Study On Mechanical Properties Of Three Commonly Used Steel Bars In High Strain Rate

HPB235, HRB335 and HRB400 are commonly used matericals in existing reinforced concrete structures, and they are also one of the main bearing material in the renforced concret strutures. In the structure design, the loa d applied to the three kinds of steel bars is usually static or quasi-static. However, it will probably suffer dynamic load in terrorist attacks, explosion of gas pipeline and other special circumstances. At this moment, the steel bars which are the main bearing material will also be affected by dynamic load inevitably. So doing research on the construction steel bars has important significance for researching the dynamic mechanical response of the reinforced concrete structure. This paper carried out the following researches:(1) Used universal material testing machine to do compression test research on three conmonly used steel bars at the strain rates of 6×10-4s-1. Got the the quasi static mechanics performance of three steel bars to provide the reference to the dynamic tests and constitutive parameters fitting.(2)Used the SHPB apparatus and Rotary Disk Impact Tensile System to do dynamic compress and tensile test research on three steel bars within the strain rate of 160 s-1~2000s-1. Analysised the result of the experiment and got the effect of srain rate on the tensile mechanical properties of three steel bars :①The yield stress of three kinds of construction steel bars increases with the increase of strain rate, the construction steel bar of low static yield stress is more strain rate-sensitive than construction steel bar of high static yield stress.②The yield stress of three steel bars change along with the equivalent plastic strain rate,the change rule is σy(1+Cεklnε)σy0.C and k are material parameter, y0s is yield stress in reference strain rate.③The plastic hardening modulus of three steel bars decreases with the increase of the strain rate, and change along with 0ln(e/ e) in a linear.(3) Analyzed and demonstrated the way to ascertain the length of the test section in impact tensile specimen. The length of the test section in impact tensile specimen should be the sum of middle straight section and arc.(4) Ameliorated the classical Johnson-Cook constitutive model and got the suitable Johnson-Cook constitutive model parameters to describe the stress-strain curve of three steel bars. Ameliorated the classical Johnson-Cook constitutive equation is as follow:σ=(A+Bεk)(1+Cεk lnε)Compared the improved constitutive model with the test data, the average error is within 6%. The Johnson-Cook constitutive model is practical and the parameters is correct and reasonable.