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Sec.5: Materials - Sandwich Structures [Table of Contents] B: Static properties

DNV-OS-C501 Composite Components

[-] Sec.5: Materials - Sandwich Structures
[-] A: General

Sec.5
A. General

Sec.5
A 100   Introduction

Sec.5 A
101   This section describes the mechanical material properties needed for design. It describes how to obtain all strength properties used in the failure criteria and all elastic properties needed for stress calculations.

Sec.5 A
102   A sandwich structure is considered here as a light weight core embedded between two faces (or skins). Faces are typically made of FRP laminates. The properties of laminates are described in section 4. This section concentrates on properties of cores and the core skin interface.

Sec.5 A
103   All properties shall be obtained directly by measurements or shall be traced back to measurements. The qualification of material properties is described in this section. Under certain conditions, typical values from databases can be used. Strength and stiffness values should be documented as characteristic values.

Sec.5 A
104   It is only necessary to obtain properties that are used in the design calculations and failure criteria.

Sec.5 A
105   General aspects that were already described in section 4 are not repeated here but only referred to.

Sec.5
A 200   Sandwich specification

Sec.5 A
201   A sandwich structure is made of many constituent material arranged and produced in a specific way. Laminate, core materials and adhesives used in a sandwich component shall be clearly specified and all materials shall be traceable. Laminate specification shall be organised as described in section 4.

Sec.5 A
202   For the core material and the adhesive, a minimum set of process parameters and constituent material characterisations is given in Table A1 and Table A2. All these items shall be specified.

Sec.5 A
Table A1 Core specifications, process parameters and conditioning parameters 
 
Constituent core material(s): 
Generic core type (e.g. foam, honeycomb, balsa etc.) 
Core trade name (e.g. xyz123) 
Type of core (e.g. linear foam) 
Type/ characteristics of microstructure 
Core manufacturer 
Batch number 
 
Process parameters: 
Laminator (company) 
Processing method 
Processing temperature 
Processing pressure 
Process atmosphere (e.g. vacuum) 
Curing temperature 
Post curing (temperature and time) 
Density of sandwich structures 
Glass transition temperature 
 
Conditioning parameters: 
Temperature 
Water content of the core (wet, dry) 
Chemical environment 
Loading rate 
Number of specimens 

Sec.5 A
Table A2 Adhesive specifications, process parameters and conditioning parameters 
 
Constituent adhesive material(s): 
Generic adhesive type (e.g. epoxy, polyester) 
Specific adhesive type trade name 
Specific adhesive type batch number 
Catalyst (trade name and batch number) 
Accelerator (trade name and batch number) 
Fillers (trade name and batch number) 
Additives (trade name and batch number) 

Sec.5
A 300   Lay-up specification

Sec.5 A
301   A sandwich structure is made of a sequence of layers. All materials, both core(s) and laminate(s), and their stacking sequence shall be clearly identified.

Sec.5 A
302   The orientation of non-homogenous or anisotropic materials shall be clearly specified on the materials level and the structural level.

Sec.5 A
303   Laminates and core(s) shall be specified such that they can be described by a sequence of stacked orthotropic plies, see also section 4.

Sec.5
A 400   Isotropic/orthotropic core layers

Sec.5 A
401   A core layer is defined as a volume element with three axis of symmetry with respect to mechanical properties.

Sec.5 A
402   All layer sequences shall be described by a combination of the three-co-ordinate systems. Ply angles shall be specified between the fibre, laminate co-ordinate system and the main core direction (x-direction).

Sec.5 A
403   Typically, there are two possible microstructure alignments:
—0/90 cell alignment found in orthotropic cores. Cells run parallel to each other within the same plane. The 3 main directions to which material properties are refereed are; width (W), length (L) and transverse (T) or x-, y- and z-direction. Typical cores are honeycomb, balsa wood and other corrugated core
—random cell alignment in quasi-isotropic core. Cells are randomly oriented without any preferred direction. A typical reinforcement type of this class is cellular foam core.


Sec.5 A
404   The following is assumed in this standard:
—for cellular cores, i.e. wood and foam, material behaviour and mechanical properties are considered at macroscopic scale, i.e. material properties are taken as an average over a volume of about cm3
—the measured material properties should be based on a scale that is compatible with the scale of the structural analysis.


Sec.5 A
405   In regions of high local stress concentrations, material properties on a microscopic scale may be needed.

Sec.5 A
406   These simplifications are generally valid. However, their applicability shall always be checked. Other modelling methods may be preferred for certain material combinations.

Sec.5
A 500   Mechanical and physical properties

Sec.5 A
501   All properties are dependent on the constituent materials, the processing and conditioning environment. It is natural to first separate the properties into laminate(s) and core(s), and interfaces. Interfaces are the core skin connection and possibly other adhesive joints between sections of cores.

Sec.5 A
502   For the sandwich facings, see section 4. If the faces are made of metallic materials, relevant codes for these materials shall be used.

Sec.5 A
503   The mechanical and physical properties of the core are very much dependent upon the nature of the material used for the core whether it is foam, honeycomb, wood or corrugated. For example, honeycomb cells can be made of paper and polyester resin, or aluminium, or Aramid and epoxy.

Sec.5 A
504   It is possible that a structure is loaded in such a way that some material properties are not relevant. In that case the non-relevant properties do not have to be known, but it shall be documented that the properties are not relevant for the application.

Sec.5 A
505   If cores of the same type are used in different layers in the component, one test series is sufficient to determine their properties.

Sec.5 A
506   Properties can be established as new, see appendix D, or checked against typical values. The procedure is given in section 4-H600.

Sec.5 A
507   Mechanical properties depend on the load conditions and the environment. Parameters related to the topics should be accounted for, see this section headings C, D and E.

Sec.5 A
508   For test data, the load conditions and the environment parameters should be reported.

Sec.5
A 600   Characteristic values of mechanical properties

Sec.5 A
601   See section 4 A600.
Sec.5: Materials - Sandwich Structures [Table of Contents] B: Static properties