the difference between the stress and strength is............
stress= load/ area ( n/mm2) .. it denotes that the load x will act in 1 mm2 of area of a structure,
strength denotes that max. stress upto which the structure get failure.

Stress is the force per unit area, it depends on area of
structure, while
Strength is the resistance to maximum stress at the time of
failure, it does not depend on area...

Strength is an extrinsic property of the material. It is
derived outcome of heat treatment processes. It is a
function of grain size, No of slip planes within a grain
etc. Therefore strength defines capacity of a material to
carry loads.
Stress is an internal resistance/force per unit area in the
material, generated due to application of external force.
Incidently, both have same units as strength is also
measured by force/area.

Stress is a measure of the load applied to a sample
relative to a cross sectional area of the sample. Strength
is a quantification of the samples ability to carry a load.

Stress is the intensity of force/resistance per unit area at
any condition due to applied force on a body.

On the other hand, Strength is the stress at time of
failure; structure can withstands.

If the structure can't withstand with the governing stress
then, it can't be specified as strength. Therefore, any
strength is the part of stress, but any stress can't be the
part of strength!! Though, the both terms have same unit to
express!!!

why loss of strength in concrete in 7 days cube test i am
not geting mim 7 days strength that is 67 percent for M-35
and my mix design is perfect there is no doughty,and my
results are near to 7days percentage but not 67 percent.