The EXPLOSIONS in to The Battle Of Britain - Storm Of War.....

[swiss]

Frag will not penetrate the tank. The blast however could cause parts of the armor plates on the inside of the tank to disintegrate and cause shrapnels inside the tank - therefore killing crew.
HESH ammo works like that.
Keep in mind all AT weapons are only anti crew weapons, none is intended to wreck the tank itself(pretty impossible).