Numerical Study On Impact Compression Performance Of Ultra-high Performance Concrete Based On SHPB Technology

As an advanced cement-base material,ultra-high performance concrete(UHPC)possesses high damage tolerance,large fracture toughness and excellent durability,resulting in extensive prospect of application in special engineering structures,including marine structures,under-ground space,nuclear waste containers,national defense and military facilities,etc.To meet the needs of impact resistance and anti-blast of building materials in the above-mentioned special structures,there has been an increasing need to estimate the impact resistance property of UHPC.At present,the impact performance evaluation of concrete materials is generally completed by Split Hopkinson Pressure Bar(SHPB).However,the friction at specimen load faces,the dispersion effect of the stress wave and the radial inertia effect of specimen will have an important impact on the stress balance and one-dimensional stress wave propagation of the specimen in the process of test loading.Considering that it is rare to evaluate the influence of the above factors on the dynamic properties of UHPC materials in the SHPB test,such as referring to the traditional concrete treatment methods,its applicability needs further verification.Based on a large-scale finite element analysis software named LS-DYNA,this paper conducts the following main work from the perspective of improving the reliability and accuracy of SHPB experimental results for UHPC specimens:(1)The dynamic damage behavior of UHPC material is fitted by calibrating the key parameters of Karagozian-Case-Concrete(KCC)and Holmquist-Johnson-Cook(HJC)damage model in the LS-DYNA software respectively.An impact compression model of UHPC based on SHPB technology is established.By comparison with the experim ental results,the modified KCC model can better simulate the dynamic mechanical pro perties of UHPC in SHPB test is confirmed.(2)The evaluation indexes of constant strain rate loading,stress equilibrium and index based on stress state during SHPB test process is proposed.Parameter study is conducted by varying the material,thickness and diameter of pulse shaper to optimize the selection and size of pulse shaper for UHPC specimen to constant strain rate loading and stress equilibrium in SHPB experiment.(3)Based on the above evaluation indexes and the optimized material type and size of pulse shaper,the methods to reduce the radial inertia effect of UHPC specimen in SHPB test are further discussed,the influences of the diameter,aspect ratio of the specimen and strain rate on the radial inertia effect were evaluated.