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Residual Mechanical Properties and Explosive Spalling Behavior of ultra-high-strength Concrete Exposed to high Temperature

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Journal of Harbin Institute of Technology(New Series) 2017年第4期24卷 62-70页

作者： Gaifei Peng Juan Yang Faculty of Civil Engineering Beijing Jiaotong University

In order to explore the characteristics of ultra-high-strength concrete exposed to high temperature,residual mechanical properties and explosive spalling behavior of ultra-high-strength concrete( UHSC) and high strength concrete( HSC) exposed to high temperatures ranging from 20 ℃ to 800 ℃ were determined. The microstructure of the specimens after exposure to elevated temperature was analyzed by means of scanning electron microscope( SEM) and mercury intrusion porosimetry( MIP). The residual compressive strengths of UHSC and HSC were first increased and then decreased as temperature increased. After exposure to 800 ℃,the compressive strengths of UHSC and HSC were 24. 2 % and 22. 3 % of their original strengths at 20 ℃,respectively. The residual splitting tensile strengths of both UHSC and HSC were consistently decreased with the temperature increasing and were approximately 20% of their original strengths after 800 ℃. However,the residual fracture energies of both concretes tended to ascend even at 600 ℃. The explosive spalling of UHSC was more serious than that of HSC. Moisture content of the specimens governs the explosive spalling of both concretes with a positive correlations,and it is more pronounced in UHSC. These results suggest that UHSC suffers a substantial loss in load-bearing capacity and is highly prone to explosive spalling due to high temperature. The changes in compressive strength are due to the changes in the density and the pore structure of concrete. The probability and severity of explosive spalling of UHSC are much higher than those of HSC due to the higher pore volume in HSC.

关键词： ultra-high-strength concrete high strength concrete residual mechanical properties explosive spalling

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Analysis of roll-stamping process for rib grooves of ultra-high-strength beam parts

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Baosteel Technical Research 2020年第1期14卷 28-33页

作者： XIAO Hua SHI Lei Research Institute Baoshan Iron&Steel Co.Ltd.Shanghai 201999China State Key Laboratory of Development and Application Technology of Automotive Steels(Baosteel) Shanghai 201999China

Roll-stamping technology,a new process with both roll-forming and stamping characteristics,is suitable for manufacturing ultra-high-strength beam parts,especially variable cross-section beam parts.The rib groove is a local shape often used in automotive parts for positioning,avoidance,and stiffness strengthening on longitudinal and stiffening beams.In this study,two typical rib grooves,the flat-and round-bottom rib grooves,were selected to investigate the characteristics of the roll-stamping process of rib grooves.Using the ABAQUS software platform,a simulation analysis model of rib-groove roll stamping was established and different size rib grooves produced by the roll-stamping process were compared and analyzed.The results show that when the fillet radius of the rib groove increases,the maximum Mises stress,the maximum strain,and the maximum thinning rate decrease.For roll stamping,the minimum safe fillet radii of the two types of rib grooves are 8 and 4 mm,respectively.

关键词： ultra-high-strength steel roll stamping beam parts rib groove

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Deformation behavior and microstructural evolution in ultra-highstrength dual-phase(UHS-DP1000)steel with different strain rates

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Journal of Iron and Steel Research(International) 2019年第2期26卷 173-181页

作者： Mei Xu Hui Li Rui-ting Jiang Di Tang Hai-tao Jiang Zhen-li Mi Institute of Engineering Technology University of Scienee and Technology BeijingBeijing 100083China College of Engineering Yantai Nanshan UniversityYantai 265700ShandongChina Collaborative Innovation Center of Steel Technology University of Science and Technology BeijingBeijing 100083China

The dynamic tensile behavior and deformation mechanism of ultra-high-strength dual-phase(UHS-DP1000)steel were investigated over a wide range of strain rates from 10^-4 to 10^3 s^-1.As the strain rate increases,the transition strain decreases from 2.73 to 1.92,and the martensite plastic deformation starts earlier.At strain rate of 10^-4-0.5 s^-l,the inhomogeneous plastic deformation ability increases because the dislocation density in the ferrite matrix increases.This leads to a decrease in uni form elongation and an increase in fracture elongation.When the strain rate increases from 0.5 to 500s^-l.the amount of mobile dislocation increases,which is the main reason for the enhancing uniform elongation and fracture elongation.Mea nwhile,because the dislocation motio n resistance rapidly in creases,the yield strength and ultimate tensile strength also increase.When the strain rate is higher than 500 s^-1.the hardening behavior caused by the dislocation motion resistance has not been offset by softening due to the mobile dislocation and adiabatic heating.The voids at the early stage of deformation could not uniformly form and grow,and thus the homogeneous plastic deformation ability decreases.

关键词： ultra-high-strength dual-phase steel Strain rate Microstructural evolution Void Adiabatic heating

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FEM simulation of flexible roll forming based on different material models

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high Technology Letters 2018年第4期24卷 434-439页

作者：管延智 Yan Yu Wang Haibo College of Mechanical and Electrical Engineering North China University of Technology

Flexible roll forming is a new roll forming process that produces parts with variable cross sections. This forming process is proposed to meet the demand of weight reduction of automobile industry. In order to study the mechanisms and material flow rules in this new forming process,the finite element mothod( FEM) model of a nine-step flexible roll forming of an ultra-high-strength steel bumper is established based on deep understanding and reasonable simplification of the process.Given that the material model is an important factor that influences the simulation accuracy,three material models which consist of different yield criteria and hardening models are adopted in the FEM models. Sheet thickness and springback amount calculated with three material models are studied comparatively. According to sheet thickness reduction and springback amounts,it is found that the MKi( Mises yield criterion and kinematic hardening law) model's result is larger than MI( Mises yield criterion and isotropic hardening law) model and HI( Hill's yield criterion and isotropic hardening law) model. Therefore,it is concluded that material models do have influences on the flexible roll forming simulation and need to be determined carefully.

关键词： flexible roll forming finite element mothod(FEM)modeling material model ultra-high-strength steel

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Microstructure and Properties of 980MPa ultrafineGrained Cold Rolled Dual-Phase Steels

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Journal of Iron and Steel Research(International) 2011年第S1期18卷 316-319页

作者： HAN Qi-hang,KANG Yong-lin,ZHAO Xian-meng (School of Materials Science and Engineering,State Key Laboratory for Advanced Metals and Materials,University of Science and Technology Beijing,Beijing 100083,China) Univ Sci & Technol Beijing Sch Mat Sci & Engn State Key Lab Adv Met & Mat Beijing 100083 Peoples R China

Two kinds of 980MPa grade cold rolled dual phase steels have been developed by designing C-Si-Mn and C-Si-Mn-Nb alloy systems.The microstructure of martensite in Nb-free steel is consisted of lath martensite and twined martensite with the volume fraction of 67%.However,the main hard phase in Nb-containing one is twined martensit with the volume percent of 59%.The size of martensite islands in Nb-containing steel is from 1μm to 3μm,and the size of NbC precipitates is from 15nm to 40nm.As to Nb-containing steel,the yield strength,tensile strength,yield ratio and elongation are 501MPa,1035MPa,0.48 and 17.5% respectively.Futhermore,Nb-containing steel has higher working hardening rate value above the critical strain 6.5%.And it decreases slowly with increasing the strain.This is mainly because of ultrafine grain size and nano-precipitates in ferrite,which improves the compatibility of phases and reduces the stress concentration at the phase interface.

关键词： ultra-high-strength dual-phase steel ultra-fine grain microstructure properties

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THE VALENCE ELECTRON STRUCTURES OF MARTENSITE IN LOW ALLOY ultrahigh-strength STEELS AND THEIR INFLUENCE ON strength AND TOUGHNESS

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Chinese Science Bulletin 1991年第5期36卷 366-371页

作者：刘志林戴天时屈庸博杨双良张振宇 Division of Applied Physics Jilin University of Technology Changchun 130025 PRC

Ⅰ. THE VALENCE ELECTRON STRUCTURES OF MARTENSITE IN LOW ALLOY ultrahigh-strength STEELS AND THE SEGREGATION OF C-ME IN MARTENSITEThe valence electron structures ofmartensite in 30CrMnSiNi2A and Gc-4 steels can be established based on Refs. [1—3]. To be brief, only σ, nA and ncD are listed in Table 1, which are the values of electron structures of martensite in 30CrMnSi2A and Gc-4 steels.

关键词： low alloy ultra-high-strength steel martensite valence electron structure strength and toughness.

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