Fracture Toughness Of Composites Research Articles

The Effects of CTBN on Mechanical and Viscoelastic Viscosity Properties of Epoxy-Silica Nanocomposites

Epoxy resin demonstrates remarkable adhesion, mechanical properties, and heat resistance, however, its inherent brittleness warrants attention. Therefore, hybrid composite was prepared using epoxy resin as the polymer matrix, with carboxyl- terminated butadiene nitrile liquid rubber (CTBN), and nanosilica as the reinforcement materials to increase the mechanical properties. The loading for CTBN and nanosilica are set to (5 wt.%, 10 wt.%, 15 wt.% and 20 wt.%); and (1 wt.%, 2 wt.%, 3 wt.% and 4 wt %.); respectively. The epoxy composites are toughened by adding various loadings of CTBN. Then, fracture toughness and viscoelastic viscosity properties of the composites are measured. At 15 wt.% of CTBN loading, nanosilica are added at different loadings to examine the improvement of composites. Then, fracture toughness (K<sub>IC</sub>), the glass transition temperature (Tg), loss modulus (E”) and storagemodulus (E’) were all measured. Incorporating CTBN into epoxy matrix improves fracture toughness up to 79.4%, with optimum loading of 15 wt.%. Nanosilica content also significantly impacts fracture toughness, with a maximum enhancement of 107.7% at 3 wt.% loading. The glass transition temperature increases with CTBN content, reaching 17.01% improvement at 15 wt.% loading and 18.32% improvement at 20 wt.% loading. Nanosilica is also found to increase glass transition temperature, reaching 74.49°C, at 3 wt.% loading and 83.33°C, at 4 wt.%. The loss modulus increases as CTBN and nanosilica loading increases. At a loading of 20 wt.% CTBN, it reaches a maximum value of up to 164.7%. Adding further 4 wt.% nanosilica to 20 wt.% CTBN, resulted in an increase in loss modulus up to 1600%. The storage modulus also increases as CTBN and nanosilica loading increases to 20 wt.% and 4wt.%, respectively and it reached 1662% from neat epoxy. In conclusion, a combination of 15 wt.% CTBN and nanosilica have increased the fracture toughness and viscoelastic viscosity properties of epoxy composites.

Reinforced High-Entropy Fluorite Oxide Ceramic Composites for Thermal Barrier Coating Application.

High-entropy ceramics hold promise for application as thermal barrier coating materials. However, a key challenge in practical applications lies in the low fracture toughness compared to that of yttria-stabilized zirconia (YSZ). Herein, we designed (Hf,Zr,Ce,M)O2-δ-Al2O3 (M = Y, Ca, and Gd) ceramic composites by following a set of fundamental guidelines. First-principles calculations predicted that the inclusion of Al2O3 in compositions containing the other four binary oxides decreased the propensity for single high-entropy phase formation. Instead, it increased the potential for Al2O3 to form a second phase within the high-entropy ceramic matrix, compared to compositions without Al2O3. Ceramic composites consisting of the Al2O3 second phase in a high-entropy fluorite oxide (Hf,Zr,Ce,M)O2-δ matrix were synthesized in situ via conventional solid-state reactions from the five constituent binary oxides. Both the hardness and fracture toughness of the ceramic composites were enhanced due to toughening mechanisms from the discrete Al2O3 particles, microcracks, and crack deflections. Additionally, the ceramic composites exhibited coefficients of thermal expansion and thermal conductivities comparable with those of YSZ. Our findings demonstrated the potential of the high-entropy (Hf,Zr,Ce,M)O2-δ-Al2O3 ceramic composites for advanced thermal barrier coating materials and offered a possible approach to reinforce other high-entropy oxide-based ceramic systems.

Enhancement mechanism of adhesion strength and mechanical properties of 6H-SiC ceramic matrix composites by graphene

Graphene as a reinforcing phase improves the mechanical properties of ceramic composites. However, an insufficient understanding of graphene on reinforcement mechanisms limits the application of SiC ceramic matrix composite. In the present work, the adhesion work, Mulliken population, and electronic structure of the graphene/6H-SiC (0001) interface are analyzed at the electronic level. The results show that C-I-terminated and Si-II-terminated interfaces have strong bonding strength due to the formation of the typical covalent bond at the interface. Moreover, the combination of strong and weak interfaces could adjust the fracture toughness and adhesion strength of composites. The strong bonding interface with covalent bonds can cause cracks to be deflected and bridged due to the large consumption of fracture energy, while the formation of the weak bonding interface makes the graphene easy to pull out. The present work is of great significance to expand the application range of SiC ceramic composites.

Wear Resistance of B4C-TiB2 Ceramic Composite

The effects of microstructure and mechanical properties on the wear resistance of B4C-TiB2 ceramic composite were studied. The composite was hot pressed from a B4C-TiO2 precursor at a temperature range of 1800 and 1850 °C. Both the relative density and amount of TiB2 secondary phase of the B4C-TiB2 composite increased with the amount of TiO2 sintering additive in B4C-TiO2 precursor. The hardness of the composite increased with a secondary phase portion up to 29.8 vol.% TiB2. However, the positive effect of TiB2 secondary phase on the fracture toughness of B4C-TiB2 composite was measured in the complete experimental range, with the highest average attained value of 7.51 MPa·m1/2. The wear resistance of B4C-TiB2 composite increased with both the hardness and fracture toughness. The best wear resistance was achieved with the composite with a higher hardness value of 29.74 GPa. This sample consisted of 29.8 vol.% TiB2 secondary phase and reached a fracture toughness value of 6.91 MPa·m1/2. The fracture-induced mechanical wear of B4C-TiB2 composite was the main wear mechanism during the pin-on-disc wear test. Transgranular fracture with pullout of the surface and micro-crack formation in the direction perpendicular to the wear direction was observed on the worn surfaces.

Enhancing Mode-I Fracture Toughness of GLARE Composites Through Pre-Crack Insert Film Thickness Variation

Enhancing Mode-I Fracture Toughness of GLARE Composites Through Pre-Crack Insert Film Thickness Variation

Assessment of fiber loading effects on mechanical properties and prediction of mechanical properties via artificial neural networks of hybrid jute /sheep wool epoxy composites

Abstract The primary purpose of this study is to realize the effect of fibre loading on mechanical properties like tensile, bending, impact, interlaminar shear strength and fracture toughness of hybrid composites made of alkaline treated jute and sheep wool hybrid fibres and epoxy. A series of composite laminates were prepared with varying fibre (30%, 40%, 50% and 60%) loadings using hand layup technique. The findings indicated that hybrid composite with equal amount of fiber and resin (JW50) showed a higher strength of 40 MPa against tensile load, maximum strength of 99 MPa against bending load, superior interlaminar shear strength (ILSS) of 3.09 MPa, and a maximum fracture toughness of 72 MPa.m1/2 compared to other fibre loadings. In terms of impact test, JW50 displayed the highest impact strength of 85.98 J/m, underscoring its exceptional capacity to absorb energy compared to other composites. The mechanical strengths of these composites were also predicted using an Artificial Neural Network (ANN) model, which generated accuracy of 87.46% for tensile strength, 86.31% for flexural strength, and 83.52% for impact strength. The absolute percentage errors were found to be 12.53%, 13.68%, and 16.47%, respectively, demonstrating the model’s reliability in estimating composite properties based on fibre content and composition. SEM images of fractured samples under tensile load reveal that higher resin content reduces fibre-matrix bonding, while a balanced fibre-to-resin ratio improves load transfer, but too much fibre leads to debonding due to inadequate resin justifying the experimental results.

Investigation of two sandwich-structured nanohybrid coating derived from graphene oxide/carbon nanotube on interfacial adhesion and fracture toughness of carbon fiber composites

Designing stronger interphase towards solving the long-standing dilemma of interfacial delamination is critical for stable application of carbon fiber composites. Herein, nano-scale sandwich-structured coatings, where carbon nanotubes (CNTs) were uniformly anchored on both sides of graphene oxide (GO) layer (abbreviated as C/GO/C) and its reverse, that is double GO layers encapsulated CNT network (G/CNT/G in short), were reported around fiber periphery via vacuum filtration method. The effects of surface structure differences on interfacial shear strength (IFSS) and fracture toughness were compared in epoxy matrix. Impressively, composite incorporating G/CNT/G modified fiber delivered prominent IFSS and interfacial fracture toughness of 114.6 MPa and 137.0 J/m2, 105.7 % and 279.5 % increases over control fiber composite. This strategy was also superior to C/GO/C and other reported GO and CNT related works. The main factors for maximal IFSS offered by G/CNT/G are that two GO panels enrich active sites to tightly bridge fiber and epoxy, as well as its layered feature and large surface area provide a stable “skeleton” at interphase for stress transfer. Additionally, the G/CNT/G “skeleton” is closer to sandwich structure of iris leaf, in which the porous CNT intermediate network creates larger deformation and adsorb more energy, leading to peak interfacial fracture toughness.

Self-Assembled Polydopamine for Enhanced Fracture Toughness of Carbon Nanofiber-Reinforced Phthalonitrile Composites

Self-Assembled Polydopamine for Enhanced Fracture Toughness of Carbon Nanofiber-Reinforced Phthalonitrile Composites

Indentation Fracture Toughness of Aluminium-Graphite Composites: Influence of Nano-particles

In the field of composite materials, extensive research has been undertaken on aluminum-graphite composites. However, a research gap has been identified regarding the specific influence of nano-sized graphite particles on their fracture toughness. Previous studies have predominantly focused on larger graphite particles or different reinforcement materials, resulting in relatively unexplored effects of nano-graphite particles. This research is deemed critical as it has the potential to generate lightweight, high-strength materials, aligning with the demands of aerospace, automotive, and structural engineering. The primary objective of this study is to investigate how the inclusion of nano-sized graphite particles affects the fracture toughness of aluminum-graphite composites. To achieve this objective, systematic dispersion and incorporation of nano-sized graphite particles into an aluminum matrix will be carried out. Mechanical testing, including fracture toughness assessments, will be conducted to evaluate the performance of the composite materials. Factors such as particle size, distribution, volume fraction, and interfacial bonding will also be characterized within the study. It is anticipated that the presence of nano-sized graphite particles will lead to a significant enhancement of the fracture toughness of the aluminum-graphite nanocomposites. This enhancement is expected to be attributed to crack deflection, tortuosity, altered stress distribution, and increased plastic deformation around cracks.

A rate-dependent crack bridging model for dynamic fracture of CNT-reinforced polymers

Carbon nanotubes (CNTs) improve the fracture toughness of polymer-based matrix composites by bridging the crack growth path. This research presents a finite element (FE) rate-dependent crack bridging model of Mode-I dynamic crack growth in CNT-reinforced polymers accounting for rate of loading and rapid crack growth. Two distinct CNT bridging and matrix cracking damage mechanisms are taken into account in the fracture process zone (FPZ) accounting for the dissipation of fracture energy. A viscoelastic-viscoplastic material model is adapted for the matrix phase to capture the strain rate effects. The crack in the matrix phase is modeled using cohesive zone elements characterized by experimental data. A rate-dependent traction-separation law obtained from CNT pull-out simulation at relevant crack opening speeds is used to simulate the CNT bridging in the FPZ. Considering the given traction-separation law as a constitutive equation, the CNTs are replaced with non-linear spring elements to facilitate the FE simulation of crack bridging with numerous CNTs in the FPZ. The proposed rate-dependent FE model for crack bridging enables the study of the effect of key CNT factors such as length, orientation, waviness, volume fraction, and agglomeration on fracture energy dissipation at various crack speeds. The developed model can simultaneously consider the interactive effects of all CNT parameters which is useful for considering all processing-induced uncertainties in analyzing the effects of CNTs on the dynamic fracture toughness of nanocomposites.

Fabrication and comparison of interlaminar fracture toughness behaviour of glass epoxy composites with recycled milled Kevlar-carbon hybrid fillers

Current research uses a novel recycled milled carbon (rmCF), recycled milled Kevlar (rmKF), and innovative Hybrid fillers (rmHF) of both to increase glass/epoxy composite laminate delamination resistance. This study examines how crack propagation and fibre orientation affect laminated composite delamination fracture toughness. Recycled milled Fillers in the interlayer increase stiffness, delamination resistance, and fracture toughness by increasing the energy needed to crack the interlaminar domain. Here, Mode I, Mode II, and Mixed Mode (I/II) with GIGII = 25 %, 50 % and 75 % were studied for four different Interface fibre orientations. It appears [06/902/06] increased delamination toughness. Adding the novel recycled milled fillers improved delamination resistance. Among the three fillers, rmCF increased fracture toughness by 271 % and rmHF and rmKF composites had 220 % and 182 % higher fracture toughness. The synergy compensated for Kevlar's lower fracture toughness in the hybrid (rmHF). SEM analysis of fractured surfaces revealed crack deflection, individual debonding, and filler/matrix interlocking, all of which increase fracture toughness on different levels.

Translaminar fracture toughness characterisation for a glass fibre/polyamide 6 laminated composite by a novel approach based on fictitious material concept

This paper proposes a novel approach for the characterisation of the material fracture toughness associated with translaminar tensile failure, consisting in the application of the Fictitious Material Concept (FMC) by using the testing configuration of the Modified Two Parameter Model (MTPM). The main advantage of such an approach is to avoid the use of nonlinear fracture mechanics for material fracture toughness characterisation. The novel approach is applied to compute the translaminar fracture toughness of a unidirectional glass fibre (GF)/polyamide 6 (PA6) laminated composite. Moreover, the experimental campaign carried out is numerically simulated by means of a micromechanical finite element model, and the fracture toughness is computed by employing two different approaches, that is, the novel one and the MTPM. The present study proves, for the first time, that the Fictitious Material Concept can be applied by considering both experimental and numerical structural responses since it provides, in both cases, quite satisfactory accuracy in term of laminated composite fracture toughness. Therefore, the great advantage is that, when a validated numerical model is available, experimental campaigns may be avoided, saving time and money. Moreover, it is proved that the FMC can be used to investigate specimen size effect on fracture toughness.

Interlaminar fracture properties of UV and plasma‐treated glass fiber epoxy composites

AbstractDespite the low density and high specific strength properties, the fiber‐reinforced composites are characterized by a relatively low interlaminar fracture toughness and their ultimate properties are strongly affected by the fiber matrix adhesion. This study aims to investigate the influence of fiber surface treatments, such as UV and atmospheric plasma, and of the interfacial shear strength, on the flexural properties and Mode I interlaminar fracture toughness of glass fiber epoxy composites. The vacuum‐assisted resin infusion technique is used for the composite fabrication. Scanning Electron Microscopy analysis is used to observe and to explain the changes in the morphology of the fibers after surface treatment. Remarkably, the results showed an overall reduction in the mechanical properties. The interfacial shear strength values of the UV and plasma‐treated samples were reduced by 34.9% and 49.5% respectively. The flexural strength was reduced by 7.9% and 5.9% respectively. The Mode I fracture toughness values for the UV and plasma‐treated samples were also reduced by 49.8% and 62.2% respectively.Highlights UV and plasma treatments were performed on glass fibers to improve performance. Push‐out tests were carried out to evaluate fiber/matrix adhesion. An aerospace grade epoxy resin curing in thermal press‐clave was used. Mechanical tests related Interfacial Shear Strength to composites performance.

Effective toughness based on Eshelby transformation theory for heterogeneous composites

Predicting fracture toughness of heterogeneous composites is an important and challenging problem in physics and mechanics. The dependence of effective toughness on elastic properties of phases remains unclear. Considering that energy plays an essential role in crack propagation, an energy approach is proposed to obtain effective toughness in this study. We built the relationship between effective toughness and the homogenized local surface energy. The energy is constructed by generalizing Eshelby’s equivalent inclusion formulation to heterogeneous case, which couples physical features with elastic properties. An analytical formula of effective toughness can be derived for heterogeneous composites. Based on this formula, effects of toughness and elastic properties of the phases are discussed in depth, which reveals that how elastic heterogeneity can influence the effective toughness fundamentally. It is demonstrated that the predictions of concretes and metal toughening glasses agree well with experimental evidences.

Exploring the influence of specimen types on the intralaminar fracture behavior of fiber-reinforced polymer matrix composites

The accurate determination of fracture toughness of fiber-reinforced composites is critical for the assessment of structural integrity. Although there have been many studies on the intralaminar fracture behavior of composites, satisfactory results have not yet been obtained regarding the influence of specimen types. In this paper, commonly used fracture specimens (DCT, CT, ESET, pin-loaded SENT and clamped SENT specimen) are applied to study their applicability in the fracture behaviors of composites with different orientations. And the impact of data processing methods for the area method, GC-compliance and GC-stress intensity factors on fracture performance was analyzed. The results showed that the above three data processing methods have obtained relatively consistent fracture properties. Different specimens obtained significantly various results, showing a gradually decreasing trend from clamped SENT, ESET, pin-loaded SENT, CT to DCT. Furthermore, considering that the clamped SENT specimen is closest to the Mode-I fracture toughness obtained from the DCB specimen, and there is no compression damage in the experiments under different orientations, this specimen type is the most recommended specimen. Finally, the failure mechanisms of carbon fiber-reinforced composite under different specimen types and orientations were revealed. As the orientation angle increases (β from 0° to 90°), the failure mode gradually transitions from matrix cracking and interface debonding to matrix shear and fiber fracture. The above achievements will contribute to a deeper understanding of the intralaminar fracture process and failure mechanism of fiber-reinforced composites.

Failure behaviors of cord-rubber composite materials under mixed mode I/II loading: Experimental and numerical simulation

Cord-rubber composites are widely used in automation with their flexibility and high strength. Interlaminar delamination damage is one of the main failure modes of this component during service. Therefore, we investigated the interlaminar delamination behavior of cord-rubber composites under different loading modes. Herein, an analytical method was proposed for determining the mode I and mode II fracture toughness of cord-rubber composites through T-peel and 0-degree peel tests. The interlaminar delamination mechanism of mixed mode I/II for cord-rubber composites was investigated using the cohesive zone model (CZM). Based on the analytical method, the interlaminar delamination failure behavior under mixed mode I/II loading conditions is accurately prediction, and the error is below 14 %. Meanwhile, cohesive failure within the cord fabric layer occurs first, followed by interfacial failure at the interface between the cord fabric and rubber layers.

Determination of Fracture Mechanic Parameters of Concretes Based on Cement Matrix Enhanced by Fly Ash and Nano-Silica.

This study presents test results and deep discussion regarding measurements of the fracture toughness of new concrete composites based on ternary blended cements (TCs). A composition of the most commonly used mineral additive (i.e., fly ash (FA)) in combination with nano-silica (NS) has been proposed as a partial replacement of the ordinary Portland cement (OPC) binder. The novelty of this article is related to the fact that ordinary concretes with FA + NS additives are most often used in construction practice, and there is a decided lack of fracture toughness test results concerning these materials. Therefore, in order to fill this gap in the literature, an extensive evaluation of the fracture mechanic parameters of TC was carried out. Four series of concretes were created, one of which was the reference concrete (REF), and the remaining three were TCs. The effect of a constant content of 5% NS and various FA contents, such as 0, 15%, and 25% wt., as a partial replacement of cement was studied. The parameters of the linear and nonlinear fracture mechanics were analyzed in this study (i.e., the critical stress intensity factor (KIcS), critical crack tip opening displacement (CTODc), and critical unit work of failure (JIc)). In addition, the main mechanical parameters (i.e., the compressive strength (fcm) and splitting tensile strength (fctm)) were evaluated. Based on the studies, it was found that the addition of 5% NS without FA increased the strength and fracture parameters of the concrete by approximately 20%. On the other hand, supplementing the composition of the binder with 5% NS in combination with the 15% FA additive caused an increase in all mechanical parameters by approximately another 20%. However, an increase in the FA content in the concrete mix of another 10% caused a smaller increase in all analyzed factors (i.e., by approximately 10%) compared with a composite with the addition of the NS modifier only. In addition, from an ecological point of view, by utilizing fine waste FA particles combined with extremely fine particles of NS to produce ordinary concretes, the demand for OPC can be reduced, thereby lowering CO2 emissions. Hence, the findings of this research hold practical importance for the future application of such materials in the development of green concretes.

Enhancing interfacial performance and fracture toughness of carbon fibre reinforced thermoplastic composites

Enhancing the interlaminar fracture toughness of composites significantly improves their load bearing capacity and structural integrity over longer service life by improving their resistance to delamination. The effect of hybrid toughening of Elium-based thermoplastic composites involving polydopamine (PDA), multi-walled carbon nanotubes (MWCNTs) sizing, and polyphenylene sulfide (PPS) veil interlayers was investigated to observe the mechanical response using 3-point bending, interlaminar shear strength, and Mode I fracture toughness tests. The enhancement of fibre–matrix adhesion contributed to improvements in both flexural strength and interlaminar shear strength, while additional toughening mechanisms, such as PDA bridging, PPS pull-out and breakage, and fibre bridging, enhanced the Mode I interlaminar fracture toughness by 218%.

Characterization of Fracture Toughness Properties of Coir Fibre Reinforced Polypropylene Composites

This study investigates the production and assessment of fracture toughness in Polypropylene (PP) composites reinforced with different weight fractions of treated and untreated coconut coir fibres. The potential of natural fibres, especially those obtained from agricultural waste like coconut coir, to create lightweight, affordable, and environmentally friendly composite materials has drawn attention. In the study, coir fibres were cleaned and chemically treated with NaOH before being incorporated into PP using injection moulding and extrusion techniques. According to ASTM guidelines, composites with 10%, 20%, and 30% coir fibre concentrations underwent Single Edge Notched Bend (SENB) testing to determine their fracture toughness. The fracture toughness of composites containing 10% and 20% untreated coir fibres was found to be higher than that of pure PP, but composites containing 30% untreated and all treated coir fibres showed reduced fracture toughness. The best composite, with 20% untreated coir, showed the best mix of fibre content and material performance, emphasizing how chemical treatment hurt fibre brittleness and the composites' overall ability to support loads. The potential of untreated natural fibres to improve composite materials for industrial applications- particularly in the automotive industry- is highlighted by this study.

Improving interfacial bonding and impact characteristics of Sandwich composites by interweaving carbon fiber

AbstractSandwich composites consist of two external face sheets and an inner core, offering enhanced strength, stiffness, and weight efficiency. While widely used across industries like construction, marine, automotive, and aerospace, they do have drawbacks such as buckling, low damage resistance, and delamination. This study focused on fabricating two sandwich composite plates using the vacuum infusion method, with PVC foam as the core and glass fiber face sheets and epoxy resin as the binding agent. One plate had carbon fibers interwoven into the core to improve interfacial fracture toughness and low‐velocity impact resistance. Testing based on ASTM standards revealed significant enhancements with the addition of interwoven carbon fibers. The composite with carbon fibers exhibited a 98.26% increase in interfacial fracture toughness and a 22.368% increase in peak force during low‐velocity impact, indicating superior load‐bearing capacity. Moreover, it demonstrated a 2.08% improvement in total energy absorption and a 9.83% increase in total deformation compared to the standard composite material. These findings highlight the effectiveness of integrating carbon fibers into sandwich composites for enhanced performance under varied conditions.Highlights Two sandwich composite sheets were manufactured using vacuum infusion process One sheet consisted carbon fiber interwoven in the core material of the composite Interfacial fracture toughness test was conducted using modified three‐point bend test Low velocity impact test was performed for the two specimens The results of the two tests for both the specimens were compared and evaluated