Toughness Of Composites Research Articles

Cactus-like ZnO decorated UHMWPE fibers to improve the strength and toughness of polyurethane matrix composites

Poor interfacial force is an important factor in preventing the development of fibers reinforced polymer composites. Fiber morphology design is an effective way to improve the interfacial property of composites. The development of nature has carried out the natural selection of survival of the fittest for organisms, and most of the surviving organisms have excellent structures and functions, which comes up with a new idea for the design of new reinforcement structure. Inspired by the cactus structure, we have prepared a new structural UHMWPE fiber reinforcement, which was characterized by a mass of cactus-like ZnO (C-ZnO) crystals decorated the UHMWPE fiber surface. The experimental results showed that the strength and toughness of C-ZnO UHMWPE fibers reinforced rigid polyurethane (RPU) composites were significantly improved. The satisfactory results were attributed to the cactus-like ZnO on the UHMWPE fiber surface, which could form a complex interfacial structure with the PRU matrix to increase the interface strength and the crack expansion paths.

Maximizing Interlaminar Fracture Toughness in Bidirectional GFRP through Controlled CNT Heterogeneous Toughening.

"Interleaving" is widely used for interlaminar toughening of fiber-reinforced composites, and the structure of interleaving is one of the important factors affecting the toughening efficiency of laminates. Several experiments have demonstrated that compared to continuous and dense structures, toughening layers with structural heterogeneity can trigger multiple toughening mechanisms and have better toughening effects. On this basis, this work further investigates the application of heterogeneous toughening phases in interlaminar toughening of bidirectional GFRP. CNT was selected to construct toughening phases, which was introduced into the interlaminar of composites through efficient spraying methods. By controlling the amount of CNT, various structures of CNT toughening layers were obtained. The fracture toughness of modified laminates was tested, and their toughening mechanism was analyzed based on fracture surface observation. The results indicate that the optimal CNT usage (0.5 gsm) can increase the initial and extended values of interlayer fracture toughness by 136.0% and 82.0%, respectively. The solvent acetone sprayed with CNT can dissolve and re-precipitate a portion of the sizing agent on the surface of the fibers, which improves the bonding of the fibers to the resin. More importantly, larger discrete particles are formed between the layers, guiding the cracks to deflect in the orientation of the toughened layer. This generates additional energy dissipation and ultimately presents an optimal toughening effect.

Polyvinyl pyrrolidone mediated exfoliation of transition metal dichalcogenides: Comparative evaluation of exfoliated MoS2 and WS2 in epoxy toughening

Abstract2D materials are considered as an effective choice for the toughening of epoxy composites and enhancing their mechanical properties. Among the 2D materials, transition metal dichalcogenides, especially MoS2 and WS2, are getting wider attention due to their behavior analogous to graphene. The restacking and agglomeration tendency of TMDs due to weak Vander Waal's forces limits their application in epoxy toughening. To overcome the agglomeration issues, we are proposing a new approach for TMD exfoliation using Polyvinyl pyrrolidone (PVP); followed by its incorporation into the epoxy matrix. The exfoliation of TMDs using PVP is characterized by various techniques like FTIR, Raman spectroscopy, XRD analysis, and so forth. The enhanced mechanical properties of PVP exfoliated MoS2 and WS2 at a very low loading of 0.1 wt% are remarkable. The highly exfoliated WS2 showcases higher toughness than MoS2, with a 614% improvement in toughness and 43.5% improvement in tensile strength, respectively. The improvement in mechanical properties of these nanocomposites can be attributed to the good dispersion of PVP‐exfoliated TMDs in the epoxy matrix.Highlights Highlights the role of Polyvinyl pyrrolidone in exfoliating TMDs. The exfoliation efficiency of PVP is compared for MoS2 and WS2. The utilization of PVP exfoliated MoS2 and WS2 in epoxy toughening is portrayed. The effectiveness of epoxy composites in aerospace and coating applications is revealed.

Investigation of fracture behavior and mechanical properties of epoxy composites supported with MWCNTs microscopically

Adding of a multi-walled carbon nanotubes (MWCNTs) to epoxy resin has shown promising results in improving fracture toughness in bulk epoxy and carbon fiber-reinforced epoxy composites (CFRP). using a hand layup proceeding followed by the so called vacuum bagging process method, carbon fiber-reinforced polymer multi-wall carbon nanotubes (MWCNTs) was added to an epoxy resin with a weight percentage mixing of 1% wt., 1.25% wt., and 1.5 % wt. MWCNTs. Furthermore, the specimen underwent analysis via Fourier-Transform Infrared (FTIR) spectroscopy, and X-ray Diffraction (XRD) spectroscopy, the composites were subjected to a microscopic examination using a Scanning Electron Microscope (SEM). FTIR and XRD verified the folding and unfolding of the polymer, in addition, the mechanical properties including tensile strength, bending stress, and impact behavior were investigated as well as the hardness test. The obtained results showed a significant improvement of about (40 %) in tensile strength, (53 %) in bending stress at 1 % wt. MWCNTs, and (70 %) percentage increment in the strength of Impact at 1.25 % wt. MWCNTs. And the gained hardness was about 40.5 HV which were compared with a reference substance named Carbon Fiber (CF) without any addition of nano materials. Carbon nanotubes have demonstrated their potential to enhance the mechanical properties of fiber-reinforced polymers, so this investigative study employs comprehensive characterization techniques, and demonstrates significant improvements in mechanical properties for the modified polymeric composite materials supported with nano materials.

Formation of heterogeneous interfaces in the TiAl/Ti2AlNb layered composite and its effect on the fracture toughness

TiAl/Ti2AlNb intermetallic-intermetallic laminated (IIL) composites featuring brittle/ductile heterogeneous interfaces were fabricated through vacuum hot-pack rolling. The microstructures and the phase transformation behaviors of the interfaces of the IIL composites before and after annealing at 900 °C/6 h were investigated. The heterogeneous interfaces are composed of four distinct regions, individually I (βo+γ+α2), II (βo/B2+ω) (brittle part), III (O lath), and IV (equiaxed O) (ductile part) regions from TiAl to Ti2AlNb side. Notably, after annealing, an equiaxed O band approximately 50 μm wide was observed in region IV of the interface. In addition, a significant microhardness variation was observed between regions II and IV of the interface, where region II exhibited higher hardness compared to the TiAl alloy, and region IV displayed lower hardness than the Ti2AlNb alloy. The enhanced fracture toughness of the IIL composites, three times that of the TiAl base alloy, is attributed to the formation of the brittle/ductile heterogeneous interfaces and the layered design incorporating the Ti2AlNb alloy. The corresponding toughening mechanism was further discussed. The brittle II region plays a role in increasing crack branching, while the ductile IV region inhibits the propagation of microcracks and prevents the formation of main cracks. This work highlights the crucial role of the brittle/ductile heterogeneous interface in the toughening of laminated composites. Furthermore, the discovery of the O band provides novel insights into the design of TiAl/Ti2AlNb heterostructures.

Carbon Fiber Reinforced Recycled Polypropylene/Polyolefin Elastomer Composites with High Mechanical Properties.

The treatment of waste plastics has gradually become a hot topic in the current scientific community. In response to the needs for high-impact performance R-PP-based composites, carbon fiber (CF)-reinforced polyolefin elastomer (POE)/recycled polypropylene (R-PP) composite (CF/POE/R-PP) was prepared by the mechanical blending method, and its mechanical and thermal properties were systematically studied. It was found that the CF could effectively improve the bending and notch impact strength as well as enhance the thermal stability of POE/R-PP. Furthermore, a stable and dispersed composite interface formed by the combination of maleic anhydride-grafted polypropylene (PP-g-MAH) with the surface of CF and the fusion alkyl chains in R-PP and POE further enhanced the CF's reinforcing effect. As a result, the addition of 9 wt.% CF successfully improved the heat resistance of the composite material, and the residual carbon content increased by 97.84% after sintering. The composite toughening of POE and CF effectively improved the impact strength of the composite material, with a maximum increase of over 1000%. This study ultimately resulted in a high-impact-resistant composite material.

The effect of resin properties on toughness translation in interleaved composites

Interleaving is a well-recognized method for enhancing the interlaminar fracture toughness of composite materials. However, theoretical toughness is often not realized since cracks tend to propagate through regions of lower toughness. While most studies have focused on the effect of interleaf properties, e.g., thickness and interleaf resin properties, on composite interlaminar fracture toughness, the effect of matrix resin properties on interleaved composite toughness has been overlooked. Recently, we hypothesized that there is a relationship between toughness translation and the ratio of matrix to interleaf resin toughness. In this work, we use additive manufacturing to test this hypothesis with a range of resins in interleaved composite. Toughness is quantified via mode I delamination resistance. Our results confirm our hypothesis that the ratio of matrix to interleaf resin fracture toughness, i.e., the ratio of [Formula: see text], is directly correlated to the degree of toughness translation. More specifically, a ratio of approximately 0.5 is required for effective interleaving; below 0.5, the toughness translation is significantly below the theoretical value. This approach has important implications for the design and fabrication of tough composites via choice of resins.

Densification of fast-growing paulownia wood for tough composites with stab resistance

Densification of fast-growing paulownia wood for tough composites with stab resistance

Characterization and Modelling of Particulate Composite with Flaky Aluminium Additives

The utilisation of flaky aluminium as an additive in the composite matrix has shown the ability to overcome the brittle nature encountered in epoxy resins. The additive increases the overall composite toughness without compromising its strength. The novelty of the present work is the demonstration of modelling the constitutive response of the particulate composite from the uniaxial tension tests conducted at three different displacement rates. Utilising two different mean-field homogenisation schemes (Dilute inclusion and Mori-Tanaka), the macro-scale properties were estimated and compared with the material constants obtained from experiments for this new particulate composite, which is proposed in the current study. The rate-independent response, at lower loading rates, is modelled by the elasto-plastic (EP) model, and the rate-dependent response, at higher loading rates, is modelled by elastic-viscoplastic (VP) model while capturing an inelastic deformation as seen in the fractographs. The EP and VP model material constants are then successfully obtained by optimisation employing the Levenberg–Marquardt algorithm and are eventually used in validating the experimental stress response.

Numerical analysis of fracture in core-shell particle reinforced composites

The fracture of core-shell particle reinforced composites was simulated using a crack phase field method. A pre-existing crack may grow along the interface between the core and shell (core debonding), may penetrate the shell and the core (trans-core fracture), or may grow in the matrix (brittle fracture in the matrix). Shell fracture behaviours resulting from the competition between the fracture resistance and fracture driving force are crucial to the crack growth mechanisms. It was found that moderate strength and low modulus of the shell favoured trans-core fracture, and low strength and high modulus of the shell favoured core debonding. The effects on the overall mechanical properties were also identified. The composite strength usually benefited from stiffer and tougher components, regardless of the crack growth mechanisms, while the composite toughness was more complex. The toughening effect was highly related to how the crack evolved, as core debonding improved the toughness at the significant cost of strength, and trans-core fracture contributed most to the toughness with a slight reduction in strength compared with the matrix. These findings indicate design strategies for epoxy composites which can achieve a balance of strength and toughness, enabling the design of safer lightweight composites for electric vehicles and transport applications.

On the high fracture toughness of wood and polymer-filled wood composites – Crack deflection analysis for materials design

Cracks oriented in the toughest direction across the grain of wood (0°) tend to deflect at 90° to the precrack rather than extending in 0° direction. Fracture toughness data across the grain are therefore difficult to interpret. Crack growth mechanisms and effects from replacing wood pore space with a polymer are investigated. Crack growth is analyzed in four-point bending fracture mechanics specimens of birch and two different polymer-filled birch composites using strain-field measurements and finite element analysis (FEA). Calibrated cohesive zone models in both precrack and 90°-directions describe fracture process zone properties in orthotropic FEA-models. Conditions for 0° crack penetration versus 90° crack deflection are analyzed based on cohesive zone properties. Stable, subcritical crack deflection takes place at low load, reduces crack tip stress concentration, and contributes to high structural toughness, provided the 90° toughness is not too low. Polymer-filled neat birch composites have the best structural toughness properties in the present investigation, since 90° toughness is not compromised by any chemical treatment.

Waste natural fibers for polymer toughening and biodegradability of epoxy-based polymer composite through toughness and thermal analysis

Polymeric materials are being increasingly used to replace many metallic components due to their beneficial properties such as higher strength-to-weight ratio and corrosion resistance. However, the widespread use of polymers poses a risk to the environment as they are not biodegradable. The addition of the waste jute fiber and sawdust fiber as reinforcement to the epoxy resin improved its toughness and induced the biodegradability of the polymer. To examine the effect of the jute fiber and sawdust fiber on biodegradability, the composites were then kept in the drainage system for one year, and the impact energy and fracture morphology of the as-cast and weathered samples were examined using a drop ball impact test and a Charpy impact test. During the weathering period, weight gain was initially observed due to the water absorption by the porous fibers, but after three months, the composites started to lose weight due to the degradation of the fiber by swelling and microbial attacks. Microorganisms in the drainage system used the fiber as their energy source, which resulted in the deterioration of the fiber and the production of CO2. The production of CO2 was identified by the FTIR analysis of the weathered composite samples. TGA analysis of the as-cast and weathered samples reveals the reduction of the onset thermal degradation temperature of the weathered composites due to the degradation of the composites. The fiber disintegrated through microbial attack and the fiber swelling caused by the absorption of water by jute fiber and sawdust fiber is identified through SEM imaging. The SEM image also reveals the formation of biofilms and the growth of microorganisms at the fibers. A higher growth rate of the microorganisms was observed in the jute fiber composite than in the sawdust fiber composite, as sawdust contains a high level of lignin that protects it from degradation. The results of this study suggest that both sawdust fiber and jute fiber composites induce biodegradability in the epoxy matrix, but jute fiber was more prominent in this regard. The discovery paves the way for using natural fibers in biodegradable polymer composites, reducing polymeric pollution in the environment.

Influence of hybrid steel-polyacrylonitrile fibers on the mechanical toughness and freeze-thaw resistance of sulfoaluminate cement composites

Sulfoaluminate cement (SAC), an environmentally friendly low-carbon cement, is commonly applied for rapid repair and construction. However, limited studies were conducted to elevate the performance of SAC-based materials by using the hybrid fiber modification, especially the durability. This study investigated the mechanical behaviors and freeze-thaw (F-T) resistance of SAC-based materials with hybrid steel-polyacrylonitrile (PAN) fibers, as well as their enhancement mechanism characterized using X-ray computed-tomography (CT) and scanning electron microscope. The results showed that incorporating hybrid fibers remarkably increased the flexural and compressive toughness of mortars, with steel fibers contributing the most critically. The fiber hybridization also significantly enhanced the F-T resistance of mortars, with PAN fiber being the main contributor. Specifically, the use of hybrid fibers caused a 61.0% improvement in the relative dynamic elastic modulus of mortars after 300 F-T cycles. CT scanning demonstrated that incorporating PAN fibers reduced the porosity of mortars and restrained the initiation and propagation of microcracks, while uniformly and randomly distributed steel fibers interspersed between macrocracks. Morphology observation illustrated that PAN fiber addition was conducive to enhance the anchoring force of steel fiber. Accordingly, the hybrid steel-PAN fibers contributed to suppress cracking at different scales and achieved a positive hybrid effect. At last, the results of this work provide a promising design solution for SAC-based composites to achieve better toughness and frost resistance.

A Bio-Inspired Approach to Improve the Toughness of Brittle Bast Fibre-Reinforced Composites Using Cellulose Acetate Foils.

Bast fibre-reinforced plastics are characterised by good strength and stiffness but are often brittle due to the stiff and less ductile fibres. This study uses a biomimetic approach to improve impact strength. Based on the structure of the spicules of a deep-sea glass sponge, in which hard layers of bioglass alternate with soft layers of proteins, the toughness of kenaf/epoxy composites was significantly improved by a multilayer structure of kenaf and cellulose acetate (CA) foils as impact modifiers. Due to the alternating structure, cracks are deflected, and toughness is improved. One to five CA foils were stacked with kenaf layers and processed to composite plates with bio-based epoxy resin by compression moulding. Results have shown a significant improvement in toughness using CA foils due to increased crack propagation. The unnotched Charpy impact strength increased from 9.0 kJ/m2 of the pure kenaf/epoxy composite to 36.3 kJ/m2 for the sample containing five CA foils. The tensile and flexural strength ranged from 74 to 81 MPa and 112 to 125 MPa, respectively. The tensile modulus reached values between 9100 and 10,600 MPa, and the flexural modulus ranged between 7200 and 8100 MPa. The results demonstrate the successful implementation of an abstract transfer of biological role models to improve the toughness of brittle bast fibre-reinforced plastics.

Heterogeneous diamond–TiC composites with high fracture toughness and electrical conductivity

The concurrent enhancement of toughness, electrical conductivity, and thermal stability in polycrystalline diamond composites represents a formidable challenge. Here, a novel diamond-TiC composites (referred to as DTC) with high fracture toughness and conductivity were synthesized through a high-temperature and high-pressure reaction sintering process utilizing two precursors: diamond mixtures containing TiH2 and Ti-coated diamonds. On the one hand, the inherent bonding and encasing of TiC onto the diamond matrix form a heterogeneous structure, providing high strength and excellent fracture toughness up to 11.6 MPa·m1/2. On the other hand, the established oxygen barrier and current pathway offer a thermal stability of 765 °C and high conductivity up to 837 S·m−1. Remarkably, this rare combination of mechanical, electrical, and thermal properties has been realized within a single material under relatively moderate sintering conditions, thus positioning diamond-TiC composites as a promising ceramic for electrical applications in high-stress environments.

Microparticle-aggregation effect of intumescent flame retardants on flame retardancy and toughening property of polypropylene

It is a widespread problem that loading intumescent flame retardant (IFR) into polypropylene (PP) always sacrificed the mechanical properties significantly. To develop PP composites with high flame retardancy and toughness, a new intumescent flame retardant (TAIC-IFR) with microparticle-aggregation structure was synthesized by a straightforward in-situ cemented method. Through its microparticle-aggregation effect, the TAIC-IFR enhanced the toughness and charring flame retardancy of PP composites, compared with the traditional intumescent flame retardant mixtures. The 3TAIC-24IFR/PP sample exhibited an increase in impact strength and elongation at the break by 71.8 % and 233.5 % respectively compared with 27IFR/PP. The cemented TAIC-IFR particles with rough surfaces and triallyl triazine triketone component enhanced the interface performance between the fillers and PP matrix. In addition, the TAIC-IFR with particulate microparticle-aggregation characteristics promoted charring reactions among different flame retardant components, thereby enhancing its char-forming flame retardant effect in PP. Specifically, 1TAIC-24IFR/PP with cemented aggregated flame retardant particles exhibited a UL 94 V-0 rating and 28.5 % of limiting oxygen index (LOI), while PP with IFR mixture performed no UL 94 rating and a lower LOI. Moreover, the residue rate of 1TAIC-24IFR/PP increased to 15.9 % from 0 % of PP in cone calorimeter test. These results were attributed to the microparticle-aggregation effect of the acid source, carbon source, and gas source in TAIC-IFR particles, which exhibited better charring effect and barrier effect. This work provides a new idea for designing construction way of flame retardants to develop polymer materials with high flame retardancy and good toughness.

Breakage of Beaded Fibers in a Polymer Matrix

Abstract Intermittent beading is a promising design strategy that enables simultaneous improvement of strength and toughness of fiber-reinforced composites. Despite the potential for amplification in mechanical properties, the failure mechanisms of beaded fiber composites are not fully understood. In this study, calculations are carried out for the breakage of beaded fibers in the polymer matrix composites. The plastic deformation of the polymer matrix and debonding of the bead–matrix, fiber–bead, and fiber–matrix interfaces are accounted for in the numerical analyses. It is found that the location of fiber break is governed by the toughness of the fiber–bead interface and fiber strength. The low toughness of fiber–bead interface promotes the emergence of break inside bead, and high fiber strength is capable of activating break outside bead. The break at the edge of bead prevails in most cases. We have further revealed that the fiber–matrix interface with high strength and enhanced toughness can give rise to large amount of fiber breaks, while low degree of fiber cracking emerges in the case of strong fiber–bead interface. For the bead–matrix interface, the intermediate interfacial strength generates a high degree of fiber breaks and low interfacial toughness suppresses fiber cracking, leading to small amount of fiber breaks. In addition, the dependence of plastic dissipation in the polymer matrix on fiber breakage is elucidated.

Fracture toughness and fiber bridging mechanism for mode-I interlaminar failure of spread-tow woven composites

Given the current lack of research data on the delamination behavior of spread-tow woven composites, this study aims to systematically characterize the mode-I interlaminar fracture behavior of plain weave spread-tow fabrics (STFs) composites. DCB tests were conducted to investigate the influence of different ply thicknesses, unit cell sizes, and interface angles on delamination behavior and fiber bridging. The experimental results revealed a stick–slip crack propagation behavior in mode-I delamination of studied material, and a detailed analysis was performed on the influence mechanism of unit cell size on this behavior. Fiber bridging was found to be the primary mechanism responsible for the increased interlaminar fracture toughness in the plain weave STFs composites. Fractography analysis indicated that regions rich in fibers and resin in thicker-ply laminates promote fiber bridging, while an interface angle inconsistent with the direction of crack propagation inhibits fiber bridging. The concept of average steady-state fracture toughness (average Gs) was introduced as a means to assess propagation fracture toughness and two methods were proposed to obtain bridging tractions for characterizing the fiber bridging phenomenon. The bridging tractions and average Gs were used as key parameters to establish a trilinear cohesive zone model (CZM) for simulating mode-I delamination. The numerical results aligned well with the experimental results, demonstrating the applicability of the parameter determination strategy based on the average Gs and bridging tractions for the selection of parameters to use in the CZM.

Mechanical Properties and Microstructure of Highly Flowable Geopolymer Composites with Low-Content Polyvinyl Alcohol Fiber

Geopolymer enhances mechanical properties with polyvinyl alcohol (PVA) fibers, but there has been limited research exploring low PVA fiber dosages for mechanical properties in 3D printing or shotcrete. This study experimentally investigated slag and fly ash-based geopolymer mixtures reinforced with 0.1%, 0.15%, and 0.2% PVA fiber by volume as well as a control group without PVA fibers. These mixtures were prepared using fly ash, quartz sand, slag powder, silica fume, and an aqueous sodium silicate solution as the alkali activator, with the addition of PVA fiber to enhance composite toughness. The mechanical properties of the composites, encompassing dog-bone tensile properties, cubic compressive strength, bending and post-bending compressive strength, and prism compressive properties, were evaluated. Significantly, specimens with 0.15% PVA fibers exhibited optimal performance, revealing a notable 28.57% increase in tensile stress, a 36.45% surge in prism compressive strain, and a 47.59% rise in tensile strain compared to fiber-free specimens. Furthermore, environmental scanning electron microscopy observations were employed to scrutinize the microscopic mechanisms of composites incorporating PVA fibers, slag, and fly ash. In comparison to fiber-free specimens, prism compressive specimens with 0.15% PVA fibers demonstrated a 27.17% increase in post-cracking loading capacity, a 44.07% increase in post-cracking ductility, a 50.00% increase in peak strain energy, and a 76.36% increase in strain energy ratio.

Synergistic toughening modification and finite element analysis of carbon fiber/epoxy resin‐reinforced composites

AbstractIn this work, the poor fracture toughness of carbon fiber‐reinforced composites (CFRPs) was improved by the introduction of a graphene oxide/nanosilica (GOS) hybrid, and short carbon fibers (SCFs) were investigated through experimental and modeling methods. The effects of the SCF content, number of SCF layers, and introduction position on the mode I fracture toughness (GIC) and mode II fracture toughness (GIIC) of the composites were considered for epoxy resin (EP) modified by GOS. The results showed that GOS and SCF exhibited a synergistic toughening effect on CFRP. The GIC and GIIC of CFRP laminate with GOS content of 0.2 wt% and SCF content of 0.4 wt% reached 0.506 and 2.15 kJ/m2, increased by 72.2% and 53.6% compared to the unmodified composite, respectively. The number of layers and the lamination mode of GC10S5‐B specimens exhibited the optimal improvement of interlaminar fracture toughness. Similarly compared with those of the original. The GIC and GIIC of the CFRP laminates reached 0.662 and 0.506 kJ/m2 (enhanced by 125.9% and 95%, respectively). In addition, the stress propagation path and distribution, and progressive damage of the CFRP composites were obtained to further reveal the toughness mechanism.Highlights Synergistic toughening of resin modification and short carbon fiber on modes I and II fracture toughness of composites were considered. Content of short carbon fiber and lay‐up methods on toughness performance were investigated thoroughly. Finite element models were established to reveal the stress progress and distribution and toughness mechanism.