Delamination Shape Research Articles

Computational modelling and prediction of nonlinear deflection responses of bonded joint component with multiple damage (crack and delamination) – An experimental validation

The present research evaluates the presence of damage, including delamination and cracks, affects the deflection response of an adhesively bonded single lap joint (SLJ). In this study, the numerical analysis is performed for intact and influence of different damages in the adherend of SLJ in the commercial simulation software (ABAQUS). The circular delamination of radius ‘R’ 10 mm and crack having length ‘l’ 20 mm, the radius of curvature ‘Rc’ 0.2 mm are imposed into the laminate adherend using node-to-surface interaction technique. The stability of the simulation model is verified by comparing the deflection values from published results and experimental data. The confirmed simulation model is broadened to examine the impact of design factors (fiber orientation, loading position, delamination shape, crack position and orientation, and delamination position with and without crack) on the deflection response for various overlapping lengths (25, 30, 35, and 40 mm) for final design recommendation. Additionally, the sensitivity analysis was performed using a surrogate model (i.e., variance-based method) by constructing the second-order polynomial function to quantify the influence of damages under the input parameters. The detailed features and multivariate model functions have been analysed for the various damage cases of SLJ.

Improving resistance to embedded delaminations by adding CNTs to epoxy in carbon/(epoxy + CNT) composites

Low-velocity impact on fiber-reinforced polymer (FRP) composites may cause subsurface interface delaminations. In the case of such multiple delaminations, neighboring delaminations may grow and coalesce into larger delamination under post-impact loading. The resistance to such growth is substantially influenced by the strength and stiffness of epoxy resins used in FRP composite laminates. Therefore, the current study attempts to determine how adding carbon nanotubes (CNTs) to epoxy might potentially enhance the resistance to such delaminations. A three-dimensional (3D) finite element analysis has been carried out for laminates having single embedded delamination as well as two neighboring embedded delaminations to determine the interlaminar stresses and strain energy release rate using virtual crack closure integral. Results from the current analysis show that while parameters like shape, size, and relative spacing of delamination influence the growth, however in all the cases, adding CNTs to epoxy significantly improves the resistance to the growth of both single and interacting delaminations. The effect is observed to be more pronounced when the delaminations are closely spaced and tend to coalesce into a large delamination.

Effects of Delamination Shapes, Sizes, Locations, and Boundary Conditions Using Modal Analysis of Composite Structure

Effects of Delamination Shapes, Sizes, Locations, and Boundary Conditions Using Modal Analysis of Composite Structure

Numerical Study on the Effect of Partial Delamination of Thermal Barrier Coating on the Cooling Effect of Turbine Blade

A localized delamination modeling method based on a thin-wall thermal resistance model is developed in this study. Numerical investigations are then conducted with this model to analyze the influence of factors such as the position, area, shape, and depth of localized delamination on blade cooling efficiency. Firstly, the simulation results of two coating modeling methods (the thin-wall thermal resistance model and the direct modeling method) are examined. Then, the overall insulation efficiency of the blade surface with a complete thermal barrier coating is analyzed based on the thin-wall thermal resistance model. Subsequently, the impact of different delamination factors on blade cooling effectiveness is explored. The research results indicate that compared to the direct modeling method, the thin-wall thermal resistance model has a simulation deviation of less than 7% and can effectively improve modeling and simulation efficiency while ensuring computational accuracy. The highest insulation efficiency of the thermal barrier coating is observed in the middle section of the blade’s back surface near the cold air inlet, reaching 8.3%. Under a constant delamination area, the shape of the localized delamination has a minor effect on blade cooling effectiveness. When more delamination occurs in areas with higher insulation efficiency, the impact on blade cooling effectiveness becomes more significant.

Study on the effect of delamination defects on the mechanical properties of CFRP composites

Delamination defects commonly occur during the preparation and utilization of CFRP laminates, which seriously affect the performance and durability. In this paper, finite element models of defective CFRP laminates with different delamination areas, delamination depths, and delamination front shapes were successfully established. Numerical simulation shows that the compression properties of CFRP are remarkably affected by the delamination area and delamination depth. When the delamination area exceeds 100 mm2, the effect on the CFRP compressive properties becomes more significant. In addition, when the delamination depth is below 1 mm, the higher the delamination depth, the more significant the effect on the CFRP compressive properties. On the contrary, the front shape of delamination has a slight influence on the compression performance of CFRP. Additionally, the feasibility of predicting the effect of delamination on the mechanical properties of CFRP laminates using the finite element model was verified by comparing the simulation results with the experimental results. The results of this study provide a theoretical reference for predicting the compressive properties of laminates with embedded delamination.

Theoretical and experimental investigations of crack propagation behavior and delamination in GLARE specimens affected by non-proportional fatigue loadings

In actual operation conditions, the structural parts of automotive, aerospace and other significant industrial applications undergo the multi axial fatigue loading with non-proportionality states. Fiber metal laminates (known as FML) are the best options to manufacture these structural parts. The current study examines the effects of a specific condition of multi-axial fatigue loadings (repeated tension with static shear stresses) on the behaviors of crack growth and delamination in GLARE specimens (abbreviated of glass laminates aluminum reinforced epoxy). Analytical model with idea of maximum tangential stress criterion modification has been adopted to represent the non-proportionality state of fatigue loading. Paris equation, equivalent stress intensity factor range, fiber-bridging effects and delamination shape were included in this model. The current idea was compared with a previous idea that depends on the principal stresses in representation of non-proportional multi-axial fatigue loadings. Specimens have coding GLARE_2A 2/1 were fabricated by VARTM technique (vacuum assisted resin transfer molding technique). Special treatments have been done on the aluminum surfaces before specimen fabrication to increasing delamination resistance. Novel fatigue apparatus was manufactured to guarantee apply the under study conditions for multi axial fatigue loading and to introduce experimental investigation of crack and delamination growths in GLARE specimens. The obtained results of the current idea were in a considerable agreement with that of the previous idea of the principal stresses. The maximum deviations between analytically extracted results were less than 1% for crack growth, 5.4% for bridging stress, 4.8% for crack opening and 6.3% for delamination growth. Experimentally, the measured results have been compared with analytical results for the purpose of validation. Acceptable matching between results with maximum difference of 7.65% was the important outcome of this study.

Nonlinear Modal Responses of Damaged Shell Structures: Numerical Prediction and Experimental Validation

The nonlinear finite element (FE) modeling approach has been adopted to model and predict the modal responses of the combined damaged (crack and delamination) layered shell structures. The damaged panel structure has been constructed mathematically using a circular meshing approach of the FE technique to include the crack. Similarly, the sublaminate approach has being used to introduce delamination of the layered structure on a mutual center. The structural distorted geometry and the deformations were modeled through the full geometrical nonlinear strain-displacement (Green–Lagrange) relations in association with higher-order polynomial functions. The modal responses of the damaged structure were obtained through an iterative method in association with the nonlinear FE technique. The predicted response accuracies were established with two-step verifications: that is, the numerical solution stability (elemental sensitivity) and the degree of deviation with published data. The maximum deviation between the developed numerical model and the reference result (first-order shear deformation theory) was 8.3%. The model’s competence and responses were compared with experimental data, with and without damages. Finally, new examples have been solved for different structural geometry-dependent parameters (shell configurations, delamination shapes, crack positions/lengths, end boundaries, etcetera) affecting final modal values. A detailed in-depth understanding of the damage and curvature (unequal/equal curvature) effects on modal responses will be discussed.

Numerical prediction of critical thrust force during drilling in polymer composites – A review

In a numerus study, it has been seen that more than 55% of parts might be declined during final assembly of polymer composite application because of delamination induced damages. Laminate quality, thrust force and drilling conditions are key factors associated with delamination. It has been seen that thrust force assumes an essential factor in the acceptance of the component and no delamination takes place below critical thrust force (CTF). Therefore, to obtain delamination free drilling, CTF can be exploited as a lucrative tool. In this paper, numerical prediction of different CTF models for drilling have been reviewed in depth for circular and elliptical delamination damage. Along with that loading conditions of drilling tool like concentrated loading (PL), distributed loading (UDL) and uniformly varying loading (UVL) have been considered in this state-of-art review paper. This paper highlights the importance of delamination shape and loading pattern for prediction of the CTF during drilling operation. This common review on numerical prediction of CTF is not only up to the date comprehensive summary from available literature but it also directs new aspiring researchers to iterate a new feasible mathematical forecast close to the actual CTF for delamination free composite materials.

Glass laminate aluminum reinforced epoxy under non-proportional multiaxial fatigue loading: Experimental testing and new fatigue apparatus development

Predominately, the structures and components in aeronautic, automotive and other important implementations suffer from non-proportional multi-axial fatigue loading. One of the best selected materials to fabricate these structures and components are fiber metal laminates (FML). In this research, fatigue crack-propagation in glass-laminate aluminum reinforced-epoxy (GLARE) specimen under the effect of special case of multi-axial fatigue loading (constant shear with repeated tensile stresses) has been studied analytically, numerically and experimentally. GLARE_2 A 2/1 specimen was fabricated using vacuum assisted resin transfer molding technique after special preparation aluminum surface procedure. New multi-axial fatigue apparatus including mechanical, hydraulic and control systems was manufactured to investigate crack growth experimentally. Analytical model using Paris relation was adopted to predict crack growth through aluminum layers of GLARE specimen. The rate of crack propagation is related to the mixed-mode equivalent stress intensity factor, which is estimated by the superposition for both fiber-bridging and far-field stress intensity factors. The crack opening contour, distribution of fiber-bridging stress, delamination growth and its shape were evaluated in simultaneous manner to find the fiber-bridging stress intensity factor. ABAQUS 2021 software has been used to simulate crack and delamination growth in GLARE specimen with the aforementioned fatigue loading. The extracted results from analytical and numerical models such as crack growth, crack opening, delamination shape and crack angle have been compared with that measured experimentally. The comparison indicates that there is good agreement between the calculated and measured results (with maximum deviation of 8.74% for crack growth).

Lamb wavefield-based monogenic signal processing for quantifying delamination in composite laminates

Delamination is one of the common damages affecting the safety of composite structures. In this paper, a Lamb wavefield-based monogenic signal processing algorithm is proposed to quantify the delamination parameters in composite laminates, including location, size, shape, and depth. A quality-guided fast phase unwrapping algorithm is developed to solve the problem of phase wrapping after Riesz transform-based monogenic signal processing. Then, space distribution of the phase of Lamb wavefield can be extracted for calculating wavenumber distribution, which is related to the structural thickness or delamination depth and can be used for delamination imaging. Simulated Lamb wavefield signals calculated by finite element simulation are employed to evaluate the parameters of delamination in composite laminates. Compared with other traditional methods, the damage identification algorithm based on Riesz transform has excellent identification effect and shorter calculation time. The results show that the algorithm can be used not only for single delamination recognition but also for multi-delamination recognition with good accuracy. In particular, the interaction between incident waves along different ply directions and delamination is explored, and its influence on delamination quantification is studied, whose results are worthy of attention in engineering application. Finally, a completely non-contact laser ultrasonic system is established to obtain the Lamb wavefield with delamination. Experiments show that the algorithm can accurately quantify the location, size, shape, and depth of delamination.

A numerical study on the effect of delamination on composite cylindrical shells subjected to hydrostatic pressure

This paper deals with the delamination damage and the effect of buckling behavior on delamination propagation of the composite cylindrical shell subjected to hydrostatic pressure. The model of the composite shell with initial delamination and geometric imperfection is elaborated numerically by using the finite element method. The virtual crack closure technique is employed to calculate the strain energy release rate, and the linear fracture criterion is used to determine the onset and growth of the delamination. The buckling deformation and delamination propagation are monitored by performing the nonlinear buckling analysis. In addition, a parametric study is carried out to investigate the influence of the initial delamination shape, area, depth, and ply orientation on ultimate pressure and delamination propagation path. The results show that local or global buckling of the shell promotes the propagation of delamination, and the ultimate buckling pressure of the shell is more sensitive to the axial initial delamination length. The initial delamination shape, depth, and ply orientation have different influences on the ultimate pressure of the shell and the delamination propagation path, and the corresponding explanations are given in this paper.

Investigation of analytical model of crack propagation under multi axial fatigue in fiber metal laminate

Mostly the aerospace and other applications parts during their service life are subjected to the multi axial fatigue with non-proportional loading. In this study, the fatigue crack growth in glass laminate aluminum reinforced epoxy subjected to special case of non-proportional multiaxial fatigue (cyclic tension with constant shear) has been investigated. New prediction analytical model used empirical Paris equation has been adopted. Crack-growth rate was in relation with the equivalent stress-intensity factor for mixed mode at the crack-tip. Bridging stress-intensity factor was superimposed with the far-field stress-intensity factors to evaluate the equivalent stress-intensity factor. Bridging stress distribution, crack opening contour, delamination shape and its growth have been estimated simultaneously to evaluate the bridging stress-intensity factor. The obtained results indicated that there was a considerable enhancement in the crack growth rate (193.8%), number of cycles required to full failure (192%) and other performance characteristic as compared with the monolithic aluminum. Numerical simulation by ABAQUS 2021 software has been implemented to verification of the analytical model. A significant convergence in behavior between the extracted results from both analytical model and numerical simulation with maximum deviation reach to 8.2%.

Particle filter-based delamination shape prediction in composites subjected to fatigue loading

Modeling generic size features of delamination, such as area or length, has long been considered in the literature for damage prognosis in composites through specific models describing damage state evolution with load cycles or time. However, the delamination shape has never been considered, despite that it holds important information for damage diagnosis and prognosis, including the delamination area, its center, and perimeter, useful for structural safety evaluation. In this context, this paper develops a novel particle filter (PF)-based framework for delamination shape prediction. To this end, the delamination image is discretized by a mesh, where control points are defined as intersections between the grid lines and the perimeter of the delamination. A parametric data-driven function maps each point position as a function of the load cycles and is initially fitted on a sample test. Then, a PF is independently implemented for each node whereby to predict their future positions along the mesh lines, thus allowing delamination shape progression estimates. The new framework is demonstrated with reference to experimental tests of fatigue delamination growth in composite panels with ultrasonics C-scan monitoring.

Relationship between Delamination Shape and Compression after Edge-on Impact Strength of CFRP Laminates

Relationship between Delamination Shape and Compression after Edge-on Impact Strength of CFRP Laminates

Numerical frequency and SERR response of damaged (crack/delamination) multilayered composite under themomechanical loading: An experimental verification

This research predicted the influences of combined damage (delamination and crack) and thermomechanical loading on the modal values and strain energy release rate (SERR) of the curved shell panel. The results are obtained computationally using a computer code (MATLAB platform) with the help of isoparametric finite element (FE) steps and the higher-order deformation polynomial. The Hamilton principle is adopted to obtain the final governing equation for the frequency analysis of the damaged structure. Additionally, the deflection, strain, and stresses are recorded by back substituting the numerical solutions to compute the desired energy values. The obtained solution accuracy and the stabilities are verified by performing the convergence and the comparison (published frequencies and SERR) studies. Moreover, a few lab-scale modal experimentations (cracked laminated composite with and without temperature increments) are carried out to accomplish the proposed model. Lastly, a series of numerical examples related to the SERR and modal responses of the current damaged curved composite structure is solved by considering the geometrical, material, and damage parameters (shape and sizes of delamination and orientation of crack). The SERR values calculated using the virtual crack closure technique. The pointwise comprehensions related to the inputs and the model are envisaged in details.

Precise damage shaping in self-sensing composites using electrical impedance tomography and genetic algorithms

Fiber-reinforced composites with nanofiller-modified polymer matrices have immense potential to improve the safety of high-risk engineering structures. These materials are intrinsically self-sensing because their electrical conductivity is affected by deformations and damage. This property, known as piezoresistivity, has been extensively leveraged for conductivity-based damage detection via electrical resistance change methods and tomographic imaging techniques such as electrical impedance tomography (EIT). Although these techniques are very effective at detecting the presence of damage, they suffer from an inability to provide precise information about damage shape, size, or mechanism. This is particularly detrimental for laminated composites which can suffer from complex failure modes, such as delaminations, that are difficult to detect. To that end, we herein propose a new technique for precisely determining damage shape and size in self-sensing composites. Our technique makes use of a genetic algorithm (GA) integrated with realistic physics-based damage models to recover precise damage shape from conductivity changes imaged via EIT. We experimentally validate this technique on carbon nanofiber (CNF)-modified glass fiber-reinforced polymer (GFRP) laminates by considering two specific damage mechanisms: through-holes (as a function of number, size, and location) and impact-induced delaminations (as a function of impact energy). Our results show that this novel technique can accurately reconstruct multiple through-holes with radii as small as 1.19 mm and delaminations caused by low velocity impacts. The reconstructed delamination shapes and sizes were shown to be in much better agreement with the actual delaminations observed using optical microscopy than is achievable by traditional EIT alone. These findings illustrate that coupling piezoresistivity with conductivity-based spatial imaging techniques and physics-based inversion strategies can enable damage shaping capabilities in self-sensing composite structures.

Imaging the delamination in multilayer structure

To achieve the interlaminar delamination imaging of multilayer structures, we proposed a systematic methodology named Integrated Reflected–Transmitted wave-based Imaging (IRTI) by using the interface wave. Based on the interaction mechanism between the interface wave and interlaminar delamination, the first step of IRTI is to extract the interlaminar delamination information. Then, the IRTI designs an appropriate probe layout according to the excitation characteristics of the interface wave. Next, two algorithms are adopted respectively in the IRTI for reflected wave-based imaging and transmitted wave-based imaging. Lastly, the two imaging results are fused to obtain the final result. Furthermore, the effectiveness of the proposed IRTI is verified by experiments on the double-layer plates with delamination. For a rectangle-shaped and the XJTU-shaped delamination with different shape characteristics, the imaging results are legible, and the identified delamination shape is with accurate contour and location.

Selection of an appropriate non-destructive testing method for evaluating drilling-induced delamination in natural fiber composites

Drilling is a principal machining process that is generally operated to make holes in composite parts to join and assemble into a complicated structures. Recently, the use of natural fiber composites (NFCs) has increased in engineering and industrial applications. Choosing an appropriate non-destructive technique to evaluate the drilling-induced delamination in NFCs is a vital and essential task. This paper investigates three different non-destructive techniques for evaluating and determining the size and shape of drilling-induced delamination in NFCs. According to the results from this research, it can be inferred that the image processing technique using a flatbed scanner can be utilized as an accessible, economical, and efficient method for assessment of drilling-induced delamination in NFCs.

Prediction of low‐velocity impact dent for composite laminates based on an anisotropic elastoplastic damage model

AbstractIn this paper, a three‐dimensional finite element (FE) model based on an anisotropic elastoplastic damage model is established to simulate the impact dent of composite laminates subjected to low velocity impact (LVI) by implementing a user‐defined subroutine VUMAT in Abaqus/Explicit. To validate the FE model, numerical results are compared with the experimental data in terms of impact dent depth, contact force‐time response, and projected delamination shape. The simulation shows that considering tension‐compression asymmetry in the elastoplastic constitutive relation has a significant influence on the prediction of dent depth. Besides, it is found that before the knee point, the formation of the impact dent is mainly related to matrix plasticity and damage; while after the knee point, the significant increase of dent depth is caused by fiber breakage on the impact side. The increase of bending stiffness for thicker laminates can decrease the overall deflection, which leads to less fiber breakage and less visible dent.

The effect of preloaded on delamination of composite laminate subjected to low energy impact

The CFRP laminate composite is used widely especially in aerospace industry. The design concern of this type of structure is on its strength under impact loading even under low energy impact. Under low impact loading, delamination occurs and reduce the residual strength of laminate, therefore the necessity to predict this phenomena prior to its utilization. In practice the aircraft structure is subjected to pre-stress loading such as due to aerodynamics loading while in the same time loaded under impact loading due to, for example, birds impact. This paper deals with the investigation on the delamination trend of pre-stressed CFRP composite laminate subjected to low energy and low speed impact. A FE model is proposed and validated using published data. After validation confirmation, 2 types of pre-stressed; compression and tension are used to vary the pre-stress parameter. The pre-stress is modelled by prescribe displacement at both edge of the laminate with 5 different values of −0.01, −0.05, −0.1, −0.15, −0.2 mm for compression and 0.01, 0.05, 0.1, 0.3, 0.5 mm for tension. The FE shows that maximum force during impact increases with pre-stress in compression and decreases in tension. The contact time between impactor and laminate remains constant for pre-stress in tension and increases in compression. The impactor displacement during impact is lower for tension and higher for compression. Delamination area increases regardless whether in pre-stress tension or compression. The same trend of delamination shape evolution during impact is observed both for compression and tension; ellipse evolution in transverse or perpendicular direction to the prestress direction.