A low energy impact face defect is likely to decrease the
face buckling load of a sandwich composite to.
P = Po (1--Wom/Wm) t.
where P0 is the buckling load without initial damage, and
wOm and wm are theinitial and failure values of
displaceme nt amplitude at the centre of the
defect. This expression represents the critical lateral
face load incompression, and is essentially unchanged
regardless whether the structure is asandwich panel or
a strut on elastic foundation.
Experimental studies suggest that the diameter of the
impact delaminationdefect du ~IN where ~is the impact
energy and N is the number of equal impacts.
This corresponds to the critical energy criterion for
fatigue. If w0m ~l, where 21 is the wavelength of the
initial irregularities, and l du, then wOm ~. This
would agree with both the equation (1) and the
experimentally fitted equation.
P = Po · (1 ~'JN/K).
where K is a constant for similar composites. If the
wavelength is proportional to the diameter of the impact
damage, then wOm dU2. However, a relation wOm du3 is
suggested by another experimentally fitted equation.
P = Po · [1 (1.5 · dU/b)3].
where b is the effective width under loading. The
observed correlation 'between defect size and strength
loss is somewhat worse with the last equation.
However, in practice using the measured defect size du
from NDT inspections is more attractive than the usually
unknown impact energy in the evaluation of strength loss
due to impacts.
|Place of Publication||Espoo|
|Publisher||VTT Technical Research Centre of Finland|
|Number of pages||25|
|Publication status||Published - 1993|
|MoE publication type||Not Eligible|
- sandwich structures
- composite materials
- impact strength
- mechancal properties
- composite structures
- performance evaluation methods
- loads (forces)
- structural members
- fatigue (materials)