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Material Properties and Testing

In document Indian Coast Guard Ships (Page 137-141)

Section 5

Table 5.1.4 (b) : Mechanical properties for woven roving (WR) reinforcements

Mechanical property [N/mm2]

Ultimate tensile strength 400 Gc - 10

Tensile modulus (30 Gc - 0.5) x 103

Ultimate compressive strength 150 Gc + 72

Compressive modulus (40 Gc – 6) x 103

Ultimate shear strength 80 Gc + 38

Shear modulus (1.7 Gc + 2.24) x 103

Ultimate flexural strength 502 Gc

2 + 106.8

Flexural modulus (33.4 Gc

2 + 2.2) x 103

Note: Gc is the glass content by weight of the reinforcement within the laminate.

5.1.5 The total thickness of a cured laminate is given by:

t = Σti , (excluding the gel coat) where,

ti = the thickness of ith layer

1.36 [mm]

Gc x 2.56 3072


 

 


wi = the weight of the reinforcement in the ith layer, [g/m2] Gc = glass content by weight in the ith layer.

5.2 Testing

5.2.1 The test pieces of sandwich panels and laminates are to represent the actual construction in respect of the raw materials used ( reinforcements, resins, additives and fillers ), lay-up sequence, production procedures, workshop conditions, etc.

The shear strength and shear modulus properties of type approved core materials as tested and certified by the supplier may be accepted subject to satisfactory supporting documentation.

5.2.2 The testing is to be carried out as per the test methods specified in Chapter 2,section 4.

5.2.3 The extent of material testing will be considered in each individual case but shall normally include the following, as a minimum :

In case of single skin laminates :

− the tensile strength, tensile modulus, bending strength and bending modulus and glass content In case of sandwich panels :

− the tensile strength and tensile modulus of the skin laminates

− the bending strength and modulus of the sandwich panel as a whole

− shear test for core materials and test for bond between the skin and core

In case of flange laminates of stiffeners and girders :

− the tensile strength and tensile modulus of the skin laminates

5.2.4 The testing is normally to be carried out at the temperatures mentioned in the relevant standards indicated in Chapter 2, Section 4. For structural members which may be subjected to elevated temperatures, e. g. in way of engine exhaust pipes, it may be necessary to carry out the tests at the relevant operating temperatures.

Section 6

Hull Girder Strength

6.1 General

6.1.1 Scantlings of hull members contributing to longitudinal and transverse hull girder strength are to comply with the requirements given in this section. In addition, members subjected to large compressive stress may also need to be checked for buckling strength.

6.1.2 In general, the longitudinal strength is to be checked for all Ships where L/D > 12 or L > 24 m.

For other vessels, longitudinal strength calculations may be required based on the deck flange area, form, construction arrangement and loading.

6.2 Longitudinal bending strength

6.2.1 The resultant longitudinal bending tensile or compressive stress within any laminate is not to exceed the allowable hull girder bending stress σa = 0.33 x σu {N/mm2], where σu is the ultimate tensile strength of the laminate.

6.2.2 The resultant tensile or compressive stress, σ, within any laminate is given by :

2] [N/mm 10

)x E (

yi Ei

Ii i


=Σ σ


M = the Rule longitudinal bending moment [ kN-m], which is the greater of : a) Total Bending Moment Mt = (Ms + Mw) given in Chapter 3, Section 4.1.2.

b) Bending Moment due to slamming Msl given in Chapter 3, Section 4.1.3 Ei = tensile modulus of the laminate under consideration [N/mm2]

yi = the vertical distance to the furthest point within the laminate under consideration from the neutral axis [m]

Ii = the moment of inertia of the laminate under consideration, about the neutral axis [ cm2- m2 ] The distance of the neutral axis, Yna, from keel is given by :

) [m]

ai (Ei

i) iz ia E ( Yna


= Σ


ai, = the cross sectional area of individual laminate [ cm2]

zi = the distance to the centre of area of individual laminate from keel [m]

6.3 Calculation of effective sectional properties and longitudinal bending stress

6.3.1 The effective sectional properties of a transverse section are to be calculated using the net area of all continuous longitudinal members after deduction of openings in accordance with Chapter 5, Section 2.3.

6.3.2 In case of sandwich panels, area of only the skin laminates are to be considered, ignoring the core material.

6.4 Openings in longitudinal strength members

6.4.1 The keel plate is normally not to have any openings. In the bilge plate within 0.6L amidships openings are to be avoided as far as practicable. Openings in strength deck are to be kept well clear of Ship’s side and hatch corners.

6.4.2 Circular openings with diameter equal to or more than 0.325 m are to have edge reinforcement. Elliptical openings are to have their major axis in the fore and aft direction. Where the ratio of the major axis to the minor axis is less than 2, the openings are to have edge reinforcement.

6.4.3 Rectangular openings are to have their corners well rounded. Where corners are of circular shape, the radius is not to be less than 20 percent of the breadth of the opening and the edges are to be reinforced.

6.5 Shear Strength

6.5.1 The shear stress, τ, at mid depth at any position along the length is not to exceed the allowable hull shear stress σa = 0.33 x τu {N/mm2], where τu is the ultimate shear strength of the laminate.

6.5.2 The shear stress τ, is to be taken as :

2] [N/mm As

=10Q τ


Q = the Rule shear force [kN], which is the greater of :

a) Total shear force QL = (Qs + Qw) given in Chapter 3, Section 4.1.2.

b) Shear force due to slamming Qsl given in Chapter 3, Section 4.1.3.

As = net sectional area of laminates of side shell plating and longitudinal bulkheads, if any [cm2]

Section 7

In document Indian Coast Guard Ships (Page 137-141)