A Numerical Study Of The Cavity Expansion Process And Its Application To Penetration Mechanics

Cavity expansion process for metal and concrete materials were investigated bynumerical simulation. The effects of strain-rate, thermal softening and damage in thecavity expansion process and penetration calculating were analyzed. The main contentsand innovative work include:(1) A three-section numerical model was built to study the cavity expansionprogress. To define the reasonable numerical model, the effects of model size and meshdivision were analyzed, and the laws of strain-rate, temperature were studied based onthis reasonable numerical model.(2) The effects of strain-rate and thermal softening to metal materials cavityexpansion progress were studied. The numerical results showed that: the Warren theorysolution was a little high due to unconsidering material compressibility in strain-rateeffects. Considering the thermal softening effects reduces the cavity surface radial stress,the effects of strain-rate hardening and thermal softening are canceled, but strain-rateeffects is higher than thermal softening effects. The effects of strain-rate and thermalsoftening in translation speed of elasticity-plasticitysurface can be ignored.(3) The effects of concrete material unaxial compressive strength, density,strain-rate and damage were studied. The numerical results show that: the relation ofcavity surface radial stress and expansion speed is a conic section. The main effects ofmaterial strength and density are embodied in the constant items. The primary constantsand the conic constants are approximated to constants. The expression of the constantitems was got, which can be apply in the concrete with the unaxial compressive strengthbetween 20MPa and 100MPa. The effects of strain rate and damage to radial stress aregreat in the low velocity and will become weak as the velocity augmenting. The error ofradial stress caused by strain rate is no more than 6%. The error of radial stress causedby damage is clear when the velocity is less than 600 m/s, which can reach 26% in themaximum.(4) The effects of strain rate, thermal softening and damage to penetrationcalculating were studied. The results from the model which consider every effect,dispensing with the friction coefficient, were well correspond to the experiments. Therelative errors of penetration depth caused by the effects above are independent of thedensity and size (length and radius) of the projectiles, only relate to the shape parameterand penetration velocity of the projectiles. The error becomes lower as the velocityaugments. The error for spherical-nose projectiles is lest, which becomes bigger as theprojectile head comes to a point.