Research On Creep-damage Performance Of Deep-sea Manned Submersible PMMA Viewport

Currently,China has developed the “Jiaolong” deep sea submersible with a largest depth capacity of 7000 m.The MWE(Manned Work Enclosure)plays an important role in the whole struction,and it mainly consists of a titanium alloy spherical pressure shell and several PMMA viewports.Under the creep load,the failure mechanism of PMMA includes void growth,crazing,and macromolecular rupture,and these mechanism reveals as damage macroscopically.Consequently,it is desperately needed to develop an updated and mature basic theoretic method,combined with numerical ananlysis and experimental research,to illuminate the creep-damage mechanism of the viewports.The creep-damage theory can be used to support the struction improvement and standard establishment.The main content includes three parts.First,based on the model of triple elements of ideal spring and dashpot,a finite element program has been developed and realized by ABAQUS-UMAT.Combined with the creep experiment and numerical analysis,parameters can be identified.At last,the program has been applied on the creep analysis of frustum and sector viewports to analyze the difference between the two types of viewports,and the influence of several factors such as depth.Second,after literature researching,it is found that most creep model and numerical analysis of PMMA and viewport didn’ t take damage into consideration.Based on the Burgers model,a creep/damage model and finite element algorithm has been developed with accelerating creep taken into consideration.The algorithm is realized by ABAQUS-UMAT.Combined with the creep experiment and numerical analysis,parameters can be identified.Theoretical model and numerical method are applied in the creep analysis of both frustum and sector viewport.Influence of several factors has been studied including depth,friction coefficient between viewport and seat and the critical damage factor of PMMA.The results have been compared with that of the three elements model.Third,in mechanical seal structure,the most used material for O-ring is nitrile butadiene rubber.Considering the friction among seat,viewport and O-ring,finite element method is employed to study the hyperelastic deformation of the O-ring under the depth of 100-500 m,and to study the influence of several factors on the sealability of the O-ring including depression ratio,depth,and hardness of rubber.