Iranian Classification Society Rules

< Previous | Contents | Next >

Section 5 Sandwich Panels


501. Consideration of buckling

Buckling strength of sandwich panels related to longitudinal hull girder strength or local axial loads are to be dealt with individually.


502. Minimum requirements to structural sandwich panels


1. The reinforcement of skin laminates is to contain at least 40 % continuous fibres.


2. The mechanical properties of the core material of structural sandwich panels are to comply with the following minimum requirements (refer to Table 3.5.1).

image


Table 3.5.1 Mechanical Properties of Sandwich Panels



Structural members

Core properties (N mm )

Shear strength

Compression strength

Hull bottom, side and transom below deepest WL or chine whichever is higher


0.8


0.9

Hull side and transom above deepest WL or chine whichever is higher


0.8


0.9

Weather deck not intended for cargo

0.5

0.6

Cargo deck

0.8

0.9

Accommodation deck

0.5

0.6

Structural/watertight bulkheads/double bottom

0.5

0.6

Superstructures/Deckhouses

0.5

0.6

Tank bulkheads

0.5

0.6


3. The mass of reinforcement (g m ) in skin laminates in structural sandwich panels should

not be less than the following.

to be submitted.

However, Details including laminating process such as work sheets



for

m


:

:


:

mass of reinforcement per unit area,

given in Table 3.5.2 (For mixed material reinforcements can be found by linear inter-

polation in the table according to the relative percentage of each material with respect to weight per unit area.)

given in Table 3.5.2.


4. Deviation from the minimum requirements

may be accepted by the Society on consideration of

yacht type and service restriction or based on documentation of equivalent resistance to loads de- scribed in Table 3.5.1.

image


Table 3.5.2

and



Structural Member




Glass

Carbon/Aramid

Hull bottom, side and transom below deepest WL or chine whichever is higher


2400


1600


0.025

Hull side and transom above deepest WL or chine whichever is higher


1600


1100


0.025

Hull bottom and side, inside of hull

1600

1100

0.013

Stem and keel, (width to be defined)

6000

4000

0.025

Weather deck (not for cargo)

1600

1100

0.0

Wet deck

1600

1100

0.0

Cargo deck

3000

2000

0.013

Accommodation deck, if adequately protected

1200

800

0.0

Accommodation deck, other

1600

1100

0.0

Decks, underside skin

750

500

0.0

Deep tank bulkheads/double bottom

1600

1100

0.0

Structural bulkheads

1200

800

0.0

Watertight bulkheads

1600

1100

0.0

Superstructure and deckhouse, outside

1200

800

0.013

Inside void spaces without normal access

750

500

0.0


503. Bending


1. Normal stresses in skin laminates and core shear stresses

(1) Maximum normal stresses in the skin laminates of a sandwich panel subject to uniform lateral pressure is given by the following formula :


N mm


: For stresses parallel to the longest edge, refer to Fig 3.5.4.

: For stresses parallel to the shortest edge, refer to Fig 3.5.4.

: section modulus of the sandwich panel per unit breadth (mm mm ). For a sandwich-

panel with skins of equal thickness =

: factor, as defined in follows.


= or


according to Fig 3.5.5, for panels with fixed edges or partially fixed

edges.

for stresses parallel to the longest edge.

for stresses parallel to

shortest edge.

(2) The maximum core shear stresses at the midpoints of the panel edges of a sandwich panel sub- ject to lateral pressure is given by the following formula :


N mm

image


= , for core shear stress at midpoint of longest panel edge, see Fig 3.5.6.

= for core shear stress at midpoint of shortest panel edge, see Fig 3.5.6.


image


Fig 3.5.4 Factors


and


image


Fig 3.5.5 factor

image


Fig 3.5.6 Factors

and


2. Local skin buckling

The critical local buckling ing formula :


stress for skin laminates exposed to compression is given by the follow-


N mm


3. Deflection

The deflection at the midpoint of a flat panel is given by the following formula :




and : refer to Table 3.5.7.

: factor, as defined in follows.

= 1.0, panels with simply supported edges.

= refer to Fig 3.5.8, panels with fixed edges or partially fixed.

: modulus of elasticity, refer to Table 3.5.3.


image

Fig 3.5.7 Factors

and

Fig 3.5.8 Factor

image


Table 3.5.3 Modulus of Elasticity




For panels with skin laminates with equal thickness and modulus of elasticity




For panels with skin laminates with different thickness and modulus of elasticity



NOTE :

1 and 2 : inner and outer skin respectively.


4. Allowable stresses and deflections

The maximum normal stresses in skin laminates, core greater than given values in following Table 3.5.4.


shear stresses and deflection are not to be


Table 3.5.4 Allowable Stresses and Deflection


Structural member




Bottom panels exposed to slamming

0.3

0.35

0.01

Remaining bottom and inner bottom

0.3

0.4

0.01

Side structures

1.3

1.4

0.01

Deck structures

1.3

1.4

0.01

Bulkhead structures

0.3

0.4.

0.01

Superstructures

1.3

1.4

0.01

Deckhouses

0.3

0.4

0.01

All structures exposed to long time static loads

0.20

0.15

0.005

NOTE:

(1) is to be in accordance with the following :

For skin laminates exposed to tensile stress : ultimate tensile stress.

For skin laminates exposed to compressive stress :the smaller of the ultimate compressive stress and critical local buckling stress.

(2) The allowable stress level for bottom panels exposed to slamming loads refer to core materials with a shear elongation of at least 20 % an increase of the allowable stress level may be accepted upon special consideration.