Experimental Stress Analysis For Impact Problem And Monitoring Of Counterforce Frame During Shield Originating

The impact problems are important in engineering field, such as collision between components of mechanical devices, bird-impact to aircraft, stamping and forming, traumatic craniocerebral injury, etc. In recent years, impact problems have been paid more attentions by the researchers in the applications in military field, including the armor protections and underground engineering protections. In an impact problem, the process is mainly affected by material properties, shapes and sizes, impact modes of the impact objects, and etc. Consequently, it is difficult to describe an impact process by an exact theoretical model or through some numerical simulation methods only. Furthermore, the more factors to be considered, such as changes of contact area and the friction effects, the more complex the impact problem will become. Hitherto, only a few approximate theoretical solutions have been achieved, but most of practical problems exceed the application ranges of these theoretical solutions. Therefore, it is significant for the academic investigations and engineering applications to study and analyze the impact problems by new experimental methods.It is a representative impact problem to project a bar to an elastic solid. Some theoretical results have been published, but only a few experimental researches have been done with low impact velocities. There is still a lack of systematic experimental analysis work as yet. In this work, the impact problem of the long-bar projectile with elastic solid is studied by means of experiments. The effects of impact factors on stress waves, such as initial impact velocity, material properties of the projectiles and impacted solids, geometric characteristics, are analyzed based on a series of experiments. Moreover, it is also discussed that the possibility for identification of the material properties and geometric characteristics from experimental information of the impact stress waves.The other work of this thesis is the experimental analysis for the safety of the shield counterforce frame in the shield originating stage. Shield method is a kind of advanced tunnel construction method, which is widely used in the tunnel construction in our country. As one of the important component of the shield system, the shield counterforce frame are used to offer the crutch force for shield excavation in the begin stage of the tunnel construction, and its safety is related with the whole shield project. In this work, the strength of the shield counterforce frame under the design limit load is simulated by Abaqus6.5 first. Using numerical results, an optimization layout of the electrometric strain sensors is designed according to the feasibilities in the on-site conditions. Then, the real-time stresses in the frame are monitored during four months. Based on the achieved testing data, the stress distributions are analyzed and the function and efficacy of the shield counterforce frame in the shield construction are evaluated.