1、AECMA PREN2746 40 W 101231L O004082 4 U, Edition approved for publication Comments should be sent within six months after the date of publication decision 88, Bd. Malesherbes 1990-08-24 A.E.C.M.A. 75008 PARIS - FRANCE A. E, C. M .A. STAN DARD NORME A.E.C.M.A. A.E.C.M.A. NORM C7 Chairman Mr. BEZAUD p
2、rEN 2746 Issue P 1 August 1990 DIT PAR LASSOCIATION EUROPENNE DES CONSTRUCTEURS DE MATRIEL AROSPATIAL 88, boulevard Malesherbes, 75008 PARIS -TL. 45-63-82-85 UDC : Key words : ENGLISH VERSION Aerospace series Glass fibre.reinforced plastics Determination of flexural properties Three point bend metho
3、d Srie arospatiale Luft- und Raumfahrt Matires plastiques renforces au verre textile Dtermination des caractristiques de flexion Glasfaserverstrkte Kunststoffe Biegeprf ung Mthode des trois pannes Dreipunkt-Verfahren This .Aerospace Series pre-standard has been drawn up under the responsibility of A
4、ECMA (Association Europenne des Constructeurs de Matriel Arospatial). It is published on green paper for the needs of AECMA-Members. It has been technicallyapprovedby the experts of the concerned Commission following comment by the Member countries. Subsequent to the publication of this pre-standard
5、, the technical content shalinot be 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
6、 countries it will be submitted as a draft European Standard to CEN (European Committee for Standardization) for final vote. - AECMA PREN2746 90 LOL23LL 0004083 b W prEN 2746 Page 2 Contents Sccpe and field of application References Def inj.tions Apparatus Test pieces Procedure Calculation and expre
7、ssion of the results Test report AECMA PREN274b 90 IOL23LL OOOLiOB4 B O * O O 1 S prEN 2746 Page 3 3pe and field of application This standard describes a method for the determination of the fiexural properties of glass fibre reinforced plastic materials in the form of rectangular bars, of standardis
8、ed dimensions or not, moulded directly or cut frorr. panels or other mouldings. It only applies to single bars, supported without constraint, loaded in the middle of the span (three point bending methocl) 1). The following properties may be determined by using the method described, 1.1 Flexural stre
9、ss and flexure at failure of materials which breok before cr on reaching normal flexure. 1.2 Flexural stress for normal flexure of materials which do not break before or at normal flexure, 1.3 Flexural stress for the ultimate load, in the case of materials which reach ultimate load before or at norm
10、al flexure. 1.4 Flexural stress at failure or for the ultimate load in cases where the normal flexure is exceeded and if this is required by the material . Note : If the flexure is greater than the normal flexure, it may not be possibie to make a direct comparison of flexural stress results for diff
11、erent test pieces. 1.5 Where applicable, the apparent elastic modulus in flexure (elastic modxlus determined by flexural test). Note : The elastic modulus in flexure should only be considered as an approximate value of YOUNGS modulus of elasticity. 2 Referen-ces EN 2374 Aerospace series - Glass fibr
12、e reinforced mouldings and sandwich composites - Production of test panels ER 2489 Aerospace series - Fibre reinforced plastics - Determination of the action of liquid chemicals 2) EN 2743 Aerospace series -a Beinforced plastics - Standard atmospheres for conditioning and testing 3) EN 2823 Ae.rospa
13、cc series - Fibre reinforced plastics - Test method for the determination of the effect of exposure to humid atmospheres on physical and mechanical characteristics 3) 1) A method in wh5ch the load is applied st 2 points (the 4 point bend method) allnws piire flexural stresses to be produced in the c
14、entral prxt of the n est piece. The. compression stresses caused by the points are Euch lower than that produced perpendicular to the central point in the three point bend method. The present European standard does not deal with the four point bend method. 2) Published as AECMA pre-standard at the d
15、ate of publication of the present standard. 3) III preparation at the date cf publication of the present standard. AECIA PREN274b 90 M 1012311 0004085 T M prEN 2746 Page 4 3 Definitions The following definitions are applicable within the framework of the present standard : 3.1 Flexure Distatice trav
16、elled during bending, from its initial position, by the lower or upper surface of the test piece in the middle of its span. 3.2 Flexural stress at a given moment during the test Ultimate stress on the external fibre of the material. in the section of the test piece located in the middle of the span.
17、 It is calculated in accordance with the general formula given in clause 7.1. 3.3 Flexural stress at specified flexure Flexural stress for a flexure equal to 1,5 times the thickness cf the test piece. 3.4 Flexural stress at ultimate load Flexural stress at the moment when the load reaches the ultima
18、te value. 3.5 Flexural stress at failure Flexural stress at the instant of failure. 3.6 Modulus of elasticity in flexure The modulus of elasticity in flexure is defined from the tangent of the initial part of the oad/deflection curve and calculated with the formula given in clause 7.2. 4 Apparatus T
19、he. testing machine, suitably constructed and calibrated, allowing relative displacement of the loading nose wi.th respect to the supports at a constant rate V, and indicating the loads with an error not exceeding $. 1 Z and the flexures with an error not exceeding + - 2 2. The supports and the load
20、ing nose shall be at least as wide as the test piece and shall be parallel to one another. The radius, r15 of the loading nose and the radius, r as follows : of the supports shall be 2 r = (5 f 0,l) mm, r1 = (2 5 0,2) mm. 2 It shall be possible to adjust the span, i., between the supports (see figur
21、e 1) AECMA PREN274b 90 a LOL23LL 0004086 L =, _- prEN 2746 Page 5 0 5 Test pieces If it- is impossible to obtain test pieces from the finished product, prepare laminates or panels according to EN 2374 or by a suitable method by prior agreement between the parties concerned and as near as possible to
22、 the method of manufacture of the product under consideration or envisaged. The test pieces shall be taken from these laminates or panels, 5.1 Dimensions of test pieces (3 + 0,2) mm - Thickness “h“ : - (15 5 0,5) mm - Width - Length “1“ : (20.h) + - im If test pieces of thickness greater than 3 mm a
23、re used, the radius of the supports may reach 1,5 times that of the thickness of the test piece. The supports shall have this size if there is a large indentation or fail.ilre in compression. 11bI . 5.2 Number of test pieces 5.2.1 A minimum of 5 test pieces shall be used. 5.2.2 The results obtained
24、from test pieces, which break outside the central third of the length between the supports shall be disregarded and further test pieces shall be tested in their place. In such cases, mention shall be made in the test report. 5.3 Conditioning III case the test is carried out in the initial state, the
25、 test pieces shall be conditioned ccording to EN 2743. In case the test is carried out after immersion of the test pieces, the conditioning shall be according to EN 2489. a In case the test is carried out after hot-wet exposure of the test pieces, the . conditioning shall- be according to EN 2823. 6
26、 Procedure 6. I. Test atmosphere Unless otherwise specified, carry out the tests at (23 i 2) OC and (50 5 5) 2 re1 ative humidity. AECMA PREN2Ltb 90 U 10L23LL OOOL1087 3 U prEN 2746 Page 6 6.2 Measurement of dimensions of test pieces In the centrd section of the test piece, measure the width b of th
27、e test piece to an accuracy of 0,1 rau, make three measurements of the thickness h to an accuracy of 0,02 mn and take their arithmetic mean for the calcu1.ati.m below. Adjust the length of the span, L, to : (16.h) 5 1 mm. 1 Measure the length of the span to an accuracy of 0,5 %. 6.3 Test procedure 6
28、.3.1 Speed of testing Regulate the test machine to the spee V, determined as follows : 6.3.1.1 If there is no specification for the material under test, the following n:ethod shall be used : V = K.h where V is expressed in mm/min, h is thickneZ7 in mm, K io 0,s min 6.3.1.2 If there is a specificatio
29、n available for the material : a) be used? either the speed of displacement of the loading nose is specified and shall b) or the rate of elongation is specified (for example 0,Ol) and, in this case, the relative speed, V, of the loading nose can be calculated from the following formula : Sr , L wher
30、e : v= 6h V is expressed in nrm/min, Sr L is the span, in mm, h is the thickness of the test piece, in mm. is the rate of elongation per minute, such as 0,Ol nun/mm/min, 6.3.2 Place the test piece symmetrically with respect to the parallel supports, ensuring that the length of the test piece is perp
31、endicular to these supports. Ensure that the central loading nose is placed exactly on the centre of the span and apply the load to the test piece at a uniform speed, LO avoid shock, 6.3.3 If the elastic modulus is to be determined, the load and flexure shall be siuultaneously recorded to enable a l
32、oad-flexure curve to be plotted. 6.3.4 For test pieces which break before reaching or on reaching the conventional flexure (see clause 3,3), note the load and flexure at failure. 6.3.5 For test pieces which OL- rZot break before reaching or at the conventional f1.exure (see clause 3.3), note the loa
33、d st the conventional flexme. Ir that is specified, continue the test without interruption, beyond the coiveritional flexure, until rupture ciccurs or until a maximum load is attained, and note the load and the flexure of whichever of these points is syecifie. 6.3.6 For test pieces which reach the m
34、aximum load before the conventional. flexure can be attained, note the maximum load and the caresponding flexure. 7 Calculation tind expression of results 7.1 Flexural stress The flexural stress is given by the formula : r 3FL - 2bl.i bf - where : o is the flexural stress, in KPa, F is the force app
35、lied, in N, L is the span, in um, b is the width of the test piece, in nm, h is the thickness of the test piece, in nm. f Note : For a nore precise calculation of .the flexural stress, taking into account the horizor.ta1 component of the flexural moment corresponding to the flexure, the following eq
36、uation may be used : 3FL 4d2 G= (i 3.- 1 2bh2 L2 f where d is the flexure, in m. 7 2 Elastic modulus in f Iexure, Troce the load-deflection curve from the results obtained. Determine the elastic modulus from the icitial rectllinear part of the oaci-deflection curve, using at least five values of the
37、 flexme and the force for the test piece, If the produced diagram is not linear, then a straight line shall be drawn between 1C! X and 25 Z of the maximum load of failure. E is given by the following formula : b L3 a P where : =i- 4bh3 * A d Eb is the elastic modulus, in MPa, is the span, in mm, 3 b
38、 is the width of the test piece, in nun, h is the thickness of the test piece, in mm, A F 4 d is the variation of the force on the initial rectilinear part of the load-deflection curve, in N, is the variatior. of the flexure corresponding to the variatior. cf the force - F, in mm. AECMA PREN2746 90
39、LOL23LL 0004089 7 = prEW 2746 Page 8 7.3 Modes of failure During ehe flexural test, three different inodes of failure can be procluced, that is : a) failure initiated at the surface by the tersile stresses, b) failure irii.tiated at the surfacc by the compression stresses, c) internal failure due to
40、 the shear stresses. Por each test piece, Indicate the mode(s) of failwe. If the mode of fail-tre of the test pieces of the same set are different, the calculated values of the flextira? stress are no longer statistically homogeneous and it would be as wel.1 to be very prudent in the evaluation of t
41、he results, 8 Test report The test report shall make reference to the present standard aad mention the following information : 8.1 The mailufacturer and product designation$ the origin, the batch number, the date of receipt sd all other useful dsta about the material siihmitted to the test. 8.2 The
42、details about the preparation of ttie test pieces, in particular the method of preparation of the I.,-,miiiate or the panel if applicable (clause 5). 8.3 TI; Tlie flexual stress at the conventional flexure (see clause 3.3), giving the arithmtlc mean mc? the standard deviation, also the number of tes
43、t qecimens 3) The flexural stress and the flexure at maxinuni force (see clause 3.4), giving the arithmetic nean and the standard deviatiali. 8.8 If necessary, the load-deflection curve, with the value of the arithmetic mean of: the elastic modulus, E and the standard deviation of E also the number
44、of test specimens. b b? 8.9 The method of conditicning and the laboratory atmosphere. 8.10 The number of test pieccc which break outside the central third of the length between tlie support (see clause 5.2.2). 8.11 The rdiuc of the supports and loading nose if this does not conform with the standard radius (see clause 5.1)+ Applied load I * Figure 1 - Detail of test appuratus
