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The present paper compares the damage and energy absorption behaviour of composites subjected to low-velocity impact using different frontal geometries for the impactor, with the composites possessing a layup of [02/902]2s. In this study, the rigid impactors with either round-nosed or flat-ended frontal geometry are employed to perform drop-weight tests at various impact energies ranging from 10 to 30 J. The measured loading response and energy absorption are analysed and compared. Additionally, the types and extent of impact-induced damage in the composite specimens are assessed via ultrasonic C-scan, optical microscopy (OM) and scanning electron microscopy (SEM) studies. It is shown that the impact energy threshold for damage initiation is greater than 20 J when using the flat-ended impactor but is less than 10 J when using the round-nosed impactor. In both cases, delamination initiates between the plies in the composite laminate. However, for the flat-ended impactor, the damage behaviour of the fibres exhibits kinking fracture, which differs from the pull-out fibre-fracture caused by the round-nosed impactor. These differences in behaviour are attributed to impactor/composite contact geometry effects which leads to different extents of indentation damage, which in turn directly affects the degree of delamination and fibre damage in the composite.

Glass laminate aluminum reinforced epoxy (GLARE) mixes an extremely thin ply of aluminum wire mesh layers with epoxy strengthened with fibers to create a hybrid composite laminates. During this investigation, plain E-glass fiber/epoxy specimens in addition to specimens with epoxy laminates reinforced with both E-glass/fiber, and wire meshes of aluminum were created. Meshes made of aluminum wire were used to increase the toughness of the E-glass fiber/epoxy combination. Tensile, bending, and hardness tests were performed to see how inserting Al wire meshes through thickness of the specimen in place of glass fiber layers affected the material mechanical characteristics. According to the outcomes from results, an influence on strength, toughness, and ductility of laminates due to using Al wire mesh instead of glass fiber. The characteristics of the generated hybrid laminates were greatly influenced by the varying position and the orienting direction of the aluminum wire mesh ply. Inclusion of Al wire mesh in the outer layers significantly made deterioration in material tensile strength and bending strength. The tensile strain also bending strain, on the other hand, were improved by 16.95 percent and 117 percent, respectively.

Low-velocity impact is one of the most critical load factors for composite laminates. Indeed, for structures submitted to low-energy impacts or small-object drops, such as tools during assembly or maintenance operations, composite laminates reveal a brittle behavior and can undergo significant damage in terms of matrix cracks, fiber breakage, or delamination. This damage is particularly dangerous because it drastically reduces the residual mechanical characteristics of the structure, and at the same time can leave very limited visible marks on the impacted surface. Impact damage tolerance is therefore an important design consideration for aircraft composite structures. The objective is to prove the composite structure can withstand the required loading, even with impact damage, and in particular if the impact is undetectable. The complexity of this design consideration is that it is necessary to consider, on one hand the impact damage, or more precisely the loss of residual strength due to the impact; and on the other hand, the impact detectability, or more precisely the permanent indentation left by the impact. The goal of this article is to present the concept of impact damage tolerance applied to aircraft composite structures.

High-velocity impact of foreign objects such as small stones will produce complex damage in composite laminates, which will severely degrade residual strength. This chapter first describes high-velocity impact tests for carbon fiber-reinforced plastic (CFRP) laminates and then observes damage states caused by near-perforation impacts. Extensive delamination and fiber breaks as well as matrix cracks appeared regardless of the stacking sequence. This study also quantitatively evaluates the influence of the stacking sequence and the material system (i.e., the presence or absence of toughened interlayers) on the damage area. Finally, the mechanisms of high-velocity impact damage in CFRP laminates are discussed, based on the observations.

Composite laminates employed in various sports products are usually subjected to large-deflection dynamic bending during their service. The chapter first describes the experimental characterisation of composites as well as investigation of various damage modes ensued under these loading conditions replicated by means of Izod-type dynamic tests. It then describes the development of three-dimensional finite-element models employing a cohesive-zone method to study the onset, progression and interaction of some damage modes observed experimentally. The developed numerical models are capable of simulating damage mechanisms in laminates and their interaction observed in the tests.

Morphing leading edge has great potential for noise abatement and aerodynamic efficiency improvement. The drooping effect is realized by bending of the flexible skin which encloses to form the leading edge. Since the flexible skin is often made of composite laminates of Glass Fiber Reinforced Plastics (GFRP), the lay-up sequences have become the determinant, which affects not only the morphing quality but also the manufacturing complexity. Two optimizing methods of lay-up sequences are comparatively studied. In the first method, the laminal quantities in 0°, ±45° and 90° vary independently, while in the second one, the concept of isotropic laminate unit [0/45/−45/90]s is employed and the unit quantity is the unique variable. Final evaluation demonstrates that for both methods there is insignificant impact to the overall morphing quality; however, specific concern is equally necessary for these two methods to the tip of the leading edge where the skin is at its minimum thickness and bears the most severe bending deformation. In terms of computational efficiency and post-processing labor, the second method has better performance.

This study investigates the tension-tension fatigue behaviour of glass/epoxy quasi-isotropic laminates. Constant amplitude tension-tension fatigue tests were performed at different stress level at a stress ratio, R = 0.1 and at a frequency of 3 Hz. The damage growth in the material was characterized by evaluating the degradation in stiffness. A phenomenological cumulative stiffness degradation based damage model was used to predict the damage development in the material. It was observed that, in the initial fatigue loading cycle, the material exhibited rapid reduction in stiffness and maintained a constant rate of degradation until failure

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2020-06-29, 資料番号: PA2120012000

This paper presents the damage location technology in glass fiber reinforced epoxy (GF/epoxy) composite laminates subject to low-velocity impact. Multi-walled carbon nanotube coated GF (MWCNT@GF) is designed and manufactured as the sensor. MWCNT@GF sensor is embedded into the laminates to form an in situ sensing network. Relative resistances of the sensors are recorded after the low-velocity impact test. An algorithm is compiled to deal with the relative resistance data and help showing the impact damage location on a contour map. Results show that the in situ monitoring method with embedded MWCNT@GF sensor could locate the impact damage with high accuracy.

A multiscale approach comprising laminate-scale finite-element (FE) analysis and fiber-diameter-scale periodic unit cell (PUC) analysis was developed to predict matrix microcracking in quasi-isotropic laminates; further, this method was validated through comparison of our predictions with experimental results. In the mesoscopic FE analysis, the nonlinear deformation in the unidirectional laminae was incorporated to reproduce the deformation behavior of the laminate and obtain deformation histories at the locations of expected crack initiation in the laminate. In the microscopic analysis, the nonlinear behavior and crack initiation in the matrix resin were simply modeled by an elasto-viscoplastic law and a stress-based failure criterion, respectively. To predict crack initiation considering both the macroscopic deformation fields and the microscopic heterogeneity of the material, the mesoscopic FE analysis was conducted first. Subsequently, the microscopic PUC analysis was undertaken based on the strain histories obtained from the mesoscopic analysis. Our multiscale approach was applied to quasi-isotropic laminates with several laminate configurations to predict the matrix cracks in the 90∘ ply of the laminates. In addition to referring to experimental data cited in literature, initial and transverse cracks were observed when conducting tensile tests of quasi-isotropic laminates using the in situ replication technique and ex situ X-ray computed tomography. Through comparison of the predicted values with experimental results quoted in literature and obtained in this work, we validated the prediction capability of our multiscale analysis and evaluated the process of crack formation from the mesoscopic and microscopic points of view. Moreover, we examined the sensitivity of the predicted results to fiber arrangement and the influence of constitutive and failure modeling of the two-scale analysis on the predicted cracking strains. The reported method can predict initial and transverse cracks on quasi-isotropic laminates; further, it depicts the damage progress wherein microcrack nucleation and coalescence occurring before the full-width transverse cracking in laminated composites are observed under tensile loading conditions.

This study explored the impact response of two bio-inspired composite laminates with linear and non-linear helicoidal fibre architectures. The helicoidal laminates, together with quasi-isotropic and cross-ply control samples, were fabricated using heterocyclic aramid fibres and tested against a spherical projectile under high impact velocities. The results revealed that helicoidal lay-ups with small rotation angles led to inferior perforation resistance and energy absorption capacity when compared to the quasi-isotropic and cross-ply counterparts. The cross-ply configuration was confirmed as the optimal fibre architecture for impact perforation. Post-impact inspections highlighted that the failure mechanisms of laminates were significantly affected by their lay-ups. The number of fractured fibres was found to reduce with the decrease of inter-ply angle. This was due to the small rotation angles promoted a wedge-in mechanism. Moreover, a smaller angle mismatch resulted in diminished overall delamination area in a laminate. Due to these two effects, therefore, helicoidal lay-up configurations with small inter-ply angles are not recommended for impact-resistant laminates reinforced by tough fibres.

A methodology is proposed to incorporate spatial distributions of micro-defects within a three dimensional multiscale modeling framework for Carbon Fiber Reinforced Polymer (CFRP) composites to predict stiffness and strength properties of laminates for use in structural design and in establishing nondestructive inspection protocols. Defects in both the fiber and matrix due to variations in the manufacturing process for fiber reinforced composite laminates are considered. Stochastic sampling of micro-defects based on experimental data using Ripley’s K-function is proposed. Three different laminate void volume fractions are used. Spatial statistical analysis is performed for the micro-defects, and then a methodology is presented for predicting stiffness and ultimate strength of three multi-directional composite laminates with distributions of microstructural defects. The results indicate that, in addition to the volume of micro-defects that are present, the spatial distribution of the micro-defects plays a significant role in mechanical properties of laminates, especially the ultimate strength for which a 3.62% reduction is seen in the simulations of laminates containing distributions of micro-defects. Based on these results, it is recommended that the spatial statistics of micro-defects in manufactured composites be incorporated into both design criteria and nondestructive inspection criteria for composite laminates.

Hybrid titanium composite laminates (HTCLs) are high-performance light-weight fiber metal laminates (FMLs) that are being increasingly used in various industries such as aeronautical, military, and marine thanks to their optimized fracture toughness, impact resistance, and thermal performance. In the current study, the low-velocity impact (LVI) characteristics of a new generation of thermoplastic (TP) HTCLs at various energy levels are investigated. To do so, Ti-6Al-4 V sheets, carbon fabrics, and ultra-high molecular weight polyethylene (UHMWPE) fabrics are used to fabricate multiple laminates with different fiber types, metal volume fractions, and lamination layups. A low-cost resin infusion process is employed for manufacturing the laminates at room temperature by using a novel liquid thermoplastic methyl methacrylate resin, Elium® 188. Before fabrication, a multi-step surface treatment method is applied on Ti alloy sheets to enhance the interfacial properties between the composite layer and the metal alloy sheet. In addition to TP-HTCLs, equivalent thermosetting (TS) HTCLs with an epoxy resin, Epolam, are fabricated to compare the results and evaluate the possibility of fabricating recyclable TP-FMLs at room temperature with enhanced out-of-plane properties. Impact properties including contact force, deflection, energy parameters, and related damage modes are investigated and presented for each laminate. It is concluded that the newly developed TP-HTCLs can be cured at room temperature and have enhanced impact properties compared to those of TS-HTCLs. Besides, the HTCL with UHMWPE fabrics on its composite sides (before the Ti alloy sheets) performs better in LVI compared to that with carbon fibers on the top and bottom (of its composite core) since UHMWPE exhibits higher strain to failure and fracture toughness compared to carbon fibers.

This paper presents an experimental investigation of the multi-scale toughening mechanisms for improving the interlaminar fracture toughness, low-velocity impact damage resistance and compression-after-impact (CAI) strength of continuous carbon fibre-epoxy composite laminates using carbon nano- and micro-fillers spanning the nanometer to millimeter length scales. The fillers used in the epoxy matrix of the composite laminates were carbon nanofibres (CNFs) and short carbon fibres (SCFs). When used together, these two fillers yielded a less-than-additive improvement to the mode I fracture toughness. However, they created a synergistic (i.e. greater-than-additive) increase to the steady-state mode II toughness, compared to when the fillers were applied separately. Hybridising the CNFs with the SCFs also improved the impact damage resistance (up to 24%) and CAI strength (up to 29%) of the laminate at various impact energies. The key toughening mechanisms imparted by the CNFs and SCFs, when used separately or in combination, were identified through analyses and scanning electron microscopy.

The study deals with the mechanical characterization of vetiver grass fiber and kenaf fiber reinforced epoxy-based hybrid composites. Five types of composite laminates were developed through the hand lay-up process by varying the percentage of vetiver grass and kenaf fibers. The tensile, flexural, compression and impact tests were conducted as per ASTM. The fractured surfaces of the tested specimens were studied using a scanning electron microscope. From the results, it was shown that properties of epoxy composites were improved by hybridization with vetiver grass and kenaf fibers. The improved mechanical properties of fiber-reinforced composites were noticed in increment of percentage composition of kenaf fibers. Keywords: Vetiver grass (Chrysopogon zizanioides), Kenaf fiber (Hibiscus cannabinus), Epoxy, Composites, Properties

Based on the Stiffness degradation rule of woven glass fiber composite under fatigue loading, a phenomenological fatigue damage model containing two material parameters in which first is directly proportional to the fatigue life and second is inversely proportional to fatigue loading level is presented in this paper by analyzing damage development effects with very nice result as fatigue modulus is inversely proportional to fatigue strain. Experimental data from Tensile Fatigue Test were employed to verify the model, and the results show that the model can describe the damage evolution of woven glass-epoxy composite laminates under different fatigue loading by verifying the predicted fatigue life of composites. Degradation of Young’s Modulus at different loading cycles, damage development corresponding to Normalized life, its accumulation subjected to constant amplitude fatigue loading including its verifications are well discussed. Keywords: Woven glass-epoxy composite, Constant amplitude fatigue, Accumulative damage, Predicted life, Normalized cycles, Damage model

The open hole composite laminates with different stacking sequence were tested and the failure modes and strength were recorded. A progressive damage model of the open-hole composite laminate under compression was developed and in-plane damage is modeled by using the three-dimensional continuum shell elements and cohesive element was adopted for delamination failure simulation. Based on the ABAQUS user subroutine UMAT, this model simulates damage initiation, propagation and final failure. With different failure criteria, the strength and failure modes of open-hole laminates under compression were predicted in this model. Compared with the experiment results, the effects of different stacking sequences on the strength and final failure modes of composite laminates are analyzed. Keywords: Open hole composite laminates, Compressive strength, Progressive damage, Finite element modeling

In order to model the progressive failure of laminates under tensile load, the finite element model adopting the floating node method combined with In-Situ effect strength theory is developed in this paper. The floating node method is based on the original finite elements to assign more additional degree of freedoms on the edges or nodes. In this way, it can realize crack propagation explicitly and prevent the singularity caused by the integration of body elements at the damage points. The calculation method of In-Situ strength theory based on the assumption of fracture mechanics is introduced and deduced, which improves the accuracy of the failure strength prediction. Two kinds of notched composite laminates’ tensile experiments were carried out. Experiment results show that different ply sequences ([453/903/-453/03]s and [45/0/-45/90]3s) have different failure strength and failure progress. In this paper, the reliability of the model is verified by comparing the experimental results with the simulation results. The comparison results demonstrate that this model can realize the explicit crack propagation and predict the failure strength precisely. In addition, this model can represent some failure modes such as fiber breakage, matrix damage, and delamination, which were observed from experimental phenomenon. The traditional failure criteria compared to the improved criteria's accuracy is significantly improved. It demonstrated that the analysis in considering the In-Situ effect is very necessary. Keywords: In-Situ theory, Floating node method, Notched laminates

A Distributed fiber Optical Sensor (DOS) was embedded inside and attached to the surface of a multi-directional continuous fiber composite laminate coupon, along with the traditional foil of Strain Gages (SG) and Digital Image Correlation (DIC), to compare the DOS measure strain response to traditional strain acquisition methods. Tensile and bending tests were performed on an Open Hole composite laminate coupon to study different modes of loading and the performance of the DOS in the presence of a strain gradient. Tensile test results show good agreement between the SG, the DIC, and the DOS strain measurements in the region far from the strain concentration. Near the hole, the DOS repeatably measured the strain concentration during tensile and bending tests. The DOS was able to measure the residual strain in the composite laminate coupon through the hole-drilling method. Finite Element Analysis was performed to obtain the theoretical distribution of axial strain along the locations corresponding to the physical placement of the DOS in the coupon. As the results indicate, the DOS readings agree well with the theoretical results for the strain distribution in the test coupons. The results obtained during these evaluations provide confidence that the DOS strain measurement method and equipment are a robust strain acquisition option with the capability to overcome some of the limitations of the traditional foil SG and DIC methods.

Due to high specific strength and stiffness ratios, composite materials are widely used in industries where minimising structural mass is of paramount importance, such as the aerospace sector. However, designing lightweight composite laminates is challenging due to the large number of discrete design variables involved, e.g. ply numbers and fibre orientations which are usually restricted to a set of predefined values. The number of possible laminate solutions grows exponentially with increasing ply count, quickly rendering complete enumeration impossible. Current mixed-integer programming techniques for designing composite laminates with many plies either exhibit insufficient design space exploration, or demand inconceivable computational effort. As a result, laminates often have sub-optimal properties, e.g. excessive weight. We propose a novel deterministic optimiser for finding the lay-up of composite laminates with many plies. Lay-ups must match desired stiffness properties called Lamination Parameters (LPs). The design-space is explored by a procedure that uses beam search to promote fast convergence towards optimal or near-optimal solutions. Additionally, the optimality of the design solutions is improved by local searches which are performed after a first guess of the stacking sequences. The proposed optimiser is shown to retrieve symmetric laminate lay-ups with as many as 300 plies within a few minutes.

This investigation presents the effect of different interlaminar hybridization and localized in-plane edge loads on the vibration and buckling characteristics of hybrid fiber metal laminates (HFMLs) by developing finite element formulation. A 9-noded heterosis plate element has been used to discretize the plate by taking into account the effect of shear deformation and rotary inertia. Since the stress distribution within the plate element is highly non-uniform in nature, the dynamic approach has been used to solve the buckling problems wherein two sets of boundary conditions are used, one for pre-buckling stresses and another for buckling load calculations. The present study consists of aluminum metal face sheets bound with four layered symmetric hybrid cross-ply and angle-ply laminate schemes. In each scheme, six different hybrid combinations have been considered. The performance of each hybrid combination is investigated under various loading combinations. Further, the effect of different parameters such as boundary condition, thickness of plate, width and position of localized edge loads, plate aspect ratio, and hybrid configurations are included in this work. The effect of each parameter is well investigated and explained by plotting mode shapes. It is revealed from the study that the hybrid configurations and localized edge loads significantly affect the vibration and buckling characteristics.

A virtual finite element framework is presented to provide the transition from a high fidelity model to a more computationally efficient continuum model for simulating fibre-dominated damage behavior in composite laminates subjected to tensile loadings. The high fidelity method in LS-DYNA is based on the use of cohesive interface elements to simulate both intra-laminar matrix cracks and delamination. Applied to IM7/8552 carbon fibre reinforced plastic laminates in over-height compact tension (OCT) tests, this modeling strategy is used to determine the effective damage parameters for the nonlocal continuum damage model, CODAM2, implemented as MAT219 in LS-DYNA. The prediction of CODAM2 is thoroughly assessed against quantitative and qualitative results obtained from the high fidelity model. Furthermore, the characterized CODAM2 model is applied to simulations of large-scale OCT, open–hole tension (OHT) and center-notched tension (CNT) specimens and results are compared to corresponding experimental data. Due to its nonlocal feature to track the crack trajectory without the need to align the mesh with fibre orientation, the continuum damage model CODAM2 is able to accurately predict the structural response in all large-scale OCT, OHT and CNT test cases with significant computational efficiency.

This paper investigates the feasibility of using a novel domain-based correlation approach derived from the complex frequency domain assurance criterion (CFDAC) for the detection and quantification of impact damage in composite laminates. The CFDAC is essentially a complex-valued two-dimensional indicator of the covariance between two sets of frequency response functions for each pair of spectral lines corresponding to vibration-response of pristine and damage states. The study focuses on damage induced by high-velocity ice impacts on carbon fiber laminated plates. The experimental results demonstrate that the proposed methodology correctly identifies the level of induced damage via a user-independent scalar damage indicator. Therefore, this approach has potential use as a damage indicator, which could be adapted as a structural assessment non-destructive method. This research aims to contribute to the further development of functional, autonomous, and reliable structural health monitoring systems for composite structures based on spectral-domain indices. This research was done with the financial support of the Spanish Ministry of Economy and Competitiveness through the projects IPT-2011-1765-920000 and DPI2013-41094-R. The authors are very grateful to Joan Fernández for constructive suggestions.

The present work applies the global–local technique to the progressive damage analysis of fiber-reinforced composite laminates. A one-way, loosely-coupled global–local approach is developed as a combination of a low-fidelity linear global analysis and a high-fidelity local nonlinear analysis of specific regions within the structure, where damage is expected to occur. The local model is based on higher-order structural theories derived using the Carrera Unified Formulation (CUF), and specifically, Lagrange polynomials are used to model each ply through its thickness, leading to a layer-wise model. Composite damage is described using the CODAM2 material model, which is based on continuum damage mechanics. Initial assessments compare the relative performance of 3D finite elements (FE), 1D-CUF, and the proposed global–local approach via the free-edge stress analysis of a stiffened composite plate. The proposed technique is then used to predict the tensile strength of an open-hole specimen. The last assessment simulates damage progression within an over-height compact tension specimen using the global–local approach. Verification and validation of results are carried out via refined models and experiments from literature. The results demonstrate the accurate evaluation of 3D stress fields and composite laminates’ mechanical response in the progressive damage regime. A multi-fold improvement in the computational cost is shown when compared to full-scale CUF analyses and indicates this technique’s strong potential towards the computationally-efficient high-fidelity analysis of complex and large-scale composite structures.

In automotive and in other engineering fields the demand for lightweight components increases, which interests the researchers across the globe to identify materials that are light in weight and good in strength, the fiber-reinforced composites are one such material. In the fiber-reinforced composites hybridization of the fiber will give a lot of opportunity for improving different specific strength requirements. If natural fiber is used it will enhance the biodegradability of the fiber-reinforced polymeric (FRP) composites. The hydrophilic nature of the natural fiber is the challenge when employing them in engineering application irrespective of their low density and biodegradabilty, comtemprory researchers have proved that this can be overcome by giving surface modifying chemical treatment to the fibers which makes them a suitable alternative reinforcement material in the field of composites. This chapter deals with the wear behavior of FRP composite laminates fabricated with flax, sisal, and glass fibers. Here both chemically treated and untreated natural fibers are used in an epoxy resin system. The laminates are fabricated using a vacuum-assisted resin transfer molding method (VARTM). The wear test is carried out to study the sliding wear behavior as per ASTM G-99 standard. The test is carried out at three different sliding velocities (1 m/s, 2 m/s, 3 m/s) at a constant load of 10 N. From the result, it is understood that the flax, sisal, and glass hybrid laminate, that is, composite laminate with relatively more natural fiber reinforcement has almost 20%–40% lower wear rate and weight loss at various speed compare to the highly affected glass and flax fiber-reinforced composite where the percentage of glass fiber is more. Hence, it could be recommended that more natural fiber can be incorporated in fiber-reinforced composite laminates for the tribological applications.

An analytical micromechanics-based multiscale model is presented, for predicting the progressive damage and failure analysis of laminated and three-dimensional woven textile composites (3DWTCs). The framework of the proposed two-scale computational method is very general and applied to two types of composites of interest and validated by experiments. The material system is IM-7/977-3 for notched, prepreg-based continuous fibre laminates and 3DWTCs are hybridized configuration of dry fibres (carbon, glass, and kevlar tows), infused with SC-15 polymer matrix. The prepeak nonlinearity, caused by matrix microdamage, is modelled at the subscale using a two-concentric cylinder model and upscaled (homogenized) to the ply level in the case of laminated composites, and the fibre tow level in the case of textile composites. At the ply level the 3D orthotropic smeared crack approach is used for modelling postpeak strain-softening behavior, caused by both fibre and matrix failure modes. Readily available 3D finite elements are used for modelling, and the input constituent properties are obtained from standard coupon level tests, by inverse analysis. The predictive capability of the proposed method is established by demonstrating the prediction of failure mechanisms, and laminate strengths, in comparison to experimental results.

The process conditions of thick thermoset matrix composite laminates are complicated by adverse effects involving large out-of-plane temperature gradients and internal heat generation. This chapter introduces the method to analyse the transient heat transfer and the curing process of thick laminates, by combining the finite element method with thermo-chemical and self-consistent field micro-mechanical models. The methods of measurement of residual stresses in thick laminates are introduced. Some experimental results are demonstrated. The techniques discussed are applicable not only to the study of thermal residual stresses, but also stresses induced by environmentally induced internal stresses, such as caused by moisture, temperature gradient, solvents, etc.

This chapter introduces a physics-based methodology for predicting ply cracking initiation, propagation, and its impact on laminate strength in general symmetric laminates under combined triaxial normal and shear loads while the effects of thermal residual stresses and statistical distribution of fracture energies caused by manufacturing defects are considered. Ply cracking in multiple off-axis plies of laminates is considered by implementing an accurate stress transfer model, namely, variational approach. A ply-level homogenization methodology is introduced to predict accurately the effective in-plane and out-of-plane properties of a damaged ply. To predict ply cracking initiation and propagation, a multiaxial energy-based framework is introduced formulated based on intrinsic material properties. The methodology is implemented in conjunction with a strain-based fibre failure criterion to predict the effects of stacking sequence and ply thickness on laminate strength. The effect of different modelling features (e.g., thermal residual stresses and statistical distribution of fracture energies, etc.) on crack initiation and propagation is discussed.

The chapter first introduces a methodology, based on Maxwell’s theory, as a powerful homogenization technique to estimate the effective properties of undamaged multiphase composite materials reinforced with particles having spherical, fibre, spheroidal, or ellipsoidal geometries. The methodology provides, for example, a method of estimating the effective thermoelastic properties of unidirectional plies for input into methods of estimating effective properties in general symmetric composite laminates. Maxwell’s original approach was, however, concerned with the estimation of the effective conductivity of a cluster of uniformly distributed isotropic spherical particles, and his methodology enables this approach to be extended to orthotropic aligned ellipsoidal particles, provided that the principal axes for matrix and particle properties coincide with the directions of the semiaxes of the ellipsoidal particles. Results of this extension have important applications in the fuel cell and batteries fields of application.

The fatigue life of composite laminates is characterized by several hierarchical damage mechanisms interacting at different length scales and synergically causing the loss of stiffness and strength. In this chapter, a framework developed by the authors to predict the damage evolution and the stiffness loss in multidirectional laminates under cyclic loadings is presented. It integrates models and criteria for predicting crack initiation and propagation under multiaxial fatigue loadings, the stress re-distributions and the stiffness loss in the presence of off-axis cracks, and a procedure to predict the crack density evolution. All the models and criteria were developed based on the damage mechanisms observed at the micro- and macro-scales during uniaxial and multiaxial fatigue tests. The comparison between the crack density and stiffness predictions and the available experimental data from the literature revealed the accuracy and the reliability of the proposed approach.

The objective of this chapter is to show the modelling of composite materials at the micro-meso level, involving the nonlinearities associated with the damage that may appear in a composite laminate. The potential damage includes debondings between the fibres and matrix where the initial damage occurs in the weakest lamina of a laminate, and the cracking of the matrix that appears when a debonding abandons the fibre–matrix interface, kinking and penetrating into the matrix. Integrated multiscale models based on the boundary element method are developed, allowing us to analyze the whole laminate in a model while also having the possibility of modelling the damage object of study at the micromechanical level in this chapter. The incidence of the features of the model in the representativity of the results is first analyzed, correlating the predictions with the experimental observations from testing laminates. The models carried out will follow a line of association with particular problems regarding the use of composites, with a special emphasis on the study of the scale effect in composite laminates, emphasizing the correspondence between the model performed to simulate the damage and the actual mechanism of damage that a laminate experiences.