Dynamic Fracture Behavior Of H-k9l Glass With Prefabricated Defects

Owing to the drive of military and civil requirements, the dynamic fracture phenomenon of materials has been one of the most important fundamental projects for materialists, dynamicists, geologists, scientists, and so on. Its kernel issue is how to use mathematic language to describe the damage, nucleation and dynamic evolution process inside materials under dynamic loading. Whether the phenomenological or semiempirical fracture model based on macroscopic physical experimental results, or the damage evolution regulation based on the dynamic evolution process of the meso-micro structure, both of them lack universality to some extent. That's to say, these models are difficult to exactly estimate the fracture of material at the complicated stress environment. The reason is that the dynamic fracture of materials involves the reciprocal chiasma of multiple disciplines and factors, which needs to combine the experimental results of multiple scale and high time-spatial resolution, together with the physical modeling close to the meso-micro damage revolution process.In this thesis, some initial damages were prefabricated inside the H-K9L glass by internal laser etching. Combing with Doppler pin system (DPS) measurement technique with high time-spatial resolution, the evolution of initial damage inside the H-K9L glass under dynamic loading and its influence on the dynamic fracture property of material were presented respectively. The main results were as follows:(1) Research achievements about the dynamic fracture of materials at home and abroad were reviewed in detail, including dynamic fracture fracture rules, description methods of damage nucleation and evolution process, inner and outer factors affecting the dynamic fracture, and their corresponding experimental investigation methods. According to a mass of literatures, the meso-micro damage nucleation and real-time evolution process inside the material has been the focus and the difficult point of such a field, and the related experimental observation and theoretical modeling from the meso-micro scale have also been the hot issue in the past 20 years. Therefore, using transparent H-K9L glass with the prefabricated damages, combing with DPS measurement technique, the dynamic evolution process of the prefabricated defects under impact loading and effects of prefabricated defects on the fracture properties of the material were discussed respectively. So that some reference data can be given for making the fracture model related with the real-time evolution of material's meso-micro structure. (2) High time-spatial resolution DPS array measurement system with 16 channels, whose time and spatial resolution was 50 ps and 127μm respectively, was established based on one-point DPS. Using such a DPS array measurement system to conduct the planar impact tests, the shock compressed behavior of H-K9L glass with initial inner prefabricated defects was experimentally studied, and the particle velocity profile influenced by prefabricated meso-micro defects inside the material was obtained. The subtle difference in the velocity reached its maximum, together with the saltation velocity of lm/s caused by the defects, which were preliminarily considered to be resulted from the spread of defect shock compression wave. In the meantime, based on the experimental results, it was deduced that there was a compression breaking stress threshold value in the prefabricated damage region under the shock compression, and this stress was lower than the shock compression elastic limit of intact material (8 GPa). According to these experimental investigations, the limitation and immaturity of high time-spatial resolution DPS array measurement system were mentioned respectively, especially, the effective recording time was sacrificed on account of considering high time-spatial resolution. Consequently, further development should be made about this measurement technique.(3) Using the internal laser etching technique, a series of initial defects with the size ofΦ10 mm X 0.2-0.4 mm were prefabricated at the designed location inside the H-K9L glass sample. The meso-micro characterization shown that these defects caused by the laser etching interpenetrated with each other on the whole. Through the planar spalling tests combined with multipoint DPS measurement technique, the velocity profile at the free surface for the dynamic evolution process of the prefabricated defects inside the H-K9L glass sample was obtained. Besides, the spalling strength corresponding with the measurement location at the rear surface of K.-K9L glass sample was also gained, which showed that the spalling strength in the prefabricated defect region was lower than that of intact material,ⅰ. e.,4.2 GPa. Reasons were as follows: prefabricated defects inside the sample leaded to the dynamic stress concentration under the influence of shock wave, as a result, the stress distribution in the vicinity of defects was changed, further the displacement and velocity fields in the probing location were also changed, and so the variation in the velocity at free surface was generated. In addition, the effect of internal prefabricated defect size on damage nucleation radius at different shock pressure was also analyzed. Concretely, the time when the base material and that around the defects broke differed a little, i. e.,0.31μs or so. Furthermore, such a difference was closely related with the defect size and its influence radius. Finally, preliminary numerical simulation was also carried out, and the effect of the dynamic evolution process of inner prefabricated defects on the velocity at free surface was obtained, such as the spalling inoculation time plateau at defect points, the spread of cleft, etc. All these were hoped to support some reference data for physical modeling relative with the real-time evolution process of meso-micro defects. Above preliminary numerical simulation was sure to be also helpful to understand experimental phenomena deeply. Is was suggested the more factors including the defect distribution in tensile area inside the sample, the variation of tensile pulse with time, the distance between defects, the dynamic spread velocity of defect, and so on, should be considered in the further numerical simulation.(4) Considering the shock transparent characteristics of H-K9L glass, and combing the DPS measurement results of particle velocity profile at collision interface, the dynamic refractive index revision relation of H-K9L glass was studied within its tensile limitation. Results were shown as below:the dynamic refractive index of H-K.9L glass was linearly related with its density within the shock pressure of 8 GPa, thus H-K9L can be used as a substitute material for optical transparent window at low pressure shock.