Higher Number Of Cycles Research Articles

Modeling Cycle-to-Cycle Variations of a Spark-Ignited Gas Engine Using Artificial Flow Fields Generated by a Variational Autoencoder

A deeper understanding of the physical nature of cycle-to-cycle variations (CCV) in internal combustion engines (ICE) as well as reliable simulation strategies to predict these CCV are indispensable for the development of modern highly efficient combustion engines. Since the combustion process in ICE strongly depends on the turbulent flow field in the cylinder and, for spark-ignited engines, especially around the spark plug, the prediction of CCV using computational fluid dynamics (CFD) is limited to the modeling of turbulent flows. One possible way to determine CCV is by applying large eddy simulation (LES), whose potential in this field has already been shown despite its drawback of requiring considerable computational time and resources. This paper presents a novel strategy based on unsteady Reynolds-averaged Navier–Stokes (uRANS) CFD in combination with variational autoencoders (VAEs). A VAE is trained with flow field data from presimulated cycles at a specific crank angle. Then, the VAE can be used to generate artificial flow fields that serve to initialize new CFD simulations of the combustion process. With this novel approach, a high number of individual cycles can be simulated in a fraction of the time that LES needs for the same amount of cycles. Since the VAE is trained on data from presimulated cycles, the physical information of the cycles is transferred to the generated artificial cycles.

Static and Fatigue Load Bearing Investigation on Porous Structure Titanium Additively Manufactured Anterior Cervical Cages.

This study investigates the static and fatigue behavior of porous and conventional anterior cervical cages. Porous structure titanium anterior cervical cages were manufactured using direct selective laser sintering technique. Four different types of cervical cages were designed and manufactured, among which three designs consist of porous structure (type 1, type 2, and type 3) and manufactured using metal 3D printing. Remaining one design (type 4) was manufactured using conventional machining and did not consist any porous structure. All types of manufactured cages were tested in compression under static and fatigue loading conditions as per ASTM F2077 standard. Static and fatigue subsidence testing was performed using ASTM F2267 standard. Static compression testing results of type 1 and type 4 cages reported higher yield load when compared to the type 2 and type 3 cages. Static subsidence testing results reported almost 11% less subsidence rate for additively manufactured cages than the conventional cages. Fatigue subsidence testing results showed that type 2 and type 3 cages can withstood approximately 21% higher number of cycles before subsidence as compare to the type 1 and type 4 cages. During fatigue testing, all the cages design survived 5 million cycles at the 3000 N loading. For 6000 N and 8000 N, loading rate type 2 and type 3 cages showed lower fatigue life when compared to other cages design. Since fatigue life of type 2 and type 3 cage designs were reported lower than other cages design, it is concluded that the performance of the additively manufactured porous cages can be significantly varied based upon the cage design features.

Analysis of the scatter in fatigue life testing of thick thermal cut plate edges

ABSTRACT Structural elements of ships are subjected to a high number of cyclic loads, which are critical to fatigue life. Especially for ultra-large container ships the cutting of thick steel plates with high finishing quality and good fatigue life is important, e.g. located at openings in walls and decks of ships. This study presents a series of fatigue tests with 50 mm thick S355 specimens that are thermally gas cut on different shipyards. The obtained stress-life (S-N) curve contains significant horizontal scatter which often occurs for specimens that spend a high number of cycles on crack initiation. However, it is found that both the local stress concentrations and the origin of failure affect the number of load cycles significantly. Accounting for local stress concentrations provides an explanation for the initially encountered scatter in the S-N curves and indicates possible limitations of the nominal stress approach for thermal cut edges.

Simultaneous reduce NO/CO2/CO emissions by modified peanut shell biochars in Ca-L/CARBONOx process

A composite of biochar (BC) derived from peanut shells—with high ash contents—blended with CaO was used in the Ca-L/CARBONOx process. BC was subjected to acid pickling (BC-A), direct nitrogen doping (BC-N), and acid pickling with nitrogen doping (BC-A-N). The efficacy of modified biochar for simultaneous reduce NO/CO2/CO emissions was investigated in this study. The results show that simultaneous NO/CO2 removal was realized in the Ca-L/CARBONOx process using peanut-shell-biochar/CaO. However, higher CO emission was also generated during the process, which increased significantly as the temperature, biochar addition, and oxygen concentration increased. CO2 produced by the oxidation of biochar accelerates CaO consumption and decreases its catalytic effect on NO reduction. The simultaneous NO/CO2 removal ratio declined with the cycle number due to CaO sintering. Acid pickling and nitrogen-doping of biochar significantly decreased the CO and CO2 emissions, whereas sintering of CaO at higher cycle numbers had little effect on NO reduction by BC-A-N.

Climate and land‐use driven reorganisation of structure and function in river macroinvertebrate communities

Understanding temporal changes in the composition of species communities over spatial and temporal scales relevant to conservation management is crucial for preventing further biodiversity declines. Here, we assessed patterns and potential drivers of taxonomic and functional temporal β diversity over 26 years (1991–2016) of 64 river macroinvertebrate communities, and the length of New Zealand (37°00'N, 46°00'S). We further examined changes in population size and range shifts of species pools, and related these to taxonomy and functional traits. We found increasing climate and land‐use driven differences in both the taxonomic and functional composition of communities over time, coupled with poleward species colonisations and increasing extirpations in northern locations. Increases in population and species range size were more prevalent than decreases in population and range size. Species shifted their ranges towards higher latitudes on average by 50 km per decade. Despite little to no relationship with taxonomy, we uncovered distinct relationships between functional traits and population trends and latitudinal species range shifts. Species with a high number of reproductive cycles per year and long‐life duration of adults tended to increase their population size, while larger size species with a high number of descendants per reproductive cycle tended to shift their range towards more southern latitudes. Our results suggest that the intensity of disturbances, the geographic location of individuals and communities, and species ecological and functional characteristics, are major determinants of riverine biodiversity reorganisation in the Anthropocene.

Fatigue in breast cancer patients on chemotherapy: a cross-sectional study exploring clinical, biological, and genetic factors

BackgroundCancer-related fatigue (CRF) is one of the most common and distressing complaints reported by cancer patients during chemotherapy considerably impacting all aspects of a patient’s life (physical, psychosocial, professional, and socioeconomic). The aim of this study was to assess the severity of cancer-related fatigue in a group of breast cancer patients undergoing chemotherapy and explore the association between fatigue scores and sociodemographic, clinical, biological, psychiatric, and genetic factors.MethodsA cross-sectional pilot study carried out at the oncology outpatient unit of Hôtel-Dieu de France University Hospital recruited 67 breast cancer patients undergoing chemotherapy between November 2017 and June 2019 to evaluate fatigue using the EORTC QLQ-C30 scale (European Organization for the Research and Treatment of Cancer Quality of Life Questionnaire). Genotyping for seven gene polymorphisms (COMT, DRD2, OPRM1, CLOCK, PER2, CRY2, ABCB1) was performed using the Lightcycler® (Roche).ResultsThe prevalence of fatigue was 46.3%. Multivariable analysis taking the fatigue score as the dependent variable showed that a higher number of cycles and a lower hemoglobin level were significantly associated with higher odds of exhibiting fatigue. Moreover, having at least one C allele for DRD2 SNP (vs. TT) was significantly associated with a 4.09 higher odds of expressing fatigue compared to TT patients. Finally, patients with at least one C allele for CLOCK SNP tended to display higher fatigue levels than TT patients.ConclusionsOur study showed that anemic breast cancer patients with a high number of chemotherapy cycles and those carrying at least one C allele for DRD2 and CLOCK SNPs are at greater risk of exhibiting fatigue. Since no previous research has reported such genetic results, future studies are necessary to confirm our findings.

Fatigue damage initiation mechanisms in bearing steel

This work deals with an experimental investigation of fatigue damage initiation mechanisms in high-grade, low-alloyed 100Cr6 bearing steel. The fatigue tests were carried out at rotative bending loading with parameters, frequency f = 50 Hz, stress ratio (coefficient of cycle asymmetry) R = −1, temperature T = 20 ± 2 °C, in the region ranged from Nf ≈ 1.5 × 103 to Nf ≈ 1.0 × 108 cycles. The surface fatigue failure mechanism was observed in the area of low number of cycles Nf ≈ 1.5 × 103–Nf ≈ 4.3 × 104 cycles (persistent slip bands from surface roughness), while subsurface fatigue failure mechanism was observed in the area of very high number of cycles, Nf ≈ 1.0 × 107–Nf ≈ 1.0 × 108 cycles (from non-metallic inclusions, mostly TiN inclusions but also from Al2O3 inclusion). The paradox is that on one hand the high fatigue life is required for bearing steels, while on the other hand, the content especially titanium is not prescribed in standard for the chemical composition of this 100Cr6 bearing steel.

Very High Cycle Corrosion Fatigue Study of the Collapsed Polcevera Bridge, Italy

Abstract A possible scenario is proposed to put into evidence how the combined effect of fatigue at very high number of cycles and corrosion could have been responsible for the failure of one of th...

AISI P20 steel under VHCF testing conditions

As more complex materials, structures and machines are created and applied in the modern world, the importance and complexity of fatigue testing methods become more indispensable for any mechanical project. This study focuses on an AISI P20 Steel in the Very High Cycle Fatigue (VHCF) regime, between 106 to 109 cycles, under different loading conditions: Tension-compression, pure torsion, and multiaxial tension/torsion. To reach such a considerable high number of cycles, no conventional fatigue testing method is energy and time reliable. Therefore, the present study conducted ultrasonic fatigue testing methods under 20kHz. Each stress type fatigue method was reached from its respective and different ultrasonic fatigue setup. Significant testing associated conditions and methodology, such as temperature, frequency and displacement, were carefully controlled, recorded, and made similar for all three methods. Stress-life results, material behaviour throughout fatigue testing and fracture surfaces for each stress type were compared for behaviour and damage correlation between pure torsion, tension-compression and the multiaxial combination of the two, tension-torsion. After all conducted fatigue tests, the obtained fatigue crack surfaces were analyzed by optical and scanning electron microscope (SEM) and compared between methods. Each tested method presented fatigue fracture surfaces with associated fracture morphologies similar to classic fatigue methods. The novel tension-torsion ultrasonic fatigue fractures showed both axial and torsion fatigue fracture dependencies and complexities, proving the induced stress field of interest.

Damage indicators for early fatigue damage assessment in WC-Co hardmetals under uniaxial cyclic loads at a stress ratio of R = −1 at elevated temperatures

WC-Co hardmetals are utilized as tool materials in metal cutting applications in which they are exposed to high mechanical cyclic loads and elevated temperatures. A better understanding of the failure mechanisms of WC-Co hardmetals under these application conditions and the ability to diagnose the damage evolution state are key factors to understand the limits of endurable cyclic load at a certain temperature. The aim of the current work was the experimental determination of stress-strain-hysteresis loops for the investigation of damage indicators in uniaxial cyclic tests at a stress ratio of R = σmin/σmax = −1 for two WC-10 wt% Co hardmetals at 700 °C and 800 °C in vacuum. An increase in the stress-strain-hysteresis loop area and tension-compression-strain asymmetry was recorded with increasing number of load cycles at 800 °C, with earlier failure than at 700 °C. The relationship between the stress-strain-hysteresis loop parameters and the damage evolution state at the microstructure level, as well as the deformation behavior of WC- and Co-phases with increasing number of load cycles, were analyzed. To this end, the microstructure for one WC-Co hardmetal grade was analyzed by scanning electron microscopy and electron backscatter diffraction after cyclic testing up to defined numbers of load cycles at 800 °C. It was observed that the hysteresis loop area and strain asymmetry coincide with the formation of nanopores at WC/WC interfaces and WC/Co phase boundaries, which enlarge to form larger cavities with increasing number of load cycles. Additionally, electron backscatter diffraction data showed that the fcc Co-phase partially transformed into hcp Co under cyclic loading. All specimens, in which an increase in the stress-strain hysteresis loop area or strain asymmetry was observed, ultimately failed when a sufficiently high number of load cycles was applied. Thus, these results indicate that the investigated parameters are reliable indicators for bulk material damage.

Contact fatigue of WC-6%wtCo cemented carbides: Influence of corrosion-induced changes on emergence and evolution of damage

The effect of corrosion-induced changes on the contact fatigue response and associated damage in a medium-grained WC-6%wtCo hardmetal grade is investigated. Cyclic contact loading tests are conducted by means of Hertzian indentation techniques. Corrosion damage is introduced in a controlled way by previous immersion of specimens in a stirred acidic medium. Results reveal that corrosion significantly affects the contact fatigue behavior of the material under consideration, in terms of decreasing the effective load bearing capability of the material as well as earlier emergence and evolution of specific damage features, as compared to those discerned under monotonic loading and in a pristine hardmetal respectively. As cycle number increases, damage evolution in the corroded condition is more gradual and diffuse than for the uncorroded one. In general, it is dominated by existence of ill-defined radial cracks together with pronounced carbide grain pull-out which finally evolve into cohesive-like spallation in regions close to the periphery of indentation imprints. These findings are rationalized on the basis of phase assemblage changes linked to corrosion, particularly in terms of lessening of toughening capability and easiness of WC grain pull-out intrinsic to the loose and porous binderless WC skeleton remnant at the surface level, after exposure to the acid medium. Although some removal of carbide grains and discrete cohesive chipping is also observed in the pristine sample for very high number of cycles, such different response, as compared to monotonic loading, is linked to oxidation phenomena of the metallic binder for this reference condition.

Quasi-static and dynamic fracture toughness of a γ-TiAl alloy: Measurement techniques, fractography and interpretation

Intermetallic titanium aluminides (TiAl) offer an enormous potential for high temperature applications due to their high specific strength, creep and oxidation resistance. However, their use for structural components is limited by their low ductility and fracture toughness. During service, along with a high number of load cycles, the material may also be subjected to unexpected impact loads, which requires therefore knowledge about dynamic material parameters for a damage-tolerant component design. Here we present a feasibility study to determine the fracture toughness of a third generation TiAl-alloy over a wide range of loading rates. Quasi-static crack resistance curves (R-curves) were determined using the direct current potential drop (DCPD) technique. The dynamic experiments were performed with a drop tower with impact velocities ranging from 1 to 10 m/s on pre-cracked SENB specimens. To exclude the influence of inertial forces, the measurements were carried out with strain gauges applied in the elastic near-field of the crack tip. Despite a critical consideration of possible systematic errors of this measurement method, it was found that the dynamic fracture initiation toughness slightly increases up to loading rates of K̇I = 106 MPa√m/s. The fracture behaviour of the material and possible reasons for the toughness increase are discussed based on comprehensive fractographic investigations as well as crack path analyses within the microstructure.

Design optimisation and cost analysis of linear vernier electric machine-based gravity energy storage systems

Energy storage technologies have been gaining increasing attention as a way to help integrate variable and intermittent renewable energy sources into the grid. In this paper, a novel gravity energy storage system which features a linear electric machine-based hoisting mechanism is investigated. The storage system utilises the inherent ropeless operation of linear electric machines to vertically move multiple solid masses to store and discharge energy. The consequent-pole linear Vernier hybrid machine is chosen as the machine topology, and a multi-objective design optimisation is conducted. The optimisation results are then used to perform a cost analysis by means of a levelised cost of storage calculation. A sensitivity analysis is also done to investigate some of the assumptions made in the levelised cost of storage calculation that have no direct influence on the design of the linear electric machine. This study shows that the proposed storage system has a cost-competitive advantage when used in applications with high power and a high number of annual cycles. The paper also highlights the most important factors that affect the economic performance, clearly indicating where further improvements can be made to further increase the viability of the storage system.

Evaluation of permanent deformation and resilient modulus of pavement base with different gradations and percentages of clay plasticiser

Characteristics of unbound granular pavement materials vary among transportation and road association around the world based on function, environmental conditions, and materials availability. Plasticity index (PI) is one of the most important characteristics of unbound granular pavement courses both in the construction stage and throughout its service life. It indicates the range of moisture contents over which the fines in the pavement material behave plastically. This study investigates the effect of a refined clay plasticiser called Claypro (CP) on the elastic and plastic behaviour of unbound granular base materials at different gradations. This paper aims to find the optimum clay content (CP) that achieves an acceptable PI and maintains high elastic performance and high plastic strain resistance under traffic loading. Elastic and plastic responses of 18 mixtures at three different gradations, representing two types of crushed rock materials namely; Hornfels and Basalt, were evaluated at three different CP contents. Repeated load triaxial (RLT) test was carried out with a high number of cycles to estimate the resilient modulus (MR) and the permanent deformation of these mixtures. The shakedown concept was also applied to assess the deformation behaviour of the tested engineered mixtures under multi-stage RLT test. Results showed that 1% Claypro (CP) content is considered the optimum for all gradations of both aggregate types considered herein.

Experiment-based estimation of the settlement potential due to dynamic loads from heavy vehicle traffic on the A 44n motorway built on the dump of the Garzweiler opencast mine

The A44 motorway was rebuilt on the dump of the Garzweiler opencast mine over a length of 7 km. The maximum thickness of the dump beneath the motorway is 185 m. Mostly sands showing a loose relative density were dumped. This leads to time-delayed settlements of the dump. In order to reduce these settlements of the dumped subsoil, which could jeopardise the serviceability limit state of the motorway, a top layer consisting of gravel and sand, with a minimum thickness of 10 m, was dumped using opencast mining equipment. This layer was compacted in the upper part using earth-moving machinery. To what extent vibrations from traffic loads can lead to grain rearrangements and thus settlements of the freshly dumped and compacted subgrade is the question of the investigation presented herein. Based on results of a customized exploration of the subsoil and dynamic field tests, in which loaded trucks drove over a measuring cross-section, it could be demonstrated that shear strain amplitudes induced by road traffic loads in the underlying compacted and loose granular soils do not exceed the strain threshold required for the accumulation of plastic deformations. Therefore, admissible settlements should not be exceeded even at very high numbers of traffic load cycles.

Combined high fluence and high cycle number transient loading of ITER-like monoblocks in Magnum-PSI

It is highly desirable to understand the long term evolution of the divertor material under the extreme steady-state and transient heat and particle loads expected during ITER operation. Here the impact of ELM-like transient loading under combined high-flux plasma and transient ELM-like heat loading in Magnum-PSI was explored to determine how plasma affects the fatigue cracking threshold of tungsten due to ELMs. Mock-ups consisting of five ITER-like monoblocks in a chain were simultaneously exposed to high flux plasma and a high power pulsed laser which closely simulated the ELM impact in terms of heat flux and duration. Loading conditions were chosen to enable comparison to existing data from electron-beam loading, while the influence of surface base temperature (750 °C, 1150 °C or 1500 °C) and impurity seeding (addition of 6.5 ion% He+ and/or 8 ion% Ne+) were also investigated. The plasma loading leads to differences in surface morphology and indicates synergistic effects on the extent of the surface damage. Base temperatures at or above 1150 °C are found to lead to a significant reduction in the fatigue cracking threshold by a factor of two or more compared to at 750 °C. Cracked surfaces are found to be more than ten times rougher than the original microstructure, and additionally when seeding impurities are added surface roughness can be significantly increased by up closely factor of two compared to roughening using pure H plasma. Overall the results indicate that avoiding fatigue cracking in ITER will be very challenging, and that understanding the level to which this can therefore be tolerated is vital for anticipating divertor lifetime and reliability.

Numerical Simulations of the Monotonic and Cyclic Behaviour of Offshore Wind Turbine Monopile Foundations in Clayey Soils

Most of the reported centrifuge tests available in the existing literature on offshore wind turbine foundations are focused on the behaviour of monopiles in sands, but very few studies on clayey soils can be found, due to the very long saturation and consolidation periods required to properly conduct experiments in such materials. Moreover, most of the reported numerical simulations using finite element analyses have been validated with monotonic centrifuge tests only. In this research, both monotonic and cyclic performance of offshore wind turbines in clay are validated and justified. The relationship between the monopile rotation in clays and the geometry and strength of the soil has been found and quantified. A prediction of the rotation for a high number of cycles of loading, based on the one experienced by the pile during the first cycle, can be obtained using the correlation derived in the paper. For those cases in which the rotation does not reach a steady value after a high number of cycles, the cumulative rate has been found significantly larger than the prediction conducted with standard analytical methods. A new design methodology for the design of offshore monopile foundations in clay is presented.

Microstructure and fatigue properties of extruded aluminum alloys 7046 and 7108 for automotive applications

This work aimed to obtain by extrusion two aluminum alloys, 7108 and 7046. The microstructural characterized at each stage of the manufacturing process and the mechanical fatigue behavior of the extruded profile were evaluated. The aluminum alloys in the as-casted condition exhibited an interdendritic microsegregation inside the grains, with intermetallic phases precipitated on the grain boundaries. In the homogenization of the billets of the AA7108 and AA7046, the precipitated phases dissolved. The AA 7046, in the as-casted condition, displayed shrinkage microvoids throughout the length of the billet and a microstructure of heterogeneous grains, with the presence of a remelted layer at a maximum depth of 10 mm. The AA7046 displayed better tensile and fatigue properties than the AA7108. A higher surface roughness facilitated the initiation and propagation of cracks during the fatigue cycles. This effect was more pronounced with low levels of maximum stress and high number of cycles to failure. Deep secondary cracks perpendicular to the growth direction of the main crack were visible on all fracture surfaces. In the medium and high cycle fatigue tests of the AA7108 and AA7046, the cracks advanced in a perpendicular direction to the elongated grains resulting from the extrusion process. The fracture surfaces of the tested samples with a high number of cycles exhibited a region with a smaller crack propagation area and a larger region of rupture due to mechanical overload. The region of crack propagation is characterized by plastic deformation and the presence of striations perpendicular to the growth direction.

Comparison Between Two Types of Seismic Tests of Racking Systems

AbstractThis paper is the result of both experimental and numeric analyses on pallet rack components. Two cyclic testing protocols for beam‐end connectors of adjustable racking systems are compared; such experiments are named as “code type” and “Castiglioni”. Both protocols share the same test mock‐up: an assembly of a doubly‐pinned upright segment with a cantilever beam specimen. These tests consist in an up‐to‐failure increasing push‐pull process at the free beam end. In the “code type” test, the imposed displacement loops are centered around zero; conversely, in the “Castiglioni” tests, both upward and downward displacement segment runs are centered around a vertical static equilibrium situation (to take the gravitational load into account). The “code type” test is expected to result in a higher number of cycles than the “Castiglioni” one because of the two following features of the latter: (i) the gravitational load is always present, thus resulting in a higher demanding test, and (ii) the failure point is precisely predefined and usually produced before the total breakdown. This paper describes and compares experiments using both protocols. Additionally, these tests are numerically simulated.

ABCL-018: Muscle Loss During Immunochemotherapy for Diffuse Large B-Cell Lymphoma and its Clinical and Prognostic Associations

Context Cancer induced cachexia is associated with poor prognosis in patients with diffuse large B-cell lymphoma (DLBCL) but it is unknown how and to what extent curable lymphoma treatments affect musculoskeletal system. Objective To investigate how immunochemotherapy affects muscle mass and whether this has prognostic consequences in newly diagnosed DLBCL patients. Design Retrospective cohort study including period from 2005-2019. Setting Tertiary hematologic center. Patients or Other Participants 104 newly diagnosed adult DLBCL patients with unfavorable features (proliferative index Ki67+ ≥80% and/or International Prognostic Index (IPI) ≥2 points) treated with the R-DA-EPOCH regimen with available baseline and end of treatment CT scans. Methods Psoas muscle area (PMA) at L3 vertebra level was compared between revision and baseline CT scans. Main Outcomes Measures PMA change during immunochemotherapy, overall survival (OS), progression free survival (PFS). Results Small but significant decline in PMA was observed during immunochemotherapy period (average loss 5%; P=0.016) with 57.7% patients experiencing muscle loss. In the multivariate logistic regression analysis higher body surface area (OR 17.98 for each m2; P=0.034), higher number of cycles with dose reduction (OR 2.86 for each cycle; P=0.039) and weaker response to therapy (OR 3.09 for each response category; P=0.052) were recognized as independent contributors to the PMA loss. Age, sex, baseline psoas muscle index, body mass index, Ki-67, Ann Arbor and R-IPI staging systems had no significant association with the extent of PMA loss. A total of 25/104 (24%) of patients experienced ≥21% PMA loss (ROC curve analysis defined optimal cut-off level) which was associated with significantly worse overall (OS; HR=8.58; P Conclusions Muscle loss occurs in approximately half newly diagnosed DLBCL patients with unfavorable disease features during R-DA-EPOCH immunochemotherapy, and if pronounced, this is associated with worse clinical outcomes irrespectively of achieved response to therapy. The most relevant predictors of muscle loss during chemotherapy period seem to be immunochemotherapy related, i.e., associated with the dose, toleration and efficacy of immunochemotherapy.