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Procedia Engineering
ProcediaProcedia Engineering 00 (2011) Engineering 24 000–000 (2011) 773 – 777 www.elsevier.com/locate/procedia
2011 International Conference on Advances in Engineering
Determination of The Dynamic Response of Q345 Steel Materials by Using SHPB Wenjuan Zhanga, Pengfei Haob,c, Yong Liuc, Xuefeng Shuc,a* a
Beijing Flight Control Center,Beijing,100094,China Taiyuan Satellite Launch Centre,Taiyuan,Shanxi,030027,China c Taiyuan University of Technology, Taiyuan,Shanxi,030024,China b
Abstract In this paper a split Hopkinson pressure bar (SHPB) setup was used to test mechanical properties of Q345 steel materials used for industrial structure under high strain rate and high temperature loading conditions such as rocket launching. To provide a consistent and accurate safety assessment to these mechanical structures, the mechanical dynamic response of Q345 steel under high strain rate loading conditions in the same high temperature in different shock times have been developed numerically and experimentally. Special emphasis is placed on determining the experimental relationship between stress and strain compared with different shock times, which is used as a basis for the data analysis procedure. Experimental results for mechanical properties of Q345 steel materials under the extreme conditions from SHPB tests are provided.
© 2011 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and/or peer-review under responsibility of ICAE2011. Keywords: industrial structure; dynamic response; shock times; Q345 steel materials
1. Introduction As well comprehensive mechanical materials, Q345 steel in industrial structure is used under extreme conditions such as rocket launching characterized by high stresses and high strain rate loading in high temperature environment. In order to design structure to be used in the extreme load conditions, the mechanical properties of the Q345 steel material under high strain rate in high temperature environment are need to be known in detail. Recently, we may find that the mechanical properties of the steel material impacted on high temperature and high strain rate loading is distinguished from impacted on ambient
* Corresponding author. Tel.: +86-351-6014455. E-mail address:
[email protected].
1877-7058 © 2011 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. doi:10.1016/j.proeng.2011.11.2735
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temperature, and quasi-static power load, such as yield stress, strength. It is not easy, however, to get the mechanical properties under the high strain rate loading condition. The split Hopkinson pressure bar (SHPB) technique has become one of the most popular experimental techniques for the study of dynamic behavior of materials. Traditionally, the SHPB has been used to investigate the dynamic behavior of metals in ambient temperature. However, in recent years there has been an interest in determining dynamic elastic and failure properties in extreme conditions. During this process, some of the limitations of the SHPB have surfaced necessitating the reevaluation of the SHPB fundamental assumptions. 2. Set up of split Hopkinson pressure bar In this study, the split Hopkinson pressure bar test facility is made up of striker bar, incident bar, transmission bar, heating furnace, digital storing oscilloscope, computer and so on [1-5]. The incident bar and the transmission bar have the same length. The environment of high temperature is produced by the heating furnace. The striker bar driven by the compressed air bumps by the incident bar. The incident, transmission and striker bar are made of aluminum alloy. The smaller the diameter of the pressure bar, the higher strain rate in the specimen will be gained. The diameters of incident bar, transmission bar and the striker bar are 8mm, meanwhile the length is 800mm. But the length of striker bar is 250mm. The heating furnace is a difficult point in the SHPB. The specimen is put in the above furnace, and the temperature raise up to anticipant stated value. By changing the gas pressure of the driver system, the velocity of the striker bar, and consequently the strain-rate of specimen, was controlled in the range of 2×102 to 2×103 per second. Schematic illustration of SHPB apparatus used for this study is shown in Fig. 1. Heating furnace
Incident bar
Striker bar
Transmission bar
Momentum trap
Specimen
Gas gun
Sensor
Strain gauge
Digital storing oscilloscope
Computer
Fig. 1 Schematic illustration of the SHPB apparatus
3. Theory The split Hopkinson pressure bar (SHPB) technique is based on one-dimensional wave propagation theory in elastic bars, where wave propagation is not distorted by wave dispersion and attenuation. Therefore, a SHPB satisfies the assumptions of one-dimensional wave propagation theory and provides
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satisfactory accuracy of experimental results. In order to test the dynamic properties of Q345 steel, heating furnace have been used in SHPB tests for materials properties under extreme loading conditions, which may produce noticeable wave dispersion and attenuation during the wave propagation in pressure bars. Some investigations have been undertaken to evaluate and correct these negative effects. An elastic compression stress wave travels and reflects in the incident bar, transmission bar and the specimen, when the incident bar bumped by the sticker bar [6-7]. A traditional analysis of the SHPB provides stress rate and strain in the specimen as follows: s t E Ab A t t
(1)
s t 2C L R t
(2)
t
s t 2C L R t dt 0
(3)
Where s is the dynamic yield stress, s is the strain, s is the strain rate, C is elasticity wave speed in the bar, L is the length of the specimen, Ab is the cross-sectional area of the incident bar and the transmission bar, A is the cross-sectional area of the specimen, E is the elasticity modulus of the incident bar and the transmission bar, R and T are the strains of the incident bar and the transmission bar, respectively. 4. Experiment The structure usually works in the condition of high temperature and high strain rate load. Test about the whole structure in the special condition above is difficult to realize. The SHPB is an effective replaced test set-up. The dynamic impact experiments under the environment of high temperature were performed on the SHPB test facility in laboratory in TYUT.
Fig. 3 Geometry of specimens (dimension: mm)
To obtain perfect contact of the incident and the transmission bar surfaces, the ends of the specimen and the bars are finely grinded by the abrasive flow mechanism technology (AFM). The specimen is fixed between the incident bar and the transmission bar. The thickness of the specimen used for this experiment is 5mm and the diameter is 5mm, respectively. The geometry of the specimen is shown in Fig. 2 and Fig. 3. 5. Results and discussion As shown in Fig. 4, Fig. 5 and Fig. 6, the stress-strain curves are obtained by the compressive signal outputs from strain gages attached on the incident and transmission bars, respectively. As mentioned before, the mechanical properties of the steel material impacted on high temperature and high strain rate load is different from impacted on ambient temperature, and quasi-static power load, such as yield stress, strength. It may be shown that the relationship between stresses and strain rate are nonlinear according to extreme loading conditions. And also it is important to notice that the stress is growing noticeably in the wake of the increasing of strain also shown in Fig. 4, Fig. 5 and Fig. 6.
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Stress(MPa)
It is interesting to note that the mechanical deformation behaviors of Q345 steel under different shock times quite differ from each other in the same temperature. As is shown in the Fig. 4, Fig. 5 and Fig. 6, it can be exhibited clearly that along with the augment of shock times after 0.005, the stress of Q345 steel increases obviously. First, a closer look tells us that the value of stress has kept growing dramatically, before about 0.000 to 0.005, impacted on 10 shock times in 100℃, shown in Fig.4. After that, the stress is changing gently. Else, the zones with sharply growing are 0.000 to 0.002 impacted on 5 shock times and 0.000 to 0.003 impacted on 5 shock times, respectively. Furthermore, it is noted that the stress of Q345 steel increases obviously in pace with the augment of shock time shown in Fig. 6. In addition, as a good case in point, the value of stress has kept growing dramatically, before about 0.009, in Fig. 5 in the curve of 10 shock times in 300℃.
800
Stress(MPa)
600
400 200
0
0.000
1 shock time 5 shock times 10 shock times 0.012
0.024 strain Fig. 5 Stress-strain curve of Q345 steel impacted on different shock times in 300 ℃
Wenjuan Zhang et al. / Procedia Engineering 24 (2011) 773 – 777 Wenjuan Zhang/ Procedia Engineering 00 (2011) 000–000 800
600
400
200
1 shock time 5 shock times 10 shock times
0 0.000
0.010
0.020 strain Fig. 6 Stress-strain curve of Q345 steel impacted on different shock times in 500 ℃
6. Conclusion The different dynamic mechanical phenomena of Q345 steel according to extreme loading conditions of high temperature and dynamic shock load are tested by using the SHPB technique and the following experimental results are obtained. The mechanical deformation behaviors of Q345 steel under high strain rate of compressive loading conditions under different shock times quite differ from each other in the same temperature. The relationship between strength and strain rate according to extreme loading conditions of high temperature and dynamic shock load is nonlinear. When the value of strain is after 0.005, the value of stress increases with the grows of shock times in the same temperature. Acknowledgements The support of this research is given by 2010 Taiyuan Satellite Launch Centre research fund. The help from the center for composite materials at Taiyuan University of Technology is greatly appreciated. Also, the support of Beijing Flight Control Center to one of the authors is acknowledged. References [1] Weiguo Guo. Journal of Experimental Mechanics. 2006;447-452e. [2] Zhouhua Li and John Lambros. Composites Science and Technology. 1999;1097-1107. [3] Mingqiao Xu and Lili Wang. Mechanics of Materials. 2006;68-75. [4] Qiang Li, Y.B. Xu and M.N. Bassim. Journal of Materials Processing Technology. 2004;1889–1892. [5] H. Meng and Q.M. Li. International Journal of Impact Engineering. 2003;677-696. [6] O.S. Lee and M.S. Kim. Nuclear Engineering and Design. 2003;119-125. [7] R.M. Guedes a, M.F.S.F. de Moura and F.J. Ferreira. Composite Structures. 2008;362-368.
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