ANALYSIS OF DOUBLE BASE PROPELLANTS SERVICE LIFE RELATING TO MECHANICAL PROPERTIES IN EXTREME CLIMATIC CONDITIONS

Transcription

1 FACULTY OF MILITARY TECHNOLOGIES UNIVERSITY OF DEFENCE BRNO Czech Republic Armed Forces INSENSITIVE MUNITIONS & ENERGETIC MATERIALS TECHNOLOGY SYMPOSIUM OCTOBER 7-10, 2013 SAN DIEGO, CA, USA ANALYSIS OF DOUBLE BASE PROPELLANTS SERVICE LIFE RELATING TO MECHANICAL PROPERTIES IN EXTREME CLIMATIC CONDITIONS Authors: Fratišek KREJČÍŘ Pavel KONEČNÝ

2 INTRODUCTION Goals of this work were to ivestigate chages i double base (DB) propellats over ageig ad to determie sigificace of itrocellulose (NC) chai decompositio for evaluatio of DB propellats service life. Reasos for this research: 1. DB propellats are log term stored. 2. DB propellats are exposed to various temperature coditios whe stored i field storages (e.g. i extreme climate zoes). 3. Polymer NC is as a bider of DB is liable to relatively fast decompositio. 4. DB propellats markedly chage its mechaical properties over operatioal temperature rage.

3 USED METHODS Artificial ageig simulatio of time-temperature loadig durig storage. Size-exclusio chromatography (SEC) - determiatio of itrocellulose polymer chai decompositio characteristics. Uiaxial compressio ad tesile tests - determiatio of chages of basic mechaical properties. Dyamic mechaical aalyses determiatio of trasitio temperatures ad its shift. Reactio kietics aalyses determiatio of predictive decompositio models.

4 TESTED DB PROPELLANTS Type 1 stadard DB made by Explosia a.s. (Pardubice, CZE). Type 2 with alterative less toxic auxiliary plasticizer. NC properties 12% itroge, wood cellulose. Extruded grais 30 mm i diameter, 300 mm log. Propellat Type 1 Type 2 Nitrocellulose 55.7 % 55.7 % Nitroglycerie 28.3 % 26.0 % Diitrotoluee 8.5 % Alterative plasticizer 11.5 % Ethyl cetralite 2,9 % 2.9 % Catalyzers 4,0 % 4.0 %

5 ARTIFICIAL AGEING Coditios set with respect to AOP-48. Ageig at two temperatures: 65 C ad 80 C. Grais loaded i polymer coated alumium bags. Ageig periods accordigly to Arrheius equatio (ad kow kietic parameters of -NO 2 group decompositio): Period of storage at 25 C [years] Correspodig period of artificial ageig at 65 C 80 C [days] [days]

6 SEC CHROMATOGRAMS

7 AVERAGE MOLAR MASS OF NITROCELLULOSE

8 MODEL OF NITROCELLULOSE DECOMPOSITION Kietic model of chai scissio (solve rate costat from molar masses) M m ( t, T) i m M (0) k M ( T) t i Arrheius equatio (solve activatio eergy from rate costat) lk Mi ( T ) i l A Ea RT i Established kietic parameters of decompositio i temperature rage 65 C to 80 C: DB propellat type 1 DB propellat type 2 Activatio eergy E a [kj.mol -1 ] Frequecy factor A [-] 1, ,

9 Compressio at break CHANGES IN MECHANICAL CHARACTERISTICS Uiaxial tesile ad compressio tests: chage of m measured at 21 C (aged for days at 65 C) i compressio -4 % ad -6 %, i tesio -7 % ad +13 % m [%] DB propellat type 1 DB propellat type Equivalet period of storage at 25 C [years]

10 Compressive stregth m [MPa] CHANGES IN MECHANICAL CHARACTERISTICS Decrease of m measured at 21 C (aged for days at 65 C) i compressio by 15 % ad 18 %, i tesio by 16 % ad 9 % DB propellat type 1 DB propellat type Equivalet period of storage at 25 C [years]

11 Storage modulus, loss modulus [MPa] Loss factor taδ [-] DYNAMIC MECHANICAL ANALYSES T a lowers durig ageig 46 C 42 C for both DB. T b does ot show ay tred -32 C, -37 C for DB type 1, 2. 1, Glassy state T b Viscoelastic state Storage modulus Loss modulus Loss factor Viscous state T a Temperature [ C]

12 [kg.mol -1 ] MODEL OF NITROCELLULOSE DECOMPOSITION Predictive model of decompositio NC for DB type 2 stored at costat temperatures 70 Number average molar mass M Predictio model of ageig at 50 C Predictio model of ageig at 60 C Predictio model of ageig at 65 C Predictio model of ageig at 70 C Predictio model of ageig at 80 C Measured values after ageig at 65 C Measured values after ageig at 80 C Degree of decompositio 0,8.M M (0) Degree of decompositio 0,6.M M (0) Degree of decompositio 0,4.M M (0) Period of ageig [days]

13 MODELING OF FIELD STORAGE CONDITIONS STANAG 2895 determies climatic categories ad timetemperature loadigs. Temperature at storage Period of temperature loadig durig oe year [ C] [hours] 71 5, , , , ,7 Data were used to establish predictive model based o Arrheius equatio i form: M ( t, T ) M 0 i M ( t i1, T i1 ) M ( t m, T i1 i1 ) m A i exp E ai RT i t i

14 Number average molar mass M [kg.mol -1 ] NC CHAIN DECOMPOSITION IN FIELD STORAGE Service life related to NC chai decompositio: 9,5 years ad 11,5 years for DB type 1 ad type 2 i climate category A1 (limitig coditio 0,4 M (0)) Model for climate category A1 Model for climate category A ,8.M (0) 0,6.M (0) 0,4.M (0) Period of storage [years]

15 CONCLUSION Performed artificial ageig of two types of DB propellat at 65 C durig days leads to decrease of values of chemical ad mechaical properties: M by 34 % ad 33 % m at 21 C i compressio by 15 % ad 18 % m at 21 C i compressio by 4 % ad 6 % T a by 4 C (46 C -> 42 C) E a of NC chai scissio at temperature rage 65 C to 80 C were established to be 85 kj.mol -1 ad 105 kj.mol -1.

16 CONCLUSION Described processes ad chages lead to: DB propellats ted to get markedly softer at temperatures ear upper operatioal limit (~ 50 C) after ageig. Service life of DB propellats related to NC decompositio ad mechaical characteristics chages could determie overall service life. Service life of DB related to M, whe stored i field coditios i extreme climates, could be limited to ~10 years (accepted coditio of limitig decompositio 0,4.M (0) ).

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