Fiber Damage Research Articles

Image fusion of ultrasonic and thermography for delamination detection of CFRP based on data post-processing methods

ABSTRACT Delamination is crucial damage in carbon fibre reinforced polymer (CFRP) composites. Various non-destructive testing methods could detect the delamination with different merits. Ultrasonic can penetrate CFRP but has the dead zone effect, whereas thermography can reveal shallow defect but is insensitive to deep delamination. Therefore, in this work, the results of ultrasonic C-scan and locked-in thermography were fused to inspect the delamination. The ultrasonic C-scan images were processed by 6 dB drop criteria to quantify defect area. Principal component thermography, thermographic signal reconstruction and phase extraction were implemented on the thermographic images. C-scan images and thermographic images were fused using the proposed fusion algorithm that combines the evidence theory and minimum values. The performances of fused images were evaluated by the index of signal-to-noise ratio. The results show that the C-scan image fused with the thermographic phase image can significantly improve the signal-to-noise ratio of shallow defect detection and reduce the error with the actual defect area.

Efficacy of carbon nanotube bucky paper for interlaminar damage sensing in composites and fiber‐metal laminates

AbstractDelamination between adjacent laminas and debonding at the fiber/metal interface are common failure modes in composites and fiber‐metal laminates (FMLs). During the initial stages, these flaws are difficult to detect because of their small size and limited applicability of existing damage‐sensing techniques due to the associated heterogeneity and anisotropy with composites and FMLs. Here, we demonstrate a feasible interlaminar damage‐sensing strategy in composites and FMLs using carbon nanotube (CNT) bucky paper (BP). The microstructure dependence of BP electrical conductivity allows it to sense the damage under varying loading conditions. The accuracy of strain sensing with BP is similar to the commercial 120 Ω strain gauge. The BP sensor accurately detects the interlaminar damage in composites (glass fiber/epoxy, carbon fiber/epoxy) and glass fiber–Al (GLARE) laminates. The delamination is marked by a steep rise in the electrical resistance of BP‐modified coupons. Moreover, the sensing capability of the BP sensor is found to be independent of the electrical conductivity of the tested coupons. Thus, the present approach is applicable to sense the interlaminar damage in a much wider class of structural composites and FMLs.Highlights Timely and accurate damage detection in composites is important to ensure their structural integrity. Electrical resistance of bucky paper (BP) varies with deformation. Performance of the BP sensor is comparable to the strain gauge at small strains. BP accurately captures interlaminar damage in composites and FMLs. BP is suitable for damage sensing in a wider class of layered materials.

Evaluation of the redox alteration in Duchenne muscular dystrophy model mice using in vivo DNP-MRI

Duchenne muscular dystrophy (DMD) is a genetic muscular disease and is the most common type of muscular dystrophy in Japan. Noninvasive magnetic resonance imaging (MRI) can be used for follow-up evaluation of myositis and muscular dystrophy, including DMD and inflammation is evaluated based on the increased muscle water as evaluated by T2-weighted MR images. However, in MDM, the redox status has not been evaluated non-invasively during the disease progression. We assessed the inflammation via the redox status in experimental animal disease models using in vivo dynamic nuclear polarization MRI (DNP-MRI) with a redox probe. The current study aimed to evaluate the skeletal muscle of mdx mice, a DMD model, in which muscle fiber necrosis, inflammation, and muscle regeneration were chronically repeated. Results showed that the reduction rate of Carbamoyl-PROXYL (CmP), one of the redox probes, radicals in mdx mice increased compared with that in normal mice. In vitro, more mitochondria or macrophages enhanced the radical form decay reaction by reducing CmP. Due to muscle fiber damage, the mdx mice had a lower mitochondrial concentration in the gastrocnemius muscle than the normal mice. However, the in vivo DNP-MRI results strongly reflected the increased reduction of CmP radicals by macrophages. In conclusion, in vivo DNP-MRI, a noninvasive imaging method is useful for locally evaluating skeletal muscle inflammation.

Performance Assessment of Reinforced Concrete Structures Using Self-Sensing Steel Fiber-Reinforced Polymer Composite Bars: Theory and Test Validation

This paper presents a novel self-sensing steel fiber-reinforced polymer composite bar (SFCB). The SFCB combines damage control, self-sensing, and structural reinforcement functions using distributed fiber optic sensing (DFOS) technology. By combining DFOS strains with theoretical and numerical models, a multilevel performance method for damage assessment is proposed from the perspectives of safety, suitability, and durability. Stiffness is a metric used to assess the complete service history of the reinforced concrete (RC) structure, which was used to define the damage variables. Initially, a basic correlation is created between the SFCB strain and several performance characteristics, such as moment, curvature, load, deflection, stiffness, and crack breadth, at characteristic points. The threshold values of damage variables for safety, serviceability, and durability were determined based on loading peak, mid-span deflection limits, and crack width limits corresponding to the damage variables. Then, a modified fiber damage model based on DFOS strain data is proposed to improve identification, quantification, and tracking for fiber damage. Finally, the reliability of the proposed theoretical and numerical models was verified by three-point flexural tests of SFCB-RC beams, and the test beams were analyzed using the proposed method. The results show that increasing the reinforcement ratio can lower the threshold at all levels and improve the ability of the flexural beams to control damage. This paper contributes to advancing the intelligence of RC structures and offers valuable insights for the design of intelligent RC structures.

Mechanism of targeted uric acid reduction by soybean protein peptide SHECN in hyperuricemia mice and improvement of liver injury

Hyperuricemia (HUA) is a chronic condition characterized by abnormal purine metabolism. SHECN (Ser-His-Glus-Cys-Asn), a soy-derived peptide, has demonstrated uric acid (UA) lowering and antioxidant properties in vitro. The aim of this study was to further explore its uric acid lowering potential in hyperuricemia mice. The results indicated that UA level in SHECN-H group (40 mg/kg) was reduced to 32.80 ± 1.23 μmol/L compared with that in HUA group (104.46 ± 7.30 μmol/L). SHECN group decreased serum xanthine oxidase (XO) and adenosine deaminase (ADA) activities, AST and ALT activities. Additionally, SHECN significantly ameliorated fiber damage observed in mouse liver tissue. We also found that under the action of SHECN, the active expression of XO and ADA in serum and liver was down-regulated, and the expression of hypoxanthine-guanine phosphoribosyl transferase (HGPRT) was up-regulated. Notably, SHECN effectively mimics interactions with XO-associated target proteins as well as key liver transporter receptor proteins. This study further confirmed that SHECN can affect the activity level of the key receptor protein of uric acid synthesis in the liver of mice, and ultimately reduce the serum uric acid level and alleviate liver injury (P < 0.05).

Low-temperature preparation of C/C-W-Cu composites with enhanced particle impact and ablation resistance

Herein, C/C-W-Cu composites were innovatively developed by a molten salt assisted reactive infiltration method, with the preparation temperature of only 1300 ℃, far lower than the traditional infiltration temperatures. The as-prepared C/C-W-Cu composites exhibited better particle erosion and high-temperature ablation resistance than C/C composites, with a linear variation rate decrease of 99.5 % and 80.3 % under particle impact (70 m/s, 10 s) and oxyacetylene ablation (2.4 MW/m2, 120 s) conditions, respectively. The improved protection performance can be attributed to the synergistic effects of ductile deformation of the surface W-Cu metal layer and transpiration cooling of the filled Cu phase, which prevents serious carbon fiber damage and ensures a low response of surface ablation temperature (∼1400 ℃).

Impact of plastic waste fiber and treated construction demolition waste on the durability and sustainability of concrete

This study explores the mechanical and durability properties of Plastic-Fibre Reinforced Concrete, incorporating hand-shredded plastic fibers sourced from polyethylene bags and PET bottles. Evaluations, including compressive and split tensile strength tests, were conducted on M40 grade mixes containing plastic fibers and 100% treated Construction and Demolition Waste (CDW), comparing them with conventional concrete. The results demonstrate a significant enhancement in strength properties with the addition of 0.25%, 0.5%, 0.75%, and 1% plastic-fibres, alongside the complete replacement of coarse aggregate with CDW, particularly noticeable at both 7 and 28-day curing ages. Although higher fiber dosages led to a slight reduction in compressive by 7% at the optimum percentage of 0.25% of PE and 0.5% of PET, the flexural strengths and split tensile strength exhibited a proportional increase of 11.7% and 18%. Surface analysis via Scanning Electron Microscopy (SEM) and elemental composition determination using Energy Dispersive Spectroscopy (EDS) revealed minimal fiber damage post-exposure, confirming its efficiency and contribution to higher strength and reduced weight loss in optimum mix. This novel approach combines manually recycled plastic waste as fibers with treated CDW, enhancing concrete properties while promoting sustainability. Sustainability analysis indicates that utilizing 100% CDW and plastic fiber contributes to reduced energy consumption, lower carbon emissions, and economic benefits. These findings underscore the potential of integrating non-degradable plastics into concrete mixtures, combined with treated CDW, offering both environmental sustainability and enhanced performance advantages in construction materials.

The critical role of size effect on internal damage and mechanical properties of flax fiber reinforced composites

The effect of the size on the strength of laminated artificial fiber reinforced composites has been extensive discussed during the design of large composites structure. With the trial as the structures in aerospace, civil engineering, automobile industry, the scaling of the properties of plant fiber reinforced composite should be studied. In this paper, the size effect and failure mechanism of tensile and impact properties of flax fiber reinforced composites were valuated. The effects of different area, thickness and volume on the tensile properties of composites were explored. Additionally, the failure mechanism of size effect on tensile specimens was proposed through the damage morphologies of composites. It is found that the twist of fiber bundle plays an important role in the size effect of composite thickness. Besides, the relationship between impact properties and size effect of composites was conducted, including the size of hammer, different impact energy and sample size. The curves of different types of impact samples were normalized to verify the linear rule in response stage. The crack length after impact was measured and the size effect of crack length was discussed. The size effect of crack area was studied by calculating the crack area with ultrasonic C-scan. Different “size effects” between flax fibers and artificial fibers were explored. The results are expected to provide a theoretical basis for the structural design of plant fiber reinforced composites.

Force model based on heterogeneous components decoupling and machining behaviors of ultrasonic grinding continuous fiber-reinforced MMCs

Continuous fiber-reinforced metal matrix composites (CFMMCs), such as SiC fiber-reinforced TC17 matrix composites (SiCf/TC17), are renowned for their exceptional mechanical properties. However, their heterogeneous compositions present significant machining challenges, including fiber pullout, matrix cracking, and accelerated tool wear. Ultrasonic vibration-assisted grinding (UVAG) has proven to be an effective technique for overcoming these challenges. The material removal mechanisms in UVAG, especially in composites with both ductile and brittle phases, remain poorly understood. To explore these issues, UVAG and conventional grinding (CG) experiments were conducted on SiCf/TC17 along two grinding directions: fiber’s transverse direction (FT) and fiber’s longitudinal direction (FL). This paper aims to provide a new dynamic mechanical model and shed light on the complex removal mechanisms in CFMMCs, which are characterized by a near one-to-one alternation of ductile and brittle phases. The findings reveal that UVAG reduces fiber damage and surface roughness compared to CG, especially when grinding along FT. UVAG lowers normal (Fn) and tangential grinding forces (Ft) by 15.3% and 12.3%, respectively. This highlights UVAG’s potential for improving the machinability of complex materials like CFMMCs. The proposed grinding force model closely matches the experimental results. This paper hopes to support the precision abrasive machining of CFMMCs, a kind of complex and highly anisotropic composite material, and promote their application in the fields such as aerospace.

Investigation of Cross‐Sectional Characteristics of Internal Meshing Screw Mixing Flow Field for Dough Paste

ABSTRACTThe internal meshing screw mixer, driven by extensional rheology, demonstrates excellent mixing efficiency for high‐viscosity materials while minimizing fiber damage. This study developed a computational model for the mixing process of high‐viscosity fluids based on the motion equations of the internal meshing screw. The model was validated through experiments involving the mixing of corn syrup, flour and water. The results reveal the flow field's cross‐sectional streamlines and confirm the presence of chaotic mixing states at the system interface through horseshoe mapping and the existence of hyperbolic points. By comparing the extensional and shear rates, as well as analyzing the distribution of mixing indices, this paper establishes that the primary mixing mechanism within the cross‐section is extensional force, highlighting the role of the internal meshing screw as a mixer dominated by extensional flow fields. We investigate the variations in fluid velocity, velocity uniformity index, extensional rate, shear rate, and mixing index over time under different conditions of eccentricity, rotor radius, and rotational speed. The findings indicate that while eccentricity has a limited impact on average velocity, it significantly enhances velocity disturbances and increases the ratio of extensional effects within the fluid domain. In contrast, rotor radius and speed lead to a linear increase in average velocity but have little effect on velocity disturbances and the extensional effects in the fluid domain. This study provides valuable insights into how various cross‐sectional parameters influence the flow field of the internal meshing screw mixing process, offering crucial support for its application in mixing high‐viscosity non‐Newtonian fluids within the food industry.

Characterization of early fatigue damage in CFRP unidirectional laminates based on Micro‐CT

AbstractFatigue damages of Carbon Fiber Reinforced Polymer (CFRP) laminates are not obvious. Obtaining the evolution of the internal fatigue damage in CFRP laminates before visible cracks occur is of vital importance for ensuring structural reliability. Micro X‐ray computed tomography (Micro‐CT) can provide micron scale nondestructive imaging of internal structure of materials. In this paper, a preliminary study was conducted on the early fatigue damage evolution of 0° UD laminates. Axial tension‐tension fatigue tests of [0]16 CFRP laminates were carried out, and the evolutionary behavior of damages was confirmed by fatigue dissipated energy. Then, the internal damages of fatigued specimens were observed and reconstructed using Micro‐CT, and statistical parameters such as damage sphericity, length and angle were calculated. The spatial distribution characteristics of cracks were further acquired by surface porosity and frequency distribution of damage positions in ROI. Early damages from tensile‐tensile fatigue in 0° UD laminates extend along the fiber direction with original defects in the interlayer resin enrichment areas as the nucleus, and tend to concentrate near the width edge of the specimens. Finally, a “sandwich” structural model was developed to analyze the internal stresses of laminates under the influence of interlayer resin enrichment. The FEA results revealed that the internal stresses σy and σz concentrate near the width edges of the specimen, resulting in cracks tend to evolve more in the regions close to edges.Highlights Imaging matrix cracks of specimens by Micro‐CT at 12.91 μm voxel size. Demonstrating evolution patterns of cracks with its morphology statistics. Revealing crack distributions in ROIs with variations of surface porosity. Analyzing internal stress distribution by “sandwich” model created from reality.

Small Fiber Neuropathy in Burning Mouth Syndrome: A Systematic Review.

Burning mouth syndrome (BMS) is a chronic idiopathic orofacial pain disorder, characterized by persistent burning sensations and pain without clear pathological causes. Recent research suggests that small fiber neuropathy (SFN) may play a significant role in the neuropathic pain and sensory disturbances associated with BMS. Following PRISMA guidelines, this systematic review aims to evaluate and synthesize current evidence supporting SFN's involvement in BMS. The protocol is registered in PROSPERO (CRD42024555839). The results show eight studies reported reductions in nerve fiber density in tongue biopsies (ranging from 30% to 60%), along with morphological changes indicative of small fiber damage. Additionally, an increase in TRPV1-positive, NGF-positive, and P2X3-positive fibers, overexpression of Nav1.7, and slight underexpression of Nav1.9 mRNA were observed in BMS patients. Quantitative Sensory Testing in seven studies revealed sensory abnormalities such as reduced cool detection and cold pain thresholds. Blink reflex and corneal confocal microscopy also indicated peripheral and central small fiber damage, along with increased artemin mRNA expression. The evidence strongly supports SFN as a key factor in the pathophysiology of BMS, particularly due to reductions in nerve fiber density and altered sensory thresholds. However, variability across studies highlights the need for larger, standardized research to establish causal relationships and guide therapeutic strategies.

Examining the effect of the shear coefficient on the prediction of progressive failure of fiber-reinforced composites

The ultimate damage of composites under tension usually results from fiber damage, which includes both tensile and shear contributions. In this study, the shear coefficient α of the fiber yarn is incorporated into the failure criterion to consider the shear effect of the fiber yarn. An analytical model is then proposed that combines a homogenization method and the enhanced failure criterion to facilitate quick evaluation of the progressive damage and failure of the composite. The sensitivity of α on the behaviors of progressive damage and failure are comprehensively explored for different types of fiber-reinforced composites, including a laminate, a plain weave composite, a two-dimensional triaxially braided composite, and a three-dimensional woven composite. The results indicate that damage and failure behaviors are generally sensitive to the shear coefficient, and composites with more complex textile structure demonstrates greater sensitivity to the α. An analysis of the sensitivity of α for different failure criteria was also conducted, and the results reveal that the Hashin–Hou criterion shows more sensitivity to α than the Chang–Chang criterion, the Hoffman criterion, or the Tsai–Wu criterion. Therefore, the identification of the shear coefficient is significant for exploring the damage and failure behaviors of fiber-reinforced composites.

Reactive sintered dense carbon fiber reinforced high‐entropy boride composite using high‐entropy silicide as reactant

AbstractA novel reactive sintering strategy using high‐entropy disilicide, B4C, and carbon as initial materials is developed to fabricate dense carbon fiber reinforced high‐entropy diboride (HEB)‐based composite (Cf/HEBs) at a relatively low temperature. The Cf/(V0.2Nb0.2Cr0.2Mo0.2W0.2)B2–SiC composite (Cf/HEB–SiC) successfully achieves nearly full densification (with a relative density of 99.2%) at 1800°C. The reactive damage of carbon fibers can be effectively restrained by preassemble carbon coating during the preparation process of the composite. Lower preparation temperature and effective coating protection contribute to the exertion of carbon fibers toughening capacity, consequently noticeably elevating the critical crack size (αcr) from 27.7 µm for HEB–SiC to 110.4 µm for Cf/HEB–SiC. The current work provides a feasible way to substantially upgrade the damage tolerance of HEB–SiC and can be extended to other HEBs‐based ceramics.

Enhancement of pin‐bearing behavior of pultruded FRP profiles by multi‐directional fiber architecture design

AbstractThe low resistance of bolted joints in pultruded unidirectional (UD) fiber‐reinforced polymer (FRP) profiles limits the load grade of truss bridges due to shear damage along UD fibers. To address this issue, this study proposes multi‐directional (MD) fiber architecture in FRP profiles to improve the ultimate bearing strength of bolted joints. The digital image correlation shows that the addition of off‐axis fibers in MD FRP profiles prevents shear failure in the UD FRP profile. As a result, the ultimate bearing strengths of MD FRP profiles are enhanced attributed to “off‐axis fiber tie action”. Micro‐computed tomography shows that fiber damage in MD FRP profiles emerged from outer plies, including fiber breakage in 90° and ±45° fibers and fiber kinking in 0° and ±45° fibers. The off‐axis fibers break due to tension when resisting the bearing load in MD FRP profiles. The fiber kinking indicated strength contribution from 0° to ±45° fibers. The fiber breakage and fiber kinking in each ply are dominant in bearing failure instead of delamination, which increases the bearing strength of the pultruded MD FRP profiles. These findings facilitate controlling damage evolution in the pultruded MD FRP profiles and designing high‐resistance bolted joints.Highlights Multi‐directional fibers improved bearing strengths of FRP profiles by 28.5%–33%. Off‐axis fibers bent under pin‐bearing, forming a tie action until breakage. Fiber breakage and kinking in each ply contributed to the bearing failure. Strain localization and redistribution were observed using DIC.

Corneal nerve loss in adolescents with obesity and acanthosis nigricans.

Obesity and related metabolic abnormalities in adults are associated with peripheral neuropathy. Acanthosis nigricans (AN) is associated with insulin resistance, fatty liver, hyperlipidemia and glucose intolerance, all of which are risk factors for neuropathy. The aim of this study was to investigate if obese adolescents with AN have evidence of small nerve fiber damage. Adolescents with obesity with and without AN underwent body composition analysis, assessment of vibration perception threshold (VPT), monofilament sensitivity and corneal confocal microscopy (CCM) to quantify corneal nerve fiber density (CNFD), branch density (CNBD), length (CNFL) and inferior whorl length (IWL). Forty-six participants with obesity with (n = 31) and without (n = 15) AN aged 15(14-17) years were compared to 20 healthy controls aged 13(12-14) years. There was no difference in VPT, monofilament sensitivity and CCM measures between adolescents with obesity and controls. However, adolescents with AN had a significantly higher weight (P = 0.022), fat% (P = 0.029) and fat-muscle ratio (P = 0.012) with a lower CNFD (P = 0.045) compared to those with obesity without AN. Adolescents with obesity and acanthosis nigricans have a higher fat mass and small nerve fibre loss, indicative of a sub-clinical neuropathy.

Study on thermal-assisted underwater friction stir welding for carbon fiber-reinforced polyetherimide

Friction stir welding (FSW) of carbon fiber-reinforced thermoplastic has shown attractive applications in industrial fields. However, the heat input during the FSW is hard to control, which leads to significant material loss and carbon fiber damage. In this paper, a carbon fiber-reinforced polyetherimide (CF-PEI) plate is joined via thermal-assisted underwater friction stir welding (UFSW). The evaluation of heat-assisted UFSW joints is conducted by studying the surface morphology, microstructure of the weld interface, the state and distribution of carbon fibers, and tensile analysis. The findings indicated that water can reduce heat input, and the water temperature has a significant impact on the weld properties. Specifically, at a water temperature of 60°C, there is a considerable reduction in material loss and carbon fiber damage. The study also reveals that this temperature facilitates the interweaving of carbon fibers into a stable structure at the interface and their integration with the PEI substrate. This reduces the inhibition of the material on carbon fiber elongation, ultimately enhancing the bonding interface and improving tensile shear properties. The maximum tensile strength value of the welds reached 33.6 MPa, equivalent to 79.6% of the CF-PEI sheet. Compared to FSW, joint tensile strength is increased by 45.5%.

Experimental study on damage of steel fiber reinforced concrete- and wood-filled GFRP tubes under axial compression

In order to reduce the self-weight of concrete structures and improve its corrosion resistance, it is an effective way to fill GFRP tubes with wood columns instead of part of concrete. However, concrete structures are prone to cracks, which will reduce the bearing capacity of the structure and affect the safety and applicability of the structure. Incorporating the steel fibers (SF) in concrete seems to be an excellent solution to limit crack propagation and improve the ductility of concrete structures. Based on the premise, in this paper, a new type of structure composite material of steel fiber reinforced concrete- and wood-filled GFRP tubes was developed. The mechanical properties, damage evolution process and crack fractal characteristics of steel fiber reinforced concrete- and wood-filled GFRP tubes under axial compression with different SF volume fractions (0 %, 1 %, 1.5 % and 2 %) were studied by acoustic emission (AE) technology. The finite element method (FEM) was established to simulate the test work and expand the analysis. The results showed that the bearing capacity and ductility of the specimens increased first and then decrease with the increase of SF content, and the specimens with 1.5 % volume fraction of SF showed the best mechanical properties. According to the characteristics of AE ringing counts, the damage process of the specimen was described by three marker events, which were concrete cracking, wood cracking and GFRP tube fracture. The incorporation of SF increased the intensity of AE signal and the proportion of shear cracks, and reduced the damage scale. The fractal dimension of concrete surface cracks had a good correlation with the degree of local damage and the complexity of crack propagation. The damage evolution model based on AE cumulative events and stress obeyed the two-parameter Weibull distribution. The incorporation of SF reduced the degree of damage, and the parameter m had a negative correlation with brittleness. In addition, the damage process of the specimens revealed by the FEM matched well with the experimental results. Additionally, the incorporation of SF made the stress distribution of each part of the specimen more uniform and avoided the phenomenon of stress concentration.

Investigating the mechanical properties and crashworthiness of hybrid PLA/GFRP composites fabricated using FDM-filament winding

The failure and crashworthiness performance of hybrid Polylactide (PLA)/Glass Fiber Reinforced Polymer (GFRP) composite tubes subjected to axial and radial quasistatic compression loads were investigated in the present study. The composite tubes are fabricated using hand lay-up and Fused Deposition Modeling (FDM)-filament winding processes. The crashworthiness performance was studied using parameters such as the peak load, energy absorption, crush load, crushing load efficiency, and specific energy absorption. The highest peak loads from the compression test results in the axial and radial directions are calculated using variations in the filament winding PLA/GFRP (FPG) specimen, whose values were 16130.50 N and 12077.33 N, respectively. The highest mean crush load is found in the material variation with the FPG specimen, which is 5734.43 J/mm for axial loading and 4886.75 J/mm for radial loading. The highest energy absorption (EA) value is found in the material variation with the FPG specimen, which is 262.18 J for axial direction loading and 94.02 J for radial direction loading. The highest specific energy absorption (SEA) value is found in the material variation with the specimen Filament Winding PLA/GFRP, which is 16.92 J/g for axial loading and 10.98 J/g for radial loading. There are three main types of failure of the composite: matrix cracking, fiber damage, and folding. The study showed that by combining Additive Manufacturing and composite lamination, the hybrid PLA/GFRP specimen outperformed the existing structures.

A char removal protocol to visualize fiber cross‐sections of carbon/epoxy composites subjected to flame

AbstractPost‐crash fires obscure or destroy critical fracture surfaces needed to determine the origin of aircraft structural failures. Our goal is to eliminate combustion residue from carbon fiber‐reinforced polymer composites to enable fractographic examination during aviation accident investigations. In this work, combustion residues were removed from burned Hexcel SGP370‐8H/8552 woven‐fabric carbon/epoxy specimens by nitric/sulfuric acid oxidations. Scanning electron microscopy identified various types of char obscuring the fiber ends. For char removal, the burned specimens were immersed in a nitric acid/sulfuric acid/water solution (0.18 wt.%, 96.25 wt.%, 3.57 wt.%) at elevated temperatures (75–150°C). Higher temperatures enhanced nitric acid decomposition in this highly acidic, low‐water environment, accelerating char oxidation and progressively enhancing the extent of char removal. At lower temperatures (T &lt; 100°C), char deposits were partially oxidized after 60 mins. At 125 and 150°C, the char was removed within 30 mins of immersion. The epoxy matrix both chemically decomposed and oxidized and the char oxidized during these oxidation treatments. Gas evolution and soluble products dissolved in the HNO3/H2SO4 media. The damage morphology created by the sawing action on the fiber ends, created before flame exposure, remained clearly visible after the acid oxidations. This occurs because oxidation rates at the carbon fiber ends are much slower than the char oxidation in these acid treatments. If the acid treatment temperature raised above 185°C, then this sawing‐induced fiber damage morphology will also be destroyed. This preliminary understanding can be applied to develop a comprehensive forensic analysis procedure for post‐crash fire investigations.Highlights Flame exposure of sawed specimen cross‐sections leads to char formation, obscuring fiber damage morphologies. HNO3/H2SO4 oxidations at elevated temperatures (75–150°C) resulted in char removal from fiber ends. Higher temperatures (T = 125 and 150°C) accelerated char oxidation. The sawing of carbon/epoxy composites caused extensive fiber damage and ply delamination. Residual decomposed resin matrix and char oxidized faster than the carbon fibers and the fiber sawing‐induced fiber damage morphologies created before flame exposure and were preserved after char removal.