials under ambient conditions. Coir and pineapple leaf fibre were used as a reinforcement, aluminium oxide as additives, and polyester as a matrix. The hybrid resources were laminated by the manual hand lay-up method. The mechanical characteristics like tensile, flexural, and fracture toughness properties were tested as per the ASTM standard. Nanoparticle weight ratio and its size variation significantly impact mechanical qualities. The hybrid composite’s water retention behaviour was tested for two types of water levels: ordinary tab water and nanofluid. The moisture uptake of the composites rose as the fibre volume increased, and after 640 hours, all of the composites had reached equilibrium. According to the results, the following combinations have the maximum mechanical strength: 15% wt.% coir, 15% wt.% pineapple, 10% wt.% nanofiller, and 60% wt.% polyester resin. The combinations mentioned above withstand the most load during the tests. Compared to 20% filler, 10% Al2O3 filler produces good interfacial adhesion in the current study. The fractured specimens were analyzed using scanning electron microscopic (SEM) pictures to recognize better the failure process of composites during mechanical testing.

Phase field modelling of progressive failure in composites combined with cohesive element with an explicit scheme

A new complementary energy based split scheme which is different from existing energy split schemes is introduced for the first time to the phase field model, and the driving forces for longitudinal failure, matrix tensile failure and matrix shear failure are derived separately to account for different failure behaviors in a complete failure process in composites. Moreover, it is successfully managed to change the underlying damage initiation criterion of the proposed phase field model from the classic maximum stress criterion to the quadratic stress criterion, and the latter is of higher acceptance in the field of composites. The global equation is solved using explicit schemes and the present theory is implemented into ABAQUS through the users’ subroutine “VUEL” with a parallel setting. In addition to the examples given to verify the present method, a mega model of the open hole tension (OHT) specimen with up to 63,000,000 degrees of freedom is ran successfully to validate the computational capability of the proposed modelling framework. The modelling is completed within an acceptable time cost on a standard workstation by resorting to using 14 threads.

Fractographic analysis of the aluminum matrix composite prepared by accumulative roll bonding

Recent research in the material science field is focused on the easy-to-apply and cost-effective production of the structural components with enhanced mechanical properties. As an answer to these new trends in the present study, the inexpensive household aluminum foils are used to produce the multilayer aluminum matrix composite. The aluminum matrix composites are manufactured by hot-rolling of the sandwiched foils and afterward subjected to microstructural characterization and mechanical testing. Analysis of the produced composite microstructure and fracture surface obtained after tensile testing was performed using the scanning electron microscopy (SEM). The qualitative fractographic analysis revealed that the ductile fracture features prevail in the overall fracture mode of the investigated multilayer composite, while the quantitative fractographic investigation allowed more detailed insight into the composite failure process and depicted critical parameters that led to the composite failure.

Yield criteria and strength conditions considering comprehensive mechanical and acoustic emission characteristics of tension–torsion composite deformation of nylon materials

Acoustic velocity measurement and the acoustic emission tests of tension–torsion composite failure process for nylon 6 and nylon 66 standard specimens under different loading rates are carried out by using acoustic emission instrument and electronic tension–torsion tester respectively. The acoustic velocity, stress–strain curve and acoustic emission energy curve of each specimen are obtained; According to the theories of the plane stress state and strength criterion, the principal stress of point on the surface of specimen at failure under the action of combined tension–torsion load is developed. The Mises yield condition is suitable for judging the yield criterion of nylon at tension–torsion failure; Based on the least square method, fitting models of the second invariant of the stress deviator are established with the density, acoustic velocity, tensile loading rate and torsional loading rate of nylon material. The results show that: For nylon 6 material at the low tension–torsion rate, with the increase of strain the secondary yield phenomenon occurs after the initial yield and finally necking occurs until fracture; With the increase of loading rate, the tension strength and normal strain of nylon 66 decreases;According to the regression model, the second invariant value of the stress deviator can be predicted well.

Optimizing matrix and fiber/matrix interface to achieve combination of strength, ductility and toughness in carbon nanotube-reinforced carbon/carbon composites

The direct attachment of carbon nanotubes (CNTs) on carbon fibers (CFs) always leads to a decrease of fiber-dominated properties (e.g., flexural strength) and a brittle fracture behavior of C/Cs, although the matrix-dominated properties (e.g., compressive strength and interlaminar shear strength (ILSS)) exhibit an obvious enhancement. To achieve the combination of mechanical strength, ductility and toughness in C/Cs, in this work, efforts were spent on simultaneously optimizing the matrix and fiber/matrix (F/M) interface. CNTs with radial orientation were grown onto the CFs by double-injection chemical vapor deposition to modify the microstructure of matrix. Pyrocarbon was deposited on the surface of CFs before CNT growth to protect CFs and to weaken interfacial strength between CFs and CNT/matrix. These optimal designs create strengthening and toughness mechanisms such as crack deflection and long pullout of CFs in the failure process of composites, which endow C/Cs with improved flexural strength of 31.5%, flexural ductility of 118%, compressive strength of 81.5% and ILSS of 82%, accompanied by a clear change from brittle fracture to pseudo-plastic fracture during flexural test. This work may provide a meaningful way to not only enhance both the fiber- and matrix-dominated strength but to substantially improve the ductility and toughness of C/Cs.

A hybrid embedded cohesive element method for predicting matrix cracking in composites

The complex architecture of many fibre-reinforced composites makes the generation of finite element meshes a labour-intensive process. The embedded element method, which allows the matrix and fibre reinforcement to be meshed separately, offers a computationally efficient approach to reduce the time and cost of meshing. In this paper we present a new approach of introducing cohesive elements into the matrix domain to enable the prediction of matrix cracking using the embedded element method. To validate this approach, experiments were carried out using a modified Double Cantilever Beam with ply drops, with the results being compared with model predictions. Crack deflection was observed at the ply drop region, due to the differences in stiffness, strength and toughness at the bi-material interface. The new modelling technique yields accurate predictions of the failure process in composites, including fracture loads and crack deflection path.

Experimental research and finite element analysis of elastic and strength properties of fiberglass composite material

This work is devoted to the research of the strength and elastic properties of the laminated fiberglass composite. Experiments were performed on tension and compression of specimens with different orientation of the reinforcement in relation to the loading direction. The predictions of three different failure criteria (Hill criterion, Tsai-Wu criterion, Zakharov criterion) were compared to experimental results. The strength and elastic properties of the composite separate components have been also researched with the aim to perfom finite element simulation of composite failure process. The elastic moduli of the composite are determined by means of the method of the finite element homogenization.

Stability condition for the evaluation of damage in three-point bending of a laminated composite

The study of the tensile strength of composite materials is far more complex than analysis of the properties of elasticity and plasticity. Indeed, during mechanical loading, micro-cracks in the matrix, the fibers break, debonding of the interfaces are created. The failure process of composites is of great diversity and cannot be described if even we know: the strength criterion of each individual component, the state of stress and strain in the material, the propagation phenomena cracks in the structure and nature of the interface between the matrix and the reinforcement. This information is only partially known and the obtained by the analysis of a stress limit beyond which there is destruction of the material is almost impossible. To partially process the issue, a solution lies in a mesoscopic approach of seeking a law to locate the ultimate strength of the material for a plane stress state. Tests on rectangular plates in bending PEEK/APC2 and T300/914 three were made and this in order to validate our approach, the calculation has been implemented in a nonlinear finite element code (Castem 2000), in order to make comparison with the numerical results. The results show good agreement between numerical simulation and the two materials; however, it would be interesting to consider other phenomena in the criterion.

Multiscale finite element modeling of failure process of composite laminates

A multiscale nonlinear finite element modeling technique is developed in this paper to predict the progressive failure process for composite laminates. A micromechanical elastic–plastic bridging constitutive model, which considers the nonlinear material properties of the constituent fiber and matrix materials and their interaction and the damage and failure in fibrous composites at the fiber and matrix level, is proposed to represent the material behavior of fiber-reinforced composite laminates. The micromechanics constitutive model is employed in the macroscale finite element analysis of structural behavior especially progressive failure process of the fiber-reinforced composites based on a 4-node 24-DOF shear-locking free rectangular composite plate element.

Stress transfer and damage evolution simulations of fiber-reinforced polymer–matrix composites

The stress transfer from broken fibers to unbroken fibers in fiber-reinforced thermosetting polymer–matrix composites and thermoplastic polymer–matrix composites was studied using a detailed finite element model. In order to check the validity of this approach, an epoxy–matrix monolayer composite was used as thermosetting polymer–matrix composite and a polypropylene (PP)–matrix monolayer composite was used as thermoplastic polymer–matrix composite, respectively. It is found that the stress concentrations near the broken fiber element cause damage to the neighboring epoxy matrix prior to the breakage of other fibers, whereas in the case of PP–matrix composites the fibers nearest to the broken fiber break prior to the PP matrix damage, because the PP matrix around the broken fiber element yields. In order to simulate composite damage evolution, a Monte Carlo technique based on a finite element method has been developed in the paper. The finite element code coupled with statistical model of fiber strength specifically written for this problem was used to determine the stress redistribution. Five hundred samples of numerical simulation were carried out to obtain statistical deformation and failure process of composites with fixed fiber volume fraction. The result indicates that the moderate interfacial shear sliding strength can weaken the adverse effect of fiber breaks on composite strength, resulting in the increase of the average strength of composites.

Effect of filler content on bending properties of dental composites: numerical simulation with the use of the finite-element method.

The purpose of this work is to investigate the influence of filler content on the bending properties of dental composites by use of the finite-element method (FEM). The proposed numerical model was constructed from isotropic shell elements representing silica filler, and isotropic beam elements representing the remaining matrix resin. The proposed model was applied to failure analysis under three-point bending conditions. The validity of applying the numerical model to the failure progression analysis of composites was checked through comparison with experimental results. The results show that, in both the analytical and experimental results, the bending properties, such as maximum bending stress and bending modulus, increase with filler content. Also, the proposed method of failure progression analysis could better simulate the failure process of composites under three-point bending conditions. In addition, close agreement between the analytical and experimental results was confirmed. The above results indicate that the proposed numerical model is effective for evaluating the bending properties of dental filler composites of any content range.

Strength evaluation and failure analysis of unidirectional composites using Monte-Carlo simulation

Tensile strength and failure process of composite materials depend on the variation in fiber strength, matrix properties and fiber–matrix interfacial shear strength. A Monte-Carlo simulation considering variation in these factors has been widely used to analyze such a complicated phenomenon as a strength and simulate the failure process of unidirectional composites. In this study, a Monte-Carlo simulation using 2-D and 3-D (square and hexagonal array) model was performed on unidirectional graphite/epoxy and glass/polyester composites. The results simulated by using 3-D hexagonal array model have a good agreement with the experimental data which were tensile strength and failure process of unidirectional composites.

Strength Evaluation and Eailure Analysis of Unidirectional Composites Using Monte-Carlo Simulation

Tensile strength and failure process of composite materials depend on the variation in fiber strength, matrix properties and fiber-matrix interfacial shear strength. A Monte-Carlo simulation considering variation in these factors has been widely used to analyze such a complicated phenomenon as a strength and simulated the failure process of unidirectional composites. In this study, a Monte Carlo simulation using 2-D and 3-D(square and hexagonal array) model was performed on unidirectional graphite/epoxy and glass/polyester composites. The results simulated by using 3-D hexagonal array model have a good agreement with the experimental data which were tensile strength and failure process of unidirectional composites.

A dynamic Monte-Carlo simulation for unidirectional composites under tensile impact

A dynamic Monte-Carlo simulation method, based on a two-dimensional model with fine mesh, sufficient fibers and adequate length, which takes the effect of the inertia and the constitutions of rate dependence into account for the unidirectional composites has been established. On the basis of the dynamic properties of carbon and glass fibers and epoxy resin, the Monte-Carlo simulations are carried out to study the tensile impact failure processes of unidirectional CFRP and GFRP. The simulated stress/strain curves and micro-failure process of the unidirectional CFRP are in good agreement with the experiments. This shows that the simulation method and the program are effective for the tensile impact failure process of the composites made from rate-insensitive fibers having a small failure strain. However, no matter whether we use the single or bimodal Weibull distribution parameters of glass fibers, the simulated results for the unidirectional GFRP are inconsistent with the experiments. This means that the method cannot simulate the tensile impact failure process of composites consisting of rate-sensitive fibers with large failure strain, although the effect of the fibre rate sensitivity (high-speed ductility) and inertia are taken into account. This indicates that some important mechanism exists to induce the high-speed ductility and stress/strain curve non-linearity of the composite other than those of high-speed ductility and cumulative failure of the fiber, and inertia. This process may be thermo-mechanic coupling.

Size effects in the distribution for strength of brittle matrix fibrous composites

This paper addresses the effects of size (both length and width) on the probability distribution for strength of a composite consisting of brittle fibers aligned in a brittle matrix. The failure process involves quasi-periodic matrix cracking, frictional sliding of the fibers in fiber break zones, and fiber bridging of matrix cracks in a global load-sharing framework. The fiber strength follows the usual Poisson-Weibull model of random flaws along the length. We first consider a composite cross-section, and develop the probability distribution for its strength in terms of certain characteristic fiber strength and length scales and the number of fibers in the cross-section. This strength distribution turns out to be a Gaussian distribution. We also calculate refined estimates of its mean and standard deviation, taking advantage of some new results based on an exact closed form solution for fragmentation of fibers in a single filament composite. We then consider the strength of a composite having a length orders of magnitude greater than the characteristic fiber length. We develop predictions for the scaling of the strength vs composite length based on certain results from the statistical theory of extremes in Gaussian processes. For this we develop an estimate of the covariance between the strengths of two nearby cross-sections of the composite. We also develop results based on a weakest-link analysis in terms of composite links of a certain length somewhat shorter than the characteristic fiber length. We then favorably compare our analytical results to numerical results from a Monte Carlo simulation of the composite failure process. This Monte Carlo model is free of various assumptions made in the analysis. The comparison suggests that predictions of a composite strength are possible for composite lengths orders of magnitude beyond what Monte Carlo simulation programs can currently handle.

Bridged versus cohesive crack in the flexural behavior of brittle-matrix composites

A nonlinear fracture mechanics model, which explains and reproduces the constitutive flexural behavior of a brittle-matrix composite, is proposed. It embraces in a unified dimensionless formulation two peculiar models, i.e., the cohesive-crack and the bridged-crack, which are used to analyze the composite failure process. Dimensionless parameters, which depend on the mechanical and geometrical properties, characterize the structure in flexure. It is shown that, based on the assumptions of the bridged-crack model, which simulates the composite as a multiphase material, the flexural response is controlled by two dimensionless parameters, whereas, based on the assumptions of the cohensive-crack model, which simulates the composite as a homogeneous material, the parameters reduce to one. The influence of the dimensionless parameters on the behavior is studied, along with the size-scale effects on the structural ductility. It is also shown how the matrix toughness affects the response. The two theoretical models are compared through the simulation of an experimental test on a fiber-reinforced beam, and it is shown that both the models can predict approximately the same overall behavior.

Micromechanics and acoustic emission analysis of the failure process of thermoplastic composites

The finite element method (FEM) and acoustic emission technique (AE) were applied to the micromechanics analysis of the failure process of composites with thermoplastic matrix materials. FEM calculations to local stress-strain distribution and the influence of very different intermediate layer properties are interpreted with regard to microscopic failure mechanisms in composite materials. The strongly differing AE behaviour of both chalk-filled Polyvinylchloride and high density polyethylene and short-glass-fibre reinforced polypropylene, polyamide, PBTP, SAN and ABS in tensile test experiments is demonstrated. Representative loading limits are derived from the nature and extent of the dominating failure mechanisms by comparison of theoretical and experimental results. The influence of critical strain, shear strength and fracture toughness properties of the modified matrix as well as the composite morphology and phase adhesion on significant deformation and failure stages is discussed. Finally some conclusions are drawn about a possible critical long-term strain of composites.

Environmental effects on fibre—Polymer composites

Moisture absorption characteristics and its effects on the mechanical properties and failure process of polymers (neat epoxy and polyester resins) and composites with simple (glass, carbon and kevlar) and hybrid (glass-carbon, carbon-kevlar and kevlar-glass) fibres were experimentally determined before and after immersion in water at 343 K for 20 days. The maximum moisture content ( M m) and diffusion coefficient ( D x) of these composites were determined. The degradation in ultimate tensile strength and Young's modulus due to the moisture content were experimentally determined and found to be quite significant. Acoustic emissions, from specimens before and after exposure, were monitored during the load cycle, and revealed a significant change in the failure process of these composites. Scanning Electron Microscope (SEM) studies on failed exposed and unexposed specimens revealed resin leach out and fibre prominence.

Examinations on Dynamic Strength Distribution and Macromodel

The present paper introduces a probabilistic failure model and aims at establishing a general assessment system to predict a decrease in reliability of composite materials due to cumulative damage. The failure model used in this system requires a good actuality and utility, i. e. : 1) Actuality-the model should represent more acurately the actual failure process of composites ; 2) Utility-the constructed model should give a good approximation to actual strength properties of composites when the program is run with currently used specimen sizes. In the previous third report, a statistical analysis on the dynamic failure process simulation model was proposed and compared with the static failure process simulation (1 st report).In this report, a statistical analysis is made based on the dynamic failure model and compared with the static one in terms of the different strength parameters. It shows that both static and dynamic simulation give little difference as far as the average values of tensile strength and maximum strain are concerned, but that the dynamic simulation gives a better estimation in terms of the dispersion of strength data and the actual failure pattern.A macro model is also proposed in this report, which is a new cumulative failure model composed of elements of micro models based on the previous dynamic failure process simulation models.A macro model is successfully used in estimating the statistical nature of strength properties of composite materials of actual size. It shows that the strength of composites depends clearly on the length but not on the width of a specimen.