Dynamic Fracture Characteristic of Sandstone After High Temperature
Jianlei Chen,
Yanbing Wang,
Baozhu Wang
Issue:
Volume 6, Issue 6, November 2021
Pages:
81-89
Received:
11 November 2021
Accepted:
29 November 2021
Published:
7 December 2021
Abstract: The increase of deep underground works has led to many concerns in relation to the dynamic characteristics of rocks subject to heating treatment, including underground rock blasting. For revelation of the dynamic mechanical properties of rocks subject to heating treatment, the sandstone treated after 22°C, 150°C, 300°C, 450°C, 600°C, and 750°C respectively were subject to dynamic fracture toughness tests using Split Hopkinson Pressure Bar (SHPB). After reaching the set temperature, it is maintained for 30 min and then cooled for 24 h to normal temperature. the morphology of microcracks on the surface of sandstone samples due to thermodynamic action was observed by electron microscope scanning (sem). The P wave velocity of rock samples after high temperature is measured, and the results can be correlated with scanning electron microscope images. Finally, the relationship between temperature and dynamic fracture toughness is analyzed. Results showed: when the loading rate was lower (<50GPa•m1/2s-1), the fracture toughness values corresponding to different temperatures of heat treatment tended to be closer with each other. However, when the loading rate was higher, the fracture toughness values varied greatly. Under certain special loading rates that are the same, the fracture toughness of sandstone at 300°C is about 6% higher than at 150°C. This can be attributed that the expansion of minerals at high temperature results in the closure of original cracks in the rocks, the change in internal structure of rocks, and the increased fracture toughness.
Abstract: The increase of deep underground works has led to many concerns in relation to the dynamic characteristics of rocks subject to heating treatment, including underground rock blasting. For revelation of the dynamic mechanical properties of rocks subject to heating treatment, the sandstone treated after 22°C, 150°C, 300°C, 450°C, 600°C, and 750°C resp...
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Differential Effect of Prior Knowledge of Manual Technical Drawing on Academic Achievement of South-East, Nigeria Colleges of Education (Technical) Students in AutoCAD
Victor Ikechukwu Oguejiofor,
Goerge Nwachkwu Ogbonna,
Veronica Nkechi Imakwu,
Osita Anthony Ezeama,
Ogbonnaya Okorie Eze
Issue:
Volume 6, Issue 6, November 2021
Pages:
90-96
Received:
10 November 2021
Accepted:
2 December 2021
Published:
10 December 2021
Abstract: The study investigated the Differential Effect of Prior Knowledge of Manual Technical Drawing on Academic Achievement on Colleges of Education (Technical) Students in AutoCAD. The design of the study was a quasi-experimental research design. The study was carried out in South-East, Nigeria. The population for the study was 122 NCE students of technical education. Federal College of Education (Technical), Umunze in Anambra State and Enugu State College of Education (Technical) were used for the study. The population of the study was manageable; there was no sample and sampling technique. The instrument for data collection was AutoCAD achievement test (AAT). The AutoCAD achievement test has three versions: pre-test, post-test and retention test, which were the same except for the reshuffling and swapping of the questions and options of the 60 questions used for the study. The AutoCAD achievement test was subjected to face and content validation. The reliability using Kuder Richardson (K-R 20) was 0.79. The scores for the pre-test, post-test and retention test were analyzed using mean with standard deviation and ANCOVA. The major findings of the study were that prior knowledge of manual technical drawing increases the academic achievement and retention of colleges of education (technical) students in the study of AutoCAD. Based on the findings it was recommended that manual technical drawing should be a perquisite course to AutoCAD in colleges of education (technical) in Nigeria.
Abstract: The study investigated the Differential Effect of Prior Knowledge of Manual Technical Drawing on Academic Achievement on Colleges of Education (Technical) Students in AutoCAD. The design of the study was a quasi-experimental research design. The study was carried out in South-East, Nigeria. The population for the study was 122 NCE students of techn...
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