4.1 The properties
of composite sections and laminates are to be determined from the
results of test data. The mechanical properties to be used for scantling
calculation purposes are to be 90 per cent of the mean first ply/resin
cracking failure values determined from accepted mechanical tests.
All test pieces are to be representative of the product to be manufactured.
This is particularly important since the material of construction
is 'manufactured' on site, at the same time as the product.
4.2 The mechanical
properties of the materials are also to be estimated from the appropriate
procedures and formulae contained within the Rules for Special Service
Craft. The acceptable design values for glass reinforced polyester
resin laminates are not to be greater than those contained with the
Rules for Special Service Craft unless agreed otherwise by LR. Additional
information on the application of the various formulae is given in
these Guidance Notes.
4.3 The various
formulae referred to above require that sufficient input data be available
which relates to each of the proposed materials. Where it is proposed
to use the design values greater than the nominal value indicated
in the Rules for Special Service Craft the designers and/or Builders
should agree on the values for use in the scantling analysis with
LR at the design stage and prior to the submission of plans and data
for appraisal.
4.4 Strength calculations
for all advanced fibre composites are to be based on the Rules values
and the results of testing of truly representative sections of the
proposed design. The sections are to be manufactured under typical
production conditions using the same materials, fibre contents, methods
of lay-up and time delays. Mechanical testing is, in general, to be
based upon the requirements specified in Ch 14 Plastics Materials and other Non-Metallic Materials of the Rules for Materials.
4.5 A through ply
analysis is required to be conducted for both plate and stiffener
elements and the resultant stresses compared with the allowable stress
limits for the particular element. Example procedures are described
in these Guidance Notes.