Fiber Fracture Research Articles

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.

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.

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.

Mechanical performance and dimensional stability of Washingtonia/Kenaf fibres-based epoxy hybrid composites

In this study, Washingtonia fibres (AW) and Kenaf fibres (KF) were utilized as environmentally friendly fillers to improve the quality of the resin matrix. The mechanical, morphological, and physical properties of the WA/KF biocomposites were assessed throughout this research. The mechanical tests (tensile strength and moduli, elongation at break, flexural strength along with moduli, and the impact properties) were carried out. The hybrid biocomposites (3AW/7KF) exhibited the highest tensile strength (16.05 MPa) and modulus (4.6 GPa) among pure and other hybrid biocomposites. The impact strength and resistance of hybrid biocomposites (1AW/1KF and 7AW/3KF) showed the highest impact strength (1694 J/m2) while the 3AW/7KF hybrid biocomposite, the impact strength value was 1630 J/m2 (17.2 J/m). SEM images indicated good distribution and bonding of hybrid biocomposites. The investigation using morphological tests (Scanning Electron Microscopy (SEM)) displays the longitudinal roughness on the surface, which acts as a very significant function in the adhesion between the AW/KF fibres and the resin. Furthermore, the results of SEM confirm better bonding in the biocomposites, fibre fracture, pull-out, fibre shearing, and tearing in the pure and hybrid composites. From the water absorption test, it was observed that, when increasing the immersion time of biocomposites, the WA percentage of KF biocomposite significantly increased (37%) compared to other biocomposites. However, the hybrid and pure biocomposites exhibited more resistance to increase the WA percentage after increasing the immersion times, compared to other biocomposites. Furthermore, the thickness swelling (TS) of hybrid biocomposites increased compared to pure biocomposites. The biocomposite sample (3AW/7KF) was thicker on the 7th day exhibiting the greatest increases in thickness swelling (4.98%) while the hybrid biocomposite exhibited greater WA value compared to other correspondence samples. Finally, the KF and AW hybrid blends can be appropriate for several applications, for example, textiles, machinery part production industries, medicine, and automobiles, and construction, specifically buildings, bridges, and structures such as boat hulls, swimming pool panels, racing car bodies, shower stalls, bathtubs, storage tanks. Overall, the findings exhibit that the hybridisation of natural fibres (KF/AW) is a sustainable approach for obtaining biocomposites with advanced mechanical and thermal performance. Hence, they could be used in numerous specific applications, including automobile panels, structural products, sporting goods and furniture tools.

Compression-after-indentation study of alumina-based oxide/oxide ceramic matrix composite with variable damage

In this study, the damage tolerance of alumina-based Oxide/Oxide ceramic matrix composite with varying extent of quasi-static indentation damage is evaluated via compression test. Pre-existing damage in the laminates are of different sizes and exist in the form of delaminations, fiber fracture, matrix cracking, and major through-thickness cracks. Digital image correlation is used to monitor the in-test displacements and strain field. When compared to undamaged compressive strength, the strength reduction in the indented specimens range from 52 % to 57 %. This shows that the compression after indentation strength is not significantly affected by variations in the extent of indentation damage. Digital image correlation results showed out-of-plane deformation originating from the indented region that grew stably with increasing load to a critical phase, beyond which they became significantly large. This resulted in the sudden catastrophic failure of the laminate, apparently caused by delamination buckling. This was confirmed by post-test X-ray computed tomography micrographs.

Effect of fiber orientation of adjacent plies on the mode I delamination fracture of carbon fiber reinforced polymer multidirectional laminates

AbstractThe extensive use of multidirectional composite laminates requires to understand the delamination behavior at interfaces between plies with different fiber orientations. In this study, double cantilever beam testing was performed to investigate the mode I interlaminar fracture of carbon fiber reinforced polymer laminates with different central interfaces (0//0, 0//+45 and +45//−45). X‐ray microtomography revealed the curved crack front shape that was incorporated to calculate fracture toughness. The fracture toughness varies with the crack length in a typical delamination resistance curve, which can be quantified by an empirical equation. Incorporation of variable fracture toughness into a cohesive zone model can better predict the delamination fracture of the laminate, compared to constant toughness. It was found that the delamination mechanism is independent of central interfaces. However, compared to unidirectional laminates, multidirectional laminates are less resistant to crack initiation, but more resistant to propagation with higher toughness and shorter fiber bridging zone.Highlights Mode I interlaminar fracture of CFRP laminates with different central interfaces was investigated experimentally and numerically. Curved crack front shape was incorporated to calculate fracture toughness. Incorporation of variable fracture toughness into a cohesive zone model can better predict the delamination fracture of the laminate. Multidirectional laminates are less resistant to crack initiation but more resistant to propagation with higher toughness and shorter fiber bridging zone.

Very high cycle fatigue properties of short glass fiber reinforced polyetheretherketone (PEEK)

The fatigue properties of 14 wt-% short glass fiber reinforced polyetheretherketone (PEEK–GF14) have been investigated in the high and very high cycle fatigue (VHCF) regime. Experiments were performed at a load ratio of –1 with servohydraulic and electrodynamic equipment at cycling frequency 10–20 Hz, and with ultrasonic equipment at 19 kHz. A new specimen geometry has been developed that allows ultrasonic tests up to high stress amplitudes. The same specimen shape was used in both testing series to exclude size effects, which enabled to focus on the influence of cycling frequency and testing technique. Ultrasonic fatigue testing with intermittent loading served to avoid heating of specimens. The S-N curves measured at 10–20 Hz and 19 kHz show a similar slope exponent (i.e., 10 % deviation). Mean S-N curve determined with ultrasonic equipment is shifted to slightly lower stress amplitudes, which may be attributed to statistical scatter. PEEK–GF14 does not show a fatigue limit and failures still occurred above 109 cycles. The VHCF strength of PEEK-GF14 is approximately two times higher compared with unreinforced PEEK. Fractographic investigations revealed fiber fracture and, less frequently, fiber pull-out.

Three-point bending damage detection of SiC coated C/C composites based on acoustic emission

In this study, the three-point bending process of needled C/C composites, pack cementation SiC coated-C/C composites (PC-SiC-C/C) and chemical vapor deposition SiC coated-C/C composites (CVD-SiC-C/C) were monitored by the acoustic emission (AE) technology. To study the bending damage evolution process of three kinds of composite materials, the K-means algorithm was used to analyze the AE characteristic parameters. The damage type was analyzed by combining the electron microscope image of the sample fracture. The findings revealed that C/C composites and CVD-SiC-C/C composites contain three distinct types of damage: matrix cracking, carbon fiber-pyrolytic carbon interface debonding, and fiber fracture under three-point bending loading. PC-SiC-C/C composites has two additional damage: coating cracking and pyrolytic carbon-SiC interface debonding. The various damages could be identified by different AE signals: matrix cracking (175.781–421.875 KHz), carbon fiber-pyrolytic carbon interface debonding (70.312–164.062 KHz), fiber fracture (2.929–46.875 KHz), coating cracking (375–585.937 KHz), pyrolytic carbon-SiC interface debonding (169.921–257.812 KHz). The cumulative AE energy shows that the order of damage types of the three composites during the three-point bending loading is different.

UV/thermal dual-cured MWCNTs composites for pipeline rehabilitation: Mechanical properties and damage analysis

Deformation and damage in underground pipelines remain challenging to monitor over the long term due to sensor degradation caused by corrosive substances present in the pipelines. This study investigates the potential of incorporating multi-walled carbon nanotubes (MWCNTs) into ultraviolet-cured-in-place pipe (UV-CIPP) material, a widely adopted trenchless repair technique, to enhance performance and enable deformation monitoring. A UV/thermal dual-curing strategy is introduced to mitigate the significant reduction in light transmittance caused by the inclusion of MWCNTs in the composite material. The addition of MWCNTs led to a 94.86 % reduction in light transmittance through glass fibers. However, this issue was effectively resolved through the incorporation of thermal curing, allowing for the production of ultra-high-strength composites using only three layers of fibers within a short curing time. Under optimal conditions (0.2 wt% MWCNTs with the impregnation layer on top), the flexural strength and modulus reached 442.75 MPa and 15.58 GPa, respectively, marking improvements of 14.01 % and 45.2 % over the base material. Additionally, the hardness on the composite's backside increased by 10.95 % compared to the front, indicating enhanced reinforcement. The tensile strength of braided glass fibers improved by 42.31 % and 197.54 % with the addition of 0.2 wt% and 1.0 wt% MWCNTs, respectively. Failure modes varied based on the location of the sensing layer, but all specimens eventually failed due to resin cracking, delamination of the MWCNTs-impregnated layer, and fiber fractures. The UV/thermal dual-cured composite material developed for pipeline rehabilitation in this study exhibits ultra-high strength and shows significant potential for multifunctional sensing applications.

In Vitro Comparison of Pulsed-Thulium:YAG, Holmium:YAG, and Thulium Fiber Laser.

Objective: To characterize the pulse characteristics and risk of fiber fracture (ROF) of the pulsed-Thulium:YAG (p-Tm:YAG) laser and to compare its ablation volumes (AVs) against Holmium:Yttrium-Aluminium-Garnet (Ho:YAG) laser and Thulium fiber laser (TFL). Materials and Methods: p-Tm:YAG (100 W-Thulio, Dornier-Medtech©, Germany) was characterized using single-use 272 μm core-diameter-fibers. p-Tm:YAG characterization included pulse shape, duration, and peak power (PP) studies. ROF was assessed after 5 minutes of continuous laser activation (CLA) at five decreasing fiber bend radii (1, 0.9, 0.75, 0.6, and 0.45 cm). p-Tm:YAG, Ho:YAG (120 W-Cyber-Ho, Quanta®, USA), and TFL (60 W-TFLDrive, Coloplast®, Denmark) AVs were compared using a 20-mm linear CLA at 2 mm/second velocity in contact with 20 mm3 hard stone phantoms (HSP) and soft stone phantoms (SSP) (15:3 and 15:5 water to powder ratio, respectively) fully submerged in saline at 0.5 J-20 Hz or 1 J-10 Hz. After CLA, phantoms underwent three-dimensional (3D) micro-scanning (CT) and subsequent 3D segmentation to estimate the AVs, using 3DSlicer©. Each experiment was performed in triplicate. Results: p-Tm:YAG presents a uniform pulse profile in all of the available preset modes. PP ranged from 564 to 2199 W depending on pulse mode. No laser fiber fracture occurred at any bend radius. p-Tm:YAG achieved similar mean AVs to TFL and Ho:YAG for HSP (8.96 ± 3.1 vs 9.78 ± 1.1 vs 8.8 ± 2.8 mm3, p = 0.67) but TFL was associated with higher AVs compared with p-Tm:YAG and Ho:YAG (12.86 ± 1.85 vs 10.12 ± 1.89 vs 7.56 ± 2.21 mm3, p = 0.002) against SSP. AVs for HSP increased with pulse energy for p-Tm:YAG and Ho:YAG and (11.56 ± 1.8 vs 6.36 ± 0.84 mm3 and 11.27 ± 1.98 vs 6.34 ± 0.55 mm3, p = 0.03 and p = 0.02), whereas AVs for SSP were similar across laser settings for all laser sources. AVs with TFL were similar across laser settings for both phantom types. Conclusion: p-Tm:YAG combines intermediate PP between Ho:YAG and TFL, a uniform pulse profile, no ROF with increasing deflection and effective ablation rates. Further clinical studies are needed to confirm these in vitro results.

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.

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.

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.

Enhancing the electromagnetic shielding and mechanical properties of CF/PEEK composites via low-concentration fluff and Ni-Co alloy plating

Carbon Fiber Reinforced Composites (CFRC) are increasingly used in aircraft to minimize weight and maximize structural designability. However, CFRCs have limitations in electrical conductivity and Electromagnetic Interference (EMI) resistance. This study introduces a process to overcome these drawbacks by chemically plating Carbon Fiber (CF) fabrics with a thin layer of Nickel-Cobalt (Ni-Co) alloy, thereby improving electrical conductivity. Subsequently, Sulfonated Polyether Ether Ketone (SPEEK) was applied to the Nickel-Cobalt coated Carbon Fibers (NiCo@CF). The resulting fuzzy surface effectively enhanced the interfacial interactions within the PEEK matrix. The results showed that the tensile strength, tensile modulus, flexural strength, and flexural modulus of the composite panels treated with 0.1 wt.% SPEEK sizing significantly increased by 32.3 %, 26.0 %, 167.9 %, and 20.7 %, respectively, compared to NiCO@CF/PEEK composite panels treated with no SPEEK sizing agent. Additionally, the introduction of SPEEK fostered a shift in the primary fracture mechanism from fiber pull-out or debonding to fiber fracture. Remarkably, compared to CF/PEEK composites, the electromagnetic shielding efficiency of NiCo@CF/PEEK was increased by 88.98 %, reaching 46.15 dB. Long-term testing of the S-NiCO@CF/PEEK composites in a humid and hot environment confirmed consistent electromagnetic and mechanical properties, alongside good fatigue and aging resistance. These advances make the S-NiCO@CF/PEEK composites promising for broader applications in the aircraft and aerospace fields.

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 an establish 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. The MTS, CCK-8 and EdU assays were used to test cell proliferation. ResultsHMGB2 expression was increased in samples from AD patients, samples from AD model mice and 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 suggested that HMGB2 promotes HASMC proliferation and vascular remodeling by regulating glucose metabolism through the PPAR-γ/SIRT1/PGC-1α pathway. HMGB2 knockdown reduced, whereas HMGB2 overexpression promoted, the occurrence of AD in mice. This study may help elucidate the underlying mechanisms and provide a new preventive target for AD.

Numerical investigation on effects of blast loading on anti-fragment performance of hollow cylindrical UHMWPE cross-ply laminate

Ultra-high-molecular-weight polyethylene (UHMWPE) fiber composites are widely applied for bullet and explosion proofing. This study numerically investigated the dynamic response of a hollow cylindrical UHMWPE cross-ply laminate subjected to combined blast and fragment loading produced by an improvised explosive device (IED). A strain-rate-dependent, anisotropic, elastoplastic constitutive model with progressive failure was adopted for the laminates via a user subroutine and comprehensively verified against the experimental results from the literature. Three sets of simulations of fragment-only loading, blast-only loading and the combined loading were performed on different configurations of IEDs and laminates. It was found that the effects of the blast loading were much weaker than those of the fragment loading and caused very small deformation of the laminate’s middle, including somewhat pre-tension along the circumferential direction but almost no fiber fracture. Both with and without blast loading, the dense penetrations of the multiple fragments dominated the response of laminates, including perforated holes that were interconnected with each other and global ply splitting. As a result, the blast effects barely affected the anti-fragment performance of the laminates.

Debonding Fiber Damage Mechanism Modeling for Machining Damage Inhibition During Rotary Ultrasonic Face Grinding SiO2f/SiO2

Abstract The debonding fiber defects on the grinding surface of SiO2f/SiO2 ceramic matrix composites deteriorate the service performance of related components. The low-damage process window is the key information to suppress machining damage by controlling grinding parameters. A mechanism model for debonding fiber damage on SiO2f/SiO2 surface was first proposed in this paper by the large deformation analysis for SiO2 fibers during rotary ultrasonic face grinding (RUFG). The established mechanism model built a bridge between grinding parameters and damage inhibition by integrating the ultrasonic stress effect, grinding force calculation, and critical fracture curvature cutting-off criterion of SiO2 fibers. The modeling mechanism for fiber deformation and fracture in grinding was validated by in situ observation of single abrasive grit scratching experiments. Besides, the low debonding damage process window predicted by the model was verified by experimental results and could be adopted to suppress the debonding fiber damage in grinding. The affected mechanism of fiber orientation, ultrasonic amplitude, and fiber-matrix interface strength on the low debonding damage process window was analyzed based on the theoretical and experimental results. The damage inhibition effect of the RUFG process was limited by the low fiber-matrix interface strength and axial cutter-relieving movement component. The ultrasonic-assisted vibration exerted its auxiliary effects through the ultrasonic stress effect and force reduction effect. The prerequisite for exerting the damage inhibition effect of RUFG was that the fiber-matrix interface strength was sufficient to resist the negative influence of the ultrasonic stress effect.