Chapter 2 Materials
2.9 Test Procedures for Core Material for Sandwich Constructions
(a) The shape and selection of test specimens used for the test of core materials for sandwich construction are to be in accordance with Table I 2-5.
(b) The manufacturing methods of sandwich constructions for the test are to be in accordance with the following:
(i) The core material is to be the largest thickness to be used as primary structural members of hull construction.
(ii) On both sides of the core, the M-R-M-R-M laminates are to be applied, where M denotes chop mats (weight per unit area 600 g/m2) and R, woven roving (weight per unit area 810 g/m2).
(iii) The glass content is to be approximately 30% at the portion of chops mats, and approximately 50%
at the portion of woven roving.
(iv) The direction of warp of the woven roving is to be aligned with the longitudinal direction of the test specimen.
(v) In the case of the fibre reinforced plastics foam, test specimens of which longitudinal direction is aligned respectively with the direction of the maximum strength and the direction of the minimum strength of the core material are to be manufactured.
2.9.2 Test Procedures
(a) The test procedures for the hard plastics foam specified in 2.5.2 are to be in accordance with the following:
(i) Specific gravity
(1) The test specimens are to be in accordance with Table I 2-5.
(2) Leave the test specimen in a thermostatic air oven (25 0.5 °C) for about 30 minutes and measure the dimension and weight.
(3) The size of the test specimen is to be measured to an order of 0.1 mm for the thickness, length and breadth.
(4) The weight of the test specimen is to be measured to the order of 0.1 g.
(5) The specific gravity is to be for the value obtained from the following formula.
W/V where:
W = Weight of test specimen, in g
V = Weight of pure water corresponding to the volume of test specimen, in g (ii) Water absorption rate
(1) The test specimens are to be in accordance with Table I 2-5.
(2) The surface skin of the test specimen, if such is the case, is to be removed, and the dimensions are to be measured to the order of 0.1 mm.
(5) The test specimens of which reference weight has been measured is to be soaked in fresh water (23 3 °C) for 24 hours with a pressure of 10 N/mm2.
(6) The weight of the test specimen (W1) is to be measured by the same procedure as specified in (4) above.
(7) The water absorption rate is to be obtained from the following formula.
2.9 Test Procedures for Core Material for Sandwich Constructions
(iii) Compressive strength and modulus of compressive elasticity.
(1) The test specimens are to be in accordance with Table I 2-5.
(2) The size of the test specimen is to be measured to the order of 0.1 mm.
(3) Compression to be applied in the direction thickness of the product.
(4) The standard compression speed is to be 5 mm/min.
(5) The compressive strength is to be obtained from the following formula.
Pc
A N/mm2
where:
Pc = Load at which 0.2% strain is occurred from the elastic limit, in N A = Pressure bearing area of test specimen, in mm2
(6) The modulus of compressive elasticity is to be obtained
(dP/dt) = Gradient of the straight portion of load-contraction curve, in N/mm (See Fig. I 2-8)
t = Thickness of test specimen
A = Pressure bearing area of test specimen, in mm2 (iv) Softening rate
The modulus of compressive elasticity at a temperature of 60 °C is to be measured by suitable means.
The method specified in 2.8.2(g) may be applied correspondingly.
(v) Tensile strength and modulus of tensile elasticity
(1) The test specimens are to be in accordance with Table I 2-5.
(2) The test procedure is to be in accordance with 2.7.2(f).
(vi) Bending strength and modulus of bending elasticity.
(1) The test specimens are to be in accordance with Table I 2-5.
(2) The testing arrangement of four point bending is to be in accordance with Fig. I 2-9.
(3) The standard loading speed is to be t/2 mm/min.
t = thickness of test specimen, in mm
(4) The bending strength is to be obtained from the following formula.
3PL1
PART I CHAPTER 2 2.9 Test Procedures for Core Material for Sandwich Constructions
CR CLASSIFICATION SOCIETY - 27 -
RULES FOR THE CONSTRUCTION AND CLASSIFICATION OF SHIPS OF FIBREGLASS REINFORCED PLASTICS 2018
Maximum load Pc Load corresponding to elastic limit
Contraction 0.2% contraction
Fig. I 2-8
Load-Contraction Diagram
(5) The modulus of bending elasticity is to be obtained from the following formula.
d
dP bt
L L 4 3
3 2 2
1 N/mm2
where:
L1 = Outer span, in mm L2 = Mid span, in mm
(dP/d) = Gradient of straight portion of load-deflection at mid point of gauge length
= Deflection at mid point of gauge length, in mm
2.9 Test Procedures for Core Material for Sandwich Constructions
Testing Arrangement of Four Point Bending
(vii) Shearing strength of sandwich constructions(1) The test specimens are to be in accordance with Table I 2-5.
(2) The testing arrangement of four point bending is to be in accordance with Fig. 2 -9 (3) The standard loading speed is to be t/2 mm/min.
t = thickness of test specimen, in mm
(4) The shearing strength is to be obtained from the following formula.
t t
btf = Mean thickness of inner layer and outer layer of FRP laminates, in mm tc = Thickness of core material, in mm
b = Breadth of test specimen, in mm
(5) The outer span (L1) is to be referred to the value obtained from the following formula.
However, in case where either the outer or inner FRP laminates fails, retest is to be carried out with the smaller outer span.
f = Tensile strength of FRP laminates, in N/mm2
c = Imaginary shearing strength of core material, in N/mm2
(b) The test procedures for balsa are to be in accordance with the following:
(i) Specific gravity
The test procedure is to be in accordance with 2.9.2(a)(i). However, the size and weight are to be measured at room temperature.
PART I CHAPTER 2 2.9 Test Procedures for Core Material for Sandwich Constructions
CR CLASSIFICATION SOCIETY - 29 -
RULES FOR THE CONSTRUCTION AND CLASSIFICATION OF SHIPS OF FIBREGLASS REINFORCED PLASTICS 2018 (ii) Moisture content
(1) After having dried the test specimen in (i) above in the thermostatic air oven to a fixed weight, the weight is to be measured to the order of 0.1g.
(2) The moisture content is to be of the value obtained from the following formula.
W1-W2
W2 ×100 (%) where:
W1 = Weight at the standard condition, in g W2 = Weight after drying, in g
(iii) Compressive strength in fibrous direction and modulus of compressive elasticity.
The test procedure is to be in accordance with 2.9.2(a)(iii). However, Pc shown in (5) is the maximum load (N). In this case, the specific gravity of the test specimen is to have been measured in accordance with (i) above.
(iv) Shearing strength of sandwich constructions.
The test procedure is to be in accordance with 2.9.2(a)(vii).