Forensic Issues from the Investigation of a Marine Shaft Failure

The starboard propeller shaft of a twin-screw diesel electric rail ferry in New Zealand failed just after the ferry left port. Weather was not a factor. The ship was on a regular schedule of three sailings a day. The starboard propeller was found in 120 meters of water approximately two nautical miles from the channel — some distance from the point where power was observed to reduce to zero on the shaft. The fracture surface of the shaft showed a classic fatigue failure pattern. However, there were questions to be answered, including what initiated the failure, and why a tension failure occurred in a shaft that was primarily under compression from the reaction forces of the propeller. This paper will look at some interesting factors in the investigation, the techniques used to limit the investigation (and its cost) to relevant areas, a few of the false trails that were followed, and the processes eventually used that were the most convincing.

Fatigue Failure Analysis of a Speed Reduction Shaft

The mining industry sector is notable for the severe service loads and varied environmental conditions that it imposes on its equipment and mechanical systems. It has become essential to identify the causes of failures and use the information to avoid similar failures and improve projects. In this paper, a study on shaft failure in a speed reduction box was carried out. A section of a fractured shaft made of hardened austempered steel was analyzed to determine the cause of the break. Fractography was performed to characterize the failure mode on the fracture surface. The microstructural analysis and hardness profile revealed that the shaft was inadequately heat treated, resulting in low resistance microstructures and the development of a thin layer of bainite at the shaft edge. Large amounts of inclusions were found in the fracture region, and the tensile tests revealed that the material had an elongation below the specification. The analyses showed that the combination of factors of a large amount of inclusions present in the low resistance banded structure, and the presence of concentrated pores in that same region, acted in a synergistic way to decrease the fatigue resistance and fatigue life of the shaft material.

Simulation of Simplified BSPD Deploying Timer Circuit for a Prototype Formula Electric Car

Now-a-days electrical vehicles are growing faster than the vehicles fuelled with conventional energy resources and are expected to replace conventional vehicles in near future,owing to its zilch emissions and environmental friendly. Albeit the electrical vehicles are contributing to the reduction in air and noise pollution, few technical issues have to be resolved for its improved performance. Currently electric vehicle is turned off automatically, for avoiding the shaft failure due to the twisting load acting on the shaft, while operator applies the accelerator pedal and brake pedal simultaneously. Hence, an attempt had been made to delay the system getting turned off by introducing a timer circuit in BSPD (Brake System Plausibility Device). The functioning of simplified BSPD with timer circuit was simulated using the Proteus software andthe outcome of the simulated results is presented in waveforms, which confirms the proper functioning of the circuit. A PCB for engaging the shutdown circuitwas also developed to control the electric vehicle’s powertrain. The hardware implementation of the simulated circuit had been carried out and the real time working of the circuit was verified.

Static analysis and strength calculation of drive shaft of large-scale cone crusher

The paper analyzes the causes of failures of coarse crushers “KKD 1500-180” at JSC “Almalyk MMC”. It has been established that the most common cause of these failures is a drive shaft failure. Static analysis of the strength of the drive shaft was performed using Autodesk Inventor 2020 CAD software. A dangerous shaft section was found, and recommendations aimed at improving its operability were proposed.

The Stability Evaluation of Shaft during Drastic Drawdown Dewatering of Alluvium

The hydrophobicity of the aquifer at the bottom of the porous alluvium will affect the stability of the shaft. According to the changes of water level and the compressive amount of alluvium, we can evaluate the shaft stability and predict the shaft failure. In this work, the simulation model of the auxiliary shaft in the Zhuxianzhuang Coal Mine is generated by using the Nsdc software to evaluate the stability of the shaft during drastic drawdown dewatering. Based on the measured hydrophobic compression ratio in an adjacent coal mine, the compressive amounts of the strata near the main and auxiliary shafts in the Zhuxianzhuang Coal Mine are predicted under the condition of drastic drawdown dewatering, which will be 249.69 mm and 302.75 mm, respectively. It is more likely that the shaft wall may fracture in the 15th day (fourth load level) under the condition of drastic drawdown dewatering. The formation compressive amount near the auxiliary shaft is approximately 320 mm, which is close to the measured predicted value. At the same time, the Fisher discriminant model is established, and it is predicted that the state of the main and auxiliary shafts will be failure under the conditions of drastic drawdown dewatering in the Zhuxianzhuang Coal Mine. Based on the simulating results, the technical means of using the ground grouting for early prevention and control is proposed.

Turbine thermomechanical modelling during excessive axial movement and overspeed

ABSTRACTThis manuscript discusses the numerical (finite element) and analytical modelling of structural interactions between gas turbine components in case of excessive axial movement and overspeed. Excessive axial movement, which may occur after a shaft failure, results in contact between rotating and static turbine components under high forces. These forces create friction which can act as a counter torque, potentially retarding the ‘free-rotating’ components. The study is based on a shaft failure scenario of a ‘three-shaft’, high ‘bypass’ ratio, civil ‘large-fan’ engine. Coupled analytical performance and friction methods are used as stand-alone tools to investigate the effect of rubbing between rotating and stationary components. The method is supported by ‘high-fidelity’, ‘three-dimensional’, thermomechanical finite element simulations using LS-DYNA software. The novelty of the work reported herein lies in the development of a generalised modelling approach that can produce useful engine design guidelines to minimise the terminal speed of a free running turbine after an unlocated shaft failure. The study demonstrates the advantage of using a fast analytical formulation in a design space exploration, after verifying the analytical model against finite element simulation results. The radius and the area of a stationary seal platform in the turbine assembly are changed systematically and the design space is explored in terms of turbine acceleration, turbine dislocation rate and stationary component mass. The radius of the friction interface increases due to the increasing radius of the nozzle guide vane flow path and stationary seal platform. This increases the frictional torque generated at the interface. It was found that if the axial dislocation rate of the free running turbine wheel is high, the resulting friction torque becomes more effective as an overspeed prevention mechanism. Reduced contact area results in a higher axial dislocation rate and this condition leads to a design compromise between available friction capacity, during shaft failure contact and seal platform structural integrity.