Origin of reversible and irreversible atomic-scale rearrangements in a model two-dimensional network glass

In this contribution, we investigate the fundamental mechanism of plasticity in a model two-dimensional network glass. The glass is generated by using a Monte Carlo bond-switching algorithm and subjected to athermal simple shear deformation, followed by subsequent unloading at selected deformation states. This enables us to investigate the topological origin of reversible and irreversible atomic-scale rearrangements. It is shown that some events that are triggered during loading recover during unloading, while some do not. Thus, two kinds of elementary plastic events are observed, which can be linked to the network topology of the model glass

Universality in the fracture of silica glass

The presence of universality of avalanches characterizing the inelastic response of disordered materials has the potential to bridge the gap from micro- to macroscale. In this study, we explore the statistics and the scaling behavior of avalanches in the fracture of silica glass on the microscale using molecular mechanics. We introduce a robust method for capturing and quantifying the avalanches, allowing us to perform rigorous statistical analysis, revealing universal power laws associated with critical phenomena. The computed exponents suggest that nanoscale fracture of silica belongs to the same universality class as depinning models. Additionally, the influence of an initial crack is explored, observing deviations from mean-field predictions while maintaining criticality. Furthermore, we investigate the strain-dependent probability density function (PDF), its cutoff function, and the interrelation between the critical exponents. Finally, we unveil distinct scaling behavior for small and large avalanches of the crack growth, shedding light on the underlying fracture mechanisms in silica glass.Comment: 11 Pages with 8 Figure

PREDICTION OF JOINT KINETICS BASED ON JOINT KINEMATICS USING ARTIFICIAL NEURAL NETWORKS

The high cost and low portability of measurement systems as well as time-consuming inverse dynamic calculations are a major limitation to motion analysis. Therefore, this study investigates predictions of joint kinetics based on kinematic data using an artificial neural network (ANN) approach. For this purpose, 3D lower limb joint angles and moments of twelve healthy subjects were calculated using inverse dynamics. Kinematic and anthropometric data was used as input parameter to train, validate and test a long short-term memory recurrent ANN to predict joint moments. The ANN predicts joint moments for subjects whose motion patterns are known to the ANN accurately. Although the prediction accuracy for unknown subjects was lower, this study proved the capability of ANNs to predict joint moments based on kinematic and anthropometric data

FEATURE SELECTION FOR THE APPLICATION OF ARTIFICIAL NEURAL NETWORKS IN MOTION ANALYSIS

The application of IMUs and artificial neural networks have shown their potential in estimating joint moments in various motion tasks. In this study, IMU data collected with five sensors during gait was used as input data to estimate hip, knee and ankle joint moments using artificial neural networks. Additionally, the original 30 features of the sensors’ data were reduced to their ten most relevant principal components and also used as input to the neural networks to evaluate the influence of feature selection. The prediction accuracy of the networks was lower for the reduced dataset. Research with a larger dataset needs to be undertaken to further understand the influence of a reduced number of features on the prediction accuracy

THE INFLUENCE OF FILTER PARAMETERS ON THE PREDICTION ACCURACY OF THE GROUND REACTION FORCE AND JOINT MOMENTS

Athletes’ movement biomechanics are of high interest to predict injury risk, especially in maximum effort cutting manoeuvres. However, using a standard optical measurement set-up with cameras and force plates influences the athlete’s performance. Therefore, alternative methods, e.g. Neural Networks, have been used to predict kinetic parameters based on easier to measure kinematic parameters. A previous study has evoked the question, whether the filtering processes of the input and output parameters used for training a feedforward neural network affect the prediction accuracy. To answer this question, four different filter combinations have been used during the pre-processing of joint angles, ground reaction force and joint moments of fast cutting manoeuvres, which were used to train a feedforward neural network. The results revealed a dependency

JOINT ANGLE ESTIMATION DURING FAST CUTTING MANOEUVRES USING ARTIFICIAL NEURAL NETWORKS

Athletes’ movement biomechanics are of high interest to predict injury risk. However, using a standard optical measurement set-up with cameras and force plates influences the athlete’s performance. Alternative systems such as commercial IMU systems are still jeopardised by measurement discrepancies in the analysis of joint angles. Therefore, this study aims to estimate hip, knee and ankle joint angles from simulated IMU data during the execution and depart contact of a maximum effort 90° cutting manoeuvre using a feed-forward neural network. Simulated accelerations and angular rates of the feet, shanks, thighs and pelvis as input data. The correlation coefficient between the measured and predicted data indicates strong correlations. Hence, the proposed method can be used to predict motion kinematics during a fast change of direction

Impact loading of bored pile wall systems

Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersKurzfassung Die Aufgabenstellung dieser Diplomarbeit entstand im Rahmen des Umbaues des Sudbahnhofes in Wien in Zusammenarbeit des Institutes fur Hochbau und Technologie, Forschungsbereich fur Baumechanik und Baudynamik und der OBB-Infrastruktur Bau AG mit dem Statik Buro TECTON consult.Bei der Planung des Bahnhofes und dessen zugehorigen Gleis- und Tunnelsystemen wurde entschieden, die Tunnelwande aus Bohrpfahlwandsystemen, bei denen die Bohrpfahle in einem Abstand zwischen 1,5 und 3,0 Meter entfernt zueinander stehen, herzustellen.Die Basis dieser Diplomarbeit ist ein gedachtes Katastrophenszenario, in dem im Tunnelsystem ein Zug entgleist und gegen die Tunnelwand prallt. Normalerweise werden bei herkommlichen Tunnelschalen beim Aufprall des Zuges nur Krafte in Querrichtung (und eventuell in Langsrichtung Reibungskrafte) erzeugt. Bei Tunnelwanden dieser Bauart ist auf Grund ihrer Beschaenheit zu berucksichtigen, dass im Falle eines Stovorganges auch Krafte in Tunnellangsrichtung erzeugt werden.Ausgewahlt zur Untersuchung wurde Tunnelabschnitt T13 (von km +1116,00 bis km +1140,00).Dieser Tunnelabschnitt ist eine Teilstrecke einer Abzweigung und be ndet sich ca. 60 - 80 m vor dem Weichenanfangspunkt im Feld SO4. Die Annahme ist, dass der Zug im Bereich der Weiche entgleist und dass es anschlieend im Feld T13 zu einem Stovorgang kommt.Es stellt sich die Frage, ob es notwendig ist, eine zusatzliche Vorsatzschale zu errichten, oder die Raume zwischen den Bohrpfahlen mit Beton auszufullen um eine Stokraft in Langsrichtung zu verhindern.Die Aufgabe dieser Arbeit ist es, die Krafte, die bei Stovorgangen dieser Art entstehen, unter Einbeziehung des Untergrundes zu ermitteln. Auerdem sind die Ergebnisse mit den Vorgaben der technischen Norm zu vergleichen um diese dann anhand dieser Arbeit qualitativ bewerten zu konnen.Fa. SIEMENS stellte ein Versuchsergebnis zur Verfugung, in dem eine Taurus-Lok mit 5 m s gegen eine starre Wand fahrt. Um einen Vergleich mit anderen Stoberechnungen zu bekommen, wurden im Rahmen der vorliegenden Arbeit diese ebenfalls mit einer Anfahrgeschwindigkeit von 5 m s durchgefuhrt. Fur die Entwurfsgeschwindigkeit von 80 km h wurde eine statisch aquivalente Anpralllast mittels direkter Zeitintegration ermittelt.Bei den Berechnungen wird das dreidimensionale Modell auf zwei zweidimensionale Rechenmodelle zuruckgefuhrt, in ein Rahmensystem in Langsrichtung und eines in Querrichtung, die beide durch den Stovorgang gleichzeitig belastet werden.Erste Ergebnisse, bei denen die Mitwirkung des Bodens noch nicht berucksichtigt wurde, liegen weit uber den Werten der technischen Norm ONORM EN 1991-1-7. Es ergeben sich Schnittkr afte, die auf keinen Fall konstruktiv in den Gri zu bekommen sind.Daraus ergibt sich die 3 Schlussfolgerung, dass ein Sto in Langsrichtung auf jeden Fall zu verhindern ist, oder mit dem Ausfall mehrerer Bohrpfahle zu rechnen ist.Bei weiteren Berechnungen wird die Wirkung des Bodens in Form von elastischer Bettung miteinbezogen und schon von Anfang an angenommen, dass Stokrafte in Langsrichtung zum System verhindert werden. Der elastische Sto wird ausgeschlossen und der Berechnung wird nur mehr ein vollkommen unelastischer (plastischer) Sto zugrunde gelegt. Die Ergebnisse dieser Berechnungen werden in Abhangigkeit des Winkels zwischen Anstorichtung und Tunnelwand und der Bettungswirkung des Bodens dargestellt.Abstract This Master's Thesis was composed in the course of the reconstruction of the Vienna Sudbahnhof in close collaboration of the Vienna University of Technology's Institute of Building Construction and Technology, Research Center of Mechanics and Structural Dynamics and the OBBInfrastruktur Bau AG together with the engineering oce TECTON consult.During the planning phase of the new railway station and the connected railway and tunnel systems, it was decided that the tunnel walls were to be constructed by the use of contiguous pile wall systems with bored pile walls being placed every 1,5 to 3,0 meters.The main topic of the present Master's Thesis is a possible accident, in which a train derails and consequently collides with the wall of the tunnel. In the case of commonly shells a train crash merely causes forces in lateral direction (and possibly friction forces in longitudinal direction).However, tunnels using contiguous pile wall systems additionally provoke forces in longitudinal direction when hit by a derailed train.For means of analysis of the consequences of a train crashing into the tunnel wall, section T13 (from km +1116.00 to km +1140.00) was selected. T13 is part of an intersection and is situated approximately 60-80 m before the beginning of the switch point in the eld SO4. The analysed scenario infers that the train derails at the switch point and hits the tunnel wall in section T13.Hereby, the question arises whether it is necessary to add an additional shell or to ll the free space between the bored piles with concrete in order to avoid forces in longitudinal direction.The challenge is to evaluate those forces, that appeare at accidents of this kind, in involvement of the geotechnical in uences. Furthermore these data have to be compared with the speci cations of the technical norm in order to appraise them.The company SIEMENS provided an experimental result, in which a Taurus-lokomotive collides with a rigid wall with the velocity of 5 m s . To compare calculations based on this szenario with the classical theory all calculations are done by assuming a velocity of 5 m s . For the design speed, which is 80 km h , a statically equivalent force has been calculated by integrating the force path, which is dependent on time.The three-dimensional system is split into two two-dimensional systems, i.e. one frame in longitudinal direction and one frame in lateral direction. During the collision both systems are strained at the same time.First data, which were calculated without geotechnical in uences, are much larger than those proposed by the standart ONORM EN 1991-1-7. The conclusion is, that collisions in longitudinal direction have to be avoided so as to avoid the complete damage of additional bored piles.The following calculations are dedicated to the consideration of the geotechnical in uence by 5 means of continous elastic support. The assumption is, that no force in longitudinal direction will occure due to the special construction and only plastic collision is considered. The results of these calculations are illustrated dependent on the angle of the direction of the collision and the elastic support of the soil.7