Papers by Keyword: Hopkinson Pressure Bar

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Authors: Raja Ahsan Javed, Shi Fan Zhu, Chun Huan Guo, Feng Chun Jiang
Abstract: Modified Hopkinson pressure bar apparatus is widely used to investigate the dynamic fracture behavior of materials at higher rate loading. While using a small sample for fracture toughness testing, plane strain conditions are compromised. In the current work, a large diameter two-bar/ three-point bend fracture setup is used to analyze stress wave propagation behavior within a larger cracked specimen. The experimental setup model consists of striker, incident bar, loading pin, cracked three-point specimen, span and transmission bar. The model is prepared using ANSYS software and the transient dynamic analysis technique is used to simulate the dynamic load. The effects of increased transient time on the stress wave propagation behavior within the cracked sample and the stress and strain values at the crack tip of the three-point bend specimen are analyzed. In addition, the effects of the hollow striker, the hollow incident bar and the specimen span are studied. It is found that during large specimen testing, an increase in the transient time results in the lower stress and strain values in the specimen crack-tip. The relationship of the specimen span, the striker and the incident bars with the strain values in the specimen is analyzed and a method for the three-point bend specimen testing at the higher strain rates is also proposed.
Authors: Raja Ahsan Javed, Shi Fan Zhu, Chun Huan Guo, Feng Chun Jiang
Abstract: For the Comprehension of the dynamic mechanical properties of the materials under the dynamic loading, Hopkinson pressure bar apparatus is used. During the compression testing of the low impedance materials the use of the hollow transmission bar is common. In the current work, the analysis is performed to analyze the effects of hollow transmission and incident bars on the specimen testing for the large diameter compression setup. Complete model of the setup is prepared using the ANSYS software and the simulation of loading is done using the LS-DYNA software. The results of analysis indicate that for the large compression testing setup, solid bars can be replaced with hollow bars. By using the hollow transmission bar the objective of high strain rate testing is also obtained.
Authors: Ning Liu, Guan Chang Jin, Xue Feng Yao, Gui Tao Li
Authors: Raja Ahsan Javed, Shi Fan Zhu, Muhammad Farid
Abstract: For design to be more safe, dynamic fracture toughness (DFT) of material needs to be determined. Compared to static loading, dynamic loading procedures are not well established. Calculation of DFT is complicated and costly. Failure process of structures is greatly influenced by dynamic loading. In the past only steel and cast iron were employed for structure design purposes but now many new materials such as (a) composite, (b) alloys (titanium, magnesium), (c) ceramic, (d) concrete, and (e) brittle materials are being used. DFT calculations of materials under dynamic loading have resulted in new theories and experimental techniques. In this paper a critical review of the developments for the calculation of DFT for the materials is presented.
Authors: Chun Huan Guo, Xin Hui Shen, Feng Chun Jiang, Guang Ping Zou
Abstract: Some fundamental issues, such as stress wave dispersion effect, loss of contact, pulse shaping effect are still needed to thoroughly understand in Hopkinson pressure bar loaded fracture experimental techniques. In order to avoid the influence of stress wave dispersion on the analysis of dynamic experimental results, a computational procedure has been developed based on the combined analytical solution of Pochhammer-Chree with Fourier spectroscopy analysis. The validity of this proposed computational procedure was confirmed via the comparison with the experimental stress pulses obtained from pulse-shaped tests. The experimental results can be easily interpreted and the testing accuracy can be improved using this computational procedure.
Authors: Raja Ahsan Javed, Shi Fan Zhu, Feng Chun Jiang
Abstract: The researchers and scientists have concluded that material dynamic fracture properties must be considered during the design stage of the modern structure. The dynamic stress intensity factor is very important in understanding of material dynamic behavior. Keeping in view the importance of the materials dynamic stress intensity factor: an efficient and reliable numerical-analytical procedure is developed for calculation of dynamic stress intensity factor. For this, three-dimensional model of a Modified Hopkinson Pressure Bar (MHPB) and a specimen is modeled and analyzed with the ANSYS software. Transient dynamic analysis technique is used for simulation of load-variations as a function of time. As an output of analysis, values of load point displacement and Crack Mouth Opening Displacement (CMOD) are obtained. These values are substituted into two different analytical formulas for calculation of a dynamic stress intensity factor. The results obtained are compared with previous published results, and a good agreement is found.
Authors: Xiao An Chen, Shun Cheng Song, Ting Hui Wang
Abstract: In order to obtain the dynamic shearing property of high N alloy steel, the plugging test was performed by using the improved Hopkinson pressure bar system. As dynamic shearing strengths, the dynamic shearing energies during plugging process of two type high N alloy steels were determined from the shearing constitutive relationship at different super high strain rates. According to the theory of dislocation dynamics in Seeger equation, a dynamic shearing damage constitutive relationship was established and the different parameters of this material were determined by using the curve fitting method. The measured results indicated that the dynamic shearing property of high N alloy steel could be obtained effectively by the improved Hopkinson pressure bar system, and the effects of strain rate could be simulated by dynamic shearing damage constitutive relationship.
Authors: Raja Ahsan Javed, Shi Fan Zhu, Chun Huan Guo, Feng Chun Jiang
Abstract: Hopkinson pressure bar apparatus is extensively used for the measurement of the dynamic fracture properties. For accurate measurement of the dynamic fracture properties we need to understand concepts and principles associated with the test setup. The understanding of stress wave in the bar and specimen is also very important. In the current work, ANSYS LS-DYNA software is used to simulate the propagation behavior of the time based loading and generation of stress wave. The stress and strain plots in the specimen and the incident bar are obtained as an output of the analysis. The analysis of the plots suggest that, for the same time duration the rising trend is observed for the plots of stress and strain of incident bar whereas a sine wave trend is observed for the plots in the specimen.
Authors: Jiang Ren Lu, Jian Zhang, Xin Li Sun, Xing Hui Cai
Abstract: In this paper, the dynamic compression-shear experiments on the closed-cell aluminum foam with porosity of 72%-92% are carried out by using improved split Hopkinson pressure bar. A high speed camera is used to observe the dynamic deformation behavior of the samples on the compression-shear loading. A finite element software ABAQUS is employed to simulate the dynamic compression-shear process of closed-cell aluminum foam. The results demonstrate that there is a compression-shear band on the samples during the compression-shear loading. The most severely damaged area of the material is on the compression-shear band; Low-porosity closed-cell aluminum foam has significant strain rate effect, however high-porosity closed-cell aluminum foam can ignore the strain rate effect. The yield stress of samples decreases with increasing samples angle, whereas shear stress increase with increasing samples angle, and also the corresponding time when the samples just begin to yield decreases with increasing samples angle.
Authors: Yong Cheng Wang
Abstract: In this paper, we make a research on the dynamic characteristics of a sphere material, mainly using golf as an example. Golf is composed of such as poly butadiene rubber or other synthetic rubber, ion resin, etc. and different viscoelastic materials. The viscoelastic characteristics of this material are selected as spectrometer for evaluation. However, the impact performance of the golf course materials cannot pass such a test to assess, because golf have great impact on the deformation and high strain rate viscoelastic spectrometer. On the other hand, the impact properties of the metal can be used to assess the split Hopkinson pressure bar. However, the rod is not suitable to be used to evaluate the strain wave interference and noise propagation in the impact properties of the polymer materials. Therefore, the split Hopkinson pressure bar has been modified to make it more applicable to the valuation of the polymer materials. The article is based on the concept of modified split Hopkinson pressure bar to make the golf impact evaluation of the performance materials.
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