GB/T 39491-2020General technical requirements of carbon fiber composites covering parts for automobiles (English PDF)

3.1 Covering Parts

Covering parts refer to panels covering the surface of the body frame.

NOTE: in accordance with functions and positions, covering parts can be divided into three categories: external covering parts, internal covering parts and skeleton covering parts.

3.2 Prepreg Compression Molding

Prepreg compression molding refers to a preparation technology of placing prepreg in a metal mold, and at a certain temperature, pressurizing and curing it into composite products.

3.3 Wet Compression Molding

Wet compression molding refers to a rapid preparation technology of laying the properly cut carbon fiber cloth on the surface of the mold and spraying it with resin, so that resin can infiltrate fibers, then, solidifying it into composite products after clamping, pressurizing and heating.

3.4 Carbon Fiber Sheet Molding Compound

Carbon fiber sheet molding compound refers to a type of molding compound made of resin paste impregnated with carbon fiber or chopped carbon fiber felt, and covered with polyethylene film on both sides.

5.1 Prepreg Compression Molding

The prepreg compression molding process shall comply with the following requirements:

a) In accordance with the design documents, lay up; the layups shall be symmetrical and balanced;

b) The starting point for laying fibers shall be reasonably selected;

c) When adopting the pre-forming process, the mold surface shall be reasonably selected in accordance with the appearance requirements;

d) When the thickness of the structure changes, the thickness transition area shall be reasonably designed; the layups shall be alternatively removed / added between successive layups; the external layups shall continuously cover the entire surface;

e) The deviation of the layup angle from the laying outline dimension line and the layup angle marking line shall not exceed ± 7°;

f) When carbon fiber parts are in direct contact with metal parts, in order to avoid electrochemical corrosion, an insulating layer can be set up on the surface, and its thickness shall be determined in accordance with the actual design requirements of the parts;

g) For parts that have rigorous requirements towards tolerances, and whose dimensional tolerances cannot be directly obtained through molding, allowances for machining shall be reserved.

5.2 Wet Compression Molding

The wet compression molding process shall comply with the following requirements:

a) In accordance with the design documents, lay up; the layups shall be symmetrical and balanced;

b) The layup angle and the number of layups shall satisfy the design requirements.

During the fabric laying process, wrinkling of the fabrics shall be avoided;

c) When the thickness of the structure changes, the layups shall be alternatively removed

/ added between successive layups; the external layups shall continuously cover the entire surface;

d) For splicing parallel to the fiber direction, butt joint shall be adopted; for splicing perpendicular to the fiber direction, lap joint shall be adopted; the fabrics shall not be butted;

e) The minimum fillet radius R generally depends on the laminate thickness t and the mold. It is recommended to use R >= Max (t/2, 3 mm);

f) The spraying, flowing and impregnating process of the resin shall be controlled in accordance with the pre-determined path, so as to ensure that the resin completely impregnates the fiber under pressure, and that no defects like lacking resin or excess resin appear. The resin shall be rapidly cured at a pre-determined temperature, and simultaneously, the phenomenon of implosion shall be avoided;

g) During the curing process, it shall be ensured that each area of the parts is uniformly heated with a temperature difference of not greater than 5 °C.

5.3 Carbon Fiber Sheet Molding Compound Compression Molding

The carbon fiber sheet molding compound compression molding process shall comply with the following requirements:

a) In accordance with the structure and shape of the parts, and the flowing properties of the materials, determine the cutting requirements. The materials are mostly cut into rectangles or circles. When multiple layers of materials are superimposed, they shall be stacked in the shape of a pagoda;

b) The materials shall be placed in the middle of the mold cavity. For asymmetric complex parts, the feeding position shall ensure that during molding, the material simultaneously reaches all ends of the mold cavity;

c) The molding temperature shall be selected as a trade-off between curing speed and optimal molding conditions;

d) The molding pressure shall be adjusted and controlled in accordance with the structure, shape, dimensions and material system of the parts. The optimal pressurization shall be carried out when approaching the resin gel temperature.

6.1 Appearance and Dimensions

6.1.1 Appearance

6.1.1.1 The appearance of the parts shall comply with the requirements of the standard templates or drawings.

6.1.1.2 The coating of painted parts shall comply with the requirements of QC/T 966.

6.1.1.3 The determination of appearance defects of the parts shall comply with the requirements of Appendix A.

7.2.1.2

The compressive properties shall be tested in accordance with GB/T 5258.

7.2.1.3

The in-plane shear properties shall be tested in accordance with GB/T 28889.

7.2.1.4

The fiber content shall be tested in accordance with GB/T 3365.

7.2.1.5

The porosity shall be tested in accordance with GB/T 3365.

7.2.1.6

The glass transition temperature shall be tested in accordance with GB/T 19466.2.

7.2.2 Properties of parts

7.2.2.1 The temperature resistance shall be tested in accordance with QC/T 15.

7.2.2.2 The weather resistance shall be tested in accordance with QC/T 17.

7.2.2.3 The chemical medium resistance shall be tested in accordance with QC/T 15.

7.2.2.4 The vibration resistance shall be tested in accordance with QC/T 15.

7.2.2.5 The impact resistance shall be tested in accordance with QC/T 15.

7.2.2.6 The scratch resistance shall be tested in accordance with QC/T 15.

7.2.2.7 The gravel impact resistance shall be tested in accordance with Appendix B.

7.2.2.8 The corrosion resistance shall be tested in accordance with GB/T 10125.

7.2.2.9 The requirements for prohibited substances shall be tested in accordance with GB/T

30512.

8.1 Type Inspection

8.1.1 Under one of the following circumstances, type inspection shall be performed:

a) during the appraisal of new parts;

b) when there are relatively significant changes in design, material and process;

c) at least once a year for normal production;

d) when there is a mass quality accident;

e) when the production has been suspended for more than one year and resumed, or when the production is transferred to another factory.

8.1.2 Specimens of type inspection shall be taken from products that have passed the exit- factory inspection. From parts with the same process, the same materials, and the same storage time, randomly take a number of parts that comply with the test requirements.

8.1.3 The items of type inspection are all items in Chapter 6.

8.1.4 If there is one disqualified item in the type inspection, then, it is allowed to double the sampling for the inspection of this item: if there are still parts with one disqualified item, then, they shall be determined as disqualified in the type inspection; if there are two disqualified items during the inspection process, then, they shall be determined as disqualified in the type inspection.

8.2 Exit-factory Inspection

8.2.1 Inspection items

The items of exit-factory inspection include appearance and dimensions.

8.2.2 Inspection schemes

8.2.2.1 Before exiting the factory, each part shall receive the visual inspection.

8.2.2.2 Take 500 parts continuously produced with the same raw materials, the same formula and the same production process, and qualified in appearance as one batch (if there are less than

500 parts, they shall still be counted as one batch). Randomly take 5 parts for the dimensional inspection. If there are less than 5 parts, inspect all of them.

8.2.3 Determination rules

When the appearance and dimensions comply with the requirements, the batch of parts shall be determined as qualified; otherwise, the batch of parts shall be determined as disqualified.

9.1 Marking

The marking of the parts shall specify the following contents: material name, enterprise identification, enterprise code, production date, left and right parts (if necessary), part No. and part name, etc. Alternatively, execute in accordance with the agreement of both parties to ensure that the requirements of traceability can be achieved.

9.2 Packaging

9.2.1 A protective film shall be attached to the surface of the parts. A special protective bag shall be used for packaging and transportation.

9.2.2 The packing box shall be accompanied by: indicated part model, quantity, packing date and certificate of conformity.

Appendix B (normative)

Test Method for Gravel Impact Resistance

WARNING---this test method may involve hazardous materials, operations and equipment. Before adopting them, the operating personnel shall be familiar with the safety and health related documents of this test method.

B.1 Overview

This test method is applicable to the testing and evaluation of the gravel impact resistance of the surface coatings. The purpose of this test is to reproduce the effect of gravels or other media striking the automobile’s exposed paint or coating surface, and obtain relevant test results. The test object is the test panel of the surface coating, which can also be extended to the parts.

B.2 Method Summary

The gravel impact testing machine throws standard road gravels onto the specimen by controlling the air pressure. The throwing device, located in front of the specimen, is composed of an inverted air nozzle with a bottom tee. The valve rod of the tee points upward and is located under the vibrating feeder. The gravels are poured into the vibrating feeder, and then, projected by the air flow to strike the specimen, which is usually kept perpendicular to the direction of the gravel impact. All tests are performed under controllable temperature conditions. After the impact of the gravels, use a tape to remove the loose paint fragments remaining on the specimen;

by counting the number and size of all damage points, and comparing them with the corresponding damage point rating benchmark, determine the degree of coating peeling.

B.3 Equipment and Materials

B.3.1 Gravel impact testing machine

B.3.1.1 Composition

The gravel impact testing machine is composed of pavement gravels, test specimen holder and gravel throwing device. The gravel throwing device is manufactured in accordance with the design requirements, as it is shown in Figure B.1.

B.3.3 Paint stripping tape

The tape can be used in accordance with the agreement of both parties. The width of the tape is

100 mm or 50 mm.

NOTE: the adhesive strength of the tape has a large effect on the degree of paint separation.

B.3.4 Temperature adjustment

The temperature of the gravel impact test shall be mutually agreed upon by both parties of the contract. The following methods shall be adopted for temperature adjustment:

a) Cold chamber method: the gravel impact testing machine and the specimens are tested in a cold chamber at the specified test temperature.

b) Cabinet freezer method: it is applicable to the test temperature of below 5.6 °C; the test panel can be frozen to the test temperature in a freezer set near the gravel impact testing machine, then, immediately transferred to the gravel impact testing machine at room temperature for testing.

c) Room temperature method: if there are no special requirements, the test is generally carried out indoors at 20 °C ~ 30 °C.

B.3.5 Transparent grid

An auxiliary tool for counting damage points of specimens, which is obtained by selecting a

101.6 mm x 101.6 mm square area on a transparent plastic sheet with the size of about 127 mm

x 127 mm x 3.2 mm, and drawing a line every 25.4 mm.

B.3.6 Damage point rating benchmark

Through the transparent grid, describe the size and shape of every damage point. The damage point rating benchmark is shown in Figure B.2.

Y---9C 1 impact mark; diameter: 3 mm ~ 6 mm

Z---3D 75 impact marks (75 ~ 99); diameter: > 6 mm

AA---4D 50 impact marks (50 ~ 74); diameter: > 6 mm

BB---5D 25 impact marks (25 ~ 49); diameter: > 6 mm

CC---6D 10 impact marks (10 ~ 24); diameter: > 6 mm

DD---7D 5 impact marks (5 ~ 9); diameter: > 6 mm

EE---9D 1 impact mark; diameter: > 6 mm

Figure B.2 -- Schematic Diagram of Damage Point Rating Benchmark

B.3.7 Specimens

There are 3 specimens. The size of the specimens is 101.6 mm x 304.8 mm. The specimen material, thickness and surface treatment shall be consistent and representative. For specimens of other sizes, they shall be determined by both parties of the contract.

B.4 Preparation and Process

B.4.1 Preparation

B.4.1.1 Before test, the temperature shall be adjusted in accordance with B.3.4. The specimens shall reach the test temperature at least 15 min before the test.

B.4.1.2 Fill the 0.473 L container with the sieved gravels. When there are multiple specimens, gravels not exceeding 4.73 L are merely allowed to be placed on the sieve.

B.4.1.3 Open the air valve; adjust the air pressure of the gravel impact testing machine to 483 kPa ± 21 kPa.

B.4.1.4 Set the feeding speed, so that the feeder sprays 0.473 L of gravels within 7 s ~ 10 s.

B.4.1.5 Both parties may agree to adopt other pressures.

B.4.2 Process

B.4.2.1 Open the specimen holder of the gravel impact testing machine; install the specimen;

clamp the specimen clamp.

B.4.2.2 Pour the gravels obtained in B.4.1.4 into the feeder; set the test time.

B.4.2.3 Tests can be performed through the mode of timed tests or manual tests. Timed test refers to the test that shuts down the machine after a preset time has passed; manual test requires the operator to shut down the machine within a specified time.

B.4.2.4 After the test is completed, remove the specimen from the specimen holder. Retrieve the gravels from the return container to facilitate the repeated use of the testing machine. If necessary, after the temperature of the specimen returns to room temperature, use a soft cloth to remove the condensed moisture.

B.4.2.5 Use the tape (B.3.3); use uniform pressure to apply one or multiple tapes side by side to cover the test area of the specimen; avoid the generation of air bubbles; straighten the tape to remove it.

B.4.2.6 In accordance with the steps of B.4.2.5, stick a new tape on the specimen again; in the opposite direction, straighten the tape to remove it.

B.4.2.7 Repeat the operations of B.4.2.5 ~ B.4.2.6, until all loose or damaged paint is removed.

B.4.2.8 Check the specimen. In accordance with the damage point rating benchmark in B.5, determine the degree of peeling of the specimen coating.

B.4.2.9 If both parties agree, other methods may also be used to handle the paint or coating of the specimen. Then, in accordance with the damage point rating benchmark in B.5, determine the degree of peeling of the specimen coating.

B.5 Damage Point Rating Benchmark

B.5.1 Evaluation method

B.5.1.1 In accordance with the following two methods, determine the degree of peeling of the upper coating of the specimen:

---accurate counting method: it requires the listing of the exact number of damage points of each size within the specified test area of the specimen, which shall be adopted where definite accuracy is required.

---visual comparison method: it conducts visual comparison using the test panel with the damage point rating benchmark shown in Figure B.2, which may be adopted when the accuracy of the accurate counting method is not required.

B.5.1.2 The evaluation area of the specimen shall be located in a square of 101.6 mm x 101.6 mm in the center of the specimen.

B.5.2 Rating system

B.5.2.1 Overview

The damage point rating system is composed of one or more numbers and letters, in which, the rating numbers 10 ~ 0 represent the number of damage points of each size, and the rating letters

A ~ D represent the size of the corresponding damage points.