Research Of Mechanical Behavior And Impact-Induced Reaction Mechanism For Reactive Materials

With the development of military science and technology,threats from the air is diverse,the air-defense becomes more and more important and its success is the decisive factor in the outcome of modern high-tech warfare.Since the traditional air-defense warhead inert fragment only rely on a kinetic energy to attack targets,it has been unable to meet the requirements in high efficiency damage technology and military application.Therefore,people actively developed a kind of novel material,named reactive material.They will crush,self-react or combust violently with air to rapidly generate high amounts of energy when subjected to intensive impact loading,leading to significant additional damage capacity.The impact response and energy release behavior of the reactive materials are closely related to their mechanical properties.Some metal/polymer and intermetallics reactive materials were prepared,and their impact mechanical performances and mechanism of impact-initiation has been investigated in this dissertation.The research works are as follows:（1）Active metal Al,Zr and ZrH₂ were used as raw materials for preparing metal/polymer（Zr/PTFE,Al/W/PTFE）and intermetallics（W/Zr）reactive materials.The influence laws of sintering method,sintering temperature,molding pressure and sintering time on the mechanical performances of metal/polymer were investigated,and the optimizing process method was developed.（2）The quasi-static and dynamic compressive performances of Zr/PTFE（room temperature³00℃）and Al/W/PTFE reactive material were studied by using MTS universal material machine and modified split Hopkinson pressure bar（SHPB）with pneumatically synchronous.Based on the obtained experimental data,an elastic-viscoplastic constitutive model that considered the effect of strain rate hardening,temperature softening and the influence of W content was established,which could accurately describe the metal/polymer reactive material dynamic compressive mechanical behavior before weakening.The results show that Al/W/PTFE reaction present detonation mode under impact loading,while Zr/PTFE no reaction occurred in the same experimental conditions.The addition of W significantly improved the compressive strength and decreased the reaction time of Al/W/PTFE;however,the initiation time almost unchanged.The strain rate threshold of impact-initiation of Al/W/PTFE was obtained by drop height method（usually used to characterize the sensitivity of the explosive）,and the results show that with the increase of W content,the strain rate threshold increase.（3）The quasi-static compression experiment of W/Zr material shows that it is a kind of high-strength brittle material,and a constant strain rate loading was performed in SHPB by employing the pulse shaping technique.The results show that the stress-strain curve of W/Zr presents linear relation,and the failure strain and compressive strength have distinguishable strain rate effect,while the elastic modulus is not so sensitive to the strain rate.The mechanical properties of W/Zr-1（Zr/wt%:W/wt%=66:34）were better than those of the other two groups（W/Zr-2（ZrH2/wt%:W/wt%=66:34）,W/Zr-3（Zr/wt%:W/wt%=43:57））.The upper limit of achievable constant strain rate is 1500 s^-1 and the compressive strength is 2780 MPa,which is analyzed based onthe variation of the compressive strength with strain rate.W/Zr presented combustion reaction under impact loading,and the fragments can be divided into small,medium,and large fragments with their reactions labeled as“fire ball,”“spark,”and“no react”respectively.The intensity and duration of the reaction are affected by the content of the active ingredient（ratio）,the degree of fragmentation（impact rate or strain rate）,and the degree of dispersion（size effect）.Normal penetration of W/Zr fragments into a steel target was performed by ballistic gun experiment,showing that the initial time of impact-induced reaction of the specimen decreases with the increase of the impact velocity.（4）The fractural surfaces of the compression tested specimens were observed using a scanning electron microscope（SEM）.The results show that the PTFE matrix fracture and interfacial debonding were demonstrative of the main compressive failure mode of metal/polymer,while the fracture mode of W/Zr was a mix of transgranular,intergranular and a small quantity of dimple fractures.Comparative observation study with W-Zr mixed powder combustion as contrast group,the Zr,ZrC and ZrC_0.32H_1.2 phases were determined as the active components in the reaction with air for W/Zr fragments,and the product is ZrO₂.Based on the theoretical analysis of the fracture toughness and crush modes of W/Zr,we established that the rising temperature at the crack tip could ignite the combustible cloud formed by the fine fragments as the simple impact-induced reaction mechanism.