GB/T 26749-2022Carbon fibre—Determination of tensile properties of resin-impregnated yarn (English PDF)

1 Scope

This document specifies the determination methods for the tensile strength, tensile elastic modulus and tensile strain of carbon fiber - resin-impregnated yarn.

This document is applicable to carbon fiber yarn.

2 Normative References

The contents of the following documents constitute indispensable clauses of this document through the normative references in the text. In terms of references with a specified date, only versions with a specified date are applicable to this document. In terms of references without a specified date, the latest version (including all the modifications) is applicable to this document.

GB/T 1040.1 Plastics - Determination of Tensile Properties - Part 1: General Principles

GB/T 7690.1 Reinforcements - Test Method for Yarns - Part 1: Determination of Linear Density

GB/T 29761 Carbon Fiber - Determination of Sizing Content

GB/T 30019 Carbon Fiber - Determination of Density

GB/T 40724 Terminology for Carbon Fiber and Carbon Fiber Composites

3 Terms and Definitions

The terms and definitions defined in GB/T 1040.1 and GB/T 40724 are applicable to this document.

4 Symbols

The following symbols are applicable to this document. Af: cross-sectional area of yarn, expressed in (mm2). Ef: tensile elastic modulus, expressed in (GPa). Ff: maximum tensile load, expressed in (N). L0: extensometer gauge length, expressed in (mm). Ttf: linear density of yarn, expressed in (tex). Tti: linear density of resin-impregnated yarn, expressed in (tex). sigmaf: tensile strength, expressed in (MPa). rhof: yarn density, expressed in (g/cm3). epsilonC: tensile strain at maximum load obtained through calculation. epsilonE: tensile strain at maximum load measured by extensometer.

DeltaF: load change value corresponding to the deformation DeltaL of the specimen between gauge lengths, expressed in (N).

DeltaL: deformation of the specimen between gauge lengths corresponding to the load change DeltaF, expressed in (mm).

5 Principle

After the yarn is uniformly impregnated in resin and cured, under the uniform loading of an appropriate mechanical device, it is stretched to break. In accordance with the tensile stress - strain curve, calculate the tensile strength, tensile elastic modulus and tensile strain at maximum load.

The tensile elastic modulus is the ratio of the change in stress to the corresponding change in strain. The stress - strain relation of carbon fiber yarn is nonlinear, so the secant modulus shall be defined. Usually it is defined by two strain points. The linear density and sizing agent content shall be separately measured.

6 Instruments, Equipment and Materials

7 Specimens

7.4 Determination of Linear Density and Density of the Same Roll of Yarn

7.4.1 The linear density of yarn shall be determined in accordance with GB/T 7690.1.

7.4.2 The content of yarn sizing agent shall be determined in accordance with GB/T 29761.

7.4.3 The carbon fiber density shall be determined in accordance with GB/T 30019.

10 Processing of Test Data

10.3.3 The tensile strain at maximum load calculated through the tensile strength and tensile elastic modulus is calculated in accordance with Formula (6):

Where, epsilonC---the tensile strain at maximum load obtained through calculation, expressed in (%); sigmaf---the tensile strength, expressed in (MPa); Ef---the tensile elastic modulus, expressed in (GPa) (see 10.2).

10.3.4 Take the arithmetic mean of the tensile strain at maximum load of all specimens as the reported value; if required by the product specification or the test entrusting party, calculate the standard deviation and coefficient of variation.

11 Test Report

The test report includes the following contents:

a) Serial No. of this document;

b) All necessary details about the yarns tested;

c) Linear density of yarn, and whether the sizing agent is removed;

d) Yarn density, and whether the sizing agent is removed;

e) Whether the tensile strain at maximum load is calculated or directly measured by the extensometer;

f) Number of specimens including the number of discarded;

g) Test speed;

h) Tensile strength, tensile elastic modulus and tensile strain at maximum load shall, if required, be provided as individual values;

i) Calculation method for tensile elastic modulus;

j) Any other details that may affect the test results. […]