Fiber Fracture Research Articles

Flexible Phase Change Materials with High Energy Storage Density Based on Porous Carbon Fibers.

Phase change fibers (PCFs) can effectively store and release heat, improve energy efficiency, and provide a basis for a wide range of energy applications. Improving energy storage density and preserving flexibility are the primary issues in the efficient manufacture and application development of PCFs. Herein, we have successfully fabricated a suite of flexible PCFs with high energy storage density, which use hollow carbon fibers (HCFs) encapsulated phase change materials (PCMs) to provide efficient heat storage and release, thereby enhancing energy efficiency and underpinning a broad range of energy applications. The flexible HCF/LA PCFs with high energy density were made by impregnating a small molecule LA solution, whereas the precursor of the PAN/ZIF-67 composite fibers was created by electrospinning. These PCFs have a high loading capacity for lauric acid (LA), demonstrating a 92% load percentage and a 153 J g-1 phase change enthalpy value. The effects of doping quantity (ZIF-67), fiber orientation, pre-oxidation treatment, and particle size on the morphological and structural characteristics of HCFs, as well as the impact of HCFs' pore structure on PCM encapsulation, were investigated. It was found that the oriented fiber structure serves to reduce the likelihood of fracture and breakage of precursor fibers after carbonization, whilst the gradient pre-oxidation can maintain the original fiber morphology of the fibers after carbonization. These findings establish a solid theoretical foundation for the design and production of high-performance flexible porous carbon nanofiber wiping phase change composites.

Research Progress on the Impact Resistance of Basalt Fiber-Reinforced Polymer Composites

Abstract Basalt fibers exhibit excellent properties and have diverse applications. This paper thoroughly investigates the impact resistance of polymer matrix composites reinforced by basalt fibers and analyzes the failure mechanisms during impact, including micro-deformation, delamination, and fiber fracture. Basalt fiber-reinforced resin matrix composites consist of a reinforcement phase, a matrix phase, and an interface phase. To strengthen the material’s resistance to impacts, various approaches have been explored, including optimizing the matrix resin (e.g., selecting vinyl resin and toughening treatments), optimizing the reinforcement phase (e.g., fiber hybridization, morphology optimization, and interlayer hybridization), and improving the interface phase (e.g., coupling agent modification and carbon nanotube grafting). These optimization measures can significantly enhance the impact resistance of basalt fiber-reinforced polymer materials under low-velocity impact loads. Under high-velocity impact loads, increasing the number of laminate layers or employing three-dimensional weaving techniques can significantly improve the material’s impact resistance. These research findings aim to provide a theoretical foundation and practical references for the application of basalt fiber-reinforced polymer materials within the domain of impact resistance.

Dynamic behaviour and failure mechanism of bamboo scrimber panels under single and repeated impacts: Experimental tests

Bamboo scrimber, as a renewable and sustainable material engineered from bamboo, is inevitably subjected to impact loadings in engineering applications. To study the dynamic behaviour and failure mechanism of bamboo scrimber panels under low-velocity impact, a series of drop hammer impact tests were conducted on 36 panels. The peak force, deformation and energy absorption of bamboo scrimber panels were obtained and analysed. The influence of impact energy, impactor shape and impact angle on the dynamic behaviour of panels was quantitatively characterised. Besides, based on test observations and microscopic views, the failure mechanism of bamboo scrimber panels under different impact types was revealed, including the energy absorption mechanism through fibre fracture, fibre debonding, fibre pull-out and matrix failure. Test results showed that with increasing impact energy, the peak force of panels impacted by the spherical and flat impactors increased, while that of panels impacted by the wedge impactor did not vary significantly. The deformation and energy absorption of panels also increased with increasing impact energy. Notably, the impactor shape obviously influenced the dynamic behaviour of panels, causing a higher peak force of panels impacted by the flat impactor and a larger deformation of panels impacted by the wedge impactor. The failure mechanism of panels depended highly on the impact energy and the impactor shape. Finally, a comparative study of single versus repeated impacts revealed that the deformation of bamboo scrimber panels under repeated impacts was less than that of panels under a single impact when the same amount of energy was imposed to the panel. This study provided a basis for the use of bamboo scrimber to resist impact loadings.

Study on dynamic mechanical properties and damage characteristics of wollastonite fiber reinforced oil well cement paste

In cement engineering, the cement sheath is not only influenced by elevated temperatures, increased pressure, and the static load confining pressure within the formation but also encounters external impact loads. These loads can rupture the cement paste, compromising the cement sheath’s interlayer sealing capability. Consequently, this can give rise to an annular flow of oil, gas, and water. Hence, this study introduces wollastonite fiber (WF) into the cement slurry to modify the cement paste. The investigation explores the mechanical properties, energy evolution, and damage characteristics of the cement paste with WF under dynamic impact loads. This is achieved by simulating the dynamic impact loads experienced downhole using the separated Hopkinson pressure bar (SHPB) technique. A straightforward SHPB model is constructed using ABAQUS finite element simulation software, and its accuracy is confirmed through experimental validation. The impact test outcomes revealed a notable enhancement in the dynamic load peak strength of the cement paste cured for 14 days. Specifically, there was an increase of 136.75%, 202.10%, and 320.55% compared to the control group at impact speeds of 6 m/s, 8 m/s, and 10 m/s, respectively. The absorption energy increased remarkably, showing 356.03%, 388.61%, and 142.14%, respectively. The simulation findings confirm that the devised simple SHPB model effectively replicates electrical signals aligned with the observed experimental results. The dispersed fibers create a three-dimensional network within the cement paste. This network enhances the impact resistance of the cement paste by leveraging the mechanisms of crack deflection, fiber fracture, and energy dissipation through fiber pull-out.

Research on frequency-domain characteristics of acoustic emission signals generated during wood damage and fracture process

ABSTRACT This research conducts three-point bending tests on air-dried beech, elm, pine, and cypress specimens to research their damage and fracture behaviour. Wavelet transform is utilized to decompose original acoustic emission signals generated during the damage and fracture process into five layers. Then, based on the principle of signal correlation, the wavelet-decomposed detail signals are adaptively reconstructed. The K-means algorithm is used to classify reconstructed AE signals into different groups based on their frequency-domain characteristic. Research results indicate that the peak frequency of low-frequency AE signals generated during the wood damage and fracture process is approximately 21 kHz. These AE signals may be generated by damage, delamination, bucking, and collapse of the cell-wall layer. When wood specimens are in the later stage of nonlinear deformation and in the macroscopic fracture stage, in addition to the mentioned microscopic damage above, there will also be formation and expansion of microcrack damage zones, as well as cell-wall rupture and macroscopic fracture of wood fibres. In addition to the low-frequency AE signals mentioned above, these AE signals are medium-frequency signals with peak frequency in the range of 25–60 kHz, and high-frequency signals with a peak frequency of approximately 165 kHz.

Pull-Out Progressive Damage and Failure Analysis of Laminated Composite Bolted Joints.

Laminated composite bolted joints are increasingly used in the aerospace field, and their damage and failure behavior has been studied in depth. In view of the complexity and stability requirements of laminated composite bolted structures, accurate prediction of damage evolution and failure behavior is significant to ensure the safety and reliability of the structures. In this paper, a novel asymptotic damage model is developed to predict the damage process and failure behavior of laminated composite bolted joints. In this model, the modified Puck criterion and the maximum shear stress criterion are used for fiber yarns. The parabolic yield criterion is adopted for the matrix, and the fiber fracture, inter-fiber fracture and matrix fracture are considered at the microscopic level. The pull-out strength and progressive failure behavior of countersunk and convex bolted joints structures are predicted by using the proposed model, and the corresponding experimental studies are carried out. The results show that the prediction results are in good agreement with the experimental data, which verifies the reliability of the model. Additionally, the effects of different structural parameters (thickness and aperture) on the progressive damage and failure behavior during pull-out is analyzed by the proposed model, and correction factors of pull-out strength are obtained, which provides a powerful tool for the design, analysis and progression of laminated composite bolted joint structures.

Fatigue Properties of Carbon Fiber–Reinforced Foams and Experimental Observation of the Damage Growth Mechanism

ABSTRACTCarbon fiber–reinforced foams (CFRFs) are expanded thermoplastic composite materials reinforced with three‐dimensional discontinuous carbon fibers. Herein, the effects of their unique internal structure on fatigue properties were investigated. Through tension‐tension fatigue tests and the digital image correlation (DIC) method, distinct stiffness reduction behavior was observed across the entire specimen and at the fracture points. The results suggest that local stiffness reduction behavior affects the fatigue properties. From the DIC method, damage was observed by scanning electron microscopy and the fiber tortuosity, and the void fraction were quantified using X‐ray computed tomography scans. In the case of three‐dimensional oriented fibers, stress was concentrated at fiber ends, fiber intersections, and bent fibers, resulting in fiber pull‐outs and matrix cracks. In the case of voids, the void size affected damage development, and the stress concentration around the voids caused fiber fracture and matrix cracks.

A novel PDA/POSS transition layer on the surface of UHMWPE fibers by co-depositing to improve the mechanical properties of composites

The surface treatment of ultra-high molecular weight polyethylene (UHMWPE) fibers is one of the key technologies for the application of UHMWPE fibers composites. In this paper, the interface transition layer of polydopamine (PDA) and polyhedral oligomeric silsesquioxane (POSS) co-deposited on the surface of corona pre-treatment fiber fabric is used to the uniform and efficient distribution of loads between the fibers and the resin matrix, especially to significantly improve the flexural modulus of UHMWPE fiber fabric composites. Under 2.5 kW corona pre-treatment, 4 g/L of dopamine hydrochloride and 2 wt% of γ-Aminopropyl triethoxysilane aqueous solution, the impact strength, flexural strength, and modulus of UH-C2.5@PDA/PA2 fiber fabric/epoxy composites are greatly improved to 218.6 kJ/m2, 151.7 MPa, and 7.8 GPa, respectively, which are 72 %, 106 % and 143 % higher than those of the untreated UHMWPE fiber composites. It may be attributed to: (1) the corona pre-treatment of UHMWPE fiber induces larger amount of active sites on fiber surface and higher surface energy, leading to a better wettability and adhesion with the matrix resin; (2) the mechanical interlocking engagement between the fibers and nano-POSS particles effectively prevents fibers extraction from the matrix resin and increases the friction of relative sliding; (3) POSS can strengthen the transition layer. The failure of UHMWPE fiber reinforced composites can be mainly attributed to energy absorption of matrix resin fracture, interface damage and relative sliding between matrix resin and fibers, fiber yield deformation and fiber fracture.

Machining holes in CFRP with laser “drilling + boring” hybrid technique

ABSTRACT This paper presents a novel approach for machining carbon fiber reinforced polymer composite (CFRP), wherein a laser “drilling + boring” hybrid technique is employed. The method consists of initial high-energy pulsed laser drilling at high speeds, followed by subsequent low-energy short-pulsed laser trimming of the hole edges. A detailed examination was carried out on machining accuracy, taper angle, surface roughness, the heat affected zone (HAZ), microstructure, and mechanical properties of the CFRP samples machined with this technique. The findings revealed that the circular holes exhibit a machining accuracy of approximately 30 μm, accompanied by a taper angle measuring 0.37°. Moreover, the regions surrounding the holes display a smooth and pristine surface, devoid of burrs, fiber fractures and serrated textures. Notably, compared with laser rotary cutting method, the “drilling + boring” hybrid technique demonstrates enhancements in surface finish, HAZ control, and mechanical property of the machined holes.

Effects of cashew nutshell biofillers on the mechanical and thermal behaviour of Basalt/Hibiscus vitifolius hybrid fabrics reinforced polymer biocomposites

Basalt-based natural fiber hybrid composites with fillers are always the most anticipated composite material candidates for lightweight structural applications. Current work focusses on the preparation, characterization and testing of Basalt (B)/Hibiscus vitifolius (HV) based epoxy biocomposites with and without cashew nutshell fillers. Individual fiber reinforced composites (with 40 vol% of fibers) and hybrid composites (with 40 vol% of fibers in the ratio 1:1) filled with 10–30 vol% of fillers were manufactured using compression moulding techniques. The X-ray diffraction spectrum showed the crystal size and crystallinity index for all biocomposites. It showed a monoclinic crystal structure with an irregular surface of the fiber and filler. The FTIR spectrum showed the chemical composition presented in the biocomposites. The presence of filler and fibers was confirmed by different spectral peaks. Hybrid biocomposites were then subjected to mechanical and thermal investigations. The mechanical properties of the biocomposites showed that the tensile, flexural, and impact strength of the biocomposites varies with the concentration of the cashew nutshell filler. The surface morphology of the fractured sample showed the presence of fabric layer, fiber fracture and pull out, and homogenous dispersion of the fillers in the biocomposites. Thermal degradation curves showed that the thermal stability of biocomposites is improved by adding filler up to 20 vol% because the filler acted as a barrier element for the thermal degradation of biocomposites. From the results, it could be understood that these biocomposites find their applications probably in lightweight structures.

Effects of Absorption on the Tribological Properties of Carbon Fiber Reinforced Polyamide-6 Composites Manufactured by Fused Deposition Modeling

Abstract The present work studied the water absorption behavior of polymeric composite materials fabricated using 3D printing technology, as well as its effect on their tribological properties. Polyamide-6 was selected as the base matrix material. Short and continuous carbon fibers are used as the reinforced material. The results showed that the moisture absorption would impair the mechanical properties of polymer matrix and interface bonding between the fiber and the matrix. As a result, the tensile strength of the fiber reinforced polymer composites (FRPCs) decreases with water absorption. Nevertheless, the effects of moisture absorption on the wear properties of FRPCs are more complicated, which are depending on the fiber length and sliding conditions. With the short fiber reinforcements, moisture absorption deteriorated the wear resistance under all the testing conditions. With the increase of moisture level, more severe fiber damage/removal was observed, associated with the higher wear loss. With a relative high volume fracture of continuous carbon fiber (∼35 vol%), however, the wear resistance of the FRPC increased with moisture level, especially under a relatively low load. Based on microscopic observations, it was proposed that water inside FRPC specimens is able to provide the lubricating and cleaning effects, which contribute to a lower friction and smooth worn surfaces. The work provides new insights into designing and selecting printed polymer materials, subjected to different loading conditions.

Comparison of low-velocity impact damage in laminated composites for two thermoplastic material systems

Aircraft manufacturers are investigating thermoplastic material systems to produce parts more quickly and efficiently. Detailed damage data is needed to evaluate existing damage analysis methods, developed for thermoset materials, to predict damage in thermoplastic materials. Damage maps were created for two thermoplastic material systems subjected to low-velocity impact over a range of impact energies. In this paper, the damage maps were used to investigate and compare the damage response of the different material systems. Impact specimens were manufactured from TC1225 LMPAEK T700G from Toray Industries and APC AS4D/PEKK-FC from Solvay. The effect of the degree of crystallinity on the damage response was also investigated using a third set of specimens manufactured using the Toray material and a quenching process. Using a combination of data obtained from X-ray computed tomography and ultrasonic testing, damage maps were created for every interface and ply for selected specimens showing matrix cracks, delamination outlines, and fractured fibers. The LMPAEK specimens were found to have fewer and smaller delaminations than the PEKK specimens for impacts at the same energy. However, the LMPAEK specimens contained a larger number of fiber breaks. A similar trend was observed when comparing low-crystallinity LMPAEK specimens with the baseline LMPAEK specimens. The LMPAEK specimens often contained lines of fiber fractures in near-surface plies emanating from the contact region that were not present in the PEKK specimens. The different damage responses may indicate that the material selection will be a function of the application and loading.

Dynamic response and damage mechanisms of 2D plain weave hybrid composites under the out-of-plane punch shear loading

A modified theoretical method for the punch shear test is derived by considering the influence of stress wave reflections caused by cross section discontinuities in the incident and transmitted bars. The dynamic punch shear behavior of 2D plain weave carbon/aramid hybrid composites was researched. The failure strength and strain are sensitive to strain rate. The stress-strain curves were obtained by the modified method. Significant shear deformation was observed under a single loading. An effective punch shear mesoscopic simulation model that accounts for the strain rate effect of the component materials was developed using the multi-scale analysis method. The model reveals the damage characteristics in the component materials. Damage modes are affected by hybridization and strain rates. The high elongation at the fracture of aramid fibers at high strain rates plays a crucial role in absorbing impact energy.

Microdroplet pull-out testing: Significance of fiber fracture results

Fiber reinforced composites are used in structural materials that required light weight and stiffness. The properties of the fibers or matrix are important, but the interfacial properties have a significant impact on the properties of fiber reinforced composite. In this study, the interfacial shear strength (IFSS) was measured using acrylic resin and epoxy resin as base materials. The chemical composition of acrylic and epoxy matrix materials was analyzed to predict the effects on IFSS. Additionally, IFSS was measured through a microdroplet pull-out test. The reliability of the experimental results was enhanced by applying a statistical analysis to IFSS results. In the case of epoxy, GF/epoxy exhibited higher IFSS to twice and half times than CF/epoxy specimens. It means that the surface treatment of the fibers has a significant impact on the interface. In the case of acrylic, IFSS could be measured for GF. But in the case of CF, IFSS was too low to get accurate results of IFSS. Through this research, methods to improve the accuracy of composite interfacial strength measurement experiments were examined, and the study suggested the need for standardized criteria to evaluate composite interfacial adhesion.

Damage Characterization of GFRP Hollow Ribbed Emergency Pipes Subjected to Low-Velocity Impact by Experimental and Numerical Analysis.

This paper investigates the low-velocity impact response and damage behavior of glass fiber reinforced polymer (GFRP) hollow ribbed emergency pipes of our design under different impact heights. Drop hammer impact tests with impact velocities of 8.41 m/s, 8.97 m/s, and 9.50 m/s were conducted using an impact platform. A progressive damage model for low-velocity impact was developed using Abaqus/Explicit finite element software. The model used the three-dimensional Hashin damage initiation criteria and a damage evolution model based on the equivalent strain method to simulate the initiation and evolution of intralaminar damage in the pipe ring. A cohesive zone model (CZM) based on a bilinear traction-separation law was used to simulate delamination. The results show that the pipe rings experienced fiber or matrix fractures and delamination damage during the impact process. Additionally, the pipe ring specimens underwent bending vibrations under the impact load, leading to fluctuating contact forces at all three impact heights. Analysis of the simulation results reveals that the primary damage modes in the GFRP hollow ribbed emergency pipe are fiber tension damage, matrix tension damage, and fiber compression damage, with delamination occurring mainly in the impact area and the interface area on both sides of the rib.

HMGB2 promotes smooth muscle cell proliferation through PPAR-γ/PGC-1α pathway-mediated glucose changes in aortic dissection

Background and aimsAortic dissection (AD) is a fatal condition with a complicated pathogenesis. High mobility group protein B2 (HMGB2) is a member of the high mobility group protein family; HMGB2 is involved in innate immunity and inflammatory diseases, but its role in AD remains unclear. MethodsHMGB2−/− mice were generated and treated with β-aminopropionitrile and angiotensin II (Ang II) to establish an AD model. An F12 gel containing AAV9-HMGB2 was applied to overexpress HMGB2 in mice. Pathological changes in the aorta were assessed by visualizing vascular collagen deposition and elastic fiber fracture via H&E, Masson and EVG staining. HMGB2 expression was measured by Western blotting and immunohistochemistry. MTS, CCK-8 and EdU assays were used to test cell proliferation. ResultsHMGB2 expression was increased in samples from AD patients, samples from AD mouse modeland human aortic smooth muscle cells (HASMCs). HMGB2 promoted HASMC proliferation. Immunofluorescence staining and plasma membrane protein isolation revealed that HMGB2 decreased GLUT1 expression and promoted GLUT4 translocation. HMGB2 was also found to inhibit the expression of SIRT1/PGC-1α, but blocking the PPAR-γ pathway attenuated this effect. HMGB2−/− significantly reduced the incidence and mortality rates of AD, whereas treatment with AAV9-HMGB2 exacerbated AD. ConclusionsThis study suggests that HMGB2 promotes HASMC proliferation and vascular remodeling by regulating glucose metabolism through the PPAR-γ/SIRT1/PGC-1α pathway. HMGB2 knockdown reduces, while HMGB2 overexpression promotes, the occurrence of AD in mice. This study may help elucidate the underlying mechanisms and provide a new preventive target for AD.

Axial compression behavior of mechanized filament-wound GFRP-steel tubed concrete stub columns

Filament-wound is presently the prevailing and efficient process in the field of molding, known for its ability to achieve optimal molding effects. This technique offers numerous advantages, including high precision, a high fiber content. Traditional FRP-steel tubed concrete stub columns (FSTCSCs) are fabricated by longitudinally wrapping FRP sheet, which results in low production efficiency. This paper introduces a mechanized filament-wound FSTCSC, which can achieve overall molding and effectively improve production efficiency. This paper presents an examination of the axial compression performance of mechanically wound FSTCSC. Two variables were considered including FRP wrapping angle and concrete strength. The experimental results reveal that fiber fracture of mechanized filament-wound FSTCSC is a gradual process, with damage starting from the outermost layer. When GFRP undergoes fracture, a higher wrapping angle results in enhanced restraint stiffness but reduced ductility. Moreover, the validated finite element model is used to analyze the parameters such as the wrapping angle and the thickness of GFRP tube, and it is found that adjusting both upward and downward wrapping angles plays a role in boosting the peak load carrying capacity. Furthermore, five models for predicting ultimate strengths were evaluated using test results, followed by the provision of recommendations for practical design.

Damage mechanism identification and failure behavior of 2D needle-punched SiCf/SiC composites based on acoustic emission and digital image correlation

In order to improve the reliability of damage analysis for SiCf/SiC composites, an identification method of damage mechanism was established by combining in-situ acoustic emission (AE) and digital image correlation (DIC). The corresponding failure behavior of 2D needle-punched SiCf/SiC composites during ambient-temperature tensile test was investigated in detail. Through a machine learning k-means algorithm, AE signals could be effectively divided into five clusters: friction and sliding, interface damage, matrix cracking, individual fiber breaks and collective fiber breaks. DIC results show that the surface strain of composites increased non-uniformly during the tensile process, and the architecture of the composites had a significant influence on the initiation and propagation of cracks. To summarize, the tensile process consisted of three stages: the elastic stage, the rapid propagation of matrix cracks, the coordinated fiber fracture within the large strain bands. The failure of composites was dominated by the limited load transferring ability of the interface.

Comprehensive analysis of the effect of braiding angle on the wettability and mechanical properties of 3D braided carbon fiber fabric-reinforced composites

Fiber-reinforced composites are designed to enhance strength, stiffness, and lightweight properties. However, while the use of continuous fibers offer substantial performance benefits it presents challenges in achieving complex configurations. This study focused on evaluating the effects of different braiding angles on the mechanical properties of braided fabric-reinforced composites (B-CFRP). Continuous fiber tows were braided around a mandrel, with meticulous control over the key process parameters to ensure consistency. The composites were then processed using the Vacuum Assisted Resin Transfer Molding (VARTM) technique to achieve optimal impregnation of the resin. Mechanical properties, including tensile, flexural, compressive strength, interlaminar shear strength (ILSS), and impact strength, were performed to establish the relationship between resin impregnation and mechanical properties with different braid angles. Additionally, resin flow experiments and scanning electron microscopy (SEM) analysis were conducted to investigate how variations in braiding angle influence fiber arrangement, resin distribution, and fracture behavior. These insights aim to guide the design and manufacturing of high-performance composites.

Optimizing tensile strength and failure prediction in hemp fiber composites: Coupling effects of microfibril angle and fiber orientation under off-axis loading

In response to environmental concerns associated with synthetic fiber-reinforced materials, plant fiber-reinforced composites are increasingly recognized as a more sustainable alternative. However, predicting the mechanical properties of these composites remains challenging due to the unique microstructure of plant fibers. This study proposes an optimized Tsai-Hill failure criterion that incorporates the microfibril angle (MFA) and fiber orientation to enhance failure predictions. The MFA of hemp fibers was measured using X-ray diffraction (XRD), and the failure mechanisms of unidirectional hemp fiber composites under off-axis tensile stresses were thoroughly analyzed. Experimental results reveal a 10.69 % increase in tensile strength at a 5° off-axis angle compared to the fiber direction. As the off-axis angle increases, the failure mode transitions from fiber fracture and pull-out to matrix tearing and interlayer shear failure. For angles above 10°, the failure stress aligns with both the maximum stress and Tsai-Hill criteria. For angles below 10°, integrating MFA into the Tsai-Hill criterion significantly improves prediction accuracy. These findings offer critical insights for optimizing the tensile performance of hemp fiber composites and predicting their behavior under off-axis loading conditions. Consequently, this study can support the use of hemp fiber composites in a broader range of applications.