Section 3 Stress control
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Special Service Craft, July 2022 - Part 8 Hull Construction in Composite - Chapter 7 Failure Modes Control - Section 3 Stress control

Section 3 Stress control

Parent topic: Chapter 7 Failure Modes Control

3.1 General

3.1.1 The nominal limiting stress for panels and primary and secondary stiffening members, subject to local and global loading conditions, are given in this Section.

3.2 Tensile and compressive stress

3.2.1 The limiting tensile and compressive stress criteria values for local and global loading conditions are given in Table 7.3.1 Limiting stress criteria for local loading and Table 7.3.2 Limiting stress criteria for global loading respectively. These values are expressed as a fraction of the ultimate tensile and compressive strength of the laminate at first ply failure.

3.2.2 The ultimate compressive strength of the sandwich skin laminate shall not be taken greater than the critical skin buckling stress given by

σ cr = 0,5 (E cps E c G)1/3

where

σ cr = critical skin buckling stress, in N/mm2
E c = compressive modulus of the core material, in N/mm2

E cps and G are as defined in Pt 8, Ch 3, 1.5 Symbols and definitions 1.5.1

3.3 Shear stress

3.3.1 The limiting shear stress criteria values for local and global loadings are given in Table 7.3.1 Limiting stress criteria for local loading and Table 7.3.2 Limiting stress criteria for global loading respectively. These values are expressed as a fraction of the ultimate shear strength of the laminate.

3.4 Interlaminar shear stress

3.4.1 The interlaminar shear strength of the proposed laminate is to be demonstrated to be not less than 13,8 N/mm2.

3.5 Core shear stress

3.5.1 The limiting core shear stress criteria values are given in Table 7.3.3 Limiting core shear stress criteria. These values are expressed as a fraction of the ultimate core shear strength of the core material, see also Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.9.

3.5.2 The ultimate core shear strength of the core material is to be taken as 90 per cent of the mean ultimate shear strength determined from accepted mechanical tests, or the mean minus two standard deviations based on a minimum of five samples, whichever is less. All test pieces are to be representative of the product to be manufactured and details are to be submitted for consideration.

3.5.3 In the absence of suitable test data, LR will consider basing the ultimate core shear strength on manufacturer recommended minimum design values based on mechanical tests performed by the core material manufacturer using accepted test methods.

Table 7.3.1 Limiting stress criteria for local loading

Item Limiting stress fraction
Tensile Compressive Shear
Shell envelope:      
(a) Bottom shell laminate:      
  • slamming zone
 0,28 0,28 –
  • elsewhere
 0,25 0,25 –
(b) Side shell laminate:      
  • slamming zone
 0,33 0,33 –
  • elsewhere
 0,30 0,30 –
(c) Keel 0,25 0,25 –
Bottom structure:      
(a) Secondary stiffening:      
  • slamming zone
 0,33 0,33 0,33
  • elsewhere
 0,30 0,30 0,30
(b) Primary girders and web frames 0,33 0,33 0,33
(c) Engine girders 0,33 0,33 0,33
Side structure:      
(a) Secondary stiffening:      
  • slamming zone
 0,33 0,33 0,33
  • elsewhere
 0,30 0,30 0,30
(b) Primary girders and web frames 0,33 0,33 0,33
Main/strength deck laminate and stiffeners:      
(a) Laminate 0,30 0,30 –
(b) Secondary stiffening 0,30 0,30 0,30
(c) Primary girders and web frame 0,33 0,33 0,33
(d) Hatch covers 0,25 0,25 0,25
Superstructures/deckhouses:      
(a) Deckhouse front, 1st tier:      
  • laminate
 0,30 0,30 –
  • stiffening
 0,33 0,33 0,33
(b) Deckhouse front, upper tiers:      
  • laminate
 0,30 0,30 –
  • stiffening
 0,33 0,33 0,33
(c) Deckhouse, aft and sides:      
  • laminate
 0,30 0,30 –
  • stiffening
 0,33 0,33 0,33
(d) Coachroof:      
  • laminate
 0,30 0,30 –
  • stiffening
 0,33 0,33 0,33
(e) House top, not subject to personnel loading:      
  • laminate
 0,40 0,40 –
  • stiffening
 0,40 0,40 0,40
(f) Lower/inner decks and house top subject to personnel loading:      
  • laminate
 0,33 0,33 –
  • stiffening
 0,30 0,30 0,30
Bulkheads:      
(a) Collision bulkhead:      
  • laminate
 0,26 0,26 –
  • secondary stiffening
 0,32 0,32 0,32
  • primary stiffening
 0,32 0,32 0,32
(b) Watertight bulkhead:      
  • laminate
 0,33 0,33 –
  • secondary stiffening
 0,40 0,40 0,40
  • primary stiffening
 0,40 0,40 0,40
(c) Watertight bulkhead doors:      
  • in collision bulkhead
 0,25 0,25 –
  • in other bulkheads
 0,33 0,33 –
(d) Structure supporting watertight doors:      
  • in collision bulkhead
 0,25 0,25 0,25
  • in other bulkheads
 0,33 0,33 0,33
(e) Minor bulkheads:      
  • laminate
 0,50 0,50 –
  • secondary stiffening
 0,50 0,50 0,50
  • primary stiffening
 0,50 0,50 0,50
(f) Deep tank bulkheads:      
  • laminate
 0,25 0,25 –
  • secondary stiffening
 0,33 0,33 0,33
  • primary stiffening
 0,33 0,33 0,33
Multihull cross-deck structure:      
(a) Laminate:      
  • slamming zone
 0,33 0,33 –
  • elsewhere
 0,30 0,30 –
(b) Secondary stiffening:      
  • slamming zone
 0,33 0,33 0,33
  • elsewhere
 0,30 0,30 0,30
(c) Primary stiffening 0,33 0,33 0,33
Vehicle deck:      
(a) Laminate 0,25 0,25 –
(b) Secondary stiffening 0,33 0,33 0,33
(c) Primary stiffening 0,33 0,33 0,33
Helicopter/flight decks:      
(a) Normal usage:      
  • laminate
 0,25 0,25 –
  • secondary stiffening
 0,33 0,33 0,33
  • primary stiffening
 0,33 0,33 0,33
(b) Emergency landing:      
  • laminate
 0,33 0,33 –
  • secondary stiffening
 0,43 0,43 0,43
  • primary stiffening
 0,43 0,43 0,43
Lifting appliance pedestal/foundation structural elements:      
(a) cargo cranes 0,25 0,25 0,25
(b) structures exposed to permanent static loads 0,22 0,22 0,22
(c) LSA davit foundations, see also Pt 8, Ch 5, 2.6 Lifting appliances and associated support arrangements. 0,22 0,22 0,22

Table 7.3.2 Limiting stress criteria for global loading

Operational mode of craft Limiting stress fraction
Tensile Compressive Shear Shear
    see Note 1 see Note 2
Γ ≥ 3,0 or 0,33 0,33 0,33 0,33
Δ ≤ 0,04(L R B)1,5
Γ < 3,0 and 0,25 0,25 0,25 0,25
Δ > 0,04(L R B)1,5

Note 1. Limiting stress fraction for the hull shear stress at any point along the craft length.

Note 2. Limiting stress fraction for the vertical shear stress for the cross-deck structure.

Note
Δ = is the displacement as defined in Pt 5, Ch 2, 2 Definitions and symbols.
Note
Note
L R and B = are as defined in Pt 3, Ch 1, 6.2 Principal particulars.

Table 7.3.3 Limiting core shear stress criteria

Core material Limiting shear stress fraction

(see Note)

SAN cores 0,60
PVC and metal/composite honeycombs 0,45
All other cores 0,35
Note For long-term static loads, the limiting shear stress fraction is to be taken as 0,20.
Copyright 2022 Clasifications Register Group Limited, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasifications Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasifications Register'. Clasifications Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasifications Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.