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GB/T 1456-2021 (GBT1456-2021)

GB/T 1456-2021_English: PDF (GBT 1456-2021, GBT1456-2021)
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BASIC DATA
Standard ID GB/T 1456-2021 (GB/T1456-2021)
Description (Translated English) Test method for flexural properties of sandwich constructions
Sector / Industry National Standard (Recommended)
Classification of Chinese Standard Q23
Classification of International Standard 83.120
Word Count Estimation 15,144
Date of Issue 2021-12-31
Date of Implementation 2022-07-01
Older Standard (superseded by this standard) GB/T 1456-2005
Quoted Standard GB/T 1446; GB/T 3356-2014; GB/T 3961
Drafting Organization Shanghai FRP Research Institute Co., Ltd.
Administrative Organization National Fiber Reinforced Plastics Standardization Technical Committee
Regulation (derived from) National Standard Announcement No. 17 of 2021
Proposing organization China Building Materials Federation
Issuing agency(ies) State Administration for Market Regulation, National Standardization Administration
Summary This standard specifies the test principles, test equipment, samples, test conditions and sample state adjustment, test procedures, test results and processing and test reports for the bending properties of sandwich structures. This standard applies to the determination of the apparent flexural strength and apparent flexural modulus of the sandwich structure when subjected to bending, the flexural stiffness and shear stiffness of the sandwich structure, the stress and modulus of elasticity of the sandwich structure panel, the shear stress and elastic modulus of the sandwich structure core. The shear modulus is also suitable for determining the strength of the flexural bond between the panel and the core of a sandwich structure.

Standards related to: GB/T 1456-2021

GB/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):
...