Search Results (193)

Addressing challenges such as the non-Newtonian fluid characteristics of melt, significant system hysteresis, and rheological thermal drift in large-scale glass fiber-reinforced polypropylene (PP-GF) screw-extrusion additive manufacturing (SEAM), this paper proposes a composite pressure control strategy based on inverse model feedforward and variable-structure feedback (VSFC-Smith). This strategy establishes a dynamic pressure benchmark through an inverse rheological model, utilizes a Smith predictor to compensate for time delay, and introduces dead-zone variable-structure feedback to smoothly suppress thermal drift. Experimental results demonstrate that, compared to traditional PID (Proportional-Integral-Derivative) controller, the VSFC-Smith strategy reduces the step pressure overshoot from 23.37% to 17.37%, decreases steady-state screw speed fluctuation by approximately 50%, and limits the error within ±0.04 MPa during complex trajectory tracking. In practical molding validation, this strategy effectively suppressed surface ripples, reducing the surface roughness (Sa) by 14.5% to 124.41 μm; simultaneously, the Z-directional interlayer tensile strength reached 12.63 MPa (a 22.5% improvement compared to open-loop control). This study successfully overcomes the limitations of traditional high-gain feedback, achieving synergistic optimization of the macroscopic morphology and microscopic mechanical properties of composite parts. Full article

Currently, the packaging sector must continue developing more sustainable systems to reduce the high quantities of single-use plastic waste generated. This study evaluated the production and characterization of bio-based composite trays with antimicrobial activity. Different formulations of polybutylene adipate co-terephthalate (PBAT) and polylactic acid (PLA) with polyethylene glycol (PEG) as plasticizer and citric acid as a compatibilizer/crosslinker were evaluated, in addition to the inclusion of plantain microfibers (PFs), TiO₂, and menthol as reinforcing and antimicrobial agents, respectively. The mixtures were subjected to pellet extrusion (165/175/185/190 °C and 60 rpm) and then to flat sheet extrusion (at 185/190/195/205 °C and 60 rpm), besides calendering (at 3.5–6.0 rpm). A single-screw extruder was used in both cases. The obtained sheets (0.317 ± 0.040 mm thick and 17 cm wide) were molded into 12.5 × 11.0 × 3.5 cm trays in a thermoforming machine (at 325 °C and vacuum pressure). For the resulting composite sheets and trays, measurements of mechanical strength, moisture absorption, barrier (WVTR), transmittance, and color were performed. FT-IR, DSC, TGA, SEM, and in vitro antimicrobial tests were also conducted. Based on these tests, an initial formulation with an 85/15 (w/w) PLA/PBAT ratio was defined, which was then reinforced with 3% (w/w) PF. Furthermore, the inclusion of 5% (w/w) menthol in the composite led to fungistatic activity against Botrytis cinerea, also resulting in homogeneous sheets (tensile strength 24.137 ± 1.439 MPa) and trays (compressive strength 0.113 ± 0.010 MPa). These findings can be applied to the packaging and preservation of perishable produce. Full article

The microstructural characteristics and fracture behavior of a magnetic pole screw were investigated here. The screw threads were produced by cold thread rolling. Microstructural analysis (OM, SEM, EBSD), mechanical testing (tensile, hardness, fastening), and fracture morphology observation were conducted. The results indicate that work hardening and microstructural deformation were introduced by the gradient plastic deformation in the screw thread. The elongated microstructure of ferrite and pearlite was obtained in the deformation zones, resulting in increased hardness and decreased plasticity. The thread root subsurface experienced severe localized indentation deformation and exhibited the highest hardness. The distinct forming stress states led to a notable difference in the hardened layer depth between the thread crest and root. The torsional overload fracture was initiated at the stress-concentrated thread root, where the work-hardened microstructure exhibited a limited capacity to accommodate large plastic deformation. The crack propagation was influenced by the gradient microstructure, following three primary propagation paths: transgranular through ferrite, along the ferrite–pearlite phase interface, and cracking through lamellar pearlite. The results provide theoretical support for material design and process optimization to achieve the production of high-performance screws with high strength and hardness at the thread surface and high plasticity in the center. Full article

Notch connections are commonly used in timber concrete composite (TCC) members because of the simple geometry of the solution making execution easy and the high strength and stiffness resulting from the mechanical interlock between the timber and concrete. However, the use of low strength lightweight concrete in TCC applications is limited in the literature. Therefore, in this work, shear tests were conducted on notch shear connections between glulam timber and low strength lightweight concrete, in which the effects of notch dimension and adding a screw in the notch have been analyzed. From the obtained force-slip curves, strength, stiffness, and the ductility of the shear connection have been assessed. The tested connections’ strength and stiffnesses are compared with the analytical approaches given in TCC Technical Specification CEN/TS 19103. The results show that the use of low strength lightweight concrete, even with a low modulus of elasticity, provides a stiff solution. The observed failure mode agrees with the EN 1995-1-1 requirement; however, an overestimation is observed for the load predictions. For the specimens with screws, an improvement in strength capacity, stiffness and deformation capacity was noticed. Full article

Residual lignocellulosic biomass represents a major resource to be incorporated into the circular economy, with up to 1400 Mt/y in EU27. Due to its complex composition of three biopolymers (cellulose, hemicellulose and lignin) combined with its seasonal and regional variability and high water content, its valorization involves manifold challenging aspects. Herein a three-step procedure is presented to transform this type of biomass into solid composite panels: hydrothermal carbonization (HTC), dry thermal treatment and curing a phenolic resin. HTC triggers chemical dehydration of the polysaccharide part of the lignocellulose and breaks up the cell structure of the plants. This facilitates the diffusion of the water and its separation by filtration, which is more energy efficient than evaporation. HTC and thermal treatment induce chemical changes that concentrate the carbon content and make the material suitable for crosslinking with a phenolic resin, achieving a 90% renewable content. The composite panels are competitive with products of the particle and fiberboard sector with respect to tensile strength and screw withdrawal resistance. Hence, the products can be employed for construction or in the furniture industry. Full article

With the wide application of Ni-Al high-temperature materials, the research on their performance has increasingly attracted attention. To further advance the development of Ni-Al high-temperature materials, it is necessary to conduct an in-depth analysis of the brittleness mechanism of Ni-Al intermetallic compounds and elucidate the fundamental nature of their brittleness. In this study, the tensile mechanical behavior and microscopic mechanism of single crystals NiAl (B2) and Ni₃Al (L1₂) at different temperatures were systematically studied by molecular dynamics simulations. It is revealed that although the mechanical properties of both NiAl and Ni₃Al degrade with increasing temperature, their deformation mechanisms exhibit fundamental differences. The high-temperature strength of NiAl is attributed to stable plastic flow dominated by 1/2 <111> screw dislocation. The early softening of Ni₃Al is associated with the formation of stacking fault formation, the phase transition to the HCP, and the slip of various incomplete dislocations (e.g., 1/6 <112> Shockley dislocation). Atomic strain analysis shows that regions of high strain exhibit a strong spatial correlation with the phase-transformed domains. This study reveals the distinct deformation mechanism of the two alloy phases at the atomic scale, providing a key theoretical basis for the rational selection of Ni-Al alloy in specific high-temperature applications. Full article

Unlike typical fiber-reinforced polymers, aerospace composites consist of 90% carbon and 10% glass fabrics impregnated with thermosetting resin. Due to the strong bonding between fibers and the thermoset nature of the matrix, recycling these materials is particularly challenging. This study evaluates mechanical recycling of aircraft composite waste via industrial grinding and chemical recycling through a solvolysis process. Recovered fibrous fractions were integrated into an epoxy matrix at 50 wt% loading using hot-pressing and into polyamide 12 at 15 wt% via a twin-screw extrusion process. The mechanical results showed that chemically recycled fibers in epoxy reached a flexural modulus of 9.9 GPa and strength of 112 MPa, significantly outperforming mechanically recycled fillers (6.1 GPa and 98.0 MPa) compared to virgin carbon fibers (11.3 GPa and 132 MPa). In PA12, the addition of chemically recycled fibers yielded a 2.14 GPa modulus and a 67.7 MPa strength. Furthermore, life cycle assessment confirmed that both recycling routes drastically reduce global warming potential and aquatic ecotoxicity compared to landfilling. These findings indicate that while mechanical recycling is simpler, chemical solvolysis provides a superior pathway for the high-value circular reuse of complex aerospace waste in new thermoplastic and thermoset applications. Full article

Background: To compare the biomechanical strength of three fixation techniques for the elbow anterior capsule and coronoid process using a synthetic ulna model. We hypothesize that a cortical suture button would be equivalent to the bone tunnel model but inferior to a screw-post construct. Methods: A biomechanical study was conducted using a composite ulna bone model to simulate coronoid process fixation with three techniques: traditional trans-osseous bone tunnel repair, suspensory fixation using a cortical button, and a screw-post construct using a 3.5 mm cortical screw. All constructs were assembled using high-strength suture. Each specimen underwent axial loading on an Instron machine until failure, defined as loss of fixation through the dorsal cortex. Peak ultimate strength was recorded. Statistical analysis was performed using one-way ANOVA and Tukey’s HSD test. Results: The suture button construct demonstrated the highest mean ultimate strength at 490.3 ± 125.2 N, significantly greater than both the bone tunnel (328.8 ± 86.4 N, p < 0.01) and screw-post constructs (273.4 ± 54.5 N, p < 0.001). While the bone tunnel construct exhibited a 20.3% higher strength than the screw-post construct, this difference was not statistically significant (p = 0.13). The screw-post construct showed the least variability in strength to failure but the lowest overall strength. The suture button demonstrated the greatest mechanical strength but also the most variability. Conclusions: Suspensory fixation using a titanium cortical suture button provides significantly greater mechanical strength compared to traditional bone tunnel and screw-post techniques in a synthetic ulna model. While variability was greatest with the suture button construct, its superior load-bearing capacity suggests potential advantages in stabilizing the elbow through anterior capsule and coronoid fracture repair. These findings support further clinical investigation of suture button fixation as a viable technique in complex elbow injuries. Full article

This study investigates the reuse of mechanically recycled polyester–glass thermoset scraps (PS) as fillers in LDPE and HDPE matrices at 10–50 wt.% loading. Composites were produced through mechanical size reduction, single-screw extrusion, and compression molding without compatibilizers, and their mechanical and microstructural properties were systematically evaluated. LDPE composites exhibited a notable stiffness increase, with tensile modulus rising from 318.8 MPa (neat) to 1245.6 MPA (+291%) and tensile strength improving from 9.50 to 11.45 MPa (+20.5%). Flexural performance showed even stronger reinforcement: flexural modulus increased from 0.40 to 3.00 GPa (+650%) and flexural strength from 14.5 to 35.6 MPa (+145%). HDPE composites displayed similar behavior, with flexural modulus increasing from 1.2 to 3.1 GPa (+158%) and strength from 34.1 to 45.5 MPa (+33%). Surface-treated fillers provided additional stiffness gains (+36% in sPL4; +33% in sPH3). Impact strength decreased with loading (LDPE: −51%, HDPE: −61%), though surface treatment partially mitigated this (+14–19% in LDPE; +13% in HDPE). Density increased proportionally (PL: 0.95 → 1.20 g/cm³, PH: 0.99 → 1.23 g/cm³), while moisture uptake remained low (≤0.25%). Optical and SEM analyses indicated increasingly interconnected fiber networks at high loadings, driving stiffness and fracture behavior. Overall, PS-filled polyolefins offer a scalable route for converting thermoset waste into functional semi-structural materials. Full article

Steel and prestressed concrete traction poles can be fixed to reinforced concrete pile foundations using typical bolted connections. The stainless steel fastening screw is connected to the ordinary steel foundation pile reinforcement by friction welding under specific friction welding process parameters. From the perspective of the structural strength of the connection between the traction pole and the foundation pile, regarding the transfer of tensile and shear forces through a single anchor bolt, the yield strength of stainless steel bolts should be R_e,min ≥ 345 MPa for M30 anchors, R_e,min ≥ 310 MPa for M36 anchors and R_e,min ≥ 300 MPa for M42 anchors. This requirement is reliably met by martensitic stainless steels, while other stainless steels have yield strengths below the required minimum. What truly determines the foundation pile’s load capacity is not the satisfactory mechanical strength of the stainless steel (here, the parameters are met), but the quality of the friction-welded end connection between the reinforcement and the threaded bars. Incorrect selection of the type of prestressing steel in the analyzed connection can have enormous consequences for foundation pile manufacturers. Annual production of foundation piles amounts to thousands of units, and an incorrect decision made by the pile designer at the design stage can result in significant financial losses and a high risk to human life. This article presents the results of studies on friction-welded connections of M30, M36, and M42 threaded bars made of austenitic 1.4301 (AISI 304) and martensitic 1.4021 (AISI 420) stainless steel with B500SP reinforcement bars. The tests yielded negative results for 1.4021 (AISI 420) steel, despite its yield strength exceeding R_e ≥ 360 MPa. Full article

Al–Al₄C₃ composites exhibit promising mechanical properties including high specific strength, high specific stiffness. However, high reinforcement contents often promote brittle behavior, making it necessary to understand the mechanisms governing their limited toughness. In this work, a microstructural and mechanical study was carried out to evaluate the energy storage capacity in Al–Al₄C₃ composites fabricated by mechanical milling followed by heat treatment using X-ray diffraction (XRD) and Convolutional Multiple Whole Profile (CMWP) fitting method, the microstructural parameters governing the initial stored energy after fabrication were determined: dislocation density (ρ), dislocation character (q), and effective outer cut-off radius (R_e). Compression tests were carried out to quantify the elastic energy stored during loading (Es). The energy absorption efficiency (EAE) in the elastic region of the stress–strain curve was evaluated with respect to the elastic energy density per unit volume stored (Ee), obtained from microstructural parameters (ρ, q, and Re) present in the samples after fabrication and determined by XRD. A predictive model is proposed that expresses Es as a function of Ee and q, where the parameter q is critical for achieving quantitative agreement between both energy states. In general, samples with high EAE exhibited microstructures dominated by screw-character dislocations. High-resolution transmission electron microscopy (HRTEM) analyses revealed graphite regions near Al₄C₃ nanorods—formed during prolonged sintering—which, together with the thermal mismatch between Al and graphite during cooling, promote the formation of screw dislocations, their dissociation into extended partials, and the development of stacking faults. These mechanisms enhance the redistribution of stored energy and contribute to improved toughness of the composite. Full article

This study examines how varying the isolated pea protein (IPP) levels (0, 10, 20, 30, 40, 50%) together with key extrusion conditions, including moisture level, barrel heating profile, and screw rotation speed, affect the physicochemical attributes and textural characteristics of high-moisture meat analogs (HMMAs). Results indicated that increased IPP content reduced the fiber structure, springiness, cohesiveness, chewiness, cutting strength, and integrity index of HMMAs. Processing conditions resulted in pronounced changes in both the physicochemical attributes and texture of HMMAs. The increase in moisture content resulted in a decrease in HMMA fiber structure and textural properties. In contrast, increases in barrel temperature and screw speed were associated with higher TPA values, greater cutting strength in both vertical and parallel orientations, and an improved integrity index in HMMAs. Furthermore, the gelation behavior of IPP played a critical role in the formation of the fibrous structure, with optimal gel strength and water retention achieved under specific extrusion conditions. These findings underscore the importance of protein gelation in structuring IPP-based meat analogs and provide insights into the gel-based mechanisms underlying their textural properties. Overall, the optimum IPP content to produce HMMAs in this experiment was 30%, and the process variables were 55% moisture content, barrel temperature of 160 °C, and screw speed of 250 rpm. Full article

Titanium alloy TC4 countersunk head bolts (CHB) are widely used in spacecraft structures, but the research on CHB does not receive enough attention at present. There are still some more opportunities worthy of in-depth research, such as insufficient research on CHB of high-strength fasteners for aerospace applications, an insufficient combination of CHB simulation tests with real working conditions, and inspection and testing methods. In this study, through the combination of finite element simulation and experiments, the working conditions of the CHB connection structure bearing tensile load and CHB screwing were analyzed, and the requirements of the CHB connection structure and installation of CHB were optimized. Based on the single-bolt tensile simulation, the working conditions of multi-bolt connection structures under eccentric load and single-bolt composite laminate connection structures under tensile load were analyzed. Meanwhile, the structure of CHB was further optimized, and the simulation analysis model of the CHB tightening process was established. The research shows that the larger fixing bolt countersunk angle θ₁ and the smaller countersunk fillet radius r, the better the ultimate bearing capacity of the connection structure will be. When the countersunk bevel angle of pressure plate θ₂ was greater than or less than 100°, the clamping force–angle slope will decrease, while when θ₂ was smaller, it will have a greater influence on the slope. The coaxiality Φ had little influence on the slope around the allowable tolerance range (0.3 mm), but the influence on the slope becomes greater when it exceeds the tolerance range. The research results provide a reference and basis for the layout of CHB and the use of composite materials in aerospace connection structures. Full article

The SBPDN (Steel Bar Prestressed Deformed Normal relaxation) bar, which has ultra-high yield strength yet much lower bond resistance than conventional deformed bars, has been recently proposed to be used as the longitudinal rebar instead of a normal-strength deformed bar to simply realize strong earthquake-resilient concrete components. To facilitate and promote the application of concrete components reinforced with SBPDN rebars to the structures located in earthquake-prone regions, it is indispensable to develop reliable and effective anchoring means and clarify the bond strength of SBPDN bars embedded in concrete and/or grout mortar. This paper presents experimental information on the pull-out tests of fifteen SBPDN bars embedded in grout mortar, along with a discussion on the effective anchorage details and the bond strength of SBPDN bars. The tested SBPDN bars have a nominal diameter of 22.2 mm, the maximum diameter currently available on the market. All SBPDN bars were embedded in high-strength grout mortar with a targeted compressive strength of 60 MPa. The primary experimental variables included the end anchorage details, the diameter of sheath ducts, and the embedded length of the bars. Test results demonstrated that either screwing two nuts and a washer at the end of SBPDN bars or providing a rolling-threaded end region was effective in preventing them from premature slip from grout mortar. If the embedment length was 20 times the bar diameter or longer, the proposed two anchorages could ensure the SBPDN bar to fully develop its specific yielding strength as high as 1275 MPa. In addition, it has also been experimentally revealed that the bond strength of SBPDN bars embedded in grout mortar was much lower than that of conventional deformed bars and varied between 2.84 MPa and 3.98 MPa. Full article

Flexible packaging often consists of multilayer films that combine different materials to achieve high barrier performance, but these structures are incompatible with current recycling technologies. Polyolefins such as polypropylene (PP) offer more recyclable alternatives but require additional oxygen-barrier materials that do not compromise recyclability. This study investigates the influence of ethylene vinyl alcohol (EVOH), Ormocer^® barrier coating, and PP labels with different adhesives on PP recyclability. Recyclates were produced using twin-screw extruder to simulate the recycling process and then injection-molding to make tensile test specimens. Mechanical properties, melt flow rate (MFR), oxygen induction time (OIT), and odor were evaluated. Findings showed that low label content (5–12.5%) has minimal impact on recyclate quality. The addition of 10% EVOH increased the elastic modulus of PP granulate and cast-PP (cPP) film by 26% and 14%, respectively, and improved oxidation stability by 9%, while reducing cPP film impact strength by 77%. Ormocer^® decreased mechanical performance, particularly elongation at break (−18%), likely due to defect-inducing particles, but had limited influence on MFR. Labels and Ormocer^® also introduced odor variations. Overall, the findings indicate that EVOH up to 10% and labels up to 12.5% yield promising results, providing guidance for designing recyclable, monomaterial packaging. Full article