摘要
超高性能混凝土(UHPC)在大跨度桥梁、机场路面及抗爆结构中广泛应用,此类结构常受到高应变率冲击荷载作用,故研究UHPC在冲击劈拉荷载下的抗拉力学性能至关重要。基于数字图像相关技术(DIC),利用分离式霍普金森杆(SHPB)装置开展不同冲击气压下的动态劈拉试验,研究UHPC在冲击荷载下的力学性能与损伤规律,分析不同冲击气压下UHPC的破坏形态和损伤演化过程,分析UHPC的动态应力–应变关系曲线,讨论动态抗拉强度、动态弹性模量、动态提高因子、动态耗散能与应变率的关系,建立UHPC极限抗拉强度的动态提高因子模型。研究结果表明,不同应变率劈拉荷载下UHPC的损伤形式略有不同:在冲击劈拉荷载作用下,随着应变率的增大,试件最终被破坏时主裂缝扩展程度增大;UHPC试件极限抗拉强度均随着应变率的增大而增大;UHPC耗散冲击能量有基于混凝土基体破坏、通过拔出或拔断钢纤维两种方式;UHPC在冲击作用下强度大,变形能力强,可有效耗散冲击能量;UHPC的抗冲击性能及极限抗拉强度的应变率敏感性均高于普通混凝土;UHPC的动态耗散能随应变率的增大而增加,但能量耗散比却呈现出先增长后降低的趋势。
Objective Ultra–high–performance concrete(UHPC)is widely used in long-span bridges,airport pavements,and explosion-resistant structures,which are often subjected to high strain rate impact loads during service.Given that the tensile properties of concrete are generally weaker than its compression properties,and tensile failure is a main damage mechanism in concrete,it is crucial to investigate the tensile properties of UHPC under impact splitting tensile load.Currently,research on UHPC primarily focuses on materials,mixing ratios,and mechanical properties under static load,with less focus on dynamic impact and microscopic damage mechanisms.Methods Digital image correlation(DIC)is an innovative optical detection technology that monitors the deformation and displacement of a test object's surface by collecting grayscale digital images and analyzing the changes over time.A split Hopkinson pressure bar is utilized to conduct dynamic tensile tests at different strain rates.The damage and crack development of the specimen were analyzed,and the crack growth rate is measured and calculated using DIC technology.The UHPC material used in the experiment is steel fiber ultra–high–performance concrete.The experiment utilized a 100 mm large diameter split Hopkinson compression rod as a dynamic loading device,Different strain rates were applied by adjusting the impact air pressure,with three repeated specimens are selected under different air pressures to minimize errors.Based on one-dimensional stress wave theory,the stress,strain,and strain rate of the specimen under dynamic impact splitting tensile load were calculated from the stress wave data collected by strain gauges on the incident and transmission rods.This research explores the changes in failure mode,dynamic compressive strength,dynamic elastic modulus,dynamic dissipated energy,and damage mechanism of UHPC under different strain rates,provid-ing theoretical support for the service performance and damage assessment of UHPC.Results and Discussions The failure modes of UHPC specimens under different impact strengths show that:as the strain rate increases,the de-gree of fracture in the specimens becomes complete;the addition of steel fibers results in a significant difference in the impact fracture morpho-logy between UHPC and ordinary concrete.From the fracture surface,it can be observed that there are numerous concrete fragments bridged by steel fibers and pulled-out steel fibers on the fracture surface,indicating that the sources of UHPC impact damage include the failure of the UHPC concrete matrix and the pulling out or breaking of the steel fibers.The splitting and tensile failure process of UHPC under different impact strengths was captured by a high-speed camera.Under impact pressure,the splitting crack first develops at the center of the specimen and gradu-ally extends toward both ends of the loading end.The degree of expansion of the main crack increases with the continuous increase in impact strength.Simultaneously,some secondary cracks develop near and parallel to the main crack as the main crack expands,demonstrating the bridging effect of steel fibers in the damage process of UHPC under impact load.The strain cloud maps of specimens under different impact strengths and the curves of the main crack width of specimens under different impact strengths as they expand over time were analyzed based on DIC technology.The above DIC analysis explains that the higher the impact strength,the faster the crack development speed,and there are dis-tinct differences in the damage characteristics of specimens under different impact strengths.The stress-strain curves of UHPC under different im-pact loads show that:the peak strain rate during the impact process of the specimen increases with the increase in impact load.As the peak strain rate increases,the dynamic tensile strength(i.e.,stress peak)of UHPC also increases.At high strain rates,the dynamic tensile strength of the con-crete specimens is significantly higher than the quasi-static tensile strength.Unlike ordinary concrete,which exhibits splitting failure after the stress reaches its peak,the rate of stress reduction in UHPC gradually slows down,and a platform segment appears.This phenomenon demon-strates the bridging effect of steel fibers in the damage process of UHPC under impact loads.By calculating the dynamic improvement factor(Dft)under different strain rates and comparing it with the concrete Dft curve provided by existing research,it is evident that the strain rate sensitivity of UHPC’s ultimate tensile strength is higher than that of ordinary concrete.Based on the law of conservation of energy,the dissipation energy and energy dissipation ratio of UHPC under different strain rates are calculated.The results showed that as the strain rate increased,the dynamic dis-sipation energy of UHPC also increased;the energy dissipation ratio shows a trend of first increasing and then decreasing with the increase in strain rate.Conclusions The research results indicate that:1)The impact resistance of UHPC is significantly enhanced compared to ordinary concrete.UHPC exhibits high strength and strong deformation capability under impact loads,and its performance in dissipating impact energy is superior.There are two ways for UHPC to dissipate impact energy:one is based on the failure of the concrete matrix,and the other is the pulling out or breaking of the steel fibers.2)As the impact strength increases,the degree of failure of UHPC gradually increases,and the extension of the main crack along the center of the specimen continues to increase until the specimen completely fractures.Except for the main crack,the development of sec-ondary cracks is significant during the failure of UHPC with strain rates in the range of 60 to 80 s^(−1);when the strain rate is higher than 100 s^(−1),the secondary crack development of UHPC is weaker.3)The dynamic ultimate tensile strength of UHPC increases with the increase in strain rate.The strain rate sensitivity of UHPC’s ultimate tensile strength is higher than that of ordinary concrete.As the strain rate increases,the dynamic dissipa-tion energy of UHPC also increases,but the energy dissipation ratio experiences a trend of first increasing and then decreasing.4)These analysis results fully demonstrate that UHPC is still a high-performance concrete material suitable for resisting impact loads and dissipating impact energy under dynamic splitting and tensile loads.
作者
陈徐东
王许阳
季韬
刘季玄
宁英杰
CHEN Xudong;WANG Xuyang;JI Tao;LIU Jixuan;NING Yingjie(College of Civil and Transportation Engineering,Hohai University,Nanjing 210098,China;College of Civil Engineering,Fuzhou University,Fuzhou 350108,China;Zhejiang Communications Construction Group,Hangzhou 310051,China)
出处
《工程科学与技术》
EI
CAS
CSCD
北大核心
2024年第6期103-112,共10页
Advanced Engineering Sciences
基金
国家自然科学基金面上项目(52379124)
中央高校基本科研业务费(B230204021)
国家重点研发计划项目子专题(2021YFB2600031)。
关键词
高性能混凝土
应变率
抗冲击性
抗拉强度
high-performance concrete
strain rate
impact resistance
tensile strength
作者简介
陈徐东(1985-),男,教授.研究方向:混凝土动力特性与性能调控.E-mail:cxdong1985@163.com。
