GB/T 41049-2021Test method for flexural properties of fibre metal laminates (English PDF)

3.1 Fibre metal laminates; FMLs

It is an interlayer hybrid composite material formed by alternately laying metal sheets (aluminum alloy, titanium alloy, etc.) and fibre (glass fibre, carbon fibre, aramid fibre, etc.) composite materials under a certain temperature and pressure.

3.2 Flexural stress

Bending moment regularization.

Note 1: The stress of the outer surface layer of the sample when it is assumed that the stress caused by bending deformation is linearly distributed.

Note 2: The unit is megapascal (MPa).

3.3 Flexural strength

Under bending failure, the flexural stress of the specimen when the damage load or the maximum load is reached.

Note: The unit is megapascal (MPa).

3.4 Span

The distance between the central axes of the two supports on the testing machine.

Note: The unit is millimeter (mm).

3.5 Deflection

The maximum height difference between the normal line of the deformation position of the sample surface during bending and the initial position.

Note: The unit is millimeter (mm).

3.6 Flexural strain

The rate of change in length of the outer surface layer of the sample at the midpoint of the span, expressed as a percentage.

3.7 Flexural modulus

The value derived from the slope of the initial section on a bending stress-bending strain curve or bending load-deflection curve.

Note: The unit is megapascal (MPa).

8.4 Sample installation

Mark the tension surface of the sample, and place the sample symmetrically on the two supports. If necessary, place a thin sheet or a thin spacer between the upper surface of the sample and the loading indenter to prevent the sample from failing under pressure.

When using strain gauges, stick the strain gauges at the center of the span below the sample along the parallel length direction; when using a deflectometer, place the deflectometer at the center of the span and perpendicular to the plane of the sample.

8.5 Test speed

The loading rate shall be between 1 mm/min~2 mm/min and kept constant.

8.6 Test

Apply the load uniformly across the width of the sample by a loading indenter located at the midpoint of the span until the sample is destroyed or the load drops by 30%.

Record the failure load to determine the flexural strength, and record the load-deflection curve or the load-flexural strain curve to determine the flexural modulus.

8.7 Data collection

Record the load value of the whole test process, and take the happening of the effective bending damage such as fibre damage or outer metal damage as the principle of data collection. The samples that show interlaminar shear failure, obvious internal defects, or damage beyond the middle one-third of the span shall be discarded. When the number of valid test results in the same batch is less than 5, the number of tested samples shall be increased to ensure the number of valid results reaches 5.

8.8 Failure modes

The fibre metal laminate will have the following failure modes under the test of this method.

a) Acceptable flexural failure modes:

1) Fibre failure, see Figure 4 a);

2) The outer metal is damaged, see Figure 4 b).

b) Unacceptable failure modes:

1) Interlaminar shear failure, see Figure 4 c);

9.5 Numerical rounding

The numerical rounding shall be carried out in accordance with GB/T 8170, the flexural strength is rounded to four significant digits, the standard deviation is rounded to three significant digits, and the flexural modulus is rounded to three significant digits.