Imperfections in the(001) plate of rubidium hydrogen phthalate(RAP, RbC8H5O4) crystals have been studied by means of X-ray topography. The main defects are the grown-in dislocations, inclusions, growth layers and the ...Imperfections in the(001) plate of rubidium hydrogen phthalate(RAP, RbC8H5O4) crystals have been studied by means of X-ray topography. The main defects are the grown-in dislocations, inclusions, growth layers and the thermal strain lobes caused by heat. The large thermal strain nature was determined by an Inclusion Probed Method (IPM), which is due to the gradient of the interplanar spacing formed by atomic displacement to <110> directions.展开更多
In recent years elastic-plastic fracture mechanics has developed rapidly and is widely used to solve various engineering problems. The application of elastic-plastic fracture mechanics on the pallet of sintering machi...In recent years elastic-plastic fracture mechanics has developed rapidly and is widely used to solve various engineering problems. The application of elastic-plastic fracture mechanics on the pallet of sintering machine is approached in detail for the first time in the present study. The theoretical results were compared with the actual data determined from sintering machine pallet. Results show that good agreement was achieved between the method suggested by the author and the actual data. The basis of determining design of the sintering machine pallet in iron and steel engineering has been provided and it will result in great economic benefits.展开更多
Thermal self-compressing bonding(TSCB) is a new solid-state bonding method pioneered by the authors. With electron beam as the non-melted heat source, previous experimental study performed on titanium alloys has prove...Thermal self-compressing bonding(TSCB) is a new solid-state bonding method pioneered by the authors. With electron beam as the non-melted heat source, previous experimental study performed on titanium alloys has proved the feasibility of TSCB. However, the thermal stress–strain process during bonding, which is of very important significance in revealing the mechanism of TSCB, was not analysed. In this paper, finite element analysis method is adopted to numerically study the thermal elasto-plastic stress–strain cycle of thermal self-compressing bonding. It is found that due to the localized heating, a non-uniform temperature distribution is formed during bonding, with the highest temperature existed on the bond interface. The expansion of high temperature materials adjacent to the bond interface are restrained by surrounding cool materials and rigid restraints, and thus an internal elasto-plastic stress–strain field is developed by itself which makes the bond interface subjected to thermal compressive action. This thermal self-compressing action combined with the high temperature on the bond interface promotes the atom diffusion across the bond interface to produce solid-state joints. Due to the relatively large plastic deformation, rigid restraint TSCB obtains sound joints in relatively short time compared to diffusion bonding.展开更多
The effect of strains on the thermal conductivity of Si/Ge superlattices was investigated by nonequilibrium molecular dynamics（NEMD） simulation. The thermal conductivities experienced a near linear drop with increas...The effect of strains on the thermal conductivity of Si/Ge superlattices was investigated by nonequilibrium molecular dynamics（NEMD） simulation. The thermal conductivities experienced a near linear drop with increasing tensile and compressive strains. It was explained by the fact that the decrease of the phonons velocities and a mass of structural defects generated under strains. Meanwhile, a theoretical calculation based on Modified-Callaway model was performed,and it was found that the theoretical results were in good agreement with the molecular dynamics results.展开更多
Tensile properties of a two phase γ Ti 47Al 1.5Cr 0.5Mn 2.8Nb alloy with a duplex microstructure were tested under strain rates ranging from 5×10 -5 to 5×10 -3 s -1 at temperatures from 1 123 K to 1 273 K. ...Tensile properties of a two phase γ Ti 47Al 1.5Cr 0.5Mn 2.8Nb alloy with a duplex microstructure were tested under strain rates ranging from 5×10 -5 to 5×10 -3 s -1 at temperatures from 1 123 K to 1 273 K. It was found that there exists approximately linear relationship between the flow stresses and the logarithm of the strain rate at different temperatures. The strain rate dependence was analyzed by thermal activation theory, and dislocation climbing has been identified as the rate controlling mechanism.展开更多
By using a self-made thermal fatigue test machine of outer-constraint mode, the influence of top-temperature of thermal cycle T t on thermal stress-strain and thermal fatigue behavior of an industrial pure iron was in...By using a self-made thermal fatigue test machine of outer-constraint mode, the influence of top-temperature of thermal cycle T t on thermal stress-strain and thermal fatigue behavior of an industrial pure iron was investigated. The T t was varied from stress/strain 773K to 1073K. The results show that, increasing of T t , the thermal stress-strain cycles can be classified into four types, they are: compressive stress cycle; compressive strain-tensile stress cycle; compressive strain-tensile stress cycle than changing to compressive tensile plastic strain cycle; and finally, compressive tensile plastic strain cycle. It is also revealed that certain relationship does exist between thermal fatigue life and characteristics of thermal stress/strain cycle. When compressive tensile plastic strain cycle were appear by increasing of T t , thermal fatigue life decreasing rapidly. The concept of thermal fatigue transition temperature, and determining method were put up in this thesis.展开更多
The design temperature of high plutonium concentration ZPPR fuel plates is 600°C. Cladding integrity of the 304 L stainless steel cladding is a significant concern with this fuel since even small holes can lead t...The design temperature of high plutonium concentration ZPPR fuel plates is 600°C. Cladding integrity of the 304 L stainless steel cladding is a significant concern with this fuel since even small holes can lead to substantial fuel degradation. Since the fuel has a higher coefficient of thermal expansion than the cladding, an investigation of the stress induced in the cladding due to the differential thermal expansion of fuel and cladding up to the design temperature was conducted. Small holes in the cladding envelope would be expected to lead to the fuel hydriding and oxidizing into a powder over a long period of time. This is the same type of chemical reaction chain that exists in the degradation of the high uranium concentration ZPPR fuel. Unfortunately, the uranium fuel was designed with vents which allowed this degradation to occur. The Pu cladding is sealed so only fuel with damaged cladding would be subject to this damage. The thermal stresses that can be developed in the fuel cladding have been calculated in this paper and compared to the ultimate tensile stress of the cladding. The conclusion is drawn that thermal stresses cannot induce holes in the cladding even for the highest storage temperatures predicted in calculations (292°C). In fact, thermal stress cannot cause cladding failure as long as the fuel temperatures are below the design limit of 600°C (1112°F).展开更多
Strained Si is recognized as a necessary technology booster for modem integrated circuit technology. However, the thermal oxidation behaviors of strained Si substrates are not well understood yet despite their importa...Strained Si is recognized as a necessary technology booster for modem integrated circuit technology. However, the thermal oxidation behaviors of strained Si substrates are not well understood yet despite their importance. In this study, we for the first time experimentally find that all types of strained Si substrates （uniaxial tensile, uniaxial compressive, biaxial tensile, and biaxial compressive） show smaller thermal oxidation rates than an unstrained Si substrate. The possible mechanisms for these retarded thermal oxidation rates in strained Si substrates are also discussed.展开更多
文摘Imperfections in the(001) plate of rubidium hydrogen phthalate(RAP, RbC8H5O4) crystals have been studied by means of X-ray topography. The main defects are the grown-in dislocations, inclusions, growth layers and the thermal strain lobes caused by heat. The large thermal strain nature was determined by an Inclusion Probed Method (IPM), which is due to the gradient of the interplanar spacing formed by atomic displacement to <110> directions.
文摘In recent years elastic-plastic fracture mechanics has developed rapidly and is widely used to solve various engineering problems. The application of elastic-plastic fracture mechanics on the pallet of sintering machine is approached in detail for the first time in the present study. The theoretical results were compared with the actual data determined from sintering machine pallet. Results show that good agreement was achieved between the method suggested by the author and the actual data. The basis of determining design of the sintering machine pallet in iron and steel engineering has been provided and it will result in great economic benefits.
基金Supported by National Natural Science Foundation of China(Grant No.51705491)
文摘Thermal self-compressing bonding(TSCB) is a new solid-state bonding method pioneered by the authors. With electron beam as the non-melted heat source, previous experimental study performed on titanium alloys has proved the feasibility of TSCB. However, the thermal stress–strain process during bonding, which is of very important significance in revealing the mechanism of TSCB, was not analysed. In this paper, finite element analysis method is adopted to numerically study the thermal elasto-plastic stress–strain cycle of thermal self-compressing bonding. It is found that due to the localized heating, a non-uniform temperature distribution is formed during bonding, with the highest temperature existed on the bond interface. The expansion of high temperature materials adjacent to the bond interface are restrained by surrounding cool materials and rigid restraints, and thus an internal elasto-plastic stress–strain field is developed by itself which makes the bond interface subjected to thermal compressive action. This thermal self-compressing action combined with the high temperature on the bond interface promotes the atom diffusion across the bond interface to produce solid-state joints. Due to the relatively large plastic deformation, rigid restraint TSCB obtains sound joints in relatively short time compared to diffusion bonding.
基金Supported by the National Natural Science Foundation of China(No.51706039)
文摘The effect of strains on the thermal conductivity of Si/Ge superlattices was investigated by nonequilibrium molecular dynamics（NEMD） simulation. The thermal conductivities experienced a near linear drop with increasing tensile and compressive strains. It was explained by the fact that the decrease of the phonons velocities and a mass of structural defects generated under strains. Meanwhile, a theoretical calculation based on Modified-Callaway model was performed,and it was found that the theoretical results were in good agreement with the molecular dynamics results.
文摘Tensile properties of a two phase γ Ti 47Al 1.5Cr 0.5Mn 2.8Nb alloy with a duplex microstructure were tested under strain rates ranging from 5×10 -5 to 5×10 -3 s -1 at temperatures from 1 123 K to 1 273 K. It was found that there exists approximately linear relationship between the flow stresses and the logarithm of the strain rate at different temperatures. The strain rate dependence was analyzed by thermal activation theory, and dislocation climbing has been identified as the rate controlling mechanism.
文摘By using a self-made thermal fatigue test machine of outer-constraint mode, the influence of top-temperature of thermal cycle T t on thermal stress-strain and thermal fatigue behavior of an industrial pure iron was investigated. The T t was varied from stress/strain 773K to 1073K. The results show that, increasing of T t , the thermal stress-strain cycles can be classified into four types, they are: compressive stress cycle; compressive strain-tensile stress cycle; compressive strain-tensile stress cycle than changing to compressive tensile plastic strain cycle; and finally, compressive tensile plastic strain cycle. It is also revealed that certain relationship does exist between thermal fatigue life and characteristics of thermal stress/strain cycle. When compressive tensile plastic strain cycle were appear by increasing of T t , thermal fatigue life decreasing rapidly. The concept of thermal fatigue transition temperature, and determining method were put up in this thesis.
文摘The design temperature of high plutonium concentration ZPPR fuel plates is 600°C. Cladding integrity of the 304 L stainless steel cladding is a significant concern with this fuel since even small holes can lead to substantial fuel degradation. Since the fuel has a higher coefficient of thermal expansion than the cladding, an investigation of the stress induced in the cladding due to the differential thermal expansion of fuel and cladding up to the design temperature was conducted. Small holes in the cladding envelope would be expected to lead to the fuel hydriding and oxidizing into a powder over a long period of time. This is the same type of chemical reaction chain that exists in the degradation of the high uranium concentration ZPPR fuel. Unfortunately, the uranium fuel was designed with vents which allowed this degradation to occur. The Pu cladding is sealed so only fuel with damaged cladding would be subject to this damage. The thermal stresses that can be developed in the fuel cladding have been calculated in this paper and compared to the ultimate tensile stress of the cladding. The conclusion is drawn that thermal stresses cannot induce holes in the cladding even for the highest storage temperatures predicted in calculations (292°C). In fact, thermal stress cannot cause cladding failure as long as the fuel temperatures are below the design limit of 600°C (1112°F).
基金supported by the National Key Basic Research Project of China(Grant No.2011CBA00607)the National Natural Science Foundation of China(Grant Nos.61106089 and 61376097)the Program B for Outstanding Ph.D.Candidate of Nanjing University,China(Grant No.201301B005)
文摘Strained Si is recognized as a necessary technology booster for modem integrated circuit technology. However, the thermal oxidation behaviors of strained Si substrates are not well understood yet despite their importance. In this study, we for the first time experimentally find that all types of strained Si substrates （uniaxial tensile, uniaxial compressive, biaxial tensile, and biaxial compressive） show smaller thermal oxidation rates than an unstrained Si substrate. The possible mechanisms for these retarded thermal oxidation rates in strained Si substrates are also discussed.
