The Crack Growth in the Imitation Model of a GTE Turbine Disk under Operating Loading Conditions

The paper presents the experimental results of growing surface cracks in the turbine disk of a gas turbine engine (GTE) under cyclic tension at room and elevated temperatures. The geometry of the imitation model of the GTE turbine disk with a stress concentration zone in the form of a bolt hole was justified. In order to ensure the similarity of the initial damage of the imitation model and the GTE turbine disc in the plane of symmetry of the stress concentration zone, a semi-elliptical notch was made. The loading conditions of the imitation model were developed based on results of a comparative stress-strain state (SSS) analysis of the stress concentration zone of the imitation model and the GTE turbine disc. As a result of the fatigue test of the imitation model at room and elevated temperatures, the experimental positions and sizes of the crack fronts with respect to the drop potential signal on the crack edges were obtained. The fixed positions and sizes of the crack fronts were used as the basis for the numerical calculation of the fracture resistance parameters. For the numerical studies, ten three-dimensional finite element models with different positions and sizes of the crack fronts were considered. The numerical calculation results based on the finite element method were used to determine the distributions of the elastic stress intensity factors along each crack front. The crack growth rate characteristics both on the free surface and at the deepest point of the crack front were obtained at room and elevated temperature conditions. A technique for the automation tests that simulate the block-type loading of the disk material at elevated temperatures was proposed.

Improvement of Gas Drainage Efficiency via Optimization of Sealing Depth of Cross-Measure Boreholes

The sealing depth of a gas-drainage borehole is critically important as it directly affects the efficiency of the whole drainage system. In order to determine the shortest reasonable sealing depth, in this paper, a theoretical drainage model using different sealing depths was proposed. Based on theoretical analysis presented, two parts of the fractures system surrounding the drainage borehole were proposed, i.e. the fractures induced by roadway excavation and the fractures induced by borehole drilling. A series of geological in-situ tests and simulations research were conducted to determine the stress and fracture distributions in the surrounding rock of the borehole. The depths of crushing zones, plastic zones and stress concentration zones were determined as 5 m, 2 m and 12 m, respectively. Meanwhile, stress simulation shows that the depth of the stress concentration zone was 12 m from the roadway wall and the stress peak was located at the depth of 8 m, which can be verified by the results of drilling penetration velocity analysis. To determine the optimum sealing depth, gas drainage holes with different sealing depths were drilled in the field. The field results revealed that the crushing zones were the main area for air leakage, and the stress concentration induced by roadway excavation assisted in the reduction of air leakage. Therefore, the optimized sealing depth should both cover the plastic zone and the stress concentration zone. The research achievements can provide a quantitative method for the determination of optimum sealing depth in cross-measure drainage boreholes.

Analysis of Cumulative Damage for Shared Rock in a Neighborhood Tunnel under Cyclic Blasting Loading Using the Ultrasonic Test

In blasting excavation of neighborhood tunnels, damage accumulation process in surrounding rock is inevitable. To explore the influence of damage accumulation of rock mass under multiple blasting loads, we analyzed the vibration damage accumulation process of ultrasonic wave velocity of rock mass in shared rock of Liuyuetian neighborhood tunnel through ultrasonic test. Moreover, the effects of cyclic blasting loads on damage to the shared rock in the neighborhood tunnel were discussed and reported. The results demonstrate that the damage accumulation to the shared rock in the neighborhood tunnel is generated after multicycle progressive blasting operations. Influenced by cyclic blasting loads during the posterior excavating tunnel, the damage range of shared rock at the anterior excavating tunnel is 1.2 to 1.4 m, and the damage range of shared rock at the posterior excavating tunnel is 2.2 to 2.4 m. The damage range of shared rock in the posterior excavating tunnel is about 1.71 to 1.83 times that in the anterior excavating tunnel. Under blasting load, the stress concentration zone of shared rock is close to the blasting excavating face and is mainly within 2 m along the longitudinal axis of the tunnel. With continuous advancement of the blasting excavating face, the stress concentration zone moves forward continuously, and a striped stress concentration zone, which is approximately 2 m deep, is formed gradually. Thus, a method was proposed to determine the damage range of shared rock in the neighborhood tunnel during blasting excavation, as well as the variation law of damage. The experiences and conclusions presented can be used as references in the design and construction of similar engineering projects in the future.

Detection of high stress concentration zone using magnetic flux leakage method

PurposeA tower crane mainly ensures the success or efficiency of building construction. Fatigue crack analysis is important for tower crane components to prevent any accidents to workers in construction sites caused by component failure and to ease the maintenance or replacement of failed components. This work aimed to characterise the damage of failed components, analyse the relationship between the metal magnetic memory (MMM) result and the damage of failed components, and to validate the relationship between MMM and finite element analysis (FEA).Design/methodology/approachMMM was used in this work to detect any irregularities or early failure on the basis of the high stress concentration zone of ferromagnetic steel using magnetic flux leakage. Magnetic flux leakage was used on the MMM device to achieve the first objective using the MMM system by detecting the irregularities. The results of MMM analysis were validated through comparison with FEA results by determining their relationship.FindingsMMM results show that the position of defects on the tower crane pulley is within the stress area shown on FEA.Originality/valueHence, MMM method is a potential tool in monitoring failure mechanism in construction site.

Methodical approach for studying kinetics of short and long fatigue cracks growth for irradiated reactor materials. Part 1. Statement of problem. The effect of the initial notch acuity on the fatigue crack rate on small-sized specimens

The paper considers methodical issues in the experimental research of fatigue crack growth kinetics when testing irradiated small-sized specimens. The effect of the initial notch acuity is studied on the long crack growth rate. The stress concentration zone sizes are estimated for notches of various types. A brif literature review of the main problems in the study of the growth kinetics of short fatigue cracks has been performed. The tasks of further research are formulated.

Working capacity of aluminum alloys in structure elements

Mechanical properties of specimens were researched for model analysis of stress-strain behavior in the stress concentration zone for plate structures using aluminum alloys. Traditional and new structure materials including Russian (1915T and 1565ch) and foreign (6082 – Russian analogue AD35) developments with different alloyage systems (Al-Mg, Al-Mg-Si and Al-Zn-Mg accordingly), strengthening methods, corrosive resistances and welding capacities are studied. Strain and fracture resistance is shown for axial and eccentric tension and for impact bending in the temperature range from -70 to +20°C. Acquired results allow us to designate loads reasonably for structure design using aluminum alloys and estimate their durability.

Property Evaluation of Q345 Welded Steel by Tangential Residual Magnetic Field

This research aims to investigate the relationship between the metal magnetic memory (MMM) signals of Q345 welded steel and its mechanical characteristics including the range of stress concentration zone and the tensile stress. A series of tensile experiments were carried out to measure the tangential residual magnetic field (RMF) on the surface of Q345 steel welded specimens under the action of stress. The variation of tangential RMF and the characteristic parameters (the peak-peak width and the peak-peak amplitude) of tangential RMF gradient curve were investigated. It was found that the tangential magnetic field curve of welded specimen has abnormal magnetic changes in the weld joint area. An analysis of the tangential RMF gradient curve shows that the range of stress concentration zone of welded specimen can be evaluated by the peak-peak width which is nearly constant under different tensile stress. Furthermore, the peak-peak amplitude of the tangential RMF gradient curve has quartic polynomial relationship with tensile stress and it is a potentially useful indictor of the tensile stress in welded steel.