Mechanical Properties Experimental Study And Finite Element Analysis Of Concrete Under The Impact Load

The study of the static performance of concrete, which is the most commonlyused building material, has lasted for many years; and it is approaching complete.However, the research on its dynamic mechanical properties is still in the exploratorystage. In this thesis, basic research on the properties of concrete under impact load isconducted by means of experiment and finite element analysis; and some dynamicconstitutive models of concrete, which are widely used in finite element simulations,are briefly discussed.A basic experimental device called the Split Hopkinson Pressure Bar (SHPB),which is used to study the dynamic properties of concrete, is introduced. Using a100mm-diameter Hopkinson rod, concrete cylinders with92mm in diameter weretested under five groups of air pressure, which were correspondent with five sets ofstrain rates. The results showed that the dynamic mechanical properties were verydifferent from the static ones, i.e. the concrete had obvious strain rate effect. Thedynamic average stress-strain curves of each specimen were obtained; and the averagestrain rate, dynamic compressive strength, peak strain, and secant stiffness were alldetermined. The dynamic increase factors under different strain rates were calculatedand compared with the theoretical values, according to the formula in the CEBstandard.As a developing technology, finite element analysis has its advantages comparedwith experimental research, including economy and extensive parameter study. Thegeneral finite element software LS-DYNA was employed to simulate the SHPB tests.The construction of the finite element model is described in detail，including theelement selection and the contact definition. In addition, the dynamic constitutivemodels of concrete in the software are reviewed, and three of them are thoroughlyintroduced. Different material models were simulated and analyzed. The impactprocess and the stress-strain curves of materials were obtained. The simulated resultswere compared with the test results; and the applicability of the constitutive modelswas discussed.