1、_ 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 any particular use, including any patent infringement arising there
2、from, 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. Copyright 2014 SAE International All rights reserved. No part of this p
3、ublication 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 ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-497
4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/ARP4991A AEROSPACE RECOMMENDED PRACTICEARP4991 REV. A Issued 1998-12 Revised 2007
5、-02 Reaffirmed 2014-02 Superseding ARP4991 Core Restoration of Thermosetting Composite Components RATIONALE ARP4991A has been reaffirmed to comply with the SAE five-year review policy. TABLE OF CONTENTS 1. SCOPE 3 1.1 Purpose. 3 2. APPLICABLE DOCUMENTS 3 2.1 SAE Publications. 3 2.2 Applicable Refere
6、nces 3 3. GENERAL . 4 4. MATERIALS 4 4.1 Repair Materials 4 4.2 Associated Materials. 4 5. CORE RESTORATION. 4 5.1 Core Filling With Resin . 4 5.1.1 Applicability . 4 5.1.2 Materials 5 5.1.3 Core Filling With Resin Method (Figure 2) 5 5.2 Core Restoration With Potting Compound 7 5.2.1 Applicability
7、. 7 5.2.2 Materials 7 5.2.3 Potting Application 7 5.2.4 Core Restoration With Potting - Methods . 8 5.3 Core Restoration With Honeycomb 12 5.3.1 Applicability . 12 5.3.2 Materials 12 5.3.3 Core Plug Preparation Method: Procedure 13 5.3.4 Thick Core Plug Preparation Method (Figure 7). 14 5.3.5 Full D
8、epth Core Restoration With Honeycomb - Method 1 (Figure 8) 16 5.3.6 Full Depth Core Restoration With Honeycomb - Method 2 (Figure 9) 17 5.3.7 Partial Depth Core Restoration With Honeycomb - Method 1 (Figure 10) . 18 5.3.8 Partial Depth Core Restoration With Honeycomb - Method 2 (Figure 11) . 20 6. C
9、ORE CLOSING. 21 6.1 Core Closing With Adhesive Paste. 22 6.1.1 Applicability . 22 6.1.2 Materials 22 6.1.3 Core Closing With Adhesive Paste Method 1 (Figure 12) 22 7.NOTES 23FIGURE 1 - SANDWICH STRUCTURES DAMAGE TYPES . 5FIGURE 2 - RESTORATION WITH RESIN METHOD . 6FIGURE 3 - CORE RESTORATION WITH PO
10、TTING - METHOD 1 PARTIAL DAMAGE REMOVAL 9FIGURE 4 - CORE RESTORATION WITH POTTING - METHOD 2 FULL DAMAGE REMOVAL 11FIGURE 5 - CORE RESTORATION WITH HONEYCOMB 12FIGURE 6 - LOADS ON A CORE PLUG 13FIGURE 7 - THICK CORE PLUG PREPARATION METHOD . 15FIGURE 8 - FULL DEPTH CORE RESTORATION WITH HONEYCOMB -
11、METHOD 1. 17FIGURE 9 - FULL DEPTH CORE RESTORATION WITH HONEYCOMB - METHOD 2. 18FIGURE 10 - PARTIAL DEPTH CORE RESTORATION WITH HONEYCOMB - METHOD 1 19FIGURE 11 - PARTIAL DEPTH CORE RESISTANCE WITH HONEYCOMB - METHOD 2 . 21FIGURE 12 - C ORE CLOSING WITH ADHESIVE PASTE - METHOD 1 . 23SAE INTERNATIONA
12、L ARP4991A Page 2 of 23_1. SCOPE This SAE Aerospace Recommended Practice (ARP) describes standard methods for restoring damaged core on commercial aircraft sandwich structures. The methods shall only be used when specified in an approved repair procedure or with the agreement of the Original Equipme
13、nt Manufacturer (OEM) or regulatory authority. The repair materials shall be defined in the approved repairs referencing these methods. 1.1 Purpose The purpose of this document is to provide a set of standard methods that may be referenced in repair documents produced by airlines or airframe and eng
14、ine manufacturers. It is intended that this document be one of a number of ARPs that will cover other aspects of the techniques required to perform composite repairs. This will provide a suite of available repair techniques that are acceptable for use throughout the commercial aircraft industry. 2.
15、APPLICABLE DOCUMENTS The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between t
16、he text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1 SAE Publications Available from SAE International, 400 Commonwealth Drive
17、, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org.AIR4844 Composite and Metal Bond Glossary ARP4916 Masking and Cleaning of Epoxy and Polyester Matrix Thermosetting Composite Materials ARP4977 Drying of Thermosetting Composite Materials
18、 ARP5143 Vacuum Bagging of Thermosetting Composite Repairs ARP5144 Heat Application for Thermosetting Resins Curing ARP5256 Mixing Resins, Adhesives and Potting Compounds ARP5319 Ply Impregnation AIR5367 Machining of Epoxy and Polyester Matrix Thermosetting Composite Structures 2.2 Applicable Refere
19、nces Original Equipment Manufacturers (OEM) Repair Manuals SAE INTERNATIONAL ARP4991A Page 3 of 23_3. GENERAL Sandwich structures can suffer various types of damage (Figure 1): a. Disbonding of the skins with or without core damage. b. Damage to one or both skins. The core is generally also damaged.
20、 c. Contamination by water, hydraulic fluid, oil, etc. d. Delamination of the plies within the skin. This is often associated with other damage at an impact site. As one of the elements in restoring the structural integrity of the part, the load carrying capability of the core will, in general, have
21、 to be restored either by stiffening the core or replacing it. This document addresses the various techniques found in repair manuals. Only a selection of those commonly used are proposed as methods. These methods are given a name and number to allow further development of the document and to facili
22、tate referencing. In this document, it is assumed that the damaged area has been cleaned, dried and that the damage has been evaluated, the repair area prepared and one skin has been repaired or is undamaged. 4. MATERIALS 4.1 Repair Materials In addition to repair design considerations, material sel
23、ection is often influenced by the repair conditions (aircraft or shop repair), and by the part orientation. Exothermic effects (heat generated by resin curing) should be also considered, especially when potting is used. The approved repair procedure shall specify which materials to use. The type of
24、material that may be used will be discussed in the following paragraphs or sections with each technique. 4.2 Associated Materials In addition to the repair materials, various other materials are needed such as cleaning agents, bagging materials, etc. Information on these materials may, in general, b
25、e found in associated ARPs or manufacturers documentation. 5. CORE RESTORATION 5.1 Core Filling With Resin When using this method, consideration should be given to the skin strength reduction due to the holes. 5.1.1 Applicability This method applies to small damage when skins are not punctured. The
26、skins can be disbonded from the core or dented with possible degradation of the honeycomb underneath. To be effective this process should only be applied to a part with an uncontaminated core. CAUTION: When the core is thicker than 0.5 in (12.5 mm), it is preferable not to fill the core completely a
27、s exothermic effects can damage the part or cause a fire. Complete filling of the cells also cause distortion of the opposite skin due to the shrinkage of the resin during cure. SAE INTERNATIONAL ARP4991A Page 4 of 23_FIGURE 1 - SANDWICH STRUCTURES DAMAGE TYPES 5.1.2 Materials Low viscosity resins o
28、r adhesives for injection with a syringe and preferably with a fast cure time and a low cure temperature should be used. 5.1.3 Core Filling With Resin Method (Figure 2) Procedure:a. Refer to the repair instructions for the following information: 1. The type of resin to use. 2. Cure time and temperat
29、ure. b. Drill (without lubrication) 0.1 in (2.5 mm) diameter holes 0.4 in (10 mm) apart in the damage area. Drill a minimum of two holes. Use a vacuum cleaner to remove dust while you drill the holes. SAE INTERNATIONAL ARP4991A Page 5 of 23_FIGURE 2 - RESTORATION WITH RESIN METHOD c. Remove any rema
30、ining dust. d. Look for liquid contamination. (Refer to ARP4977) If contamination is found, the part is not repairable by this method. e. Calculate the amount of resin that will be needed to fill the core to the depth specified. Prepare the resin in accordance with ARP5256 or OEM Repair Instruction.
31、 CAUTION: When using air or mechanically operated syringes, avoid applying too much pressure as it can damage the honeycomb cells. f. Fill a clean syringe with the resin. CAUTION: Depending on the design used, when the part cannot be turned over, the core should be filled and cured in steps if thick
32、er than 0.5 in. This is recommended to avoid exothermic effects and possible damage to the part. g. Through each hole insert the syringe at an angle to reach the surrounding cells and fill them to an approximate height of 0.3 to 0.5 in (7 to 12.5 mm). If the part cannot be turned so that the repair
33、surface is down, fill the honeycomb cells fully.h. Put an adhesive tape that can be readily released over the holes and, if possible turn the component so that the repair surface faces down. SAE INTERNATIONAL ARP4991A Page 6 of 23_i. Let the resin cure. j. Remove the tape. Make sure that the holes a
34、re sealed with resin. If any holes are not sealed, repeat the procedure for the unfilled holes. 5.2 Core Restoration With Potting Compound When core restoration with potting is requested in a repair directive it should be specified as a core restoration method (see 5.2.4) combined to a potting appli
35、cation method (see 5.2.3). 5.2.1 Applicability Core restoration with potting generally applies to relatively small damage when one skin only is punctured. Potting quantity may be limited for weight reasons or to avoid damage due to exothermic effects and partial core filling might be required. As a
36、general rule, potting thickness should not exceed 0.5 in (12.5 mm). 5.2.2 Materials Different potting materials may be used for this application. a. Resin or adhesive filled with an additive to obtain a thick paste (refer to ARP5256). b. Ready to use potting compound. 5.2.3 Potting Application The r
37、emaining honeycomb in the area to be potted may be filled partially or completely (Potting application Method 1 and Method 2 respectively). When no honeycomb remains, the cavity has to be completely filled (Potting application Method 3). 5.2.3.1 Potting Application - Method 1 - Complete Honeycomb Co
38、re Filling A spatula or a pressure gun can be used. a. Method with a spatula: 1. Apply part of the potting in the core cavity. 2. Force the potting inside each cell by moving the spatula over the honeycomb in different directions. 3. Add more potting and force it into the honeycomb until no more pot
39、ting can be pushed into the cells. 4. Fill the remaining core cavity and make the surface smooth and above the surface contour of the surrounding area to take into account resin shrinkage. CAUTION: Take care when applying pressure to the potting in the cells. Damage can occur. SAE INTERNATIONAL ARP4
40、991A Page 7 of 23_b. Method with a pressure gun: Use a hand or air operated pressure gun with a nozzle that can go into the honeycomb cells without damaging them. 1. Fill each cell of the honeycomb from bottom to top by inserting the nozzle into the cell. 2. Fill the remaining core cavity. 3. With a
41、 spatula remove excess potting to make the surface smooth and above the surface contour of the surrounding area to take into account resin shrinkage 5.2.3.2 Potting Application - Method 2 - Partial Honeycomb Core Filling a. With a spatula apply a layer of potting approximately 0.16 in (4 mm) to 0.25
42、 in (6 mm) thick over the open cells of the honeycomb trying not to force too much potting into the cells. b. When the thickness appears even, then force the potting into the cells with the spatula. c. Without applying too much pressure, fill the remaining core cavity and make the surface smooth and
43、 above the surface contour of the surrounding area to take into account resin shrinkage 5.2.3.3 Potting Application - Method 3 - Core Cavity Filling It is assumed that the core has been removed completely in the damage area and the bottom skin abraded. a. Using a spatula or a pressure gun, fill the
44、cavity from bottom to top. Make sure that the potting makes intimate contact with the surrounding core, and bottom skin. b. With a spatula remove excess potting to make the surface smooth and above the surface contour of the surrounding area to take into account resin shrinkage 5.2.4 Core Restoratio
45、n With Potting - Methods 5.2.4.1 Core Restoration With Potting - Method 1 - Partial Damage Removal: Procedure (refer to Figure 3) a. Refer to the repair instruction for the following information: 1. The potting application method to use (see 5.2.3). - Method 1: Complete Honeycomb Core Filling - Meth
46、od 2: Partial Honeycomb Core Filling 2. The type of potting or resin mixture to use. 3. Cure time and temperature. b. Remove loose fibers and honeycomb as follows: 1. Use a sharp knife and tweezers to remove loose skin and honeycomb material. 2. Cut off pieces of honeycomb that are folded over the e
47、nd of the cells. This is to allow potting to go into the cells. SAE INTERNATIONAL ARP4991A Page 8 of 23_FIGURE 3 - CORE RESTORATION WITH POTTING - METHOD 1 PARTIAL DAMAGE REMOVAL c. Clean the repair area. Refer to ARP4916 Composite Cleaning Method 4 or 5 and Honeycomb Cleaning Method 3. d. Dry the repair area. Refer to ARP4977 Absorbed Moisture Removal - Method 1, 2, 3, 4,
