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Dynamic and Damage Characteristics of Mortar Composite under Impact Load
Qing Li,Tong-de Zhao,Chen Huang,Bing-bing Yu,Zheng-Hua Gao,Kai Wang 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.3
In the process of underground construction, it is common to spray concrete on the working surface, which will form a concrete-rock composite structure, to achieve the expected reinforcement effect. Compared with pure concrete or rock structures, composite structures have different mechanical properties, energy evolution and damage characteristics. Understanding the dynamic mechanics and damage characteristics of composite structures under impact loads is important to the safety of underground engineering construction. First, dynamic compression tests on different grades of mortar-sandstone composite specimens were carried out by using a Hopkinson pressure bar system to discuss the effect of impact velocities on the mechanical properties and failure modes of composite specimens. The results show that the dynamic peak stress, strain energy density and fragmentation block of the mortar-sandstone composite have an obvious strain rate effect. With an increase in impact velocity, the internal cracks of the sample do not have sufficient time to expand, and the energy absorbed by the sample leads to the continuous initiation of new cracks in the sample, resulting in an increasing damage degree of composite specimens. The increase in mortar strength can significantly increase the peak stress, improve the load-bearing capacity of the sample, and reduce the degree of sample damage. At the same impact velocity, the fragmentation degree of the mortar sample is more severe than that of sandstone, and the mortar sample is broken into powder debris, while the sandstone is broken into fragments. In addition, according to the failure properties of the composite sample, the mortar and sandstone samples are described by different damage models, and the dynamic damage constitutive model of the mortar-sandstone composite is established based on the overlay principle. The dynamic test results were fitted. The research shows that the fitting curves of the model are well fitted with the test curves and that the model accurately reflects the changes in the mechanical parameters of the composite specimens.
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Chen, Peng-Lai,Zhao, Ting,Feng, Rui,Chai, Jing,Tong, Gui-Xian,Wang, De-Bin Asian Pacific Journal of Cancer Prevention 2014 Asian Pacific journal of cancer prevention Vol.15 No.15
National cancer registration reports provide a huge potential for identifying patterns and trends of important policy, research, prevention and treatment significance. As summary reports written on an annual basis, the China Cancer Registry Annual Reports (CCRARs) fall short from fully addressing their potential. This paper attempts to explore part of the patterns and trends hidden behind published CCRARs. It extracted data for cancer incidence rates (IRs) and mortality rates (MRs) for 2004, 2006 and 2009 from relevant CCRARs and portrayed 4 kinds of indicators in line graphs. The study showed that: a) all of the line graphs of age-specific IRs and MRs characterized typical "growth curves or histogram"; b) graphs of IRs and MRs for males and urban areas had higher peaks than that for females and rural regions; c) most of the line graphs of IR/MR ratios comprised a starting peak, a secondary peak and a decreasing tail and the secondary peaks for females and urban areas were higher than those for males and rural areas; d) most of the urban versus rural IR ratios valued above one, but most the urban versus rural MR ratios, below one; e) the accumulative IRs and MRs showed a stable increasing trend from 2004 to 2009 for urban areas, but mixed for rural regions.
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