Standards related to:

GB/T 1456-2021GB/T 1456-2021

NATIONAL STANDARD OF THE

PEOPLE’S REPUBLIC OF CHINA

ICS 83.120

CCS Q 23

Replacing GB/T 1456-2005

Test method for flexural properties of sandwich

constructions

ISSUED ON: DECEMBER 31, 2021

IMPLEMENTED ON: JULY 01, 2022

Issued by: State Administration for Market Regulation;

Standardization Administration of the People’s Republic of China.

Table of Contents

Foreword ... 3

1 Scope ... 5

2 Normative references ... 5

3 Terms and definitions... 5

4 Test principle ... 6

5 Test equipment ... 7

6 Test pieces ... 8

7 Test conditions and conditioning of test pieces ... 9

8 Test procedures ... 10

9 Test results and processing ... 12

10 Test report ... 14

Appendix A (Informative) Span reference table ... 16

Appendix B (Informative) Determination of bending stiffness and shear stiffness of

sandwich constructions by multi-span method ... 17

Appendix C (Normative) Calculation formulas for bending stiffness of the different

sandwich constructions of facing and stresses of facing ... 20

Appendix D (Informative) Calculation formulas for honeycomb wall shear stress and

honeycomb wall shear modulus of honeycomb core ... 22

References ... 23

Test method for flexural properties of sandwich

constructions

1 Scope

This document specifies the test principle, test equipment, test pieces, test conditions

and conditioning of test pieces, test procedures, test results and processing and test

report for flexural properties of sandwich constructions.

This document applies to the determination of the appearance bending strength and

appearance bending modulus of sandwich constructions subjected to bending, the

bending stiffness and shear stiffness of sandwich constructions, the stress and elasticity

modulus of sandwich-construction face sheets, the shear stress and shear modulus of

sandwich-construction cores; it also applies to the determination of flexure adhesive

layer strength between the facing and the core of a sandwich construction.

2 Normative references

The following documents, in whole or in part, are normatively referenced in this

document and are indispensable for its application. For dated references, only the

version corresponding to that date is applicable to this document; for undated references,

the latest version (including all amendments) is applicable to this document.

GB/T 1446, Fiber-reinforced plastics composites - The generals

GB/T 3356-2014, Test method for flexural properties of orientational fiber

reinforced polymer metrix composite materials

GB/T 3961, Terms for fibre reinforced plastics

3 Terms and definitions

Terms and definitions determined by GB/T 3961 and the following ones are applicable

to this document.

3.1

Tension or compression strength of facing

The maximum stress of the sandwich construction under the action of bending load

when the facing is damaged.

3.2

Core shear strength

The maximum shear stress of the sandwich construction under the action of bending

load when the core fails.

3.3

Flexure adhesive layer strength

The maximum shear stress of the sandwich construction under the action of bending

load when the adhesive layer is damaged.

3.4

Overhanging beam three point bending

A bending test where there is a long beam with overhanging arm, a concentrated load

is applied in the midspan, and three displacement sensors are installed on the midspan

and two overhanging points, to measure the deflection of the midspan, left and right

overhanging points.

3.5

Appearance bending strength

Bending strength of the sandwich construction.

3.6

Appearance bending modulus

Flexural modulus of the sandwich construction.

3.7

Nominal thickness of facing

The thickness of facing that is obtained by theoretical calculation (design value) or by

measuring the blank facing.

4 Test principle

Measure the tension or compression strength of facing by three point bending of the

long-beam test piece of the sandwich construction; measure the core shear strength by

three point bending of the short-beam test piece of the sandwich construction; measure

the bending stiffness and shear stiffness by overhanging beam three point bending of

the long-beam test piece of the sandwich construction, so as to determine the elasticity

modulus of facing and shear modulus of core.

5.3 Place a hard rubber gasket between the loading indenter and the test piece, where

the size is not smaller than the indenter spacer, the thickness is 3 mm ~ 5 mm, and the

length shall cover the width of the test piece.

5.4 Deformation measuring equipment such as displacement sensor, with an accuracy

of 0.001 mm.

5.5 Dimension measuring equipment such as vernier caliper, with an accuracy of 0.01

mm.

6 Test pieces

6.1 The test piece shall be of rectangular shape with a rectangular cross-section.

6.2 The thickness of the test piece shall be the same as that of the sandwich-construction

product. When the thickness of the sandwich-construction product is not fixed, in order

to determine the tension or compression strength of facing, core shear strength or shear

modulus of core, it is recommended that the core thickness be 15 mm, and the thickness

of facing be 0.3 mm ~ 1.0 mm.

6.3 The width of the test piece shall be less than half of the span, and not less than twice

the total thickness. The width of the test piece is recommended to be 60 mm. For lattice

cores such as honeycomb and corrugation, the width of the test piece shall include at

least 4 complete lattices.

6.4 The length of the test piece is the span plus 40 mm or half of the thickness,

whichever is larger. When an overhanging arm is required, the length shall meet the

overhanging arm, and the span shall be calculated and selected according to the test

purpose:

a) When measuring the core shear strength, the span of the three-point bending (see

Figure 1) shall satisfy Formula (1):

Where:

L – support span, in millimeters (mm);

σfd – allowable tension or compression stress of facing, in megapascals (MPa);

tf – thickness of facing, in millimeters (mm);

τcb – core shear strength, in megapascals (MPa).

Note 1: All the same formula symbols in the text have a unified meaning; the

symbols in the subsequent formulas shall refer to the definition of the

previous formula symbol.

Note 2: The allowable stress is provided by the designer; the tensile strength,

compressive strength and shear strength are provided by the

manufacturer or obtained by testing according to the national standards

for the corresponding materials.

b) When measuring the tension or compression strength of facing, the span of the

three-point bending shall satisfy Formula (2):

Where:

σfb – tension and compression strength of facing, in megapascals (MPa);

τcd – allowable shear stress of core, in megapascals (MPa).

c) When measuring the bending stiffness and shear stiffness of the sandwich

construction, use the overhanging beam three point bending (see Figure 2), where

the span is generally the value of Formula (1), the length a of the overhanging

arm is one-third or one-half of the span, which is increased depending on the

deformation device such as the displacement sensor.

d) For composite sandwich constructions such as fiber reinforced plastics, see

Appendix A for spans, overhanging arm lengths, etc.

6.5 When measuring the appearance bending strength and appearance bending modulus,

the width of the test piece is 60 mm, and the span-thickness ratio and length are as

specified in Table 1 in GB/T 3356-2014.

6.6 For orthotropic constructions, the test pieces are divided into two types: longitudinal

and transverse.

6.7 Test piece processing shall be in accordance with the provisions of GB/T 1446.

6.8 For number of test pieces, there shall be at least 5 valid test pieces.

7 Test conditions and conditioning of test pieces

The test environmental conditions and conditioning of test pieces shall be in accordance

with the provisions of GB/T 1446.

Where:

σf – tensile and compressive stress in the facing, in megapascals (MPa).

When P is the maximum load, and failure phenomena such as breaking or compressive

wrinkling of facing occur, the result calculated by Formula (6) is the tension or

compression strength of facing.

9.4 The bending stiffness of the sandwich construction is calculated according to

Formula (7):

Where:

D – bending stiffness of the sandwich construction, in Newton square millimeters (N

mm2);

a – overhanging arm length, in millimeters (mm);

ΔP – load increment of the initial segment of the load-deflection curve, in millimeters

(mm);

f1 – deflection increment of the overhanging point corresponding to ΔP (take the

average value of the left and right points), in millimeters (mm).

9.5 The elasticity modulus of facing is calculated according to (8):

Where:

Ef – elasticity modulus of facing, in megapascals (MPa);

J – moment of inertia of the sandwich construction, in fourth power millimeters (mm4).

Note: The bending stiffness of core and the facing itself has been omitted in Formula

(9).

9.6 The shear stiffness of the sandwich construction is calculated according to Formula

(10):

Where:

U – shear stiffness of the sandwich construction, in Newtons (N);

f – increment of deflection at the midspan of the test piece corresponding to ΔP, in

millimeters (mm).

9.7 The shear modulus of core is calculated according to Formula (11):

Where:

Gc – shear modulus of core, in megapascals (MPa).

9.8 The appearance bending strength and appearance bending modulus are calculated

according to the bending strength and bending elasticity modulus of GB/T 3356-2014.

9.9 The bending stiffness of different sandwich constructions of facing and the tension

or compression strength of facing shall be calculated according to Appendix C.

9.10 See Appendix D for calculation of honeycomb wall shear stress and honeycomb

wall shear modulus of honeycomb core.

9.11 The test results shall be in accordance with the provisions of GB/T 1446.

10 Test report

The test report generally includes the following contents:

a) reference to this document and name of test items;

b) source and preparation of test pieces, variety and specification of materials;

c) number, shape and size of test pieces, thickness, appearance quality and quantity

of the facing used in the calculation (if it is an anisotropic material, the

longitudinal or transverse direction shall be indicated), and elasticity modulus of

the facing used in the calculation (when the modulus is known);

d) test temperature, relative humidity and sample conditioning;

e) name and model of the test equipment;

f) test speed, test span;

Appendix B

(Informative)

Determination of bending stiffness and shear stiffness of sandwich constructions

by multi-span method

B.1 This method obtains the bending stiffness and shear stiffness of the same test piece

by loading it twice with different spans. Formula (B.1) reflects the test principle.

Where:

l – deflection at the midpoint of the span, in millimeters (mm);

P – applied load, in Newtons (N);

L – support span, in millimeters (mm);

S – span of four-point bending loading head, in millimeters (mm);

D – bending stiffness of the sandwich construction, in Newton square millimeters

(N·mm2);

U – shear stiffness of the sandwich construction, in Newtons (N).

See GB/T 3356-2014 for the test procedures; test a test piece to obtain the failure load

under the first support span (L1).

For the test speed and loading method, see method A of GB/T 3356-2014 for three-

point bending, and method B of GB/T 3356-2014 for four-point bending.

B.2 Load the support span L1 to 10% ~ 30% of the failure load, and obtain the load

difference P1 of the linear segment and the corresponding deflection difference l1.

B.3 Load the support span L2 to 10% ~ 30% of the failure load, and obtain the load

difference P2 of the linear segment and the corresponding deflection difference l2.

Note: The greater the difference between L2 and L1, the better the result.

B.4 When selecting a specific loading span and support span, it can be simplified to the

following formula:

a) When the two loading spans are 0, and the support spans are L1 and L2, see

Formula (B.2) and Formula (B.3):

...