Search Results (60)

This study investigates the reliability of Francis turbines and highlights the critical need for an improved deformation monitoring system for bolts that fasten a hydroturbine head-cover to its casing. During different operational stages of the hydraulic unit, such as start-up, partial load, and full load, the hydroturbine head-cover and its fastening bolts are subjected to static and cyclic loads. The loads generate vibrations and different deformations that must be monitored. Although various measuring instruments, such as vibration sensors and accelerometers, have been developed to monitor hydroturbine vibrations, only two systems—KM-Delta-8-CM and PTK KM-Delta—are currently applied to measure fastening bolt deformation. Furthermore, only one system, SKDS-SISH, was found to monitor the forces inducing this deformation. After analysis, it is evident that the described systems for monitoring the deformation of the fastening bolts do not guarantee the trustworthiness of the measuring sensors and there is a need for their improvement. The implementation of a self-checking function (including metrological features), the development of a digital twin of the sensor, and the application of technologies based on artificial intelligence could solve this problem. Full article

In this study, a probabilistic model within the dislotwin constitutive framework of DAMASK (the Düsseldorf Advanced Material Simulation Kit) was established to describe the cyclic loading behaviors of AZ31B magnesium alloys. Considering the detwinning procedure within the twinned region, this newly developed dislocation–twinning–detwinning model was employed to accurately simulate stress–strain behaviors of AZ31B magnesium alloys throughout tension–compression–tension (T-C-T) cycle loading. The investigations revealed that the reduction in yield stress during the reverse loading process was attributed to the active operation of twinning and detwinning modes. Furthermore, the evolution of the twin volume fraction during cycle loading scenarios was quantitatively determined. According to these results, the relative activities of plastic deformation modes during T-C-T loading were further analyzed. Full article

Twin-roll casting is a technology for the production of thin strips directly from liquid metal by combining continuous casting with hot rolling in a single step. The thermo-mechanical cyclic interaction with the solidifying strip causes fatigue crack formation at the outer surface of the rolls. A 2D FEM model with Eulerian boundary conditions and the interference fit load on the rolls was defined. The influence of the roll–strip thermal contact, the inlet temperature of the liquid aluminum, the efficiency of the water cooling and the production rate on the fatigue damage of the rolls was analyzed with a parametric study. The maximum temperature of the rolls, the maximum contact pressure, the accumulated plastic strain and the equivalent strain computed (considering a multiaxial out-of-phase fatigue criterion) were considered to investigate the thermo-mechanical fatigue load on the rolls. The results showed that, in the considered range, the most influential parameters on the fatigue mechanism are the heat contact conductance coefficient, which dominates the thermo-mechanical load, and the tangential velocity of the rolls, which contributes to the thermal field and determines the roll–strip mechanical contact interaction. Full article

The deformation behavior of a high-strength Mg-Al-Sn-Zn alloy under loading reversals has been thoroughly examined through a combination of experimental measurements and crystal plasticity modeling. We focused on an age-treated alloy fortified by distributed Mg₂Sn particles and Mg₁₇Al₁₂ precipitates, which underwent two distinct loading cycles: tension-compression-tension (TCT) and compression-tension-compression (CTC), aligned with the extrusion direction (ED). The initial and deformed microstructures of the alloy were analyzed using the electron backscattering diffraction (EBSD) technique. Notably, the alloy displays tensile and compressive yield strengths (YS) of 215 MPa and 160 MPa, respectively, with pronounced anelastic behavior observed during unloading and reverse loading phases. Utilizing the elasto-viscoplastic self-consistent model incorporating a twinning–detwinning scheme (EVPSC-TDT), the cyclic stress–strain responses and resultant textures of the alloy were accurately captured. The predicted alternation between various slip and twinning modes during plastic deformation was used to interpret the observed behaviors. It was found that prismatic <a> slip plays an important role during the plastic deformation of the studied alloy, and its relative activity in tensile loading processes accounts for up to ~66% and ~67% in the TCT and CTC cases, respectively. Moreover, it was discerned that detwinning and twinning behaviors are predominantly governed by stresses within the parent grain, and they can concurrently manifest during the reverse tensile loading phase in the TCT case. After cyclic deformation, the area fractions of residual twins were determined to be 7.51% and 0.93% in the TCT and CTC cases, respectively, which is a result of the varied twinning–detwinning behavior of the alloy in different loading paths. Full article

Additive manufacturing (AM) offers new possibilities in soft robotics as materials can easily be combined in multi-material designs. Proper sensing is essential for the soft actuators to interact with the surroundings successfully. By fabricating sensors through AM, sensors can be embedded directly into the components during manufacturing. This paper investigates NinjaTek Eels electrical resistance response to strain and the feasibility of using the material to create strain sensors. Strain sensors were 3D-printed out of NinjaTek Eel, a soft conductive TPU, and was tested during cyclic loading. A custom resistance–strain test rig was developed for measuring sensor behavior. The rig was calibrated for electric resistance, able to measure electric resistance as a function of strain. A parabolic response curve was observed during cyclic loading, which led to ambiguous readings. A 10-specimen validation test was conducted, evaluating the statistical variation for the first 100 loading cycles. The validation test showed that the sensor is capable of accurate and predictable readings during single load cases and cyclic loading, with the overall root mean square error being 66.9 Ω. Combining two sensors of different cross-sections gave promising results in terms of calibrating. By monitoring load cycles and strain rates, calibration can also be achieved by machine learning models by the microcontroller used to extract data. The presented work in this article explores the potential of using conductive TPUs as sensors embedded in products such as soft robotics, life monitoring of products with structural, and digital twins for live product to user feedback. Full article

Nickel-based superalloys exhibit pronounced elastic anisotropy and, hence, the local grain orientation strongly affects the stress and strain distribution in the material under mechanical loadings. Therefore, the crack initiation and failure behaviour of components made from nickel-based superalloys are complex and hardly predictable. A better fundamental understanding of the phenomena that occur in nickel-based superalloys under a quasistatic and cyclic load is therefore desired. Previously, a continuum mechanics-based model has been successfully developed, considering the grain structure, the elastic anisotropy, and the Schmid factor, based on data from electron backscatter diffraction (EBSD). The E·m model was confirmed by the finite element method (FEM) simulations and experimental observations regarding the resulting average stresses and strains in the individual grains as well as the formation of slip bands under a quasistatic load with few restrictions. The behaviour under cyclic loadings has been investigated in this work to correlate the mechanical behaviour, simulated by the previously developed FE models, with the local stiffness and Schmid factors considering fatigue failure. For this purpose, the fatigue behaviour of Inconel 617 samples was characterised up to the high-cycle fatigue (HCF) regime, accompanied by EBSD measurements for stress amplitudes that resulted in strains close to the elastic–plastic regime. The EBSD data were used to create digital twins of the samples to simulate the mechanical reaction to a displacement similar to the associated strain of the fatigue tests. An analysis of the fractured samples by scanning electron microscopy was performed to retrace the location of the crack initiation supported by the EBSD measurements before and after fatigue testing. Two samples were investigated in detail that showed different fracture types. Sample 1 showed transcrystalline failure in a grain that showed a high Young’s modulus, Schmid factor, and resolved shear stress that indicates a failure due to the properties of the grain itself. In contrast, an intercrystalline failure was observed for sample 2 that showed large differences in the orientation and, hence, largely different mechanical properties in the area of failure as well. The observed failure types, the resulting stresses and strains calculated by the FE model, and the consideration of the E·m model showed an agreement of all the methods. Therefore, the findings of this work complement previous investigations of the mechanical behaviour of coarse-grained anisotropic nickel-based superalloys with a focus on the orientations of the grains towards the loading direction. Full article

In this study, the microstructural evolution of a Ti-15Mo medical alloy was investigated, when the in situ cyclic tensile strain had 2% amplitude and the tension–compression cyclic deformation had 1%, 2%, and 3% amplitude. The Vickers hardness and wear resistance of the alloy were also optimized due to the grain-refining effect after cyclic deformation and annealing. The twinning-induced plasticity (TWIP) was considered the main deformation mechanism of the Ti-15Mo alloy during the tensile–compressive cycle deformation with suitable strain amplitude. The {332}<113> twins and boundaries were the main contributors to the grain refinement. The optimal microstructure, hardness, and wear resistance were obtained in the alloy deformed by tension–compression cyclic strain with a 3% strain amplitude. The wear resistance of the annealed alloy in Hank’s solution was excellent in contrast to the original Ti-15Mo alloy due to its reasonable microstructure and hardness. It is clear that abundant twins were formed and retained in the coarse grains of the original alloy after cyclic deformation and annealing, which provided the expected refined grains and performance. Full article

Dynamic crossflow filtration (DCF) is the state-of-the-art technology for solid–liquid separation from viscous and sensitive feed streams in the food and biopharma industry. Up to now, the potential of industrial processes is often not fully exploited, because fixed recipes are usually applied to run the processes. In order to take the varying properties of biological feed materials into account, we aim to develop a digital twin of an industrial brownfield DCF plant, allowing to optimize setpoint decisions in almost real time. The core of the digital twin is a mechanistic–empirical process model combining fundamental filtration laws with process expert knowledge. The effect of variation in the selected process and model parameters on plant productivity has been assessed using a model-based design-of-experiments approach, and a regression metamodel has been trained with the data. A cyclic program that bidirectionally communicates with the DCF asset serves as frame of the digital twin. It monitors the process dynamics membrane torque and transmembrane pressure and feeds back the optimum permeate flow rate setpoint to the physical asset in almost real-time during process runs. We considered a total of 24 industrial production batches from the filtration of grape juice from the years 2022 and 2023 in the study. After implementation of the digital twin on site, the campaign mean productivity increased by 15% over the course of the year 2023. The presented digital twin framework is a simple example how an industrial established process can be controlled by a hybrid model-based algorithm. With a digital process dynamics model at hand, the presented metamodel optimization approach can be easily transferred to other (bio)chemical processes. Full article

A cyclic plasticity constitutive model was developed for materials with asymmetric cyclic behavior to explain the stabilized stress–strain response under variable amplitude loading. The proposed constitutive model incorporated the von Mises yield function with an adjustment to accommodate asymmetric yielding under tension and compression. A combined isotropic–kinematic hardening model was proposed to describe the evolution of the yield surface in the reference uniaxial frame and the actual frame. The history of plastic deformation is memorized by introducing internal variables, accumulated slip, and residual twins, which govern the cyclic flow behavior in the subsequent reversal. The additional conditions required to predict the stabilized hysteresis response of a material under variable amplitude loading were set out and incorporated into the constitutive model. The model was numerically implemented and programmed into a user material (UMAT) subroutine to run with the commercial finite element program, Abaqus/Standard 2019. The model was calibrated using the stabilized hysteresis response of ZEK100 and AZ31B sheets under constant amplitude strain-controlled cyclic loading for different strain amplitudes. To verify the model, constant amplitude and four different variable amplitude load spectra tests were performed and the stabilized stress–strain hysteresis response predicted by the model was compared with test results. It was demonstrated that the results are in very good agreement. Full article

This study explores the comparative fatigue performance of decarburized surfaces in railway components, emphasizing rolling contact fatigue, crack propagation, and acoustic emission. The investigation entails the examination of two grades of railway steels, namely R260 and U71Mn, to analyze crack and surface characteristics subsequent to fatigue testing employing a Twin Roller Machine. The purpose is to discern the impact of decarburization on the fatigue life of these materials. The results reveal distinct patterns in crack propagation and acoustic emission between decarburized and non-decarburized surfaces, providing valuable insights into the fatigue behavior of railway components. This comparative analysis contributes to a nuanced understanding of the material’s response to cyclic loading. Full article

Scaled rolling contact fatigue tests, used to practically simulate the wear of the wheel and rail material under laboratory conditions, are typically classified into two categories. Tests in the first category use twin-disc stands, while the second group of test rigs use two discs of different diameters considering the rail disc as the larger one. The latter setup is closer to the real situation, but problems can occur with high contact pressures and tractions. The focus of this paper is on two main contributions. Firstly, a case study based on finite element analysis is presented, allowing the optimization of the specimen geometry for high contact pressures. Accumulated plastic deformation caused by cycling is responsible for abrupt lateral deformation, which requires the use of an appropriate cyclic plasticity model in the finite element analysis. In the second part of the study, two laser profilers are used to measure the dimensions of the specimen in real time during the rolling contact fatigue test. The proposed technique allows the changes in the specimen dimensions to be characterized during the test itself, and therefore does not require the test to be interrupted. By using real-time values of the specimen’s dimensional contours, it is possible to calculate an instantaneous value of the slip ratio or the contact path width. Full article

In this work, we search for observational evidence of higher-order secular perturbations in three eclipsing binaries. These are slightly eccentric binaries, and they form the inner pairs of tight, compact, hierarchical triple star systems. Simultaneously, we analyze the high-precision satellite (Kepler and TESS) light curves; eclipse timing variations; combined spectral energy distributions (through catalog passband magnitudes); and, where available, radial velocities of KICs 9714358, 5771589, and TIC 219885468. Besides the determination of the robust astrophysical and dynamical properties of the three systems, we find evidence that the observed unusual eclipse timing variations of KIC 9714358 are a direct consequence of the octupole-order secular eccentricity perturbations forced by unusual, resonant behavior between the lines of the apsides of the inner and outer orbital ellipses. We also show that, despite its evident cyclic eclipse depth variations, KIC 5771589 is an almost perfectly coplanar system (to within $0.3^{\circ }$), and we explain the rapid eclipse depth variations with the grazing nature of the eclipses. Finally, we find that the inner pair of TIC 219885468 consists of two twin stars; hence, in this triple there are no octupole-order three-body perturbations. Moreover, we show that this triple is also coplanar on the same level as the former one, but due to its deep eclipses, it does not exhibit eclipse depth variations. We intend to follow this work up with further analyses and a quantitative comparison of the theoretical and the observed perturbations. Full article

In this study, Cr-Ni-Ti austenitic stainless steel was subjected to rotary swaging in various modes, followed by annealing. The effect of processing conditions on the resulting microstructure and, therefore, on the mechanical properties under static and cyclic loading was studied. After RS the formation of an ultrafine-grained predominantly twinned structure, with structural elements sized between 100–250 nm in Cr-Ni-Ti stainless steel, was observed. The stepwise temperature reduction during rotary swaging allows the manipulation of the microstructure transformations, which eventually leads to the desired properties of the steel. As a result, the ultimate tensile strength increased from 610 MPa to 1304 MPa when the elongation decreased from 40% to 10.5%, and the fatigue limit increased from 425 MPa to 700 MPa. The Cr-Ni-Ti steel is strengthened through the formation of an ultrafine-grained structure, twinning in austenite, and martensitic transformation. Subsequent annealing at a temperature 475 °C triggers the active precipitation of nanosized TiC carbides in the deformed steel. On one hand, the presence of these carbides increases the tensile strength up to 1938 Mpa, while on the other hand, slows down crack propagation with a slight decrease in ductility (ε = 8%) of the deformed sample. At the same time, dispersion hardening does not affect the fatigue limit of steel. Full article

The current challenges of commercial cyclic adsorption processes for biogas upgrading are associated with either high energy consumption or low recovery. To address these challenges, this work evaluates the performance of a range of configurations for biogas separations, including pressure swing adsorption (PSA), pressure vacuum swing adsorption (PVSA), and twin double-bed PSA, by dynamic modelling. Moreover, a sensitivity analysis was performed to explore the effect of various operating conditions, including adsorption time, purge-to-feed ratio, biogas feed temperature, and vacuum level, on recovery and energy consumption. It was found that the required energy for a twin double-bed PSA to produce biomethane with 87% purity is 903 kJ/kg CH₄ with 90% recovery, compared to 961 kJ/kg CH₄ and 76% recovery for a PVSA process. With respect to minimum purity requirements, increasing product purity from 95.35 to 99.96% resulted in a 32% increase in energy demand and a 23% drop in recovery, illustrating the degree of loss in process efficiency and the costly trade-off to produce ultra-high-purity biomethane. It was concluded that in processes with moderate vacuum requirements (>0.5 bar), a PVSA should be utilised when a high purity biomethane product is desirable. On the other hand, to minimise CH₄ loss and enhance recovery, a twin double-bed PSA should be employed. Full article

To study the fatigue failure and microstructure evolution behavior of SS304, low-cycle fatigue tests are conducted at room temperature (RT), 300 °C, and 650 °C. The results indicate that, because of the influence of the dislocation walls, carbon-containing precipitates, and deformation twins, the cyclic hardening behavior is presented at RT. However, different from the cyclic hardening behavior at RT, the cyclic softening behavior of SS304 can be observed due to the dynamic recovery and recrystallization containing dislocation rearrangement and annihilation at 300 °C and 650 °C. In addition, two fatigue crack initiation modes are observed. At RT, the single fatigue crack initiation mode is observed. At high temperatures, multiple crack initiation modes are presented, resulting from the degradation of material properties. Furthermore, a new fatigue life prediction model considering the temperature is conducted as a reference for industrial applications. Full article