1、AEROSPACERECOMMENDEDPRACTICEDRYING OF THERMOSETTING COMPOSITE MATERIALSIssued 1996-08ARP4977 TABLE OF CONTENTS1. SCOPE. 31.1 Purpose 32. REFERENCES. 32.1 Applicable Documents 32.1.1 SAE Publications 32.2 Applicable References . 33. GENERAL 33.1 Visible Liquid 43.1.1 General. 43.1.2 Detection 53.1.3
2、Removal Methods 53.1.4 Drying Time 53.1.5 Control Methods. 53.2 Absorbed Moisture . 63.2.1 General. 63.2.2 Detection 93.2.3 Removal Methods 93.2.4 Drying Temperature . 93.2.5 Drying Time 93.2.6 Control Method. 104. DRYING METHODS 104.1 Visible Liquid Removal . 10Reaffirmed 2011-11RATIONALEThis docum
3、ent has been reaffirmed to comply with the SAE 5-year Review policy. SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for
4、any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions.Copyr
5、ight 2011 SAE International All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT OR
6、DER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-4970 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/ARP4977SAE ARP49
7、77- 2 -TABLE OF CONTENTS (CONTINUED)4.1.1 Visible Liquid Removal - Method 1 (Water) 104.1.2 Visible Liquid Removal - Method 2 (Liquid Other Than Water) 114.2 Absorbed Moisture Removal 114.2.1 Absorbed Moisture Removal - Method 1 (Vacuum Bag and Heating Blanket) 114.2.2 Absorbed Moisture Removal - Me
8、thod 2 (Radiant Heater) 144.2.3 Absorbed Moisture Removal - Method 3 (Hot Air Dryer) 154.2.4 Absorbed Moisture Removal - Method 4 (Portable Oven) 184.2.5 Absorbed Moisture Removal - Method 5 (Oven) 20SAE ARP4977- 3 -1. SCOPE:This SAE Aerospace Recommended Practice (ARP) describes standard methods fo
9、r dryingcommercial aircraft composite structures prior to repair and gives general guidelines on use andapplicability.It addresses the removal of liquids that have collected inside the structures through open damage,microcracks, or porosity and the removal of absorbed moisture from the composite mat
10、erial. Themethods described in this document shall only be used when specified in an approved repairdocument or with the agreement of the original equipment manufacturer (OEM) or regulatoryauthority. If this document is used for the drying of materials other than thermosetting compositematerials, th
11、e fitness for this purpose must be determined by the user.1.1 Purpose:The purpose of this document is to provide a set of standard drying methods that may bereferenced in repair documents produced by airlines or airframe and engine manufacturers. It isintended that this document be one of a number o
12、f ARPs that will cover other aspects of thetechniques required to perform composite repairs. This will provide a suite of available repairtechniques that are acceptable for use throughout the commercial aircraft industry.2. REFERENCES:2.1 Applicable Documents:The following publications form a part o
13、f this document to the extent specified herein. The latestissue of SAE publications shall apply. The applicable issue of other publications shall be the issuein effect on the date of the purchase order. In the event of conflict between the text of thisdocument and references cited herein, the text o
14、f this document takes precedence. Nothing in thisdocument, however, supersedes applicable laws and regulations unless a specific exemption hasbeen obtained.2.1.1 SAE Publications: Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.AIR4844 Composites and Metal Bonding GlossaryARP49
15、16 Masking and Cleaning of Epoxy and Polyester Matrix ThermosettingComposite MaterialsARP5143 DRAFT Bagging Procedures for the Local Repair of Thermosetting CompositeMaterialsARP5144 DRAFT Heat Application for the Local Repair of Thermosetting Composite Materials2.2 Applicable References:Original Eq
16、uipment Manufacturers (OEM) Manuals3. GENERAL:In this document reference is made to visible liquids and absorbed moisture.Visible Liquids: Visible liquids are split into two categories.SAE ARP4977- 4 -3. (Continued):Liquids that dry in open air or under heat, leaving no residue or residue that can b
17、e easily wiped awayand cleaned using the standard methods described in ARP4916. Water and solvents are the mostcommonly found types.Liquids that do not dry with standard methods but leave a residue or some remaining liquid thatstandard cleaning methods will not remove. The most common types are skyd
18、rol, jet fuel, and toiletservicing fluid (blue water).Either category of liquid may result in a degradation of the composite structure.Absorbed Moisture: Composite structures tend to saturate with moisture. The moisture level, if toohigh, could be detrimental to the quality of a bonded repair. Dryin
19、g should be performed in areas thatwill be in contact with the repair bondline, including repair parts and materials (honeycombreplacement pieces may be dried prior to using when absorbed moisture is a concern).Some types of composites can also absorb solvents used in solvent cleaning (Aramid reinfo
20、rcedlaminates and honeycomb absorb more solvent). The method of absorbed moisture removal (refer to4.2) may also be used to ensure that solvent has completely evaporated in a shorter time. Bondingprior to complete solvent evaporation can cause low bond strength.Drying a composite structure will in g
21、eneral consist of:a. Removing visible liquids.b. Cleaning (when liquid is other than water) and removing any permanently contaminated area.c. Drying to obtain a visually dry structure before proceeding with the repair area preparation.d. Performing the final drying before bonding.3.1 Visible Liquid:
22、3.1.1 General: Liquid can collect on structures or inside through existing openings or damaged areas. It can generally be removed by mopping, vacuuming, or by blowing with compressed air (when itis water).Liquid can also be found inside sandwich panels as the result of skin damage, delamination,debo
23、nding, skin microcracks, skin porosity, or a combination of these cases.Visible liquid in honeycomb panels can cause damage due to freezing (water), to galvaniccorrosion of aluminum honeycomb, or to a possible reduction of the structural strengthcharacteristics if left for a long period of time. The
24、re is also a risk of having steam pressure buildup during a hot bond repair causing delamination or debonding.Unlike water, other fluids may deteriorate not only the honeycomb and honeycomb/skin bond line,but also the skins. Degradation should be suspected when the substrate shows discoloration.SAE
25、ARP4977- 5 -3.1.1 (Continued):Removal of liquid from honeycomb panels will usually require the cutting of one skin to obtainaccess. Contaminated areas that cannot be cleaned (refer to ARP4916) will also have to be cutaway.When the honeycomb or honeycomb/skin bond line is suspected to be degraded the
26、 honeycombshould be replaced. Replacement may be considered in all cases to speed up the repair process.Before proceeding with the repair area preparation the structure must be clean and visually dry.3.1.2 Detection: Liquid can be detected visually on or inside structures and in open damage.The pres
27、ence of liquid inside honeycomb panels must be suspected when debonding is found orwhen the surface is in a poor condition (paint deterioration and/or erosion) or shows signs ofporosity. A discoloration of the composite is usually the indication of a contamination.Nondestructive Testing Inspection (
28、NDI) methods such as thermography, ultrasonic checks, orX-rays can confirm the presence of trapped liquid. On glass or aramid structures, moisture meterscan also be used.OEMs Nondestructive Testing Manuals (NTM) must be consulted for details of the variousmethods and their applicability.3.1.3 Remova
29、l Methods: Depending on the type of fluid and on the location and time available, variousmethods may be used.Mopping, vacuuming, blowing compressed air, and vacuum bagging the affected area arepossible methods for water removal (refer to 4.1 for details of the various methods). Mopping andvacuuming
30、are also commonly used for the removal of liquids other than water. A thoroughcleaning should follow (refer to ARP4916). Should cleaning prove unsuccessful, the contaminatedarea shall be removed.3.1.4 Drying Time: The criteria are to have a clean and visually dry structure. The time required willdep
31、end on the method used.3.1.5 Control Methods: A visual check will generally show if all the liquid has been removed. Onhoneycomb panels, standard nondestructive methods can be used to confirm removal (refer to3.1.2). If in doubt, additional cells can be cut open. With liquids other than water, once
32、the area isvisually clean, local heating (not exceeding 176 F (80 C) could help reveal more absorbed fluiddue to the tendency of fluid to seep to the skin surface during heating. A water break test (refer toARP4916 - Water Break Test Method) will confirm the cleanliness of the structure.SAE ARP4977-
33、 6 -3.2 Absorbed Moisture:3.2.1 General: Composites, as a result of their chemical structure, will absorb moisture when in contactwith humid air. The absorption can reach a maximum value (saturation) that depends on the resinsystem and fiber reinforcement used (carbon, aramid, or glass), on the temp
34、erature and on thehumidity of the surrounding air. Saturation values can range from 1 to 3% by weight). Nonmetallichoneycomb will generally reach saturation at a higher value (up to 5% for Nomex honeycomb).This moisture saturation combined with a hot environment (hot/wet condition) is one of the mos
35、tadverse condition met by a structure. It is taken into account at the aircraft design stage and in thetesting of the main components.The effect of moisture during a repair will depend mainly on the curing time and temperature andto a lesser extent on the repair and parent materials. The strength ch
36、aracteristics of the bond lineand the repair patch quality could be affected.Experience has shown that, for repair purposes, complete drying of a composite structure is notnecessary. A dry surface will in general be sufficient provided it remains dry for the complete curecycle. Moisture migration ba
37、ck to the surface during the cure cycle should be taken into accountto determine the drying time and temperature. One way of ensuring a dry surface is to carry out afinal drying cycle (after the laminate appears dry) at the temperature of the cure for the time of thecure (refer in all cases to OEMs
38、recommendations).Because only the surface of the laminate will be dried, the drying must take place after allstepping, scarfing, or other material removal steps have been completed.The repair should be accomplished as soon as possible after drying because the moisture in thelaminate will return to t
39、he surface at room temperature over a period of time.Figures 1 and 2 are given to illustrate the length of time typical laminates take to absorb moistureand the time to completely remove all absorbed moisture. These figures are given for informationand education only and should not be used to determ
40、ine drying cycle time and temperature. Theslow migration of moisture explains why surface drying is used and shows the importance ofdrying after material removal.Figure 1 shows the average moisture content plotted against drying time of a composite laminatefirst saturated with moisture and then drie
41、d. The curves represent laminates of differentthicknesses. Graphs for two different drying temperatures are shown.Figure 2 shows a graphical representation of the percentage saturation across a laminatethickness at different time.Figure 2B represents the values for a skin initially dry and exposed t
42、o humid atmosphere from oneside.Figure 2C represents the values for a skin initially saturated and then dried.SAE ARP4977- 7 -TYPICAL DRYING CURVE: CARBON EPOXY MONOLITHIC LAMINATE70 C (158 F) Drying TemperatureTYPICAL DRYING CURVE: CARBON EPOXY MONOLITHIC LAMINATE90 C (194 F) Drying TemperatureFIGU
43、RE 1 - Moisture Content of Typical Laminates(Average Moisture Through the Thickness)SAE ARP4977- 8 -FIGURE 2 - Graphical Representation of the MoistureContent Across a Composite Skin (Fick Law)SAE ARP4977- 9 -3.2.1 (Continued):Absorption and desorption time are affected by the composite skin thickne
44、ss, material type,temperature, and relative humidity.3.2.1.1 Low Temperature Repairs (Temperature 212 F(100 C): A high moisture level will generallyaffect the repair lay-up bond to the structure and the repair patch quality. Additionally there is ahigh risk of debonding/delamination in areas outside
45、 the repair area if the whole part is to beheated.When performing a high temperature repair it is necessary to have a dry structure.The moisture content of the structure is generally unknown and could be suitable for hightemperature repairs without any further drying. Nevertheless, when water is sus
46、pected to havebeen inside the structure for a long period of time, it is essential to perform a final drying beforebonding. Dry the part after the repair area preparation on a visually dry structure.3.2.2 Detection: Although equipment exist that can detect the presence of moisture, there is nopracti
47、cal method to quantify the moisture content of a structure.3.2.3 Removal Methods: The method will depend on the repair conditions and size of damage (refer toSection 4 for details of the various methods).3.2.4 Drying Temperature: Recommendations of the part manufacturer should be followed. However,c
48、ommon practice is to heat the structure between 140 F (60 C) and 180 F (82 C) with a rate oftemperature rise of approximately 5 F (3 C) per minute.3.2.5 Drying Time: Recommendations of the part manufacturer should be followed.NOTE: After all evidence of visible moisture has been removed, a safe appr
49、oach would be toheat the part at the repair cure temperature and for the time of the cure. This wouldrequire special care and should be performed using the same repair conditions (thesame jig, tool, heat application methods, vacuum bag, etc.) to avoid possible distortion. Heat rise should also be controlled to avoid local debonding/delamination due to trappedmoisture/water.SAE ARP4977- 10 -3.2.5.1 Low Temperature Repairs: Common practice is to heat the structure for a minimum of 1 h, toremove residual moisture and to create a dry surface l
