Study On The Fracture Characteristics Of Ampoules In The Process Of Automatic Collection Of Bacteria And The Design Of The Opening System

In view of the problems in the process of automatic bacteria collection of ampoule test liquid,which is easy to produce glass debris and pollute the test liquid and the efficiency of manual opening ampoule is too low,this paper proposed to study the fracture characteristics of ampoule and automatic opening system,mainly calculated the stress intensity factor of ampoule,crack shape coefficient,and crack growth path and other fracture characteristics parameters.According to the calculation results,an intelligent and efficient ampoule opening linkage bacteria collection system was designed independently,including:（1）The important parameters characterizing brittle fracture of ampoules were analyzed in depth,and the calculation method of fracture characteristic parameters of non-penetrating three-dimensional crack stress intensity factor（SIF）coefficient K was proposed based on finite element method（FEM）,and the theoretical calculation and analysis of SIF was carried out by interaction integral method.The mechanical model and mesh model of ampoules with V-shaped notch were established.The results show that the crack ellipticity（a/c）and the relative crack depth（a/t）have significant effects on K_I,K_II and K_III of SIF.K_I played a dominant role and distributed symmetrically in the bilaterally symmetric position of the deepest crack point,while K_II and K_III were negligible.（2）Based on the theoretical calculation formula of the stress intensity factor（SIF）coefficient K,in order to calculate and verify the stress intensity factor,the crack shape coefficient F,which represents the characteristic parameters of the fracture,was modified.It is concluded that the shape coefficient curve and fitting polynomial after F_I modification are obtained,and that F_I decreases with the increase of ellipticity（a/c）and increases with the increase of relative depth（a/t）under the combined action of tensile stress and bending load.Compared with the literature,it is shown that the modified shape coefficient based on finite element method has higher accuracy,applicability and reliability for non-penetrating three-dimensional cracks.（3）Based on the brittle fracture characteristics of the ampoule,an experimental device was designed to test the dynamic fracture propagation process of the ampoule.The dynamic propagation process of macroscopic crack defects on the surface of the ampoule under external load was photographed by two high-speed cameras simultaneously,and the position of possible debris in the ampoule was recorded,and the key points of the crack propagation path were analyzed and discussed reasonably;At the same time,the dynamic crack growth of ampoule bottle under the same constraint conditions was simulated by finite element method,and the differences between experimental results and simulation results were compared and analyzed.The brittle crack growth characteristics of ampoules were obtained,and the possible crack branching and debris generation behaviors were deeply understood.（4）According to the fracture characteristics of the ampoule bottle,an intelligent and efficient ampoule opening linkage device is designed,its working principle and operation function are described,and according to the actual situation of automatic bacteria collection,the overall design scheme in line with the ampoule bottle opening is proposed,the key structural components are analyzed,and the feasibility of automatic ampoule opening operation is verified through experiments.In this paper,the study on the fracture characteristics of ampoule and the design of ampoules automatic opening system have important reference value and significance for the development and application of automatic bacterial collection instrument for ampoules.