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Q0 0 1708 tialld. Test additional groups of specimens as described above, beginning at one weight incre- ment below the lowest missile weight at which 100 qe failure occurred. Continue testing speci- men groups at increasingly lower missile weights employing the new uniform increment, until a result of 0 % failure is obtained (note that one or more of the percentage points found in 11.8 may be usable in this series employing a smaller weight increment). if the minimum fire results have now been obtained. testing is complete. If not. select a still smaller weight increment and repeat the above process, contin- uing in this manner until the minimum live results at uniform weight increments have been obtained. 12. Calculations 12.1 Determine impact failure weight, WF, by calculation as described in 12.2 or by graphing as described in 12.4. These two ap- proaches give essentially the sans_ results. 12.2 Calculate WF as follows: WF - Wt - 1JW(Sj 100 - I. 211 with percent failure on the probability scale and weight on the linear scale after having dimen- sioned the linear scale such that the resultant straight line defined by the points will have a slope between about 0.3 and 1.0. Draw the best fitting straight line through the points and read WF from the graph as that missile weight corresponding to the intersection of the straight line with the 50 % probability line. 12.5 Examples of the graphical method for determining WF are given in Fig. 3. For the three cases shown, values of WF determined by calculation by 12.2 are (1) 138. (_) I17, and (3) 92S. 13. Routine Inspection and Acceptance 13.1 For routine inspection of thin plastic film of a specified gage received from an approved supplier. it shall be satisfactory to accept lots on the basis of testing a minimum of ten specimens at a specified weight as stated in the relevant' material specification. l'rider this procedure. a result of no more than five failures shall be acceptable. where: u'F = impact failure weight, g. W" = uniform weight increment used. g. id', - lowest missile weight, g. according to the particular A W used, at which 100 t( failure occurred, and S - sum of the percentages of breaks at each missile weight (from a weight corresponding to no failures up to and including WO. 12.3 Example of calculation: G1sen: Missile weight. g Failure 91 0 106 10 121 20 136 60 151 too S. 190 ,W. 15 g. We.1518 Wr W, - I, W(S 100 - 1 211 = 15 1 - 1151190, 100 - 1, 211 - 151 - 115tt.i11 - 1308 12.4 .average successive pairs of missile weight -percent failure results, including 0 `, and 100 `%