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While deposited thin film coatings can help enhance surface characteristics such as hardness and friction, their effective incorporation in product design is restricted by the limited understanding of their mechanical behavior. To address this, an approach combining micro-indentation and meso/micro-scale simulations was proposed. In this approach, micro-indentation testing was conducted on both the coating and the substrate. A meso-scale uniaxial compression finite element model was developed to obtain a material model of the coating. This material model was incorporated within an axisymmetric micro-scale model of the coating to simulate the indentation. The proposed approach was applied to a Ti/SiC metal matrix nanocomposite (MMNC) coating, with a 5% weight of SiC nanoparticles deposited over a Ti-6Al-4V substrate using selective laser melting (SLM). Micro-indentation testing was conducted on both the Ti/SiC MMNC coating and the Ti-6Al-4V substrate. The results of the meso-scale finite element indicated that the MMNC coating can be represented using a bi-linear elastic-plastic material model, which was incorporated within an axisymmetric micro-scale model. Comparison of the experimental and micro-scale model results indicated that the proposed approach was effective in capturing the post-indentation behavior of the Ti/SiC MMNC coating. This methodology can also be used for studying the response of composite coatings with different percentages of reinforcements.

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A bolted joint is one of the most common fastening techniques. While the behavior of bolted joints under static or quasi-static conditions is well documented, their behavior under shock/impact loading is not well-understood. In many applications, where a bolted joint connects a sensitive component to the rest of a structure, it is important to interpret shock propagation through the bolted joints. This problem is further complicated owing to the fact that a bolted joint exhibits multiple types of nonlinearities, due to the interaction between the bolts and clamped parts, thread friction between the shank and nut, pre-tension, damping characteristics, and interference with the hole. This study was focused on developing computational techniques for understanding shock propagation through a bolted joint. As a case study, the behavior of a bolted joint within a two-component cylindrical structure subjected to impact loading was considered. A finite element (FE) model of the fixture was developed. Two different approaches were considered. The first one modeled the bolt assembly as one part. The second model had the bolt and nut as separate parts. In this model, the tie contact between the bolt shank and the nut was defined using a shear failure criterion. Both models included bolt pre-tension. The two models were compared based on energy balance, acceleration signal, and displacement at the base of the fixture. The results indicated that the model with the separate bolt and nut resulted in a more realistic performance.

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