PBX Fracture Behavior Based On Digital Image Correlation Method

Polymer-bonded explosive (PBX) is a kind of high-energy mixed explosives that consist of one or more elemental powder and polymer binder, and PBX plays an important role in the weapon systems. The mechanical behavior of PBX material may directly affect the powder charge safety and reliability. As fracture failure occupy an important component in PBX failure, the study of fracture has an important practical significance in PBX mechanical behavior research.This work aimed to understand the fracture characteristics of PBX and to establish a practical experimental method for the determination of the fracture toughness. Both digital image correlation method (DICM) and high-speed photography technology were utilized in the research. Experiments on a TATB based PBX were conducted, to study the fracture behavior with strain concentration and determine the fracture toughness. Semi-circular bend (SCB) specimens were applied to measure the quasi-static fracture toughness, and preliminary effort was devoted for the determination of dynamic initiation fracture toughness.A plate-with-hole specimen was designed to study the fracture behavior of the specimen under quasi-static tension load. Mode I brittle fracture took place at the center hole, and the strain field distribution and evolution was analyzed with the aid of DICM. The study shows that the material inhomogeneity and the microscopic defects are the critical reasons for the imperfect strain distribution. The defects near the hole may remarkably deteriorate the strength of the structure, while the strain concentration around the hole remains the critical reason of specimen failure.Quasi-static fracture toughness of the material was determined by semi-circular bend experiments. The crack initiated and propagated then specimen broke into two pieces, this process is so fast that can barely obtain any details without high speed photography. DICM analysis results indicate that the horizontal displacement field is antisymmetric about the central crack, and a distinct layered distribution phenomenon is observed in the vertical direction. The full-field strain analysis consists with the observed crack propagation form, and confirms the failure took place only on the propagation path. The measured fracture toughness is about 0.5 MPa.m1/2, and further study is needed to reach a more accurate result.In the preliminary study of dynamic initiation fracture toughness Kid determination, the ISRM suggest method that measure the dynamic fracture toughness using a notched semi-circular bend specimen with SHPB apparatus. The pulse-shaper technique was used to generalize the dynamic force balance of the specimen. The high-speed photography was applied to survey the failure process. The dynamic fracture toughness was calculated using the formulas proposed in the suggested method, the relation between Kid and loading rate was analyzed roughly.