Buckets are a vital substructure of all digging machines, and are intended for the realisation of the fundamental machine function - soil excavation. This paper presents the results of the ...experimental-numerical investigation of the cause of the bucket wheel excavator SRs 470 buckets failure. The chemical composition and mechanical properties, the impact toughness, hardness, tendency to cracks and the microstructure were determined using appropriate tests. Experimental examinations of working and residual stresses were performed using strain gauges. The superposition of the experimentally determined working and residual stresses and the calculation of the total principal stresses were conducted using the originally developed procedure presented in this paper. The bucket working stress state was calculated by applying the linear finite element method. Conclusions based on the investigation results show that the main reasons for the buckets failure were the ‘design-in defects’ - oversights made during the procedures of geometrical shaping and material selection. Furthermore, high values of residual stresses, as well as the cold cracking observed on the welded joint of the knife and the bucket body, suggest that the ‘manufacturing-in defects’ also played a significant role in the failure. The superposition of influences of the ‘design-in defects’ and the ‘manufacturing-in defects’ has conditioned the appearance and propagation of long-term fatigue cracks, leading to the total destruction of the buckets. The fact that buckets' failure appeared due to oversights made during geometrical shaping, material selection and manufacturing further points to the importance of the critical approach implementation during the design phase of the earthmoving machines working devices.
•We analysed the causes of buckets fractures.•Results of experimental and numerical investigations are discussed.•Superposition method of experimentally determined stresses is developed.•The ‘design-in’ as well as ‘manufacturing-in’ defects are dominant fracture causes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The bucket wheel boom tie-rods are vital structural parts of the bucket wheel excavators (BWE). Their failures inevitably cause BWE collapse and are followed, among other things, by a substantial ...financial loss (millions of €). Non-destructive testing revealed a flaw in the butt welded joint of the body and eye-plate of the bucket wheel tie-rod. Its size exceeds the level allowed by current technical regulations. An integrity assessment of the bucket wheel tie-rod has been carried out, i.e. the remaining fatigue life has been determined based on the stress-state characteristics in the welded joint and defined by experimental research in real working conditions. The calculation results show that despite the excessive size of the internal flaw the welded joint integrity is not compromised. During periodical inspections of the welded joint in the past two years (BWE was put into operation in December 2007) changes that could compromise the structural integrity were not observed. In this way, by using a “fail-safe” philosophy design, a considerable financial saving (ca. 1,600,000 €) was achieved while at the same time there was no threat to the worker’s safety and life, the safety of the machine and the production process in the open pit mine.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
► The original procedure of wheel static overstressing is presented. ► Calculated contact stress level exceeds the permissible values. ► Material tensile and impact properties were lower than ...required. ► Primary heat treatment was done on too high a temperature. ► Damages were caused by ‘designing-in’ and ‘manufacturing-in’ defects.
The superstructure of the ARs 2000 spreader leans on three crawlers of identical length, width and height. Serious damage to the track wheels threads occurred already during the spreader’s travel from the erection site to the open pit mine as well as immediately after the overburden system exploitation started. The goal of the study presented in this paper was to diagnose the cause of the track wheels premature damage. Contact stresses on the track wheel bearing surface are defined by applying Hertz’s theory and FEM. In order to clarify the causes of the damages, experimental investigations were performed with the purpose of defining the chemical composition, tensile properties, impact toughness and macro and microhardness of the track wheel material. Metallographic examinations were also conducted. Based on the results of the analytical–numerical–experimental analysis, it can be concluded that track wheels failures are predominantly caused by the ‘design-in’ and ‘manufacturing-in’ defects.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Failures of the cranes’ structural parts unavoidably lead to serious damages or total collapses; these accidents are often followed by very high financial losses and possibly serious injuries or ...crane-related fatalities. The objective of this research was to identify the causes that led to the failure of the hammerhead tower crane (xl425C) counterjib. The crane is used for assembly works at the hydropower dam. The counterjib collapse resulted from a gusset plate failure and caused such significant damage of the whole crane structure that the crane was dismantled and removed from operation. The study of the accident includes: (1) Identification of the stress-state, where a FEM model is developed to provide a useful tool for studying stress analysis; (2) Laboratory investigations are conducted in order to define the chemical composition and mechanical properties of the material, the tensile properties, hardness, impact toughness, as well as the metallographic analyses. The analysis of the obtained results showed that the principal reasons behind the gusset plate failure originated from design and fabrication faults. The working stress was higher than the allowable one. Also, impact toughness was too low and the fabrication of welds was incorrect.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Stacker ARs 2000 presents the final link in the system for continuous overburden removal in the open pit mine “Kostolac” – Serbia. Its superstructure leans on three crawlers of the same length, width ...and height. During the stacker's travel from the erection site to the open pit mine, three crawler chain links fractured, presenting an indication of the problems that were to occur during exploitation. In fact, after only 1000 working hours (about three months), 30 chain links sustained fractures resulting in direct and indirect costs due to the downtime that substantially diminished the effects of the overburden removal system. The goal of the study presented in the paper was to diagnose the cause of chain link breakdown occurrence. Working stresses in the chain link are defined by applying FEM. Experimental investigations define the chemical composition, the tensile properties, the impact toughness and the macro and microhardness. Metallographic examinations are conducted additionally. Based on the results of the numerical-experimental analysis, it can be concluded that chain link breakdown is predominantly caused by (a) substantial deviation of the mechanical properties of the material with respect to those prescribed by the standard and (b) the existence of macro and microcracks in the material structure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Mining, construction, and other special vehicles for heavy use are designed to work under high-performance and off-road working conditions. The driving and executive mechanisms of the support ...structures and superstructures of these vehicles frequently operate under high loads. Such high loads place the equipment under constant risk of an accident and can jeopardize the dynamic stability of the machinery. An experimental investigation was conducted on a refuse collection vehicle. The aim of this research was to determine the working conditions of a real vehicle: the kinematics of the waste container, that is, a hydraulic rotate drum for waste collection; the dynamics of the load manipulator (superstructure); the vibrations of the vehicle mass; and the strain (stress) of the elements responsible for the supporting structure. For an examination of the force (weight) on the rear axle of a heavy vehicle, caused by its own weight and additional load, a universal measurement system is proposed. As a result of this investigation, we propose an alternative system for continuous vehicle weighing during waste collection while in motion, that is, an on-board weighing system, and provide suggestions for measuring equipment designs.
A 26-year-old woman had a masticatory dysfunction, straight profile, retrognathic maxilla and mandible, and Angle’s class I with a tendency to class III malocclusion on both sides, with bilateral ...posterior crossbites and a 4 mm anterior open bite. Orthognathic surgery and orthodontic camouflage with and without tooth extraction were considered as treatment options. The patient’s preferred method of treatment was orthodontic camouflage without extraction. The transpalatal arch had been placed for the bilateral molars’ derotation. After 3 months, the upper segmented fixed appliance was implanted to address the posterior crossbites in the premolar’s region. One mini-implant was inserted into the anterior palatum after the transpalatal arch was removed, and a supporting device was attached to the first permanent molars to give indirect skeletal stability. Orthodontic treatment’s active phase lasted 23 months, and all treatment objectives were achieved during that time: the desired facial profile, adequate occlusion, appropriate overbite, and overjet.
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CMK, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Loads at vital steel structures occur during their production and assembly (residual stresses), during the execution of functional tasks in exploitation (stationary and dynamic loads) and during the ...disturbed process of exploitation (non-stationary dynamic loads). Considering the fact that stress concentrators, corrosion and unpredictable effects that occur during exploitation must be taken into account as well, it is clear that loading of vital structures during the design phase can not be represented with a model in which the parameters change uniformly. Therefore only experimental non-destructive tests performed at large steel structures during exploitation enable the assessment of their current condition, need for particular repairs and assessment of integrity. In that way the data necessary for determination of causes of degradation of material and welded joints at structures, for the evaluation of mutual influence of equipment parts, as well as for determination of functionality and reliability of operation of drive systems. This primarily refers to vital steel structures of bucket-wheel excavators, dredgers and cranes, as well as to vital steel structures at hydroelectric equipment, thermal power plant equipment, bridges etc. This paper presents the analysis of causes for the occurrence of damages at the support structure of the boom of the bucket-wheel excavator, which is operating at the open pit coal mine near Kostolac (Serbia), that was executed on the basis of non-destructive tests. The paper also contains the procedure for the repair of damaged structure through the application of adequate welding, performed at existing and newly produced components, and the assessment of structural integrity after the repair based on non-compliances detected during the design process, as well as during the making of the support structure of the bucket-wheel excavator boom due to inadequate radiuses defined during the processes of design and production and due to the existence of flaws on the surface and within welded joints.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Visual short-term memory (VSTM) is defined as the ability to remember a small amount of visual information, such as colors and shapes, during a short period of time. VSTM is a part of short-term ...memory, which can hold information up to 30 seconds. In this paper, we present the results of research where we classified the data gathered by using an electroencephalogram (EEG) during a VSTM experiment. The experiment was performed with 12 participants that were required to remember as many details as possible from the two images, displayed for 1 minute. The first assessment was done in an isolated environment, while the second assessment was done in front of the other participants, in order to increase the stress of the examinee. The classification of the EEG data was done by using four algorithms: Naive Bayes, support vector, KNN, and random forest. The results obtained show that AI-based classification could be successfully used in the proposed way, since we were able to correctly classify the order of the images presented 90.12% of the time and type of the displayed image 90.51% of the time.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Increased temperature risk in cities threatens the health and well-being of urban population and is fueled by climate change and intensive urbanization. Consequently, further steps must be taken for ...assessing temperature conditions in cities and their association with public health, in order to improve public health prevention at local or regional level. This study contributes to solving the problems by analyzing the connection between extreme temperatures and the tendencies of all-cause hospital admissions. The analyses used (a) 1-h air temperature data, and (b) daily data of all-cause hospital admissions. The datasets include the summer period (June, July, August) for the years 2016 and 2017. We tested the effects of two temperature indices, day-to-day change in maximum temperature —
T
max,c
and daily temperature range —
T
r
, with all-cause hospital admission subgroups, such as all-cause cases —
H
a
, hospital admissions in the population below 65 —
H
a
<65, and hospital admissions in the population aged 65 and over —
H
a
≥65. The results show the highest values of
H
a
when
T
max,c
is between 6 and 10 °C. Therefore, more intensive hospital admissions can be expected when
T
max
increases from day-to-day (positive values of
T
max,c
), and it is more visible for
H
a
and
H
a
<65 (1 °C = 1% increase in hospital admissions). Also,
T
r
values between 10 °C and 14 °C cause an increase in the number of hospital admissions, and it is more noticeable for
H
a
≥65.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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