Geometric Discontinuities Research Articles

Fog Harvesting Via Multistage Edge‐Effect Condensation

AbstractThe escalating global population and rapid industrialization have precipitated a severe freshwater scarcity crisis. To address this challenge, innovative strategies are essential to exploit unconventional water sources such as atmospheric vapor. This study proposes a novel approach integrating 3D printing technology with surface chemistry principles for atmospheric fog harvesting. The approach entails leveraging 3D printing technology, chosen for its cost‐effectiveness, unparalleled design flexibility to design intricate geometries, and time efficiency to fabricate cylindrical millimeter‐scale size vertical pillars. Harnessing the intricate interplay of surface phenomena, condensation preferentially occurs on the pillar tops due to surface phenomena. The pillars are imbued with nonadecane, a hydrocarbon renowned for its low surface energy characteristics ensures the uninterrupted progression of water droplet formation, coalescence, and seamless transportation, unveiling a symphony of molecular interactions at the microscale. The design demonstrates promising results, yielding an impressive yield of ≈3.956 g of water per hour from 1 cm2 area. Geometric discontinuities associated with parahydrophobic pillars amplify water harvesting via an edge effect. This study represents a significant step toward a more sustainable and technologically advanced solution for the global water crisis.

A quadrilateral inverse plate element for real-time shape-sensing and structural health monitoring of thin plate structures

The inverse finite element method (iFEM) emerged as a powerful tool in shape-sensing and structural health monitoring (SHM) applications with distinct advantages over existing methodologies. In this study, a quadrilateral inverse-plate element is formulated via a sub-parametric approach using bi-linear and non-conforming cubic Hermite basis functions for engineering structures, which can be modeled as thin plates. Numerical validation involves dense and assumed sparse sensor arrangements for in-plane, out-of-plane, and mixed general loading conditions. iFEM analysis reveals efficient monotonic convergence to analytical and high-fidelity finite element reference solutions. After successful numerical validation, defect detection analysis is performed considering minute geometric discontinuities and structural stiffness reduction because of latent subsurface defects under tensile and transverse loading conditions. The inverse formulation successfully resolves the presence of simulated defects under a sparse sensor arrangement. The proposed inverse-plate element is accurate in the full-field reconstruction of shape-sensing profiles and reliable in defect identification and quantification in thin plate structures.

Effect of circular and elliptical cutouts on the free vibration analysis of sandwich FGM plate under the elastic foundations

The present article investigates the effect of circular and elliptical cutouts on vibrational characteristics of porous sandwich functionally graded material (SFGM) plates with FGM core resting on Pasternak elastic foundation. The structural kinematics of the plate are formulated based on nonpolynomial-based higher-order shear deformation theory (HSDT). Geometric discontinuities have been incorporated in terms of circular and elliptical cutouts in the SFGM plates. The sandwich structure is considered to be comprised of two homogeneous face sheets and a porous FGM core with various cutout shapes and sizes. The variation of material properties from the homogeneous face sheet to the FGM core has been carefully modeled using modified power law distribution. Further, a C0 continuous finite element formulation with a four-noded, isoparametric quadrilateral element with seven degrees of freedom (DOFs) per node has been employed to accomplish the results. The accuracy of the present results has been demonstrated through convergence and validation studies. A comprehensive study has been carried out to investigate the influence of volume fraction index, even and uneven porosity distribution, circular and elliptical cutouts, as well as H-elliptical and V-elliptical type cutout shapes on the frequency parameter of SFGM plates with the elastic foundation. The numerical results demonstrate the aforementioned parameters significantly impact the vibrational frequency of the SFGM plates.

Tensile Properties of Open Hole and Unhole Sugar Palm ‘Ijuk’ (SPI) Fibre Composite Treated with Sodium Hydroxide (NaOH)

This study evaluates the effects of sodium hydroxide (NaOH) treatment on tensile properties of sugar palm 'ijuk' (SPI) fibre-reinforced polymer (FRP) composites, with and without an open hole that acts as a stress concentrator. The NaOH treatment is aimed to improve the interfacial adhesion between SPI fibres and polymer matrix. Composite specimens were prepared using the hand lay-up method, incorporating SPI fibres in various orientations, and featuring a 6 mm diameter hole. Tensile tests were conducted to evaluate the mechanical performance of SPI FRP composite, including ultimate tensile strength, Young's modulus, and elongation at break. The research also compared the properties of SPI to those of synthetic glass fibre in fibre-reinforced polymer composites. The results showed that NaOH treatment significantly improves the fibre-matrix adhesion with 26% increase in tensile strength, leading to enhanced tensile properties in both samples, regardless of hole presence. The 0° orientation provides the highest strength and stiffness when the load is applied in the direction of the fibres. While for the 90° orientation, strength reduces by 14%. The impact of the hole on stress concentration and the subsequent mechanical behaviour of the open-hole specimens is substantial. The findings of this study offer insightful perspectives on the potential use ofNaOH-treated SPI fibre in structural and other applications, demonstrating its ability to withstand tensile stresses, even with geometric discontinuities like holes.

On the notch sensitivity of as‐built Laser Beam Powder Bed–Fused AlSi10Mg specimens subjected to Very High Cycle Fatigue tests at ultrasonic frequency up to 109 cycles

AbstractThe notch effect significantly influences the fatigue response of components and is particularly relevant for parts produced with additive manufacturing (AM) processes, characterized by complex geometries and possible geometric discontinuities inducing local and critical peak stresses. Moreover, the low surface quality, as well as manufacturing defects and residual stresses, interacts with the local peak stress induced by geometric discontinuities, complicating the assessment of the notch effect for AM parts and requiring extensive experimental fatigue investigations. In the present paper, the notch sensitivity of as‐built AlSi10Mg specimens produced with the laser beam powder bed fusion in the Very High Cycle Fatigue regime is investigated. Ultrasonic fatigue tests up to 109 cycles have been carried out on rectangular bars and rectangular bars with a central through‐thickness hole. The notch effect has been found to significantly affect the fatigue response of the investigated AlSi10Mg specimens, with surface defects having a main role and pointing out the influence of the surface quality on the crack formation.

Combining phase field method and critical distance theory for predicting fatigue life of notched specimens

Notch features, widely used in engineering components, have negative effect on the fatigue life of structural parts due to the stress concentration caused by their geometry. This highlights the importance of numerical methods to help assessing the adverse effect of geometrical discontinuities like notch on the fatigue properties of structural components. In this study, a new phase field fatigue formulation was proposed to predict the fatigue behavior of metallic notched specimens, suggesting a dimensionless parameter based on the critical distance theory to capture the notch effect. The slope of S-N curve was regarded as a function of the effective stress ratio obtained from different critical distances, and the fatigue damage threshold was varied with the slope of the S-N curve. Two S-N curves of smooth and notched specimens were used to calibrate the fatigue model parameters for each material. Numerical examples validated by experimental data of various configurations in terms of geometry, stress ratio and loading mode indicated the validity of the proposed model and its ability to accurately predict the fatigue life of notched specimens with different notch geometries and materials, as the predicted fatigue lives mostly fell within the ± 2 scatter band. The results indicated that compared with the traditional TCD method the proposed model eliminates the requirement to recalculate the critical distance at different fatigue lives, and the stress ratio effect can be naturally captured without recalibrating the critical distance.

Numerical investigation of residual stress and strain in blades caused by foreign body impact. Comparison of impact modeling on real blade and flat surface

Damage caused by the impact of a foreign object on the turbine blades is caused by the entry of millimeter-sized foreign particles such as sand, stones, or small pieces of broken parts. Consequently, the remaining damage resulting from the impact of a foreign body on the blades is in the form of geometrical discontinuities such as craters or grooves on the blades, which create suitable conditions for the creation and growth of cracks and the complete failure of the blades. One of the most important aspects of foreign body impact damage is the study of the resulting residual stresses at the impact site, which plays a significant role in the creation and growth of cracks. In the present article, the main aim of this work was to analyze the residual stresses due to foreign object damage by expanding the simulation on the blades, considering a real blade model as well as the leading-edge curvature effect. To validate the numerical modeling, the impact of a spherical particle on a flat plate was modeled and the residual stresses and damages resulting from the modeling were compared to the experimental results available in the articles. Finally, the impact of the spherical foreign body on different places of the leading edge of a blade with different impact velocities was investigated. Moreover, the examined blade sample was replaced with a plate with the same material, and the impact of the foreign object on the flat surface was modeled for two different service temperatures. In this study, the resulting residual stresses and strains in three critical areas were compared.

Vibration localization and reduction of double-plate structures

A thin plate-type resonator is attached to a host-stepped plate to achieve vibration localization and reduction in initial low-order global vibration modes. A semi-analytical method is proposed to analyze the free and forced vibrations of the double-plate structure, considering the geometric configuration's heterogeneity and discontinuity. The double plate structure is divided into several sub-plates for individual modeling, with admissible functions constructed for the displacements of each subdomain. These subdomains are then combined into a unified whole through displacement compatibility conditions. The no-orthogonality between global vibration and localized modes is determined using analytic mode functions obtained by the Ritz method with special admissible functions, which is crucial for suppressing the multiple resonance peaks of global vibration using the integrated plate-type resonator. An intriguing finding is that at the frequency veering point of global vibration modes and localized modes, the non-orthogonality can lead to two coupled global-localized modes that are similar to the initial localized mode, and the vibration of initial global modes can be mainly concentrated in the resonator region outside the plate during free vibration. For force vibration of the double plate, the initial resonance peak splits from one into two smaller resonance peaks due to the two coupled global-localized modes. Furthermore, the coupled global-localized mode allows for a substantial reduction in the host plate vibration while making a negligible impact on the total mass and global vibration frequency. This study presents a promising approach for reducing multimodal vibrations in lightweight structures.

Vibration analysis of sandwich functionally graded material plate with cut-outs using artificial neural network technique

In the present article, the effect of geometric discontinuities on the vibrational response of porous sandwich functionally graded material (SFGM) plates with double FGM facesheets has been investigated using the artificial neural network (ANN) technique. Generalized governing equations for the SFGM plate have been derived based on nonpolynomial based higher-order shear deformation theory (HSDT). Geometric discontinuities have been incorporated in terms of cut-outs in the SFGM plates. The FGM layers integrate a porosity model, while the core layer is considered a ceramic layer within the SFGM plate structure. Further, a C° continuous isoparametric finite element formulation with a four-noded, isoparametric quadrilateral element with seven degrees of freedom (DOFs) per node has been employed to accomplish the results. The accuracy of the present results has been demonstrated through convergence and validation studies. A comprehensive study has been carried out to investigate the influence of volume fraction index, even and uneven porosity distribution and cut-outs on the frequency parameter of SFGM plates. However, the finite element method (FEM) is computationally challenging. Therefore, the motivation behind adopting ANN technique to develop a predictive model for reasonable accuracy with less computational time. The ANN technique is proposed to predict the NDFP of the SFGM plate using cut-outs under various conditions using numerical simulation datasets. An optimised ANN model has been developed with an architecture of (6–5–10–5–1), exhibits best performance based on mean error value, which accurately predicts the Non-Dimensional Frequency Parameter (NDFP) of the SFGM plate.

Effects of differential hardening on energy absorption prediction of AA6061-T6 thin-walled rectangular tube

In this study, the energy absorption characteristics and deformation modes of AA6061-T6 thin-walled rectangular tube are investigated experimentally and numerically under different crushing conditions, including axial crushing, three-point bending and oblique crushing. Mechanical tests are carried out on four specimens of uniaxial tension, uniaxial compression, shear and plane strain tension along different loading directions for AA6061-T6. Besides, the effect of differential hardening behavior on the energy absorption prediction of AA6061-T6 rectangular tubes is illustrated by comparing Lou2022, von Mises and SY2009 functions. The mechanical experiment results indicate that AA6061-T6 shows obvious anisotropy, differential hardening behavior and tension-compression asymmetry, and its plastic evolution is accurately characterized by the Lou2022 model. The axial crushing properties show that the AA6061-T6 thin-walled rectangular tube undergoes the progressive symmetrical folding deformation mode. The introduction of geometric discontinuity can obviously reduce the peak force and improve the crashworthiness performances under the axial load. The main crushing mode is bending with a small amount of indentation for three-point bending. Moreover, the three-point bending simulation shows that the Lou2022 function considering differential hardening behavior has the highest simulation accuracy. Three different oblique crushing simulations of 10∘, 20∘ and 30∘ illustrate that the AA6061-T6 rectangular tube at 10∘ mainly occurs progressive folding deformation. while the other two oblique crushing angles undergo global buckling deformation. The total energy absorption at 10∘ is 1.87 and 2.43 times of that at 20∘ and 30∘, respectively. The crushing force efficiency of 20∘ and 30∘ is 41.28 % and 31.8 % lower than that of 10∘, respectively. A comprehensive understanding of the energy absorption performance of AA6061-T6 thin-walled rectangular tube under different crushing conditions is helpful to determine its position and shape as a vehicle safety structure, and to exert its optimal plastic deformation potential to dissipate the collision energy and ensure passenger safety.

Estimation of mode I quasi-static fracture of notched aluminum–lithium AW2099-T83 alloy using local approaches and machine learning

Aluminum–lithium (Al–Li) alloys offer superior performance under different conditions that involve mechanical loading, high temperature and corrosive environment. Therefore, Al–Li alloys are being used in the defense, aerospace, and aircraft industries, specifically in structural parts such as fuselage, empennage, and wings. By modifying the chemical composition, a third generation of Al–Li alloys has been introduced to overcome the mechanical and thermal shortcomings of previous Al–Li generations. As structural parts usually contain notches, it is of paramount importance to study the strength of the newly introduced alloys in the presence of such geometrical discontinuities to select the suitable alloy for a particular application. The aim of this work is to analyze the strength of U and V-notched specimens machined from extruded AW2099-T83 Al–Li alloys under quasi-static loading. The fracture stress of specimens with various notch radii and angles were estimated using strain energy density (SED) and the theory of critical distances (TCD) methods. A support vector machine (SVM) regression model was also implemented to assess the applicability of estimating fracture stress using machine learning approaches. The results show an average absolute discrepancy of 6.6 %, 7.8 % and 2.8 % for SED, TCD and SVM methods, respectively.

Notch corrosion fatigue behaviour and simplified strain energy density-based notch fatigue life assessment of Grade-A shipbuilding steel

Corrosion fatigue is a key challenge in lifecycle management of ship hull structures. Although sea wave fatigue stresses are linear-elastic, highly-damaging elastic–plastic conditions occur at geometrical discontinuities or notches. Estimation of notch stress-strains to characterize notch fatigue behaviour conventionally requires large computational efforts. Also, constant strain energy density (SED), as a driving force, is far more effective in realistic applications versus constant stress and strain fatigue life approaches. Identified research gaps were the development of a simplified SED approach for fatigue life assessment of hole-notched structures. Fatigue studies were conducted on hole-notched specimens of Grade-A shipbuilding steel in air and corrosion mediums. Strong synergistic interactions of corrosion and fatigue damage mechanisms were studied by scanning electron microscope (SEM) fractography. Notch corrosion fatigue life was reduced by 70% from notch air fatigue life due to environmental effect. Two new parameters are proposed to improve the efficiency of notch fatigue life assessment, namely “fatigue notch strain energy density concentration factor (K_SED) and “fatigue notch toughness”. This improved fatigue life assessment method was demonstrated as equally reliable but much simpler to implement, eliminating the complex computational analysis. This improved method has promising applications in real-time structural health monitoring (SHM) of ship hull structures.

Mesoscopic simulation of uniaxial compression fracture of concrete via the nonlocal macro–meso-scale consistent damage model

To capture the uniaxial compression fracture of concrete composite is still a great challenging problem. To this end, the newly proposed nonlocal macro–meso-scale consistent damage (NMMD) model is extended to simulate uniaxial compression fracture of concrete composites. In the NMMD model, a mesoscopic structure composed of material point pairs is attached to each material point. A decomposition scheme suitable for masonry-like materials is adopted to decompose the elongation quantity of point pairs. The topologic damage is defined as the weighted summation of mesoscopic damage in neighboring material point pairs driven by the decomposed elongation quantity. The physically-based energetic degradation function is employed to bridge the geometric discontinuity in solids and the energy dissipation, and thus the topologic damage is integrated into the framework of continuum damage mechanics. The Monte-Carlo method and two-phase random field model are employed to generate stochastic circular and irregular aggregates representing the meso structure of concrete, respectively. The interface transition zone is prescribed by reducing the critical value of interface point pairs. Numerical results indicate that both the crack patterns and stress–strain curves of the uniaxial compression experiments on concrete panels can be well captured by the proposed NMMD model without mesh size sensitivity. The influence of horizontal constraints on the top and bottom surfaces is investigated and shown to have an effect on the crack patterns, strength and deformation capability of the specimen. The necessity of decomposition is also illustrated.

Fracture assessment of polyamide 12 (PA12) specimens fabricated via Multi Jet FusionTM in the presence of geometrical discontinuities

This study aims to study the fracture resistance of additively manufactured polyamide 12 (PA12), specifically when subjected to notches and cracks, and how it varies with the printing direction using Multi Jet Fusion (MJF). The methodology involved conducting tensile tests on V-notched samples, with a focus on different combinations of opening angle (0°-120°) and tip radius (0.2–2 mm). The findings revealed that the sensitivity to the notch opening angle decreased with an increase in the notch tip radius. Furthermore, the fracture resistance for different mode mixities was examined using semi-circular bend (SCB) specimens, with the crack angle varied between 0° and 53°. The results demonstrated two distinct fracture behaviours, namely brittle and ductile, depending on the crack angle. Theoretical analyses revealed that with appropriate tuning, average strain energy density (ASED) can predict the load capacity of notched and cracked PA12 parts manufactured with MJF, within an error range of ± 20 %.

Tire–road contact modelling for multibody simulations with regularised road and enhanced UA tire models

AbstractMultibody simulations play an important role in the study of the dynamic behaviour of road vehicles, being one of the key aspects the modelling of the tire-road interaction. The tire-road contact modelling is required to detect the contact between the tire and road and to obtain the tire contact forces from the tire-road relative motion. The first part of the problem is solved by a contact detection algorithm, whereas the second part is handled by a tire model. In both cases, the trade-off between accuracy and computational cost needs to be addressed in the road dynamics scenario. For the contact detection problem, this work proposes a methodology in which the road is described by a mesh of triangles while the tire is described by a toroid. The triangular mesh road input can be directly extracted from any CAD model. To avoid the geometric discontinuities due to the transition between triangular patches, a set of auxiliary points is used to obtain a continuous variation of the road surface normal, based on the method proposed by Rill (Multibody Syst. Dyn. 45:131–153, 2019. In the process of contact detection, all kinematic quantities required by the tire-road contact model are evaluated. The tire–road forces are evaluated using the enhanced UA tire model, which is a numerically stable and efficient development of the original tire model proposed by Gim and Nikravesh (Int. J. Veh. Des. 12, 1991; Int. J. Veh. Des. 12:19–39, 1991; Int. J. Veh. Des. 12:217–228, 1991). Both the contact and tire models have smooth transitions between their internal transitions, thereby reducing the need for the variable-step ODE integrators to unnecessarily decrease time steps. The advances on contact detection and the tire–road contact models, proposed here, are demonstrated with a set of road vehicle simulation scenarios in which the influence of various modelling parameters on the stability and efficiency of the simulations is addressed. The novelties of the work consist not only in the demonstration of the enhanced UA tire model in practical situations but also in the description of the new tire–road contact methodology that employs a simple description of the road geometry, to achieve smooth tire–road contact forces.

An Ice Protection System Based on Phased Piezoelectric Transducers

This study focuses on a system constituted of two piezoelectric transducers installed on a slat representative element, with ice protection purposes. The waves generated by these actuators can cause, in fact, shear actions between the slat panel and the ice accretion, with the final effect of breaking and detaching it. A property of the system is, however, the possibility of regulating the phase between the excitation signals of the two transducers. This capability can be exploited to produce local advantageous wave interference with a consequent amplification of the shear actions. Benefits can be obtained in terms of: (1) reduction of needed power; (2) recovery of signal intensity losses due to distance, geometric, and mechanic discontinuities; (3) recovery of non-optimal functionality due to off-design conditions. The work starts with an overview of the impact of the ice on the aeronautic and other sectors. Then, attention is paid to the systems currently used to protect aircraft, with a specific focus on ultrasounds generated by piezoelectric transducers. The concept proposed in this work is then presented, illustrating the main components and the working modality. On this basis and considering the specific nature of the physical phenomenon, the modeling approach was defined and implemented. At first, the impact of some critical parameters, such as the temperature and the thickness of the ice, was investigated. Then, the impact of the phase delay parameter was considered, estimating the increase of magnitude potentially reachable by means of optimal tuning. Finally, a preliminary experimental campaign was organized and a comparison with the numerical predictions was performed.

Analysis of the influence of mechanical element discontinuities on unbalancing

The study of rotor unbalancing is essential for safety and reliability in the design of machinery and other mechanical structures with rotating parts. By understanding the dynamic behavior and effects of unbalanced components, engineers can address this issue and establish a maintenance program to safeguard mechanical systems from excessive vibrations and prevent catastrophic failures, primarily due to fatigue. Balancing in one and two planes is the most common procedure to correct unbalanced masses in rotating parts. In this work, the aim is to advance the understanding of the effects of mass distribution in irregular-section parts and develop a tool to calculate and improve balancing. In certain situations, there are local limitations to corrections, such as adding correction mass due to irregularities and machine element constraints. To validate the proposed solution, a sample of a crankshaft and a camshaft actuation mechanism was used, where unbalancing is a common issue due to the inherent geometric discontinuities in these types of components. The achieved result demonstrated the validity of the application, allowing the balancing of the samples within the levels recommended by the standard.

Decoupling the role of microstructure and geometric discontinuity introduced by weld reinforcement height on corrosion behavior of SA106B/316L SS welded joint in the flowing 0.5 M NaCl solution

The flow-influenced corrosion (FIC) behavior of SA106B/316L stainless steel (SS) welded joints with SS located upstream and downstream is investigated experimentally and numerically. The damage components of microstructure heterogeneity and geometric discontinuity are quantified. The FIC of the welded joint is affected by the combination of galvanic corrosion, mass transfer, and charge transfer. The electrochemical measurements indicate that the corrosion is aggravated by a flow disturbance component of 18.70∼26.96%. The corrosion of SA106B carbon steel is more severe than 52M and 316L SS due to galvanic effect, which is further promoted by flow disturbance. The FIC mechanism is also discussed.

A threshold criterion of stress intensity range in a steel sheet

Fatigue fractures often originate and propagate from geometric discontinuities or material defects in equipment or components. The occurrence and propagation of cracks near the fatigue limit were observed in notched specimens of a steel sheet that simulated this situation, and analyzed using fracture mechanics parameters. The notch caused strain concentration, and local plastic strain arose even at low stress amplitudes. Transgranular fracture occurred, and arrested cracks were observed near the threshold stress amplitude Δσth. The threshold stress intensity range ΔKth had a good power function correlation with the effective notch length aef, but it depended on the length and did not reach a constant value. By identifying and applying the critical power exponent, we proposed a prediction model using the function ΔKthc=Yπ1/2Δσthaef1/κ, which is the critical threshold stress intensity range that has a constant value. κ is equal to 5 for the steel sheet under transverse bending. Since ΔKth c obtained using this critical exponent method does not depend on the crack length, it can be used as a material constant and a failure criterion, and can be applied as a new strength prediction model.

Probabilistic notch fatigue assessment under size effect using micromechanics-based critical distance theory

Geometrical discontinuities are inevitable in engineering structures due to various functional requirements, which often yield complex stress–strain state and thereby significantly impact their fatigue performances. In this study, crystal plasticity theory is coupled with traditional critical distance theory for notch effect modelling considering microstructural heterogeneity. Specifically, microstructural and geometrical size effects on critical distance and fatigue performance are studied based on Sub-modelling approach. In addition, critical distance theory is coupled with Weibull distribution for probabilistic fatigue life evaluation of notched components. The developed method is verified and compared by using experimental data of GH4169 alloy. The findings demonstrate that the evaluated P-S-N curves exhibit strong agreement with tested data and geometrical size effect poses larger influence than the grain size effect on critical distance and fatigue life.