为分析高地温水工隧洞衬砌结构温度应力特性,基于拉普拉斯变换推导出衬砌结构瞬态温度场的解析解,并借助弹性抗力法推导出衬砌结构的弹性温度应力分量。依托新疆布伦口水电站监测数据对衬砌结构瞬态温度场及应力场进行计算分析,并采用...为分析高地温水工隧洞衬砌结构温度应力特性,基于拉普拉斯变换推导出衬砌结构瞬态温度场的解析解,并借助弹性抗力法推导出衬砌结构的弹性温度应力分量。依托新疆布伦口水电站监测数据对衬砌结构瞬态温度场及应力场进行计算分析,并采用抗拉强度准则和裂缝尖端强度因子对衬砌结构破坏进行分析,提出合理的温控防裂措施。结果表明:1)衬砌温度场前期整体温度迅速上升,在第7天左右达到最大值,其中衬砌内壁温度可达到37℃,外壁温度可达到56℃。2)衬砌结构外墙环向应力可达到2.2 MPa,体现为拉应力状态;径向应力可达到2.7 MPa,呈现为压应力状态。3)衬砌结构强度的破坏主要受温度及结构本身稳定性2方面影响,可通过采用低热水泥、控制混凝土的入模温度以及严格监控施工过程来提高衬砌的稳定性。其中,采用低热水泥可降低衬砌结构的温升值,混凝土的最终水化热每降低50 k J/kg,衬砌结构内外壁的温差可降低1.85℃左右;适当提高入模温度可缩短水化热的放热周期及降低衬砌内外壁温差。展开更多
The effect of different microstructures on the polarization resistance (Rp) and the hydrogen-induced cracking (HIC) of a micro-alloyed steel austenitized and submitted to different cooling rates was studied.Samples 19...The effect of different microstructures on the polarization resistance (Rp) and the hydrogen-induced cracking (HIC) of a micro-alloyed steel austenitized and submitted to different cooling rates was studied.Samples 19.1 x 6 x 2 mm,containing the whole thickness of the plate were extracted from a 20 mm plate and heat treated on a quenching dilatometer,were submitted to Rp and HIC corrosion tests.Both Rp and HIC tests followed as close as possible ASTM G59 and NACE standard TM0284-2003,in this case,modified only with regard to the size of the samples.Steel samples transformed from austenite by a slow cooling (cooling rate of 0.5℃.s-1) showed higher susceptibility to hydrogen-induced cracking,with large cracks in the middle of the sample propagating along segregation bands,corresponding to the centerline of the plate thickness.For cooling rates of 10℃.s-1,only small cracks were found in the matrix and micro cracks nucleated at non-metallic inclusions.For higher cooling rates (40℃.s-1) very few small cracks were detected,linked to non-metallic inclusions.This result suggests that structures formed by polygonal structures and segregation bands (were eutectoid microconstituents predominate) have higher susceptibility to HIC.Structures predominantly formed by acicular ferrite make it difficult to propagate the cracks among non-oriented and interlaced acicular ferrite crystals.Smaller segregation bands containing eutectoid products also help inhibit cracking and crack propagation;segregation bands can function as pipelines for hydrogen diffusion and offer a path of stress concentration for the propagation of cracks,frequently associated to non-metallic inclusions.Polarization resistance essays performed on the steel in theas received condition,prior to any heat treatment,showed larger differences between the regions of the plate,with a considerably lower Rp in the centerline.The austenitization heat treatments followed by cooling rates of 0.5 e 10℃.s-1 made more uniform the corrosion resistance along the thickness of the plate.The effects of heat treatments on the corrosion resistance are probably related to the microconstituent formed,allied to the chemical homogenization of the impurities concentrated on the centerline of the plate.展开更多
文摘为分析高地温水工隧洞衬砌结构温度应力特性,基于拉普拉斯变换推导出衬砌结构瞬态温度场的解析解,并借助弹性抗力法推导出衬砌结构的弹性温度应力分量。依托新疆布伦口水电站监测数据对衬砌结构瞬态温度场及应力场进行计算分析,并采用抗拉强度准则和裂缝尖端强度因子对衬砌结构破坏进行分析,提出合理的温控防裂措施。结果表明:1)衬砌温度场前期整体温度迅速上升,在第7天左右达到最大值,其中衬砌内壁温度可达到37℃,外壁温度可达到56℃。2)衬砌结构外墙环向应力可达到2.2 MPa,体现为拉应力状态;径向应力可达到2.7 MPa,呈现为压应力状态。3)衬砌结构强度的破坏主要受温度及结构本身稳定性2方面影响,可通过采用低热水泥、控制混凝土的入模温度以及严格监控施工过程来提高衬砌的稳定性。其中,采用低热水泥可降低衬砌结构的温升值,混凝土的最终水化热每降低50 k J/kg,衬砌结构内外壁的温差可降低1.85℃左右;适当提高入模温度可缩短水化热的放热周期及降低衬砌内外壁温差。
文摘The effect of different microstructures on the polarization resistance (Rp) and the hydrogen-induced cracking (HIC) of a micro-alloyed steel austenitized and submitted to different cooling rates was studied.Samples 19.1 x 6 x 2 mm,containing the whole thickness of the plate were extracted from a 20 mm plate and heat treated on a quenching dilatometer,were submitted to Rp and HIC corrosion tests.Both Rp and HIC tests followed as close as possible ASTM G59 and NACE standard TM0284-2003,in this case,modified only with regard to the size of the samples.Steel samples transformed from austenite by a slow cooling (cooling rate of 0.5℃.s-1) showed higher susceptibility to hydrogen-induced cracking,with large cracks in the middle of the sample propagating along segregation bands,corresponding to the centerline of the plate thickness.For cooling rates of 10℃.s-1,only small cracks were found in the matrix and micro cracks nucleated at non-metallic inclusions.For higher cooling rates (40℃.s-1) very few small cracks were detected,linked to non-metallic inclusions.This result suggests that structures formed by polygonal structures and segregation bands (were eutectoid microconstituents predominate) have higher susceptibility to HIC.Structures predominantly formed by acicular ferrite make it difficult to propagate the cracks among non-oriented and interlaced acicular ferrite crystals.Smaller segregation bands containing eutectoid products also help inhibit cracking and crack propagation;segregation bands can function as pipelines for hydrogen diffusion and offer a path of stress concentration for the propagation of cracks,frequently associated to non-metallic inclusions.Polarization resistance essays performed on the steel in theas received condition,prior to any heat treatment,showed larger differences between the regions of the plate,with a considerably lower Rp in the centerline.The austenitization heat treatments followed by cooling rates of 0.5 e 10℃.s-1 made more uniform the corrosion resistance along the thickness of the plate.The effects of heat treatments on the corrosion resistance are probably related to the microconstituent formed,allied to the chemical homogenization of the impurities concentrated on the centerline of the plate.
