Design And Analysis Of Thin-ply Carbon And E-glass Hybrid Laminates With Pseudo-ductile Property

Thin-ply hybrid composites have been recently adopted to produce high-performance ductile composites.These are composite laminates that avoid a catastrophic failure by developing a plateau before failure known as the pseudo-ductile strain.The favorite materials used in achieving this pseudo-ductile property are hybrid laminates consisting of thin-ply carbon with either standard E-glass or S-glass prepregs.Some initiators are adopted to engineer the pseudo-ductile property in these high-performance thin-ply laminates.These initiators can be either continuous unidirectional thin-ply carbon,partially discontinuous unidirectional thin-ply carbon(platelets),or different orientations of thin-ply carbon fiber.A combination of two of these initiators in a hybrid laminate with glass using a specific lay-up architecture has been reported to have the capability to produce pseudo-ductility.However,the mechanical properties are relatively low.Since this idea provides a vast field for more lay-up design variations,more exploration is required to improve the mechanical properties and still achieve the pseudo-ductile property to avoid catastrophic failures.Hybrid composites(made up of carbon and glass)have widely adopted acoustic emission(AE)as a technique to study their structural behavior under various loading conditions.However,the fiber breakage damage mechanisms from the AE signal are only limited to bulk fiber,which prevents the analysis of the constituent fiber behavior towards failure.Consequently,there are no reports on AE characterization of the signals related to the constituent fibers separately.This finding provides ground for research to distinguish the signals or AE events attached to a specific fiber in a hybrid composite laminate.This breakthrough will significantly assist in studying the contribution of one particular type of fiber to the characteristic stress-strain response of the hybrid laminate.Numerous analytical models have been developed for the prediction of designs that achieve pseudo-ductility in thin-ply hybrid laminates.However,these models are restricted to only two materials in the hybrid.These models either included continuous thin-ply carbon or partially discontinuous unidirectional thin-ply carbon with standard glass as the materials.Therefore,using these models to predict pseudo-ductility in a hybrid containing a combination of continuous and partially discontinuous thin-ply carbon with glass materials is complex.A numerical model is a versatile tool that can predict the stress-strain response of any combination of materials.However,the prediction and analysis of pseudo-ductility in thin-ply laminates has been carried out only on hybrids of two materials,and the models are two-dimensional.Experimental tensile tests on several new architectures to achieve pseudo-ductility with improved mechanical properties were carried out.These hybrid designs included a combination of two initiators dominantly continuous(CC)and partially discontinuous(DC)thin-ply carbon with glass.A combination of continuous unidirectional and ±45° thin-ply carbon plies as the initiators with glass was also included in the designs to explore the field of combined initiators further.The first batch of tests included different lay-up arrangements of the combined initiators.This batch was further analyzed using acoustic emission.Tests from this batch discovered that pseudo-ductility is achieved by dispersing the continuous unidirectional carbon by partially discontinuous carbon layers.A second batch was developed with the lay-up arrangement that produced the pseudoductile properties but with different ratios of continuous to discontinuous carbon layers.The number of glass layers in the second batch was kept constant similar to the pseudo-ductile sample in the first batch.Tensile tests on the second batch samples were coupled with a three-dimensional digital image correlation(DIC)acquisition system and were also numerically predicted and analyzed using Abaqus software finite element analysis(FEA).Prior to these experiments with new designs,tensile tests coupled with an AE acquisition system were carried out on pure carbon,pure glass,and a pseudo-ductile hybrid laminate designed in a previous report.This adopted hybrid laminate design was now prepared using materials in this dissertation.These tests were done explicitly to develop an AE post-processing procedure to separate the signal or events of the constituent fibers in the hybrid and assess their behavior under tensile loading.From the first batch tensile tests sandwiched DC layers with CC layers(H212)achieved pseudoductility with good mechanical properties compared to a sample with similar carbon layer thickness but with CC sandwiched by DC layers(H412).An improvement of 13% on the modulus and 2% on the yield strength was registered.The second batch tensile tests results revealed that pseudo-ductility increases with the increase in DC layers,and pseudo-yield strength and strain increase with the increase in CC layersAn AE post-processing procedure was proposed introducing new derived AE parameters and Cronbach's alpha test in the feature selection process.The feature selection process obtained the desired parameters that enabled signal clustering of the constituent fibers breakage mechanism separately.Moreover,delamination,pull-out,and matrix cracking signals were also captured.Pseudo-ductility was discussed using the clustered AE signals showing the constituent fibers fracture trends towards failure.Furthermore,the AE procedure was used in the first batch of tests,and the damage mechanisms leading to the characteristic failures were discussed.Sentry functions were also derived for the respective damage mechanisms in the first batch samples.The sentry function analysis revealed that the observed bilinear response observed in all the samples was due to fiber damage initiation.A Finite Element model was proposed using Abaqus to predict pseudo-ductility in thin-ply laminates consisting of three materials.These materials comprised continuous carbon(CC)and continuous glass sandwiched by partially discontinuous carbon(DC).The model adopted the Hashin criterion for damage initiation in the fibers and the mixed-mode Benzeggagh-Kenane criterion on cohesive surfaces for delamination initiation and propagation.Numerically predicted stress-strain results were verified with the second batch test results under tensile loading,and they showed good agreement.3D-DIC results indicated delamination growth on pseudo-ductile laminates,and the calculated Poisson's ratios showed pseudo-ductility occurs below 0.27.Moreover,Poisson's ratio decreased with an increase in pseudo-ductility.