Sudden Overload Research Articles

The effect of failure mechanics on the fatigue responses of lumbar intervertebral disc

Lumbar disc herniation is usually caused by the accumulation of long-term mechanical loads and sudden overload damage. Therefore, this study aims to illustrate how fatigue failure in lumbar spine segments is influenced by both cyclic loading magnitude and pre-existing damage. Eighty-six sheep intervertebral disc samples were divided into four groups to test the fatigue responses in healthy and damaged intervertebral discs. Both before and after fatigue loading, the specimens were performed on loading–unloading tests to analyze the viscoelasticity changes, while the specimens were performed on MRI examination to analyze the geometric and morphological changes. The Stress-Failure curve (SN curve) was examined, while the number of cycles to failure of damaged specimens was much smaller than that of healthy specimens at the same stress level during cyclic loading, and the relationship was approximately linear on a logarithmic scale. In addition, the healthy specimens will not accumulate fatigue failure if the compression force remains below 50% of the ultimate compressive tolerance (UTC). Before and after fatigue loading, the loading–unloading curves do not coincide and show obvious strain-rate-dependent viscoelastic characteristics, while the elastic modulus of the damaged specimen is significantly smaller. For magnetic resonance imaging, morphological changes included the changes of nucleus pulposus (NP) shape and area, while fatigue has a more significant effect on ruptured and herniated disc specimens. The dissipated energy of the intervertebral discs under cyclic loading was then calculated based on viscoelastic constitutive equations, which show that the load and preexisting damage both have significant effects on the dissipation rate.

A Comparitive Study of Physical Activity, Academic Performance and Stress Level Among Pharmacy and Non-Pharmacy Students - Before, During and After Covid19 Lockdown

Aims and Objectives: To compare the impact of COVID19 lockdown on physical activity, academic performance and stress levels among Pharmacy and Non-Pharmacy students in 3 timeframes- before, during and after lockdown. Methods: This is a Cross-sectional retrospective study conducted for a period of 6 months. The data was collected both online and offline. All college going students who had attended regular offline classes before lockdown were included. A total of 880 students were included in the study. A self-prepared questionnaire was used to collect data. The association was calculated using Chi-square test and p-value of less than or equal to 0.05 was fixed as level of significance. Results: Analysing the data from 880 students, we found that while non-pharmacy students exercise regularly (67% vs 55.7%), they also spend more time (>8 hours/day) using electronic gadgets (62.9% vs 51.8%). Sleep duration was less, 4-6 hours/day for all students after lockdown (80%), due to sudden overload of class work. Both groups reported difficulty in online learning due to network issues, unfamiliarity with online classes, difficulty in notes taking and unavailability of book resources. Stress levels were high for all, but pharmacy students showed higher anxiety about academics and future careers, while non-pharmacy students reported greater stress in interpersonal relationships. Conclusion: We thus conclude that Pharmacy students might benefit from targeted workshops on exam anxiety and future career planning, while Non-Pharmacy students might benefit from support groups or workshops on building positive interpersonal relationships. Both categories of students may benefit from counseling regarding time management, effective phone usage and the importance of 7-8 hours sleep at night.

Progressus as an Explanatory Model: An Anthropological Principle Illustrated by the Russia-Ukraine War

At the beginning of the Russian Federation’s attack on Ukraine in February 2022, the European Union put up massive resistance, but due to its sudden overload, it was unable to deal with the situation adequately. It was in a state of paralysis for some time. Therefore, five explanatory models for the Russian actions are presented: an offensive, a defensive, a situational, a socio-cultural, and an ideological-historical one. It is then shown that the German term Gewalt, which combines the English terms violence, power, and force ontologically, is best suited to summarize and describe all these models. It is also shown that Gewalt is a neutral, fundamental human concept that can be described as one of the basic driving forces of man. By piercing society, Gewalt constitutes an impulse, a motivation that stimulates and fuels the individual and society in toto. This leads to what we call Progressus, which depends on four variables – group desire, potential means of violence and force, group aims and objectives, as well as group comparison and evaluation. Progressus is inherent in all persons and in all societies. It can be analyzed and managed in a variety of different ways. Combined with the foundation of Gewalt, seen as neutral agent in varying levels of intensity, Progressus forms a matrix for efficient analysis to describe positive and frictional interaction, establishes social relations from friendship up to war; and this between individuals, groups and/or states. How this is possibly implemented in practice is described at the end using an example from the previously presented explanatory models.

Failure analysis of a tandem mill ring gear

A roll end ring gear of a tandem hot rolling mill suddenly fractured in service after 21 years, with no record of a sudden overload. The component was made of hardened and tempered Nitralloy N steel with a core hardness of 40 HRC. The case hardness specified in the construction project was 60 HRC. Two goals were set in this investigation: to verify whether the component followed the chemical, microstructural, and mechanical properties established in AMS 6475L standard and in the gear project and to determine the fracture mechanism and its probable root cause in order to propose preventive actions and to avoid similar failures in the rolling mill. Metallographic and fractographic examinations showed that the roll end ring gear failed due to a corrosion fatigue mechanism in which multiple cracks nucleated from corrosion pits on the outer surface of the component, and propagated through the wall with the cyclic stresses associated with its operation. The corrosion mechanism was differential aeration corrosion promoted by the formation of sludge deposits, possibly aided by microbiologically influenced corrosion (MIC).

Maximum current injection method for grid‐forming inverters in an islanded microgrid subject to short circuits

AbstractIn islanded microgrids, when a short circuit or a sudden overload occurs, it provokes an abrupt increment in the currents supplied by the generation nodes, which feed the load collaboratively. This is particularly challenging for inverter‐based nodes, due to its reduced power capacity. This work takes advantage of the droop‐method basic configuration to propose an additional closed‐loop control, which ensures maximum current injection during any kind of short circuit maintaining the underlying droop control. Ensuring that any node injects its maximum rated current during the short circuit, it emulates the most common low‐voltage ride‐through protocols for grid‐feeding sources oriented to support the grid and, in this way, the voltage unbalance is reduced. To develop the control proposal, a model of the faulted system is presented in order to evaluate the stability of the closed‐loop system. A general modelling methodology is introduced in order to derive the control for any microgrid configuration. Finally, selected experimental results are reported in order to validate the effectiveness of the proposed control.

Tromboembolismo pulmonar

Pulmonary thromboembolism is a potentially serious disease, secondary to pulmonary arterial obstruction by thrombotic material, which alters ventilation-perfusion balance with secondary hypoxaemia, and entails a sudden overload for the right ventricle that can result in life-threatening haemodynamic failure. Management should be based on stratifying the severity of the clinical picture to then undertake a specific diagnostic process, using algorithms based on the patient's clinical characteristics, laboratory tests (especially D-dimer and markers of myocardial damage) and imaging techniques (echocardiography, CT angiography, etc.). Treatment should be initiated early, and consists on haemodynamic and respiratory support measures, along with treatment with fibrinolytics or anticoagulants depending on the patient's clinical situation. Finally, the indication for long-term anticoagulation should be assessed on individual basis taking risk/benefit into account.

Enhancement of Electrical Distribution Networks Performance Using the Load Management Methodology

This paper presents the importance of load management methodology (LM) and helps in clarifying the difference between load management versus demand-side management (DSM), as LM is a crucial method of controlling the loads especially in peak periods, to prevent tripping. It was found that the previous researches focused on the dual tariff meters to force and motivate the consumer to change the demand time which was a gleam in overcoming the phenomena. However, the dilemma of the DSM was relying mainly on the consumer, who has to change the time of his needs. Therefore, it is difficult to be controlled. Consequently, they cannot find effective feedback as well. On the other hand, LM relies only on the designer or service provider in re-distributing loads according to the load behavior studies (time, location, and type of user) without depending on the consumer in solving the phenomena of extreme fluctuations of loads on the electrical equipment. In this paper, the second methodology is by the service provider, it is going to be handled and discussed by Selecting medium voltage (MV) feeders, re-distribute loads equally, and variously on transformer preventing unifying load which causes overloaded transformer on one period rather than the other. Consequently, it will lead to protect electrical equipment from no-load or overload effects, selecting the exact size. That will improve the economic status and will lead to a stable, balanced system, besides reduce heat island effects and prevent load shedding caused by sudden overloading. The model was created by using DIgSILENT power factory software.

Study of adaptive hydraulic drive of rotary drilling machine

The article deals with drilling machines in which the ratio of the load between the power to rotate and the power to feed is carried out automatically due to the structure of the adaptive machine, with the provision of self-regulation for drilling modes close to optimal. Changing drilling conditions automatically results in a change in the ratio of speed to feed force, providing maximum performance while protecting against sudden overloads, for example, when encountering solid inclusions in the drill rock, or when shading a well. The ratio of frequency of rotation and feed rate determines the specific depth of cut (specific feed) and determines the performance of the working process of the drilling machine. A typical example of such a machine is a drilling machine rotary type with hydraulic rotation and feed. The cutting theory determines the rational drilling conditions, known rational specific feed, rational speed, minimum and maximum feed force, depending on the strength of the material being drilled and the degree of blunting of the cutting tool.The block diagram of such a drilling machine is considered and the analysis of the influence of parameters and characteristics of individual hydraulic elements on the drive setting on the rational mode of operation is given. The research stand and its structure are given, some results of experimental researches are given. It is established that the chokes of the drive settings can adjust the degree of adaptation, change its sensitivity to external influences and change the range of operating conditions for the rational functioning of adaptive drilling.

Fatigue life assessment of concrete members under variable amplitude loading: An analytical approach

As structural design and analysis become more refined there is an increased demand for fundamental information on the performance of concrete under loads other than static. Apart from the application of different types of loading, the material behaviour of concrete is highly heterogeneous and complex in nature due to the occurrence of extensive micro-cracking and toughening mechanisms. In this work, an attempt has been made to estimate the crack growth in concrete members under the action of fatigue loading considering complex material behaviour. In addition to the dependency of size and shape of the member on fatigue behaviour, the effect of loading history under the action of varying amplitude load cycles with sudden overload is important and has been considered in this work. Further, the effect of loading frequency on crack growth and fatigue life has been demonstrated through thermal diffusion coefficient. The mathematical formulation for the prediction of crack growth rate has been derived on the basis of theoretical arguments utilizing the concepts of self-similarity and intermediate asymptotic. Available experimental data on concrete fatigue has been taken up from the literature and are used to determine the unknown coefficients in the formulation. The predicted results based on the proposed formulation are found to capture the effects of loading history, sudden overload, and loading frequency in addition to the effect of structural size. The proposed model is then solved using higher-order numerical integration techniques enabled by surrogate modelling followed by a sensitivity analysis. Loading frequency and energy release rate due to overload cycle are found to be less sensitive on the fatigue life prediction.

Measurement of strain evolution in overloaded roller bearings using energy dispersive X-ray diffraction

Abstract There are several mechanisms contributing towards detrimental damage in wind turbine gearbox bearings, with sudden overload events believed to reduce their expected operational life. The generation of subsurface plasticity, followed by rolling contact fatigue, may lead to the initiation of either surface or subsurface cracking. This study presents a novel technique capable of measuring subsurface strain evolution in a rotating roller bearing, using energy dispersive X-ray diffraction. A pre-overloaded bearing was tested dynamically and consequently failed prematurely, supporting the hypothesis that overloads accelerate bearing failure. Throughout the test, an increase in compressive radial strain was observed, indicative of material softening, generally associated with the unstable stage of rolling contact fatigue, which occurs prior to definitive bearing failure.

Lift monitoring and analysis of multi-storey corridors in buildings

Based on the steel corridor of the first-stage construction for Panzhihua City Government Service Centre, this paper introduces the integral lifting scheme of multi-storey long-span beam grillage steel corridor. To ensure the safety and stability in the lifting process of steel corridor construction and to prevent sudden overload from affecting the later normal use, the finite element simulation of steel corridor before lifting and real-time monitoring during the lifting process were carried out. The results of finite element simulation were compared with the stress and deflection data monitored in real time. It shows that the numerical data obtained from the finite element methods (FEM) are slightly larger than those from the actual monitoring. It follows that the results obtained from FEM for the lifting is safer, the data obtained from FEM and monitoring agree with each other, and, accordingly, the study shows that the monitoring approach is applicable. The integral lifting scheme and monitoring approach presented here can be used as an interesting reference for similar projects. • The integral lifting scheme of multi-storey beam grillage steel corridor is reasonable. • The method of monitoring stress and deflection data is simple and practical. • The remote monitoring system ensures the safety of the monitors. • Deflection monitoring device is a new inventive device. • The monitoring data are in good agreement with the finite element simulation data.

Experimental and theoretical assessment of functional and operational qualities of mechanical protection mechanisms used in safety couplings of drive systems of mining machines

Safety couplings, also called overload couplings, are used to mechanically protect the drive systems of machines – especially mining machines – against sudden overloads. Among these, couplings with shear pins are characterized by the simplest structure. The material and the diameter of the pin is selected by the designer based on the threshold moment at which the shearing should occur. The paper presents a theoretical method of selecting protective pins for specified threshold moment values for a selected Dodge®Raptor series coupling that shall find its application in the drives of mining machines (such as conveyors, crushers, pumps, etc.). Subsequently, a verification of the calculations has been performed by means of an experiment conducted on a special stand. Notable discrepancies between the results of calculations and experiments have been noted. The authors have attempted to explain that fact by testing the hardness of the pins in two planes. Incorrectly performed heat treatment of two batches of pins provided for testing has been discovered.

Mitochondrial Hyperactivation and Enhanced ROS Production are Involved in Toxicity Induced by Oncogenic Kinases Over-Signaling.

Targeted therapy is an effective, rational, and safe approach to solid and hematological tumors treatment. Unfortunately, a significant fraction of patients treated with tyrosine kinase inhibitors (TKI) relapses mainly because of gene amplification, mutations, or other bypass mechanisms. Recently a growing number of papers showed how, in some cases, resistance due to oncogene overexpression may be associated with drug addiction: cells able to proliferate in the presence of high TKI doses become also TKI dependent, undergoing cellular stress, and apoptosis/death upon drug withdrawal. Notably, if a sub-cellular population survives TKI discontinuation it is also partially re-sensitized to the same drug. Thus, it is possible that a subset of patients relapsing upon TKI treatment may benefit from a discontinuous therapeutic schedule. We focused on two different hematologic malignancies, chronic myeloid leukemia (CML) and anaplastic large cell lymphoma (ALCL), both successfully treatable with TKIs. The two models utilized (LAMA and SUP-M2) differed in having oncogene overexpression as the sole cause of drug resistance (CML), or additionally carrying kinase domain mutations (ALCL). In both cases drug withdrawal caused a sudden overload of oncogenic signal, enhanced mitochondria activity, induced the release of a high amount of reactive oxygen species (ROS), and caused genotoxic stress and massive cell death. In LAMA cells (CML) we could rescue the cells from death by partially blocking downstream oncogenic signaling or lowering ROS detrimental effect by adding reduced glutathione.

Mapping of axial plastic zone for roller bearing overloads using neutron transmission imaging

Premature failure of wind turbine gearbox bearings is an ongoing concern for industry, with sudden overload events potentially contributing towards raceway damage, significantly hindering performance. Subsurface stresses generated along a line contact cause material yielding, and a probable crack initiation site. Currently, the ability to study subsurface plastic zone evolution using non-destructive techniques is limited. Neutron Bragg edge imaging is a novel technique, allowing for two-dimensional mapping of the Bragg edge broadening parameter, indicative of bulk plastic deformation. An experiment on the ENGIN-X strain scanning instrument, at the ISIS neutron source, UK, was setup for Bragg edge transmission imaging, to measure the effect of in situ loading on the raceway of a bearing, scaled-down from a traditional wind turbine gearbox bearing. Results demonstrate a strong correlation between load and the Bragg edge width, and allow for future experimental development in studying, not only the effect of overloads on fatigue life, but also the use of neutron imaging for evaluating plastic deformation in engineering components.

Welding assessment of a damaged crane pedestal of a container ship

A structural integrity assessment of a damaged crane pedestal/column of a container ship is presented. Crane cabins and pedestal/columns are subjected to fatigue coupled with sudden overloads during cargo operations and corrosion effects due to sea environment. Significant number of surface cracks was detected around the pedestal/column, at inner and outside of the crane foundation, close to the main weld seam and, in consequence, the ship-owner ordered a survey. The main weld seam and the sites where cracks were found are evaluated in the present study. For the purpose, the sample material (hot rolled steel plate and upper ring) of the pedestal was provided by the shipyard and macro and micrographics were observed. Results did not show any cracks, although they have been found by the NDT technical services of the shipyard which have decided to remove them by the grinding process. The weld seam did not also show relevant defects, whereby the replacing of the pedestal/column by a new one would not had been necessary. Regardless of some occasional overloads, the surface cracks found on the pedestal/column could be a consequence of the normal operation conditions of the crane during the last 5 years and also due to poor maintenance.

Improvement of the feed system of the coal combine by means of load forecasting

This article presents the consideration of the methods of increasing effectiveness of protection against overloads of electric drives and executive bodies of the booty combine with outrigger feed system. The main purpose of the study is validation the ways to improve efficiency protection against sudden overloads and improving the dynamic properties of the outrigger feed system. It is developed a computer simulation of transient processes in outrigger feed system and it is shown the process of formation of dynamic overloads on the executive bodies of the booty combine. It is justified ways of improving transient towards decrease dynamic overloads. For this purpose it is proposed the use of preliminary smooth decrease feed rate before the abrupt change of the mechanical properties of the mine for a period of 2 to 5 seconds. Further research may focus on the justification of the methods of analysis of the mechanical properties of the mine and the parameters of the system software load control combine with outrigger feed system.

Microplane damage model for fatigue of quasibrittle materials: Sub-critical crack growth, lifetime and residual strength

In contrast to metals and fine grained ceramics, fatigue in concrete and other quasibrittle materials occurs in a large fracture process zone that is not negligible compared to the structure size. This causes the fatigue to be combined with triaxial softening damage whose localization is governed by a finite material characteristic length. A realistic model applicable to both has apparently not yet been developed and is the goal of this paper. Microplane model M7, shown previously to capture well the nonlinear triaxial behavior of concrete under a great variety of loadings paths, is extended by incorporating a new law for hysteresis and fatigue degradation, which is formulated as a function of the length of the path of the inelastic volumetric strain in the strain space. The crack band model, whose band width represents a material characteristic length preventing spurious localization, is used to simulate propagation of the fatigue fracture process zone. Thus the fatigue crack with its wide and long process zone is simulated as a damage band of a finite width. For constant amplitude cycles, the model is shown to reproduce well, up to several thousands of cycles, the Paris law behavior with a high exponent previously identified for concrete and ceramics, but with a crack growth rate depending on the structure size. Good agreement with the crack growth histories and lifetimes previously measured on three-point bend beams of normal and high strength concretes is demonstrated. The calculated compliance evolution of the specimens also matches the previous experiments. The model can be applied to load cycles of varying amplitude, to residual strength under sudden overload and damage under nonproportional strain tensor variation. Application to size effect in fatigue is relegated to a follow-up paper, while a cycle-jump algorithm for extrapolation high-cycle fatigue with millions of cycles remains to be researched.

Investigation of Compressor Failure in a Military Turbojet Engine

During altitude maneuver loud bang sound was observed followed by rapid winding down of engine rotation and jet pipe temperature. Compressor casing top half was found severely ruptured and broken into many pieces. On viewing through the ruptured area compressor rotor blades were found sheared at the root. Systematic investigation revealed that the failure of compressor casing was due to sudden overload. Analyzing the possible reasons of sudden overload it could be concluded that the rupture of compressor casing was most probably due to surge during the maneuvers. Remedial measures are suggested to address such failures.

Analysis of abnormal fatigue failure of forklift forks

The analysis of an abnormal failure of forklift forks is presented in this work. The investigation results suggested that failure occurred due to fatigue mechanism followed by sudden overload fracture. The orientation of fatigue fracture indicates abnormal lifting operation, favouring crack initiation from outer fork area which is the compression designed zone. Moreover, various surface flaws and weakness areas (such as surface marks, decarburized microstructures and weld zones) identified on the outer fork zone, compromise fatigue strength inducing premature crack nucleation and fast growth towards final failure.

Adaptive admission control algorithm in a QoS-aware Web system

Internet traffic tends to show significant growth of demand at certain times of the day, or in response to special events. The consequence of these traffic peaks is that Web systems that are responding to user demands are congested due to their inability to serve a large volume of requests. The case for admission control in these situations is even stronger when Quality of Service (QoS) is considered as a primary objective in the Web system. In this work, we address two issues: on one hand, we consider and compare five throughput predictors to be used in a Web system in order to track its performance and, on the other hand, we propose a QoS-aware admission control and load balancing algorithm that prevents the Web system from sudden overload. The admission control algorithm is based on a resource allocation scheme that includes a throughput predictor. In order to obtain a low overhead, the monitoring of traffic arriving at the Web system is performed following an adaptive time slot scheduling based on the burstiness factor that we defined in previous work. Results show the benefits of our adaptive time slot scheduling compared to a fixed time scheduling. A discussion of the results of the five throughput predictors and the admission control algorithm is provided. We also compare the performance of our algorithm with Intelligent Queue-based Request Dispatcher (IQRD). The algorithm is designed to be included in a Web system composed by a set of Web servers distributed locally, which can also form part of a wider geographically distributed load balancing architecture.