INFLUENCE OF THE HTPB/IDP-RATIO ON THE MECHANICAL PROPERTIES OF THE CAST CURED HMX-EXPLOSIVE PBXN-110

摘要

In so-called PBX explosives, explosive crystals are bonded into a polymer matrix. It is important which such systems to understand the factors which affect their mechanical properties: there is usually a conflict between the various requirements and an optimum has to be sought. For the use in ammunitions which are fired with a high acceleration, much importance is attached to a higher mechanical strength, which forcibly resulted in lower strain values. For other applications a high strain is desired: the objective of the present investigations was to determine the extent to which the properties can be modified with a modification of the value of the HTPB/IDP-Ratio. Otherwise the MIL-DTL-82901A for PBXN-110 demands a.o. that the HTPB/IDP ratio must be between 0.95 and 1.05. It soon became evident that the specified combination of minimum mechanical strength, minimum strain and minimum hardness cannot be achieved, not even with the highest allowed HTPB/IDP ratio of 1.05: the mechanical strength and the hardness are significantly too low. But the strain is very high. The minimum mechanical strength and minimum hardness per MIL-DTL-82901A can only be reached from an HTPB/ IDP ratio of approx. 1.13. High strength with appreciable strain values can be attained with a ratio of approx. 1.20. By means of an unsophisticated hardness measurement (Shore A) it is possible to assess whether or not the minimum mechanical strength will be reached. With the prevailing production parameters the hardness must be above approx. 15 Shore A, but it must not exceed approx. 28 Shore A. It is then guaranteed that the minimum values are maintained for both strain and mechanical strength. Interestingly enough there exist quite good relations between viscosity of the unpolymerized explosive and the mechanical properties of the polymerized explosive. By these one could estimate already during casting whether or not the desired hardness range, in substitution of mechanical strength and strain, will be maintained with our production parameters.