Evaluation of large-scale load-carrying structures of machines with the application of the dynamic effects factor
(*) Tekst artykułu w polskiej wersji językowej dostępny w elektronicznym wydaniu kwartalnika na stronie www.ein.org.pl in the construction industry which are usually designed to transfer only static loads and thus only need to fulfill the ultimate strength requirement. Dynamic loads accelerate the progressing degradation of the load-carrying structure, which is manifested in an increasing number of fatigue cracks. Fig 1 shows an example of a fracture and its location. Such faults are difficult to spot and if the fracture is located in a critical area, it can grow uncontrollably and lead to a catastrophic failure. A fracture similar to the one in Fig. 1 caused the catastrophe of the KWK 1400 excavator (Fig. 2). Such load-carrying structures are most often found in the mining, rock processing or bulk material handling industry. The situation in this case is even more special because some of the basic technological processes (e.g. excavating, crushing) are very often subject to large dynamic loads [15, 16]. Due to the environment in which such machines most often operate, it is difficult to use solutions that are effective at reducing vibrations but are not susceptible to damage [2, 48]. In addition, the design of load-carrying structure can be prone to excitation [7,17] (e.g. long-span superstructures of surface mining machines). Such machines are still being designed in accordance with standards from the 1980s, which define the dynamic effects factor, which, in turn, is used in calculations of fatigue life. Both the definition of this factor and its assumed values, in accordance with the standards, do not reflect the actual operating conditions. This is manifested in the occurrence of numerous cracks in superstructures [1, 12, 37] and undercarriage structures[1, 4, 13, 46]. Over the years several studies have been carried out aimed at solving this problem
Selected Aspects of Technical Condition State Assessment of Spreaders Operating in Lignite Mines
On the basis of spreader A2RsB 15400 the method for technical condition state assessment of machines, after many year of operation, in lignite mines is presented. In purpose to identify the structure hot spots and cracks, both numerical and experimental methods were applied. Additionally, the dynamic behavior of the structure was assessed with use of the experimental methods. The paper presents the meaningful results chosen from the assessment procedure.
Fatigue effects on the coordinative pattern during cycling: kinetics and kinematics evaluation.
The aim of the present study was to analyze the net joint moment distribution, joint forces and kinematics during cycling to exhaustion. Right pedal forces and lower limb kinematics of ten cyclists were measured throughout a fatigue cycling test at 100% of PO(MAX). The absolute net joint moments, resultant force and kinematics were calculated for the hip, knee and ankle joint through inverse dynamics. The contribution of each joint to the total net joint moments was computed. Decreased pedaling cadence was observed followed by a decreased ankle moment contribution to the total joint moments in the end of the test. The total absolute joint moment, and the hip and knee moments has also increased with fatigue. Resultant force was increased, while kinematics has changed in the end of the test for hip, knee and ankle joints. Reduced ankle contribution to the total absolute joint moment combined with higher ankle force and changes in kinematics has indicated a different mechanical function for this joint. Kinetics and kinematics changes observed at hip and knee joint was expected due to their function as power sources. Kinematics changes would be explained as an attempt to overcome decreased contractile properties of muscles during fatigue.