Currently, considerable attention has been directed towards the significant role of the interphase in dictating the mechanical properties of composites. Herein, the mechanical behavior of SiCf/SiC ...composites with two distinct interphases, BN and BN/SiC, was delved into under a three-point bending. Meanwhile, analyses of the damage process and failure mechanism of the composites were conducted using acoustic emission (AE), digital image correlation (DIC), and dynamic mechanical analysis (DMA) methods. The results demonstrated the moderate interfacial bond strength of composites with BN/SiC interphase. Cracks were observed to be repeatedly deflected at the matrix/SiC interphase and fiber/BN interphase, leading to a larger bending strength and a pseudoplastic fracture mode. Ultimately, shear forces led to the failure of the composites. Overall, this study indicates that damage analysis provides a theoretical basis for comprehending potential damage in composites and optimizing interphase design.
•Multi-scale analysis of damage mechanisms using non-destructive testing.•The crack deflection mechanisms of different interphases were analyzed.•The correlation of AE, DIC and DMA test methods in damage monitoring was established.
Two of the most important of the loads exposed to the structures whose construction material is pultruded GFRP are buckling and vibration loads. Therefore, it is crucial to determine the behavior of ...this material against buckling and vibration loads considering the fiber and layer configurations. Pursuant to this goal, comprehensive experimental, numerical and analytical studies have been undertaken. An exact analytical solution based on first order shear deformation plate theory was used for the solution of stability and vibration problems. The virtual displacement principle was utilized herein to derive governing differential equations. Effective material properties of pultruded GFRP composites were obtained by using the mixture rule model. The laminated plate was assumed to be a plate strip in cylindrical bending. The solutions were obtained with an infinite series. On the other hand, a numerical study was conducted by a finite element software, ABAQUS. Burn-out and mechanical tests were performed to determine the mechanical properties of the obtained pultruded GFRP composite specimens. The buckling and modal analysis for natural frequencies tests were utilized to investigate the performance of pultruded GFRP specimens. The experimental findings were compared with the calculated analytical and numerical results, and good conformance was obtained. Macro and micro mechanical damage analyzes were performed to better understand the behavior of the pultruded GFRP composite specimens.
Fiber reinforced polymer (FRP) composite materials produced by pultrusion technique attract the attention of researchers due to their superior properties. Limited studies are available in the ...literature where experimental and theoretical investigations on the FRP composites are carried out together. In this study, the flexure performances of pultruded glass FRP (P-GFRP) composite beams were investigated experimentally and theoretically. Theoretical approaches for flexural analysis of P-GFRP composite beams were developed with the help of variational methods. Kinematic relations of composite beams were defined based on high order shear deformation beam theory. Effective material properties of composite beams were obtained by using mixture rule model. The differential field equations were transformed to functional with Gâteaux differential method. The element matrix with a total of 10 degrees of freedom was obtained by using the mixed finite element method (MFEM). Moreover, classical finite element modeling (FEM) was performed with the help of ABAQUS program. Various beam specimens with different fiber orientations were extracted from the P-GFRP box profile. Tensile and burnout tests were performed to determine the mechanical properties of the obtained P-GFRP composite beam specimens. Three-point bending test was utilized to investigate flexure performance. Kinetic, macro and micro mechanical damage analyzes were performed to better understand the behavior of the P-GFRP composite beams. Experimental results, theoretical solution results and FEM simulation results were compared and numerical values were found to be very close to each other.
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In this study, two methods of CFRP applications were utilized to strengthen the shear deficient beams with circular holes and a comprehensive experimental program consisting of 11 ½ ...scaled specimens was undertaken. The beams with hole diameter (D)/beam height ratio (H) of 0.30, 0.44, 0.64 ratios, symmetrically drilled in shear span were tested under vertical loading. D/H ratio of 0.30 did cause not only a decrease in load carrying capacity but also increased the ductility of the beam. However, significant decreases in load carrying capacities were observed as the hole diameters increase. The load carrying capacity and ductility were significantly improved owing to different CFRP configurations. The fact that the hole diameter and CFRP strengthening method are very important parameters for strengthening is observed. No CFRP strengthening alternative was successful in the beams with a D/H ratio of 0.64. A detailed macro and micro damage analyses are presented.
In the first part of this two-part study, filament wound hybrid composite pipes with various stacking sequences were manufactured and mechanical properties such as hardness, ring tensile strength, ...and burst strength were experimentally investigated. After determining mechanical properties, drilling tests were performed to research machinability characteristics. The second part of the study consists damage analysis and surface quality examination including ring test damage analysis, push-out delamination analysis, borehole damage examination and borehole surface quality. The experimental data suggested that cutting parameters, stacking sequence, and the use of back-up were impactful on the formation and propagation of various types of damages. Especially, the effect of stacking sequence was remarkable. A larger delamination area was formed in Glass-Glass-Carbon (GGC) sample after the ring tensile tests compared to Glass-Carbon-Glass (GCG) and Carbon-Glass-Glass (CGG) samples. In all cases, the utilization of back-up lead to decrease of delamination with 9–40% reduction in surface roughness. When the back-up is not used during drilling, an excessive push-out delamination occurred in all drilling tests. Moreover, CGG samples represented lower push out delamination. In addition, position of the hole depending on the winding angle plays a key role on damage formation and surface quality.
Prefabricated structures supported with purlins are exposed to numerous damages due to the excessive snow loadings as vertical loadings. The thinned regions of the purlins are responsible with the ...failure of the structure since the shear cracks usually initiate at these regions and propagate along with the purlins, and as a result, a total collapse may occur. In this study, carbon fiber reinforced polymer (CFRP) composites with four different configurations (P2–P5) were employed for strengthening prefabricated purlins in order to increase the strength of the purlin against shear damage generated under vertical loading. The load carrying capacities and damage patterns of the purlins were compared. The failure of the reference purlin (P1) was occurred as a shear damage at the thinned regions before reaching its bending capacity. However, the failure characteristic of the CFRP reinforced purlins was dominated by the bending damage and the vertical loading capacity of the purlins were increased up to 59% depends on the CFRP wrapping. Damage analysis of the CFRP composite was also performed. Various damage modes of the structure such as cover separation, air voids, delamination, debonding, fiber bundles breakage, matrix cracks, fiber bundles debonding, fiber breakage and buckling were observed and explained thoroughly.
In this paper, the low velocity impact (LVI) on a quasi-isotropic laminate 45/0/–45/903s (QIL) is studied to predict the deformation response and damage state of the laminate. This stacking of a QIL ...is a benchmark case that results in a “rotating-fan” pattern of delamination damage due to the impact. Drop-tower tests were performed with an impact energy of 25 J and an impactor mass of 7.5 kg. 3D digital image correlation (3D DIC) was carried out to measure the in situ deformation of the laminate. Non-destructive inspection (NDI) including ultrasound C-scanning and X-ray micro computed tomography (micro-CT) were done to characterize the overall damage footprint and the internal detailed damage morphology. The computational model is an extension and refinement of the model developed in Refs. 74,76. Enhanced Schapery Theory (EST) is used as the constitutive model and implemented with a user material subroutine in the commercial code Abaqus. The EST uses Schapery theory for pre-peak damage and the crack band model for post peak failure. The major contributions reported in this paper are as follows; in the experimental study, the damage mechanisms have been illustrated with high-resolution micro-CT scanning, while in the numerical study, the “rotating-fan” pattern, damage-free cone and damage modes interaction have been accurately and efficiently captured with a uniform, non-fiber-aligned mesh.
•A novel non-orthogonal FE model with local stress smoothing technique is proposed.•The spurious stresses in the vicinity of the different material interface of non-orthogonal FE model are ...efficiently eliminated.•The effects of shear angle and local stress smoothing on the compressive mechanical properties and failure mechanisms are obtained efficiently.•The prediction accuracy of pre-deformed 3D woven composites by proposed model is significantly improved.
3D angle interlock woven fabric usually needs to produce pre-deformation to meet the requirements of the complex shape of the target configuration. This cause the internal fabric angle to change, which makes it difficult to predict the mechanical properties and damage evolution. A novel non-orthogonal mesoscale finite element (FE) model considering local stress smoothing is proposed to predict the effective mechanical properties and reveal the damage evolution process of shear pre-deformed 3D angle-interlock woven composites under compressive load. The spurious stresses in the vicinity of the different material interface caused by the stepped block-like voxel boundaries are efficiently eliminated to improve the failure prediction accuracy. The predicted warp directional compressive stress-strain curves are good agreement with that of experiments, and the failure morphologies are verified by Scanning Electron Microscopy (SEM). The validated simulation model is further to investigate the effects of shear angle on the effective compressive stiffness and strength of 3D angle-interlock woven composites in different direction. And the effects of shear pre-deformation and stress smoothing on the damage and failure mechanisms are discussed. This study is great helpful of providing reliable guidance for analyzing and designing the pre-deformed 3D woven composite complex structures, such as aero-engine fan blades.
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In this work, we study the fatigue behavior of a C/SiC composite produced by several cycles of polymer infiltration and pyrolysis (PIP). Fatigue tests were performed with maximum stresses ...corresponding to 60–90% of the tensile strength of the composite. During the fatigue tests, acoustic emission (AE) monitoring was performed and the measured AE energy was utilized to quantify the damage and distinguish possible damage mechanisms. Most of the fatigue damage in the form of matrix cracking, interface damage and fiber breakage occurs in the first cycle. As loading cycles proceeded, damage in form of matrix crack re-opening and interfacial friction constantly accumulates. Nevertheless, all samples survived the run-out of 1,000,000 cycles. After the fatigue tests, an increase of the tensile strength is observed. This phenomenon is associated with the relief of process-induced internal thermal stresses and the weakening of the fiber-matrix interface. In general, the studied material shows very high relative fatigue limit of 90% of its tensile strength.
Spectral method based on Fast Fourier Transforms (FFT) is developed to study the mechanical properties of three-dimensional (3D) braided composites with complex internal microstructures. The ...FFT-based method can calculate the material properties by directly using real microstructure images, which could avoid conformal meshing geometry and assembling stiffness matrix similar as FEM. Combing with damage model, the FFT-based method is used to study the progressive damage of the braided composites. The strength and dominated failure modes of the braided composites obtained by the FFT-based method are also verified by the experimental results. Due to the high computation efficiency, the FFT-based method also has a great potential to be used in multi-scale computation analysis for textile composites.
