A b s t r a c t -An e x p e r i m e n t a l a r m a t u r e p r o g r a m at t h e US Army Armament R e s e a r c h a n d D e v e l o p m e n t E n g i n e e r i ng Center is in-place and on-going.The goal of the program is to design and develop a 50 mm solid trailing a r m armature that is capable of operating efficiently in the 800 kA to 1,500 kA c u r r e n t range.An iterative design a n d test methodology was created to optimize the a r m a t u r e electrical e f f i c i e n c y .A six p a r t test p l a n investigates t h e effect of a r m a t u r e compliance, c u r r e n t pulse s h a p e , c o n t a c t size a n d c o n t a c t material on the magnitude of the muzzle voltage a n d the time of transition. The a r m a t u r e design a n d test plan seek to v a l i d a t e a c a n d i d a t e e l e c t r i c a l c o n t a c t wear model a n d establish t h e required r e l a t i o n s h i p b e t w e e n c o m p l i a n c e a n d optimum contact normal force for a given launch current.Currently, the affect of a r m a t u r e compliance a n d c u r r e n t pulse s h a p e o n the a r m a t u r e performance a r e being investigated a t velocities in excess of 2.0 km/sec. As a n outcome of the test program Armature Quality Factor has been defined a s a new figure of m e r i t for a r m a t u r e performance.T h e test results a n d analysis of t h e muzzle voltage a r e p r e s e n t e d .
In this work we further develop a model to predict hydrogen-assisted fatigue crack growth in steel pipelines and pressure vessels. This model is implemented by finite element code, which uses an elastic-plastic constitutive model in conjunction with a hydrogen diffusion model to predict the deformation and concentration of hydrogen around a fatigue crack tip. The hydrogen concentration around the crack tip is used to inform our fatigue crack growth model and account for the effect of hydrogen embrittlement. We first use our model to predict the fatigue crack growth of X100 pipeline steel at different levels of applied hydrogen pressure. The simulated results are within a factor of ± 2 of the experimental X100 results.
In this work, we applied a finite element model to predict the cyclic lifetime of 4130 steel cylinders under the influence of hydrogen. This example is used to demonstrate the efficacy of a fatigue crack growth (FCG) model we have developed. The model was designed to be robust and incorporate features of stress-assisted hydrogen diffusion, large-scale plasticity, hydrogen gas pressure, loading frequency, and effects of microstructure. The model was calibrated to the 4130 steel material by use of tensile tests and experimental FCG results of a compact tension specimen. We then used the model to predict the hydrogenassisted FCG rate and cycle life of a pressurized cylinder with a deliberate initial thumbnail crack. The results showed good correlation to the cyclic lifetime results of 4130 pressurized cylinders found in the literature.
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