Search Results (89)

Accurate AFM nanoindentation analysis requires models that account for the rounded apex of real pyramidal indenters. Although exact force-indentation equations for n-sided blunt pyramids exist, their numerical complexity limits routine use. In this work, a simple closed-form analytical approximation is developed that directly relates force to indentation depth for blunt pyramidal indenters. The method employs first-order Maclaurin series expansions of the geometric terms and the generic indentation differential equation, yielding a closed-form second-degree polynomial expression that is readily implemented in AFM data analysis. Comparison with the exact solutions showed that the approximation error decreases with indentation depth and is governed by the pyramid geometry rather than the tip radius. Simulated and experimental AFM data confirmed accurate Young’s modulus estimation above a geometry-dependent validity threshold. For a four-sided blunt pyramidal indenter, the proposed criterion predicts minimum indentation depths ranging from approximately $10.4 R_c$ for θ = 15° to 2.4 $R_c$ for θ = 45° where $R_c$ is the tip radius and θ is the pyramid’s semi-included angle. Application of the model to simulated AFM datasets yielded Young’s modulus values between 18.5 and 19.8 kPa for a true modulus of 20 kPa, corresponding to errors below 8% in all examined cases. Furthermore, the closed-form equation provided very good agreement with AFM nanoindentation data obtained from human prostate cancer cells. It is also shown that the generic derived equation includes the case of a spheroconical indenter as a limiting case. Young’s modulus is obtained directly from the quadratic coefficient, eliminating the need for tip-radius calibration. In addition, the formulation is applicable to heterogeneous materials, providing an effective local modulus through the weighted mean value theorem for integrals. The approach offers a practical and computationally efficient alternative for AFM data processing, improving the robustness of modulus estimation for soft biological materials. Full article

This study develops a theoretical and computational mechanics framework for regular dimples produced by rotary ball burnishing on an external cylindrical surface. The model combines the local quadratic ball–cylinder gap, an effective mean indentation pressure $H_{\mathrm{eff}}$, an unloading factor $\lambda$, residual dimple geometry, a Greenwood–Williamson pressure–approach law for the load-bearing lands, and an elastic spectral reference calculation. The dimple area fraction $F_{\mathrm{n}}$ is obtained from the periodic union of loaded-imprint footprints for the nominal stiffness maps, whereas the residual profile determines the specific oil capacity, defined as retained cavity volume per unit nominal area. Numerical checks include algebraic consistency, mesh-converged periodic FFT-BEM calculations, and a separate sinusoidal benchmark. For a representative $3\mathrm{mm}$ ball and $25\mathrm{mm}$ cylinder with $H_{\mathrm{eff}}=2\mathrm{GPa}$, the model maps burnishing force and texture pitch to idle- and working-pressure secant stiffness. Within the stated range $F_{\mathrm{n}}\le 0.20$, the low-fidelity index preserves the ordering of all evaluated non-tied design points; the mean and maximum differences from the spectral reference are $6.6\%$ and $15.2\%$. A discrete force–pitch grid yields three feasible points under illustrative stiffness windows and two candidates after non-dominated sorting and secondary selection by specific oil capacity. The selected textures reduce idle-pressure stiffness slightly more than working-pressure stiffness, increasing the nonlinearity ratio from $5.70$ to $5.91$. The framework provides a reproducible model-based tool for preliminary force–pitch selection; application to a specific material–process pair requires identification of $H_{\mathrm{eff}}$, $\lambda$, and the load-bearing-land response and validation against process-specific measurements. Full article

Rotary and vibro-rotary burnishing create regular arrays of imprints whose geometric interaction depends on the pitch, indentation depth, and relative curvature of the tool–workpiece pair. This paper develops a unified kinematic–curvature model that maps machine settings to an imprint layout on the unwrapped cylindrical surface and constructs the relative curvature tensor. The tensor state and full normalized neighbor metric assign the contact state to one of four mutually exclusive categories: non-elliptic, cell-limited, near-conformal (warning), or isolated elliptic. The tensor formulation is invariant under rotation of the tangent basis and provides a common geometric mapping for external cylinders and internal tubes. The kinematic map and tensor classification are independent of the rigid-plastic mean-pressure approximation and are verified by the factor relation between the center-line slope and imprint orientation, tensor invariance, limiting cases, and a closed-form identity. The calibrated approximation is used solely to estimate the maximum-load penetration and an equivalent projected footprint. At a fixed normal force and effective hardness, the projected area is identical in all curvature cases, whereas the curvature changes the penetration and footprint aspect ratio. Neglecting the workpiece curvature underestimates the external cylinder indentation depth by about 5.8% relative to the full tensor calculation; this ratio is independent of the force and effective hardness within the approximation. For the stated internal tube row pitch and hardness, the axis-aligned cell-limited transition force is 5–8 N. Evaluation with the full metric shows that the consecutive-event vectors are separated well; the periodic-row neighbor nevertheless places the reference case in the cell-limited class. A closed-form expression for this transition force is derived. The model provides a transition criterion verified by analytical identity and consistency checks; residual geometry and post-threshold pressure redistribution require unloading calibration and a periodic unilateral contact formulation, respectively. Full article

The acoustic black hole (ABH) effect, achieved through a power-law thickness profile, has emerged as a powerful technique for passive vibration and noise control in thin-walled structures by slowing and trapping bending waves. However, prevailing research and designs predominantly focus on concave ABH indentations, which inherently require material removal and can consequently compromise structural strength and load-bearing capacity. To overcome this limitation, this paper introduces a novel symmetrical ring-shaped convex acoustic black hole (CX-ABH) plate. This innovative configuration transitions from the conventional concave geometry to a convex profile, aiming to preserve or even enhance vibration reduction performance while simultaneously improving structural integrity. A finite element model of the proposed ring-shaped CX-ABH plate is established and its calculation accuracy has been numerically validated through mesh independence testing. Vibration response analyses demonstrate its superior performance against a baseline rectangular plate at approximately 1270 Hz, achieving a maximum vibration reduction of 28.26 dB; the kinetic energy density is decreased by up to 2.82 J/m³ and effective energy concentration is achieved within the CX-ABH region. A parametric study was conducted to investigate the influence of key geometric parameters: the ABH radius R, the power exponent m, and the central frustum radius d. To achieve an optimal design, a Kriging surrogate model is constructed based on simulation data and subsequently coupled with a multi-objective genetic algorithm (MOGA) for systematic optimization. The derived optimal parameter set (d = 13.5 mm, m = 2.4, R = 58.9 mm) yields a 16.53% reduction in the mean peak kinetic energy density, validating the effectiveness of the optimization framework. The results conclusively demonstrate that the ring-shaped CX-ABH plate offers a promising and novel structural paradigm, successfully balancing high-efficiency broadband vibration attenuation with a robust structural design. Full article

Scratch tests have emerged as a promising technique for evaluating the fracture behavior of cementitious materials. However, conventional fracture toughness (K_c) calculations rely on empirical groove geometry models, which may not accurately represent the actual scratch morphology. In this study, X-ray computed tomography (X-CT) and probe profilometry were employed to characterize the three-dimensional morphology of scratch grooves in white cement paste. Scratch tests were conducted under a linearly increasing load up to 30 N. Groove boundaries were identified through grayscale statistical analysis of X-CT images, and the obtained morphological parameters were incorporated into a linear elastic fracture mechanics framework to evaluate fracture toughness. The results showed that the indentation depth increased with the applied load, whereas the lateral force exhibited a nonlinear power-law relationship with the normalized penetration depth. X-CT measurements yield an average elastic recovery rate of 26.05% relative to instantaneous sensor depths, and 15–20% larger groove widths than empirical predictions due to edge spalling and debris accumulation, with discrepancies that amplify with increasing load. The X-CT-corrected K_c averages 0.21 MPa⋅m^1/2, about 30% lower than values derived from empirical geometric fitting. Good agreement between X-CT and probe profilometer measurements validated the reliability of the proposed approach. The main contribution is the correction of the K_c calculation using actual geometry. The results demonstrate that X-CT is an effective and non-destructive method for accurately characterizing fracture toughness evaluation of cementitious materials. Full article

This work presents the design and preliminary experimental validation of deformable sensors based on time-domain reflectometry (TDR) for rehabilitation-oriented interaction monitoring. Three architectures were investigated: a planar multilayer sensor and two coaxial configurations based on foam and engineered TPU–Hilbert structures. Controlled indentation tests were performed at different positions and deformation levels, extracting two TDR-derived features: the minimum reflection coefficient ${\rho }_{min}$, related to deformation intensity, and the perturbation time $t_{\mathrm{pert}}$, related to contact localization. Preliminary calibration curves and two-dimensional maps were used to analyze the coupled dependence of the response on position and indentation depth. Application-oriented manual tests confirmed the different suitability of the three geometries for localized finger pressing, distributed two-hand grasping, and controlled single-hand squeezing. Overall, the results support TDR-based deformable sensors as low-complexity and geometry-adaptable tools for spatially resolved monitoring of motor rehabilitation interactions. Full article

Coreless filament winding (CFW) enables the material-efficient digital fabrication of lattice fiber composite lightweight structures with high geometric freedom. However, the unconstrained formation of fiber bundle leads to variable cross-sectional shapes, rugged surfaces, and limited predictability of bundle-level geometry. This study evaluates an industrial epoxy spray coating and a custom epoxy immersion coating as post-processing technologies for improving the cross-sectional geometry of CFW fiber bundles at different compaction levels. Three groups of samples were compared: manually squeezed high-compaction elongated samples with immersion coating, wrapped medium-compaction circularized samples with spray coating, and low-compaction elongated samples with spray coating. Loop specimens were fabricated, modified after winding where applicable, cured, coated, sectioned into samples, and analyzed using digital light microscopy. Image-based analysis quantified layer thickness, coverage interruptions, roundness, ruggedness, roughness, second moments of area distribution, volumetric phase fractions, surface gain, mass gain, and simplified area-estimation errors. Wrapping was the most effective measure for improving global roundness and squeezing improved compaction without circularization. Coating reduced ruggedness in all groups, including the highly rugged low-compaction samples, where part of the contour regularization resulted from bridging indentations, causing higher surface than mass gain. Coating improved the mass-specific second moment in every sample group, with an anisotropy reduction in the immersion-coated sample group. Full article

With the development of three-dimensional high-density integration, low-temperature co-fired ceramic (LTCC) technology has become an important substrate platform for electronic packaging. However, screen-printed Au films on LTCC substrates often contain boundary roughness, local thickness variation, pores, and particle-packing non-uniformity caused by the printing process. These features may affect both the macroscopic resistivity of printed patterns and the local mechanical response of the film. In this study, edge-related structural non-uniformity in screen-printed Au/LTCC films was evaluated using SEM observation, macroscopic resistivity–temperature fitting, nano-indentation, XRD, and nano-scratch testing. The resistivity results show that the stripe pattern has approximately 10–13% higher resistivity than the grid patterns within the measured temperature range, indicating a geometry-dependent electrical response. Nano-indentation results reveal large spatial dispersion in reduced modulus and hardness, and statistical analysis shows that differences among annealing conditions are not significant at the 0.05 level when indentation data alone are considered. Therefore, nanomechanical data are treated as an indirect structural indicator rather than a direct proof of local electrical uniformity. Among the investigated temperatures, 200 °C provides a favorable balance of local hardness, scratch resistance, and microstructural stability, whereas 300 °C should be interpreted cautiously because the higher scratch load is not supported by direct post-scratch failure analysis. Overall, the results provide a cautious but clear structure–property correlation for screen-printed Au/LTCC conductors and identify 200 °C as the preferred annealing condition among the investigated temperatures. These results provide practical guidance for evaluating structural non-uniformity in screen-printed Au/LTCC conductors. Full article

Traumatic brain injury (TBI) is increasingly recognized as a relevant initiating factor in tau-related neurodegenerative processes, yet the quantitative link between a controlled mechanical insult and the long-term spatiotemporal evolution of tau pathology remains insufficiently defined. In the present study, a translational computational framework is proposed to predict post-traumatic tau accumulation by combining region-specific Avrami-type nucleation-growth kinetics with a finite-element simulation of controlled cortical impact (CCI) at human scale. The temporal component of the model is calibrated independently for cortex, hippocampus, and brainstem using experimental post-TBI tau-burden measurements derived from a tau-transgenic mouse model of CCI. The formulation preserves anatomical specificity by calibrating each region independently. The biomechanical component is built around a localized indentation framework designed to mimic the experimental CCI configuration. To transfer the loading concept from mouse to human, the indenter geometry is scaled using cortical thickness as the primary characteristic length, ensuring that the local indentation problem remains mechanically interpretable across species. The resulting strain field is then normalized and used to distribute tau spatially within each region while preserving the calibrated regional mean kinetics. The proposed framework provides a region-aware and mechanically grounded route for studying how a controlled cortical insult may trigger heterogeneous tau accumulation over time, thereby offering a computational basis for investigating early mechanobiological pathways relevant to trauma-associated tauopathy and chronic traumatic encephalopathy (CTE). Full article

This study investigates the mechanical performance of a pulsed laser butt-welded IN792 DS joint and its relationship to its microstructure by means of grid nanoindentation. A new ISE-free (rate-derived) hardness parameter (H_R) has been introduced to account for the local bulk elastoplastic behavior of the material in combination with the stable contribution of residual stress, thus overcoming the limitations of the current standard codes. It allows performance comparability between different welding experiments, materials, and joint configurations. It offers an alternate means to mechanically determine the HAZ width when microscopic and metallurgical methods fail to detect it. Moreover, the spectra of two independent indentation parameters have been utilized as an input within an iterative statistical deconvolution scheme to estimate the composition of the relevant phases present within the fused zone. While one parameter spectrum acted as a predictor in the first stage, the second one served as a corrector for the final estimation of the four detected phases, thereby self-validating the iteration procedure with 5% tolerance. The validity of phase estimation was first determined over the entire FZ and then at three levels of the weald seam (top, neck and bottom) for further validation. The results indicate that the γ-matrix and ultrafine fine/hard second phases in the fused zone amounted to 54% and 43% volume fractions, respectively. The associated deconvoluted mechanical performance, expressed in terms of E_IT, H_IT, and H_R, corresponded to approximately 209 ± 4.5, 6.3 ± 0.2, 4.4 ± 0.1 and 224 ± 7.0, 6.7 ± 0.1, and 4.6 ± 0.1 GPa, respectively. A correlation between the estimated phases and the local mechanical performance via the conventional indentation parameter (H_IT and E_IT) and the new H_R parameter in the three relevant regions of the fused zone was discussed while discerning the effect of cooling rate on precipitate size, heterogeneity, porosity, residual stresses, and grain orientation. Further validation studies on different sample geometries, materials and joint configurations are needed to confirm the generality of the proposed methodology. Full article

The complex geometries feasible with Laser Powder Bed Fusion (PBF-LB/M) lead to varying sizes of scanned cross sections within the layers and hence differing cooling rates. Since PBF-LB/M results in intragranular cell structures, which cause relatively high strengths in the austenitic steel AISI 316L, the influence of changes in the specimen size on the cell structure was investigated. The results obtained from the geometries realized in this work showed no significant influence of the specimen size on the cell sizes. To analyze the relation between the cell structure and the mechanical properties, cyclic indentation tests (CIT) were performed accordingly, revealing no clear influence of the specimen size on the mechanical properties and no correlation between the cell size and the mechanical properties. Additionally, the impact of the cell size on the well-known anisotropy in mechanical properties of AISI 316L produced via PBF-LB/M was investigated. While the cell size was observed to be independent of the specimen orientation on the build plate, the orientation between the direction of loading and the building direction reveals a slight influence on the mechanical properties obtained from CIT. In comparison to the properties determined using CIT, a stronger influence of the orientation between the load and the building direction was observed in tensile tests, which was not caused by the intragranular cells. It was concluded that the anisotropy in the tensile properties is mainly affected by the texture, the elongated grains, and the layer orientation. Full article

Accurately estimating the internal structure of deformable objects from sparse measurements remains a significant challenge in robotics. This work proposes a three-stage identification framework for this problem. First, a classification strategy determines a minimal informative set of indentation locations using a generalized error computed from pre-simulated FEM force reactions of baseline cavity models and flat-punch indentation estimation. Using this set, the estimation stage detects the cavity type and provides a preliminary estimate of its geometric parameters based solely on measured indentation responses. The correction stage then refines these parameters by replaying measured indentation depths in FEM simulations and deriving geometry corrections from the discrepancy between simulated and homogeneous force responses. Robust loss functions at both stages limit the influence of measurements where local contact conditions deviate from the assumed model, improving reliability across all tested cases. Indentation depth was obtained through gripper proprioception, with an RGB-D camera limited to global pose alignment. Experiments on soft cubes with spherical, cuboid, and pyramidal cavities demonstrate that, within known cavity families and fixed material parameters, the minimal indentation set reliably distinguishes cavity types and the pipeline reconstructs dimensions within error bounds. Extending the framework to non-centered structures and unknown materials remains future work. Full article

Fused deposition modeling (FDM)-based three-dimensional (3D) fabrication offers a viable approach to manufacturing highly customized carbon fiber-reinforced polyether ether ketone (CFR-PEEK) components with complex geometries. However, the mechanical properties and surface roughness of FDM-fabricated parts are strongly influenced by processing parameters, particularly layer thickness. This study investigates the influence of layer thickness (0.1 mm and 0.2 mm) on the surface roughness, crystallinity, mechanical properties, and morphological characteristics of FDM-printed 10% CFR-PEEK specimens. The specimens were characterized using mechanical testing, differential scanning calorimetry (DSC), confocal laser microscopy, X-ray micro-computed tomography (µCT), and scanning electron microscopy (SEM). The results show that specimens printed with a 0.2 mm layer thickness exhibit higher crystallinity and ball indentation hardness while also showing increased surface roughness and porosity, with µCT analysis revealing larger and more spatially clustered voids near the sub-perimeter regions. In contrast, specimens printed with a 0.1 mm layer thickness demonstrate higher tensile strength, elastic modulus, elongation at break, and compressive stress. SEM fractography further indicates improved interlayer bonding and a relatively cohesive fracture surface in specimens printed with a 0.1 mm layer thickness. These findings demonstrate clear layer-thickness-dependent processing–structure–property relationships in FDM-printed CFR-PEEK composites and provide guidance for optimizing printing parameters to achieve improved mechanical performance. Full article

Background: A novel titanium scleral buckle implant (TSBI) was developed for the treatment of posterior pole retinal detachments, analytically modeled and structurally tested as part of preclinical approval studies. The strength and stiffness requirements to apply pressure for retinal reattachment also suggested potential benefits for correcting high myopia greater than 8 diopters. Methods: Laboratory load testing and analytical calculations were complemented by nonlinear finite element modeling (FEM), applied for the first time to capture the interaction between the highly deformed myopic eye and the TSBI. Simulations were used to visualize posterior pole indentation and force distribution across anatomical regions. Seven TSBI units were tested in the transverse direction and six in the longitudinal direction. Results: The simulations confirmed that stable indentation is maintained even in areas distant from the sutures. The TSBI’s minimum midspan bending capacity was 40 N at yield and 60 N at ultimate. These values, together with FEM predictions, demonstrated a very large safety margin and showed that the implant deforms insignificantly under high intraocular pressure changes. Conclusions: The TSBI withstands ocular forces, cushions the sclera safely, and retains its geometry, a behavior that may differ from softer buckle materials, which can exhibit time-dependent deformation under sustained loading. Early controlled clinical applications outside the USA, followed for over three years, further validate its safety and potential effectiveness. Full article

Adhesive quasi-static tangential contact between a rigid indenter and a linearly viscoelastic half-space is investigated numerically using the Boundary Element Method. The indenter geometry is described by a power-law profile including parabolic (n = 2), conical (n = 1), and sharp-tip (n = 1/2) indenters. Adhesion is incorporated through a stress-based detachment criterion with effective works of adhesion derived from an energetic approach for quasi-static viscoelastic contacts. During sliding, elements at the leading edge of the contact attach, while those at the trailing edge detach. Due to the viscoelastic response of the material, adhesion at the leading edge is weak, whereas adhesion at the trailing edge is significantly stronger. This asymmetry generates a tangential force acting at the contact boundary. Numerical simulations performed for different ratios of the shear moduli G₀/G₁ show that the friction force strongly depends on the indenter geometry and follows different power-law relations to the normal force: a one-third power for parabolic indenters, a square-root dependence for conical indenters, and a two-thirds power for sharp-tip indenters. Full article