Intralaminar Damage Research Articles

Material parameter sensitivity analysis for intralaminar damage of laminated composites through direct differentiation

Material parameter sensitivity analysis for intralaminar damage of laminated composites through direct differentiation

Numerical model of curved composite tiles under low-velocity impact loading

In recent years, composite structures have seen widespread application across diverse industries, including automotive and aerospace, owing to their favourable strength-to-weight ratio. However, these structures, particularly high-pressure vessels, are susceptible to extreme loadings such as impact forces, resulting in visible and latent damage, ultimately leading to catastrophic failures. Hence, it is imperative to assess such damages diligently. Given the cost implications associated with experimental investigations, numerical methodologies emerge as a potent means for conducting relevant analyses. This paper will introduce a numerical model approach to conducting virtual tests to assess curved carbon fibre composite tiles subjected to low-velocity impact. The primary focus of this study is to consider the impact-induced delamination on composite tiles through a numerical model. The composite tiles are conducted to 90J impact loading. Specifically, the study evaluates filament winding structures’ interface properties (shear resistance) variability during manufacturing. Notably, the parameter of shear resistance significantly impacts the anticipation of intralaminar damage (delamination) after impact loading. Three-point bending tests were performed to calibrate the composite material’s shear interface properties, followed by low-velocity impact tests on the curved composite tiles. The findings indicate that the shear resistance values, which ranged from 14.25 MPa to 60 MPa, play a critical role in predicting delamination, with lower shear resistance leading to increased damage areas. The results underscore the importance of accurately calibrating interface properties to enhance the predictive accuracy of numerical models for curved composite structures under impact loading.

Quantitative analysis of the impact of wrinkle defects on the strength of wind turbine blade main spars

Abstract Understanding the impact of wrinkle defects on the main spar of wind turbine blades is crucial for maintaining structural integrity and ensuring operational efficiency. This paper focuses on a quantitative analysis to determine how varying severities of wrinkles affect the structural strength of wind turbine blades. First, the study employed infrared nondestructive testing technology to inspect in-service wind turbine blades, identifying wrinkle characteristics. Based on these detected characteristics, finite element models were established to simulate the structural behavior. The Hashin failure criterion was employed to forecast the initiation of intralaminar damage, while a cohesive model with a bilinear traction-separation criterion was used to evaluate the interlaminar stress state and damage behavior of the laminates. Last, to achieve accurate simulation, a VUMAT subroutine was developed and executed in the ABAQUS software environment. The simulation results for ultimate tensile strength at different ratios of amplitude to wavelength were found to be within 10% of the experimental values. This level of accuracy underscores the reliability of the models used. The study revealed that as the ratio of amplitude to wavelength increases from 0.4 to 0.69, the ultimate tensile strength of the laminate structure decreases to one-fourth of its original value. This significant reduction highlights the severe impact that wrinkle defects can have on structural performance.

Low-Velocity Impact Resistance and Compression After Impact Strength of Thermoplastic Nanofiber Toughened Carbon/Epoxy Composites with Different Layups.

This study investigates the effectiveness of polyether block amide (PEBA) thermoplastic elastomeric nanofibers in reducing low-velocity impact damage across three carbon fiber composite lay-up configurations: a cross-ply [0°/90°]2s (CP) and a quasi-isotropic [0°/45°/90°/-45°]s (QI) lay-up utilizing unidirectional plies, and a stacked woven [(0°,90°)]4s (W) lay-up using twill woven fabric plies. The flexural strength and interlaminar shear strength of the composites remained unaffected by the addition of nanofibers: around 750 MPa and 63 MPa for CP, 550 MPa and 58 MPa for QI, and 650 MPa and 50 MPa for W, respectively. The incorporation of nanofibers in the interlaminar regions resulted in a substantial reduction in projected damage area, ranging from 30% to 50% reduction over an impact energy range of 5-20 J. Microscopic analysis showed that especially the delamination damage decreased in toughened composites, while intralaminar damage remained similar for the cross-ply and quasi-isotropic lay-ups and decreased only in the woven lay-up. This agrees with the broad body of research that shows that interleaved nanofibers result in a higher delamination resistance due to toughening mechanisms related to nanofiber bridging of cracks. Despite their ability to mitigate delamination during impact, nanofibers showed limited positive effects on Compression After Impact (CAI) strength in quasi-isotropic and cross-ply composites. Interestingly, only the woven fabric composites demonstrated improved CAI strength, with a 12% improvement on average over the impact energy range, attributed to a reduction in both interlaminar and intralaminar damage. This study indicates the critical role of fiber integrity over delamination size in determining CAI performance, suggesting that the delaminations are not sufficiently large to induce buckling of sub-layers, thereby minimizing the effect of nanofiber toughening on the CAI strength.

Experimental and numerical investigation of the damage propagation in regularly arrayed short fiber reinforced composite laminates under low‐velocity impact

AbstractThe outstanding mechanical performance and flowability of unidirectionally arrayed chopped strands (UACSs) give them an advantage in the manufacture of engineering structures with complex geometry. For the application of practical structures, the impact responses and damage evolution of material under low‐velocity impact must be investigated in advance. In this study, UACS laminates and continuous carbon fiber laminates with a stacking sequence of [0/90]4s and a thickness of 2 mm were fabricated for low‐velocity impact tests at 7, 11, 15, and 20 J. The impact responses and postimpact intralaminar damage area were analyzed according to the experimental results, including impact load responses and ultrasound C‐scan inspections. Moreover, to predict the damage evolution of the internal structure, the 3D finite element models were constructed in ABAQUS using a progressive damage model (PDM) through a user‐material subroutine VUMAT. Compared with continuous carbon fiber laminates, the dissipated energy of UACS laminates increases by approximately 10.64% and 57.37% for the 15 and 20 J, respectively. However, the intralaminar damage area of UACS laminates decreased by 29.96% and 28.16% at 15 and 20 J, respectively, since the discontinuous slits in UACS laminates can guide damage paths and suppress damage propagation.Highlights The regularly arrayed short fiber reinforced composite was studied. Revealed the low‐velocity impact responses and predicted the damage evolution. UACS and CFRP laminates have comparable impact performance. Illustrated the slits design can suppress the damage to a relatively small area.

Coupled thermal-electrical–mechanical characteristics of lightning damage in woven composite honeycomb sandwich structures

In this study, lightning strike damage of woven carbon fibre-reinforced polymer laminates (W-CFRPs) and woven composite honeycomb sandwich panels (W-CHSPs) are simulated using the proposed sequential thermal-electrical–mechanical finite element (FE) coupling model incorporating dielectric breakdown of materials. Surface current with an amplitude of 200 kA and corresponding lightning shockwave overpressure were applied on each composite. The FE model coupled with LaRC05 criterion was used to study the failure behaviours of intralaminar damage and interlaminar delamination of the W-CFRPs and W-CHSPs. A series of lightning strike tests were performed to validate the FE model. Detailed lightning damage assessments and mechanisms were characterized by a combination of visual inspection, image processing, ultrasonic scanning and micro computed tomography (Micro-CT) and showed good agreements with the FE-predicted results. It can be concluded that shockwave overpressure significantly impacts lightning-induced damages, thereby supporting the effectiveness of the newly proposed sequential thermal-electrical–mechanical coupling model, which demonstrates improved predictive accuracy.

Low-velocity impact resistance behaviors of bionic hybrid-helicoidal composite laminates

The exoskeleton of the Homarus americanus lobster feature a hybrid-helicoidal structure of chitin-protein fibers, with distinct helicoidal configurations in the exocuticle and endocuticle, exhibiting strong impact resistance. Taking inspiration from this biological structure, combined with single-helicoidal and double-helicoidal structures, various helicoidal configurations of composite laminates were designed. Both linear and nonlinear helicoidal angles, including sinusoidal and exponential configurations, were considered. The interlaminar and intralaminar damage mode were adopted to simulate material damage initiation and evolution. The effect of helicoidal angles, position, thickness and angle variations of endocuticle on low-velocity impact resistance was analyzed, revealing the damage mechanisms of bio-inspired laminates. The results show that bio-inspired hybrid helicoidal structures with special features could significantly enhance the impact resistance of composites, with laminates featuring sinusoidal-exponential double helicoidal structures showing superior performance. Sinusoidal configurations, being less prone to penetration, are more suitable for the exocuticle. The introduction of double-helicoidal configurations could enhance the toughness and strength of the structure. This studying deepened an understanding of failure mechanisms of bio-inspired helicoidal composite laminates under low-velocity impact and provide a design strategies for developing high-performance, impact-resistant composite materials.

Combined loading of unreinforced and Z-pin reinforced composite pi joints: An experimental and numerical study

Blind predictions of experimental responses of non-reinforced and z-pin reinforced composite pi joints were established using a progressive damage and failure model. The finite element model used a novel mixed-mode cohesive formulation to model intra-laminar and inter-laminar damage. A deliberate meshing strategy was used for cohesive interlayers to capture the interaction between intra- and inter-laminar damage modes. A smeared cohesive zone modeling approach was implemented to efficiently include the effects of z-pinning for the z-pin reinforced specimens. Using material properties obtained through experimental correlation of simpler joint configurations, blind predictions for large element specimens subjected to combined loading (axial compression and push-off loading) were established. To assess the predictive capabilities of the model, experimental and numerical comparisons were made in terms of load-displacement response, critical loads, and failure progression. Comparisons between the experimental results and predictions for the unreinforced joints were found to be in good agreement across the range of compressive loads tested. For the z-pin reinforced joints, initial responses were accurately predicted; however, ultimate loads and the toughening effect of the z-pin reinforcement was overpredicted.

Comprehensive investigation on modelling of low-velocity impact damage response of composite laminates − Experimental correlation and assessment

Low velocity impact (LVI) experiments are performed to provide correlations with the simulation results based on numerical modeling of the intralaminar matrix damage and interlaminar delamination damage of composite laminates. The good agreement between the numerical simulation and experimental results provided validation of the numerical modeling approach. The validated numerical modeling is then used in the parametrical assessment of the influence of material properties and model- related parameters on the global LVI deformation responses and the evolution characteristics of the intralaminar and interlaminar damage. It is observed that the element deletion method is not suitable to resolve the element distortion problem induced by the progressive damage. The numerical convergence problem caused by element distortion can be resolved with appropriate selection of threshold value of the critical damage parameter without element deletion. The parametrical numerical investigations showed that the variations of material properties and parameters related to interlaminar damage exhibited significant influence on the LVI global deformation responses and progressive damage evolutions. Meanwhile, insignificant influence of the material properties related to the intralaminar damage was observed for the normal variations within material scatters.

Impact morphology characteristics and damage evolution mechanisms in CFRP laminates for hydrogen storage cylinders

In instances of impact, the preeminent load-bearing framework for on-board hydrogen storage cylinders manifests in the carbon fiber reinforced polymer (CFRP) composite layer. Investigating the morphology of impact and elucidating the mechanism governing damage evolution in CFRP is crucial for optimizing the impact resistance of the cylinder. In this work, impact tests were performed on CFRP laminates with six types of interlaminar mismatch angles, under varying impact energies. The impact damage of laminates was characterized using an extended depth-of-field 3D microscopy. A numerical model, implemented in ABAQUS/Explicit, was devised to scrutinize the mechanical properties and damage mechanisms in laminates. A subroutine (VUMAT) was crafted to effectively predict intralaminar damage, while the application of a bilinear cohesive model served to capture interlaminar damage. In addition, this study delves into the ramifications of impact energy and interlaminar mismatch angles. The results reveal that the increase of impact energy leads to more irreversible damage and energy dissipation within laminates. Compared to damage depth (D) and cross-sectional area (Ac), the assessment of damage volume (V) and surface area (As) are more reflective of energy dissipation in laminates. The laminates with mismatch angle of 0° and “helicoidal” lay-up sequence exhibit the worst impact resistance. Within the range of 24°–90°, laminates with a smaller interlaminar mismatch angle demonstrate better impact resistance. These findings lay the groundwork for optimizing the composite layer to enhance the impact resistance of hydrogen storage cylinders.

Mesoscale Model for Composite Laminates: Verification and Validation on Scaled Un-Notched Laminates.

This paper presents a mesoscale damage model for composite materials and its validation at the coupon level by predicting scaling effects in un-notched carbon-fiber reinforced polymer (CFRP) laminates. The proposed material model presents a revised longitudinal damage law that accounts for the effect of complex 3D stress states in the prediction of onset and broadening of longitudinal compressive failure mechanisms. To predict transverse failure mechanisms of unidirectional CFRPs, this model was then combined with a 3D frictional smeared crack model. The complete mesoscale damage model was implemented in ABAQUS®/Explicit. Intralaminar damage onset and propagation were predicted using solid elements, and in-situ properties were included using different material cards according to the position and effective thickness of the plies. Delamination was captured using cohesive elements. To validate the implemented damage model, the analysis of size effects in quasi-isotropic un-notched coupons under tensile and compressive loading was compared with the test data available in the literature. Two types of scaling were addressed: sublaminate-level scaling, obtained by the repetition of the sublaminate stacking sequence, and ply-level scaling, realized by changing the effective thickness of each ply block. Validation was successfully completed as the obtained results were in agreement with the experimental findings, having an acceptable deviation from the mean experimental values.

Effects of drilling-induced defects on tensile damage evolution of CFRP laminates

The reliability and service safety of composite structures are compromised by drilling defects on carbon fiber reinforced polymer (CFRP) materials. However, the synergism effect of different types of drilling defects on the mechanical behavior of structures remains unclear. To address this gap, this study focuses on investigating the intralaminar and interlaminar tensile damage evolution response of open-hole CFRP laminates while considering drilling quality. A model is developed, incorporating drilling delamination and tearing defects using the LaRC05 failure criterion and extended finite element method (XFEM). The model implemented in Abaqus/Standard software and the UDMGINI user subroutine is validated through experimentation. Subsequently, three types of open-hole CFRP laminates with typical drilling defect factors are subjected to tensile failure analysis. The results show a notable decline in the mechanical performance of CFRP laminates when drilling defect factors exceed certain levels. Moreover, a progressive damage evolution pattern is analyzed for open-hole CFRP laminates with respect to ply stacking sequences. The interaction between interlaminar delamination propagation and intralaminar crack evolution paths is discussed, highlighting that the concentration of in-plane shear stress primarily influences the location of crack initiation in CFRP laminates.

Numerical study on the heat effect on the drilling damage of Ti/CFRP stacks

AbstractCarbon fiber reinforced plastics (CFRP) has strong sensitivity to temperature, as the stacking sequence is titanium alloy (Ti) to CFRP, the damage of CFRP is more severe due to the accumulation of cutting heat. In this study, a stress‐strain constitutive model of CFRP with the effect of thermal stress is proposed. On the basis, a simulation model of drilling Ti/CFRP stacks is established to explore the heat effect on the drilling damage. Based on the results, it can be concluded that the burr of Ti at hole exit is generally low due to the support of CFRP, and the burr height increases by 56.61% as the temperature rises from 182.02 to 355.69 °C. Besides, the intralaminar damage of CFRP is mainly caused by the fiber tensile failure and matrix tensile failure, and the matrix tensile failure is more affected by temperature. Moreover, delamination of CFRP decreases slightly with the reduce of drilling temperature. In addition, serious damage of CFRP on the hole wall usually occurs within the cutting angle of 90° to 135°, and pit defects can be reduced in a lower drilling temperature.Highlights A thermal effect stress‐strain constitutive model of CFRP is proposed. Ti/CFRP drilling model is developed based on the proposed constitutive model. Fiber and matrix tensile failure are main form of intralaminar damage of CFRP. Matrix tensile failure is more sensitive to temperature.

Impact response of semicylindrical woven composite shells: The effect of stacking sequence

The existing literature extensively explores the influence of stacking sequences on symmetric flat laminates subjected to low-velocity impacts. However, this is not true in the case of curved laminates. Therefore, the main goal of this study is to analyse the effect of stacking sequences on the impact response of semicylindrical woven composite shells. For this purpose laminates with [0]8, [45]8, [＋15,−15]2S, [＋22.5,−22.5]2S, and [＋30,−30]2S, were considered in order to evaluate the impact response of layer orientations. Additionally, laminates with [02, 452]S, [0,45]2S, [0,452, 0]S, and [452, 02]S were employed to analyse the effects of changing the positioning of the layers in relation to the laminate mid-plane. The FE model was validated with the experimental results obtained for [0]8 laminates, where good numerical–experimental correlation was obtained. The findings suggest that an increase in impact bending stiffness (IBS) leads to a rise in maximum force, accompanied by a decrease in maximum displacement, contact time, and dissipated energy. The primary mechanism responsible for dissipating the majority of impact energy is intralaminar damage, followed by delaminations and friction. Importantly, changing the layer positions has a significant impact on how each layer within the semicylindrical quasi-isotropic composite shell distributes and dissipates energy during the impact event.

Fracture mechanism of carbon fiber-reinforced thermoplastic composite laminates under compression after impact

Thermoplastic carbon fiber-reinforced plastics (CFRPs) are increasingly utilized in the aerospace industry owing to their beneficial properties and enhanced formability relative to thermoset CFRPs. Despite the extensive use of these materials, studies focusing on compression after impact (CAI) tests with impact energies exceeding 20 J for thermoplastic CFRPs remain scarce. This study examines CAI tests on quasi-isotropic laminates of thermoplastic CFRP, subjected to a low-velocity impact energy of 27.04 J. For comparison, quasi-isotropic laminates of thermoset CFRP were subjected to a low-velocity impact energy of 36.5 J. These tests reveal that the CAI strength of both materials is comparable, notwithstanding the lower fiber volume fraction in the thermoplastic CFRP. Further, this research incorporates a finite element (FE) analysis to investigate the damage mechanisms in thermoplastic CFRP. The FE model, integrating interlaminar damage observed during the impact tests, accurately predicted the relationship between compressive stress and strain, correlating closely with the experimental outcomes. It was observed that both interlaminar and intralaminar damage propagation were constrained until the point of maximum compressive stress. Prior to reaching this maximum, a region of elevated compressive stress in the fiber direction was noted in the 0° layer near the non-impacted side. These findings indicate that the compressive stress in the fiber direction in the 0° layer adjacent to the non-impacted side is pivotal in dictating the final failure, which determines the CAI strength of thermoplastic CFRP laminates.

Damage Assessment of Low-Velocity Impacted Sandwich Composite Structures Using X-Ray Micro-Computed Tomography

Sandwich composite structures offer significant versatility in structural system design but are susceptible to low-velocity impact damage, impacting their structural robustness. This study focused on nondestructive testing, particularly using X-ray micro-computed tomography, to assess damage on these structures, comprised of thin glass fibre reinforced polymer face sheets and a polyvinyl chloride foam core, under low-velocity impacts. Impacts were induced by a constant mass of 5.61 kg, dropped from various heights, generating impact energies between 2 and 22 J. This resulted in varied damage levels, from indentations to full perforations. The X-ray micro-computed tomography technique was chosen for its ability to detect internal damage. However, the system’s efficacy in accurately assessing damage depends on numerous factors like focus-to-detector distance, focus-to-object distance, and spatial resolution of the detector, among others. The system yielded an approximated resolution range of 10–25 μm for a focal spot size of 4 μm and the resolution range of 11–26 μm for a spot size of 7 μm. To this end, the system was able to reveal damage inflicted across the specimen through captured and reconstructed images. The quality of the reconstructed images was validated using ImageJ2 software by comparing with the processed images. The median filter was found to deliver images that closely resembled the original ones, albeit with a slight reduction in quality. Damage types varied based on impact energies. Low-level impacts caused matrix cracking and delamination at the foam interface. Medium-level impacts led to intralaminar and interlaminar damage, fibre fractures, and significant damage to the foam core through shearing and crushing. High-level impacts resulted in near or full perforations, with more pronounced delamination at the bottom interface, and fibre fractures in the impact zone, displaying a distinctive diamond-like damage pattern. These findings can be instrumental in developing a predictive impact damage model.

Experimental and numerical investigation on the compression after high-velocity impact behavior of composite laminates

Considering the differences in damage mechanism between high-velocity impact (HVI) and low-velocity impact (LVI), this study conducted HVI tests and compression-after-impact (CAI) tests to reveal the post-impact compression behavior of laminates manufactured by unidirectional prepreg tape and exposed a completely different mechanical response in residual strength compared to that of LVI. By controlling the impact velocity within the range of 200 m/s ̃ 380 m/s, three kinds of impact results were obtained, including un-penetrated and penetrated conditions. Different CAI damage morphologies can be observed in these laminates. In order to fully understand the CAI damage mechanism induced by different HVI events, a surface-based cohesive behavior and a CDM intralaminar damage model were implemented. In addition, a more complete picture of the compression behavior after HVI was observed through the simulation results, which is of great help in estimating the residual strength of post-impact laminates. However, the HVI damage was introduced through the spherical steel projectiles, and the sample size was determined based on ASTM D7137, which might be different factors from the application conditions.

Study on the low‐velocity impact response of the repaired carbon fiber‐reinforced plastic laminates: Bonded versus scarf repair

AbstractExperimental and simulation studies of the response of bonded‐repaired and scarf‐repaired carbon fiber‐reinforced polymer laminates under the low‐velocity impact (LVI) were carried out. The center‐ and eccentric‐repaired laminates were prepared for experiments. The experimental results verify the validity of the finite element model in terms of the force response and different modes of damage. The effect of impact energy and the variation of repair position on the impact response of the laminate was investigated based on the benchmark model. The bonded repaired laminates have higher peak impact forces and lower energy absorption than the scarf‐repaired laminates; the damage of the bonded repaired laminate is mainly intralaminar damage and delamination damage of the patch; the adhesive of the scarf repair is prone to failure, leading to poor impact resistance. The relative positions of the impact point and the patch determine the impact response of a laminate repaired at different locations. The impact point at the edge of the patch has a detrimental effect on the repaired laminate. The impact point vertical position near the bottom hole edge of the parent plate in the scarf‐repaired case harms the impact resistance of the laminate.Highlights The low‐velocity impact response of bonded versus scarf‐repaired laminates was compared. Bonding repairs provide superior impact resistance to damaged laminates than scarf repairs. The risk of adhesive failure in scarf repair is significantly higher than in bonded repair. The relative position of the damage (repair) to the impact point critically influences the impact response. Impacts near the edge of the initial damage hole can cause severe damage to scarf‐repaired laminates.

Predicting damage behaviors of composite laminates under multiple low‐velocity impacts

AbstractIn present investigation, experimental and numerical approaches were combined to investigate the distance between impact positions (DBIP) effects upon impact response and damage accumulation regarding carbon/glass hybrid laminates with multiple low‐velocity impacts. Force/energy‐time curves as well as force‐displacement curves with respect to the laminates with three various impact energies at four different impact positions were obtained from experiment data. Then C‐scans were made to quantify the damage of all the impacted specimens. Additionally, an integrated multi‐impact model was created considering both interlaminar delamination and intralaminar damage. Continuum damage mechanics model (CDM) was developed to calculate the impact resistance regarding laminates under various impact loadings with high efficiency. The simulation and experimental results agreed well. Moreover, the qualitative effects of impact positions on the laminates' mechanical responses were summarized utilizing predictive model that validated.Highlights The effect of the DBIP on the impact response and damage accumulation of carbon/glass hybrid laminates subjected to multiple low‐velocity impacts was studied. An integrated multi‐impact model was developed to predict the impact resistance of laminates under various impact loadings with high efficiency. The qualitative effects of impact positions on the laminates' mechanical responses were summarized using a validated predictive model.

Numerical investigation of the low velocity impact behavior of CFRP laminates

The impact response and failure mechanism of carbon fiber reinforced composite laminates under low velocity impact was investigated using ABAQUS®. A finite element model was developed based on the progressive damage theory to study the impact response of CFRP laminates with hemispherical impactor. The impact tests were conducted on cross-ply (0/90)2s and quasi-isotropic, QI (0/45/-45/90)s laminates with different impact velocities. From the numerical simulation, the damage initiation and propagation in the CFRP laminates were found in terms of damage location, size and shape. The intra-laminar damages such as fiber and matrix damages were predicted using in-built Hashin criterion of ABAQUS®. The traction separation based cohesive surface modelling approach was utilized for capturing the inter-laminar failure initiation and propagation induced by impact loading. The numerical results of different impact energy levels were analysed for different failure modes for varying impact force, displacement and kinetic energy. The total volume of fiber damage and the total area of delamination were calculated for each laminate sequence. From numerical simulations, it was observed that the delamination was less on cohesive surfaces above the mid-thickness plane due to high compression through the thickness. The fiber damage was found at 65 J of impact energy. The first load drop was observed in the cross-ply laminates due to the delamination between lamina 5 and 6. The study revealed that the QI laminates had higher impact resistance and smaller damage zone than the cross-ply laminates.