This paper presents the development of ultra high strength concrete （UHSC） using local materials. UHSC mixture proportions were developed using local materials so that UHSC may be made more affordable to a wider var...This paper presents the development of ultra high strength concrete （UHSC） using local materials. UHSC mixture proportions were developed using local materials so that UHSC may be made more affordable to a wider variety of applications. Specifically, local sand with a top size of 600 um, and locally available Type I/II cement and silica fume were used in this research. Each of these material selections is seen as an improvement in sustainability for UHSC. Two mixtures （one with and one without fibers） were recommended as the UHSC mixtures. The greatest compressive strengths obtained in this study were 165.6 MPa for UHSC with steel fibers and 161.9 MPa for UHSC without fibers. The compressive and flexural strengths obtained from the UHSC mixtures developed in this work are comparable to UHSC strengths presented in the literature. Producing this innovative material with local materials reduces the cost of the material, improves sustainability, and produces mechanical performance similar to prepackaged, commercially available products.展开更多
In this paper, the optimization design of the low strength mechanical test and orthogonal test have been analyzed in order to simulate the mechanical properties of thick and extra-thick coal seam accurately in a simil...In this paper, the optimization design of the low strength mechanical test and orthogonal test have been analyzed in order to simulate the mechanical properties of thick and extra-thick coal seam accurately in a similar material simulation test. The results show that the specimen can reach a wider range of strength when cement has been used compared to that of gypsum, suggesting that cement is more suitable for making coal seam in similar material simulation tests. The uniaxial compressive strength is more sensitive to cement than coal or sand. The proportion of coal and sand do not play a decisive role in uniaxial compressive strength. The uniaxial compressive strength and specimen density decrease as the mass percent of coal and aggregate–binder ratio rise. There is a positive correlation between uniaxial compressive strength and density. The No. 5 proportion(cement: sand: water: activated carbon: coal = 6:6:7:1.1:79.9)was chosen to be used in the similar material simulation test of steeply dipping and extra-thick coal seam with a density of 0.913 g/cm^3 and an uniaxial compressive strength of 0.076 MPa which are in accordance with the similarity theory. The phenomenon of overburden stratum movement, fracture development and floor pressure relief were obtained during the similar material simulation test by using the proportion.展开更多
Most of the challenges experienced by many engineering materials originate from the surface which later leads to total failure,hence affecting the resultant mechanical properties and service life.However,these challen...Most of the challenges experienced by many engineering materials originate from the surface which later leads to total failure,hence affecting the resultant mechanical properties and service life.However,these challenges have been addressed thanks to the invention of a novel surface mechanical attrition treatment(SMAT)method which protects the material surface by generating a gradient-structured layer with improved strength and hardness without jeopardizing the ductility.The present work provides a comprehensive literature review on the mechanical properties of materials after SMAT including the hardness,tensile strength and elongation,and residual stress.Firstly,a brief introduction on the different forms of surface nanocrystallization is given to get a better understanding of the SMAT process and its advantages over other forms of surface treatments,and then the grain refinement mechanisms of materials by SMAT from the matrix region(base material)to the nanocrystallized layer are explained.The effects of fatigue,fracture,and wear of materials by the enhanced mechanical properties after SMAT are also discussed in detail.In addition,the various applications of SMAT ranging from automotive,photoelectric conversion,biomedical,diffusion,and 3 D-printing of materials are extensively discussed.The prospects and recent research trends in terms of mechanical properties of materials affected by SMAT are then summarized.展开更多
The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles.However,sheet metal forming process not only produces desirable changes in ma...The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles.However,sheet metal forming process not only produces desirable changes in material properties but also causes material damage that may adversely influence the service performance of the material formed.Thus,an investigation is conducted to experimentally quantify such influence for a commonly used steel（the 22MnB5 steel） based on the hot and cold forming processes.For each process,a number of samples are used to conduct a uniaxial tensile test to simulate the forming process.After that,some of the samples are trimmed into a standard shape and then uniaxially extended until fracture to simulate the service stage.Finally,a microstructure test is conducted to analyze the microdefects of the remaining samples.Based on the results of the first two tests,the effect of material damage on the service performance of 22MnB5 steel is analyzed.It is found that the material damages of both the hot and cold forming processes cause reductions in the service performance,such as the failure strain,the ultimate stress,the capacity of energy absorption and the ratio of residual strain.The reductions are generally lower and non-linear in the former process but higher and linear in the latter process.Additionally,it is found from the microstructure analysis that the difference in the reductions of the service performance of 22MnB5 by the two forming processes is driven by the difference in the micro damage mechanisms of the two processes.The findings of this research provide a useful reference in terms of the selection of sheet metal forming processes and the determination of forming parameters for 22MnB5.展开更多
离心模型试验的准确性与可靠性取决于模型与原型的相似程度,选择合理的相似材料是离心模型试验的关键环节。以广州某垃圾填埋场挡坝加筋边坡的工程设计为背景,为合理开展离心模型试验,选取6种编织布进行分析。考虑强度相似原则和界面摩...离心模型试验的准确性与可靠性取决于模型与原型的相似程度,选择合理的相似材料是离心模型试验的关键环节。以广州某垃圾填埋场挡坝加筋边坡的工程设计为背景,为合理开展离心模型试验,选取6种编织布进行分析。考虑强度相似原则和界面摩擦因素,基于窄条拉伸试验、直剪摩擦试验合理比选相似替代材料。按该边坡设计方案,模型边坡在离心场中能够保持稳定。边坡设计中应进一步参照数值分析和工程类比进行方案确定。如按强度相似进行材料选择,通过调整模型土层厚度,所选择的6种材料可对抗拉强度在13~360 k N/m的土工布进行模拟。展开更多
文摘This paper presents the development of ultra high strength concrete （UHSC） using local materials. UHSC mixture proportions were developed using local materials so that UHSC may be made more affordable to a wider variety of applications. Specifically, local sand with a top size of 600 um, and locally available Type I/II cement and silica fume were used in this research. Each of these material selections is seen as an improvement in sustainability for UHSC. Two mixtures （one with and one without fibers） were recommended as the UHSC mixtures. The greatest compressive strengths obtained in this study were 165.6 MPa for UHSC with steel fibers and 161.9 MPa for UHSC without fibers. The compressive and flexural strengths obtained from the UHSC mixtures developed in this work are comparable to UHSC strengths presented in the literature. Producing this innovative material with local materials reduces the cost of the material, improves sustainability, and produces mechanical performance similar to prepackaged, commercially available products.
基金support of National Natural Science Foundation Project of China (51304128 & 51304237) the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents of China (2013RCJJ049)
文摘In this paper, the optimization design of the low strength mechanical test and orthogonal test have been analyzed in order to simulate the mechanical properties of thick and extra-thick coal seam accurately in a similar material simulation test. The results show that the specimen can reach a wider range of strength when cement has been used compared to that of gypsum, suggesting that cement is more suitable for making coal seam in similar material simulation tests. The uniaxial compressive strength is more sensitive to cement than coal or sand. The proportion of coal and sand do not play a decisive role in uniaxial compressive strength. The uniaxial compressive strength and specimen density decrease as the mass percent of coal and aggregate–binder ratio rise. There is a positive correlation between uniaxial compressive strength and density. The No. 5 proportion(cement: sand: water: activated carbon: coal = 6:6:7:1.1:79.9)was chosen to be used in the similar material simulation test of steeply dipping and extra-thick coal seam with a density of 0.913 g/cm^3 and an uniaxial compressive strength of 0.076 MPa which are in accordance with the similarity theory. The phenomenon of overburden stratum movement, fracture development and floor pressure relief were obtained during the similar material simulation test by using the proportion.
基金supports of the National Key R&D Program of China(Project No.2017YFA0204403)Hong Kong Themebased Research Scheme Ref.(T13-402/17-N).
文摘Most of the challenges experienced by many engineering materials originate from the surface which later leads to total failure,hence affecting the resultant mechanical properties and service life.However,these challenges have been addressed thanks to the invention of a novel surface mechanical attrition treatment(SMAT)method which protects the material surface by generating a gradient-structured layer with improved strength and hardness without jeopardizing the ductility.The present work provides a comprehensive literature review on the mechanical properties of materials after SMAT including the hardness,tensile strength and elongation,and residual stress.Firstly,a brief introduction on the different forms of surface nanocrystallization is given to get a better understanding of the SMAT process and its advantages over other forms of surface treatments,and then the grain refinement mechanisms of materials by SMAT from the matrix region(base material)to the nanocrystallized layer are explained.The effects of fatigue,fracture,and wear of materials by the enhanced mechanical properties after SMAT are also discussed in detail.In addition,the various applications of SMAT ranging from automotive,photoelectric conversion,biomedical,diffusion,and 3 D-printing of materials are extensively discussed.The prospects and recent research trends in terms of mechanical properties of materials affected by SMAT are then summarized.
基金Supported by National Natural Science Foundation of China(Grant No.51375201)CSAE(Beijing)Automotive Lightweight Technology Research Institute Development Fund Project of China
文摘The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles.However,sheet metal forming process not only produces desirable changes in material properties but also causes material damage that may adversely influence the service performance of the material formed.Thus,an investigation is conducted to experimentally quantify such influence for a commonly used steel（the 22MnB5 steel） based on the hot and cold forming processes.For each process,a number of samples are used to conduct a uniaxial tensile test to simulate the forming process.After that,some of the samples are trimmed into a standard shape and then uniaxially extended until fracture to simulate the service stage.Finally,a microstructure test is conducted to analyze the microdefects of the remaining samples.Based on the results of the first two tests,the effect of material damage on the service performance of 22MnB5 steel is analyzed.It is found that the material damages of both the hot and cold forming processes cause reductions in the service performance,such as the failure strain,the ultimate stress,the capacity of energy absorption and the ratio of residual strain.The reductions are generally lower and non-linear in the former process but higher and linear in the latter process.Additionally,it is found from the microstructure analysis that the difference in the reductions of the service performance of 22MnB5 by the two forming processes is driven by the difference in the micro damage mechanisms of the two processes.The findings of this research provide a useful reference in terms of the selection of sheet metal forming processes and the determination of forming parameters for 22MnB5.
文摘离心模型试验的准确性与可靠性取决于模型与原型的相似程度,选择合理的相似材料是离心模型试验的关键环节。以广州某垃圾填埋场挡坝加筋边坡的工程设计为背景,为合理开展离心模型试验,选取6种编织布进行分析。考虑强度相似原则和界面摩擦因素,基于窄条拉伸试验、直剪摩擦试验合理比选相似替代材料。按该边坡设计方案,模型边坡在离心场中能够保持稳定。边坡设计中应进一步参照数值分析和工程类比进行方案确定。如按强度相似进行材料选择,通过调整模型土层厚度,所选择的6种材料可对抗拉强度在13~360 k N/m的土工布进行模拟。
