Alright I am right by saying that a plate fractures when impacts right? Yes
So 41 pellets impact it all over the place. ( many many fractures ) It is more likely to not work the next time right? again Yes
The plate wouldn't completely fracture all the way through to the back, it would only fracture on the surface. Assuming you're talking about a level IV plate (rated to 30-06 AP) its going to take quite a few shots to break through. Though, in theory subsequent shots will have a better chance at penetrating.
That's assuming we're talking about SAPI plates and other ceramics, if the guy is wearing steel, you're going to be waiting a long time for anything to penetrate. Steel doesn't fracture when it is shot, it either penetrates or it doesn't. You may get a little backface deformation/spall, but that's of little consequence when the wearer is shooting back. Remember that a plate distributes the force of the shot around the whole plate rather than the one point of impact which means less injury to the wearer when compared to soft armor.
Also, considering that I can get 2 level III steel plates rated to stop multiple .308 hits for $160*, I think its at least worth thinking about that an assailant may be wearing some armor. And hell, I may be buying some for myself at that price.
And as for a pellet finding its way around the plate, its definitely possible, but it depends a lot on range and where the center of your pattern is located. At household distances, your pattern is only about the size of a softball. Remember, its a shotgun, not a claymore on a stick
Edit: I think a lot of people here are confused about armor levels. Level I, II, and
IIIA are soft armor similar to what police wear. It is made of soft woven threads and is flexible. It catches the rounds, but the energy still transfers to the wearer at the point of impact. Level III, and IV are hard plates (steel and ceramic) which are rated to stop multiple hits of up to .308 and 30-06 AP, respectively. They distribute the force of the impact across the entire plate causing in less injury.
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bulletproofme.com about half way down the page. 8x10" steel plate.