Peter Sivák

Influence of Material Structure and its Properties on Predicting Life of Pressure Pipelines

Pressure pipelines belong to the group of technological carrying structures that are designed in accordance with Standard Eurocode 3: STN EN 1993: Design of steel structures. These standards are used also later in the stage for assessment of failure states and fatigue life. Standard Eurocode 3: STN EN 1993-4-3 establishes the requirements for material properties of pipes and welds, associated with mechanical properties. A serious problem in estimating fatigue life of structure is the consideration of gradual degradation. The article also discusses the analysis of fatigue failure of the pressure pipeline, where it was found that the initiation of fatigue failure occurred in the area of poor weld. The further spread of the crack then occurred in the base material of the pipeline.

Operational Safety of Compressor Station Pipeline

Failure of pipeline system can endanger human lives and cause serious damage; therefore it is necessary to check it in terms of strength and life reliability. Inspection was performed on compressor station pipeline, where in terms of resistance to brittle failure it was discovered, that the weakest point of the pipeline is the weld. At lower temperatures danger of brittle failure of weld joint can arise. To assess the strength of the pipeline in investigated cross-section, with respect to state of plane stress, strength theories were applied. Values of reduced stresses were assigned based on main normal stresses resulting from experimentally set components of state of plane stress. Fatigue assessment was done, based on currently valid standards.

The Fatigue Fracture Caused by a Random Operating Process

The whole structures, mostly the structural nodes or elements work in time-varied stress instead of the static one. The stress concentrators are such changes of shape of mechanical part which evoke the changes of force flow. They influence the stress which loads this part. The risk of fatigue damage concerns structural components, structural knots and even whole structures subjected to random loading. This can initiate the accumulation of fatigue damage in critical points of the structure, growth and spreading of fatigue cracks and, eventually, fatigue fracture. Final failure of structural components may have fatal consequences. Damage and fatigue failure may occur due to a combination of cyclical stress and improper technology for producing a structural element, e.g. during welding. These failures are documented on the example of the holder of a crusher moving knife and of the turbine rotor shaft.

Analysis of Sandwich Structures by the FEM

The use of sandwich structures is increasing rapidly. This paper is aimed on mechanical properties of sandwich structured composites and their usage in technical practice. The main contribution in paper is realized static analysis of simple sandwiches composed from various materials of core and face sheets. Final results of analysis were fields of data about maximum stresses, displacement fields of structural points of sandwich composite.

Selection of a Significant Numerical Model of Plasticity for the Purpose of Numerical Analysis of Plastic Reinforcement

The paper is focused on the process of selecting a suitable material plasticity model. Such a model would be used in the future numerical analysis of the behaviour of selected structural elements in the elastic-plastic deformation of the steel in the SolidWorks software environment. These analyzes should include monitoring the behaviour of the material under the conditions of its plastic reinforcement (strain - hardening). Numerical modelling used two models of plasticity, namely the von Mises and Trescas models. Subsequently, a comparison of the match between the real load-deformation diagram, possibly stress-strain diagram, obtained by the experimental static tensile test and the diagram obtained from the numerical simulation of two different steel-based structural materials was performed. The results of the dual tensile test analysis showed that the von Mises model achieves greater consistency with the tensile curve based the actual tensile test. Therefore, this model will be later used in subsequent numerical simulations of the material under the conditions of its plastic reinforcement.

Dynamic Analysis of Lathe Machine Tool

The thesis presents a theoretical analysis of the task, while practical knowledge of selected parts of the dynamics is used to solve individual involved transfers. Further for the two types of programs includes detailed diagrams that is rev/min (rpm) increasing and rev/min reduction. The centre lathe is the object of exploring. Specifically transmission parts such as shafts, gears and pulleys then it is electric drive device, and finally driven parts such as spindle and chuck. Analyze of angular velocities, moments of inertia, kinetic energy, performance and labor of each part of the kit is performed using reduction method, and the system is reduced to a first member, which is an electric motor. We have developed integration of individual gears for the machining modes. Specifically for conventional turning 2800 rpm and for winding springs 14 rpm. In technical practice it is not possible to measure two same results of performance parameters, for reason of passive resistance.

Applying of Stress Collectives in the Design of Structural Elements of Heavy Load-Bearing Structures

The article deals with the analytical-experimental means of determining the rate, respectively, the degree of fatigue damage for the analysis of limit state of main supporting structural element of the main beam on the twin beam of the bridge crane. Taken into account it is the dynamic effect of load hoisting and the application of load collectives and the position of the crane crab obtained experimentally for the development of stress collectives. In this analysis, the expression of the link between random load process and fatigue properties of material the Palmgren-Miner linear theory on fatigue damage accumulation was applied.

Use of FEM in Identification of Stress in Place of Concentration Factor

Stress concentrators are sudden changes of shape of mechanic part, which evoke changes of force flow, so they influence tensions, which load this part. The same goes for the static or the cyclic loading. The notches which are on the surfaces of various components increase the stress. Such kind of stress creates instability and weakening of the component. However, it is possible to reduce that influence by adding such notches which are spaced apart in some distance.

Experimental and Numerical Analysis of the Damage Causes of Rail Traction Vehicles

This paper presents the results of the investigation of the causes of the occurrence and the influence of the dynamic effects in the couplers of the remotely controlled electric shunting locomotives and a set of fully loaded rail cars. These are typical rail-road sets, working at the logistic area of the central ore trans-shipment of large steelworks with heavy rail traffic. The stated effects lead to excessive deterioration of the supporting structure of the locomotives, axle gripping, drive mechanisms and braking systems. To achieve the desired goal, the methods and means of numerical and experimental modelling have been used. Based on the performed numerical and experimental analyses were then specified the recommended design and operational measures to prevent the failures mentioned above.

Analysis of Stresses and Deformations in Container with Flat Bottom

There is a general condition of the stress created by superficial forces in praxis. It can be also simplified when the shifting the forces and bending torques are equal to zero, or we can ignore them because they are too low. In term of draft it is just a condition which has the best result when the material for the construction is exploited. The edge of the cylindrical container failures are the differential base for the axisymmetric shell within an internal pressure. That main point of that contribution is the effect of the internal load and the bending effects to joining pressure of the slice cylindrical part and the plate bottom.