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gSlh D 1709 3.2 The results obtained by Methods A and B are great!% influenced by the quality of film under test. The confidence limits of data ob- tained be this procedure can. therefore. vary significantly. depending on the sample quality. uniformite of film gage. die marks. contami- nants. etc. (see Section 15). 3.3 %1 ethods .A and B have been found useful for specification purposes. Correlation between test results and field performance can usually be established. 3.4 The impact resistance of polyethylene film. while partly dependent on thickness. has no simple correlation with sample thickness. Hence. impact values cannot be normalized over a range of thickness %%ithout producing misleading data as to the actcal impact resist- ance of the material. Data tram these methods are comparable onl% for spect,nens that vary by no more than =2> cc frog the nominal or average thickness of the specimens tested. 4. Definitions 4.1 impact failure weight—that missile weight. estimated statistically. at which 50 cc of the specimens would fail in the specified test. 4.2 missile weight—the weight (mass) of the dart plus the total value of incremental weights attached plus the locking collar. 5. Apparatus 5.1 The apparatus shall be constructed es- sentiall as show n in Fig. 1. using the following components common to both methods: 5.1.1 Specimen Clamp—A two-piece annu- lar snecimen clamp having an inside diameter of 127 mm (5 in.) and conforming to the following requirements: - 5.1.1.1 The lower or stationer% half of the clamp shall he mounted rigidly so that the plane othe specimen is horiiontal. The upper or movahlc part of the clamp shall he designed to maintain po,.itivc and plane contact with th.: h,wer part of the clamp %%hen to position. The cIan.!+, •hall he provided with.suitahlc means k1t ntaintatmng ,ullicient conte, t io hold ;ne film sample 6rm1% ,n place during +he try:• Pneumaticalh operated clamps have leen .ucceN,lull% Cmpio%cd. 5.1.1.: Ruhher-hnc gaskets ma% he affixed to the specimen contact surfaces of both clamps 8> to provide a cushion which minimizes thickness variation effects. Rubber gasketing 3.1 mm (0.125 in.) thick. of 50 to 60 Shore A durometer hardness. 127 mm (5 in.) in inside diameter and 152 mm (6 in.) in outside diameter has been found satisfactory for this purpose. 5.1.1.4 Slippage of films greater than 0.10 mm (0.004 in.) in thickness ma} be minimized or eliminated by securing crocus cloth or 50D garnet abrasive paper to the gaskets with double sensitive tape so that the abrasive sur- face is in direct contact with the film. There should be sufficient clamping force to eliminate detectable slippage. Other means of reducing slippage such as additional clamping devices or positive clamping surfaces mar be used pro- vided that the film is not weakened at the inside i wall of the specimen clamps and that the effective diameter of 127 mm (5 in.) of the film ' is not changed. 5.1.2 Electromagnet, capable of supporting a 2 -kg weight for use in supporting and releab- ing the dart assembly. It shall be equipped with a centering device to ensure reproducible dror and a suitable source of electric power which , may be interrupted to energize and de -energize the electromagnet. Alternativel%. the use ul air -operated or other mechanical release mech' anisms is permitted. provided uniform ani reproducible release is obtained. 5.1.3 Positioning Device -0 cans shall he provided for positioning the dart at a drof height of 0.660 m (26.0 in.) (Method A) an° 1.524 m (60 in.) ( Method B) from the impinging surface of the dart head to the surface of the test specimen. The dart shall he positioned le" ttcally above the center of the test specimen - 5. L4 pecimen.5.1.4 Micrometer. accurate to x0.00:5 ear (=0,0001 in.) in the range from 0.00:5 tnr (11.0001 in.) to 0.254 mm (0.010 in.) for meP ins specimen thickness (see 'Methods D 5.1.5 Cushioning and Shielding Devices- n protect personnel and to avoid damaging the impinging surface of the dart. . 5.1.6 Collar with inside diameter of appro% mate! 7 mm 10.2g in.► and with set screw t` securing collar to dart shaft. 5 = Darts for 'Methods .A and B shall h� hemispherical heads. Cath --fitted w tth a ^ (0.25 in.) diameter shalt at least 115 mitt t� in.) long to accommudate removable incren,cr