If something makes it through into the crew compartment, it would have penetrated the nearly meter thick plate on the way in, the energy unleashed turns the crew compartment into a pressure cooker, killing everyone.
There are many documented cases of penetration of MBTs that do not "turns the crew compartment into a pressure cooker, killing everyone". There are likewise documented cases where the penetrator damaged specific parts along the path of penetration and left the rest of the interior pretty much unscathed.
Most modern penetrators are either APFSDS or HEAT. In either case, the penetrator itself is a heavy metal long rod - inert and devoid of any explosive content. Almost all post-penetration effect is provided from the kinetic mass of bits of penetrator and defeated armour, collectively known as Behind Armour Debris (BAD).
APFSDS or HEAT, all such penetrators do not grow hot enough to cause significant pressure increase. Typical temperatures are around 600C. Take a hot metal rebar and throw it into a container ... not going to cause much drama unless it starts to vapourise liquids or deflagerate explosives. The one inherent component of a penetrator that will contribute explosive energy to post-penetration effects (as opposed to just KE effects from BAD) are penetrators made of pyrophorric materials. eg. DU penetrators are still being used because of this property (and also because of their tip adiabatic shearing properties which aid penetration) - the temperature and exposure to air within the penetrated space often results in a conflagaration of the DU powder/shards that adds significantly to the mess already being created by BAD. Also hence the use of Alu liners (amongst others) for Shape Charges (HEAT/EFP) as opposed to Cu liners for the pyrophorric effects despite it's poorer penetration capabilities.
"Penetration" itself can be also a whole spectrum of partial penetrations, limit penetrations, over-penetrations etc. Basically, there is no guarantee that a penetrator that "penetrated the nearly meter thick plate on the way in" is going to generate tremendous amounts of BAD. An example on the opposite end of the spectrum, a case of over-penetration, is hits on lightly armoured APCs being penetrated through-through on both sides with nothing touched or torched. Likewise, some at-limit penetrations will likely result in very little BAD or very low energy BAD which may be totally mitagated by anti-spall liners in the AFV. There is such a wide spectrum of penetration energy states to categorically state that any penetration will result in catastrophic consequences.
There is also the matter of the composition of the meter thick armour being mentioned. What is it made of? Spaced plates with large air gaps do a good job of distrupting long rods and also mitigating BAD (cos each succesive spaced plate actually acts as a witness plate that traps small shrapnel). A lot of composite materials also disrupt the penetration channel and significantly reduces/captures fragments that would form BAD via side-wall collisions.
Penetration mechanics is a complex topic. If you want to read more, you can trawl through this website of resources (
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