PREN-2850-1991.pdf

cen *pren*2850 91 3404589 o019600 2 w i edition approved for publication 1991 -1 1-29 a. e.c.m.a. stan dard norme a.e.c.m.a. a.e.c.m.a. norm comments should be sent within six months after the date of publication decision a.e.c.m.a. teechnopolis - 175, rue jean-jacques rousseau 921 38 issy-les-moulineaux cdex - france pren 2850 issue p 1 november 1991 edite par lassociation europeenne des constructeurs de materiel aerospatial technopolis - 175, rue jean-jacques rousseau - f-92138 issy-les-moulineaux cdex - tl. (1) 47.36.98.76 udc : key words englist version aerospace series carbon thermosetting resin unidirectional laminates compression test parallel to the fibre direction luft- i srie arospatiale d raumfahrt stratifis unidirectionnels unidirektionale kohlenstoffaser- carbone/rsine thermodurcissable duroplast-verbundwerkstoffe essai de compression druckversuch parallel paralllement au sens des fibres zur faserrichtung this aerospace series pre-standard has been drawn up under the responsibility of aecma (association europenne des constructeurs de matriel arospatial). it is published on green paper for the needs of aecma-members. it has been technically approved by the experts of the concerned commission following comment by the member countries. subsequent to the publication of this pre-standard, the technical content shall not 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 countries it will be submitted as a draft european standard to cen (european committee for standardization) for final vote. nota - extra copies can be supplied by b.n.a.e. - technopolis 54 199. rue jean-jacques rousseau - 92138 issy-les-moulineaux cedex i i c7 chairman mr. bezaud aecma 1991 cen *pren*k2850 7 1 = 3404587 ool7bol 4 i pren 2850 page 2 contents 1 2 3 4 5 6 7 8 9 10 11 12 object and field of application references principle of the method definitions designation specimens apparatus conditioning procedure calculation of results validity test report annex a annex 8 copyright association europeene des constructeurs de materiel aerospace licensed by information handling services copyright association europeene des constructeurs de materiel aerospace licensed by information handling services cen *pren*2850 91 3404589 o019602 6 i pren 2850 page 3 1 this specification defines a method for the determination of the stress at failure and the youngs modulus in compression of carbon thermosetting resin unidirectional laminates, object and field of application the method only covers specimens whose axis is parallel to the fibre direction. this method covers other fibres (or fabrics) than carbon, when the relevant technical specification explicitely mentions it. 2 references en 2372 en 2489 en 2565 en 2743 en 2744 en 2823 en 2859 en 3783 aerospace series - nuts, hexagon, thin steel, cadmium plated - classification 1100 mpa/235 o c aerospace series - fibre reinforced plastics - determination of the action of liquid chemicals 2, aerospace series - preparation of carbon fibre reinforced resin panels for test purposes 2) aerospace series - reinforced plastics - standard procedures for conditioning prior to testing 2) aerospace series - non-metallic materials preferred test temperatures aerospace series - fibre reinforced plastics - test method for the determination of the effect of exposure to humid atmospheres on physical and mechanical characteristics 2, aerospace series - bolts, hexagonal normal head, close tolerance shank, short thread in steel cadmium plated - classification 1100 mpa/235 o c 2, aerospace series - procedure of the normalisation of tests results of fibre dominated composite mechanical properties 3, 3 principle of the method the method consists of the measurement of longitudinal strain of the material as a function of the applied load during a compression test carried out at constant rate until failure. the load applied to the material may be introduced in two different ways : - either in shear through co-cured or bonded tabs, (method a) - or in compression by direct end loading of the specimen. (method b) it is important to realise that the test results obtained by these two methods are not comparable. published as aecma standard at the date of publication of the present standard. 2, published as aecma pre-standard at the date of publication of the present standard. 3, in preparation at the date of publication of the present standard. copyright association europeene des constructeurs de materiel aerospace licensed by information handling services copyright association europeene des constructeurs de materiel aerospace licensed by information handling services cen *pren*k2850 91 3404587 0019603 8 i pren 2850 page 4 4 definitions 4.1 compression str.ess at any point in time during the test (a 1 c compression load per initial unit cross sectional area in the gauge length sustained by the specimen at each point in time during the test. 4.2 compression stress at failure (a cl 1) compression stress at moment of failure. it is caculated using the formula given in paragraph 10.1. 4.3 strain (cl 1 change in the distance between reference points within the gauge length of the specimen produced by a compression load expressed in relation to the original distance between points. is the strain measured parallel to the fibre axis. 9 1 4.4 secant compression modulus two methods of calculation are available. the one based on the strain shall be prefered. in default, the one based on the load shall be used. 4.4.1 secant compression modulus (ecl 1 (a,b) slope of the straight line passing through the stress /longitudinal strain diagram at a point corresponding to 01 % strain with respect to the gauge length of the specimen and a point corresponding to /3 % strain on the same diagram. a and 0 are defined in the material standard. it is calculated using the formula in paragraph 10.2.1. 4.4.2 secant compression modulus (ecl 1 (pr/1 o, pr/2) slope of the straight line passing through the stress/longitudinal strain diagram at a point corresponding to a stress calculated from pr/lol and a point corresponding to a stress calculated from pr/2 i where pr is the load at failure of the specimen. it is calculated using the formula in paragraph 10.2.2. copyright association europeene des constructeurs de materiel aerospace licensed by information handling services copyright association europeene des constructeurs de materiel aerospace licensed by information handling services cen *pren*z850 91 3404589 o039604 t - : pren 2850 page 5 5 designation o the designation of the method shall conform to the following example : corndression test en2850 a i - test type specification no. specimen type (see 0 61 1 6 specimens 6.1 preparation of test panels o specimens shall be prepared from panels made according to en 2565. manufacturing parameters, such as environmental products, curing cycle, applicable technical specification. 6.2 form and dimension two types of specimen are given : = type a (see annex a), - type b (see annex b). type a variants are possible if they satisfy the following requirements : + i o mm - gauge. length g = 10 shall comply with the - thickness h = (2 f 0,2) mm - total thickness h = (4,5 f 0,5 mm - width b = (io f 0,2)mm - tab length t = - 5 0 mm angle of misalignment of the fibres with respect to the compression loading axis shall be less than i 0,50. 6.3 tabs the material forming the tabs shall be the same as that of the specimens. it is preferable to form the tabs in a co-curing operation in the case of testing at high temperature and/or after humidity ageing. in the case of bonded tabs, it shall be checked that the temperature of the bonding cycle does not induce any undesirable post-curing effect in the laminate, 0 copyright association europeene des constructeurs de materiel aerospace licensed by information handling services copyright association europeene des constructeurs de materiel aerospace licensed by information handling services cen *pren*k2850 93 e 3404589 o039605 pren 2850 page 6 6.4 number at least 5 specimens shall be used. 7 apparatus 7 . 1 micrometer having flat faces of 2 mm diameter ; accurate to the nearest 0,o mm. 7.2 test machine accurate to within 1 % in the load range used. 7.3 by means of a suitable device (guiding of the jaws with respect to each other for example). in order to avoid any buckling, which would affect the test, accurate alignment shall be assured misalignment shall be less than an angle of 1 o . 7.4 means of strain measurement as a function of load accurate to within 1% in the strain range used. the equipment shall not produce marks on the specimen liable to cause premature failures. the chosen means of measurement shall allow any possible buckling during the test to be detected. 7.5 if required, controlled temperature cabinet and recording thermocouple for tests at temperatures (conforming to en 2744) other than ambient. 8 conditioning in the case of test at initial state, conditioning shall conform to en 2743. in the case of test after immersion, conditioning shall conform to en 2489. in the case of tests after hot-wet exposure, conditioning shall conform to en 2823. 9 procedure 9.1 0,ol mm within the gauge length of the specimens. make two measurements of the thickness to the nearest 0,ol mm of the width to the nearest 9.2 position the strain measuring device (see 7.4) on the specimen. copyright association europeene des constructeurs de materiel aerospace licensed by information handling services copyright association europeene des constructeurs de materiel aerospace licensed by information handling services cen *pren*285o 9 1 i 3404589 0039606 3 i! pren 2850 page 7 9.3 for test at a temperature other than ambient, the time between the conditioning and the start of the test shall meet the following requirements. 9.3.1 for specimens that have neither been subjected to ageing nor immersion, the period of soak at the test temperature shall be determined by prior investigatory tests and be noted on the report. 9.3.2 for specimens that have experienced immersion, follow the instructions in en 2489. 9.3.3 defined in en 2823. for specimens that have been subjected to ageing in humid environment, follow the procedure 9.4 loads. to en the grips (if part of the jig) shall cover the length of in the case of type b, apply a gripping load of 0,05 m 2859 and en 2372, for example. he tabs so .dan, using as not to introduce standard fasteners, abnormal according 9.5 apply load at a constant rate of grip movement of 1 mm/min. o 9.6 detect any onset of buckling. as an approximation : e i 1 = where : - 11 - e record during the entire test the strains el and cnl1 with respect to the load in order to 11 c11 + e”11 2 strain parallel to the fibre axis (tool face or lower platen), - 11 - strain parallel to the fibre axis (bag face or upper platen). e” 9.7 note the load at failure p , 1 o calculation of results 10.1 stress at failure (a 1 c l 1 pr acll =- bh where : pr b h = load at failurein n = width in mm = thickness in mm. l note : u according to en 3783. may be calculated as a function of actual thickness and/or the theoretical thickness, c l 1 - a l copyright association europeene des constructeurs de materiel aerospace licensed by information handling services copyright association europeene des constructeurs de materiel aerospace licensed by information handling services pren 2850 page 8 10.2 secant modulus (ecl 1 measured from the load/strain recording, the secant compression modulus is given by the formulas : 10,2.1 where : cy = strain parallel to the fibres p = strain parallel to the fibres pa = cy corresponding load in n pp = p corresponding load in n b = width in mm h = thickness in mm 10.2.2 where : = = = load at failure in n strain parallel to the fibres corresponding to pr/2 strain parallel to the fibres corresponding to pr/l o pr (c, )b (c1 ia b = width in mm h = thickness in mm note : (ecl according to en 3783. may be calculated as a function of actual thickness and/or theoretical thickness copyright association europeene des constructeurs de materiel aerospace licensed by information handling services copyright association europeene des constructeurs de materiel aerospace licensed by information handling services cen *pren*2850 93 w 3404589 0039608 7 pren 2850 page 9 11 . validity the test is valid only if failure occurs in the free length of the specimen. there shall be no bushing of the ends. buckling is acceptable if the difference between strains recorded on each face of the specimen throughout the duration of the test until failure is such that : 12 test report the test report shall give the following information : 12.1 details concerning the tested material. reference to this standard, the frade mark, reference c6de, origin, date of receipt and other 12.2 all information regarding the preparation f the specimens, the tabs and the tab bonding. 12.3 measured dimensions of the specimens and the fype of specimens chosen. 12.4 specification. the test conditions, for example temperature, relative humidity if these deviate from the 12.5 (see en 24891 or hot-wet exposed (see en 28231. the period of time held at test temperature in the case of specimens that have been immersed 12.6 the case of a modulus measurement. present a diagram giving recorded load as a function of