Search Results (3,921)

Elasticized expanded polystyrene (EPS-T) is widely used as a resilient layer in floating floors, where dynamic stiffness is the key input for impact-sound prediction, while FEM modelling additionally requires elastic parameters and damping descriptions consistent with the adopted test or modelling configuration. This study investigates whether ISO-type dynamic stiffness testing and acoustic-response modal identification can provide consistent vibroacoustic parameters for EPS-T. Rectangular specimens of different thicknesses were tested for dynamic stiffness and damping using an ISO 9052-1-type setup. Additional cylindrical compression tests were used to examine apparent Young’s modulus and Poisson’s ratio, while impulse-excited acoustic responses of clamped specimens were combined with inverse FEM identification. The ISO-type dynamic stiffness decreased from approximately 53.3 MN/m³ for nominal 17 mm specimens to 27.0 MN/m³ for nominal 53 mm specimens. This trend was described by a compliance model with an effective Young’s modulus of 2.04 MPa and an equivalent contact/support stiffness of 101.2 MN/m³. Acoustic-response inverse FEM gave consistent Young’s modulus values, ranging from 1.77 MPa to 2.16 MPa, with a mean close to 2.05 MPa. Direct use of s′ = E/h overestimated stiffness and underestimated predicted ΔL_w by approximately 2–5 dB. The two routes provided consistent estimates of the effective modulus, but this consistency applies only to modulus identification and not to direct stiffness conversion or damping transfer. Full article

The metastable β-phase Ti21S titanium alloy, characterised by its low Young’s modulus, oxidation resistance, creep strength, and high biocompatibility, has potential applications in aeronautical and biomedical fields. Despite these advantages, its adoption in additive manufacturing (AM) processes, particularly powder bed fusion with electron beam (PBF-EB), remains limited. A critical aspect of PBF-EB is the sintering phenomenon during preheating, which influences powder behaviour, thermal dissipation, and part quality. Insufficient sintering leads to poor energy dissipation and charge accumulation, while excessive sintering compromises powder reusability. This study investigates the sintering conditions required to optimise the PBF-EB preheating step for Ti21S. Thermogravimetric (TG) apparatus was employed as a controlled thermal treatment system to conduct a preliminary screening of the influence of temperature on powder sintering over a range of 400 °C to 700 °C. Parallel experiments were conducted using a PBF-EB machine to evaluate sintering behaviour. Scanning electron microscopy (SEM) was used to analyse the degree of sintering, while powder reusability was assessed by comparing the morphology and flowability of virgin and reused powders. The results show that conventional thermal treatment and PBF-EB preheating produce different sintering responses, likely because of the localised and rapid energy deposition associated with electron-beam heating. Nevertheless, controlled thermal treatment may provide a preliminary screening method for identifying temperature ranges for subsequent PBF-EB optimisation. Full article

Plastic production and consumption have increased substantially due to the favorable properties of these materials, raising significant environmental concerns because most plastics do not fully decompose. A substantial portion of ocean plastic waste comes from ghost gear, including abandoned fishing nets. In this context, mechanical recycling offers a promising route for recovering these materials and reducing their environmental impact. This study evaluates the feasibility of using recycled fishing nets made of polyamide 6 (PA6) to manufacture injection-molded parts. Injection-molded specimens produced from recycled fishing nets were descriptively compared with specimens obtained from commercially available extruded PA6 plates, used as a commercial processing reference. Both materials were also subjected to an additional post-injection mechanical recycling cycle to evaluate short-term property retention after reprocessing. The feasibility of producing cardholders by injection molding was also examined as a proof of concept. Physical and mechanical characterization showed that the recycled fishing-net PA6 exhibited higher average yield stress and Young’s modulus, but lower stress and strain at break and lower impact toughness than the commercial PA6 reference. The second recycling cycle did not produce a consistent deterioration across the measured properties, although statistical equivalence between the two recycling conditions was not established. The successful production and assembly of cardholders demonstrated the laboratory-scale processability of recovered fishing-net PA6, while further characterization, additional recycling cycles, and process optimization are required to assess long-term recyclability and industrial viability. Full article

This research introduces an analytical model based on a semi-rigid nodal bar system. In this model, carbon–carbon covalent bonds are represented as beam elements, while carbon atoms are treated as semi-rigid nodes connecting these elements. A spring coefficient is incorporated to quantify nodal stiffness. Building upon this construct, spatial stiffness equations for the semi-rigid beam elements are derived, enabling a systematic exploration of how boundary conditions and dimensional factors influence the Young’s modulus and buckling stress in both pristine and defect-laden graphene. The findings reveal that defect-free graphene exhibits remarkable dimensional stability, with its Young’s modulus consistently approximating 1.0 TPa and fluctuating within ±2%. Upon the introduction of defects, the material’s stiffness diminishes significantly, with a maximum reduction of 19% observed when the density of defective elements surpasses a critical threshold. Moreover, the relationship between boundary conditions and buckling stress aligns closely with classical thin plate theory. Under identical dimensional constraints, the buckling stress ratios for fully fixed, fixed-simple, simply supported, and cantilevered boundaries conform to the theoretical ratio of 16:8:4:1. Full article

The flexural behaviour of body-centred cubic (BCC) lattice beams fabricated by stereolithography remains supported by limited experimental evidence, and available homogenized beam models are rarely confronted with data in the combined regime of high relative density, non-slender struts, and low span-to-depth ratios. This work presents an experimental campaign on polymeric BCC lattice beams with three unit-cell edge lengths ($L=3$, 4, and 5 mm) and a constant strut-to-cell ratio $R/L=1/6$, yielding a relative density ${\rho }^{*}\approx 0.423$. Specimens were tested under uniaxial compression and three-point bending for nine combinations of geometry. The experimental data are compared with three analytical frameworks: a classical Euler–Bernoulli homogenized beam model and a BCC-specific shear-corrected formulation at the structural level, both evaluated without calibration to the bending tests, together with a strain-gradient extension whose intrinsic length scale is calibrated against them. For the effective Young’s modulus, the closed-form expression of Lee et al. reproduces the compression data within 10%, whereas the Tancogne-Dejean and Mohr model remains markedly stiffer even after the strut-level Timoshenko correction is included. In bending, none of the models proves adequate over the full geometric range: the Euler–Bernoulli model is accurate for several configurations (errors below 16% in five of nine cases) but overestimates the stiffness by up to 108% for the deepest specimen; the shear-corrected model reduces the global root mean square error from 97.94 to 24.44 N/mm (approximately a factor of four), but introduces excessive flexibility in some slender and intermediate configurations; and the strain-gradient correction, being strictly stiffening, yields no appreciable improvement. To avoid assigning the discrepancy to a single mechanism, the bending data are further analysed through an experimental compliance decomposition. The additional compliance relative to Euler–Bernoulli theory is small or negative in several cases, showing that shear flexibility alone cannot explain the full dataset, but becomes dominant for the deepest beams. The results therefore delineate the range of validity of simple homogenized beam models for dense finite BCC lattice structures and identify the combined influence of structural shear, non-slender struts, nodal-region morphology, finite-cell and boundary effects, local roller-contact compliance, and the discrete distribution of struts across the cross-section as the main mechanisms requiring more refined descriptions. These findings correspond to a single relative density (${\rho }^{*}\approx 0.423$) and a single strut-to-cell ratio ($R/L=1/6$), so the resulting span-to-depth indicator ($L_0/h\approx 2.5$) should be regarded as indicative for this class of dense lattices rather than as a general design rule. Full article

The addition of hydroxyapatite (HAP) to electrospun poly-L-lactide (PLLA) scaffolds promotes cell adhesion and differentiation but generally leads to a significant deterioration in mechanical properties due to particle agglomeration. Moreover, the encapsulation of HAP particles within a polymer layer makes them inaccessible to body fluids and cells, thereby limiting the bioactivity of the resulting composite scaffold. In this work, HAP microparticles with median size of 26.3 µm were used to obtain exposed HAP particles on the surface of electrospun PLLA fibers. SEM images and EDX maps revealed that individual particles, particularly the larger ones, were exposed from the polymer scaffold surface. The addition of HAP particles significantly altered the scaffold morphology and structure, increasing the fiber diameter and surface roughness by 2.8–4.1-fold, promoting the formation of fused fiber junctions, and inducing the appearance of semicrystalline PLLA domains. These structural changes significantly improved the mechanical properties of the scaffolds. Specifically, the tensile strength and Young’s modulus of the prepared scaffolds are increased by 2.3–3.8-fold following HAP incorporation. Compared with neat PLLA scaffolds, HAP-containing scaffolds exhibited 1.2–1.4-fold higher osteocalcin and osteopontin expression by human adipose-derived mesenchymal stromal cells (hADSCs). Compared to tissue culture plastic, the expressions of osteocalcin and osteopontin on the composite scaffolds were 7.1–7.9-fold and 2.8–3.0-fold higher, respectively. Full article

Ti–Nb alloys are widely recognized as highly promising materials for orthodontic applications due to their excellent functional properties, including superior biocompatibility and a relatively low Young’s modulus that better matches that of human bone. The formation of Ti–Nb surface alloys or surface-modified layers is particularly attractive, as the surface properties of biomedical materials strongly influence their mechanical and biological interactions during service. In the present study, Ti-Nb coatings were fabricated on commercially pure titanium substrates using an electron beam surface treatment (EBST) technique. Initially, a 1 μm thick Nb layer was deposited onto the Ti substrates by direct current (DC) magnetron sputtering. Subsequently, the samples were modified through scanning electron beam irradiation, with beam power varied between 1000 and 2000 W to promote Ti-Nb alloyed layers. The phase composition of the resulting structures was analyzed by X-ray diffraction (XRD). Microstructural characteristics and chemical composition were examined using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Mechanical properties were evaluated in terms of hardness and Young’s modulus. The findings of this study demonstrate the feasibility of tailoring the structural and mechanical properties of Ti–Nb surface alloys through controlled electron-beam processing and support their further investigation for potential orthodontic and dental applications. Full article

We prove the existence and uniqueness of weak solutions to an obstacle problem for a nonlinear elliptic operator in divergence form. The variational inequality under consideration involves an integral over the domain of the Frobenius inner product of the operator $\mathcal{S}(z,\nabla u-\mathcal{O}(u\left)\right)$ with the gradient difference $\nabla (v-u)$, plus the Euclidean inner product of u and $v-u$, which is required to be nonnegative for all admissible functions v. The admissible set consists of functions in the Sobolev space $W^{1,2}(\mathrm{\Omega };{\mathbb{R}}^m)$ with prescribed Dirichlet boundary trace and lying above a given obstacle $\psi$ almost everywhere. The obstacle condition $v\ge \psi$ a.e. models a lower bound constraint (e.g., a membrane or a displacement limit) that the admissible functions must respect, while the boundary value $\delta$ prescribes the Dirichlet data. The principal part contains a solution-dependent shift $\mathcal{O}\left(u\right)$, which is Lipschitz continuous, while $\mathcal{S}$ is assumed to be globally Lipschitz and strongly monotone with respect to equal shifts, with quadratic growth and coercivity. This structural framework can be interpreted in terms of symmetry: the strong monotonicity condition expresses a quantitative symmetry property of $\mathcal{S}$ with respect to equal shifts, and the shift $\mathcal{O}\left(u\right)$ introduces a symmetry-breaking coupling. The smallness condition ensures that this asymmetry remains under control. However, we do not pursue a full group-invariance or Lie-symmetry analysis; the symmetry perspective is used here as a heuristic and interpretative tool. The main difficulty lies in the mismatch of shifts when comparing two admissible functions. This is resolved by a three-term decomposition of the monotonicity estimate, combined with Young’s inequality and Poincaré’s inequality, under the smallness condition that the product of the Lipschitz constant of $\mathcal{S}$, the Lipschitz constant of $\mathcal{O}$, and the Poincaré constant is bounded above by one quarter of the strong monotonicity modulus. Existence follows from the Kinderlehrer–Stampacchia theorem; uniqueness is obtained from the same decomposition. The result unifies and extends previous contributions that treated either the lower-order term or the shift coupling separately, and it does so within a unified quadratic framework that avoids the technical overhead of variable exponents and Young measures. Full article

MAX-phase materials exhibit metallic–ceramic properties. The Ti₄AC₃ (A = Si, Au, Ir) 413-type MAX phases are investigated here using systematic density functional theory to examine structural stability, elastic behavior, mechanical performance, thermal properties, and electronic characteristics. Optimized lattice parameters agree with existing theoretical and experimental data. Single-crystal elastic constants satisfy the Born criteria, confirming mechanical stability. Using the Voigt–Reuss–Hill method, polycrystalline moduli are derived: Ti₄IrC₃ has the highest bulk modulus (B = 227.7 GPa), and Ti₄SiC₃ has the largest shear modulus (G = 148.1 GPa) and Young’s modulus (E = 354.5 GPa). Ti₄AuC₃ shows lower moduli, indicating greater ductility (ν = 0.293; G/B = 0.481). Elastic anisotropy is significant in all three phases, with Ti₄AuC₃ being the most anisotropic. Electronic density of states analysis reveals strong Ti–C covalent bonding that underpins stiffness, while A-site bonding (Si, Au, Ir) influences ductility and anisotropy. This comprehensive comparison elucidates the structure–property relationships of Ti₄AC₃ (A = Si, Au, Ir) MAX phases and supports their design for targeted applications in aerospace, energy, and mechanical engineering. Full article

This study investigates the evolution of microstructural, mechanical, and transport properties in AZ31 magnesium alloy surface composites reinforced with Ti₂AlC MAX-phase particles at volume fractions of 6, 9, and 12 vol.%, which were fabricated by solid-state friction stir processing (FSP). In contrast to conventional brittle ceramics, Ti₂AlC MAX-phase mitigates interfacial reactivity and thermal mismatch. FSP successfully fabricated a highly consolidated, macroscopically defect-free, dynamically recrystallized fine-grained stirred zone with homogeneous particle distribution and metallurgically clean interfaces. Mechanically, the addition of 12 vol.% Ti₂AlC significantly improved the elastic response, increasing the Young’s modulus from 51 GPa to 67 GPa. The microhardness of the stirred zone reached 60.14 HV, a 53.4% increase over the base metal. The controlled electron and phonon scattering, enabled by the introduction of heterogeneous Mg/Ti₂AlC interfaces, decreased the electrical and thermal conductivities from initial values of 1.15 × 10⁷ S/m and 86.0 W/m·K for the unreinforced matrix down to 7.8 × 10⁶ S/m and 76.0 W/m·K, respectively, and caused a significant reduction in the coefficient of thermal expansion. Theoretical analysis, utilizing the Wiedemann–Franz law and Maxwell–Eucken approximations, provided a supportive baseline indicating the dominance of electronic thermal transport and interfacial scattering mechanisms. These results outline a viable route for developing lightweight magnesium-based composites with tailored mechanical and thermal characteristics for advanced structural applications. Full article

In order to provide a theoretical framework for the synergistic optimization of the “rigid backbone-flexible network” in the molecular design of polyimides with high Young’s modulus, high toughness, and excellent creep resistance for wearable electronics applications, the effects of sequence structure on the mechanical properties of siloxane-containing polyimides were investigated by molecular dynamics simulations. A series of poly(siloxane-imide) block copolymer models with distinct sequence structures were constructed via molecular dynamics (MD) simulations based on 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,2′-bis(trifluoromethyl)benzidine (TFDB) as hard segment A, and 6FDA and 1,3-bis(3-aminopropyl)tetramethyldisiloxane (SiDA) as soft segment B. The results indicate that extending hard segment length enhances Young’s modulus and suppresses creep because of the enhancement of chain rigidity and formation of stable physical aggregates. Appropriately extending soft segment sequence length can improve the failure strain through rapid conformational adjustment, while excessively long soft segments lead to stress concentration, thereby reducing the failure strain. The (A₅B₅)₂ model structure exhibits superior comprehensive performance among all systems, with a relatively high Young’s modulus, failure strain, and creep recovery rate. This is attributed to the synergistic balance between the rigidity of the hard segment and the mobility of the soft segment. Full article

This study develops a finite element analysis (FEA) framework to quantify hydrostatic consolidation of ultra-high-molecular-weight polyethylene (UHMWPE) fibril arrays containing interstitial voids. Hexagonal and stochastic representative volume elements (RVEs) were constructed from experimentally measured fibril diameters and embedded in a nearly incompressible Mooney–Rivlin medium to transfer hydrostatic pressure to irregular fibril surfaces. Molecular dynamics (MD)-derived fibril properties at 300 K and 400 K were used to evaluate the effects of temperature, elastic–plastic deformation, and stochastic microstructure on void collapse and effective fiber properties. The 300 K elastic model required pressures approaching 1.3 GPa to reach approximately 1–2% void content, whereas the combined effects of elevated temperature, elastic–plastic fibril behavior, and stochastic fibril packing reduced the corresponding pressure to approximately 160 MPa. The stochastic RVE exhibited a higher initial void content, earlier plastic dissipation, lower initial effective stiffness, and nonuniform fibril–fibril contact evolution compared to the idealized hexagonal RVE. As void content decreased, both models converged toward the dense fibril response. The framework establishes a processing–microstructure–property relationship linking consolidation pressure to the evolving void morphology, fibril shape and contact development, and the resulting effective plane-strain bulk modulus and the transverse compressive stress–strain response, including the Young’s modulus and Poisson’s ratio, of UHMWPE fibers. Full article

Stereocomplexes derived from natural polylactides are an important class of renewable plastics. Although neat polylactides generally exhibit low elongation at break and low Young’s modulus, stereocomplex formation significantly enhances their thermal resistance and stiffness (rather than toughness), dimensional stability, and controlled degradability, compared with simple polylactides. Consequently there has been significant research efforts to discover improved uses of these stereocomplexes—formed when the two enantiomers are combined—reported in many previous reviews. Here, we discuss improvements in them reported in the last five years, including a wide range of applications from simple packaging to biomedical aids, which make use of polylactide biodegradability, and self-assembing micelles, with quite complex structures, that are used for drug delivery and agricultural uses. We also noted that many general claims for degradability in PLA based polymers need to be qualified: the polymers will degrade, but very slowly in normal, low humidity conditions. However, degradation may be accelerated by heat, moisture, and enzymes—and also by fabricating with functional groups. Full article

This study reports a comparative evaluation of natural polymeric biomaterial films impregnated with silver nanoparticles (AgNPs) synthesized using the ethyl acetate (EA) extract of Centratherum anthelminticum (CA), yielding CA-EA extract-mediated AgNPs (CA-EA-AgNPs). The biopolymeric films were solution cast and confirmed for nanoparticle impregnation using techniques such as FTIR, XRD, and FESEM-EDAX. In addition to possessing antimicrobial activity, AgNPs also act as structural modifiers. AgNPs significantly enhanced tensile strength from 19.00 ± 0.62 MPa to 24.52 ± 0.97 MPa and Young’s modulus from 106.2 ± 18.2 MPa to 143.8 ± 7.15 MPa for chitosan (CH)-based films. For agar (AA)-based films, tensile strength increased modestly from 105.31 ± 1.18 MPa to 111.81 ± 1.78 MPa, maintaining a high Young’s modulus (1411.8 MPa). The water contact angle changed from 31.5° to 49.9° and from 56.9° to 86.7° for CH and AA films, respectively. The nanocomposite films demonstrated controlled equilibrium swelling kinetics without structural disintegration. The films exhibited moderately improved antibacterial activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Proteus mirabilis, yielding zones of inhibition (diameter) from 7.67 ± 0.47 mm to 10.33 ± 0.47 mm, 7.33 ± 0.47 mm to 9.67 ± 0.47 mm, and 7.67 ± 0.47 mm to 8.67 ± 0.47 mm for chitosan-based films and from 7.67 ± 0.47 mm to 11.67 ± 0.47 mm, 7.67 ± 0.47 mm to 10.67 ± 0.47 mm, and 7.33 ± 0.47 mm to 8.67 ± 0.47 mm for agar-based films, respectively, against their respective controls. The above findings demonstrate the potential of these nanoparticle-loaded biopolymer films as potent antimicrobial biomaterials for prospective wound management applications. Full article

Cardiovascular diseases (CVDs) remain a leading cause of mortality worldwide, and ageing is strongly associated with progressive arterial stiffening. Age-related alterations in extracellular matrix (ECM) mechanics influence vascular smooth muscle cell (VSMC) behaviour, while sympathetic innervation represents an additional regulator of vascular homeostasis. However, how neural signalling interacts with ageing-associated mechanical conditions to regulate VSMC behaviour remains unclear. In this study, an in vitro sympathetic neuron–VSMC co-culture model was established to investigate neuro-mechanical regulation. Primary rat sympathetic neurons and A7r5 VSMCs were cultured on glass or polydimethylsiloxane (PDMS) substrates with defined stiffness (20 and 130 kPa), representing healthy and ageing-associated stiffened arterial environments, respectively. VSMC behaviour was assessed through analysis of cell area, proliferation, migration, cellular Young’s modulus (YM), and DNA damage marker γH2AX. Sympathetic neuronal co-culture was associated with reduced VSMC spreading and decreased γH2AX levels. Under the conditions tested, neural signalling exerted limited effects on cell proliferation and migration. In contrast, increased substrate stiffness promoted cell proliferation and elevated YM. Both neuronal input and substrate stiffness were associated with increased cellular YM. Together, these findings indicate that neural and mechanical cues may jointly influence VSMC behaviour within ageing-associated mechanical environments. This co-culture system provides a controllable platform for studying neuro-mechanical interactions in vascular biology. Full article