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1、INTERNATIONAL STANDARD IS0 7765-2 First edition 1994-08-l 5 Plastics film and sheeting - Determination of impact resistance by the free-falling dart method - Part 2: Instrumented puncture test Film et feuille de plastiques - D a decrease in the velocity of the striker of 20 % is acceptable. This ene
2、rgy requirement is met by falling-dart ma- chines if m 2 3W-dgHo where m is the falling mass, in kilograms; g is the acceleration due to gravity (9.81 m/s*); Ho is the height of fall, in metres; W is the total penetration energy, in joules, The falling-dart system used shall be capable of hold- ing
3、and releasing a weighted striker so that the striker falls constrained by a guide or guide(s). The fall shall be largely without friction or losses through windage. Any friction shall be taken into account in the calcu- lations. NOTES 4 In most cases, a weighted striker with a total mass m of 10 kg
4、is sufficient. 5 A velocity-measuring sensor should be placed close to the point of impact to eliminate errors due to friction be- tween the dart and the guides and to air resistance. With hydraulically driven high-speed tensile-testing machines, any deviation of the velocity during impact shall be
5、proved, e.g. by plotting the deformation-time curves and checking their slope. 5 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 22:08:09 MDTNo reproduction or networking permitt
6、ed without license from IHS -,-,- IS0 7765-2:1994(E) 0 IS0 5.1.2 Striker The preferred striker has a polished, hardened, hemispherical striking surface with a diameter D, = 20 mm f 0,2 mm. Alternatively, a striking sur- face of 10 mm f 0,l mm diameter may be used. The striker shall be constructed of
7、 steel. The load cell on the striker shall be mounted as close as possible to the tip to minimize the effect of extra- neous forces. An example is shown in figure4. The head of the striker may be powdered with talcum or lubricated with oil to reduce friction, provided that the interested parties agr
8、ee on this procedure and use identical material. In some cases, this can reduce the statistical scatter of the results. It should be borne in mind, however, that lubricating the striker may influ- ence the test results considerably. The natural frequency f, of the striker/load-cell as- sembly shall
9、be higher than the value specified in 5.2. 51.3 Clamping device The test-specimen clamping device shall have an in- side diameter D, of 40 mm + 2 mm. The clamping device shall be constructed in such a way that the circular specimen can be clamped flat and held securely during the test. Moreover, the
10、 clamping de- vice shall not cause any radial pre-stretching of the specimen greater than 0,Ol %. Both requirements can be met with manual or hydraulic clamping faces. Furthermore, placing a ring of fine emery paper on the specimen support has been found to be useful. Figure 5 shows a recommended cl
11、amping-device de- sign. 5.2 Instruments for measuring force, specimen deformation and specimen thickness The instruments for measuring force and deformation shall be capable of measuring the force and defor- mation to within 5 % of their maximum value. EXAMPLE If an electronic device has an accuracy
12、 of 0,4 % at full scale (FS) then, for a value of 20 % FS, the accuracy is 2 %. 52.1 Load cell Because of the very short duration of the impact, only electronic load cells with a high natural frequency can be used. The shortest time interval AfF,i” which the device shall be required to measure shall
13、 be 2 5/f, where f, is the natural frequency of the striker/load-cell assembly. For the bandwidth BT of the amplifier train (direct- current or carrier-frequency amplifier) with a lower bandwidth limit of 0 Hz, the following applies by analogy: .3). s x (v. - p/34 x t . . . NOTE 7 The pre-stretch ca
14、n be determined by means of a measuring microscope. The usual clamping device, how- ever, always fulfills the above condition. where m is the falling mass, in kilograms; 7.4 Impact-penetration test VQ is the impact velocity just before impact, in metres per second; The impact-penetration test is con
15、ducted with an im- f is the time to peak force or the time to pact velocity of 4,4 m/s f 0,2 m/s, corresponding to failure in seconds; 7 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/2
16、2/2007 22:08:09 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7765-2:1994(E) 0 IS0 P is the impulse imparted up to the time of occurrence of the peak force or up to the time of failure, in newton seconds (the area under the force-time diagram), given by the equation p
17、 = I F(r)dr . . . 0 (2) NOTE 9 The exact calculation of the deformation s re- quires double integration: s = - (1 /m-t) f PM and pF are calculated from equation (2) with an Upper integration limit Of tM and +, re- spectively. The mean, standard deviation and coefficient of vari- ation of the paramet
18、ers defined in clause 4 are cal- culated for each test series. NOTE 10 Instead of a curve, or concomitantly with it, the values of the peak force and the deformation at peak force can be recorded electronically. This also applies to the en- ergy to peak force and the total penetration energy after e
19、lectronic integration. 9 Precision The precision of this test method is not known be- cause interlaboratory data are not available. When interlaboratory data are obtained, a precision state- ment will be added with the next revision. 10 Test report The test report shall include the following informa
20、tion: a) a reference to this part of IS0 7765; cl d) e) f) 9) h) 0 j) k) I) n-4 n) 0) PI the date of measurement; the method of sampling and preparation of the test specimens; the average value of the measured thickness d of each test specimen; the test conditions and the conditioning procedure used
21、; details of the way in which the test specimens were clamped; the diameter D, of the striker and the nature of the striker surface; the number of test specimens used; the agreed point of failure, if used; the arithmetic mean, standard deviation and coef- ficient of variation of the - peak force FM,
22、 in newtons, - deformation at peak force sM, in metres, - energy to peak force WM, in joules, - total penetration energy W, in joules, and optionally the - failure force the force-deformation curve F(s) or force-time curve F(f); the natural frequency the appearance of the test specimens after the te
23、st (possibly with a representative test specimen as an illustrative example); the test velocity vo, if not 4,4 m/s; if a lubricant was used, the lubricant type, grade, quality and manufacturer. b) the type, identification mark, origin and date of receipt of the material tested, plus any other per- t
24、inent data concerning the material; 8 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 22:08:09 MDTNo reproduction or networking permitted without license from IHS -,-,- Q IS0 IS0
25、 7765-2:1994(E) Annex A (informative) General remarks In the testing of plastics, tough/brittle transitions are frequently encountered when the test temperature is lowered in stages from high values. At such tran- sitions, the failure energy, for example, rises from a lower to a higher level. These
26、transitions are caused by molecular relaxation processes which become ef- fective only above a certain temperature and which increase the absorption of the impact energy. Penetration time plays a role similar to that of tem- perature. If the penetration time is shortened, the transition temperature
27、is shifted to higher tempera- tures. The relationship between time and temperature is determined by the temperature dependence of molecular relaxation times, which is approximated by the Arrhenius equation: z = T,exp(E/kT) where z is the relaxation time or penetration time; T is the thermodynamic te
28、mperature or pos- ition of the tough/brittle transition on the temperature scale; E is the activation energy. If the test temperature is in a transition region, a wide scatter of results is frequently observed because the rupture of some specimens is brittle and the rupture of others is tough. In hi
29、gh-density polyethylene, for example, such a transition region lies in the tempera- ture range between - 105 “C and - 140 “C, depend- ing on the relative molecular mass and degree of crystallinity. The tough/brittle transition can be recognized in the puncture test by the appearance of the damaged s
30、pecimens, which reveals whether rupture occurred with or without deformation. The two types of rupture behaviour can also be distinguished by means of the force-deformation diagram. For tough/brittle plastics, the performance and evalu- ation of impact tests are subject to certain limitations, since
31、 the test specimens of a single test series must be assigned to two different parent populations, namely one exhibiting brittle-material behaviour and one exhibiting tough-material behaviour. In such cases, the means and variances are not statistically defined over the entire range of measurements.
32、Nevertheless, it is helpful to employ the mean and standard deviation calculated from the individual measurements to characterize the behaviour of the material. Where there is a sufficient number of measurements for both parent populations, the characteristic quan- tities can be calculated separatel
33、y for the brittle and the tough specimens. If necessary, the choice of as- signing measurements to one of the two parent pop- ulations should be decided by use of the statistical procedure normally employed for this purpose. Copyright International Organization for Standardization Provided by IHS un
34、der license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 22:08:09 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7765-2:1994(E) Annex B (informative) Bibliography l GRIMMINGER, H. A theory of the interaction typical for the instrum
35、ented puncture test by a drop mass. Z. Werkstofftechnik, 18 (1987), pp. 218-224. 10 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 22:08:09 MDTNo reproduction or networking perm
36、itted without license from IHS -,-,- IS0 7765-2:1994(E) Q IS0 ICS 83.140.00 Descriptors: plastics, films, sheets, plastic sheets, tests, Impact tests, punching tests, determination, shock resistance Price based on 10 pages Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 22:08:09 MDTNo reproduction or networking permitted without license from IHS -,-,-