Research on Impact Stress and Fatigue Simulation of a New Down-to-the-Hole Impactor Based on ANSYS

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In the present work, a down-to-the-hole electric hammer driven by linear motor is reported for drilling engineering. It differs from the common hydraulic or pneumatic hammers in that it can be applied to some special occasions without circulating medium due to its independence of the drilling fluid. The impact stress caused by the reciprocating motion between stator and rotor and the fatigue damage in key components of linear motor are analyzed by the ANSYS Workbench software and 3D model. Based on simulation results, the hammer’s structure is optimized by using special sliding bearing, increasing the wall thickness of key and multilayer buffer gasket. Fatigue life and coefficient issues of the new structure are dramatically improved. However buffer gasket reduces the impactor’s energy, different bumper structure effect on life improving and energy loss have also been elaborated.

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... This paper is aimed to design the structure of electromagnetic hammer to meet drilling requirements, the pipe limitation and electric-mechanic requests. For example, the structure design must consider the request of structural strength and fatigue life [11]. ...
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Percussive-rotary drilling is an effective method for the hard rock drilling. As hydraulic and pneumatic hammers have many problems especially in the deep core drilling, a new electromagnetic hammer driven by a tube linear motor is introduced in this study. The study mainly covers the mechanical structure and electromagnetic design of the hammer, respectively. Due to the direct use of electric power, the electromagnetic hammer has the advantage of high efficiency while it must meet the minimal percussive energy requirement under the limitation of drill pipe diameter. In this study, the validity of electromagnetic design is verified through the finite-element analysis software Ansoft/Maxwell 2D and numerical calculation of electromagnetic force. The working temperature in deep down-hole is relatively high, the influence of high temperature in deep hole on the electromagnetic thrust of the linear motor is then analysed. A motion model of linear motor hammer is established to calculate and analyse the impact power and frequency under different conditions. The results show that the performance of linear motor hammer can reach or even exceed the one of same diameter hydraulic hammer, especially in the low-frequency range. The prototype test also confirms the validity of the design.
Offset bearings provide an alternative design approach for problematic applications lacking both load reversals and adequate angular velocity. Offset factor plays an important role and is classified as the ratio of the minimum clearance to the radial clearance. Offset bearing are usually subjected to loads and due to these loads acting on the offset bearing, the compressive and the bending stresses will be developed into the offset bearing. While designing the bearing it is important to analyze the stresses for safety operations. In this project the offset bearing is modelled in SOLIDWORKS and imported to Ansys workbench for static analysis and modal analysis. Static analysis is performed on the offset bearing to determine the deformation and von-mises stresses and to check the variation in result of deformation and stresses with change in mesh from coarse to fine. Modal analysis is performed to determine the natural frequencies and mode shapes for the offset bearing. The results were analyzed, and first ten natural frequencies are calculated for offset bearing for material like structural Steel, Gray Cast Iron, Aluminum Alloy and Epoxy E glass UD (Uni-Directional) to get better information for the suitability of composite material for the offset bearing.
Fatigue failure of dissimilar metal weld structures occurs when it is subjected to fluctuating loads. The structures made of dissimilar metal weld joints were found in many industrial applications. This paper is aimed to estimate the fatigue life of 0.76 mm 304 L stainless steel and mild steel laser welds using energy balance equation and infrared camera. The laser welding experiments are conducted as per the L4 Taguchi’s method, and optimal process parameters were estimated using Taguchi approach. The weld joint prepared at optimal process parameters is considered for prediction of fatigue life. The fatigue tests are conducted by varying pretension load and keeping amplitude constant. The rise in temperature of the specimen is captured during the fatigue life test using infrared camera. The results obtained from this approach are in good agreement with the experimental results. This study helps to predict the fatigue life of the welds quickly based on rise in temperature information acquired during the initial stages of fatigue test.
The concept of abstract fractal characteristic of damage parameter is put forward based on the internal physical meaning of damage and applied to the destruction phase of rock. The relationship between fractal damage and rock fragment sizes is studied. According to the principles of energy dissipation and dynamic fracture of rock impacted by loads, the damage evolution equation in the destruction phase of rock is presented. The results of experiment show that the two methods coincide well with each other.
The dropping simulation and design improvement of a washing machine were conducted based on finite element (FE) analysis. An initial design model for a washing machine was established using the CAD software Unigraphics. Then, its FE model was set up and the dropping analysis was performed with the FE software Abaqus. The simulation results showed that wrinkling and deformation of parts of the machine body occur in the dropping process. The predicted results agreed well with the test ones. The initial design of the washing machine was modified and the analysis was performed again. The improved design made the washing machine have stronger strength and meet the requirement of dropping test. This simulation-based design approach provided a new and effective means for the further development of household appliances.
The key problems in impact response study of reticulated shell were specified, and the effective analysis method for impact response of reticulated shell was established. In the method, characteristic indices (load and characteristic response), analysis schedule for impact response and its calculation model were presented. Taking Kiewitt-8 single-layer reticulated shell as an example, the impact response of reticulated shell was studied. Load characteristic, law of velocity and displacement changing for main joints, law of stress changing for main members and characteristic of energy changing for structure were mainly concerned. The results show that the load is a half sine pulse with short impact duration and high peak value. The local impact response increases abruptly when impact happens, then the impact response spreads to supports gradually. The local response of structure arrives at peak value from impact zone to supports successively. Moreover, time-history curves of velocity and energy may break due to the failure of impact zone. The result lays the foundation for study on reticulated shell against impact, and provides a reference to research on other large structures under impact.
The theoretical mechanics of the percussive drilling of rock are developed from analysis of stress-wave interactions in the drilling system. Particular attention is given to 1.(i) the efficiency of impact energy transfer from drill steel to rock, and2.(ii) the minimum thrust force needed to ensure bit-rock contact at the beginning of each impact.A simple expression is derived from which the penetration rate of a percussion drill can be predicted, provided the amount of impact energy per unit volume of rock broken is known for the appropriate drill bit and rock type, together with certain and operational parameters of the drilling machine.
By use of the finite difference method, the non-linear equations governing the elastic dynamic post-buckling deformations are solved for two types of impact buckling problems for straight bars. The initial dynamic buckling mode with a small amplitude parameter, given by the twin-characteristic-parameter solution, is used as the initial condition of the non-linear post-buckling solution. Particular attention is paid to the mechanism of growth and spread of buckling deformation in the bar and the interaction between the axial stress wave and the buckling deformation in the process of impact. It is found that the initial buckling deflection with one half-wave, occurring near the impacted end, spreads forward and develops into the higher mode as the axial stress wave propagates in the bar. The theoretical results are in good agreement with the experimental results reported in the literatures.
Two critical conditions for the dynamic buckling of columns are derived on the basis of the consideration of energy transformation and conservation at the instant when the buckling occurs. The first critical condition is that the amount of released compressive deformation energy must be equal to the sum of buckling deformation energy and buckling kinetic energy in the instant course of the dynamic buckling. The second is that the rate of energy transformation meets the conservation law in the instant course. The governing equations, the boundary conditions and the continuity conditions derived by use of the first condition are the same as those obtained by use of Hamilton's theorem. These equations and conditions are insufficient for the determination of the critical load parameter and the exponent of transverse inertia term involved in the problem. A supplementary restraint equation at compression wave front is derived by use of the second condition.Two characteristic equations for the two parameters are derived by use of the solution of the governing equations and the above-mentioned restraint conditions. The two characteristic parameters and the corresponding buckling modes are calculated accurately from the solution of the characteristic equations. The simple formulas for the relation of the critical force with the buckling time are given. The theoretical results predicted by use of the formula are in reasonable agreement with the existent experiment results.
Conference Paper
In this paper, we review some major research results in traveling wave tubular linear induction motors technology, based on "open literature" publications, which were obtained in the world in the last decades. One database analysis shows that coil launchers are covered in 68 of over 1000 electromagnetic launcher papers published, referred to 53 of them in this paper. The research program includes studies of history, types, applications, theories and analysis, design, and power conditioning of coil launchers with emphasizing on traveling wave induction (linear induction launcher) one. In the theories and analysis section, a preview is given of current sheet model, current filament model, finite element method, and wavelet transform. In the design section, local and global optimisation algorithms and designing results is reviewed. In the final section, we review power conditioning of capacitor driven coilguns and generator driven coilguns, and concepts of "magnetic flux compression" for generating pulses required to efficiently drive the coil launchers and "double-fed induction launchers".
Stress wave reflecting attenuation to improve anti-shock capacity by gasket
  • P Z Xu
  • H D Huang
  • PZ Xu
Dynamic analysis method of impact problem
  • Y G Wang
  • YG Wang