update

-"spacetime get permanently deformed after gaining a critical threshold of stress,curvature or pressure like plastic do". firstly we will focus on the dark energy and our motivation of solving these problem with the core idea will be --"dark energy might be the left over permanent curved spacetime which are still gravitationally active present now like a fossil in the vacuum of past high energetical astrophysical event such as neutron star collapse, stellar collapse, supernovae explosion, blackholes collison etc . Moreover u can say any such events which leads the spacetime to gain a critical threshold by after that the spacetime get permanently curved even though the source of the curvature or gravity (ordinary matter) vanished from that area where the physical event happend. any such high energy astrophysical event may be the reason of that physical phenomenon because our core idea is that any event which can be the reason of leading the spacetime into a critical threshold can get generate a permanence curvature in the spacetime which are gravitationally active. there size might be small and bigger depends on how the event engaged with the spacetime and lead the spacetime to be permanently curved . .  There might also be some exceptions. Some curved spacetime regions might not be permanently deformed they could return to their primary, inertial (flat) state. The process of returning
to that state would require relaxational energy or decaying energy.
For example, if you put a ball on a fabric and then remove it, the fabric returns to its flat state.
But if you put a much heavier object on it, the fabric could stretch beyond its elasticity limit
becoming permanently deformed and unable to return to its original flat state.
This analogy also helps explain another mysterious problem of our universe dark energy. even though 
spacetime does cross the critical threshold for permanent deformation, it can relax back to 
its flat, inertial state. This process would involve the release of relaxing energy similar to
removing a ball from a stretched fabric, causing the fabric to expand and return to normal.
The same principle might apply to the spacetime fabric itself: curved regions could return to
their inertial, flat state by expanding, decaying, or releasing the stored curved stress energy.

if we say that the curvature might be bigger or smaller like every event may not produce same permanency size or curvature in the spacetime. less energetic but still the even which leads the spacetime to a critical threshold may be make a smaller curved zone than the bigger or higher energetic astrophysical event . i didn't mean that curvature decay energy radiations or matter . i meant the permanently spacetime curvature slowly relaxes and come it's flat inertial state . like if u put off a ball from a string or fabric the fabric slowly relaxes . and the relaxation that happens , referes to to that fabric length or size increases than before or u can it come to it's primary state and that's why spacetime expand that means the curvature slowy vanish and the spacetime come it's inertial state.