1 Scope
This document specifies a method for the determination of the dimensions and aspect ratio of carbon fibre reinforced plastic (CFRP) fractions, mainly for recycled CFRP. this document treats the shape of CFRP fractions as rectangular and specifies the method for the determination of length and width. This document applies to the following average sizes of fragments:
Length: 5 mm to 50 mm;
Width: 1 mm to 10 mm.
This document provides three measurement methods, two manual test methods using a microscope and a scale and a third automatic test method using a measuring instrument.
This document applies to CFRP pulverised materials made from thermosetting or thermoplastic resins as a substrate.
Note: If the CFRP comminuted material contains a large number of small fragments and fine particles, it is recommended that a sieve with an aperture of 1 mm be sieved out prior to the measurement.
2 Normative references
The contents of the following documents form an integral part of this document by means of the normative text. Where a reference document is dated, only the version corresponding to that date applies to this document; where a reference document is not dated, the latest version (including all amendment sheets) applies to this document.
ISO 472 Plastics-Vocabulary
Note: GB/T 2035-2008 Plastics terms and their definitions (ISO 472:1999, IDT)
3 Terminology and definitions
The terms and definitions defined by ISO 472 apply to this document.
4 Symbols
The following symbols apply to this document.
5 Principle
The fragments obtained from crushed CFRP laminates are sampled uniformly and measured.
The shape of the CFRP fragment is approximated as a rectangle and the length and width of the rectangle are measured by looking at each fragment through an optical microscope or equivalent device.
A minimum of 100 pieces need to be measured. The dimensions and aspect ratios of the CFRP fragments are recorded and used to calculate the mean and standard deviation of W and L and the mean of the aspect ratio R.
6 Instruments
6.1 Stereo microscope, including light source, scale and glass table with CFRP fragments. Magnification should be 10x and scale readings should be accurate to 0.1 mm.(Method A)
6.2 Projection microscope, including projector, light source, scale and stage for showing slides of CFRP fragments. Magnification should be 10x and scale readings should be accurate to 0.1 mm.(Method B)
Note: A computer connected to a projection microscope and software to measure the length and width of the fragments makes the measurement method (Method B) quicker and simpler.
6.3 Automatic size and shape measuring devices, such as image analysers with magnification, are able to measure the length and width of CFRP fragments semi-automatically. (Method C)
6.4 Calibration scales or scales for calibrating scales on microscopes and projection equipment.
7 Sampling
Unless otherwise specified, the following sampling procedure should be followed.
7.1 Take a sample from a pile of CFRP pulverised material and place it in a bag with a volume of 20 L to 50 L.
Warning - CFRP pulverised material should be sampled with care. Unprotected hands can easily cause minor irritation/injury due to broken flakes of CFRP when taking samples and protective gloves made of impermeable material should be used.
7.2 Three specimens should be taken from the bag. Avoid taking samples from approximately 20% of the volume of the bag to the outside and take 3 samples evenly from the top, middle and bottom of the bag to the inside.
Note: The size or shape distribution of the CFRP fragments may not be the same at different locations within the bag due to sampling or transport.
7.3 The 3 specimens are mixed well before measurement and a minimum of 100 pieces should be measured.
8 Measurement
8.1 General rules
The shape of each fragment can be approximated as a rectangle, as shown in Figure 1. The rectangular shape is chosen in such a way that the W-value is minimised.
8.3 Method B: Projection microscopy
8.3.1 Place a number of fragments on the carrier table and separate them to avoid contact and overlap. 8.3.2 Set up the microscope with the glass table plate connected to the computer.
8.3.3 Use the calibration scale to calibrate the measuring scale of the computer.
8.3.4 The magnification of the microscope is adjusted appropriately for the average size of the fragments.
8.3.5 The observed fragments are projected on the monitor and the length L and width W of the fragments are measured to an accuracy of 0.1 mm.
8.3.6 The measurement is repeated for a minimum of 100 fragments.
8.4 Method C: Automatic shape and size measuring device
8.4.1 A number of fragments are placed on the device's carrier table and separated to avoid contact and overlap.
8.4.2 The observed fragments are projected on the display.
8.4.3 All CFRP fragments are approximated as rectangles, as shown by the construction lines in Figure 3. The length L and width W of each fragment were measured to an accuracy of 0.1 mm and recorded automatically.
8.4.4 The measurement was repeated for at least 100 pieces.
8.2 Method A: Manual method (stereo microscope)
8.2.1 Each fragment was placed on the stage plate of the stereomicroscope and the magnification of the microscope was adjusted appropriately for the average size of the fragment.
Figure 2a) and Figure 2b) show examples of unidirectional fibres on the microscope stage plate (y-like CFRP and fabric-like CFRP, respectively.
8.2.2 Calibrate the scale with a calibrated scale or graduated scale.
8.2.3 Make the long side of the fragment parallel to the scale.
8.2.4 Measure the length of the long side of the fragment as length I; the length of the hungry side as width W. The length and width are measured to an accuracy of 0.l mm.
8.2.5 Repeat the measurement for at least 100 fragments.
9 Calculation and presentation of results
10 Precision
Table 1 gives repeatability data for the three materials tested in the same laboratory with four samples selected from each pile of CFRP crushed material. The test result for each sample is the average of 100 individual values measured using Method B.
11 Test report
The test report shall include the following:
a) the number of this document, GB/T 41709-2022
b) The method used;
c) all necessary details of the CFRP crushed material measured;
d) The mean value of the width w and its standard deviation o(W);
e) Mean value of the length Ⅰ and its standard deviation o(L);
f) the mean value of the aspect ratio RA.
1 Scope
2 Normative references
3 Terminology and definitions
4 Symbols
5 Principle
6 Instruments
7 Sampling
8 Measurement
9 Calculation and presentation of results
10 Precision
11 Test report
