Determination of Residual Fatigue Life of Welded Structures at Bucket-Wheel Excavators through the Use of Fracture Mechanics

This paper presents a methodological approach for the assessment of service life of vital welded structures of a bucket-wheel excavator Sch Rs 650/5x24 ('Thyssen Krupp', Germany) boom, subjected to cyclic loading with a variable amplitude through the use of experimental tests carried out in order to determine operational strength and growth of a fatigue crack. Realized researches and results presented in this paper offer great possibilities for the analyses of behaviour of vital welded structures of the bucket-wheel boom. By the application of the measurement device with 8 channels for registration and processing of electric signals HBM Spider 8 and measurement tapes HBM 6/350xXY31 deformations were measured at vital welded structures of the boom in the area of the bucket-wheel, made of steels St 37.2 and St 52.3 in accordance with standard DIN 17100, or steels S235J2G3 and S355J2G3 in accordance with standard EN 10025-2. The objective of the test is to determine if there is a possibility of occurrence of plastic deformations or initial cracks due to fatigue at vital welded structures. Tests that refer to the growth of the fatigue crack located at the welded joint have been carried out by bending at three points with asymmetric load R = 0.5 (R = sigma(min) / sigma(max)) at the specimen with a single edge notch. Tests were performed through the use of controlled force, ranging between F-max and F-min at the high frequency pulsator 'Cracktronic', while obtainment of data regarding the crack growth was carried out through the use of measurement gauge ARM A-10

Analysis of welding of the rear bridge semi-housing assembly of a firefighter truck by the semi-automatic procedure in gas protection

The problem considered in this paper is the welding technology of the steel assembly of a firefighter truck rear bridge semi-housing. Since in this procedure the welding is done of the two dissimilar steels, it is necessary to analyze effects of welding on mechanical properties and microstructure of individual joint's zones. The weldability of the base metal was considered first (semi-housing tube and flange), then the welding method and the filler metal were selected and, finally, the technological parameters of welding were calculated. The computational and experimental methods were used for the base metal weldability estimate, based on the hardness measurements in the joint's critical zones and analysis of their structures. Experimental investigations performed were aimed for verification and/or eventual correction of the proposed welding technology

Analysis of welding of the rear bridge semi-housing assembly of a firefighter truck by the semi-automatic procedure in gas protection

The problem considered in this paper is the welding technology of the steel assembly of a firefighter truck rear bridge semi-housing. Since in this procedure the welding is done of the two dissimilar steels, it is necessary to analyze effects of welding on mechanical properties and microstructure of individual joint's zones. The weldability of the base metal was considered first (semi-housing tube and flange), then the welding method and the filler metal were selected and, finally, the technological parameters of welding were calculated. The computational and experimental methods were used for the base metal weldability estimate, based on the hardness measurements in the joint's critical zones and analysis of their structures. Experimental investigations performed were aimed for verification and/or eventual correction of the proposed welding technology

The correlation of the organization of activities and walk disorders stroke patients

Мождани удар је клинички синдром васкуларне етиологије који се карактерише наглим настанком фокалног или глобалног можданог дефицита, који траје дуже од 24 сата или завршава смртним исходом. Подаци Светске здравствене организације говоре да је и поред дијагностичких и терапијских могућности, мождани удар болест на трећем месту узрока смртности у свету (иза кардиоваскуларних и малигних), а на другом месту узрока функционалне онеспособљености. Око 50% свих преживелих, активностима дневног живота се врати 30%, док 20-30% није способно да самостално функционише. Степен функционалне онеспособљености се креће од лаког (35,8%); средње тешког (23,3%); тешког (30,9%). Имајући у виду постојећу статистику, сасвим је разумљива улога и значај медицинске рехабилитације. Рехабилитација болесника после можданог удара је комплексан и мултидимензионални проблем. Предпоставља се да постоји условљеност квалитета моторног опоравка и функционалног оспособљавања са степеном очуваности когнитивних функција. Способност планирања и организација активности као когнитивна особина којом ће бити спроведене намере и остварен циљ, представља највиши ниво функционисања фронталних режњева. Предмет нашег истраживања је био испитивање корелације способности организације активности и пажње и поремећаја хода после можданог удара и у каквој је вези тај однос са постизањем функционалне независности болесника. У оквиру циља истраживања анализиран је однос између нивоа способности организације активности и пажње и поремећаја хода код болесника после можданог удара; између способности организације активности и пажње и функционалног оспособњавања болесника после можданог удара; између поремећаја хода и функционалног оспособљавања болесника после можданог удара. Испитани узорак чинило је 50 болесника после можданог удара, укључених у процес рехабилитације и 50 испитаника одабраних методом случајног узорка, усклађених према старосној доби, који у својој анамнези немају дијагностикована неуролошка обољења...A stroke is a clinical syndrome of vascular ethiology characterized by a fast occurence of the focal or global brain deficit which lasts more than 24 hours or ends up with a death outcome. World Health Organization information says that, although there are both diagnostic and therapeutic options, a stroke is the third frequent cause of death in the world (after cardiovascular and malignant diseases), and the second frequent cause of functional disabilities. About 50% of those who survive, 30% return to daily life routines, while 20-30% are not capable of functioning on their own. The level of functional disability ranges from light (35.8%), medium hard (23.3%) to hard (30.9%). Bearing in mind the existing statistics, the role and importance of medical rehabilitation is quite understandable. Patient rehabilitation after a stroke is a complex and multidimensional problem. It is assumed that the relation between the quality of motor recovery and functional capability of cognitive functions is preconditioned. The ability of planning and organization of activities as a cognitive characteristic with which an intention will be carried out and the aim accomplished represents the highest level of frontal lobes functioning. The subject of our study was the examination of correlation ability of the organization of activity and attention and walk disorders after a stroke and how that relation can influence the recovery process and achieving the functional independence of a patient. Within the aim of the research, the relation between the levels of organization activities and attention and walk disorders at patients after a stroke has been analysed; between the ability of organization of activities and attention and functional recovery of patients after a stroke; between the walk disorders and functional recovery of patients after a stroke. The examined sample consisted of 50 patients after a stroke, included in the rehabilitation process and 50 patients chosen by accident, according to their age, who do not have diagnosed neurological diseases. The tests for the evaluation of executive functions, attention, cognitive state, the tests for the evaluation of motor functions including the evaluation of all gait parameters and the test for the evaluation of functional abilities have been used in the paper. The results were analysed in relation to the qualitative test parametres, as well as from the aspect of the existing knowledge in the scientific field which deals with the patient rehabilitation after a stroke..

The influence of heat input on the toughness and fracture mechanism of surface weld metal

Surface welding is a way to extend the exploitation life of damaged parts and constructions and the heat input has a major influence on the weldment properties. In this paper is shown the influence of the heat input on the toughness and the fracture mechanism of the surface welded joint. Surface welding of high carbon steel with self shielded wire was conducted with three different heat inputs (6kJ/cm, 10 kJ/cm and 16 kJ/cm). Total impact energy, crack initiation and crack propagation energy were estimated at room temperature, -20 degrees C and -40 degrees C. Fracture analysis of fractured surfaces was also conducted and it has been found that increasing of heat input leads to an increase of share of transgranular brittle fracture, what is in complete accordance with the obtained energy values. Based on all obtained results, the optimum value of heat input for welding procedure applied was defined

Failure Analysis of the Stacker Crawler Chain Link

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

Failure Analysis of the Tower Crane Counterjib

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 (x1425C) counteijib. The crane is used for assembly works at the hydropower dam. The counteijib 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

Effect of locally damaged elbow segments on the integrity and reliability of the heating system

This paper presents the integrity and reliability evaluation of the heating system as a whole, based on results of metallographic tests performed on parent material and the ultrasonic measurement of wall thickness of elbows made of steel St 35.8

Determination of damage and repair methodology for the runner manhole of Kaplan turbine at the hydro power plant 'Djerdap 1'

Results of non-destructive testing of the Kaplan turbine runner manhole welded structure are presented, on the basis of which the repair methodology is defined. During repair, the welding technology for elements of the manhole is modified along with the proposal given for the modification of its structural design, because the finite element method calculation proved that the rectangular welded structure of the manhole was significantly better than round welded structure when it comes to integrity and service life

Failure Analysis of the Tower Crane Counterjib

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 (x1425C) counteijib. The crane is used for assembly works at the hydropower dam. The counteijib 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