Failure Of Composite Materials Research Articles

Peridynamic analysis of fiber-reinforced composite materials

Damage growth in composites involves complex and progressive failure modes. Current computational tools are incapable of predicting failure in composite materials mainly due to their mathematical structure. However, peridynamic theory removes these obstacles by taking into account nonlocal interactions between material points. This study presents an application of peridynamic theory to predict how damage propagates in fiber-reinforced composite materials subjected to mechanical and thermal loading conditions.

Mode III crack propagation in a bimaterial plane driven by a channel of small line defects

We consider the quasi-static propagation of a Mode III crack along the interface in a bimaterial plane containing a finite array of small line defects (microcracks and rigid line inclusions). The microdefects are arranged to form a channel around the interface that can facilitate (or prevent) the crack propagation. The two dissimilar elastic materials are assumed to be weakly bonded, so that there is no kinking of the main crack from the straight path. On the basis of asymptotic formulae obtained by the authors, the propagation is analysed as a perturbation problem and the incremental crack advance is analytically derived at each position of the crack tip along the interface relative to the position of the defects. Numerical examples are provided showing potential applications of the proposed approach in the analysis of failure of composite materials. Extension to the case of infinite number of defects is discussed.

Peridynamic Theory for Damage Initiation and Growth in Composite Laminate

A recently introduced nonlocal peridynamic theory removes the obstacles present in classical continuum mechanics that limit the prediction of crack initiation and growth in materials. Furthermore, damage growth in composites involves complex and progressive failure modes. Current computational tools are incapable of predicting failure in composite materials mainly due to their mathematical structure. However, the peridynamic theory removes these obstacles by taking into account non-local interactions between material points. This study presents an application of the peridynamic theory for predicting damage progression from a central crack in fiber reinforced composite plates subjected to uniaxial tension loading.

Retrofit of Bridge Bents with the Use of Composite Materials

In this paper, the Finite Element Model of a typical bridge bent has been created. The 3-D eight-node solid element with the ability of the consideration of concrete cracking in tension and crushing in compression has been employed for the modeling of concrete and the uniaxial tension–compression two-nodes element has been used for the modeling of longitudinal reinforcement. The transverse reinforcement has been included as the concrete element volumetric ratio. For the composite material modeling, the 3-D eight-node laminated element has been used to represent the layers of the material. First, the bridge bent has been modeled in the as-built as well as the retrofitted condition. The numerical analysis results are compared with previously reported experimental results. Good correlations between the numerical and the experimental results have been observed. With the consideration of the observed modes of failure of the composite materials during the experiments, some suggestions have been made here in order to improve the lateral load capacity as well as the ductility of the bent system. This consists of the use of appropriate addition of composite materials in various proposed ways and configurations at the junction of the column to the bent beam connections. Analysis results demonstrated that both the lateral load carrying capacity and ductility of the bridge bent will improve considerably with the aid of the suggested methodology.

Post-buckling failure in multi-delaminated composite wind turbine blade materials

This study models the inter-laminar damage due to low velocity impacts on hybrid composite materials typical of those used in wind turbine blade structures. The effect of z-pinning using natural flax yarn on the critical buckling load and post-buckling behaviour of multi-delaminated composite beams was investigated. Laminated composite beams were pinned through their thickness using natural flax yarns to control delamination failure during the post-buckling process. A multiple delamination with a triangular shape was inserted into each of the beams to simulate the damage caused by a low velocity impact e.g. ice, on composite wind turbine blades. For a laminate design of [C 90/G 90] 4, global collapse caused no delamination failure during the post-buckling test while delamination failure occurred for a laminate design of [C 0/G 0] 4. In this case, z-pinning can significantly increase the failure resistance within a composite structure and it can then postpone the failure process. The buckling process of a multi-delaminated composite beam was also simulated by finite element software ANSYS and the results were substantially verified by relevant experimental results.

Non-destructive Inspection of Multi-layered Composite Using Ultrasonic Signal Processing

Composites exhibit higher strength and stiffness, better design practice and greater corrosion resistance compare to metal material. However, composites are susceptible to impact damage and the typical damage behaviour in the laminated composites is fibre-breakage and delamination. Detection of failure in laminated composites is complicated compared with ordinary non-destructive testing for metal materials as they are sensitive to echoes drown in noise due to the properties of the constituent materials and the multi-layered structure of the composites. In the current study, the detection of failure in multi-layered composite materials is investigated. To obtain a high probability of defect detection in composite materials, signal processing algorithms were used to resolve echoes associated with defects in glass fibre-reinforced plastics (GRP) detected by using ultrasonic testing. Pulse-echo method with single transducer was used to transmit and receive ultrasound. The obtained signals were processed to reduce noise and to extract suitable features. Results were validated on GRP with and without defects in order to demonstrate the feasibility of the method on defect detection in composites.

Ultimate Strength Analysis of Ship Hulls of Continuous Basalt Fiber Composite Materials

Based on effective composite material failure criteria and property limited degradation model, axial compressive ultimate strength of composite laminated stiffened panels are analyzed by nonlinear laminated degenerated 3D finite element analysis, which is based on incremental continuum-based updated Lagrangian formulation. Comparison between analytical solutions and test results in this article indicates that this article provides an effective and practical method to evaluate the axial compressive ultimate strength of composite laminated stiffened panels. Using this method, ultimate strength of hull girders made of continuous basalt fiber composite materials are analyzed . Comparing the results，it can be seen that the ship hull in basalt fiber composite materials has equivalent longitudinal ultimate strength to S-2 glass fiber composite materials, basalt fiber composite material could replace the S-2 glass fiber composite materials used in shipbuilding engineering. The gist for building ship with basalt fiber composite materials was provided by this paper.

BEM analysis of crack onset and propagation along fiber–matrix interface under transverse tension using a linear elastic–brittle interface model

The behavior of the fiber–matrix interface under transverse tension is studied by means of a new linear elastic–brittle interface model. Similar models, also called weak or imperfect interface models, are frequently applied to describe the behavior of adhesively bonded joints. The interface is modeled by a continuous distribution of linear-elastic springs which simulates the presence of a thin adhesive layer (interphase). In the present work a new linear elastic–brittle constitutive law for the continuous distribution of springs is introduced. In this law the normal and tangential stresses across the undamaged interface are, respectively, proportional to the relative normal and tangential displacements. This model not only allows for the study of crack growth but also for the study of crack onset. An important feature of this law is that it takes into account the variation of the fracture toughness with the fracture mode mixity of a crack growing along the interface between bonded solids, in agreement with previous experimental results. The present linear elastic–brittle interface model is implemented in a 2D boundary element method (BEM) code to carry out micromechanical analysis of the fiber–matrix interface failure in fiber-reinforced composite materials. It is considered that the behavior of the fiber–matrix interphase can be modeled by the present model although, strictly speaking, there is usually no intermediate material between fiber and matrix. A linear-elastic isotropic behavior of both fiber and matrix is assumed, the fiber being stiffer than the matrix. The failure mechanism of an isolated fiber under transverse tension, i.e., the onset and growth of the fiber–matrix interface crack, is studied. The present model shows that failure along the interface initiates with an abrupt onset of a partial debonding between the fiber and the matrix, caused by presence of the maximum radial stress at the interface, and this debonding further develops as a crack growing along the interface.

Strain-rate effects on deflection/penetration of crack terminating perpendicular to bimaterial interface under dynamic loadings

Strain-rate effects on the deflection/penetration behaviors of a crack terminating perpendicular to a linear elastic bimaterial interface under dynamic tensile loadings are investigated numerically with the so-called Cohesive Crack Model and quasistatic material parameters. The competition between the deflection and the penetration is found to depend markedly on the loading rate (or the strain rate) and amplitude as well as the interfacial strength. The crack can penetrate through the interface only when the strain-rate is higher than a threshold value (or the critical strain-rate) which decreases with the interfacial strength, or else the crack will deflect into and then propagate along the interface; the minimum loading amplitude needed for the crack penetration increases with the strain-rate, and, startlingly, such a strain-rate dependence is found to be independent of the interfacial strength. Furthermore, two inferences can be drawn directly: one is that the second phase failure in composite materials or concrete can occur at high strain-rate, which has been observed experimentally by previous authors (Brara and Klepaczko in Int J Impact Eng 34:424–435, 2007); the other is that the strain-rate effects of the dynamic failure strength of composite and concrete can be induced only by the structural response of materials, which sustains the argument proposed by Cotsovos and Pavlovic (Int J Impact Eng 35:319–335, 2008).

Fatigue damage evolution of fiber reinforced composites with digital image correlation analysis

Several studies on Digital Image Correlation technique allowed this methodology to be recognised in the last decade as a welloptimised tool for mechanical experimental measures, but much work is to be done to apply DIC based analyses on advanced applications, such as fatigue damage studies and composite materials failure investigations. DIC based methodology gives direct measure of the displacement field using a well defined formulation of matching the images of loaded and load free component, so that displacement vectors can be evaluated for a certain number of grid reference points on the analysed surface.In this work, the authors present the latest research with this method, and analyse fatigue damage phenomena in GFRC laminates under tensile fatigue load employing notched and notch-free specimens. Damage analysis based on optical DIC technique has been performed to detect the damaged areas on the specimen surface and to follow failure mechanisms during lifetime; the damage evolution in composites was performed monitoring two parameters: the local hysteresis area of stress strain cycles, the local stiffness variation. These parameters are evaluated on a grid by means of DIC strain measurements during the entire fatigue life showing encouraging results.

Mechanical Property Degradation of Naval Composite Materials

The effect of heat and fire on the mechanical properties and failure of polymer composite materials used in naval ship structures is investigated. Coupled thermal-mechanical models are presented for predicting the loss in strength and failure of load-bearing polymer laminates when heated from one-side. The thermal component of the models predicts the temperature and decomposition rate of a laminate. Using this information, several mechanical models based on progressive softening analysis or laminate analysis can be used to predict the reduction in strength and time-to-failure. A coupled thermal-mechanical model that is solved using finite element analysis is also presented. Experimental fire-under-load tests are performed on several types of polymer laminate materials to evaluate the accuracy of the models. The tests were performed at different heat flux levels between 10 kW/m2 and 75 kW/m2, which is equivalent to surface temperatures between about 250°C and 700°C. The temperature, mass loss and char formation of a laminate can be accurately predicted for a wide range of thermal conditions using the models. The models can also predict the time-to-failure of laminates under static tension or compression loading. The models presented in this chapter are considered useful analytical tools for naval architects to estimate the loss in mechanical performance and time-to-failure of composite ship materials in fire.

Test and Modelling of Impact on Pre-Loaded Composite Panels

Currently test and simulation of low and high speed impact of Aerospace composite structures is undertaken in an unloaded state. In reality this may not be the case and significant internal stresses could be present during an impact event such as bird strike during landing, or takeoff. In order to investigate the effects of internal loading on damage and failure of composite materials a series of experimental and simulation studies have been undertaken on three composite types having different fibres, resins and lay-ups. For each composite type panels have been manufactured and transversely impacted under the condition of ‘unloading’ or ‘pre-loading’. For preloading a rig has been constructed that can impose a constant in plane strain of up to 0.25% prior to impact. Results have clearly shown that preloading does lower the composite impact tolerance and change the observed failure modes. Simulation of experiments have also been conducted and have provided an encouraging agreement with test results in terms of both impact force time histories and prediction of the observed failure mechanisms.

Thermodynamically consistent coupled viscoplastic damage model for perforation and penetration in metal matrix composite materials

Accurate modeling and efficient analysis of the metal matrix composite materials failure mechanism during high velocity impact conditions is still the ultimate goal for many researchers. The objective is to develop a micromechanical constitutive model that can effectively simulate the high impact damage problem of the metal matrix composite materials. Therefore in this paper, a multiscale micromechanical constitutive model that couples the anisotropic damage mechanism with the viscoplastic deformation is presented here as a solution to this situation. This coupled viscoplastic damage model is formulated based on thermodynamic laws. Nonlinear continuum mechanics is used for this heterogeneous media that assesses a strong coupling between viscoplasticity and anisotropic damage. It includes the strong directional effect of the fiber on the evolution of the back stress and the development of the viscoplastic strain in the material behavior for high velocity impact damage related problems.

Mode I quasi–static and fatigue delamination characterisation of polymer composites for wind turbine blade applications

Ambitious electricity generation targets from renewable sources set by many governments have lead to the rapid growth of the wind energy industry over the last two decades. The need for larger wind turbine blades for increasing energy generation has considerably increased the demand and use of high performance composites in wind turbine applications, mainly in blades. A common type of failure in composite materials is delamination of adjacent layers, which can occur either due to manufacturing inconsistencies or due to in service loads. Understanding and characterising delamination is very important in order to implement damage tolerant design methodologies. The present research work focuses on the assessment of the delamination behaviour of composites for wind turbine applications. Several composite systems were tested and their fracture toughness and fatigue delamination propagation behaviour under mode I (peeling) loading conditions were evaluated. Quasi–static tests were performed and delamination initiation values were evaluated. Fatigue delamination growth rate curves (da/dN versus G Imax) were also produced. The carbon/epoxy and glass/epoxy material systems tested were compared in terms of resin type, fibre type and interfacial characteristics.

Degradation, fatigue, and failure of resin dental composite materials.

The intent of this article is to review the numerous factors that affect the mechanical properties of particle- or fiber-filler-containing indirect dental resin composite materials. The focus will be on the effects of degradation due to aging in different media, mainly water and water and ethanol, cyclic loading, and mixed-mode loading on flexure strength and fracture toughness. Several selected papers will be examined in detail with respect to mixed and cyclic loading, and 3D tomography with multi-axial compression specimens. The main cause of failure, for most dental resin composites, is the breakdown of the resin matrix and/or the interface between the filler and the resin matrix. In clinical studies, it appears that failure in the first 5 years is a restoration issue (technique or material selection); after that time period, failure most often results from secondary decay.

Fastener pull-through in a carbon fibre epoxy composite joint

Abstract This paper considers the capability of finite element (FE) modelling to accurately predict fastener pull-through failure of composite laminates. Such failures are dominated by inter-ply delamination and through-thickness shear failure of the laminate and the common modelling approach is to use computationally expensive, detailed three-dimensional models that include delamination for every ply interface, fastener contact and prestress. This paper considers a simplified FE modelling strategy achieved through judicious use of symmetry boundary conditions, hybrid shell/solid modelling and reduced numbers of interfaces for delamination. The LS-DYNA FE software was used for this study using the available composite material and cohesive failure models. The conclusion drawn from this work is that the use of simplified FE models does have merit in modelling fastener pull-through provided the material is quasi-isotropic and the boundary conditions are uniform around a circular perimeter. Additional work is however required to determine suitable cohesive properties and progressive shear failure parameters.

A micromechanical view of inter-fibre failure of composite materials under compression transverse to the fibres

The optimal design of composite structures requires progresses in the understanding of the mechanism of failure of fibrous composite materials. As regards the micromechanical structure of fibrous composites, the authors have already shed light on several not completely understood aspects of composites behaviour. In particular, the mechanism of failure of a fibrous composite under tension transverse to the fibres has recently been explained by the authors, establishing a relation between the observed failure and the predictions of initiation and extension of the damage. The objective of this paper is to contribute to find an explanation for the appearance of an angle of failure of about 53°, referenced by several authors, in the case of compression transverse to the fibres. The analysis is carried out by means of Boundary Elements, using the concepts derived from Interfacial Fracture Mechanics. The study developed shows that, following a scheme of analysis of the damage mechanism analogous to that employed for the tension case, the initial direction of failure predicted agrees with that observed in experiments.

Failure Analysis of Fiber Reinforced Composite Materials Used in Malaysian Industries

The main objective of this paper is to determine the curves bounding the actual load carrying capacity in terms of the First Ply Failure and the Last Ply Failure of composite materials used in Malaysian Industries. A mathematical model and computational model are presented for the analysis. Higher Order Shear Deformation plate theory is employed to predict the deformation of the plate. The selected material properties through thickness is used and accommodated by a discrete layer approach. A program based on finite element method is developed using Fortran-90 to determine the lamina stresses. These stresses are then used in the present failure model to determine the First Ply Failure and Last Ply Failure, by progressively reducing the stiffness of the laminas. Finally, the First Ply Failure and Last Ply failure results are analysed, in terms of lower and upper bound within which the true load carrying capacity lies.

Failure Analysis of Fiber Reinforced Composite Materials Used in Malaysian Industries

The main objective of this paper is to determine the curves bounding the actual load carrying capacity in terms of the First Ply Failure and the Last Ply Failure of composite materials used in Malaysian Industries. A mathematical model and computational model are presented for the analysis. Higher Order Shear Deformation plate theory is employed to predict the deformation of the plate. The selected material properties through thickness is used and accommodated by a discrete layer approach. A program based on finite element method is developed using Fortran-90 to determine the lamina stresses. These stresses are then used in the present failure model to determine the First Ply Failure and Last Ply Failure, by progressively reducing the stiffness of the laminas. Finally, the First Ply Failure and Last Ply failure results are analysed, in terms of lower and upper bound within which the true load carrying capacity lies.

On inception of cracking in composite materials with brittle matrix

The primary mechanism that leads to failure in composite materials with brittle matrix is the formation of macrocracks. In general, the specification of the conditions at the onset of cracking requires an elaborate analysis of the stress field throughout the domain. Such an analysis is not always feasible in view of the complexity of the problem. In this work, an attempt is made to formulate some macroscopic criteria that define the conditions at the inception of macrocracks. The approach involves generating a set of data from a homogenization analysis that is subsequently used for the identification of closed-form criteria derived based on critical plane approach and/or microstructure tensor approach. The methodology is illustrated using an example of reinforced concrete specimen subjected to different loading conditions. A numerical study is conducted to examine the efficiency of this approach. The primary focus is on assessment of the influence of volume fraction of the reinforcement and its orientation (relative to the loading direction) on the onset of macrocracking. It is noted that the proposed approach can be employed for other composite materials, such as fiber-reinforced composites with ceramic or brittle polymeric matrix.