Fracture Failure Analysis of the Connecting Bolt of Circuit Breaker in 500kV Converter Station

Through a macroscopic inspection, a stereomicroscopic inspection, a material analysis, a hardness inspection, a metallographic analysis, scanning electron microscope and energy spectrum analysis, the reasons for the breakage of the connecting bolts of the circuit breaker in a 500kV converter station are studied. The results show that the bolt fracture is caused by the combined effect of a hydrogen embrittlement and a high-stress low-cycle fatigue. The corresponding recommended measures are proposed to improve the reliability of the bolts and ensure the safe operation of the circuit breaker.

Failure analysis of bolt fracture in GGH guide bearing end cover pressure plate in a thermal power plant

Gas gas reheater is an important device for waste heat recovery and flue gas purification in thermal power plant. In this paper, the fracture failure reason of pressing plate bolt of guide bearing end cover of flue gas reheater in thermal power plant is analyzed. The results of optical microscope analysis show that there is no obvious abnormality in the metallographic structure of the two guide bearing bolts. The mechanical analysis results show that the hardness value, tensile strength and yield strength meet the requirements of relevant standards. SEM analysis showed that the fracture began at the root of the thread. The research results can provide reference for the operation and maintenance of flue gas reheater in relevant enterprises.

Effect of loading rate on tensile and fracture behavior of AA2050-T84 alloy at high temperature

AA2050-T84 alloy is commonly used in the fabrication of modern commercial aircraft wing parts. Load and temperature variation during aircraft take-off, flight, and landing at different environmental conditions is substantial. Mechanical properties variation of AA2050-T84 alloy at sub-zero and room temperatures are significant and well documented in the literature. In the present work, at a high temperature of 200°C, the effect of load rate variation on tensile and fracture properties of AA2050-T84 alloy are experimentally and numerically studied. The load rates represented in strain rates were applied at 0.01, 0.1, and 1s−1. Experimental tensile tests exhibited the positive strain rate dependency on the yield and ultimate strength of the alloy. 2D numerical elastic-plastic fracture analysis was carried out using Abaqus 6.14. Similar to tensile results, the fracture parameters dependency on strain rates was witnessed. Overall, higher strain rate causes the increased susceptibility of fracture failure with the increase in yield stress of the material.

Fracture Failure Analysis of the Energy Storage Spring of the Circuit Breaker in the 110kV Substation

Through a macro inspection, chemical composition analysis, hardness inspection, graphite carbon inspection and energy spectrum analysis, the reason for the break of the energy storage spring of the circuit breaker in a 110kV substation are analyzed. The results show that poor manufacturing technology and anti-corrosion technology of the spring are the main reason for its fracture. Corresponding control measures are put forward to avoid similar failures from happening again.

Numerical Investigation of the Fracturing Effect Induced by Disturbing Stress of Hydrofracturing

Fracturing induced by disturbing stress of hydraulic fracturing is the frontier common core scientific problem of reservoir stimulation of coal bed methane and shale gas. The finite-discrete element method, numerical calculation method, is used to analyze the basic law of shear failure and tension failure of natural fractures induced by the disturbing stress of the hydraulic fracture. The simulation results show that when natural fractures and other weak structures exist on the front or both sides of hydraulic fracture, the shear stress acting on the surface of natural fracture will increase until the natural fracture failure, which is caused by the disturbing stress of hydraulic fracturing. The seepage area on the front and both sides of the hydraulic fracture did not extend to the natural fracture while the natural fracture failure occurred. It indicates that the shear failure of natural fractures is induced by the disturbing stress of hydraulic fracturing. When the hydraulic fracture propagates to the natural fracture, the hydraulic tension fracture and disturbed shear fractures are connected and penetrated. As the fluid pressure within the natural fracture surface increases, the hydraulic fracture will continue to propagate through the natural fracture. Meanwhile, due to the action of fluid pressure, a tensile stress concentration will occur at the tip of the natural fracture, which will induce the airfoil tension failure of the natural fracture. With the increase of the principal stress difference, the range of the disturbing stress area and the peak value of the disturbing stress at the front of the hydraulic fracture tip increase, as well as the shear stress acting on the natural fracture surface. During the process of hydraulic fracture approaching natural fracture, the disturbing stress is easier to induce shear failure of natural fracture. With the increase of the cohesive force of natural fracture, the ability of natural fractures to resist shear failure increases. As the hydraulic fracture approaches natural fractures, the disturbing stress is more difficult to induce shear failure of natural fracture. This study will help to reveal the formation mechanism of the fracture network during hydraulic fracturing in the natural fractures developed reservoir.

Investigating Fracture Failure in Origami-based Sheet Metal Bending

Origami-based sheet metal (OSM) bending is a promising new die-free folding technique for sheet metal. OSM bending principle is based on deforming the material along a pre-defined fold line, which is determined using material discontinuity (MD) produced by laser or waterjet cutting. The objective of this work is to study and evaluate the fracture in OSM bending under the influence of various MD types, kerf-to-thickness (k/t) ratios, and sheet thicknesses. The research goal is to provide information on selecting an optimized k/t ratio and type of MD that allows for fracture-free bending. Four different ductile fracture criteria (DFC) are used and calibrated from experimental data to forecast fracture. The DFC calibration is used to produce a set of critical damage values (CDV) for assessing the possibility of fracture in the OSM bending. In addition, the study provides fracture evaluation using finite element analysis (FEA) integrated with experimental cases for a broader range of OSM bending parameters and MDs. The results demonstrated that an MD with a higher k/t ratio is less likely to fracture during the OSM bending, whereas a higher sheet thickness increases the possibility of fracture. Furthermore, the study identifies the k/t ratio limit that ensures successful bending without fracture and categorizes MD types into two groups based on fracture likelihood. The fracture in the first group is dependent on the limiting k/t ratio, whereas the possibility of fracture in the second group is independent of the k/t ratio due to its topology.