Study On The Enhancement Of Tensile Strength Of Concrete Under Impact Load

Concrete is a common kind of building materials, which is widely used in both civil engineering and military facilities. During their service life might be subjected to shock loading such as blast and earthquake. It is important to study the dynamic properties of concrete material. The split Hopkinson pressure bar(SHPB) technique has been widely used to measure the dynamic tensile strength of the brittle materials such as concrete and rock materials. however, the dynamic tensile strength of concrete materials derived from The SHPB test is affected by lateral inertia confinement. which may lead to overestimate the dynamic mechanical properties of concrete. Therefore, the true dynamic characteristics of concrete materials that do not necessarily reflect by those the test data, however, it is nearly impossible to completely eliminate the influence of lateral inertia confinement in SHPB testing. In order to study the increase of tensile strength of concrete that is cause by the true strain rate effect under impact loading, main works are as follows:(1) Two different thickness of Brazilian disc specimen were produced, static and dynamic splitting experiment was carried. The static tensile strength and the dynamic tensile strength of concrete are obtained.(2)The SHPB tests is simulated using software Ansys/ls-dyna to study the tensile strength of concrete after eliminate the influence of inertia effect on SHPB experiment when strain rates between 30/s and 150/s. In the numerical simulation, a rate-insensitive material model is used in order to study the influence of lateral inertia confinement, five different thickness of Brazilian disc specimen and three different Flattened loading angle of Flattened Brazilian disc specimen is simulated, it is in order to study the factors on inertia effect.(3)A method is proposed to eliminate the effect of inertial effect in SHPB experiment, the dynamic tensile strength of concrete obtained from experiment is compared with from numerical simulation. The tensile strength of concrete can be obtained after eliminate the influence of the inertia effect in the SHPB experiment, which can reflect the real dynamic mechanical properties of concrete.According to the results, Concrete is a kind of rate-dependent material, and the tensile strength increases with the increasing of strain rate; The dynamic tensile strength of concrete obtained from SHPB test is related to the size of the specimen; The dynamic tensile strength enhancement is strongly influenced by the inertial effect in a SHPB test. the influence of lateral inertia confinement is related to the size of the specimen and the strain rate, the influence increases with the increasing of strain rate and the thickness of specimen; Flattened loading will increase the impact of inertia effect, the greater the Flattened loading angle, the greater the impact of the inertia effect; The enhancement of dynamic tensile strength is influenced by strain rate effect and the inertia effect; The DIF obtained from true strain rate of concrete is smaller than recommended by CEB, The dynamic tensile strength of concrete materials derived from The SHPB test will overestimate the dynamic mechanical properties of concrete.