mode-I Interlaminar Fracture Toughness Research Articles

Influence of Oxygen/Argon/Nitrogen multi-component plasma modification on interlayer toughening of UHMWPE fiber reinforced composites

The study reveals the influence of glow discharged three gas sources of Oxygen/Argon/Nitrogen plasma modification on interlayer toughening of ultra-high molecular weight polyethylene (UHMWPE) fiber reinforced composite. The failure modes under bending, tensile and interlayer fracture toughness testing were analyzed through acoustic emission (AE) technology. The results showed that Oxygen/Argon/Nitrogen multi-component plasma modified fiber introduced more hydrophilic groups such as hydrogen and hydroxyl groups, and significantly enhanced the binding of fiber and matrix. The GⅠC (Mode-I interlaminar fracture toughness) of multi-component plasma modified composites exhibited increased by 61.67 %, 40.88 % and 18.01 % compared to untreated, Oxygen and Oxygen/Argon plasma, respectively, while GⅡC (Mode-II interlaminar fracture toughness) increased by 38.57 %, 25.57 % and 23.09 %. AE cluster analysis exhibited that multi-component plasma modified composites formed an energy dissipation mechanism dominated by fiber breakage. Additionally, the oxygen, argon, and nitrogen plasma modification have a synergistic effect on interlayer toughening.

An investigation of the impact of functionalized MWCNT reinforcement on interlaminar strength of glass/epoxy composites: a comparative view

ABSTRACT In the present investigation, diverse functionalized states of multi-walled carbon nanotubes (MWCNT) were employed in fabricating glass/epoxy composites, with the MWCNT consistently incorporated at a 0.5 wt.% concentration. These functionalization states included pristine, hydroxyl, amine, and carboxylic conditions, systematically compared against neat glass/epoxy composites. The findings elucidated that all three functionalizations positively influenced the enhancement of interlaminar shear strength, mode-I interlaminar fracture toughness, and mode-II interlaminar fracture toughness properties. Notably, the amine-functionalized MWCNT exhibited superior performance relative to other formulations. The composite reinforced with amine MWCNT demonstrated significant improvements in ILSS, mode-I ILFT, and mode-II ILFT by 41.82%, 37.75%, and 40.93%, respectively. These enhancements are attributed to factors such as the presence of a more functional group, the quantity of individual MWCNT, and the introduction of additional damage mechanisms, including MWCNT pullout and bridging.

Critical thrust force prediction in unidirectional CFRP drilling: An analytical modeling approach

In recent trends, unidirectional carbon fiber laminates have been extensively used in the aviation sector due to their remarkable material properties. Delamination is a major damage introduced during drilling in composite laminates. One of the prime contributing factors for delamination-induced damages is considered as the thrust force. A mathematical model is proposed using an analytical approach for accurate prediction of the thrust force for the last lamina, which experience the most damage. The linear elastic fracture mechanics (LEFM), the classical bending plate theory (CPT) and the theory of elastic behavior of composite lamina are taken into consideration for the proposed analytical model because numerical prediction greatly depends on material properties and the nature of force as well. In the current research, the mathematical equation is proposed based on assumption of combined loading of drill tip and chisel edges for the elliptical delaminated area. The Mode-I interlaminar fracture toughness of unidirectional CFRP (CTC1-FUD160/CT-E556) is experimented with as per ASTM D5528 for better experimental substantiation of the proposed model. When the outcomes of the proposed model are compared with the experiment results and available literature as well, a plausible relationship between the suggested analytical model and the experimental results is found. The result also reveals that the contribution of the drill tip is more profound than the chisel edges of drill bit in drilling operations.

Improving film adhesive joining performance of poly(phenylene sulfide)/carbon fiber thermoplastic composite laminates by plasma surface treatment

The main purpose of this study was to observe the degree of the improvement on the film adhesive joining performance of Poly(phenylene sulfide)/Carbon Fiber (PPS/CF) thermoplastic composite laminates when their surfaces were treated by atmospheric plasma technique. For this purpose, plasma treated surfaces were compared with untreated and the traditional grit-blasted surfaces. Treated surfaces were characterized by various techniques including contact angle, surface energy, surface roughness, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. Then, joining performance of the PPS/CF composite samples bonded by an epoxy-based film adhesive was determined by using three different mechanical tests; single-lap shear strength, mode-I interlaminar fracture toughness energy, and drop-weight impact toughness. Grit-blasting surface treatment increased surface roughness of the specimens enormously (7 times more), leading to mechanical interlocking as the dominant bonding mechanism. Contrarily, plasma surface treatment resulted in formation of chemically reactive sites, thus dominant bonding mechanisms in the film adhesive joining were certain polar interactions and chemical bonding. Mechanical tests pointed out that compared to grit-blasting, plasma surface treatment resulted in considerably higher joint performance regarding interlaminar shear strength (35% more), interlaminar fracture toughness (67% more) and impact toughness (28% more), with the cohesive failure mode. Accordingly, it could be stated that traditional grit-blasting could be replaced with plasma surface treatment applied before film adhesive joining of PPS/CF composite parts in aircraft industry.

Simultaneous enhancement in interlaminar– shear strength and fracture toughness through nano Al2O3 dispersion in glass fiber/IPN multiscale composites

Simultaneous implementation of two polymer hybridisation routes, namely, interpenetrating polymer network (IPN) formation and nanofiller (nano Al2O3) addition, resulted in considerable increments in the mechanical performance of GFRP composites. Improvements of ∼18%, ∼8%, ∼14%, ∼19 %, and ∼29% in flexural strength, tensile strength, interlaminar shear strength (ILSS), critical strain energy release rate (GIC) during mode-I interlaminar fracture toughness (ILFT), and GIIC during mode-II ILFT values of nano-Al2O3 modified composites, respectively, were observed over composite without nano Al2O3. Composite with 0.1 wt.% of nano Al2O3 showed the highest mechanical properties in all the modes of testing except for mode-II ILFT testing, where composite with 0.4 wt.% of nano Al2O3 showed the highest toughness value. The synergy between the constituents and the thermal stability of the composites were analyzed via Fourier transform infrared spectroscopy and differential scanning calorimetry, respectively. Fractography was performed to understand the composites' failure criteria and toughening mechanisms.

On the Residual Stresses and Fracture Toughness of Glass/Carbon Epoxy Composites.

The resistance to delamination in polymer composite depends on their constituents, manufacturing process, environmental factors, specimen geometry, and loading conditions. The manufacturing of laminated composites is usually carried out at an elevated temperature, which induces thermal stresses in composites mainly due to a mismatch in the coefficient of thermal expansion (CTE) of fiber and matrix. This work aims to investigate the effect of these process-induced stresses on mode-I interlaminar fracture toughness (GI) of Glass-Carbon-Epoxy (GCE) and Glass-Epoxy (GE) composites. These composites are prepared using a manual layup technique and cured under room temperature, followed by post-curing using different curing conditions. Double cantilever beam (DCB) specimens were used to determine GI experimentally. The slitting technique was used to estimate residual stresses (longitudinal and transverse direction of crack growth) inherited in cured composites and the impact of these stresses on GI was investigated. Delaminated surfaces of composites were examined using a scanning electron microscopy (SEM) to investigate the effect of post-curing on the mode-I failure mechanism. It was found that GI of both GE and GEC composites are sensitive to the state of residual stress in the laminas. The increase in the GI of laminates can also be attributed to an increase in matrix deformation and fiber–matrix interfacial bond with the increase in post-curing temperature.

Inherent relationship between process parameters, crystallization and mechanical properties of continuous carbon fiber reinforced PEEK composites

High-performance thermoplastic composites have been developed as significant structural materials for cutting-edge equipment in the aerospace and defence fields. However, the internal mechanism of processing parameters on mechanical properties in the manufacturing process of thermoplastic composite structures is still a serious challenge. The purpose of this study is to investigate the process/crystallization/property relationships for continuous carbon fiber (CF) reinforced polyether-ether-ketone (PEEK) composites. The composite laminates are fabricated according to orthogonal experiments via the thermoforming method. The mechanical performance is investigated in terms of crystallization properties and fracture morphology characterizations. Experimental results show that the mechanical performance and crystallization properties of thermoplastic composites are significantly affected by the coupling of processing parameters. The increased molding temperature, pressure, and holding time improve the degree of fiber/matrix infiltration and affect the crystallinity and crystalline morphology of the matrix, which further influences the mechanical properties of the composites. This is reflected in the test results that crystallinity has an approximately linear effect on mode-I interlaminar fracture toughness and transverse flexural modulus. As well as the higher molding temperature can destroy the pre-existent crystals to improve the toughness of the matrix, and the well-defined crystalline structures can be observed when fabricated at higher temperatures and longer periods of holding time.

Vol4 num4-15 X-ray tomography investigation of the use of veils to improve the impact tolerance of thin-ply composite laminates

Interleaving high fibre areal weight veils, typically used to improve the interlaminar fracture toughness and impact tolerance of composite laminates, impairs their tensile and compressive properties. We characterized the mechanical response of a thin-ply quasi-isotropic baseline laminate and laminates interleaved with two types of light (4 g/m2) co-polyamide veil: tension, compression, mode-I interlaminar fracture toughness, impact and compression after impact. X-ray tomography provided comprehensive understanding into the effect interleaving has on the microstructure, impact resistance and fracture process zone of double cantilever beam specimens. The veil fibre diameter was the key-parameter controlling the tensile properties (the veil with thinner fibres avoided resin accumulation at the interfaces and left the baseline tensile properties unaffected). The adhesion between veil fibres and resin controlled mode-I interlaminar fracture toughness (the veil with a suspected higher adhesion deflected crack propagation to the surrounding 0° plies, which enhanced mode-I interlaminar fracture toughness by 43%). Both veils reduced pristine compressive strength by up to 9%; however, the veil with thinner fibres improved CAI strength by up to 28% for impact at 14 J.

Enhancing interlaminar fracture toughness of woven carbon fibre/epoxy composites with engineering thermoplastic and carbon-based nanomaterials

Carbon fibre reinforced polymer (CFRP) composites based upon epoxy matrices containing polyethersulfone (PESU) and/or graphene nanoplatelets (GNPs) and/or multi-walled carbon nanotube (MWCNTs) were prepared by hand lay-up without any solvent. The influence of individual and hybrid toughened particles on flexural properties and mode I interlaminar fracture toughness were examined. The maximum value of normalised flexural strength (858 MPa) was measured for CFRP with PESU toughened epoxy. There are no noticeable changes in flexural modulus between all modified laminates. Mode-I interlaminar fracture toughness of crack initiation (GIc ini) and crack propagation (GIc prop) were enhanced when the matrices of laminates were toughened by whether thermoplastic or carbon-based nanomaterials. The epoxy laminates with 5 %wt PESU and a hybrid ratio of GNP/MWCNT 0.4/0.1 (%wt/%wt) exhibits the greatest GIc ini (228 J/m2) and excellent GIc prop (676 J/m2). Surface fracture revealed that this enhancement is due to the simultaneous toughening mechanism of PESU rich particles (crack deviation, crack pinning, debonding), GNPs (crack deviation), and MWCNTs (pull out). This work also evidences that it is important to introduce similar size of tougheners for improving interlaminar toughness of multifunctional CFRP composites.

Mode-I interlaminar fracture of aramid and carbon fibers reinforced epoxy matrix composites at various SiC particle contents

Abstract The Mode-I interlaminar fracture characteristics of aramid fabric andcarbon fabric reinforced epoxy composites along with the influence of SiC particle content were explored. Double cantilever beam (DCB) tests were performed in accordance with ASTM D 5528 for the purpose of examining the behavior of Mode-I delamination. The results showed that, the adhesion strength of an SiC particle within an aramid/ epoxy composite system was better than that within a carbon/epoxy composite system. The highest values of Mode-I fracture toughness of an aramid fabric/epoxy specimen and a carbon fabric/epoxy specimen were 1391 J × m-2 and 701 J × m-2 with SiC particle contents of 10 wt.-% and 5 wt.-%, respectively. The micrographs from optical and scanning electron microscopes verified the enhancements of Mode-I interlaminar fracture toughness behavior.

Mode-I interlaminar fracture behavior of laminated bamboo composites

Mode-I interlaminar fracture behavior of laminated bamboo composites was characterized by mechanical testing in a bonded double cantilever beam configuration. No obvious fiber bridging was observed during the test. At the front of crack tip, nonlinear response was relatively small and negligible. The failure mode of laminated bamboo composites was mainly governed by brittle fracture. Mode-I interlaminar fracture toughness ([Formula: see text]) calculated using the modified beam theory was 501.08 J/m2. Besides, numerical simulation combined with cohesive elements was used to simulate the mode-I interlaminar fracture behavior. A direct method for the determination of cohesive parameters without recourse to iterative fitting was presented in detail. The applicability and effectiveness of this method for interpretation of the fracture behavior of laminated bamboo composites were verified by comparing numerical predictions with experimental results.

Hybrid fiber metal composite laminate interlaminar reinforcement through metal interlocks

Aircraft and automobile industries are continually seeking high-performance and lightweight solutions. Fiber-reinforced composites in conjunction with metals are being considered in the form of hybrid materials. There is a continuous need for improvement of interfacial bonding between composite layers and metal constituents. In this study, an innovative hybrid fiber interlocking metal hooks laminate (FIMHL) system was developed in which fiber-reinforced thermoset composite, and metal sheets are mechanically bonded together using out of plane hooks stamped in the metal. Process optimization was performed to gain the full benefit of the through-thickness reinforcement. Microstructural analysis showed improved interaction between the metal hooks and the fiber layers which reduced porosity and resin richness. This was reflected in mechanical properties, as tensile and flexural strength of FIMHL was enhanced by 38.5 and 18.8%, respectively, after process optimization. Normalized weight fraction (76.4%) properties of FIMHL also confirmed that the increase in mechanical properties of optimized panel were not only due to increased reinforcement (glass fiber + aluminum) volume fraction but also because of improved metal hooks and fibers interaction. There was no significant effect on lap shear and fracture toughness, as they depend on bend back behavior of the hooks. A bilinear traction-separation model was used to characterize mode-I interlaminar fracture toughness properties, and 4.5% variation was recorded when modeling and experimental values were compared.

Interlaminar mechanical properties of carbon fiber reinforced plastics-thermoformed steel super-hybrid laminates

The synergistic effects of the metal surface treatments and interleaves on the interlaminar mechanical properties of the carbon fiber reinforced plastics (CFRP) composite-thermoformed steel super-hybrid laminates were investigated. Double cantilever beam tests (DCB) show that the Mode-I interlaminar fracture toughness of the laminates can be greatly improved by combining metal surface treatment and inserting interleaf. Among them, the interlaminar Mode-I fracture toughness of the specimens with sandblasting/adhesive film interleaves (GB36#/AF) and sandblasting/epoxy resin interleaves (GB36#/EP) increase by 343% and 129% compared with that of the degreased specimens respectively. In addition, based on the cohesive zone model, the delamination of the CFRP-thermoformed steel super-hybrid laminates was analyzed by finite element method. Finally, to uncover the toughing mechanism, confocal laser scanning microscopy (LSM), contact angle goniometer (CAG) and scanning electron microscopy (SEM) were employed to characterize the surface morphology of the thermoformed steel and the fracture surface of the tested laminates.

Damage monitoring of glass/epoxy laminates with different interply fiber orientation using acoustic emission

This article investigates the effects of interface fiber orientation on the mode-I interlaminar fracture toughness, and the evolution of damage was monitored using acoustic emission technique. The results show that changing the interply fiber orientation improved the fracture toughness and delamination resistance significantly. The GIC initiation fracture toughness was found to increase by 87%, 71%, and 69% for 0°/45°, 0°/90°, and ±45° interfaces, respectively. The improvement in fracture toughness was attributed to the crack path diversion along the interply fiber orientation which offered more resistance to crack propagation. In addition, sentry function was also computed based on the correlation between the mechanical strain energy accumulated in the laminates, and the acoustic energy that propagates by fracture events made it possible to evaluate the delamination resistance. The results show that 0°/45° has high resistance to crack propagation followed by 0°/90°, ±45°, and 0°/0°. Finally, scanning electron microscopic analysis was used to determine the fracture surface in different interply fiber orientation of glass/epoxy laminates.

Enhanced out of Plane Electrical Conductivity in Polymer Composites Induced by CO2 Laser Irradiation of Carbon Fibers

The creation of a hierarchical interface between the carbon fiber (CF) and the epoxy resin matrix of fiber-reinforced polymer (CFRP) composites has become an effective strategy for introducing multifunctional properties. Although the efficacy of many hierarchical interfaces has been established in lab-scale, their production is not amenable to high-volume, continuous, cost effective fiber production, which is required for the large-scale commercialization of composites. This work investigates the use of commercially available CO2 laser as a means of nano-structuring the surface of carbon fiber (CF) tows in an incessant throughput procedure. Even though the single carbon fiber tensile strength measurements showed a decrease up to 68% for the exposed CFs, the electrical conductivity exhibited an increment up to 18.4%. Furthermore, results on laminates comprised of irradiated unidirectional CF cloth, demonstrated an enhancement in out of plane electrical conductivity up to 43%, while preserved the Mode-I interlaminar fracture toughness of the composite, showing the potential for multifunctionality. This work indicates that the laser-induced graphitization of the CF surface can act as an interface for fast and cost-effective manufacturing of multifunctional CFRP composite materials.

Effect of Heating Process on Flexural Strength and Toughness of CFRTP Molded by Multi-layer Press -Investigation on Effect of Residual Stress-

This study investigated the effect of differences in heating process of each mold due to the molding with multi-layer press on changing in mechanical properties of CFRTP. CFRTP specimens molded with 10 pages multi-layer were prepared for 3 point bending tests and DCB tests, ENF tests in order to investigate the different of mechanical properties. The change in the mechanical properties of CFRTP molded by multi-layer press were investigated considering residual stress occurred by differences in heating process of each mold. Average of flexural strength, mode-I interlaminar fracture toughness and mode-II interlaminar fracture toughness of the specimen molded at 5th page were decreased compared with that of 1st page. Assuming the fiber as a rigid and considering the thermal shrinkage of resin, compressive residual stress should be occurred in the fiber since free shrinkage of the resin was constrained. It was considered that the reduction of flexural strength with the failure close to the compression surface was caused due to this additional compressive residual stress. The tensile residual stress also should be occurred in the resin due to constraint of free shrinkage of the resin. The observed reduction of toughness in the resin was also occurred for the procedure of crack propagation. The reduction rate of mode-I interlaminar fracture toughness was much remarkable than that of mode-II interlaminar fracture toughness. Tensile residual stress in the resin was dominant since the mode-I fracture is a crack opening mode.

Halloysite nanotube reinforcement endows ameliorated fracture resistance of seawater aged basalt/epoxy composites

Seawater aging-dominated delamination failure is a critical design parameter for marine composites. Modification of matrix with nanosized reinforcements of fiber-reinforced polymer composites comes forward as an effective way to improve the delamination resistance of marine composites. In this study, we aimed to investigate experimentally the effect of halloysite nanotube nanoreinforcements on the fracture performance of artificial seawater aged basalt–epoxy composites. For this, we introduced various amounts of halloysite nanotubes into the epoxy and the halloysite nanotube–epoxy mixtures were used to impregnate to basalt fabrics via vacuum-assisted resin transfer molding, subsequently. Fracture performances of the halloysite nanotubes modified epoxy and basalt/epoxy composite laminated were evaluated separately. Single edge notched tensile tests were conducted on halloysite nanotube modified epoxy nanocomposites and the average stress intensity factor (KIC) was increased from 1.65 to 2.36 MPa.m1/2 (by 43%) with the incorporation of 2 wt % halloysite nanotubes. The interlaminar shear strength and Mode-I interlaminar fracture toughness (GIC) of basalt–epoxy hybrid composites were enhanced from 36.1 to 42.9 MPa and from 1.22 to 1.44 kJ/m2, respectively. Moreover, the hybrid composites exhibited improved seawater aging performance by almost 52% and 34% in interlaminar shear strength and GIC values compared to the neat basalt-epoxy composites after conditioning in seawater for six months, respectively. We proposed a model to represent fracture behavior of the seawater aged hybrid composite based on scanning electron microscopy and infrared spectroscopy analyses.

On the Crack Quasi-Static Growth

The theoretical model of quasi-static crack growth in the elastic-plastic material under load variation in a wide range. Small-scale yielding is principal assumption and main restriction of proposed theory. The model of crack growth provides for continues and interrelated both the crack propagation and plastic deformation development. The nonlinear first-order differential equation describes the quasi-static process of crack growth. In dimensionless form this equation invariant in respect to geometrical configuration and material. The critical size of the plastic zone is proposed as the characteristics of material resistance which is directly connected with the fracture toughness, but more convenient in practical applications of invariant equation. The demonstration of solution is performed for the double cantilever beam that widely used as the standard (DCB) sample for measurement of the mode-I interlaminar fracture toughness. he short analysis of some properties of solution of the invariant equation and its application is done.

Interleaving light veils to minimise the trade-off between mode-I interlaminar fracture toughness and in-plane properties

Interleaving heavy micro-fibre veils, commonly used to improve interlaminar fracture toughness, severely compromises tensile and compressive properties. To reduce the trade-off, this study interleaved two different types of light (4 g/m2) co-polyamide veils into a thin-ply quasi-isotropic baseline laminate. Sub-micron resolution X-ray micro-computed tomography provided insight into the after-manufacturing state of the veil fibres as well as into the fracture process zone of mode-I interlaminar fracture toughness specimens. The veil fibre diameter was the key parameter in determining the tensile properties (the veil with thinner fibres avoided resin accumulation at the interfaces and left the baseline properties unaffected). Both veils decreased the compressive strength by up to 9%. Mode-I crack propagation was controlled by the adhesion between the veil fibres and resin. Veils fibres with the higher adhesion deflected crack propagation to the surrounding 0° plies, which improved mode-I initiation and propagation interlaminar fracture toughness (by 101% and 43%).

Mode-I interlaminar fracture toughness of flax, glass and hybrid flax-glass fibre woven composites: Failure mechanism evaluation using acoustic emission analysis

The mode-I interlaminar fracture toughness of flax, glass and hybrid flax-glass fibre woven composites was studied by using a DCB test. The acoustic emission signals recorded during the tests and scanning electron microscope images were used to analyse the damage mechanism of each composite. The crack initiation for the flax-fibre laminate needs the highest energy (1079 versus 945 for hybrid flax-glass fibre and 923 J/m2 for glass-fibre laminates). The morphology of the flax fibres, short and bonded together in bundles to manufacture the twill fabric, allows the creation of a larger amount of fibre bridging as the origin of this highest energy. Furthermore, hybridisation of glass fibres with flax fibres in an appropriate combination offers an interesting solution when the toughness of glass fibre composites needs to be increased. More interesting is the considerable advantage of the composite structure weight reduction due to the low flax fibre density.