Honeycomb Core Wrinkling Stress Equation and Calculator

Related Resources: calculators

Honeycomb Core Wrinkling Stress Equation and Calculator

Structural Composite Honeycomb Core Wrinkling Stress Equation and Calculator

Wrinkling of Facings Under Edgewise Load of Honeycomb Core Calculator

Wrinkling of honeycomb facings, as shown in Figure 1, may occur if a honeycomb facing buckles as a plate on an elastic foundation. It may buckle into the core or away from the core depending on the relative strengths of core in compression and adhesive in flat wise tension.

Figure 1, Face Wrinkling

The facings of a honeycomb shall not wrinkle under design load. The wrinkling stress formulas are given for two types of sandwich; sandwich with continuous cores and sandwich with honeycomb cores for which elastic-moduli in the plane of the core are very small compared with the elastic modulus in a direction normal to the core plane.

Determine parameter K from Figure 2:

Eq. 1a,
η/t_c

Eq. 1b,
F_c / E_c

Eq. 2, From Figure 3 and using K value and ( E_c t / E_f t_c )^1/2 obtain F_cr / E_f

Eq. 2a
( E_c t / E_f t_c )^1/2

Eq. 3, Stress at which face wrinkling occurs:
F_cr = ( F_cr / E_f ) E_f

Where

E_c = core flatwise Modulus of elasticity, lbs/in²
E_f = Facing modulus of elasticity, lbs/in²
η = total amplitude of initial facing waviness usually between 0.005 - 0.005 inch
F_c = flatwise strength of core or bond, whichever is less
t = thickness of facing, in
t_c = thickness core, in
λ = (1 - µ²)
µ = Poisson's ratio
K = See Figure 2

Figure 2

Figure 3, Parameters for determining wrinkling of facings of sandwich with continuous cores

Figure 4, Graph for the wrinkling stress of facings for sandwich with honeycomb cores

Source

Bell Helicopter Structural Design Manual, 1977