Fiber Breakage Research Articles

Effect of Ammonium Polyphosphate/Silicate Content on the Postfire Mechanics of Epoxy Glass‐Fiber Composites Using Facile Chocolate Bar‐Inspired Structures

ABSTRACTThis study investigates the postfire mechanical properties of epoxy glass‐fiber reinforced composites (EP GFRCs) using increasing concentrations of ammonium polyphosphate (APP) and inorganic silicate (InSi) to modify the char and fire residue. A facile chocolate bar‐inspired structure was introduced for fire exposure and subsequent flexural testing of the GFRCs. The resin matrix used here was a diglycidyl ether of bisphenol‐A (DGEBA) resin, cured with dicyandiamide (DICY), and accelerated by Urone. The microstructures of the degraded composites after three‐point bending tests, were evaluated using scanning electron microscopy (SEM) and x‐ray computed tomography (XCT) imaging. A previous study showed that increasing the APP and InSi content significantly enhanced flame retardancy, via improved char formation under fire conditions. However, flexural properties and fire resistance were adversely affected after fire exposure, highlighting a trade‐off effect. Fiber breakage and delamination of the composites increased upon failure with increasing APP + InSi content in the composite due to unconsolidated char. The experimental values for the postfire flexural mechanics were in good agreement with the two‐layer model proposed in literature. This paper presents a preliminary basis for postfire mechanical testing of epoxy composites for use in fire‐safe structures, using a combination of standardized testing norms.

Sandwich‐structured light‐transmitting composites based on waste textiles: Fabrication, optical properties, and bending failure behavior

AbstractCurrently, glass fiber‐reinforced resin composites, as an advanced optically transparent material, have garnered widespread attention and research. In the context of new‐era developments, there is a growing demand and expectation for the visual artistic expression of light‐transmitting composites. In this study, glass fiber fabric, silk fabric, and recycled polyester jacquard fabric were used as reinforcement materials, while epoxy resin was selected as the matrix material. A green decorative light‐transmitting composite with uniform light diffusion and soft light effects was prepared using the vacuum bag molding process. By altering the woven structure (plain weave, twill weave, satin weave), yarn density, and yarn twist of the silk fabric, the optical properties of the composites can be regulated. The unique triangular cross‐section, woven structure, and large folds of the plain‐woven silk fabric were particularly conducive to the reflection and refraction of light within the composite, thereby significantly enhancing the uniform light diffusion and soft light properties of the material. Furthermore, the bending failure behavior of the composites was investigated through three‐point bending tests, acoustic emission (AE) test, and micro‐computed tomography (Micro‐CT) scanning. The laminate specimens reinforced with plain‐woven silk fabric exhibited the best bending performance, with bending strength and modulus reaching 434.4 MPa and 19.0 GPa, respectively. The combination of AE and micro‐CT scanning techniques successfully established the correlation between AE signals and damage modes. This study identified the main failure modes for plain woven, twill woven, and satin woven silk reinforced composites as fiber breakage, interlayer delamination, and fiber/resin debonding, respectively.Highlights Waste textiles were recycled for use in transparent composites. Silk fabric's weave structure affected composites' optical properties. Fiber breakage was the main failure in bending of plain woven composites. Plain woven composites exhibited optimal diffuse light, superior flexural performance.

Deep Autoencoder Framework for Classifying Damage Mechanisms in Repaired CFRP

This study investigates the classification of damage modes in adhesively bonded carbon fiber-reinforced plastic (CFRP) composites, a critical factor in advancing lightweight automotive design. Adhesive bonding, replacing traditional riveting, improves structural integrity while reducing weight and CO2 emissions. Mechanical testing on CFRP composites was performed, and acoustic emission (AE) signals were collected to evaluate damage mechanisms. A deep autoencoder (DAE) framework was developed to automate damage characterization by reducing AE signal dimensionality through singular value decomposition (SVD) and classifying features using the k-means algorithm. This approach effectively identified three primary damage modes: matrix cracking, interfacial debonding, and fiber breakage. Traditional AE features, such as entropy and amplitude were also classified and validated using spectral analysis. The DAE-based strategy demonstrated superior capability in real-time damage mode differentiation. Fractographic analysis confirmed crack growth in the adhesive layer, leading to interfacial debonding, fiber-matrix separation, and eventual fiber rupture. These findings highlight the DAE framework’s effectiveness in enhancing damage mode characterization, offering valuable insights for optimizing the structural performance of bonded CFRP composites in automotive applications.

High‐velocity impact response and damage behavior of bio‐inspired helicoidal composite laminates: Experimental and numerical investigation

AbstractBio‐inspired helicoidal composite laminates have been found to have better impact resistance and energy absorption than conventional laminates. To study the impact responses and damage behaviors of bio‐inspired helicoidal composite laminates under high‐velocity impact, the composite laminates with three helix angles were designed and tested. Two types of light‐gas gun were used to provide low and high impact energies, the velocity was measured using a velocimeter and the damage to the laminate profile was observed by scanning electron microscopy. Numerical simulation is then used to simulate the damage behavior of the helicoidal laminates based on the Hashin failure criterion and the revised dynamic increase factor. The results show that: under an impact of low energies, the helicoidal mechanism serves to absorb the impact energy through the generation of additional delamination. The laminates with the helix angle of 15° exhibits the maximum delamination area and the minimum residual velocity. However, under the impact of higher energies, the helicoidal mechanism is unlikely to improve the energy absorption and will inhibit the delamination damage. The laminates with the helix angle of 45° have the greatest inhibitory effects on delamination damage, with a delamination area reduction of 35.41%. Due to these differences, therefore, the use of helicoidal laminates should be more cautious in high‐velocity impact resistance and better avoid high‐energy situations. These findings can support the design of novel impact resistance structures.Highlights High‐velocity impact tests and FEM simulation of helicoidal laminates are carried out Damage behaviors and failure mechanism of helicoidal laminates are studied Delamination and fiber breakage are the main failure modes The laminates with the helix angle of 15° has the best impact resistance.

Fast 3D printing of fine, continuous, and soft fibers via embedded solvent exchange

Nature uses fibrous structures for sensing and structural functions as observed in hairs, whiskers, stereocilia, spider silks, and hagfish slime thread skeins. Here, we demonstrate multi-nozzle printing of 3D hair arrays having freeform trajectories at a very high rate, with fiber diameters as fine as 1.5 µm, continuous lengths reaching tens of centimeters, and a wide range of materials with elastic moduli from 5 MPa to 3500 MPa. This is achieved via 3D printing by rapid solvent exchange in high yield stress micro granular gel, leading to radial solidification of the extruded polymer filament at a rate of 2.33 μm/s. This process extrudes filaments at 5 mm/s, which is 500,000 times faster than meniscus printing owing to the rapid solidification which prevents capillarity-induced fiber breakage. This study demonstrates the potential of 3D printing by rapid solvent exchange as a fast and scalable process for replicating natural fibrous structures for use in biomimetic functions.

Investigation of the structural performance and failure mechanisms of 3D printed continuous carbon fiber‐based composites

AbstractAdditive manufacturing of continuous fiber‐based polymeric composites has attracted global attention. This contemporary technology enables the flexibility of manufacturing customized, partially and fully functional, and advanced composite components for numerous semi‐structural and structural applications. The current study investigates the structural performance of 3D‐printed carbon fiber‐based composites in the context of tensile, flexural, and high‐cycle fatigue. The crucial S‐N curves for the unidirectional (UD) (0°) and cross‐ply (CP) (0, 90) composites have been plotted. The dominating failure mechanisms responsible for the failure of 3D printed composites under tensile, flexural, and high cycle fatigue loading at the micro‐scale have been thoroughly investigated. The influence of fiber orientation on the failure mechanisms under different structural loading has been rigorously studied. The current findings conclude that cross‐ply (0, 90) composites exhibited superior fatigue performance than the unidirectional composites when investigated at 70% of their ultimate tensile strength. The current investigation reveals that the formation of voids during 3D printing and majorly during loading is one of the leading causes of the failure of additively manufactured composites under mechanical and cyclic loads. The fiber pull‐out, fiber breakage, de‐bonding, and voids are the dominating failure mechanisms observed under tensile loading. In addition to the failure mechanisms listed under tensile loading, matrix fractures have also been observed under flexural loading. The dominating failure mechanisms differed for UD, CP (0, 90), and CP (45, −45) composites.Highlights Investigated tensile, flexural, and fatigue properties of continuous fiber 3D‐printed composites. Examined failure mechanisms under tensile, bending, and fatigue loading. Developed test coupons with built‐in tabs for tensile and fatigue testing. Cross‐ply composites showed better fatigue performance than unidirectional.

Synergistic enhancement of the dynamic impact damage resistance and energy absorption of ultra‐high molecular weight polyethylene fiber reinforced composites with multiple plasma modification

AbstractThe study reveals the dynamic impact damage resistance and energy absorption of oxygen/argon/nitrogen multiple plasma modified ultra‐high molecular weight polyethylene (UHMWPE) fiber reinforced composites. The interface bonding properties and impact resistance of the composite were studied by microsphere debonding test, low‐velocity and high‐velocity impact test. The modified parameters are optimized based on quadratic polynomial equation. The impact resistance of the composite was evaluated from the aspects of ballistic limit velocity, failure mode and energy dissipation mechanism. The results showed that compared with untreated composites, the depth of dents and damage area of multiple plasma modified composites were reduced by 43.53% and 11.73%, respectively. The energy absorption and limit velocity of high‐velocity impact were increased by 14.64% and 25.58%, respectively. The modified composites formed an energy dissipation mechanism dominated by fiber breakage. The impact damage resistance and energy absorption of UHMWPE fiber reinforced composites were enhanced with multiple plasma modification.Highlights Multiple plasma modification enhance synergistic energy absorption of composites. The optimum treatment parameters of composites plasma modification were analyzed. Interface bonding properties were evaluated from microscopic perspective.

The Influence of pH Environments on the Long-Term Durability of Coir Fiber-Reinforced Epoxy Resin Composites

This study investigates the effects of different pH environments on the durability of coir fiber-reinforced epoxy resin composites (CFRERCs). The CFRERCs were prepared by combining alkali-treated coir fibers with epoxy resin and exposing them to acidic, alkaline, pure water, and seawater environments for a 12-month corrosion test. The results show that an alkaline environment has the most significant impact on the tensile strength of CFRERCs, with a 55.06% reduction after 12 months. The acidic environment causes a 44.87% decrease in strength. In contrast, tensile strength decreases by 32.98% and 30.03% in pure water and seawater environments, respectively. The greatest reduction in tensile strain occurs in the alkaline environment, with a decrease of 36.45%. In the acidic environment, tensile strain decreases by about 25.56%, while in pure water and seawater, the reductions are 18.78% and 22.65%, respectively. In terms of stiffness, the alkaline environment results in a 49.51% reduction, while the acidic environment causes a 54.56% decrease. Stiffness decreases by 43.39% in pure water and 36.72% in seawater. Field emission scanning electron microscope (FE-SEM) analysis shows that corrosive agents in different pH environments cause varying degrees of damage to the microstructure of CFRERCs. In the acidic environment, corrosive agents erode the fiber–resin interface, leading to delamination and fiber breakage. In the alkaline environment, corrosive agents penetrate the fiber interior, increasing surface roughness and porosity. While pure water and seawater also cause some damage, their effects are relatively mild.

Cellulose-mediated mechanical property tuning in small intestinal submucosal matrix to enhance stem cell osteogenic differentiation.

Natural extracellular matrices (ECM) provide a more accurate simulation of the cellular growth environment, making them excellent substrate materials for in vitro cell culture. The porcine small intestinal submucosa (SIS) is one of the most widely used natural ECM that display superior bioactivity. However, decellularization operations often result in fiber breakage and failure to recover mechanical strength in the SIS. In the current study, 2,3-dialdehyde cellulose (DAC) was synthesized and cross-linked with SIS gel to form hydrogels. The introduction of DAC into the SIS matrix resulted in a tunable increase in stiffness, which was instrumental in promoting stem cell adhesion and spreading, crucial factors for osteogenic differentiation. The cytotoxicity assessment confirmed the biocompatibility of the SIS-DAC hydrogels indicating their suitability for prolonged cell culture. Moreover, the degradation rate of the hydrogel could be effectively controlled by adjusting the DAC content, addressing the rapid degradation issue associated with SIS gels. This work confirmed the feasibility of using cellulose derivatives to modulate the mechanical properties of matrix gels and influence cell differentiation which offers a valuable experimental foundation for the development of advanced matrix gels tailored for cell culture and regenerative medicine applications.

Surface Damage Mechanism and modes in single abrasive grinding Twill carbon fiber-reinforced-polymer laminates Basing on Stress Field Analysis

The scratch 2D twill carbon fiber-reinforced-polymer (CFRP) removal and surface evolution mechanism was studied with single abrasive scratch experiments, and the single abrasive scratch finite element model (FEM) was constructed considering progressive damage models. The surfaces evolution mechanism are revealed by FEM stress field analysis and by scanning electron microscope (SEM) images. There is weft -warp fiber woven coupling structure inside 2D twill CFRP, in this paper, woven structure coupling effect means the impedance force fields are formed by the other adjacent carbon fibers during single abrasive scratching weft or warp fibers inside CFRP. The FEM stress fields for the fiber bundles, interfaces and matrices can be analyzed, and provide an effective way to study scratch damage mechanism. Scratch damage mode for weft-containing CFRP starts with resin matrix cracks under low stress as the main feature, gradually transits to carbon fiber pull-out due to stress above interface strengthen and matrix cracks as the main features, and the damage modes finally characterize with weft carbon fibers breakage due to stress above carbon fiber shear fracture strength, fiber pull-out and matrix breakage as the main features. Scratches damage mode for warp-containing starts with the resin matrix breakage, woven structure coupling effect results in fibers stress above the tensile strength, and scratches damage mode transits to the warp fibers pull-out damage and warp carbon fibers breakage as the main features. By comparing the FEM to experimental results for scratch force and SEM, the FE model proves to be valid and accuracy.

Pretreatment of Oryza sativa (Rice) and Musa cavendishii (Banana) Waste Biomass Using Ionic Liquids of Choline Amino Acid for Nanoscale Cellulose Production

The species Oryza sativa (rice) and Musa cavendishii (banana) are sources of cellulose-rich waste biomass in the Amazon region, Tocantins State. This research investigates the nanoscale production of cellulose through the interactions between three choline amino acid ionic liquids Ch[AA]IL and the respective fibers by pretreatment. To this end, the synthesis of three ILs was carried out: choline arginate Ch[Arg], choline glycinate Ch[Gly] and choline lysinate Ch[Lys], characterized by Fourier transform infrared spectroscopy (FTIR). The samples resulting from the pretreatment were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). It was possible to infer from the SEM micrographs that Ch[Arg] caused greater fiber breakage than the other ILs. The TEM analyses identified fibers up to 16 nm in diameter. Positive effects were observed in the diffractograms, although no crystallinity was obtained in the pretreated samples. Thermogravimetry curves showed that the fibers treated with Ch[Arg] showed higher thermal stability.

Toughening of thermoset composites using glass/polypropylene commingled stitching yarns.

This paper investigates the damage resistance and tolerance of thermoset composite laminates stitched by glass and hybrid glass/polypropylene commingled yarns. Different impact energies (10-70J) were applied to stitched composite laminates before compression after impact (CAI) tests were conducted. The results showed that, except for 70J, commingled yarn-stitched laminates absorbed more energy than glass-stitched laminates. Compression tests revealed that glass-stitched and commingled composites had, respectively, 2% and 5% higher compressive strengths than unstitched laminates. After being impacted to 10-70J energies, glass yarn stitched laminates kept 83-36% of their compressive strength, while commingled yarn stitched laminates retained 73-40%, showing that the commingled yarns were more efficient at higher energies. The study found that integrating plastically deformed fibres into hybrid stitching yarns increased energy absorption and composite fracture mechanism by encouraging fibre/matrix debonding, resulting in fewer fibre breakages.

Unveiling the Impact of Acetic Acid: Multi-Analytical Assessment for Characterizing Accelerated Aging in Raw Silk and Sappanwood-Dyed Silk

ABSTRACT In this study, raw and sappanwood-dyed silks were exposed to varying concentrations of acetic acid vapor to investigate aging degradation by colorimetry, SEM, FTIR, ATR-FTIR, and HPLC. The findings illustrate that acetic acid gas could lead to increase in color difference, decrease in the relative contents of crystalline regions, and changes in amino acid contents. Therefore, the aging process could be characterized as a progressive procedure: (i) initial stages were marked by color changes, (ii) gradual acid hydrolysis occurred within the protein crystalline region in the intermediate phase, and (iii) diverse trends of increase or decrease in different amino acids prevailed during the final stage of aging. Additionally, raw and sappanwood-dyed silks deteriorated further with acetic acid solution. Colorimetry and SEM showed more severe damage in dyed silk with rougher surfaces and more fiber breakage, indicating that acidic gas in water could cause greater damage and highlighted greater vulnerability of dyed silk. This study innovatively used multiple analytical methods to explore the long-term effects of acidic environments on silk and filled gaps in gas-induced aging research. It emphasized the necessity and importance of addressing gas pollution in museums and sounded the alarm of its damaging effects on silk artifacts.

Synergistic toughening of carbon fiber/vinyl ester resin composites with core–shell rubber particles and polyphenylene sulfide veils

AbstractIn this work, the interlaminar fracture toughness of carbon fiber/vinyl ester resin (VER) composites was improved through the synergistic effects of core–shell rubber (CSR) particles and polyphenylene sulfide (PPS) veils. First, a systematic investigation was conducted to assess the impact of the CSR particles on the viscosity, tensile properties, fracture toughness, and thermal properties of the modified VERs. Compared with the pristine VER, the modified VER containing 10 wt% CSR particles exhibits a 124% improvement in the critical stress intensity factor (KIC) and a 512% improvement in the critical strain energy release rate (GIC). The predicted tensile properties and fracture toughness calculated by the empirical formulas and theoretical models show a good concordance with the measured values. Compared with those of the unmodified composite, the Mode I and Mode II interlaminar fracture toughness of the composite modified by the CSR particles and PPS veils increase by 110% and 132%, respectively. Scanning electron microscopy observations indicate that the multiscale toughening mechanisms include matrix plastic deformation, plastic void growth, fiber pull‐out, fiber breakage, fiber bridging and so forth.Highlights The toughening behavior of CSR particle‐modified VERs was investigated. Empirical formulas and theoretical models were used. The synergistic toughening effect was exerted by CSR particles and PPS veils.

Cilia-Mimic Locomotion of Magnetic Colloidal Collectives Enhanced by Low-Intensity Ultrasound for Thrombolytic Drug Penetration.

Rapid thrombolysis is very important to reduce complications caused by vascular blockage. A promising approach for improving thrombolysis efficiency is utilizing the permanent magnetically actuated locomotion of nanorobots. However, the thrombolytic drug transportation efficiency is challenged by in-plane rotating locomotion and the insufficient drug penetration limits further improvement of thrombolysis. Inspired by ciliary movement for cargo transportation in human body, in this study, cilia-mimic locomotion of magnetic colloidal collectives is realized under torque-force vortex magnetic field (TFV-MF) by a designed rotating permanent magnet assembly. This cilia-mimic locomotion mode can generate more disturbances to the fluids to improve thrombolytic drug transportation and the increased height and area of colloidal collectives boosted the imaging capability. In addition, low-intensity ultrasound is applied to enhance colloids infiltration by producing the fiber breakage and inducing erythrocyte deformation. In vitro thrombolytic experiments demonstrate that the thrombolysis efficiency increased by 16.2 times compared with that of pure tissue plasminogen activator (tPA)treatments. Furthermore, in vivo rat models of femoral vein thrombosis confirmed that this approach can achieve blood flow recanalization more quickly. The proposed cilia-mimic locomotion of magnetic colloidal collectives combined with low-intensity ultrasound irradiation mode provides a new insight of therapeutic interventions for vascular thrombus by enhancing drug penetration.

Defining patterns in the intensification of hemp stalk retting processes

The object of this study is the technological operations of primary hemp stalk processing, factors that intensify the retting process, and stalk crushing. The task addressed was the identification of technical and technological solutions that would enable intensification of the production processes for hemp retting. Based on the research results, it was established that placing the flattened stems in natural and polypropylene bags, compared to cellophane bags, accelerates the preparation time of retted stalks in a vertical position by 1.19 times, and in a horizontal position by 1.38 times. The retting time for horizontally placed crushed stalks with weekly moistening twice a week is 2.16 times shorter than for uncrushed ones. It was determined that the process of crushing pre-prepared and cured stalks, whether in a vertical or horizontal position, allows for a significant reduction in retting period by 2.14 times, and for freshly cut stalks – by 1.27 times. The intensity of the reflected light flux changed in the case of reaching the retting phase for unflattened stems with their vertical placement from the initial 32.0 lux to 18.0 lux. In flattened stems under the conditions of their vertical placement – from 50.7 to 16.3 lux, respectively. In the case of horizontally placed crushed stalks, the light intensity at the retting phase was 20.3 lux. The lowest fiber breaking load value of 5.0 daN was established for the retted stalks obtained from freshly cut flattened stems in a vertical position, as well as in non-flattened stems in the vertical (7.0 daN) and horizontal (3.5 daN) positions

Analytical modeling of energy-based matrix crack growth and fiber breakage in unidirectional ceramic matrix composites under static tensile behavior in the longitudinal direction

An analytical model was developed to characterize the material behavior of ceramic matrix composites (CMCs). The model incorporates energy-based matrix crack growth, accounting for thermal residual and debonding stresses. Matrix crack growth was analyzed using the Monte Carlo method to represent the random nature of crack growth, which considers the distribution of defects within the material. Additionally, a periodic matrix crack growth model was examined. The results from the model, enhanced with correction factors, showed strong agreement with those obtained from Monte Carlo simulations. Furthermore, the global load sharing (GLS) model that includes the probability of matrix cracks propagating into the fibers was proposed and integrated with the periodic matrix crack growth model. This combined model accurately expressed the stress–strain and crack density–stress relationships up to the point of fiber breakage. The study also examined the propagation of matrix cracks into the fibers in relation to debonding stress and energy, leading to the successful validation of the proposed model.

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.

Finite Element Simulation of Acoustic Emissions from Different Failure Mechanisms in Composite Materials

Damage in composite laminates evolves through complex interactions of different failure modes, influenced by load type, environment, and initial damage, such as from transverse impact. This paper investigates damage growth in cross-ply polymeric matrix laminates under tensile load, focusing on three primary failure modes: transverse matrix cracks, delaminations, and fiber breaks in the primary loadbearing 0-degree laminae. Acoustic emission (AE) techniques can monitor and quantify damage in real time, provided the signals from these failure modes can be distinguished. However, directly observing crack growth and related AE signals is challenging, making numerical simulations a useful alternative. AE signals generated by the three failure modes were simulated using modified step impulses of appropriate durations based on incremental crack growth. Linear elastic finite element analysis (FEA) was applied to model the AE signal propagating as Lamb waves. Experimental attenuation data were used to modify the simulated AE waveforms by designing arbitrary magnitude response filters. The propagating waves can be detected as surface displacements or surface strains depending upon the type of sensor employed. This paper presents the signals corresponding to surface strains measured by surface-bonded piezoelectric sensors. Fiber break events showed higher-order Lamb wave modes with frequencies over 2 MHz, while matrix cracks primarily exhibited the fundamental S0 and A0 modes with frequencies ranging up to 650 kHz, with delaminations having a dominant A0 mode and frequency content less than 250 kHz. The amplitude and frequency content of signals from these failure modes are seen to change significantly with source–sensor distance, hence requiring an array of dense sensors to acquire the signals effectively. Furthermore, the reasonable correlation between the simulated waveforms and experimental acoustic emission signals obtained during quasi-static tensile test highlights the effectiveness of FEA in accurately modeling these failure modes in composite materials.

Design and characterization of natural fiber reinforced cotton-epoxy composites

This research paper focuses on the design and fabrication of natural cotton epoxy composites. By combining natural cotton fibers with epoxy resin, the study aims to develop composite materials with desirable mechanical properties. To evaluate their performance, the composites were subjected to three-point bending tests, which revealed an average flexural strength of 50 MPa and a flexural modulus of 3.8 GPa, highlighting the material’s capacity to bear bending loads. The bending tests provided insights into the composite’s response to flexural loads, including its strength, stiffness, and failure mechanisms. Post-test analysis using an optical microscope revealed that the primary failure modes included delamination and fiber breakage. Delamination, characterized by the separation of layers within the composite, and fiber breakage, caused by the fibers’ inability to withstand stress exceeding their tensile strength of approximately 300 MPa, led to crack propagation through the material. These findings indicate that the composite's failure was primarily driven by these mechanisms. This study provides valuable insights into improving the composite's design and enhancing its mechanical properties, contributing to the broader understanding of natural fiber-reinforced composites and their behavior under mechanical stress.