Fiber-matrix Interphase Research Articles

Analysis of the fracture behavior and mechanism of PIP-C/SiC composites at high temperatures

The high-temperature fracture toughness of C/SiC composites is of great significance for the tolerance assessment and safety application of components in service. In this work, combining the high-temperature experimental technique and phase field method, the fracture toughness of PIP-C/SiC composites at 25–1600 ℃ in inert atmosphere was tested, and the microcrack propagation at different temperatures was simulated. The fracture model considers the effects of residual stress, temperature-dependent properties of constituents and interfacial graphitization on the crack propagation process. The results show that the fracture toughness and modes of C/SiC composites have significant temperature dependence and difference in in-plane and out-of-plane orientations. As the increase of temperature, the cracks exhibit three typical modes of deflection, penetration and long-debonding at the fiber–matrix interphase. It is worth noting that C/SiC composites show a unique fracture mode at 1600 ℃ with the work of fracture increasing significantly. Overall, the work provides a guidance for the damage tolerance assessment of C/SiC composites in engineering.

Effect of matrix modification and fiber surface treatment on the properties of basalt fiber reinforced polypropylene composites

With a focus on sustainable natural fiber reinforced polypropylene composites in varied industries like automotive and aerospace, this study investigates the impact of matrix modification and surface treatment of basalt fibers on the thermomechanical properties of basalt fiber reinforced heterophasic polypropylene composites. Polypropylene matrix modification was achieved by adding maleic anhydride grafted polypropylene (PP-g-MA), resulting in composites that exhibited a 133 % improvement in the tensile strength and 256 % improvement in the tensile modulus at 30 % fiber weight compared to neat polypropylene. The short basalt fibers underwent a silane treatment; However, the thermal treatment used to strip the default manufacturer's sizing resulted in a fluffy fibres texture, which led to agglomeration and feeding issues during processing. Although the silane treatment helped establish a better fiber-matrix interphase, no significant improvement in tensile strength was observed. However, the tensile modulus saw a 343 % improvement at 30 % fiber weight as compared to neat polypropylene. Resizing short basalt fibers following fiber recovery at the end-of-life stage of the composite would be challenging due to the fluffy nature of the fibers. Therefore, any fiber treatment should be done at the initial fiber manufacturing stage, and surface treatment at later stages requires detailed study.

Nanomechanical characterization of carbon nanotube-based composite interfaces tailored by electrophoretic deposition

Carbon nanotube (CNT) addition to composite materials can offer both nanoscale reinforcement and a multifunctional element due to their extraordinary mechanical, thermal and electrical properties. Electrophoretic deposition (EPD) offers a scalable processing technique to incorporate CNTs into conventional fiber-reinforced polymer composites (FRPCs), facilitating the production of unique nanoscale structures in the critical interphase region. In this study, CNTs functionalized with polyethyleneimine (CNT-PEI) were deposited onto a planar substrate via EPD followed by the infusion of epoxy matrix in order to replicate the nanocomposite interphase region present in nanomodified FRPCs. The nanocomposite films have thicknesses ranging from several hundred nanometers to a few microns to represent different fiber-matrix interphase regions found in FRPCs. The morphology and mechanical performance of CNT-PEI/epoxy nanocomposites are examined using atomic force microscopy (AFM) in both tapping and nanoindentation modes. The EPD creates a homogeneously distributed porous CNT network bridged by PEI, forming the pathway of epoxy resin infusion through interconnected pores with diameters less than 100 nm. CNT-PEI/epoxy nanocomposites exhibited significant improvements in stiffness, hardness, and creep resistance compared to constituent porous CNT-PEI films and neat epoxy. The improvement was directly related to the ability of the load bearing CNTs chemically bonded with the epoxy matrix through the grafted PEI, providing an efficient load transfer mechanism. The chemical bond between the porous CNT-PEI and epoxy also produced far greater fracture surface in nanoscale scratch tests compared to unmodified epoxy, indicating the CNT-PEI/epoxy nanocomposite is capable of distributing load and absorbing more energy prior to fracture.

The synergy of the matrix modification and fiber geometry to enhance the thermo‐mechanical properties of basalt fiber‐polypropylene composites for automotive applications

AbstractBasalt fiber reinforced polypropylene composites with two initial fiber lengths (3.2 and 6.4 mm) were fabricated using twin‐screw extrusion compounding. In the case of composites with smaller initial fiber length, basalt fibers predominantly served as nucleating agents for polypropylene thereby resulting in an increase in the degree of crystallinity. The addition of polypropylene‐g‐maleic anhydride (PP‐g‐MA) caused the matrix to become amorphous, which was due to the establishment of a fiber–matrix interphase. This behavior was different for the composites with relatively larger initial fiber length especially at higher fiber content. The reduction in fiber length in the composites caused a decrease in crystallinity, as this hindered the ability of the polypropylene matrix to form crystals. Addition of PP‐g‐MA established a fiber–matrix interphase thereby synergistically contributing to the increased matrix amorphousness of the basalt fiber reinforced polypropylene composites with 6.4 mm initial fiber length. Reduced fiber length due to processing also accelerated the thermal degradation of the composites with an initial fiber length of 6.4 mm. However, the reduction in fiber length due to processing resulted in increased fiber orientation, which contributed to the improvement in tensile and flexural properties of the basalt fiber reinforced polypropylene composites with an initial fiber length of 6.4 mm. At 30% fiber content, the tensile strength and modulus of basalt fiber reinforced matrix modified polypropylene composites with 6.4 mm initial fiber length improved by 18% and 13% as compared with the composites with 3.2 mm initial fiber length.

Enhancement of the contact behavior of a quasi-isotropic carbon fiber/epoxy matrix laminate with an elastic body by modifying the fiber-matrix interphase using graphene nanoplatelets

This study analyzed the effect of incorporating graphene nanoplatelets in the fiber-matrix interphase on the behavior of a multiscale composite laminate based on carbon fibers and epoxy resin subjected to contact loads. The selected loading mode was the contact between an elastic surface and a cylinder. The multiscale composite material used was a quasi-isotropic laminate with graphene nanoplatelets (GnPs) added at the fiber-matrix interface. The specimens were prepared with 0.0%, 0.1%, and 0.25% by-weight GnPs. Laminate beams were used according to the ASTM D7264 standard, and contact was studied in two configurations, applying the load at the edge of the laminate and in the other, in the plane of the test pieces. The normal strains in the contact region were determined experimentally using the interferometric Moiré technique. These results were compared with estimations using the Hertz contact theory and the finite element method (FEM). The normal strains in the contact area of specimens with fibers modified with 0.1% GnPs were lower than those with 0.25% or fibers without surface modification. Excellent agreement between the experimental results along lines in the contact zone with those estimated with the FEM. The normal strains in a direction perpendicular to the applied load obtained by the Hertz theory for the maximum deformation were slightly higher than those obtained by FEM. Except for those calculated for the normal strain in εy for the load in the direction of the thickness, although the distribution was very similar to those obtained by FEM as well as the experimental one.

Hybrid heterophasic polypropylene composites with basalt fibers and Magnesium oxysulfate reinforcements for sustainable automotive materials

Hybrid heterophasic polypropylene (PP) composites comprising basalt fibers and Magnesium oxysulfate reinforcements were fabricated for the next generation of automobile plastic parts. The prepared composites were tested and characterized for their thermo-mechanical performance. Addition of polypropylene-grafted-maleic anhydride (PP-g-MA) increased the tensile and flexural strength signifying the establishment of an adequate fiber-matrix interphase in case of hybrid composites. While basalt fiber addition played a reinforcing role in all the composites, Magnesium oxysulfate agglomeration and lack of an adequate fiber – matrix interphase reduced the reinforcing efficiency of the hybrid reinforcements at higher Magnesium oxysulfate contents. Nevertheless, the hybrid composites had higher mechanical properties than the neat polypropylene and Magnesium oxysulfate reinforced polypropylene. Hybrid composites offer enhanced mechanical properties, improved impact performance, and increased sustainability, making them a promising choice for the automotive industry.

Hydrothermal aging effect on crushing characteristics of intraply hybrid composite pipes

In this study, the crushing properties of hybrid glass, basalt, and carbon fiber-reinforced composite pipes under a hydrothermal aging environment were investigated. Hybrid and non-hybrid composite pipes manufactured by filament winding technique were immersed in distilled water and seawater at 30 °C for four months. The water sorption parameters of the samples were calculated theoretically and weighed experimentally. Dry and aged pipes were subjected to quasi-static axial compression to examine aging effects on the crushing properties. The experimental weighing results showed that all composites exhibited a Fickian-like water absorption line. The non-hybrid basalt pipes were the most water-absorbing among all groups. In addition, the results proved that the hybridization effect in pipes is highly effective on water absorption parameters. In line with the results of non-hybrid pipes, hybrid pipes containing basalt fiber absorbed more water than other hybrid ones. Additionally, pipes aged in different environments showed that composite pipes absorbed more distilled water compared to seawater. Also, it was found that hydrothermal aging having adverse effects on the crushing characteristics of the pipes led to significant decreases. This can be explained by the degradation of the fiber–matrix interphase due to aging. However, maximum specific energy absorptions were achieved from non-hybrid carbon pipes regardless of environmental conditions. Also, the hybridization enhanced the crushing properties of the non-hybrid pipes that have lower characteristics. Additionally, it can be said that hybrid samples providing better stability in crushing showed better mean crushing load values since they mostly had a progressive crushing mode. The maximum mean crushing loads were obtained from the unconditioned hybrid GC samples as 36.2 kN which was 9.5 % and 34 % higher than unconditioned hybrid CB and BG samples. In conclusion, the study proved that the samples with low crushing properties can be improved by hybridization even if they are subjected to harsh environmental conditions.

Reversible and irreversible effects on the epoxy GFRP fiber-matrix interphase due to hydrothermal aging

Epoxy R-Glass Fiber-Reinforced Polymer (GFRP) composite plates were hydrothermally aged at 60 °C for 23, 75, and 133 days. The water content reached 0.97 wt%, 1.45 wt% and 1.63 wt%, respectively. The studied GFRP matrix was inert to hydrolysis or chain scission, allowing for investigation of irreversible changes in the fiber-matrix interphase due to hydrothermal aging upon re-drying. During each period, a subset of the specimens was removed from the water bath and dried in a chamber. The weight loss upon drying was explained with epoxy leaching (impurities), sizing-rich interphase hydrolysis, glass fiber surface hydrolysis, accumulated degradation products escaping, and water changing state from bound to free. The influence of hydrothermal aging on the fiber-matrix interfacial properties was investigated. Lower interfacial strength of hydrothermally aged (wet) samples was attributed to plasticization of the epoxy, plasticization and degradation of the sizing-rich interphase (including formation of hydrolytic flaws), and hydrolytic degradation of the glass fiber surface. The kinetics of epoxy-compatible epoxysilane W2020 sizing-rich interphase hydrolysis provided an estimate of ca. 1.49%, 4.80%, and 8.49% of the total composite interphase degraded after 23, 75, and 133 days, respectively. At these conditions, the interface lost 39%, 48%, and 51% of its strength. Upon re-drying the specimens, a significant part of the interfacial strength was regained. Furthermore, an upward trend was observed, being 13%, 10% and 3% strength, respectively; thus, indicating a possibility of partial recovery of properties.

Length-scale discrepancy in the properties of epoxy resin specimens

In studies of the fibre-matrix interphase with microscale single fibre methods, the dependence of results on conversion of the thermoset resin – or degree of cure as it is often called – remains an issue. In the microbond method specifically, the curing of picolitre volume drop-on-fibre systems differs significantly from that of macroscale resin batches. The surface-to-volume ratio and vapour pressure can cause volatile components of the resin to evaporate, potentially limiting the degree of cure. Atomistic scale modelling along with experimental thermal analysis were used to understand the curing process and how it translates to resin properties, while nanoindentation was used to experimentally compare the mechanical performance of samples prepared in different length-scales. The evaporation is experimentally verified. Comparable variation in mechanical properties is shown in atomistic scale models of the epoxy network with no evaporation. The origin is in the network morphologies created by varying the curing process. Thus attributing the length-scale discrepancy solely to conversion is likely an oversimplification and understanding the network morphology from different curing conditions is also needed.

CNT coating and anchoring beads enhance interfacial adhesion in fiber composites

The fiber-matrix interface is a critical component in fiber composites, affecting both their strength and toughness. In this study, glass fibers were treated with thin coating of CNT bundles, creating a strong scaffold using evaporation-driven deposition. Epoxy beads were applied to the coating, implementing the Plateau-Rayleigh liquid instability phenomenon. The coated and beaded fibers were embedded in epoxy matrix and subjected to pullout tests, yielding a significant increase of 140% in strength and 400% in toughness, compared to untreated fibers. Electron microscopy and 3D micro-CT imaging elucidated the improvement mechanisms, including strengthening and toughening of the fiber-matrix interphase by the scaffold and anchoring of the epoxy beads. Composites reinforced by such fibers should potentially lead to significant enhancement of simultaneously both strength and toughness. Similarly, the mechanical and electrical properties of flexible functional composites can be enhanced by weaving the coated and beaded fibers into a smart fabric.

Insights into the effect of fiber–matrix interphase physiochemical- mechanical properties on delamination resistance and fracture toughness of hybrid composites

Insights into the effect of fiber–matrix interphase physiochemical- mechanical properties on delamination resistance and fracture toughness of hybrid composites

Carbon fiber/epoxy composite property enhancement through incorporation of carbon nanotubes at the fiber-matrix interphase – Part II: Mechanical and electrical properties of carbon nanotube coated carbon fiber composites

A new method to achieve a uniform coating of carbon nanotubes (CNTs) onto carbon fibers (CFs) has been developed which enables the scalable fabrication of CNT modified CF/epoxy composites. In this method, CNTs are coated onto CFs by immersion into a CNT/water suspension resulting in a uniform coating of CNTs. Unidirectional CF/epoxy composites with the CNT layer of 100–200 nm were fabricated by a prepregging method and mechanical/electrical properties were evaluated. The results show that the compressive, short beam shear strengths and Mode I interlaminar fracture toughness were improved by 22 %, 11 % and 48 % respectively after the incorporation of only 0.39 wt% CNTs. Electrical conductivities in 90˚ and through thickness direction were improved by two or three orders of magnitude (Log Resistivity: 1.24 and 2.31) respectively. These results indicate the importance of designing the fiber–matrix interphase to improve fiber reinforced polymer composite mechanical and electrical properties.

Improved interfacial adhesion of epoxy composites by grafting porous graphene oxide on carbon fiber

The fiber–matrix interphase governs the performance of composites. Herein, porous graphene oxide (prGO) was innovatively employed as active nanoscale reinforcement for the chemical grafting onto the carbon fiber to improve the interfacial adhesion, owning to its large surface area, anti-restacking ability and different chemical functionalities from GO. The obtained prGO/fiber hybrid reinforcement presents 110.4 MPa of interfacial shear strength, respectively 78.64 % and 22.53 % superior to those of untreated fiber (61.8 MPa) and GO/fiber reinforcement (90.1 MPa). The increase is mainly ascribed to the formation of rich interfacial interactions (covalent bonds, electrostatic adherence and hydrogen bonds) in virtue of the synergism of polyethylenimine (PEI), the improved surface energy and the wettability of prGO/fiber with epoxy resin. In addition, a “rigid-soft” transition zone formed by prGO and PEI for stress dissipation also contributes the improvement in interfacial adhesion. The advantages of prGO displayed in this paper provides more access to further gain composites with great interfacial bonding via in-depth and meticulous design of prGO.

Recovery and reuse of carbon fibre and acrylic resin from thermoplastic composites used in marine application

The development of new sustainable routes towards better environmental footprint of composites for marine boatbuilding is motivated by the absence of eco-friendly and economically viable recycling techniques to deal with growing end-of-life thermoset boats waste and increasing restrictive legislation. Thermoplastic composites may offer the possibility to recover raw materials from retired parts, which could have a substantial environmental and economic benefit. This study investigates the feasibility of recovery and reuse of both reinforcement and matrix from a carbon fibre reinforced thermoplastic Elium composite. An original pyrolysis process allowed the depolymerisation of the acrylic matrix and recovery of clean carbon fibres and matrix monomer. Distillation was used to purify the monomer from impurities and a recycled Elium resin was synthesized and reused as matrix with long and aligned recycled carbon fibre reinforcement. The study of the morphological and composition differences at fibre scale resulted in concluding that sizing has been decomposed during depolymerisation process and only small traces of polymer were left on fibre surface. Virgin and recycled resin reinforced with carbon fibre laminates were produced by resin infusion. While tensile modulus, strength and strain at break were nearly unchanged, interlaminar shear strength results showed enhanced fibre-matrix interphase bonding. Dynamic mechanical analysis confirmed the good quality of recovered carbon fibres as well as similar virgin and re-polymerised resin properties. The new composite made from both recycled fibre and matrix could be used in the same application field.

Chemical and physical interactions of regenerated cellulose yarns and isocyanate-based matrix systems

In the development of structural composites based on regenerated cellulose filaments, the physical and chemical interactions at the fibre-matrix interphase need to be fully understood. In the present study, continuous yarns and filaments of viscose (rayon) were treated with either polymeric diphenylmethane diisocyanate (pMDI) or a pMDI-based hardener for polyurethane resins. The effect of isocyanate treatment on mechanical yarn properties was evaluated in tensile tests. A significant decrease in tensile modulus, tensile force and elongation at break was found for treated samples. As revealed by size exclusion chromatography, isocyanate treatment resulted in a significantly reduced molecular weight of cellulose, presumably owing to hydrolytic cleavage caused by hydrochloric acid occurring as an impurity in pMDI. Yarn twist, fibre moisture content and, most significantly, the chemical composition of the isocyanate matrix were identified as critical process parameters strongly affecting the extent of reduction in mechanical performance. To cope with the problem of degradative reactions an additional step using calcium carbonate to trap hydrogen ions is proposed.

Simulated Lamb wave propagation method for nondestructive monitoring of matrix cracking in laminated composites

The estimation of the damping coefficient may help to improve the damage detection in composite materials. The purpose of this study was to develop the simulated Lamb wave propagation method for nondestructive monitoring of matrix cracking in laminated composites via the accurate estimation of their damping coefficient. Cross-ply composite specimens with different crack densities were fabricated and tested by the Lamb wave propagation technique. The phase velocity of the Lamb wave and the damping coefficient of the specimens were measured. The finite element models were developed at micro-scale (representative volume elements) and macro-scale (laminated specimens) levels to simulate the Lamb wave propagation in composite specimens. An optimization process was performed through the model updating procedure to achieve finite element models that were in good agreement with experiments. The phase velocity and damping coefficient, obtained from the updated FE models for two crack densities other than those used in the model updating procedure, were successfully examined by experimental results. It was also revealed that the damping coefficient and the rate of increase in the damping coefficient in terms of the crack density were higher for the composite laminates with a higher number of 90° layers. The damping of the fiber–matrix interphase and crack regions were considered in the model and shown as a significant contribution to the overall damping of the composite specimens. The proposed simulated Lamb wave propagation method can be used as a virtual lab for in-situ monitoring of laminated composites with different material properties, stacking sequences, and crack densities.

Enhancement of the in-plane and pin-load bearing behavior of a quasi-isotropic carbon fiber/epoxy matrix multi-scale laminate by modifying the fiber-matrix interphase using graphene nanoplatelets

The present work examines the effect of incorporating two different concentrations, 0.1% and 0.25%, of silane-functionalized graphene nanoplatelets GnP-GPTMS onto the carbon fiber surface of a quasi-isotropic laminate with the aim to enhance both, the laminate in-plane and the bearing strength, in a pin-loaded joint. Delamination damage modes associated with high-stress gradients were also suppressed in the in-plane loaded laminates, significantly increasing load-carrying capability. The bearing strength of a pin-loaded hole is correlated to the tensile, compression, and shear properties. The results showed an improvement of 13.8% in tensile strength for the 0.1% GnP-GPTMS concentration, as well as 17.3% for compressive strength, while for shear strength, the improvement was 11.89% for the laminate. On the other hand, the behavior of the material in the pin-loaded joint showed an increase of 10.83% for the bearing strength with the 0.1% GnP-GPTMS, fiber surface treatment. Distinct differences were noticed between the tensile stress-loaded area and the area of the residual impression of the pin in the failure mode between the only-resin treated carbon fiber composites and GnPs treated fibers. It was evident, that the interfacial shear strength (IFSS) played an important role on the failure mode. In the compression area in the pin-loaded region, there was a marked presence of a permanent deformation in the matrix. With a closer look at the local failure phenomena at the compression loaded area, there was no fiber kinking and the degree of matrix plasticity disappeared according to the level of interfacial adhesion.

The effect of environmental ageing in the interphase of a glass fibre/vinyl ester composite designed for wind turbine applications

The use of advanced fibre reinforced polymer (FRP) composites in the renewable energy sector has significantly increased over the last decade. However, the durability and damage tolerance of such materials when exposed to environmental conditions still remains under investigation. This creates some uncertainty for their introduction and development in the sector. The scope of the present work is the assessment of the durability of composite laminates and structures through providing a fundamental understanding of the micromechanical performance of the glass fibre/vinyl ester fibre-matrix interphase as a function of the environmental history. An accelerated ageing study has been conducted in order to create a correlation between the moisture sorption at the interphase and its effect in the micromechanical performance of the composite system. The composite interphase performance has been assessed by measuring the Interfacial Shear Strength (IFSS) using the microbond test. An estimation of the moisture sorption of each microbond sample has been obtained by the gravimetric analysis of thin film neat resins specimens of similar thickness to the microbond sample diameter. These results have also been coupled to results obtained by Fourier-transform Infrared Spectroscopy (FTIR). Additionally, moisture induced degradation has been characterised by recording the change in the Tg of the vinyl ester resin as a function of environmental ageing by a number of thermal analysis techniques.

SiC/SiC mini-composites with yttrium disilicate fiber coatings: Oxidation in steam

Solutions of YPO4 were used to precipitate YPO4 on pre-oxidized Hi-Nicalon-S SiC fibers. Tows of the coated fibers were then infiltrated with a preceramic polymer loaded with SiC particles to form mini-composites. During pyrolysis of the matrix, SiO2 and YPO4 on the fibers reacted and formed a Y2Si2O7 fiber matrix interphase. Mini-composites were exposed to steam at 1000 °C for 10, 50, and 100 h, tensile tested, and the effect of oxidation in steam on the functionality of the Y2Si2O7 fiber coating was investigated. The minicomposites oxidized at 1000 °C for 10 h retained 100 % of their unoxidized strength, and those oxidized for 50 and 100 h retained 92 % and 90 % of unoxidized strength, respectively. Strength retention and fiber pullout in both unoxidized and oxidized minicomposites suggests that the Y2Si2O7 interphase was effective in maintaining a weak fiber-matrix interface.

A novel model for quantification of the moisture absorption of polymeric laminated composites

In the present study, a new model was developed that considers the amount of the environmental fluid absorption by different constituents of polymeric laminated composites including fibers, resin, fiber-matrix interphase region, ply interface region, and voids. By knowing the fluid absorption behavior of the composite constituents, the present model can predict the amount of fluid absorption of different constituents of polymeric laminated composites with an arbitrary resin volume fraction and stacking sequence. Test specimens were fabricated by glass fibers and vinyl ester resin. The environmental fluids, examined in this study, were distilled and saline water under different temperatures and salt concentrations. To investigate the absorption behavior of different constituents of polymeric composite, various tests were conducted on fibers, pure cured resin, unidirectional composite specimens, and laminated composites. Based on the results of the tests, a new theoretical model was developed to quantify and predict the amount of fluid absorption of different constituents of laminated polymeric composites. The thickness of the interphase region between the fiber and matrix was also measured using the scanning electron microscope (SEM) images and nano-indentation tests. The consistency of experimental results with the outcomes of the theoretical model indicates the accuracy of the model.