摘要: Fatigue failure is the most common failure mode of boring bar in the deep-hole boring processing system. For solving the problem of fatigue failure on boring bar, the new fatigue strength criterion of boring bar is proposed considering the working state including internal and external cutting fluid vortex, linear crack of the across-section, and the maximum bending - torsion coupled stress of boring bar. Firstly, approximate calculation formula of the maximum bending stress was derived considering internal and external cutting fluid coupled effect induced vortex motion. Secondly, near the region of crack tip, the maximum shearing stress was studied when the failure modes of boring bar was considered to linear crack on its cross-section. Finally, the new fatigue strength criterion was established based on bending-torsion combination alternating stress fatigue strength theory. An example calculation in practice showed that if fatigue strength of boring bar is satisfied to the new fatigue strength criterion, its static strength must be satisfied. The new fatigue strength criterion can be used in analyzing the boring bar’s fatigue strength on both complicated working conditions and also single working conditions. The mechanism of failure and destruction of boring bar on BTA deep hole drilling in generally actual working conditions were studied in this paper which are helpful to promote the service life cycle of boring bar in practice. Some rules are also derived to assess the dynamic performance of working boring bar, which structure parameters will be selected reasonably according to it.

2264

作者: Feng Qiang Gong, Xi Ling Liu, Ke Gao

摘要: For rock-like materials, large diameter SHPB (Split Hopkinson Pressure Bar,SHPB) is necessary and essential in dynamic test. Based on the finite element software ANSYS/LS- DYNA, the transmission of different stress pulse waveform in large diameter bar was simulated and the loading waveform dispersion effect was investigated in this paper. Three typical stress pulses (rectangular waveform, triangular waveform and half-sine waveform) with the same duration time and maximum stress amplitude value were loaded on input bar of SHPB. The time-stress curves of different transmission distance on input bar were traced and recorded and four specific aspects were discussed respectively. Compared with rectangular waveform and triangular waveform, the results of numerical analysis indicated that there isn’t pulse waveform dispersion for half-sine waveform to transmit in large diameter SHPB and there is enough increased time to satify stress equilibrium before rock-like materials failure. The half-sine stress wave is able to meet the one-dimensional assumptions in the propagation process and can be used in large diameter SHPB test.

2419

作者: Peng Fei Hao, Xiao Bo Hou, Jia Zhi Gao, Yong Liu, Xue Feng Shu

摘要: Mechanical properties of Q345 steel used for industrial structure under high strain rate and high temperature loading conditions such as rocket launching are required to provide appropriate safety assessment to these mechanical structures. The split Hopkinson pressure bar (SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high strain rate loading conditions. In this paper, dynamic deformation behaviors of Q345 steel under both high strain rate compressive and high temperature loading are determined using the SHPB technique.

483

作者: B. Hou, S.B. Tan, R. Xiao, Han Zhao

摘要: This paper presents a new method based on the split Hopkinson pressure bar (SHPB) to perform impact combined shear-compression test for cellular materials. For this purpose, a bevelled end is cemented to the input bar and the output bar are rotatable to be parallel to the inclined plane of the bevelled end. The system uses the friction between the specimen and the pressure bars to apply the combined shear compression loading on the honeycomb specimen. Such a testing method is validated by the simulation of the whole loading system (split bar + specimen) using ABAQUS code. It shows that this combined shear-compression test provides a quite accurate measurement. Tests on the 5052 aluminium honeycombs are performed. The shear stress-strain behaviour and the compressive behaviour are separated. The experiment result confirms previous testing results and reveals that the shear component will weaken the compressive strength of the honeycomb at high strain rate.

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