| As one of the most widely used engineering materials, concrete are characterised by the inherentlow tensile strength and brittleness. Research has shown that high fiber content, large fiberlength-diameter ratio and well-proportioned distribution are beneficial to the strength and toughness ofsteel fiber reinforced concrete(SFRC), which consequently result in excellent anti-blast andanti-penetration performance, and obvious reduction of explosion induced spalling This research aimsat integrating3D braiding technique with SFRC and developing3-D braided steel fiber reinforcedconcrete (3D-BSFC).. Since fibers are not mixed in, fiber content in BSFC is not limited by the mixprocess as in SFRC, and the fiber orientation and distribution can also be designed. Furthermore, asbraided steel fibers can work integrally. It provides a new concrete material with high quality forvarious national defense and civil engineering. This paper obtained the main research results are asfollows:The manufacturing procedures of making3D-BSFC include: Layered placement-castingtechnology and three-dimensional skeleton of steel fibers woven-casting technology.Then specimens of3D-BSFC and2D-BSFC with steel fiber volume content (V f) of0(SC0),5%(SC05)and10%(SC10) were prepared, and the mortar volume filling rate was100%.Specimens with matrix strength of the C50were tested uniaxially by a multifunctionservo-controlled testing machine under three types of quasi-static low strain rate (10-4s-1and10-2s-1).The whole stress-strain curve, strength, toughness and compression elasticity modulus were obtained.Compressive characteristics of3D-BSFC and influences of steel fiber content and strain rate on thebasic mechanical performances were investigated. The results show that the strength of3D-BSFCaresignificantly increased to3times as the matrix,and the ability of deformation is also improved withcompressive ductility increased to3.87times as the matrix. With the increase of strain rates, strengthand elastic modulus increase10%30%respectively. At the same time, according to the mechanicalproperties of different fiber volume ratio, different fiber types and different fiber permutation,3D-BSFC is optimized,3D-BSFC specimens with superior performance were prepared.Dynamic compressive properties of3D-BSFC specimens were tested by a75mm Split HopkinsonPressure Bar (SHPB), dynamic increasing factors(DIF) and stress-strain relations were obtained underdifferent strain rates, and dynamic failure modes were observed. And the effect of fiber-content andtype of fiber on the dynamic properties of materials were discussed. The results show that, Impactcompressive strength of3D-BSFC had a significant strain rate hardening effect, the impactcompressive strength and elastic modulus increased when the strain rate increased, but the peak straindecreased.The DIF of3D-BSFC and the logarithm of strain rate was double linear function; Thenotable contribution of steel fiber to3D-BSFC was toughening in shock compression, the toughnessbasically increased when the strain rate increased. In the same strain rate, the bigger of steel fibervolume ratio, the greater of the toughness. There is a critical strain rate k between strain rate and theimpact compressive strength of concrete materials, when the strain rate exceeds k, the DIF increasedsignificantly. It was found that the dynamic strain rate critical value of3D-BSFC increased when thestatic compression strength increased. The3D braid steel fiber skeleton played an enhanced role inanti-cracking resistance, effectively limited the destruction of materials under the action of lateral tensile damage.3D-BSFC had ability of strong resistance to dynamic destructive capacities. Shaperemains intact, only a few edge falls off, three-dimensional steel fiber complete still, did not loose.Dynamic strain rate critical value of concrete materials increased when its static compression strengthincreased.For the first time, high-speed camera system and SHPB impact experiment system workedtogether, deformation fields and strain fields of specimens in the process of the high-speed impactwere obtained. By analying displacement field and strain field of the3D-BSFC specimens of impactduring compression, the results show that,in the impact process,the displacement field and strain fieldof the specimen along the impact direction is not uniform, and the displacement direction of differentpoints in the same radial cross section of the specimen change over time. Then it was found that frictioneffect, dispersion effect and the inertia effect of experimental impact of SHPB experiments wereunavoidable. In later study, the hardware and software environment would be changed through accurateanalysis of deformation fields and strain field, then the development of SHPB experiments theory ofconcrete materials would also be pushed forward.Based on the experimental research work,3D-BSFC dynamic simulation of stress-strain curvecan be achieved by choosing ZWT considering damage constitutive model, The results show that, ZWTconstitutive model can accurately reflect of the the rising phase of dynamic stress-strain curve of the3D-BSFC specimens.Using the HJC model, ANSYS/LS-DYNA finite element software was chosen to simulate theprocess of impact and anti-penetration of3D-BSFC. Impact strength of numerical calculation is closeto measured value of experiments, and the effectiveness of experiment is verified from the numericalperspective. Then the process of projectiles penetrating targets of3D-BSFC were simulated, resultsshowed that: when the projectiles went through the targets, under the same initial velocities ofprojectiles and the same thickness of the targets, the higherV fof the targets, the greater decline of thevelocity, the better anti-penetration characteristic, the smaller the shrapnel, the greater residual strain ofthe hole edge, and the better deformation performance of targets; and the smaller the angle of incidencewith the longer distance and duration,the smaller residual velocity, the greater difficulty going through;compared the oblique incidence of60°and the vertical incidence of90°, the former had the greaterresidual strain than the latter, and which produced more serious damage. When the projectiles verticallypenetrated the thick targets, the penetration depth of targets of SC10and SC05were57%and80%ofSC0; as the initial conditions were same, the higherV fof the targets,the smaller the penetrationdepth, the greater the residual strain, the better the plastic deformation performance, the stronger theenergy absorption; the faster the projectile velocity decreases, the stronger the anti-penetrationability.The conclusions above were very important guiding significance for the protection engineering,anti-penetration, and anti-collapse. |
PDF Full Text Request