The roztr\u017een\u00ed kalhot<\/strong> Metoda definovan\u00e1 v norm\u011b ASTM D1938 m\u011b\u0159\u00ed s\u00edlu pot\u0159ebnou k \u0161\u00ed\u0159en\u00ed jednoho trhnut\u00ed p\u0159es vzorek plastov\u00e9 f\u00f3lie. Vzorek je p\u0159ipraven se st\u0159edovou \u0161t\u011brbinou, kter\u00e1 tvo\u0159\u00ed dv\u011b \"nohavice\" p\u0159ipom\u00ednaj\u00edc\u00ed kalhoty. Ka\u017ed\u00e1 nohavice se upne do tahov\u00e9ho zku\u0161ebn\u00edho stroje a \u00fachyty se odd\u011bluj\u00ed konstantn\u00ed rychlost\u00ed.<\/p>\n\n\n\n B\u011bhem testu p\u0159\u00edstroj zaznamen\u00e1v\u00e1 s\u00edlu pot\u0159ebnou k dal\u0161\u00edmu p\u0159etr\u017een\u00ed f\u00f3lie na definovanou vzd\u00e1lenost. Tato s\u00edla odr\u00e1\u017e\u00ed vlastnosti materi\u00e1lu odolnost proti \u0161\u00ed\u0159en\u00ed trhlin<\/strong>, kter\u00e1 se li\u0161\u00ed od pevnosti v tahu nebo odolnosti proti prop\u00edchnut\u00ed. V praxi m\u016f\u017ee m\u00edt f\u00f3lie s vysokou pevnost\u00ed v tahu p\u0159esto \u0161patn\u00e9 v\u00fdsledky p\u0159i zkou\u0161ce trh\u00e1n\u00ed plastov\u00e9 f\u00f3lie, pokud se trh\u00e1n\u00ed po zah\u00e1jen\u00ed snadno \u0161\u00ed\u0159\u00ed.<\/p>\n\n\n\n U plastov\u00fdch f\u00f3li\u00ed m\u00e1 odolnost proti roztr\u017een\u00ed vliv na v\u00fdkon i bezpe\u010dnost. Obalov\u00e9 f\u00f3lie pro potraviny, l\u00e9\u010diva a zdravotnick\u00e9 prost\u0159edky mus\u00ed b\u00fdt odoln\u00e9 proti roztr\u017een\u00ed p\u0159i uzav\u00edr\u00e1n\u00ed, manipulaci a distribuci. Podobn\u00e9 po\u017eadavky jsou kladeny na zem\u011bd\u011blsk\u00e9 f\u00f3lie, pr\u016fmyslov\u00e9 f\u00f3lie a ochrann\u00e9 f\u00f3lie.<\/p>\n\n\n\n The metoda zkou\u0161ky trh\u00e1n\u00edm<\/strong> popsan\u00e9 v norm\u011b ASTM D1938 pom\u00e1h\u00e1 v\u00fdrobc\u016fm:<\/p>\n\n\n\n Proto\u017ee se metoda zam\u011b\u0159uje na odolnost proti \u0161\u00ed\u0159en\u00ed trhlin, poskytuje \u00fadaje, kter\u00e9 dob\u0159e koreluj\u00ed s mnoha re\u00e1ln\u00fdmi zp\u016fsoby poruch.<\/p>\n\n\n\n Norma ASTM D1938 stanov\u00ed p\u0159\u00edsn\u00e9 po\u017eadavky na rozm\u011bry vzork\u016f, rovnom\u011brnost tlou\u0161\u0165ky a \u00fapravu. Spr\u00e1vn\u00e1 p\u0159\u00edprava zaji\u0161\u0165uje, \u017ee v\u00fdsledky odr\u00e1\u017eej\u00ed sp\u00ed\u0161e chov\u00e1n\u00ed materi\u00e1lu ne\u017e variabilitu zkou\u0161ky. Vzorky se obvykle zkou\u0161ej\u00ed ve sm\u011bru stroje i v p\u0159\u00ed\u010dn\u00e9m sm\u011bru, aby se zachytily anizotropn\u00ed vlastnosti b\u011b\u017en\u00e9 u vytla\u010dovan\u00fdch f\u00f3li\u00ed.<\/p>\n\n\n\n D\u016fle\u017eitou roli pro konzistenci v\u00fdsledk\u016f hraje kondicionov\u00e1n\u00ed p\u0159i \u0159\u00edzen\u00e9 teplot\u011b a vlhkosti. Plastov\u00e9 f\u00f3lie \u010dasto vykazuj\u00ed citlivost na podm\u00ednky prost\u0159ed\u00ed a standardizovan\u00e9 kondicionov\u00e1n\u00ed zlep\u0161uje opakovatelnost v r\u016fzn\u00fdch laborato\u0159\u00edch.<\/p>\n\n\n\n V\u00fdsledek zkou\u0161ky podle normy ASTM D1938 se obvykle vyjad\u0159uje jako pr\u016fm\u011brn\u00e1 s\u00edla \u0161\u00ed\u0159en\u00ed trhliny. U m\u00e9n\u011b rozta\u017eiteln\u00fdch f\u00f3li\u00ed z\u016fst\u00e1v\u00e1 s\u00edla b\u011bhem trh\u00e1n\u00ed relativn\u011b stabiln\u00ed. Vysoce rozta\u017eiteln\u00e9 f\u00f3lie mohou vykazovat kol\u00edsav\u00e9 hodnoty s\u00edly, co\u017e vy\u017eaduje pe\u010dlivou interpretaci k\u0159ivky zat\u00ed\u017een\u00ed-rozta\u017een\u00ed.<\/p>\n\n\n\n P\u0159i porovn\u00e1v\u00e1n\u00ed materi\u00e1l\u016f je t\u0159eba br\u00e1t v \u00favahu tlou\u0161\u0165ku, sm\u011br a strukturu vrstvy. \u00dadaje normy ASTM D1938 \u00fa\u010dinn\u011b \u0159ad\u00ed materi\u00e1ly do podobn\u00fdch skupin, i kdy\u017e samy o sob\u011b ne v\u017edy p\u0159edpov\u00eddaj\u00ed kone\u010dn\u00e9 vlastnosti p\u0159i kone\u010dn\u00e9m pou\u017eit\u00ed.<\/p>\n\n\n\n Existuje n\u011bkolik metod slzn\u00fdch test\u016f, v\u010detn\u011b Elmendorfova testu a testu slzen\u00ed jazykem. Norma ASTM D1938 se li\u0161\u00ed t\u00edm, \u017ee klade d\u016fraz na odolnost proti \u0161\u00ed\u0159en\u00ed trhlin<\/strong> p\u0159i kontrolovan\u00e9m odd\u011blen\u00ed \u00fachopu, nikoliv p\u0159i m\u011b\u0159en\u00ed n\u00e1razov\u00e9 nebo vrcholov\u00e9 s\u00edly. U plastov\u00fdch f\u00f3li\u00ed a tenk\u00fdch f\u00f3li\u00ed poskytuje tento p\u0159\u00edstup relevantn\u011bj\u0161\u00ed \u00fadaje, zejm\u00e9na pokud u f\u00f3li\u00ed doch\u00e1z\u00ed k pomal\u00e9mu, kontinu\u00e1ln\u00edmu trh\u00e1n\u00ed v provozu.<\/p>\n\n\n\n V\u00fdb\u011br spr\u00e1vn\u00e9 metody zkou\u0161ky trh\u00e1n\u00ed zajist\u00ed smyslupln\u00e9 v\u00fdsledky a zabr\u00e1n\u00ed nespr\u00e1vn\u00e9 interpretaci p\u0159i hodnocen\u00ed kvality.<\/p>\n\n\n\nPro\u010d z\u00e1le\u017e\u00ed na odolnosti proti \u0161\u00ed\u0159en\u00ed trhlin?<\/h3>\n\n\n\n
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P\u0159\u00edprava vzork\u016f a podm\u00ednky zkou\u0161ek<\/h2>\n\n\n\n
Interpretace v\u00fdsledk\u016f zkou\u0161ky trh\u00e1n\u00ed plastov\u00e9 f\u00f3lie<\/h2>\n\n\n\n
ASTM D1938 v porovn\u00e1n\u00ed s jin\u00fdmi metodami zkou\u0161ek trh\u00e1n\u00ed<\/h2>\n\n\n\n
Testovac\u00ed \u0159e\u0161en\u00ed od Cell Instruments<\/h2>\n\n\n\n