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The ultra-high performance cement based composites (UHPCC) with the additions of steel fibers and basalt coarse aggregates was prepared under ambient temperature and pressure. In order to apply the UHPCC in the constructions of anti-strike protective structures, the impact resistance of UHPCC was investigated experimentally by conducting the high-speed projectile penetration tests with the broad striking velocities from 510 m/s to 1320 m/s. The rigid and mass abrasive penetration regimes are observed when the projectile striking velocity was lower than 1 km/s and increased up to 1–1.5 km/s, respectively. The experiments validated that UHPCC material has excellent projectile impact resistance, such as reducing the depth of penetration (DOP) and the crater dimensions of the rigid projectile, as well as defeating the structure and deviating the terminal ballistic trajectory of the abrasive projectile. The previously proposed models for rigid penetration depth on fiber reinforced high strength concrete as well as the limit striking velocity causing the structural destruction of mass abrasive projectile are both well validated. The parameters influential analyses further indicate that UHPCC with the compressive strength of 90 MPa and steel fiber mixing ratio of 1.5% is the most efficient and economical choice for protective structure constructions. In details, within the discussed ranges: (i) the projectile impact crater dimensions enlarges with the increase of the compressive strength of the target and the projectile striking kinetic energy, and which was reduced with the increase of fiber mixing fraction and the mixed coarse aggregate. The influential degree of mixing fibers on reducing the cratering dimensions is much greater than which of compressive strength on enlarging the cratering dimensions; (ii) both of the compressive strength, the fiber mixing fraction as well as coarse aggregates can help decreasing the DOP of the projectile so as to enhance the impact resistance of the target, while the contribution of fibers is very limited for the relatively low addition ratio (⩽3%). The DOP of the projectiles are no longer decreasing obviously when the compressive strength of the target is larger than nearly 90 MPa. [ABSTRACT FROM AUTHOR]

• Reason of the scaling effect of rigid projectile penetration into concrete target is clarified. • Generation algorithms of 3D mesoscopic concrete models are proposed. • Compared to the homogeneous concrete model, the scaling effect is reproduced numerically based on the verified 3D mesoscopic concrete model. • The parametric analyses show that the maximal 26% deviations for predicting DOP can be induced when the scaling effect is considered or not. The scaling effect of rigid projectile penetration into concrete target should be paid great attention in ballistic performance evaluation of earth-penetration-weapon and design of protective structures, and this paper aims to discuss the scaling effect based on the three-dimensional (3D) mesoscopic concrete model. Firstly, by evaluating the existing typical (semi-)empirical formulae and penetration tests, it is found that the scaling effect is mainly attributed by the inconsistent variations of projectile diameter and coarse aggregates size in the scaled impact tests. Secondly, based on MATLAB, the generation algorithms of 3D mesoscopic concrete models with the randomly distributed sphere and convex polyhedron coarse aggregates are proposed, respectively. The influences of two coarse aggregates shapes on the compressive strength and impact resistance of concrete target are further discussed, and the sphere coarse aggregates are adopted to guarantee both the calculation accuracy and efficiency. Then, based on five sets of projectile penetration/perforation tests on concrete targets, the 3D mesoscopic concrete model with randomly distributed sphere coarse aggregates and the corresponding constitutive parameters are validated numerically by LS-DYNA. Finally, the scaling effect is reproduced numerically based on the verified 3D mesoscopic concrete model. The influences of projectile diameter, volume fraction and size of coarse aggregates on the scaling effect are further assessed. In the discussed scenarios, the maximal 26% deviations for predicting depth of penetration (DOP) can be induced when the scaling effect is considered or not. [ABSTRACT FROM AUTHOR]

Ultra-high performance cementitious composites (UHPCC) has become the most prospective construction materials for both civil and military protective structures. In order to facilitate the structural design and calibration/validation of the constitutive model, the dynamic tensile (spalling) behavior of UHPCC is experimentally studied. By using a 50 mm-diameter conic variable cross-sectional Split Hopkinson Pressure Bar (SHPB), the dynamic spalling test on Φ48mm × 400 mm cylindrical UHPCC specimen is conducted. The tensile strain rate ranges from 14.3 s −1 to 214.8 s −1 , and two typical steel fibers (micro-straight and hooked) with three volume fractions of 0%, 1.0% and 2.0% are investigated. The effects of steel fiber content and type as well as the strain rate on the dynamic spalling strength of UHPCC are experimentally assessed. It indicates that the dynamic spalling strength of UHPCC increases obviously with the strain rate rising up to ∼110 s −1 , and also improves with increasing the content of both two typical steel fibers. When the strain rate increases higher than 60 s −1 , the micro-straight steel fiber has relatively better effect on improving the dynamic spalling strength than the hooked one with the volume fraction of 1.0%. Furthermore, corresponding to each steel fiber content and type, the empirical dynamic increase factors (DIFs) for the dynamic tensile strength of UHPCC are formulated. [ABSTRACT FROM AUTHOR]

The split Hopkinson pressure bar (SHPB) test on Ultra-high performance cementitious composites (UHPCC) specimens is performed, in which the strain rate ranges from 17.6 s −1 to 328.4 s −1 and two typical steel fibers (micro-straight and hooked) with three volume fractions of 0%, 1.0% and 2.0% are considered. It indicates that, (i) the dynamic elastic modulus, compressive strength and peak strain as well as the toughness of UHPCC increase obviously with the increase of strain rate; (ii) the steel fiber content and type almost have no effects on the dynamic elastic modulus and peak strain, and show relatively small strengthening effects on the dynamic compressive strength of UHPCC; (iii) the present micro-straight steel fiber has slightly better effect on improving the dynamic compressive strength than the hooked steel fiber, particularly for the steel fiber volumetric ratio of 2.0%; (iv) the peak dynamic toughness almost has no relation to the steel fiber reinforcement, while the ultimate dynamic toughness increases with increasing the steel fiber content, and the influence of the micro-straight steel fiber is more obvious. Furthermore, the empirical dynamic increase factors (DIFs) for the dynamic compressive strength of UHPCC are formulated, and a modified visco-elastic damage model is established for UHPCC under dynamic loadings. [ABSTRACT FROM AUTHOR]

A series of cubic/axial compressive, direct tensile, four-point and three-point flexural tests on Ultra-high performance cementitious composites (UHPCC) specimens are conducted, in which six volume fractions (0–2.5%) and two types (micro-straight and hooked) of steel fibers are considered. The full compressive and tensile stress-strain curves, the flexural load-deflection/CMOD (crack mouth opening displacement) curves are obtained. It indicates that, (i) the steel fiber content and type have obvious strengthening effects on the cubic compressive strength; (ii) for the axial compressive strength, the steel fiber type has little influence and the enhancing effect of the steel fiber content becomes less obvious when the volume fraction exceeds 1.0%; adding steel fibers has little effect on the compressive elastic modulus and Poisson’s ratio; (iii) for the direct tensile strength, the steel fiber content has remarkable effect; the present micro-straight steel fiber has relatively better effect than the hooked steel fiber under same mixing ratio; (iv) the steel fiber content and type almost have no effects on the first crack flexural strength and the corresponding deflection, but show considerable effects on the flexural strength, load carrying capacity, energy absorption capacity, fracture toughness and fracture energy. [ABSTRACT FROM AUTHOR]

Ultra-high performance cement based composite (UHPCC) has prominent projectile impact resistance. Aiming to theoretically predict the depth of penetration for rigid projectile penetrating UHPCC target, an improved dynamic cavity expansion model was proposed to describe the plastic behavior of UHPCC material under projectile penetration with a hyperbolic yield criterion and nonlinear equation of state (EOS). Then, combined with the Newton’s second law, rigid projectile penetration model into UHPCC target was established, which was verified by comparing with the previous penetration test data, classic empirical formula and prediction of previous cavity expansion model based on linear yield criterion and EOS. Besides, a series of practical parameters of the hyperbolic yield criterion and nonlinear EOS for the improved dynamic cavity expansion model were given and validated. [ABSTRACT FROM AUTHOR]