Search Results (375)

This study investigates the elastoplastic behavior of phenol formaldehyde/polyvinyl butyral matrix (70% PF/30% PVB) reinforced with Kevlar^® fibers through comprehensive in-plane tensile testing. Cyclic loading–unloading tests were conducted at a 100%/min strain rate using a universal testing system at room temperature on $\left(0_4\right)$, $\left({90}_4\right)$, and ${\left(\pm 45\right)}_s$ laminates. The experimental results revealed significant nonlinear hardening behavior beyond yield stress, accompanied by yarn stiffening effects during loading cycles. A novel elastoplastic constitutive model was developed, incorporating Hill’s yield criterion adapted for orthotropic materials and an isotropic hardening function that accounts for equivalent plastic strains and progressive yarn stiffening. Laminates with other stacking sequences were also tested and the accuracy of the predictions of the nonlinear behavior was assessed. In these laminates, delaminations took place and the model provided an overestimation of the stress–strain response. Since the model could not predict delamination onset and propagation, an adaptation of the model considering fully delaminated interfaces brought a lower bound of this response. Despite the limitations of the model, it can be used to provide reasonable limits to the stress–strain response of laminates accounting for plastic strains within plies. This study provides essential mechanical properties and constitutive relationships for designing Kevlar^® composite structures with tailored stiffness characteristics for impact-resistant applications. Full article

The increasing use of carbon fiber reinforced polymer (CFRP) composites in industries such as aerospace, due to its high strength-to-weight ratio, durability, and resistance to corrosion has led to a growing demand for more efficient machining processes. However, the multilayered structure of CFRP composites, composed of densely packed fibers, presents significant challenges during machining. Additionally, when cutting fluids are used to improve effective cooling and lubrication, the material tends to absorb the fluid, causing damage and leading to problem of weaking of composite structure. To address these issues, this study compares ultrasonic-assisted drilling (UAD) and minimum quantity lubrication (MQL) techniques with conventional drilling (CD) and dry cutting to improve the performance of CFRP composite drilling. The results show that using UAD and MQL together reduced thrust force by up to 27%, improved surface roughness inside the holes by up to 31%, reduced improved hole diameter, cylindricity, roundness, and delamination. Full article

Drilling-induced damage in fiber-reinforced polymer composite materials was measured excavating four laminates, basalt (B₁₄), glass (G₁₄) and their two sandwich type hybrids (B₄G₆B₄, G₄B₆G₄), with 6 mm twist drills at 1520 revolutions per minute and 0.10 mm rev⁻¹ under dry running with an uncoated high-speed steel (HSS-R), grind-coated high-speed steel (HSS-G) or physical vapor deposition-coated (high-speed steel coated with Titanium Nitride (TiN) and Titanium Aluminum Nitride (TiAlN)) drill bits. The hybrid sheets were deliberately incorporated to clarify how alternating basalt–glass architectures redistribute interlaminar stresses during drilling, while the hard, low-friction TiN and TiAlN ceramic coatings enhance cutting performance by forming a heat-resistant tribological barrier that lowers tool–workpiece adhesion, reduces interface temperature, and thereby suppresses thrust-induced delamination. Replacement of an uncoated, grind-coated, high-speed-steel drill (HSS-G) with the latter coats lowered the mechanical and thermal loads substantially: mean thrust fell from 79–94 N to 24–30 N, and peak workpiece temperatures from 112 °C to 74 °C. Accordingly, entry/exit oversize fell from 2.5–4.7% to under 0.6% and, from the surface, the SEM image displayed clean fiber severance rather than pull-out and matrix smear. By analysis of variance (ANOVA), 92.7% of the variance of thrust and 86.6% of that of temperature could be accounted for by the drill-bit factor, thus confirming that the coatings overwhelm the laminate structure and hybrid stacking simply redistribute, but cannot overcome, the former influence. Regression models and an artificial neural network optimized via meta-heuristic optimization foretold thrust, temperature and delamination with an R² value of 0.94 or higher, providing an instant-screening device with which to explore industrial application. The work reveals TiAlN- and TiN-coated drills as financially competitive alternatives with which to achieve ±1% dimensional accuracy and minimum subsurface damage during multi-material composite machining. Full article

In this work we investigate the integration possibility of a thermistor paste from ESL (ElectroScience Laboratory, now Vibrantz) to see if it is adapted for Vibrantz Low Temperature Cofired Ceramics (LTCC) L8 and A6M-E materials. An alumina-based sample is used as a reference circuit throughout this study. Square, two-squares-in-parallel and two-squares-in-series thermistors are tested, placed internally and externally. Resistive values are measured in a range from 25 °C to 300 °C. The variation in the resistive values among similar thermistors is significant, with a maximum standard deviation of 67%. However, in all cases, there is a positive linear relationship between resistance and temperature. The Temperature Coefficient of Resistance (TCR) value is calculated before and after annealing. In general, the L8 and Al₂O₃ samples exhibit higher TCR values than the A6M-E sample. Additionally, when placed internally, the TCR value decreases approximately 30% for both tested LTCC materials. An Energy-Dispersive X-ray Spectroscopy (EDX) material analysis has also been conducted on the samples, revealing that the main chemical components are oxide, silicon, calcium, and ruthenium but also some barium and titanium, which indicates SiO₂, TiO₂, BaTiO₃ and RuO₂ oxides in the thermistor paste. The possibility to implement thermistors internally and externally on Vibrantz LTCC without delamination problems is endorsed by this study. Full article

Carbon fiber-reinforced plastics (CFRPs) offer excellent in-plane mechanical performance, but their relatively low interlaminar fracture toughness makes them vulnerable to delamination, particularly around intralaminar discontinuities such as resin-rich regions or fiber gaps. This study investigates the effectiveness of polyamide (PA) mesh inserts in improving interlaminar toughness and suppressing delamination in CFRP laminates with such features. Two PA mesh configurations were evaluated: a fully embedded continuous layer and a 20 mm cut mesh strip placed between continuous and discontinuous plies near critical regions. Fracture toughness tests showed that PA mesh insertion improved interlaminar toughness approximately 2.4-fold compared to neat CFRP, primarily due to a mechanical interlocking mechanism that disrupts crack propagation and enhances energy dissipation. Uniaxial tensile tests with digital image correlation revealed that while initial matrix cracking occurred at similar stress levels, the stress at which complete delamination occurred was approximately 60% higher in specimens with a 20 mm mesh and up to 92% higher in specimens with fully embedded mesh. The fully embedded mesh provided consistent delamination resistance across the laminate, while the 20 mm insert localized strain redistribution and preserved global mechanical performance. These findings demonstrate that PA mesh is an effective interleaving material for enhancing damage tolerance in CFRP laminates with internal discontinuities. Full article

This research paper employed novel sustainable alternative materials to reduce the environmental impact of thermoset/synthetic fibre composites. The effect of seawater hydrothermal ageing at 45 °C for 45 and 90 days on the physical and interlaminar fracture toughness (mode I and mode II) of a semi-unidirectional non-crimp basalt fibre (BF)-reinforced acrylic matrix and epoxy matrix composites was investigated. Optical and scanning electron microscopes were used to describe the fracture and interfacial failure mechanisms. The results show that the BF/Elium composite exhibited higher fracture toughness properties compared to the BF/Epoxy composite. The results of the mode I and mode II interlaminar fracture toughness values for the BF/Elium composite were 1280 J/m² and 2100 J/m², which are 14% and 56% higher, respectively, than those of the BF/Epoxy composite. The result values for both composites were normalised with respect to the density of each composite laminate. The saturated moisture content and diffusion coefficient values of seawater-aged samples at 45 °C and room temperature for the BF/Elium and BF/Epoxy composites were analysed. Both composites exhibited signs of polymer matrix decomposition and fibre surface degradation under the influence of seawater hydrothermal ageing, resulting in a reduction in the mode II interlaminar fracture toughness values. Enhancement was observed in mode I fracture toughness under hydrothermal ageing, particularly for the BF/Epoxy composite, due to matrix plasticisation and fibre bridging. Full article

Patients undergo total knee arthroplasty (TKA) at younger ages with the expectation that the devices will perform well over two to three decades. During this time, the ultra-high molecular weight polyethylene (UHMWPE) bearing material properties of the implant may change due to aging induced by radiation and oxygen diffusion or other effects. Vitamin E or other antioxidants are promoted since several years to improve the oxidation resistance of UHMWPE. To compare the effectivity of these substances against established materials, a six weeks aging process was used and the chemical, mechanical and bio-tribological properties were analysed. Highly crosslinked and two weeks aged UHMWPE served as a reference for the currently established aging standards and virgin UHMWPE was aged for six weeks to separate the effects of crosslinking and vitamin E blending. Six weeks artificially aging changed the chemical, mechanical and bio-tribological properties of cross-linked UHMWPE significantly compared to only two weeks artificially aging, leading to cracks and delamination during the highly demanding activities wear test. The degradative effect of extended aging was also observed for virgin UHMWPE. These observations are in good accordance to retrieval findings. Minor changes on the chemical properties were observed for the cross-linked UHWMPE blended with vitamin E without impact on the mechanical and bio-tribological properties. Full article

Modern aerospace engineering places increasing emphasis on materials that combine low weight with high mechanical performance. Fiber metal laminates (FMLs), which merge metal layers with fiber-reinforced composites, meet this demand by delivering improved fatigue resistance, impact tolerance, and environmental durability, often surpassing the performance of their constituents in demanding applications. Despite these advantages, inspecting such thin, layered structures remains a significant challenge, particularly when they are difficult or impossible to access. As with any new invention, they always come with challenges. This study examines the effectiveness of the fundamental anti-symmetric Lamb wave mode (A0) in detecting weak interfacial defects within Carall laminates, a type of hybrid fiber metal laminate (FML). Delamination detectability is analyzed in terms of strong wave dispersion observed downstream of the delaminated sublayer, within a region characterized by acoustic distortion. A three-dimensional finite element (FE) model is developed to simulate mode trapping and full-wavefield local displacement. The approach is validated by reproducing experimental results reported in prior studies, including the author’s own work. Results demonstrate that the A0 mode is sensitive to delamination; however, its lateral resolution depends on local position, ply orientation, and dispersion characteristics. Accurately resolving the depth and extent of delamination remains challenging due to the redistribution of peak amplitude in the frequency domain, likely caused by interference effects in the acoustically sensitive delaminated zone. Additionally, angular scattering analysis reveals a complex wave behavior, with most of the energy concentrated along the centerline, despite transmission losses at the metal-composite interfaces in the Carall laminate. The wave interaction with the leading and trailing edges of the delaminations is strongly influenced by the complex wave interference phenomenon and acoustic mismatched regions, leading to an increase in dispersion at the sublayers. Analytical dispersion calculations clarify how wave behavior influences the detectability and resolution of delaminations, though this resolution is constrained, being most effective for weak interfaces located closer to the surface. This study offers critical insights into how the fundamental anti-symmetric Lamb wave mode (A0) interacts with delaminations in highly attenuative, multilayered environments. It also highlights the challenges in resolving the spatial extent of damage in the long-wavelength limit. The findings support the practical application of A0 Lamb waves for structural health assessment of hybrid composites, enabling defect detection at inaccessible depths. Full article

Enhancing damage tolerance and wear resistance in Al–Si-based alloys under thermomechanical stress remains a key challenge in lightweight structural applications. This study investigates the microstructural and tribomechanical behavior of hypoeutectic Al–Si–(Cu)–Mg alloys with varying Cu:Mg ratios (3:1 vs. 1:3) under a T6 heat treatment. Alloys A and B, with identical Si contents but differing Cu and Mg levels, were subjected to multiscale microstructural characterization and mechanical and wear testing at 25 °C, 150 °C, and 250 °C. Alloy A (Cu-rich) exhibited refined α-Al(FeMn)Si phases and homogeneously dissolved Cu in the Al matrix, promoting lattice contraction and dislocation pinning. In contrast, Alloy B (Mg-rich) retained coarse Mg₂Si and residual β-AlFeSi phases, which induced local stress concentrations and thermal instability. Under tribological testing, Alloy A showed slightly higher friction coefficients (0.38–0.43) but up to 26.4% lower wear rates across all temperatures. At 250 °C, Alloy B exhibited a 25.2% increase in the wear rate, accompanied by surface degradation such as delamination and spalling due to β-AlFeSi fragmentation and matrix softening. These results confirm that the Cu:Mg ratio critically influences the dominant hardening mechanism—the solid solution vs. precipitation—and determines the high-temperature performance. Alloy A maintained up to 14.1% higher tensile strength and 22.3% higher hardness, exhibiting greater shear resistance and interfacial stability. This work provides a compositionally guided framework for designing thermally durable Al–Si-based alloys with improved wear resistance under elevated temperature conditions. Full article

The Shenduntou Site, a significant Zhou Dynasty settlement in Anhui Province, provides rare insights into early Chinese woodcraft. This study examines exceptionally preserved wooden structures from Well J1, dating to the Western Zhou period (9th–8th c. BCE). Anatomical analysis identified the timber as Firmiana simplex (L.), indicating ancient selection of this locally available species for its water resistance and mechanical suitability in well construction. Comprehensive degradation assessment revealed severe structural deterioration: maximum water content (1100% ± 85% vs. modern 120% ± 8%) demonstrated extreme porosity from hydrolysis; X-ray diffraction (XRD) showed a 69.5% reduction in cellulose crystallinity (16.1% vs. modern 52.8%); Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy confirmed near-total hemicellulose degradation, partial cellulose loss, and lignin enrichment due to chemical recalcitrance; Scanning Electron Microscopy (SEM) imaging documented multiscale damage including vessel thinning, pit membrane loss, and cell wall delamination from hydrolytic, microbial, and mineral degradation. These findings reflect Western Zhou inhabitants’ pragmatic resource utilisation while highlighting advanced material deterioration that poses significant conservation challenges, providing critical insights into Zhou-era woodcraft and human–environment interactions in the lower Yangtze region. Full article

In this paper, a series of polyaniline (PANI)/Ti₃C₂ MXene composites (PMCs) with a biomimetic structure were prepared and employed as an anticorrosion coating application. First, the PANI was synthesized by oxidative polymerization with ammonium persulfate as the oxidant. Then, 2D Ti₃C₂ MXene nanosheets were prepared by treating the Ti₃AlC₂ using the optimized minimally intensive layer delamination (MILD) method, followed by characterization via XRD and SEM. Subsequently, the PMC was prepared by the oxidative polymerization of aniline monomers in the presence of Ti₃C₂ MXene nanosheets, followed by characterization via FTIR, XRD, SEM, TEM, CV, and UV–Visible. Eventually, the PMC coatings with the artificial biomimetic surface structure of a macaw feather were prepared by the nano-casting technique. The corrosion resistance of the PMC coatings, evaluated via Tafel polarization and Nyquist impedance measurements, shows that increasing the MXene loading up to 5 wt % shifts the corrosion potential (E_corr) on steel from −588 mV to −356 mV vs. SCE, reduces the corrosion current density (I_corr) from 1.09 µA/cm² to 0.035 µA/cm², and raises the impedance modulus at 0.01 Hz from 67 kΩ to 3794 kΩ. When structured with the hierarchical feather topography, the PMC coating (Bio-PA-MX-5) further advances the E_corr to +103.6 mV, lowers the I_corr to 7.22 × 10⁻⁴ µA/cm², and boosts the impedance to 96,875 kΩ. Compared to neat coatings without biomimetic structuring, those with engineered biomimetic surfaces showed significantly improved corrosion protection performance. These enhancements arise from three synergistic mechanisms: (i) polyaniline’s redox catalysis accelerates the formation of a dense passive oxide layer; (ii) MXene nanosheets create a tortuous gas barrier that cuts the oxygen permeability from 11.3 Barrer to 0.9 Barrer; and (iii) the biomimetic surface traps air pockets, raising the water contact angle from 87° to 135°. This integrated approach delivers one of the highest combined corrosion potentials and impedance values reported for thin-film coatings, pointing to a general strategy for durable steel protection. Full article

This study presents colorless polyimides (PIs) suitable for use as plastic substrates in flexible displays, designed to be compatible with controlled soft adhesion and easy delamination (temporary adhesion) processes. For this purpose, we focused on a PI system derived from norbornane-2-spiro-α-cyclopentanone-α′-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride (CpODA) and 2,2′-bis(trifluoromethyl)benzidine (TFMB). This system was selected with the aim of exhibiting excellent optical transparency and low linear coefficient of thermal expansion (CTE) properties. However, fabricating this PI film via the conventional two-step process was challenging because of crack formation. In contrast, modified one-pot polymerization at 200 °C using a combined catalyst resulted in a homogeneous solution of PI with an exceptionally high molecular weight, yielding a flexible cast film. The solubility of PI plays a crucial role in its success. This study delves into the mechanism behind the significant catalytic effect on enhancing molecular weight. The CpODA/TFMB PI cast film simultaneously achieved very high optical transparency, an extremely high glass transition temperature (T_g = 411 °C), a significantly low linear coefficient of thermal expansion (CTE = 16.7 ppm/K), and sufficient film toughness, despite the trade-off between low CTE and high film toughness. The CpODA/TFMB system was modified by copolymerization with minor contents of another cycloaliphatic tetracarboxylic dianhydride, 5,5′-(1,4-phenylene)-exo-bis(hexahydro-4,7-methanoisobenzofuran-cis-exo-1,3-dione) (BzDAxx). This approach was effective in improving the film toughness without sacrificing the low CTE and other target properties. The peel strengths (σ_peel) of laminates comprising surface-modified glass substrates and various colorless PI films were measured to evaluate the compatibility with the temporary adhesion process. Most colorless PI films studied were found to be incompatible. Additionally, no correlation between σ_peel and PI structure was observed, making it challenging to identify the structural factors influencing σ_peel control. Surprisingly, a strong correlation was observed between σ_peel and CTE of the PI films, suggesting that the observed solid–solid lamination is closely linked to the unexpectedly high surface mobility of the PI films. The laminate using CpODA(90);BzDAxx(10)/TFMB copolymer exhibited suitable adhesion strength for the temporary adhesion process, while meeting other target properties. The modified one-pot polymerization method significantly contributed to the development of colorless PIs suitable for plastic substrates. Full article

Under service conditions, randomly distributed cracks in the top coat (TC) layer of thermal barrier coatings (TBCs) lead to local stress concentrations, which serve as the primary drivers of crack propagation and coating delamination. This study systematically analyzes the influence of crack defects on the thermal stress distribution in TBCs, based on their microstructural characteristics, using a multi-physics-coupled finite element model. Numerical analysis of crack characteristics reveals that crack length significantly influences the stress distribution in the coatings, with the maximum tensile stress at the crack tip increasing from 104.02 to 238.51 MPa as the crack half-length extends from 400 to 1000 μm. Shorter cracks induce lower tensile stresses, thereby retarding crack propagation and delaying coating delamination. Crack depth also influences the stress distribution, with the maximum tensile stress decreasing from 205.88 to 101.65 MPa as the crack is buried deeper, from 50 to 200 μm, indicating a more stable stress state less prone to propagation in deeper cracks. For inclined cracks, increasing the inclination angle induces a shift in stress from tensile to compressive, with larger inclination angles exhibiting greater stability. Accordingly, this study proposes a laser scribing strategy to mitigate crack-tip stress concentration, which is validated through comparison with two-dimensional crack models. Laser scribing shortens crack length by interrupting crack continuity, relieves localized thermal expansion strain, effectively suppresses crack growth, and significantly enhances the crack resistance and thermal shock stability of the coating. Full article

High-Bandwidth Memory (HBM) enables the bandwidth required by modern AI and high-performance computing, yet its three dimensional stack traps heat and amplifies thermo mechanical stress. We first review how conventional solutions such as heat spreaders, microchannels, high density Through-Silicon Vias (TSVs), and Mass Reflow Molded Underfill (MR MUF) underfills lower but do not eliminate the internal thermal resistance that rises sharply beyond 12layer stacks. We then synthesize recent hybrid bonding studies, showing that an optimized Cu pad density, interface characteristic, and mechanical treatments can cut junction-to-junction thermal resistance by between 22.8% and 47%, raise vertical thermal conductivity by up to three times, and shrink the stack height by more than 15%. A meta-analysis identifies design thresholds such as at least 20% Cu coverage that balances heat flow, interfacial stress, and reliability. The review next traces the chain from Coefficient of Thermal Expansion (CTE) mismatch to Cu protrusion, delamination, and warpage and classifies mitigation strategies into (i) material selection including SiCN dielectrics, nano twinned Cu, and polymer composites, (ii) process technologies such as sub-200 °C plasma-activated bonding and Chemical Mechanical Polishing (CMP) anneal co-optimization, and (iii) the structural design, including staggered stack and filleted corners. Integrating these levers suppresses stress hotspots and extends fatigue life in more than 16layer stacks. Finally, we outline a research roadmap combining a multiscale simulation with high layer prototyping to co-optimize thermal, mechanical, and electrical metrics for next-generation 20-layer HBM. Full article

In today’s aviation industry, research and studies are carried out to manufacture and design lightweight, high-performance materials. One of the materials developed in line with this goal is glass laminate aluminum-reinforced epoxy (GLARE), which consists of thin aluminum sheets and S2-glass/epoxy layers. Because of its high impact resistance and excellent fatigue and damage tolerance properties, GLARE is used in different aircraft parts, such as the wing, fuselage, empennage skins, and cargo floors. In this study, a survey was carried out and a low-velocity impact model for GLARE materials was developed using the ABAQUS (2014) version V6.14 software and compared with the results of low-velocity impact tests performed according to the American Society for Testing and Materials (ASTM) D7136 standard. This article introduces a novel integrated approach that combines detailed numerical modeling with experimental validation of GLARE 4A FMLs under low-velocity impact. Leveraging ABAQUS, a robust FEM featuring explicit analysis, cohesive resin interfaces, and custom VUMAT subroutines was developed to accurately simulate energy absorption, dent depth, and delamination. The precise model’s predictions align well with test results performed according to ASTM D7136 standards, exhibiting less than a 0.1% deviation in the displacement (dent depth)–time response, along with deviations of 4.3% in impact energy–time and 5.2% in velocity–time trends at 5.5 ms. Full article