Search

Los datos presentados se corresponden con distintas campañas experimentales llevadas a cabo por el grupo de investigación de dinámica ferroviaria de la Universidad de Sevilla, RAILDYNUS. Los ensayos se corresponden con el recorrido de un vehículo ferroviario denominado "Vehículo auscultador", a lo largo de una vía a escala que posee el grupo de investigación. Todos los datos tanto de la vía a escala como del vehículo utilizado se pueden consultar en https://grupo.us.es/raildynus/infrastructure

Los datos presentados se corresponden con distintas campañas experimentales llevadas a cabo por el grupo de investigación de dinámica ferroviaria de la Universidad de Sevilla, RAILDYNUS. Los ensayos se corresponden con el recorrido de un vehículo ferroviario denominado "Bogie 2021", a lo largo de una vía a escala que posee el grupo de investigación. Todos los datos tanto de la vía a escala como del vehículo utilizado se pueden consultar en https://grupo.us.es/raildynus/infrastructure

Se presenta los resultados obtenidos tras la medida geométrica de la vía a escala. Tras un procedimiento experimental que comprende el uso de una estación total, inclinómetro y sensor de distancia, se ha obtenido la medida de referencia de la vía, así como las irregularidades asociadas. Todos los datos de la vía a escala se pueden consultar en https://grupo.us.es/raildynus/infrastructure

This paper presents an investigation into the real-time explicit co-simulation of mobile harbor cranes under hoisting operation. The system is divided into two subsystems, with Subsystem 1 representing the payload and Subsystem 2 encompassing the wire-rope system. To capture the real-time behavior of the wire ropes accurately, the ALEM (Arbitrary Lagrangian–Eulerian Modal) method is employed in this study. Using this formulation, the intricate behavior of the wire ropes, encompassing elasticity, bending effects, and dynamic influences, is rigorously considered. The dynamic equations governing the payload are solved using the Runge–Kutta4 method, while the Generalized Alpha method is utilized to solve the wire-rope system. Both the Gauss–Seidel and Jacobi methods are investigated as two coupling techniques to connect the subsystems. Additionally, the study delves into the impact of the extrapolation method and macro time step on results accuracy and efficiency. The findings demonstrate that co-simulation employing the Gauss–Seidel method and FOH (First-Order Hold) extrapolation yields optimum and accurate simulations. Moreover, the study successfully achieves real-time simulation by optimizing the wire-rope system simulation, accounting for all degrees of freedom inherent in a 3D system. Remarkably, the maximum error observed in the axial force amounts to a mere 0.6% when employing real-time simulation. These findings can hold practical value for employing the current wire-rope subsystem in the interface modeling of real-world industrial cranes.

This article investigates the appearance of periodic mechanical oscillations associated with the transition between static and dynamic friction regimes. The study employs a mechanical system with one degree of freedom and a friction model recently proposed by Brown and McPhee, whose continuity and differentiability properties make it particularly appropriate for an analytical treatment of the equations. A bifurcation study of the system, including stability analysis, transformation to normal form and numerical continuation techniques, reveals that stable periodic orbits can be created either by a supercritical Hopf bifurcation or by a saddle-node bifurcation of limit cycles. The influence of all system parameters on the appearance of periodic oscillations is investigated in detail. In particular, the effect of the friction model parameters (static-to-dynamic friction ratio and transition speed between the static and dynamic regimes) on the bifurcation behavior of the system is addressed.

In this paper, a detailed and comprehensive linear stability analysis of a rolling toroidal wheel is performed. The wheel is modeled as a rigid toroid-shaped body rolling without slipping on a horizontal surface. The nonlinear equations of motion constitute a Differential-Algebraic Equations system, given by the dynamic equilibrium equations augmented with the nonholonomic constraints, which arise from the no-slip condition. The circular steady motion and the linearized equations of motion along this relative equilibrium are obtained, for both the solid and hollow tori. The expressions of the linearized equations and the corresponding eigenvalues are derived analytically as a function of the torus aspect ratio. The variation of the stability boundary with the torus aspect ratio is shown. A comparison of the results obtained in the solid and hollow scenarios is included, and all the results are validated with the rolling hoop, which corresponds to a degenerate torus with zero aspect ratio. In the particular case of the steady straight-line rolling and spinning about a vertical diameter, which constitute limit motions of the circular steady motion, the critical rotational and angular speeds required for stabilization are obtained.

In this paper, the handling of the dependent coordinates in the linearization of constrained multibody systems is clarified. To this end, a brief but comprehensive overview of linearization approaches used in the field of Multibody System Dynamics is presented. These procedures are illustrated by using a common notation and classified into four groups, depending on the initial form of the nonlinear equations of motion and the selection of the generalized coordinates (a redundant or a minimal set). The handling of the dependent coordinates in each of the procedures is discussed. The linearized equations of motion of constrained multibody systems are of great importance in several applications, such as linear stability and modal analyses, the design of linear state feedback controllers or the building of state and input estimators, like Kalman filters. When modeling a constrained multibody system, a number of coordinates greater than the number of degrees of freedom of the system is usually used. While some linearization approaches make use of the complete set of coordinates, several procedures are based on a coordinate partition in terms of independent and dependent coordinates to reduce the number of linearized equations of motion. In this latter scenario, the role of the dependent coordinates in the linearization is important and, in a general case, these dependent coordinates cannot be ignored to obtain the correct linearized equations of motion. This aspect, which may seem obvious, is not straightforward and is addressed in this work. The importance of considering the set of dependent coordinates in the linearization is demonstrated with a well-acknowledged bicycle benchmark multibody model and an electric kickscooter multibody model with rear and front suspensions. To this end, the Jacobian matrix and the linear stability results of these case studies are computed by considering different choices of independent and dependent coordinates.

This research work presents an experimental investigation on the formability and failure of additively manu- factured polymer sheets. To this regard, Nakajima formability tests following different principal strain paths have been conducted on 2 selected FDM-printed polymer sheet materials, polyethylene terephthalate glycol and polycraprolactone, this being carried out for the first time ever, as far as the plastic behavior and formability study of this kind of 3D printed materials has been limited so far uniquely to conventional tension or compression tests. The analysis includes the evaluation of the different types of failure under plastic deformation for each material considered, allowing the assessment of the overall formability limits within the materials forming limit diagrams combined with the failure evaluation performed via optical microscopy. Thus, the results provided the overall characterization in terms of sheet formability and the comprehensive assessment of the different failure modes and the forming conditions upon which each type of failure is attained for each of the two printed ma- terials. Furthermore, these results allow the authors to create an essential evaluation framework for the ongoing research on process hybridization including the combination of 3D printing technologies with innovative forming processes such as incremental sheet forming.

This contribution analyses the formability of incrementally hole flanged parts using different tool radii (10, 20 and 47.9 mm). The smallest radius (10 mm) can induce full incremental benefits in the hole-flanged specimen, whereas the biggest one generates a formability behaviour closer to a conventional press forming. In the first case, the necking process is clearly delayed, being the development of a fracture in the middle of the wall flange the mechanism that controls the failure of the specimen. In contrast, in the second case, failure is governed by the appearance and development of a neck at the edge of the flange, which ends in material fracture. The intermediate tool radius (20 mm) shows midway features between a conventional and a fully incrementally formed specimen. The location and fracture mode of the flanged parts with different tool sizes are experimentally analysed and discussed within the Forming Limit Diagram (FLD) using the optical strain measurement system ARGUS®.

In this work, a detailed multibody model of an electric kickscooter is presented. The model includes toroidal wheels as well as rear and front suspensions. The equations of motion are derived and linearized along the steady forward motion of the vehicle. Using an efficient linearization approach, suitable for complex multibody systems with holonomic and nonholonomic constraints, allows for obtaining the reduced linearized equations of motion as a function of the geometric, dynamic, wheels’, and suspensions’ parameters. The proposed electric kickscooter multibody model is validated with the stability results of a previously presented electric kickscooter benchmark. Since the resulting eigenvalues are parameterized regarding the design parameters, a detailed linear stability analysis of the system is performed. In particular, the influence on the stability of the toroidal geometry of the wheels, the elliptic cross-section of the toroidal wheels, the rider model, the steering axis inclination angle, the inertia tensor of the front frame, and the rear and front suspensions is analyzed. The model presented, together with the linearized equations of motion obtained in this work, enables a systematic analysis of the stability of these vehicles, which helps design new electric kickscooters with improved vehicle safety conditions and oriented to a wider range of potential users.

The flanging of metal sheets is extensively used in the automotive and aeronautical industries to provide rigidity or support for subsequent assembly. Flanging by rubber pad forming is one of the most common processes for small and medium batch production. Flanges with nonlinear bending lines are exposed to severe conditions that significantly hinder our comprehension of the geometrical, material, and process factors associated with flange formability (i.e., flangeability). This work presents a numerical study of the flanging process by a tailored rubber pad of hollow AA7075-O parts with continuous concave and convex flanges. The flangeability limits, the geometric capabilities of the forming process, and the deformation mechanisms of stretched and shrunk flanges as well as in the transition zone between them are analysed.

A model-based methodology for the estimation of both lateral and vertical track irregularities is presented. This methodology, based on Kalman filter techniques, was developed for an independent and compact measuring system comprising an instrumented axle equipped with a limited set of low-cost sensors: a 3D gyroscope, a linear variable differential transformer (LVDT) distance sensor, and an encoder. The instrumented axle can be used on any railway vehicle traveling at moderate forward speed to provide measurements in real-time. The proposed methodology, combined with the instrumented axle, enables precise and prompt measurement of track irregularities. An experimental campaign carried out on a 1:10 scale track facility at the University of Seville validated both the system and the methodology. In the testing, 80 m of scaled track was measured at an operational speed of V = 0.65 m/s in just 2 min. Simulation estimates for track irregularities compared against the measured data from the testing showed a good performance of the proposed methodology, with maximum errors of 0.45 mm in the short wavelength range D1, the range most influential to vehicle dynamic behavior.

Se han usado varios modelos propuestos en la literatura para predecir el límite de fatiga de componentes con entallas sometidos a carga cíclica biaxial. Las predicciones de estos modelos se basan en las tensiones elásticas a lo largo de una línea considerada representativa de la dirección de la grieta. La línea utilizada en los modelos cambia considerablemente, siendo para un modelo la dirección del Modo I, para otro la dirección del Modo II y para otros dos una dirección mixta Modo I-II, a pesar de que, evidentemente, la dirección experimental de la grieta es única. En los últimos años se ha realizado un estudio experimental de direcciones de grieta en probetas cilíndricas con agujero circular de tres materiales sometidas a carga cíclica axial, torsional y biaxial en fase, obteniéndose direcciones similares para los tres materiales y cercanas al Modo I. Los modelos analizados dan, en general, buenas predicciones, aunque utilizan direcciones completamente diferentes entre sí y a las experimentales. Las predicciones de los modelos utilizando, de manera forzada, las direcciones experimentales medidas son buenas en la mayoría de los casos, lo que revela una sorprendente insensibilidad de dichos modelos a las hipótesis principales en que se basan sus propias formulaciones., Several models from the literature were used to predict the fatigue limit in notched components subjected to biaxial cyclic loading. The predictions of these models are based on the elastic stresses along a line, which is considered to be representative of the crack direction. The line used in the models changes considerably, being for one model the direction of Mode I, for another the direction of Mode II and for two others a mixed direction Mode I-II, despite the fact that, evidently, the experimental direction of the crack is unique. In recent years, a study of experimental crack directions for three materials has been carried out in cylindrical specimens with a circular hole subjected to cyclic axial, torsional and in-phase biaxial loading, providing similar directions for the three materials and close to Mode I. The analysed models give, in general, good predictions, although they use completely different directions from each other and from the experimental ones. The predictions of the models using, in a forced way, the measured experimental directions are good in most cases, which reveals a surprising insensitivity of these models to the main hypotheses on which their own formulations are based.

Single Point Incremental Forming (SPIF) is a dieless and flexible forming technology that allows performing complex shapes and presents a high economic payoff for low production series. In this context, this research presents an experimental investigation of Polyether ether ketone (PEEK) sheets deformed by SPIF at room temperature, determining the influence of the process parameters on the material formability. The research is performed in terms of principal strains that are evaluated within the material Forming Limit Diagram (FLD) obtained by means of Nakajima tests allowing to establish the forming limits of PEEK sheet material. On the other hand, the results of the SPIF tests performed gave rise to an analysis in terms of formability, modes of failure, temperature, forming force, and geometry accuracy. These experiments allow assessing the optimal parameters and forming methodologies/procedures for the manufacturing of cranio-maxillofacial prostheses. In this sense, it was performed a global study in terms of the formability of the manufactured prostheses, as well as the shape accuracy, temperature and roughness analysis, among others. This research showed that the maximum strains attainable by the two prostheses were still found far away from the Fracture Forming Limit (FFL) of the material, showing the feasibility to obtain extra formability within the forming safe zone. In conclusion, this work proved the high potential of manufacturing prostheses in the biomedical field using Incremental Sheet Forming (ISF) processes in combination with advanced biocompatible polymers such as PEEK.

This study investigates the discrete extended Kalman filter as applied to multibody systems and focuses on accurate formulation of the state-transition model in the framework. The proposed state-transition model is based on the coordinate-partitioning method and linearization of the multibody equations of motion. The approach utilizes the synergies between the integration of states and estimator covariances without overly simplifying the integrator structure. The proposed method is analyzed with a forward dynamics analysis of a four-bar mechanism. The results show that the stability of the state-transition model in the forward dynamics analysis is significantly enhanced with the proposed method compared with the forward Euler-based methods. The computational efficiency of the novel method was significantly lower in comparison to forward Euler-based methods, which was found to be mainly due to the computation of the Jacobian matrix of the nonlinear state equation. However, the increase in computational cost can be considered acceptable in Kalman-filtering applications, where the exact Jacobian of the state equation is needed.

This paper presents an analytical solution for the rope-sheave contact problem in static conditions, also applicable to belt-pulley problems and similar mechanisms. The rope is assumed under constant and unequal loads at the two ends, as in an elevator when the brake is acting on the drive sheave and the weights of the cabin and counterweights are different. The rope is assumed to behave as a rod without bending stiffness. Assuming a bristle model for the rope-sheave contact and Coulomb friction, the balance of forces in a differential slice of the rope is used to obtain a closed-form solution for the axial force field and the normal and tangential contact force fields. This analytical solution is found first in the case of a bristle model with tangential flexibility but axially rigid. Then, the model is extended to axially flexible bristles, that allows the rope to sheave relative penetration. The solution is valid until one cross-section of the rope achieves the saturated tangential friction force. The value of the axial load when this condition is met is identified. If the high-load further increases, the rope in contact with the sheave is separated in two areas, the area next to the low-load remains fully stuck to the sheave while the area next to the high-load shows exactly the saturated friction force. This paper calculates the angle of separation between the two areas and the axial force field and normal and tangential contact force fields, being all these functions piece-wisely defined. Finally, the paper presents numerical results for a particular example of all the analytical solutions.

The effect of ageing and anisotropy in 3D-printed composites including short carbon fibres embedded in a polyamide (PA/nylon®) matrix is analysed experimentally. A testing campaign including tensile and fracture toughness coupons with 100% infill is studied. The effect of anisotropy induced by the Fused Deposition Modelling (FDM) procedure, caused by the alignment of the fibres with the deposition direction (raster angle), is presented. Specifically, results showed that the Young modulus and the elastic limit values are lower for the ＋45/−45 infill configuration with respect to the 0/90 infill configuration. Conversely, the ultimate tensile strength, the ultimate tensile strain, and the fracture toughness values are higher for the ＋45/−45 infill configuration. Moreover, the crack path obtained in fracture toughness coupons always followed the raster angle. Additionally, experimental results show that the 3D-printed composite parts keep the hygrothermal properties associated to the matrix, thus an ageing effect is observed even for standard environmental conditions (room temperature, 50% relative humidity). Specifically, Young modulus, elastic limit and ultimate tensile strength values are lower for the older coupons. The ultimate tensile strain is higher for the older coupons while the fracture toughness is similar. Coupons stored in a desiccator also varied the properties but in a slightly manner.

Fretting fatigue is a material damage phenomenon that produces damage on the contact surface, such as wear and surface cracks that can grow through the specimen. It is possible to reproduce the phenomenon in a laboratory using different geometries. In the absence of a common guide, this work studies the effect of different geometries of specimens and contact pairs on the fretting fatigue behaviour. This paper compares the results of a fretting fatigue test campaign made with cylindrical contact pairs made of AL7075-T651 alloy. In addition, 3D numerical models are developed to analyse the stress/strain fields and asses the total life. According to the experimental and numerical results, the differences of total life obtained between the geometries considered are negligible.

This work presents a comprehensive investigation of an experimental study conducted on ultra-high molecular weight polyethylene (UHMWPE) sheets using single point incremental forming (SPIF). The analysis is performed within a previously established research framework to evaluate formability and failure characteristics, including necking and fracture, in both conventional Nakajima tests and incremental sheet forming specimens. The experimental design of the SPIF tests incorporates process parameters such as spindle speed and step down to assess their impact on the formability of the material and the corresponding failure modes. The results indicate that a higher step down value has a positive effect on formability in the SPIF context. The study has identified the tool trajectory in SPIF as the primary influencing factor in the twisting failure mode. Implementing a bidirectional tool trajectory effectively reduced instances of twisting. Additionally, this work explores a medical case study that examines the manufacturing of a polyethylene liner device for a total hip replacement. This investigation critically analyses the manufacturing of plastic liner using SPIF, focusing on its formability and the elastic recovery exhibited by the material.

This study addresses the influence of the Sommerfeld effect on the behaviour of vibrocompacting machines driven by unbalanced electric motors. Based on a simplified model with 4 degrees of freedom previously published by the authors, we investigate the dynamics of quasistatic vibrocompaction processes, i.e. those in which the compaction is achieved through a sufficiently slow increase in the input power of the electric motors. The main novel contribution of the paper is the characterization of the evolution of the system state through a quasistatic torque curve, which is analytically derived. This curve provides the maximum compaction that can be quasistatically achieved and the amount of motor torque required to reach a desired compaction level, while also revealing the specific way in which the Sommerfeld effect takes place in the system under study. The analytical results are used to give a clear physical interpretation to the numerical results previously published by the authors. Good agreement is found between numerical and analytical results.

The present research work deals with the fatigue assessment of an Al 7075-T651 subjected to fretting fatigue testing characterised by cylindrical contact. A small rolling of the pads is experimentally observed and, consequently, the contact surface stresses are different to the hertzian one. Therefore, the methodology, recently proposed by some of the present authors for the fatigue assessment of fretting-affected metallic components, is here employed for the first time in conjunction with a FE numerical model able to take into account the effect of the rolling of the pads, in order to find out both the crack nucleation orientation and the lifetime for each specimen of the experimental campaign analysed.

Hydraulics is often used to actuate mechanisms in the applications of heavy machinery. In this work, a linearization approach for hydraulically driven multibody systems is presented. The approach allows linearizing the equations of motion of general multibody systems with holonomic and nonholonomic constraints, augmented with the hydraulic equations of the hydraulic subsystem. The derivation of this linearization approach is of interest in many applications, such as the performance of linear stability analyses. The procedure is tested with a three-dimensional multibody model of a hydraulically actuated four-bar mechanism. The validation of the approach is performed by means of the forward dynamics simulation of the linear and nonlinear systems. The results show the power of the approach, obtaining the linearized equations of motion around the equilibrium position of the four-bar mechanism multibody model in terms of the mechanical and hydraulic parameters. A comparison of the proposed procedure with a conventional counterpart approach is included, demonstrating the great accuracy and computational efficiency of the approach developed in this work.

BACKGROUND: 3D-printed bioceramic scaffolds have gained popularity due to their controlled microarchitecture and their proven biocompatibility. However, their high brittleness makes their surgical implementation complex for weightbearing bone treatments. Thus, they would require difficult-to-instrument rigid internal fixations that limit a rigorous evaluation of the regeneration progress through the analysis of mechanic-structural parameters. METHODS: We investigated the compatibility of flexible fixations with fragile ceramic implants, and if mechanical monitoring techniques are applicable to bone tissue engineering applications. Tissue engineering experiments were performed on 8 ovine metatarsi. A 15 mm bone segment was directly replaced with a hydroxyapatite scaffold and stabilized by an instrumented Ilizarov-type external fixator. Several in vivo monitoring techniques were employed to assess the mechanical and structural progress of the tissue. RESULTS: The applied surgical protocol succeeded in combining external fixators and subject-specific bioceramic scaffolds without causing fatal fractures of the implant due to stress concentrator. The bearing capacity of the treated limb was initially altered, quantifying a 28–56% reduction of the ground reaction force, which gradually normalized during the consolidation phase. A faster recovery was reported in the bearing capacity, stiffening and bone mineral density of the callus. It acquired a predominant mechanical role over the fixator in the distribution of internal forces after one postsurgical month. CONCLUSION: The bioceramic scaffold significantly accelerated in vivo the bone formation compared to other traditional alternatives in the literature (e.g., distraction osteogenesis). In addition, the implemented assessment techniques allowed an accurate quantitative evaluation of the bone regeneration through mechanical and imaging parameters.

Three-dimensional (3D) printable lead-free piezocomposites offer scalable and environmentally friendly solutions in many engineering applications. Typically, the composite system consists of polymeric matrices reinforced with active polycrystalline particles, and possibly nanoadditives. The presence of interfacial inclusion/matrix damage could not only compromise the structural integrity of the component but also significantly alter its ability to act as functional smart materials. In addition, both the agglomeration of the nanoadditives, such as carbon nanotubes (CNTs), and the degree of polarization could also affect the electromechanical behavior of the composite. In this paper, we develop a computational micromechanical model for the study of the influence of three types of internal defects on the piezoelectric performance of such composites. We investigate the influence of (a) the texture of the active phase, which is linked to the degree of polarization; (b) the effect of agglomerations of the CNTs; and (c) the presence of damage in the inclusion/matrix interphase region. Performance is assessed through the macroscopic response in various figures of merit. This work provides numerical evidence that the effective piezoelectric constants related to normal strain modes are strongly affected by the presence of damage in the interphase. Instead, the piezoelectric constant related to the shear strain remains unchanged by interfacial damage. Near the percolation threshold of the CNTs, piezocomposites exhibit a notable improvement in the piezoelectric response compared to the composite without nanomodification, as noted in previous works. Interestingly, this trend also applies in the presence of interfacial damage, and it is described in this work. The piezoelectric performance also depends on the texture of the active particles. We find, under some simplifications, the optimal orientation for the crystallites, and we find how the texture changes the performance in th

This article presents an experimental research performed on a polycarbonate sheet deformed by single point incremental forming (SPIF). The analysis is implemented within the framework developed in previous research work for assessing formability and failure by necking and fracture of polymeric sheets in conventional and incremental sheet forming (ISF) processes. The experimental plan is taking into account a series of process parameters, including tool diameter, feed rate, spindle speed and step down. The results allow an evaluation of the influence of these parameters on the formability and their effect on the failure modes. In this regard, three modes of failure were observed: fracture, twisting and crazing. It was shown that most of the typical forming conditions in SPIF lead to failure by fracture in the absence of necking (crack opening in mode I), and all the test conditions presented a combination of twisting and fracture. Higher values of the step down increased the intensity of twisting whereas high values of spindle speed resulted in crazing. A scanning electron microscopy (SEM) evaluation was performed as well as an integral temperature analysis to provide a complete window for understanding the conditions upon which the different failure modes of this thermoplastic material are developed in SPIF.

This paper describes a novel method for the estimation of the trajectory and orientation of a rigid body moving along a railway track. Compared to other recent developments in the literature, the presented approach has the significant advantage of using inertial sensors only, excluding global position and orientation sensors. The excluded sensors are compensated with an odometry system and previous knowledge of the design track geometry. The procedure is based on a kinematic model of the relative motion of the body with respect to the track, together with a Kalman filter algorithm. Two different approaches are used and compared for the estimation of the noise covariance matrices in the Kalman filter. One is based on the use of experimental results with a known output. The other one relies upon constrained maximum likelihood estimation. The calculated trajectory and orientation are applied in this research to the problem of track geometry measurement. A scale track is used for experimental validation, showing that results are sufficiently accurate for this application. The obtained results also reveal that the constrained maximum likelihood estimation performs similarly to the known-output method. This is very convenient because it allows a straightforward application of the algorithm in different scenarios.

This paper presents an efficient and reliable approach to study the low-velocity impact response of woven composite shells using 3D finite element models that account for the physical intralaminar and interlaminar progressive damage. The authors’ previous work on the experimental assessment of the effect of thickness on the impact response of semicylindrical composite laminated shells served as the basis for this paper. Therefore, the finite element models were put to the test in comparison to the experimental findings. A good agreement was obtained between the numerical predictions and experimental data for the load and energy histories as well as for the maximum impact load, maximum displacement, and contact time. The use of the mass-scaling technique was successfully implemented, reducing considerably the computing cost of the solutions. The maximum load, maximum displacement, and contact time are negligibly affected by the choice of finite element mesh discretization. However, it has an impact on the initiation and progression of interlaminar damage. Therefore, to accurately compute delamination, its correct definition is of upmost importance. The validation of these finite element models opens the possibility for further numerical studies on of woven composite shells and enables shortening the time and expenses associated with the experimental testing.

Electrical analogues of linear mechanical systems have traditionally been obtained using a set of rules that can potentially be tedious when applied to complex systems. In addition, such rules do not cover all the possibilities of mechanical systems including rotational and translational generalized coordinates. The present work establishes a comprehensive and systematic methodology for obtaining the electrical analogue of any mechanical system modelled by rigid bodies, springs, and dampers. The method is simple and straightforward. First, the dynamic equations of the mechanical system are derived into matrix form. These equations are then translated to the electrical domain by means of the electromechanical analogy and, finally, the electrical circuit is obtained by direct inspection of the matrices. In addition, the method can deal with a combination of translational and rotational coordinates in the definition of the mechanical model. To support the proposed method, and beyond the planar vehicle models found in the literature, the electrical analogue of a linear 3D 7-DOF full car model is presented in this work.

Observations of enhanced fast-ion losses during edge localized modes (ELMs) have been reported in the ASDEX Upgrade tokamak, revealing losses above the injection energy. This suggests that fast ions can be accelerated and lost due to the ELMs. Recent analysis of the ELM-induced losses suggests that the fast ions are lost due to a resonant interaction with the electromagnetic perturbation during the ELM crash. The fast-ion transport and acceleration during ELMs is modelled using electromagnetic fields computed using the hybrid kinetic-MHD code MEGA, while fast-ion full orbits are tracked with the ASCOT code. Time-evolving 3D electromagnetic fields have been implemented in ASCOT to compute fast-ion orbits in the presence of fast MHD events such as ELMs. The simulations successfully reproduce a field-aligned pattern of the losses on the tokamak wall and the formation of an accelerated population in the lost fast-ion distribution, while they predict an accelerated population in the confined distribution. A parametric study of the fast-ion constants of motion suggests a resonant interaction between the fast-ions and the electromagnetic fields arising during the ELM crash. In the case of fast-ion acceleration, the perpendicular electric perturbation, with scales smaller than the fast-ion gyroradius, breaks magnetic moment conservation and resonantly modifies the fast-ion energy.

Several models from the literature were used to predict the fatigue limit in notched components subjected to biaxial cyclic loading. The predictions of these models are based on the elastic stresses along a line which is considered to be representative of the crack direction in its initial part. The line used in the models changes considerably. For one of the studied models, the line direction corresponds to Mode I, while for another it is Mode II, and for the other two models considered the direction is between Mode I and Mode II. However, quite naturally, the experimental crack direction is unique. In recent years, a study of experimental fatigue limits and crack directions in its initial part for three materials was carried out in hollow cylindrical specimens with a circular hole subjected to cyclic axial, torsional and in-phase biaxial loading. The directions of the cracks that were measured experimentally are on average similar for the three materials and close to Mode I. The analysed models give, in general, good predictions of the experimental fatigue limits, although they use directions that are completely different and that they too differ markedly from the experimentally found ones. The predictions of the models using, in a forced way, the measured experimental directions are good in most cases, which reveals a surprising insensitivity of these models to the main hypotheses on which their own formulations are based.

Reconfigurable Manufacturing Systems (RMS) have gained attention in the aerospace industry in the past years, as post-pandemic context shows drastic production capacity changes and new environmental regulations to which it must adapt quicker than before to maintain competitiveness. Nevertheless, current RMS design methods have not thoroughly considered this industry specificities, nor industrial resources requirements in the current concurrent design practice. These limitations have been identified in several recent research works. Ontology-based Engineering (OBE) systems can stand overly complex collaborative design processes involving multidisciplinary stakeholders and various digital tools, integrating different levels of decision. Models for Manufacturing (MfM) is an OBE methodology aiming to enable industrial design and decision-making in manufacturing by preserving the company knowledge in ontology models, usable as knowledge base to generate and integrate the aircraft and manufacturing systems design. This paper presents an MfM application for RMS design in aerospace, introducing innovative design concepts that allow implementing RMS in a collaborative engineering process of an aerospace product. An implementation is shown designing the RMS of a model aircraft family to illustrate the concepts introduced and considerations are given to transfer this knowledge base into an OBE system to support complex real-life applications. © 2023 Informa UK Limited, trading as Taylor & Francis Group.

In this article a new fretting fatigue life prediction model is presented. The model can be classified as a variable crack initiation length: the crack initiation and crack propagation phases are calculated as a function of the crack initiation length, and among all the feasible crack initiation lengths and orientations, that producing the minimum fatigue life is considered. In this new proposal the crack direction is automatically determined as a function of fatigue parameters in both phases: initiation and propagation. The model is applied to a wide experimental campaign of fretting fatigue tests, and excellent correlation is obtained between experimental and predicted fretting fatigue lives and crack paths.

In this work, the fatigue and cellular performance of novel superficially treated porous titanium dental implants made up using conventional powder metallurgy and space-holder techniques (30 vol.% and 50 vol.%, both with a spacer size range of 100–200 µm) are evaluated. Before the sintering stage, a specific stage of CNC milling of the screw thread of the implant is used. After the consolidation processing, different surface modifications are performed: chemical etching and bioactive coatings (BG 45S5 and BG 1393). The results are discussed in terms of the effect of the porosity, as well as the surface roughness, chemical composition, and adherence of the coatings on the fatigue resistance and the osteoblast cells’ behavior for the proposed implants. Macro-pores are preferential sites of the nucleation of cracks and bone cell adhesion, and they increase the cellular activity of the implants, but decrease the fatigue life. In conclusion, SH 30 vol.% dental implant chemical etching presents the best bio-functional (in vitro osseointegration) and bio-mechanical (stiffness, yield strength and fatigue life) balance, which could ensure the required characteristics of cortical bone tissue.

Fretting fatigue is a material damage phenomenon produced in mechanical contacts. This phenomenon mainly produces surface cracking, and depending on the fretting regime, surface wear. In the bibliography many different types of fretting tests, with different geometries have been proposed. This paper numerically analyses, via FEM models, some fretting tests with cylindrical pads and test specimens having different geometries that are frequently used in the literature. In such cases, non-negligible 3D effects are produced. The differences between the contact stress field obtained with different approaches are analysed and discussed.

This paper presents new advances in the arbitrary Lagrangian–Eulerian modal method (ALEM) recently developed for the systematic simulation of the dynamics of general reeving systems. These advances are related to a more convenient model of the sheaves dynamics and the use of axial deformation modes to account for non-constant axial forces within the finite elements. Regarding the sheaves dynamics, the original formulation uses kinematic constraints to account for the torque transmission at the sheaves by neglecting the rotary inertia. One of the advances described in this paper is the use of the rotation angles of the sheaves as generalized coordinates together with the rope-to-sheave no-slip assumption as linear constraint equations. This modeling option guarantees the exact torque balance at the sheave without including any nonlinear kinematic constraint. Numerical results show the influence in the system dynamics of the sheave rotary inertia. Regarding the axial forces within the finite elements, the original formulation uses a combination of absolute position coordinates and transverse local modal coordinates to account for the rope absolute position and deformation shape. The axial force, which only depends on the absolute position coordinates, is constant along the element because linear shape functions are assumed to describe the axial displacements. For reeving systems with very long rope spans, as the elevators of high buildings, the constant axial force is inaccurate because the weight of the ropes becomes important and the axial force varies approximately linearly within the rope free span. To account for space-varying axial forces, this paper also introduces modal coordinates in the axial direction. Numerical results show that a set of three modal coordinates in the axial direction is enough to simulate linearly varying axial forces.

The numerical and computation aspects of the Knife-edge Equivalent Contact (KEC) constraint and lookup table (LUT) methods are compared in this paper. The LUT method implementation uses a penetration-based elastic contact model for the flange and a constraint-based formulation at the wheel tread. For the KEC method, where an infinitely narrow rail contacts an equivalent wheel, regularization of the tread-flange transition is adopted to simultaneously account for tread and flange contacts using constraints. A comparison between the two methods is carried out using well-known numerical integrators to show the applicability and limitations of both methods. Two fixed-step-size integrators, the explicit Runge–Kutta (RK4) and the predictor–corrector Adam–Bashforth–Moulton (ABM) methods, and two variable-step-size Matlab built-in function integrators, the explicit ode45 and implicit ode15s, were applied to get the numerical solutions to the dynamic problems and study the relative numerical performance of the two contact description methods. To complete the railway vehicle model, both contact methods were implemented for the multibody model of a benchmark railway vehicle (the Manchester wagon 1). Numerical results were obtained for different railway tracks with and without irregularities. Profiles of the S1002 wheel and LB-140-Area rail, which demonstrate the two-point contact phenomenon, were considered. Both methods were implemented in Matlab and validated against commercial simulation software. The kinematic results for both approaches show good agreement, but the KEC method was up to 20% more efficient than the LUT method regardless of integrator used.

Bone remodelling models (BRM) are often used to estimate the density distribution in bones from the loads they are subjected to. BRM define a relationship between a certain variable measuring the mechanical stimulus at each bone site and either the local density or the local variation of density. This agrees with the Mechanostat Theory, which establishes that overloaded bones increase their density, while disused bones tend to decrease their density. Many variables have been proposed as mechanical stimuli, with stress or strain energy density (SED) being some of the most common. Yet, no compelling reason has been given to justify the choice of any of these variables. This work proposes a set of variables derived from the local stress and strain tensors as candidates for mechanical stimuli; then, this work correlates them to the density in the femur of one individual. The stress and strain tensors were obtained from a FE model and the density was obtained from a CT-scan, both belonging to the same individual. The variables that best correlate with density are the stresses. Strains are quite uniform across the femur and very poorly correlated with density, as is the SED, which is, therefore, not a good variable to measure the mechanical stimulus.

Alendronate is the most widely used drug for postmenopausal osteoporosis (PMO). It inhibits bone resorption, affecting osteoclasts. Pharmacokinetics (PK) and pharmacodynamics (PD) of alendronate have been widely studied, but few mathematical models exist to simulate its effect. In this work, we have developed a PK model for alendronate, valid for short- and long-term treatments, and a mechanistic PK-PD model for the treatment of PMO to predict bone density gain (BDG) at the hip and lumbar spine. According to our results, at least three compartments are required in the PK model to predict the effect of alendronate in both the short and long terms. Clinical data of a 2-year treatment of alendronate, reproduced by our PK-PD model, demonstrate that bone response is site specific (hip: 7% BDG, lumbar spine: 4% BDG). We identified that this BDG is mainly due to an increase in tissue mineralization and a decrease in porosity. The difference in BDG between sites is linked to the different loading and dependence of the released alendronate on the bone-specific surface and porosity. Osteoclast population diminishes quickly within the first month of alendronate treatment. Osteoblast population lags behind but also falls due to coupling of resorption and formation. Two dosing regimens were studied (70 mg weekly and 10 mg daily), and both showed very similar BDG evolution, indicating that alendronate accumulates quickly in bone and saturates. The proposed PK-PD model could provide a valuable tool to analyze the effect of alendronate and to design patient-specific treatments, including drug combinations.

Denosumab (Dmab) treatment against postmenopausal osteoporosis (PMO) has proven very efficient in increasing bone mineral density (BMD) and reducing the risk of bone fractures. However, concerns have been recently raised regarding safety when drug treatment is discontinued. Mechanistic pharmacokinetic-pharmacodynamic (PK-PD) models are the most sophisticated tools to develop patient specific drug treatments of PMO to restore bone mass. However, only a few PK-PD models have addressed the effect of Dmab drug holidays on changes in BMD. We showed that using a standard bone cell population model (BCPM) of bone remodelling it is not possible to account for the spike in osteoclast numbers observed after Dmab discontinuation. We show that inclusion of a variable osteoclast precursor pool in BCPMs is essential to predict the experimentally observed rapid rise in osteoclast numbers and the associated increases in bone resorption. This new model also showed that Dmab withdrawal leads to a rapid increase of damage in the bone matrix, which in turn decreases the local safety factor for fatigue failure. Our simulation results show that changes in BMD strongly depend on Dmab concentration in the central compartment. Consequently, bone weight (BW) might play an important factor in calculating effective Dmab doses. The currently clinically prescribed constant Dmab dose of 60 mg injected every 6 months is less effective in increasing BMD for patients with high BW (2.5% for 80 kg in contrast to 8% for 60 kg after 6 years of treatment). However, bone loss observed 24 months after Dmab withdrawal is less pronounced in patients with high BW (3.5% for 80kg and 8.5% for 60 kg). Finally, we studied how to safely discontinue Dmab treatment by exploring several transitional and combined drug treatment strategies. Our simulation results indicate that using transitional reduced Dmab doses are not effective in reducing rapid bone loss. However, we identify that use of a bisphosphonate (BP) is h

This work performs a detailed analysis of the cracks obtained in fretting fatigue tests with cylindrical contact in the presence of a small oscillatory rolling of the contact pad. To do so, fretting fatigue tests have been carried out. Preliminary observations indicate that the contact area is larger than the theoretical one according to Hertz’s theory. This could mean that, due to the contact geometry and the stiffness of the test setup, rolling of the contact pad is occurring during tests. To reproduce this phenomenon, a 2D numerical model is developed. The results are compared with actual crack profile measurements.

The asymmetries study between both legs of the forces applied to the pedals in cycling is important because they may affect the performance of the cyclist or prevent the occurrence of injuries. Studies focused on analysing asymmetries in forces tend to consider only the effective force, disregarding the three-dimensional nature of the force. Furthermore, these studies do not analyse the possible physical or neurological causes that may have led to the appearance of the asymmetries. This paper presents a methodology to carry out three-dimensional analysis of the asymmetries of the forces applied in both pedals and discriminate the possible sources of these asymmetries. Seven participants, amateurs and without pathologies, were analysed. Two commercial pedals were instrumented to measure the three components of the force applied to each pedal. The Normalized Symmetry Index (NSI) and the Cross Correlation Coefficient (CCC) were used for the asymmetries analysis. Results showed that both indexes need to be used in conjunction to analyse the causes of asymmetry in the pedal forces from a 3D perspective along the pedal cycle. The NSI is an index that makes it possible to evaluate asymmetry by considering only the value of the force applied by each leg at each instant. The CCC makes it possible to evaluate whether the temporal evolutions of the forces applied by each leg are similar. Preliminary results suggest that the proposed methodology is effective for analysing asymmetries in the forces in a pedalling cycle from a three-dimensional point of view. Forces in the sagittal plane showed a high level of symmetry. The lateral-medial force presented the highest level of asymmetry due to the difference in the magnitudes of the applied forces by both legs and the existing time shift between the two force patterns. The results of this work will allow for more complete and accurate three-dimensional dynamic analyses of the lower body during pedalling.

The influence of the ratio between specimen thickness () and grain size () on the tensile and fatigue properties of plain and notched aluminium plate specimens has been studied. Grain sizes ranging from 66 m to 9.74 mm have been prepared and used in the tests. The observed decrease on tensile properties when is comparable, or even exceeds, can be accounted for by adding an additional negative exponential term to the Hall–Petch equation. An exponential decrease has also been found in endurance limits as grain size approaches plate thickness in plain specimens. In notched specimens, however, increasing grain size has two opposing effects, namely: a decrease in the plain endurance limit associated with the decrease in thickness relative to grain size and an increase in notched fatigue strengths brought about by a decrease in notch sensitivity.

The aim of this work is to perform a detailed analysis of the cracks paths obtained in fretting fatigue tests with cylindrical contact but taking into account the presence of an unavoidable (due to the fretting device’s stiffness) small oscillatory rolling. In order to obtain the crack paths crack surfaces were measured with a confocal microscope after the tests. Besides, the contact area and the surface crack initiation location were obtained by means of an optical microscope. The measurements indicate that the contact area is substantially larger than the theoretical one according to Hertz´s theory, contrary to tests done with only static normal load, in which both theoretical and experimental areas match perfectly. This observation means, that, due to the surface contact pad’s geometry (cylindrical) and the stiffness of the test setup, rolling is occurring during tests when tangential loading is developed. To reproduce this phenomenon, a 2D FEM model is developed. Stress/strain fields along the fretting cycle are analysed, noticing a substantial change of the contact surface hot-spot point and surface contact stress distribution, when compared with the non-rolling case. To predict the initial crack path, a previously developed model, based on a critical plane parameter, is applied using FEM stress/strain results. The results obtained show a better prediction of the surface hot-spot point and initial crack orientation estimation, when compared with the non-rolling case, and considering as a reference the experimental crack paths measured via confocal microscope.

This study presents a numerical analysis of the tube expansion process by conventional tube-end forming versus single point incremental forming (SPIF) using DEFORM. The work includes the assessment of the strain paths within the principal strain space of these processes with respect to the formability limits as well as their evaluation within the equivalent strain versus stress triaxiality space. The results obtained demonstrated that the mechanics of tube flaring process in conventional and incremental forming are substantially different. This analysis of formability in the light of the accumulated equivalent strain and the average stress triaxiality allowed a better understanding of the differences between both processes in terms of the fracture limit strains.

The experimental detection of localized necking is an important issue in sheet metal forming. Today, the most common and extended techniques are strain-based methods using digital image correlation (DIC). The present work discuses a thermal methodology to detect the onset of necking in metals based on the analysis of the temperature gradient using digital infrared thermography (DIT). A series of tensile tests of H240LA-O3 high-strength steel of 1.2mm thickness is analysed using DIC and DIT techniques. It is proposed that necking initiates when the temperature difference at a reference distance from the necking point reaches a critical value, which allows identifying the necking time and estimating the limit strains from the visible images using circle grid analysis.

The objective of this article is to present the design and manufacture of a scaled railroad track to be used as a laboratory track for the study of different railway applications. It could be a guideline for future laboratory railroad tracks. The ideal concept was based on possible future studies and, according to them, design requirements have been specified. The main characteristic of the track is that its geometry can be mechanically modified and irregularities can be introduced under controlled conditions in any kind of track sections: straight, curved and transition ones. Finally, the current installed track is shown and the performed quality controls are described.

This study develops a geometrically nonlinear model of a wind turbine blade utilizing finite strain theory for the calculation of elastic forces. The model is based on the floating frame of reference (FFR) formulation, which is a common choice in the modeling of long and flexible wind turbine blades. To model the nonlinear deformation of blades, the FFR formulation divides the structure into several substructures, which involves a significant increase of the system degrees of freedom. In the presented model, a nonlinear description of the elastic forces is introduced to achieve the convergence of the dynamic blade model at a lower number of substructures. The nonlinear elastic forces are formulated according to the Euler-Bernoulli beam theory, and they account for third-order terms of the potential elastic energy, the so-called geometric stiffness. The developed blade model is formulated in two dimensions and tested in a blade of 44.8 m length, which corresponds to a 2.75 MW wind turbine. Firstly, the results show that linear models do not accurately represent tip blade transverse displacement, and the substructuring technique becomes necessary to account for geometric nonlinearity. Secondly, using nonlinear elastic models significantly reduces the number of substructures needed to achieve convergence of the solution.

The rotating beam problem has been extensively used as a benchmark for testing nonlinear finite element implementations. The remarkable characteristic of this benchmark is the coupling between axial a transverse deformations due to the centrifugal forces. The rotating beam dynamics exhibits a centrifugal stiffening effect that can only be captured either by including a kinematic coupling between axial and transverse deformation or by using a nonlinear description of the elastic forces. This paper presents simplified models of the rotating beam that capture the centrifugal stiffening effect due to the inclusion of an axial to transverse kinematic coupling of the beam centreline. The simplified models allow a discussion on their accuracy and a meaningful analysis of the nonlinear oscillations present in the steady state rotation. The results of the simplified models are compared to finite element solutions obtained by using the absolute nodal coordinate formulation and a commercial FEM code.

Callus tissue exhibits a viscoelastic behavior that has a strong influence on the distribution of stresses and their evolution with time and, thus, it can affect tissue differentiation during distraction procedures. For this reason, a deep knowledge of that viscoelastic behavior can be very useful to improve current protocols of bone distraction and bone transport. Monitoring stress relaxation of the callus during distraction osteogenesis allows characterizing its viscoelastic behavior. Different procedures have been used in the literature to fit the response of a given viscoelastic model to the force relaxation curve. However, these procedures do not ensure the uniqueness of that fit, which is of the utmost importance for statistical purposes. This work uses a fitting procedure already validated for other tissues that ensures that uniqueness. Very importantly too, the procedure presented here allows obtaining more information from the stress relaxation tests, distinguishing relaxation in different time scales, which provides a deeper insight into the viscoelastic behavior and its evolution over time. As it was observed in the results, relaxation is faster at the first days after osteotomy and becomes slower and more gradual with time. This fact can be directly linked to the temporal evolution of the callus composition (water, organic phase, and mineral content) and also to the progression of tissue differentiation, with a prevalence of hard tissues as time passes.