1、9EAEROSPACERECOMMENDED PRACTICEARP1926Issued 1994-10Reaffirmed 2014-08Cure Monitor, Electrical MethodsRATIONALEARP1926 has been reaffirmed to comply with the SAE five-year review policy.FOREWORDThis SAE Aerospace Recommended Practice (ARP) is intended as a guide for thecollection of electrical prope
2、rties of resins during cure or thermal cyclingTABLE OF CONTENTS1. SCOPE 3 1.1 Systems Addressed1.2 Assumptions1.3 Correlation and Data Reduction 3 1.4 Field of Application1.5 Interpretation2. REFERENCES 4 2.1 Applicable Documents .43. PROCESSING EQUIPMENT AND PROCEDURES 5 3.1 General 5 3.2 Dielectri
3、c Instrumentation3.3 Computer Requirements 5 3.4 Dielectric Sensors3.4.1 General Construction3.4.2 Sensor Types 6 3.4.3 Data Reporting, Sensors 7 3.5 Selection and Use of Sensors3.5.1 Location 7 3.5.2 Protection from Shorts (Electrical) 7 SAE Technical Standards Board Rules provide that: “This repor
4、t is published by SAE to advance the state of technical and engineering sciences. The use of this report isentirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.“SAE reviews each t
5、echnical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments andsuggestions.Copyright 2014 SAE InternationalAll rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transm
6、itted, 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) SAE values your input. To provide feedbackTel: +1 724-776970 (outside USA) on this Techni
7、cal Report, please visitFax: 724-776-0790http:/www.sae.org/technical/standards/ARP1926Email: CustomerServicesae.org |_SAE WEB ADDRESS: http:/www.sae.orgSAE INTERNATIONAL ARP1926 Page 2 of 11TABLE OF CONTENTS (Continued)3.5.3 Leads 7 3.5.4 Testing 8 3.5.5 Disposable Sensors 8 3.5.6 Reusable Sensors3.
8、6 Connections and Cables 9 4. OPERATION 9 4.1 Setup 9 4.1.1 System Integrity4.2 Data Collection 9 4.2.1 Setup Data 9 4.2.2 Cure Data or Thermal Cycling 104.2.3 Material Data 104.3 Reporting 114.3.1 Format 115. DISCUSSION 11SAE INTERNATIONAL ARP1926 Page 3 of 111. SCOPE:This document describes a stan
9、dard method to collect and report dielectricdata for the purpose of monitoring or studying the cure of composites.1.1 Systems Addressed:Only systems commercially designed for dielectric cure monitoring areaddressed.1.2 Assumptions:I t i s assumed that the purpose for recording dielectric (and electr
10、ical)parameters is one of the following:a. Investigationb. Quality assurancec. Process controlA certain degree of computerization is required.1.3 Correlation and Data Reduction:The methods for correlation and data reduction are quite varied and out ofthe scope of this publication. The novice should
11、refer to Section 4 and thereferences listed in Section 2 as required.1.4 Field of Application:The monitoring of electrical properties during cure has been found useful forbonded joints and composite materials. Variations of this procedure havebeen used to evaluate the cure on a wide variety of produ
12、cts includingaircraft structure, printed circuit boards, automotive parts, and otherapplications where process monitoring can lead to greater knowledge of theprocess, cost savings, or product improvements.1.5 Interpretation:A detailed discussion of the interpretation of dielectric data and itsapplic
13、ation to the monitoring and control of cure is beyond the scope of thisdocument. In general, a dielectrometer makes admittance measurements of thecircuit that includes the dielectric sensor. If the geometry of the sensoris known, then the measured permittivity and loss factor of the material canbe c
14、alculated and correlated to a change in the chemical and mechanicalproperties of the resins. The papers listed in Section 2 provide readings onindustry studies.SAE INTERNATIONAL ARP1926 Page 4 of 112. REFERENCES:2.1 Applicable Documents:This section has a list of articles published by researchers us
15、ing anddeveloping dielectric cure monitoring techniques.2.1.1 Senturia, S.D., Shepphard, N.F., “Dielectric Analysis of Thermoset Cure,“Advances in Polymer Science, Vol. 80, Springer-Verlag, 19862.1.2 Ciriscioli, P.R., Springer, G.S., “Dielectric Cure Monitoring - A CriticalReview,“ 34th Internationa
16、l SAMPE Meeting, May 19892.1.3 Sanford, W.M., McCullough, R., “Modelling the Viscosity and DielectricBehavior During the Cure of Epoxy Matrix Composites,“ 34th InternationalSAMPE Meeting, May 19892.1.4 Michaeli, W., Burkhardt, G., “Dielectric Sensors for Low Cost CureControl,“ 34th International SAM
17、PE Meeting, May 19892.1.5 Yalof, S., “ETMA 1 above 1000 Hz.3.3 Computer Requirements:3.3.1 The dielectric system should be capable of being driven by a computercapable of automating the process of acquisition and reduction of data.This is especially important if the method of cure monitoring involve
18、s themonitoring of the relaxation time.3.3.2 Software available to conduct automatic cure monitoring once measurementintervals and cure monitoring parameters are chosen. There should besoftware available for sensor checks, i.e., testing routines.3.4 Dielectric Sensors:A dielectric sensor is a capaci
19、tor in which the monitored material acts asthe dielectric material. There are many sensors available from a variety ofsources. The sensors should be selected based on the user need fortemperature, pressure, distance of sensor from measuring device, potentialfor damage, space constraints, and so on.3
20、.4.1 General Construction: While the sensors vary significantly in size, shape,materials, and construction they all share some common features. The usershould become f amiliar with the sensor construction and the means by whichthe following are achieved:a. How the resin is caused to function as the
21、dielectric material.b. Protecting the sensor from short circuits.c. Wetting or contact of sensor.d. Connection to the measurement circuit.SAE INTERNATIONAL ARP1926 Page 6 of 113.4.1.1 Resin as the Dielectric: The sensor construction will typically havehighly conductive surfaces separated by an air g
22、ap. In order for thesensor to function properly, the resin must flow to the conductivesurface and fully fill the gap in between. The initial calibration ofthe sensor shall be done prior to the resin wetting sensors.3.4.1.2 Short Circuit Prevention: Since the function of the sensor is to measurethe c
23、onductivity of the resin that has been caused to flow into the gapbetween two conductors, it is vital that no foreign conductive materialsfind their way across the gap. For nonconductive reinforcements, thesensor may be placed directly onto the material being cured. Forconductive fibers, such as gra
24、phite, adequate filtering must be used toprevent fibers from contacting the sensor surface.3.4.1.2.1 Care should always be taken in handling sensors with exposed electrodesto prevent hand oils and electrolytes or other conductive contaminationfrom reaching the sensor area. It is good practice to use
25、 filtercovered sensors for all materials, including nonconductive prepregs.3.4.1.3 Wetting of Sensors: To achieve a meaningful reading the resin must fullyfill the gap between the conductive surfaces (see 3.4.1.1). Thus theresin must melt and flow into or become intimate with the sensor prior tothe
26、data being interpreted as a meaningful measure of the cure process.Data collection and reporting shall account for the wetting or contactprocess and flag the beginning of meaningful data.3.4.1.4 Sensor Attachment: The failure of the sensor connection is the mostfrequent cause of erroneous data durin
27、g a resin cure cycle. The resin isoften in an autoclave or oven during the cure, making i t difficult orimpossible to access the sensor junction during the cure. Connectionsmust remain sound throughout the cure process and under all the cureprocessing conditions.3.4.2 Sensor Types: There are many sp
28、ecialized sensors. The following sensorsrepresent some major types:a. Comb on filmb. Circuit on a chipc. Ceramicd. Other3.4.2.1 Comb Sensor: Comb sensors are constructed of interdigitated metal foil(e.g., copper) on a nonconductive film (e.g., kapton) substrate. Thesesensors are generally considered
29、 disposable and can be cured between theplies of a laminate.3.4.2.2 Circuit on a Chip: Interdigitated electrodes are on a silicon dioxidewafer with field effect transistors and a thermal diode. This sensor canprovide temperature as well as dielectric readings. It still requiresexternal circuitry sim
30、ilar to other sensors.SAE INTERNATIONAL ARP1926 Page 7 of 11Ceramic Sensors: Electrodes may be imbedded or plated onto a ceramicsubstrate. Because the ceramic substrate is usually thick, the sensorcan only be used on the surface of a laminate. This type of sensor isuseful for multiple cure cycles. T
31、he sensor may be imbedded into a tool.Other Sensor Types: There are many other possible sensor designs such asparallel plate electrodes between which the part is the dielectric. Thedesign must take into account the considerations mentioned in 3.4.1.3.4.3 Data Reporting, Sensors: Because sensor const
32、ruction varies as noted in3.4.1 and 3.4.2, all reported data needs to include the source,construction, and filter type (if any) of the sensors used.3.5 Selection and Use of Sensors:Different resin systems require different sensors for optimum data. Theselection of sensor type will be influenced by t
33、he range of the dielectricproperties exhibited by the resin during the cure cycle, the maximumtemperature during the cure cycle, the pressure and pressure transients inthe material during the cure cycle, and the part of the cure cycle that ismost important to the control of the process or product. T
34、he manufacturer ofthe dielectric equipment should be consulted for recommendations.3.5.1 Location: Sensors may be located at any point in or on the test piece. Ingeneral, the sensors are placed in the trim area of the part. Fornonconductive materials, the sensor may be built into the tool surface.Se
35、nsor data only monitors the cure in the local area where the sensor isplaced. Extrapolation of the data to the entire part should be done withcare and a knowledge of the thermal distribution of the part.3.5.2 Protection from Shorts (Electrical): Sensor electrodes must be protectedfrom direct contact
36、 with electrically conductive materials. If the sampleis a graphite composite, an appropriate nonconductive filter must be placedbetween the sample and the sensor. The barrier layer must be permeableenough to allow resin to flow through i t . It must not react with theresin, degrade at cure temperat
37、ures, or allow the conductive filaments topass. The filter should be checked for a dielectric response over thetemperatures used for cure. Filters made from glass fibers have been usedwith success for many applications.3.5.3 Leads: The electrical leads associated with the sensor should not be indire
38、ct contact with metal surfaces as this may result in abrasion of theinsulation and shorting of the leads.3.5.3.1 If significant compaction occurs in a die or mold during curing, sensorleads may be sheared since the sensor may be displaced with respect tofixed portions of the die or mold. This moveme
39、nt can be eliminated ifthe sample is either precompacted before the sensor is completelyrestricted or the sensor is located in a bottom layer so that compactiondoes not cause appreciable movement of the sensor.SAE INTERNATIONAL ARP1926 Page 8 of 113.5.4 Testing: Considering the time and cost involve
40、d in making a part it isprudent to test sensors before cure. Acceptance limits for the parametersfor each type of sensor should be obtained from the manufacturer.3.5.5 Disposable Sensors: These are sensors designed for one time use only. Itmay be desirable to leave the sensor imbedded in the laminat
41、e after cureeither to save the cost of removal or to monitor the laminate for futurechanges in dielectric properties due to moisture absorption or for otherreasons.3.5.5.1 Disposable sensors must be regarded as a potential flaw in the finishedpiece and should be positioned with that consideration in
42、 mind. Partintegrity may be maintained by placing the sensor in trim area, outsidethe bleeder material, or in a separate test panel.3.5.5.2 If the sensor is placed in the laminate, the prepreg may have to benotched to accommodate the sensor to avoid force concentration duringpressure application. *M
43、ATERIAL SHOULD NOT BE REMOVED WITHOUT APPROVALBY AUTHORIZED PERSONNEL*3.5.6 Reusable Sensors: Care must be taken to minimize damage to the sensorduring the manufacturing process and to verify sensor functionability priorto a subsequent cure.3.5.6.1 Reusable ceramic sensors may be brittle and should
44、not be subjected toimpact with a hard object. Also, the electrode may be subject to damagedue to scratching or gouging. The manufacturer should be consulted forproper handling.3.5.6.2 The physical size and shape of the ceramic sensor are such that it willbe in contact only with the outer surface of
45、the part being cured. Inmany cases the sensor will be built into the wall of a tool or die. Ingeneral, the location of the sensor w i l l have been predetermined and thelayup procedure will be concerned solely with cleaning and testing ofsensor functionality.3.5.6.3 The surface of the sensor may be
46、treated with a mold release compound.The sensor supplier and material supplier should be consulted for theproper choice of release compound. The mold r elease must not change thedielectric data significantly. The release compound must not react withthe resin in the part. The thinner the coating of m
47、old release, the lessit will affect dielectric measurements.3.5.6.4 At the conclusion of a cure cycle, the surface of the ceramic sensor maybe covered with cured resin. If the surface has been treated with a moldrelease, the cured material can usually be pried off using a flat wideblade such as a pu
48、tty knife. The blade should be wider than the activesurface of the sensor and used so that the sharp edge i s parallel to theactive surface of the sensor. The sharp corners of the blade should notbe allowed to scratch the surface of the sensor. Often it will only benecessary to lift an edge of the c
49、ured mass and it will easily lift off.SAE INTERNATIONAL ARP1926 Page 9 of 113.6 Connections and Cables:In the general case there will be several cables and connectors required tomake the electrical connections between the sensor and the dielectrometer.One of the most important considerations from the viewpoint of the dielectricmeasurement i s the distance between the dielectric sensor and the dataacquisition unit. The connecting cables are part of the measuring circuit.The induced current of long cables may affect the dielectric measurements.3.
