Strain Measurements and Deformation Behavior of Brittle Material in the Split-Hopkinsion-pressure-bar Experiment
| Autor: | Lin wei-jen, 林維仁 |
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| Rok vydání: | 2014 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 102 Split Hopkinson Pressure Bar was initially applied to metallic materials. Recently, this testing method was introduced to the rock and brittle materials, such as ceramics and concrete due to its simple structure and convenience for operation. Lots of studies focused on the relationship between strength and strain rate of materials, but less studies investigated the deformation of the materials. The material strain obtained from traditional SHPB test was calculated by relative shifts between planes of elastic rod and material, and brittle materials were easily damaged, which led to the difference in transmission of stress waves. The issues about if the traditional methods were suitable for brittle materials and the different results obtained from one-wave method and three-wave method should be further discussed. Certain proportion of the gypsum mortar and maintenance procedures were utilized in this study for preparing brittle materials, and they were compared with ductile materials by difference methods of measurement and analysis to investigate the deformation characteristics of brittle materials under SHPB tests, while using high-speed cameras to record development of specimen fracture. Secondly, natural rocks were underwent SHPB tests, except for comparing strength and deformation with ductile materials, observations and discussions were also being made over development of fracture and mechanism of damage. The results showed that dynamic uniaxial compression strength, strain, dynamic deformation modulus and Poisson's ratio of materials were improved with the increased stress rate, and stress balance between both planes of the specimen was relatively worse. When the damaged level of specimen was lower, there is no huge difference in duration of strain and stress between one-wave method and three-wave method. Differences were becoming significantly at high damaged level, and the strains measured by strain gage measurements were below one-wave method and three-wave method. In addition, there were different development of fracture and destruction in brittle materials and rocks. The experimental results confirmed that strains of materials can be obtained by using strain gage and laser displacement measurement, while the latter required models with more stable signals and adjusted positions of measurement to meet the measuring requirements. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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