Damage In Composite Materials Research Articles

Experimental evaluation of the effect of carbon fibres on acoustic emission parameters obtained during compressive strength tests of alkali-activated slag composites

The generation of acoustic emission signals is directly associated with formation of cracks in materials during loading. This paper deals with possibilities of acoustic emission method application as the tool for the identification of structural damage in alkali-activated composite materials during compressive strength test. In experimental part, the three piezoelectric sensors were occupied for the continuous record of emission signals of stressed material feedback on applied mechanical load in real time. Detection of specific acoustic emission signals in the course of deformation of the test samples indicates that irreversible structural changes occur in the composite. Four different mixtures of alkali-activated slag mortars were prepared, the first one was reference without the addition of carbon fibres. The others contain the carbon fibres in amount 0.5, 1.0 and 2.0 % from the weight of the slag.

Modeling the damage of composite materials subjected to fatigue loading

A two-parameter damage model based on residual strength, applied stress and cycle ratio is presented in this paper to predict progression of damage at different stress levels. Using the proposed model, damage factor progression was predicted for E-glass/vinyl ester laminate at three different stress levels. It is observed that proposed model predicts the damage progression closely even though it is not reporting the type of damage. Also, the damage is reported even at low cycles of loading because of anisotropic nature and inherent damages present in the composite materials.

High sensitive damage sensors based on the use of functionalized graphene nanoplatelets coated fabrics as reinforcement in multiscale composite materials

Functionalized graphene nanoplatelets networks created through glass fiber fabrics were used to detect and locate damage in multiscale composite materials. The electrical behavior of multiscale composite materials was strongly influenced by microstructural features. Coated fabrics presented high sensitivity to breakage of fibers due to the preferential orientation of f-GNPs through fibers. This sensitivity was higher when damage was induced perpendicular to the fiber direction and the region where damage could be detected was bigger in the case of locating the measuring electrical channels perpendicular to fiber direction. These phenomena are related again to the morphology of the electrical network through the coating. Due to the insulating character through thickness of composites, detection and location was limited to layers of fabric of the composite. Nevertheless, self-sensors had the capacity of detecting and locating damage with high sensitivity by means of abrupt increases in electrical resistance induced by breakage.

Understanding how arc attachment behaviour influences the prediction of composite specimen thermal loading during an artificial lightning strike test

High speed image analysis of experimental lightning strike testing on composite specimens has demonstrated complex time-dependent arc attachment behaviour. To date simulation studies of lightning strike direct effects on composite materials have overlooked or idealised the observed arc attachment behaviour. This is significant as these preceding studies have also demonstrated joule (resistive) heating is a major contributor to composite material damage and thus the application of the current load is critically important. The objective of this paper is to quantify how arc attachment behaviour influences the prediction of composite specimen thermal loading during a simulated lightning strike test. This is achieved through a simulation study modelling experimental arc attachment behaviours referenced in the literature. The simulation results are compared with measured test specimen damage. The results quantify for the first time the significance of arc attachment behaviour, demonstrating how realistic representation of arc expansion and arc movement can alter the predicted thermal loading and generate thermal damage patterns comparable to measured experimental damage.

A progressive fatigue damage model for composite structures in hygrothermal environments

An improved progressive fatigue damage model (PFDM) involving hygrothermal effects was proposed to predict fatigue failure of composite structures in hygrothermal environments. In the improved PFDM, a unified model was established to evaluate the variation of composite material properties caused by hygrothermal environments. The hygrothermal-induced material properties were utilized in the stress analysis model, material degradation models and fatigue failure criterion. The hygrothermal strains were introduced into the constitution equation to account for the hygrothermal effects. A residual-strain-based gradual material degradation model and a micromechanics-based sudden material degradation model were enhanced to describe the damage of composite materials in hygrothermal environments. Besides, fatigue tests and progressive fatigue damage analyses of an open-hole laminate were performed in hygrothermal environments. The good consistency between the numerical and experimental results validated the improved PFDM. Both the experimental and numerical outcomes indicate that the effective moisture equilibrium considerably reduces the compressive strength and compressive fatigue life of the open-hole laminate made of T800 carbon/epoxy composites.

Local damage evaluation of a laminate composite plate using ultrasonic birefringence of shear wave

Abstract This paper presents an ultrasonic non-destructive testing method to locally characterize composite material damage through the analysis of the anisotropy behavior variation induced by damage. The approach is based on shear wave contact measurements and analyses shear wave birefringence to estimate variation of the attenuation coefficient and shear moduli ratio between warp and weft directions. The method only requires a single piezo-electric contact sensor and thus, is easy to implement for practical applications. Moreover, unlike other methods, it does not require any reference measurement in a calibrated medium such as water to evaluate attenuation coefficient variation and shear moduli ratio. It is shown that the proposed method allows to locally qualify damage with good repeatability and robustness.

A review of non-destructive techniques used for mechanical damage assessment in polymer composites

Polymer composite materials are being increasingly used in primary load-bearing structures in several advanced industrial fields such as aerospace vessels, railway wagons and mega-scaled wind turbines where detection of subcritical damage initiation can significantly reduce safety issues and maintenance costs. It is therefore crucial to inspect these composite structures in order to assess their structural health and to ensure their integrity. Non-destructive testing techniques (NDT) are used for this purpose, making it possible to monitor mechanical damage of composite materials under in situ or ex situ service conditions. This paper reviews the capabilities of the most common NDT techniques used to inspect the integrity of composite materials. Each technique has a detection potential and cannot allow a full diagnosis of the mechanical damage state of the material. Thus, depending on the occurring damage mechanism and the conditions of use, one technique will be preferred over another, or several techniques should be combined to improve the diagnosis of the damage state of the structures.

Progressive damage of a unidirectional composite with a viscoelastic matrix, observations and modelling

In this paper phenomenological observations of the creep rupture under maintained combined traction and torsion loading are first presented. They show the importance of the matrix’s behavior in the long-term durability of the material. Understanding and foreseeing creep rupture of unidirectional fiber reinforced polymers (UD FRP) involves comprehension at the fibers’ scale of various time-dependent interactions among the fibers and between the matrix and the fibers. Shear-lag models have been successfully applied in the modeling at the micro-scale of these interactions, some of them even introducing time dependence. Long-term durability of macro-scale structure demand further developments of such models to be able to predict the macro-damage cluster and their evolution. The aim of the present contribution that is an extension from existing models is to investigate the progressive damage of a 0o UD composite material subjected to combined shear-traction loading including a high number of interacting fibers, with a viscoelastic matrix, debondings and random distribution of fiber flaws. Results of simulations including different loadings and matrix viscoelastic properties will be shown and discussed for a better comprehension of the role of composite’s components in the creep rupture phenomenon. In particular, the long-term influence of matrix’s shear stiffness on the material’s lifespan is shown, and the impact of an additional uniform shear stress is studied. This combined shear-traction loading is of interest in real-scale structures where shear stress can result from torsion or shear forces (such as those due to anchor points, misalignment and coupling). Moreover, this model is a first step to approach the long term failure of 0o composites subjected to torsion-bending loading, what is shown decisive in the second section of this work. Further experimental works in combined traction-torsion loadings are needed to validate this simulations with a specific attention on the identification of required parameters.

Material and morphology parameter sensitivity analysis in particulate composite materials

This manuscript presents a novel parameter sensitivity analysis framework for damage and failure modeling of particulate composite materials subjected to dynamic loading. The proposed framework employs global sensitivity analysis to study the variance in the failure response as a function of model parameters. In view of the computational complexity of performing thousands of detailed microstructural simulations to characterize sensitivities, Gaussian process (GP) surrogate modeling is incorporated into the framework. In order to capture the discontinuity in response surfaces, the GP models are integrated with a support vector machine classification algorithm that identifies the discontinuities within response surfaces. The proposed framework is employed to quantify variability and sensitivities in the failure response of polymer bonded particulate energetic materials under dynamic loads to material properties and morphological parameters that define the material microstructure. Particular emphasis is placed on the identification of sensitivity to interfaces between the polymer binder and the energetic particles. The proposed framework has been demonstrated to identify the most consequential material and morphological parameters under vibrational and impact loads.

A multi-level damage and creep behaviour of material subjected to high pressure: metal versus composite – A micromechanics approach

This current study reports on multi-level damage and creep behaviour of metal and composite material under external high pressure using finite element concept. A fatigue damage model with microcracks with improper interface has been portrayed in the present investigation. In addition, the overall elastic properties and damage evaluation are also studied and comparative study of mechanical properties has been outlined. Further thermo-elastic creep response of materials based on Norton’s law is also presented. The results showed that the proposed nonlinear constitutive model and overall elastic damage behaviour of composite material are in agreement. Implemented nonlinear constitutive model is secured by comparing predicted stress–strain curves with experimental data available in the past literature under uniaxial tension. The time-dependent behaviour creep stresses and displacements are studied and plotted. The analysis provides significant new insights of micromechanical damage, creep and collapse behaviour of composite material. For the structural composites, some notable techniques have been developed over the past three decades; review of these techniques is also outlined here in this paper and state of art is established together with insights for upcoming development.

Early Diagnostics of Damage and Fracture Zones in Composite Materials Using Brittle Strain Gauges and Acoustic Emission

The integrated use of the acoustic emission technique and brittle oxide strain gauges for testing the deformation of damage and fracture zones in samples of polymer composite materials (PCM) at the early phases is considered. For the realization of the proposed technique, integrated parameters were used and software including the cluster analysis and the classification of registered AE pulses was developed, which made it possible to differentiate crack formation signals in the brittle layer of a strain gauge from all the other signals that occur at the early phase of the deformation of PCM samples in the online mode. The use of acoustic emission testing and control video recording for the registration of cracks in a brittle oxide strain gauge with the threshold deformation value of 1000 μm/m provided the precise diagnostics of the forthcoming fracture zone in a sample at the early loading phase under the load level of 10–15% of the limiting one long before the beginning of the active PCM structural degradation phase and made it possible to determine the distribution fields of the highest main deformations in the region of a strain gauge and to perform their quantitative evaluation.

On a discrete element method to simulate thermal-induced damage in 2D composite materials

The present contribution deals with a discrete element method to simulate thermal-induced damage in 2D composite materials. We consider a hybrid particulate-lattice model based on the equivalence between a granular system and a network of cohesive beam elements. This choice is mainly motivated by previous papers exhibiting its ability to model heterogeneous materials in which complex fracture phenomena occur. Our objectives are twofold. First, we aim to introduce a thermo-elastic coupling using a recently developed model of thermal expansion based on the dilatation of the beam element. Second, we are interested in studying the suitability of the discrete element method to model the thermal-induced damage due to thermal expansion mismatch. For that purpose, several preliminary studies are performed to verify the validity of the thermal expansion model in the context of continuous media. Then, damage effects and interfacial debonding are taken into account and the model is applied to the case of 2D metallic fiber composites with a brittle alumina matrix. Results exhibit the ability of the present approach to simulate the suitable damage mode as a function of thermal conditions. Besides, realistic failure patterns with radial propagations are obtained in the context of cracks opening.

A Review on detecting and characterizing damage mechanisms of synthetic and natural fiber based composites

The damage to composite structures caused by impact events is one of the most critical behaviors that inhibit the widespread application of composite material. As the application of synthetic and natural based composite material increases over time, improved knowledge of composite damage in areas such as automotive and aerospace is exceedingly necessary. It is important to study and understand the damage mechanism of composite structures to produce effective designs. The failure caused by damage in structural design can result in unintended consequences. Extensive research has been conducted to detect impact damage in synthetic fiber. There are various methods to identify and characterize the damage. This article provides a comprehensive review of recent literature focusing on the broader scope of impact damage and incipient thermal damage of synthetic and natural fiber-based composites. In this report, the available research is reviewed by considering all aspects related to damage in composite materials, particularly the work done on detecting and characterizing damage mechanisms of synthetic and natural fiber-based composites.

Failure analysis of laminated composites based on degradation parameters

This paper presents an approach to the formulation of models characterizing nonlinear deformation and damage of composite materials and includes the consideration as the simplest model as more complex ones. In this research a number of assumptions to build up a theory for failure prediction in laminated composites are presented, which are generalized enough to serve as the basis for explanation of current models and for further development of modelling theory. The presented approach is a phenomenological one and introduces degradation parameters explicitly influencing on the stiffness characteristics of composite materials. The first part of the article describes common assumptions for material degradation theory and the main part of the research focuses on development of simplified constitutive relations suitable for practical application in testing and characterization of composite materials. Additionally, the rest part of this work is dedicated to the extension of formulated approach to capture and take into account the complex effects such as initial nonlinear shear deformation behavior of laminated composites and the influence of high strain rate on strength properties. The results obtained show a good correlation between the results obtained with proposed modelling method and analyzed experimental data.

A regularized orthotropic continuum damage model for layered composites: intralaminar damage progression and delamination

Predicting progressive damage in composite materials is essential for the design of most lightweight constructions. When laminated composite structures are considered, both intralaminar and interlaminar (delamination) damage evolution need to be addressed. Typically, these different damage modes are treated separately. On the contrary, in this paper, a continuum damage model is presented which is capable of modeling orthotropic damage progression within layers as well as delamination. The model is formulated in a thermodynamically consistent manner. Moreover, the results are mesh independent due to a fracture energy based regularization scheme.

A Multiphysics Simulation Approach for Efficient Modeling of Lightning Strike Tests on Aircraft Structures

A numerical approach is proposed and demonstrated for efficient modeling of the thermal plasma behavior present during a lightning strike event. The approach focuses on events with timescales from microseconds to milliseconds and combines the finite element method, magnetohydrodynamics, and similitude theory. Similitude theory is used to scale the problem to require considerably less computing resource. To further reduce the computational burden and to resolve the numerical difficulty of simulating the nearly zero electrical conductivity of air at room temperature, an approach based on cold-field electron emissions is introduced. Simulations considering turbulent flow have been considered, modeling a test configuration from literature designed to inspect composite material performance and applying an aerospace standard test profile (Waveform-B). Predicted peak temperatures (of the order of ~40 000 K) and pressures (of the order of 0.1–0.2 MPa) suggest that the pressure loading during a Waveform-B event will have a minimal effect on composite material damage.

Experimental research on damage detecting in composite materials with FBG sensors under low frequency cycling

This paper discusses the problems associated with the use of Fiber Bragg Grating (FBG) sensors to detect internal damage to composite specimens under low frequency cycling. This work utilized FBG sensor embedded cantilever beam specimens with and without known damage. FBG sensor measurement parameters which can reflect the location and degree of damage were obtained. Finally, the results obtained from the FBG sensors were compared to theoretical strain deviations, as calculated using ANSYS, to confirm the feasibility and range of sensitivity of FBG sensors for damage monitoring of composite material specimens. The research shows that FBG sensors can be used in detecting damage in composite materials under low frequency cycling and when the FBG senor is within 15mm of the extent of the damage is over 2mm.

Effect of Weaving Type on Damage Behaviour of Carbon/Epoxy Laminate under Low Velocity Impact Loading

The main purpose of the present investigation was to determine the damages generated by the low velocity impact by mean of the finite element method. The commercial transient finite element package LS-dyna used to model the effect of slug impactor induced damage in composite material subjected to low velocity impact. Four types of weaving were considered; serge (2/2), serge (0/30/-30/0), serge (0/45-45/0) and taffeta. The Texgen package was used to build the laminate pattern weaves. The composite material was subjected to stainless steel slug impactor in the transverse direction dropping the composite laminate at the center with a velocity about of 15m/s. The analysis was carried out using the model 001-ELASTIC for matrix, 002-ORTHOTROPIC_ELASTIC for fibersand a rigid body model MAT20 for the slug impactor. The contact automatic single surface has been used between the yarns and the automatic_surface_to_surface between the matrix and the impactor and the contact automatic_surface_to_surface_tiebreak between the matrix and yarns and the contact automatic_surface_to_surface_tiebreak between layers.The impact load, energy, displacements were reported as function of impact time. The delamination area was represented at the layer interfaces for each material.

Study of damage evolution in composite materials based on the Thermoelastic Phase Analysis (TPA) method

Abstract Standards and conventional procedures used for analysing fatigue damage in composite materials involve high experimental campaign costs due to time-consuming tests. This aspect becomes relevant for large structures where the cost of experimental setup tends to rise according to structure dimensions. In this regard, in recent years, efforts to produce fatigue characterisation of materials have made use of several experimental techniques, i.e. thermographic techniques. Most of these, however, refer to Standard specimens and laboratory equipment and set-up. Through the use of Thermography, in this work a new procedure has been developed which is capable of monitoring damage in GFRP composite material. The analysis of thermal signal in the frequency domain allows for the isolation of indexes which are related to the thermoelastic and dissipative heat sources. In particular, the phase of thermoelastic signal, associated with intrinsic dissipation processes occurring in the material, has been used to localize and assess the damaged areas in a quantitative manner. Moreover, the thermoelastic phase analysis leads to an evaluation of the endurance limit of composites. In fact, by comparing the results with those provided by the standard test methods, the potential has been shown of the proposed procedure firstly as a non-destructive technique for continuous monitoring of damage in composite structures undergoing fatigue loadings, and secondly, as a fatigue limit index.

Localized Temperature Variations in Laser-Irradiated Composites with Embedded Fiber Bragg Grating Sensors.

Fiber Bragg grating (FBG) temperature sensors are embedded in composites to detect localized temperature gradients resulting from high energy infrared laser radiation. The goal is to detect the presence of radiation on a composite structure as rapidly as possible and to identify its location, much the same way human skin senses heat. A secondary goal is to determine how a network of sensors can be optimized to detect thermal damage in laser-irradiated composite materials or structures. Initial tests are conducted on polymer matrix composites reinforced with either carbon or glass fiber with a single optical fiber embedded into each specimen. As many as three sensors in each optical fiber measure the temporal and spatial thermal response of the composite to high energy radiation incident on the surface. Additional tests use a 2 × 2 × 3 array of 12 sensors embedded in a carbon fiber/epoxy composite to simultaneously measure temperature variations at locations on the composite surface and through the thickness. Results indicate that FBGs can be used to rapidly detect temperature gradients in a composite and their location, even for a direct strike of laser radiation on a sensor, when high temperatures can cause a non-uniform thermal response and FBG decay.