Uneven frost heave deformation can shorten the operational lifespan of foundation engineering.Clarifying the mechanisms of uneven frost heave facilitates the targeted mitigation of frost damage.This study focused on a...Uneven frost heave deformation can shorten the operational lifespan of foundation engineering.Clarifying the mechanisms of uneven frost heave facilitates the targeted mitigation of frost damage.This study focused on a water conveyance channel in Jilin Province,northern China,and found after monitoring that the frost heave at the channel bottom lining exceeded that at the crest by 44.5 mm,with the freezing temperature at the bottom being over 2℃lower than that at the crest.Soil columns with an initial gravimetric moisture content of 12%,16%,18%,and 20%were then prepared.The effects of temperature and moisture content on frost heave were analyzed under two freezing conditions(-5℃and-10℃)through unidirectional freezing tests.A coupled thermo-hydro-mechanical(THM)frost heave model,validated by the test results,was further established.In the soil with an initial moisture content of 20%,the formation of ice lenses associated with substantial water migration contributed to a large temperature gradient,which can jointly induce frost heave.Under the-10℃condition,the temperature gradient in the soil column with a 20%initial moisture content reached 0.84℃/cm,the total water migration reached 10.72%,and the frost heave deformation was 1.86 mm.The THM coupling results indicated that,under the interaction of a large temperature gradient and moisture accumulation,the volumetric ice content remained high in the bottom soil during freezing and peaked at 0.36.The frost damage to the bottom soil was severe,and the maximum deformation reached 57 mm.展开更多
Hypoeutectic Al-Si alloys are becoming increasingly popular in automotive and aerospace engineering fields due to their excellent overall performance,and grain refinement is regarded as an important way to improve cas...Hypoeutectic Al-Si alloys are becoming increasingly popular in automotive and aerospace engineering fields due to their excellent overall performance,and grain refinement is regarded as an important way to improve casting and mechanical properties.Titanium(Ti)is a basic element for grain refinement;thus,a certain amount of Ti is often included in Al-Si alloys.In the present work,the changes in the grain re-finement,mechanical,and casting properties of Al-Si alloys with different Ti concentration levels under various grain refinement conditions were systematically investigated.The specific roles of Ti in the het-erogeneous nucleation ofα-Al grains were summarized,and the formation mechanism of Ti-rich zones in Al-Si alloys was revealed.Excess Ti concentration could not efficiently reduce the grain size of Al-Si alloys and eventually resulted in inferior mechanical and casting qualities;hence,the recommended Ti concentration level for the aluminum alloy grades of A356 and A357 is≤0.1 wt%.Furthermore,an opti-mized technique for the grain refinement of hypoeutectic Al-Si alloys was presented.A small amount of an Al-TCB master alloy was introduced to achieve the best grain refinement and mechanical properties in a trace Ti environment.The addition of 0.5 wt%of the Al-TCB master alloy at the Ti concentration level of 0.06 wt%increased the ultimate tensile strength,elongation,and quality index of the Al-7Si-0.45Mg alloy to 328.8±5.0 MPa,14.4%±0.6%,and 970.7±33.1 MPa,respectively.展开更多
基金funding support from the National Natural Science Foundation of China(Grants Nos.42330708 and 42302329)the Graduate Innovation Research Program of Jilin University(Grant No.2024CX118).
文摘Uneven frost heave deformation can shorten the operational lifespan of foundation engineering.Clarifying the mechanisms of uneven frost heave facilitates the targeted mitigation of frost damage.This study focused on a water conveyance channel in Jilin Province,northern China,and found after monitoring that the frost heave at the channel bottom lining exceeded that at the crest by 44.5 mm,with the freezing temperature at the bottom being over 2℃lower than that at the crest.Soil columns with an initial gravimetric moisture content of 12%,16%,18%,and 20%were then prepared.The effects of temperature and moisture content on frost heave were analyzed under two freezing conditions(-5℃and-10℃)through unidirectional freezing tests.A coupled thermo-hydro-mechanical(THM)frost heave model,validated by the test results,was further established.In the soil with an initial moisture content of 20%,the formation of ice lenses associated with substantial water migration contributed to a large temperature gradient,which can jointly induce frost heave.Under the-10℃condition,the temperature gradient in the soil column with a 20%initial moisture content reached 0.84℃/cm,the total water migration reached 10.72%,and the frost heave deformation was 1.86 mm.The THM coupling results indicated that,under the interaction of a large temperature gradient and moisture accumulation,the volumetric ice content remained high in the bottom soil during freezing and peaked at 0.36.The frost damage to the bottom soil was severe,and the maximum deformation reached 57 mm.
基金financially supported by the National Natu-ral Science Foundation of China(Nos.52071189,U2241230,and 52301167).
文摘Hypoeutectic Al-Si alloys are becoming increasingly popular in automotive and aerospace engineering fields due to their excellent overall performance,and grain refinement is regarded as an important way to improve casting and mechanical properties.Titanium(Ti)is a basic element for grain refinement;thus,a certain amount of Ti is often included in Al-Si alloys.In the present work,the changes in the grain re-finement,mechanical,and casting properties of Al-Si alloys with different Ti concentration levels under various grain refinement conditions were systematically investigated.The specific roles of Ti in the het-erogeneous nucleation ofα-Al grains were summarized,and the formation mechanism of Ti-rich zones in Al-Si alloys was revealed.Excess Ti concentration could not efficiently reduce the grain size of Al-Si alloys and eventually resulted in inferior mechanical and casting qualities;hence,the recommended Ti concentration level for the aluminum alloy grades of A356 and A357 is≤0.1 wt%.Furthermore,an opti-mized technique for the grain refinement of hypoeutectic Al-Si alloys was presented.A small amount of an Al-TCB master alloy was introduced to achieve the best grain refinement and mechanical properties in a trace Ti environment.The addition of 0.5 wt%of the Al-TCB master alloy at the Ti concentration level of 0.06 wt%increased the ultimate tensile strength,elongation,and quality index of the Al-7Si-0.45Mg alloy to 328.8±5.0 MPa,14.4%±0.6%,and 970.7±33.1 MPa,respectively.
