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In this study, we propose an efficient computation method to estimate the critical ricochet angle (CRA) for oblique penetration into concrete targets which is based on the spherical cavity-expansion theory. During penetrating event, the resistance force on the projectile nose is approximated by semi-empirical function from the spherical cavity-expansion theory and projectile motion of oblique penetration is predicted to verify the proposed numerical method with the aid of finite differential approach. In order to enhance the accuracy of projectile motion, the empirical constants of the semi-empirical function are obtained with respect to the oblique angle by conducting finite element analyses of the oblique penetration. CRA is then obtained by predicting the projectile motion at the various oblique angles and verified with results of finite element analysis. Our work presents that the reliable CRA can be estimated efficiently by employing a series of the numerical simulations. We believe that our proposed numerical method will provide a useful analysis platform for designing penetrator warhead which hits the target at an oblique impact angles.

The development and use of composite materials for several manufacturing industries require reliable adhesives and joints. However, the use of composite joints decreases the strength in the z-direction where composite laminates have lower strength. In this way, several methods have been proposed to reinforce CFRP laminates in the z-direction. Based on previous studies, a new technology in the through-thickness reinforcement for composite laminates called I-Fiber stitching process has been introduced, and the development continues under investigation. In the present research, the experimental results obtained from a unit-cell specimen under pull-out load with three different thicknesses and stitched with a single yarn using the I-Fiber stitching process were analyzed using the finite element method. Microscope image analysis was performed to obtain the best approach of the numerical model. Stress distribution of the I-Fiber and interface analysis using cohesive elements were achieved to understand the performance of the single stitch for each unit-cell case. Finally, a failure load comparison was performed between the experiments and the numerical analysis. The results showed the complexity of the I-Fiber shape under different laminate thicknesses and how the fiber volume of the reinforcement can vary along the thickness using the same stitching yarn for all cases.

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