1、AECMA STANDARD NORME AECMA AECMA NORM Edition approved for publication prEN 4238 Edition P 1 February 1998 C7 Chairman Comments should be sent within six months after the date of publication to PUBLISHED BY THE EUROPEAN ASSOCIATION OF AEROSPACE INDUSTRIES (AECMA) Gulledelle 94 - 8-1200 BRUXELLES - T
2、el. (+32) 2 775 81 10 - Fax. (+32l 2 775 81 11 ICs: Descriptors: ENGLISH VERSION Aerospace series Fibre reinforced plastics Determination of the effect of dry heat on physical and mechanical characteristics Srie arospatiale Luft- und Raumfahrt Plastiques renforcs de fibres Dtermination de linfluence
3、 de la chaleur sche sur les caractristiques physiques et mcaniques Fasewerstrkte Kunststoffe Bestimmung des Einflusses trockener Hitze auf die physischen und mechanischen Eigenschaften This “Aerospace Series“ Prestandard has been drawn up under the responsibility of AECMA (The European Association o
4、f Aerospace Industries). It is published on green paper for the needs of AECMA-Members. It has been technically approved by the experts of the concerned Technical Committee following comment by the Member countries. Subsequent to the publication of this Prestandard, the technical content shall not b
5、e changed to an extent that interchangeability is affected, physically or functionally, without re-identification of the standard. After examination and signature of the AECMA Standard Checking Centre (NPS) and formal agreement of the Official Services of the Member countries it will be submitted as
6、 a draft European Standard to CEN (European Committee for Standardization) for formal vote. 1998-02-27 AECMA Gulledelle 94 I 6-1 200 BRUXELLES I Mr Wright aecma 1998 STDmAECMA PREN q23-ENGL 1998 LOL23LL 0011i33b 790 m Page 2 prEN 4238: 1998 Contents Page O 1 2 3 4 5 6 7 8 9 10 11 12 Foreword . 3 Sco
7、pe . 3 Normative references 4 Definitions . 4 Principle . 4 Apparatus 5 Test specimens and samples . 6 Conditioning before exposure 7 Procedure 8 Expression of results . 8 Designation . 11 Exposure conditions 7 11 Annex A . 12 O STD-AECMA PREN 9238-ENGL LA W LO323L3 0034337 b27 a Page 3 prEN4238: 19
8、98 Foreword Fibre reinforced plastic materials are sensitive to effects of heat; the temperature level and the length of time they are exposed to heat lead to a change or even a deterioration in the physical, chemical and mechanical properties of the material. The behaviour of reinforced plastic mat
9、erials, when subject to thermal ageing, depends: a) on the material - chemistry of the fibre, interface and matrix product constituents; - fibrous structure of the material; - differences in physical and/or mechanical properties between the different component materials; - internal stresses induced
10、during processing. b) on environmental conditions - temperature level; - pressure and oxygen content of the air; - radiation. c) on operating conditions (stress, environment, etc.) The effects of thermal ageing on the laminate are: - change and/or deterioration in its physical appearance; - internal
11、 deterioration (cracking, delamination, etc.); - change in the amount of cross linkage, in the level of crystallinity followed by an irreversible deterioration in the matrix and/or interface; - variations in mass; - changes in the different mechanical characteristics dependent on the matrix and/or t
12、he interface. The use of fibre reinforced plastic for applications in a hot atmosphere shall be qualified by: - ageing tests, which cover the intended range of operating conditions (.e., temperature and time). Care shall be taken with any extrapolation of the data outside the qualified range; - meas
13、uring the properties most representative of those which will be experienced in the intended application. The main purpose of this test method is to allow a relative classification of the different materials exposed in identical conditions to be produced. 1 Scope This standard defines a method of eva
14、luating the influence of exposure to constant temperature, under dry atmospheric pressure conditions, and without mechanical loading, on the characteristic properties of fibre reinforced plastics for aerospace applications. This standard is applicable to all fibre reinforced materials, irrespective
15、of the fibre or organic resin matrix, when specified by the technical specification or material standard. This specification shall be used only to compare the characteristics: - of a material at different stages of exposure compared to this material in its initial state before exposure. - of differe
16、nt materials at the same state of exposure (same temperature and same ageing times). This specification will not allow the change in characteristics of a material in a real configuration to be predicted because of the absence of any eventual interactions created by the environment mechanical loading
17、s and the thermal cycles. Page 4 prEN 4238: 1998 2 Normative references This Standard incorporates by dated or undated reference provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated referen
18、ces, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. EN 2331 Aerospace series - Textile glass fibre preimpregnat
19、es - Test method for the determination of the resin and fibre content and mass of fibre per unit area EN 2564 Aerospace series - Carbon fibre laminates - Determination of the fibre, resin and void contents 1) EN 2743 Aerospace series - Fibre reinforced plastics - Standard procedures for conditioning
20、 prior to testing 1 ) EN 2744 Aerospace series - Non metallic materials - Preferred test temperatures EN 3615 Aerospace series - Fibre reinforced plastics - Determination of the conditions of exposure to humid atmosphere and moisture absorption 3 Definitions For the purpose of this standard the foll
21、owing definitions apply: - Intermediate (semi-finished product): Supplied material constituted of products having been subjected to a partial process giving it, at delivery, a state different to that of final use (prepregged fabric, moulding compounds, etc). - Interface: In a laminate, the interface
22、 is the contact surface between reinforcement and matrix. - Matrix: Material which links the reinforcements products (fibres, fabrics, etc) between them to form the composite laminate. - Component products (basic constituents, raw materials): Supplied material used for the manufacture of intermediat
23、es (resins, hardeners, accelerators, solvents, additives, fibres, fabrics, etc.). - Initial state: State of the material prior to exposure. 4 Principle Test specimens or test samples are exposed for pre-determined periods, under controlled conditions protected from light, to a gentle regular dry air
24、 flow. The air, which is at atmospheric pressure, is held at the exposure temperature for defined time periods and is regularly renewed. At the end of each exposure period the most meaningful characteristics are measured and compared to those measured in the initial state. 1) Published as AECMA Pres
25、tandard at the date of publication of this standard STD-AECMA PREN Li238-ENGL L978 LOIIZIIII 0011i337 4TT Page 5 prEN4238: 1998 The exposure conditions are: - either, those defined in the technical specification and(or) the appropriate material standard; - or, where a material needs to be evaluated
26、within a particular thermal range, those establised by means of preliminary tests to determine the reference temperature for the evaluation programme; for example, the reduction in a (or a number of) characteristic(s) of x % (25%, 40%, etc.) after 2 O00 h of exposure at the reference temperature. NO
27、TE: The hygrometry of the air circulating in the oven is the natural hygrometry occuring in the surroundings. However, particular hygrometric conditions, with a nitrogen/oxygen (altitude) and/or pressure ratio (altitude, engine environment, etc.) may be specified by a material standard or technical
28、user specifications. The characteristics to be measured in order to assess the deterioration of the material shall normally correspond to those which best show this change, these are usually: - changes in physical appearance; - change in mass of the material; - reduction in mechanical characteristic
29、s linked to the plastic matrix material and(or) the fibre/matrix interface. NOTE: A comparison between different matrices, according to this standard, is only possible if the samples are: - subjected to the same exposure conditions; - of the same geometry and surface state; - reinforced, with the sa
30、me reinforcement (fibre, volume content, number of plies, structure of fibres within the ply, etc.). 5 Apparatus 5.1 Balance accurate to: - 0,l mg for a mass of test piece M 5 1 O g; - l O-4 M (sampling mass) if M 10 g. 5.2 5.3 Oven Magnifying glass with magnification 10 X An air circulating oven ca
31、pable of achieving a regular and continuous change of air, and maintaining temperature uniformity within the specified limits for each specimen situated in the effective volume of the oven: - in use, the oven shall be protected from radiation, ie light, ultra-violet, infra red etc.; - the capacity o
32、f the oven shall be such that the total volume of test specimens/test samples for each test campaign does not exceed 2 % of the effective volume; - the oven shall be equipped with means of supporting or suspending the test specimensltest samples. A distance of 10 mm between test specimens/test sampl
33、es and 50 mm between test specimens/tect samples and the oven wall shall be maintained; - the type of material used to support the test specimendtest samples shall not influence the action of oxygen or humidity on the test specimens/test samples. The renewal of air in the oven shall range from 3 to
34、10 times the effective volume of the oven per hour in order to ensure a more or less constant oxygen content. The oven shall be equipped with an integrated and derivative proportional (IDP) temperature control system or equivalent. Page 6 prEN 4238: 1998 - At the start of exposure: The oven shall be
35、 capable of a rise in temperature, when empty, of between 2 OC/min and 5 OC/min. The thermal controls shall be set such that during heat up overshooting of the exposure temperature does not occur. - A preliminary check of the temperature uniformity within the oven shall be made using a dummy load, r
36、epresentative of the actual intended test specimens/test samples to be tested, to ensure that the temperature control probes and temperature monitoring probes are suitably positioned. - A temperature indicator with a minimum of six measurement channels shall be used for this check. - In stabilised m
37、ode, each test piece shall be maintained at the specified temperature within the tolerances given in EN 2744. - Continous monitoring of temperature as a function of time during exposure shall be made using a minimum of two recording channels, one monitoring the low temperature zone, and one monitori
38、ng the high temperature zone of the effective oven volume. If a continous recording equipment is not available, the oven shall be fitted with a device to determine: - the maximum temperature attained; - the instant that maximum temperature is attained should a fault occur during the exposure period.
39、 5.4 Dessicator Dessicator containing a drying agent such as silica gel or phosphoric anhydride. For dessicator use conditions, see EN 361 5 (Method BI. 6 Test specimens and samples Exposure to dry heat may be carried out using: - Test samples prior to machining of test specimens - option P. - Test
40、specimens machined to final dimensions prior to exposure - option E Unless otherwise specified by the technical specification or material standard option E shall be used. 6.1 Material The process for manufacturing the material for test samples or test specimens shall be as that specified in the mate
41、rial standards or that recommended by the prepreg manufacturer. In the case of an evaluation programme for a new unknown material, the ply orientation of the test panels shall whenever possible conform to the following criteria: - Mirror image symmetry of the plies (fibres orientation and position o
42、f fabric faces) with respect to the mid-plane of the lay-up. - Alternate crossing of plies (lamination most sensitive to the effects and action of oxygen). - Laminate thickness 1,5 mm to 3mm. The fibre content shall be in conformity with the material standard. The laminate faces are as-made, that is
43、 corresponding to those obtained after removal of the peel plies. 6.2 Test specimen The geometry of the test specimen shall conform to the requirements of the relevant test method. The number of test specimen shall conform to the requirements of the relevant technical specification or the material s
44、tandard. Test specimen shall be in the as machined condition. Particular attention shall be paid to the condition of the edges of the test specimen, in particular over heating and delamination of the plies shall not be accepted. When tabs are required to be bonded to the test piece to enable testing
45、 to be carried out after exposure, these may be bonded to the test specimen after exposure, particularly where there is a risk of the bonded joint being degraded during exposure. Test specimen dimensions shall be measured prior to exposure. STD-AECMA PREN Li238-ENGL 1998 LOL23LL OOL43LiL 058 Page 7
46、prEN4238: 1998 6.3 Marking Identification markings shall be in a area of the test specimen/sample which is not critical to the subsequent testing. The method of marking shall be non-agressive to the material and shall be resistant to the exposure conditions. 7 Conditioning before exposure 7.1 The te
47、st specimens/samples shall be maintained, before the start of exposure, at room temperature in the conditions defined in EN 2743-A. Method A - Specimens in as-cured state 7.2 The test specimens/samples shall be subjected to a conditioning procedure specified in the material standard (e.g. pre-drying
48、 of the test specimens according to EN 361 5-Bi. Method B - Specified conditioning 8 Exposure conditions 8.1 Temperatures Unless otherwise specified, the exposure temperature (t) and associated tolerances shall be taken from EN 2744. 8.2 Exposure periods The total exposure period (d) is fixed by the
49、 material standard or the qualification programme for the material. It is recommended that if a single stringent ageing temperature or exposure period is to be carried out, some specimens are checked at convenient intervals chosen from table 1. Intermediate sampling during exposure may be specified, in which case the intervals shall normally be chosen table 1. Table 1 : Recommended exposure periods 8.3 8.3.1 Hours 1 2 4 8 16 24 48 96 168 Code AA AB AC AD AE Al= AG AH AJ Exposure period designation codes Weeks 2 4 8 16 26 52 Choice of exposure conditions Specified exposure con
