#### 5.3.5.3. Shear Crimping Failure

Shear crimping failure [ 39 ] appears to be a local mode of failure, but is actually a form of general overall buckling in which the wavelength of the buckles is very small because of low core shear modulus. The crimping of the sandwich occurs suddenly and usually causes the core to fail in shear at the crimp. It may also cause shear failure in the bond between the facing and core.

Equation 5–119 describes the shear crimping allowable force which is a function of the core and the face sheet properties in the direction of loading.

| (5–119)

where

= allowable compressive force [Force/length]
= weighting factor
= shear modulus in the loading direction
= thickness
= bending stiffness in the loading direction
= core
= face sheet

The shear crimping factors and are derived from test data. If the face sheets are much thinner compared to the core thickness and no characteristic value is available, can be set to 0 (default). The default value of is 1.

For uniaxial compression the effort is:

| (5–120)

where [Force/length] is the in-plane laminate load.

In the case of shear loading, the effort in Equation 5–120 is evaluated with respect to the principal direction of loading. The material parameters of Equation 5–119 can be easily rotated into the principal direction of loading to get the allowable forces and with respect to the first and second principal directions of loading.

In the case of biaxial compression, the failure condition of shear crimping is the sum of the efforts in the first and second loading direction:

| (5–121)

where and are the first and second principal laminate loads, respectively.

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