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A: General [Table of Contents] C: Properties under long term static and cyclic and high rate loads

DNV-OS-C501 Composite Components

[-] Sec.4: Materials - Laminates
[-] B: Static properties

Sec.4
B. Static properties

Sec.4
B 100   General

Sec.4 B
101   All material properties shall be given with full traceability of materials and conditions. Test results are only valid if the information given in Table A1 is available. Tests shall be reported as mean, standard deviation, and number of tests.

Sec.4 B
102   For many applications the static properties after exposure to long term loads and environments are more important than the static properties of a new material. This fact should be kept in mind when selecting materials and developing a test programme. Long term properties are described in the following sections.

Sec.4
B 200   Static properties

Sec.4 B
201   The complete list of orthotropic ply data is shown in Table B1. Recommended test methods to obtain the properties are given in Appendix C. Fibre and matrix dominated properties are identified in the column 'characteristic' as F and M respectively.

Sec.4 B
202   Static properties are generally assumed to be identical to quasi-static properties, measured at a testing rate of about 1% per minute. If loading rates in the component differ from this rate, tests should be made at the relevant rates or corrections of the data should be considered.

Sec.4 B
Table B1 Static properties 
In-plane orthotropic elastic constants Mechanical parameter Unit Char. Reference Appendix C
for measurement method 
E1 fibre UD-ply Modulus of elasticity in main fibre direction  [GPa] F B100 
E2 matrix UD-ply Modulus of elasticity transverse to main fibre direction  [GPa] M B100 
E1 linear cross-ply Modulus of elasticity in 0° fibre direction in the liner range [GPa] M, F B100 
E2 linear cross-ply Modulus of elasticity normal to the 0° fibre direction in the liner range [GPa] M, F B100 
E1 non-linear cross-ply Secant modulus of elasticity in 0° fibre direction at the failure point [GPa] F B100 
E2 non-linear cross-ply Secant modulus of elasticity normal to the 0 fibre direction at the failure point [GPa] F B100 
G12 linear In plane shear modulus in the liner range [GPa] M B300 
G12 non-linear In plane secant shear modulus at the failure point [GPa] M B300 
n12 Ply major Poisson's ratio  F, M B100 
n21 Ply minor Poisson's ratio  F, M B100 
In-plain
Strain to Fail 		    
raster fibre Tensile strain at break for the fibres  F B100 
raster Fibre Compressive strain at break for the fibres  F, M B200 
raster matrix Tensile strain at break for the matrix in direction normal to the fibre direction, in the fibre plane.  M B100 
raster matrix Compressive strain at break for the matrix in direction normal to the fibres.   M B200 
raster matrix Shear strain at failure in ply plane  M B300 
In-plane Strength     
raster Fibre Tensile stress at break in the fibre direction  N/mm2 (MPa) F B100 
raster Fibre Compressive stress at break in fibre direction N/mm2 (MPa) F, M B200 
raster matrix Tension stress at break normal to the fibre direction. N/mm2 (MPa) M B100 
raster matrix Compressive stress at break normal to the fibre direction N/mm2 (MPa) M B200 
raster shear Shear stress in ply plane at failure. N/mm2 (MPa) M B300 
Through -thickness     
E3  Modulus of elasticity normal to the fibre plane. GPa M B400 or B500 
G13 Shear modulus normal to the fibre plane, including the fibre direction GPa M B600 
G23 Shear modulus normal to the fibre plane, including the direction normal to the fibres. GPa M B600 
n13 Poisson's ratio normal to the fibre plane, including the fibre direction, when tensioning in the fibre direction.  M B100 or B600 
n23 Poisson's ratio normal to the fibre plane, including the direction normal to the fibres.  M B100 or B600 
raster  Tensile strain at break normal to the fibre plane.  M B400 
raster  Compression strain at break normal to the fibre plane.  M B500 
raster  Shear strain at failure normal to the fibre plane, including the fibre direction.  M B600 
raster  Shear strain at failure normal to the fibre plane, normal to the fibre direction.  M B600 
raster  Tension stress at break normal to the fibre plane. N/mm2 (MPa) M B400 
raster  Compression stress at break normal to the fibre plane. N/mm2 (MPa) M B500 
raster  Shear stress at failure normal to the fibre plane, including the fibre direction. N/mm2 (MPa) M B600 
raster  Shear strain at failure normal to the fibre plane, normal to the fibre direction. N/mm2 (MPa) M B600 
Fracture toughness     
Critical length Maximum tolerable In-plane length of crack. mm F/ M B700 
G1c Critical strain energy release rate. (Mode I). N/m M B800 
G2c Critical strain energy release rate in the fibre plane (Mode II). N/m M B800 
G3c Not used    



Sec.4 B
203   If only one sub index is given in the Table B1, it is identical to two indices of the same kind, e.g. raster = raster .

Sec.4 B
204   The index fibre indicates ply properties in fibre direction. Failure stresses and strains with the index fibre describe ply failure in fibre direction. It does not mean that a single fibre has failed, usually a number of fibres fail before the ply breaks.

Sec.4 B
205   The index matrix indicates matrix dominated ply properties perpendicular to the fibre direction. Failure stresses and strains with the index matrix describe matrix cracking inside the ply. This is usually the initiation of matrix cracks.

Sec.4
B 300   Relationship between strength and strain to failure

Sec.4 B
301   For analysis purposes it is important to have a consistent set of data. The relationship below shall always be valid for all linear and bi-linear materials:

s = E e



Sec.4 B
302   Strain to failures shall be calculated from strength measurements based on the above equation and using the non-linear secant moduli at failure if relevant.

Sec.4 B
303   The coefficient of variation COV of the strain to failure shall be taken as the same as the COV of the measured strength. Without using this procedure the characteristic values will not follow Hook's law as described in 301.

Sec.4
B 400   Characteristic values

Sec.4 B
401   Characteristic values shall be used for all strength values in this standard.

Sec.4 B
402   Characteristic values shall be established with 95% confidence.

Sec.4 B
403   The sample mean of the measurements is:

raster


where xi is the individual measurement and n is the number of measurements.

Sec.4 B
404   The standard deviation is estimated from the measurements by:

raster



Sec.4 B
405   The coefficient of variation COV is estimated as:

raster



Sec.4 B
406   The characteristic strength value is:

raster


with raster given in Table B2.

Sec.4 B
Table B2 Values of km 
 km 
 Definition of characteristic value 
Number of test specimens 2.5% quantile in distribution of arbitrary strength 
3 9.0 
4 6.0 
5 4.9 
6 4.3 
10 3.4 
15 3.0 
20 2.8 
25 2.7 
Infinite 2.0 



Sec.4 B
407   The characteristic values of Young's moduli and Poisson's ratios are mean values.

Sec.4 B
408   Characteristic values of strains to failure shall be based on strength measurements (see B300)

Sec.4 B
409   Characteristic values shall be used throughout the standard.

Sec.4
B 500   Experimental measurement of matrix and fibre dominated strain to failure

Sec.4 B
501   For unidirectional plies or laminates, the matrix dominated strain to failure raster fibre can simply be measured as the strain to failure in fibre direction.

Sec.4 B
502   For unidirectional plies or laminates, the fibre dominated strain to failure raster matrix can simply be measured as the
strain to failure perpendicular to the fibre direction.

Sec.4 B
503   For measurements taken on other laminates the onset of matrix cracking can be defined as the knee point of the stress- strain curve. Some matrix cracking tends to develop before this level, but significant cracking can be defined this way. The knee point is defined as the cross over of the lines defining the initial modulus of the laminate and the tangential modulus of the final part of the stress strain curve. An example for a 0/90 laminate is given in Figure 1.

raster

Fig. 1   Example of a stress strain curve of a 0/90 laminate


Sec.4 B
504   The strain to failure transverse to the fibre direction is identical to the strain at onset of matrix cracking.

Sec.4 B
505   The strain to failure (rupture) of the laminate is the strain to failure of the fibres.

Sec.4 B
506   The remaining ply properties can be calculated with laminate theory and considering B300.

Sec.4 B
507   For properties with matrix cracking, see 4I.

Sec.4
B 600   Experimental measurement of ply shear properties

Sec.4 B
601   The shear properties of a ply are typically non-linear. In order to perform a linear analysis an initial non-degraded shear modulus should be defined.

Sec.4 B
602   For a strength analysis initial, undamaged shear modulus may be defined as the secant modulus between 0 and any point on the non-linear stress strain curve as long as:
—only nonlinear deformation, but no matrix cracking is observed in the experiments
—the point is below 80% of the failure strength
—the point is below 50% of the strain to failure

An example is given in Figure 2.

raster

Fig. 2   Example of a shear stress strain curve


Sec.4 B
603   For deflection calculations the modulus should be secant modulus at the maximum design shear stress and all requirements of 602 should be fulfilled.

Sec.4 B
604   The remaining properties can be calculated by laminate theory and considering B300.

Sec.4 B
605   For properties with matrix cracking or non-linear deformations, see 4I.

A: General [Table of Contents] C: Properties under long term static and cyclic and high rate loads