Ablation and Plasma Effects during Nanosecond Laser Matter Interaction in Air and Water

Despite extensive research work, a clear understanding of laser matter interaction i

FVPM simulation of scratching induced by a spherical indenter

International audienceThis article presents a single particle scratching simulation using the Finite Volume Particle Method (FVPM). FVPM is a variant of the well-known Smooth Particles Hydrodynamics method (SPH) which is locally conservative and consistent, what's more it features advantages of mesh-free methods for handling moving interfaces and multi-scale interpolation. The test material is represented by overlapping particles and data exchanges occur through the interfaces. The indenter is modeled as a rigid sphere whose path is a straight horizontal line. The resulting surface topography as well as constraints and scratching efforts have been numerically studied. The FVPM simulation code assessed in this article has been found suitable for the scratching simulation based on a comparison with other results from the literature. The presented results suggest the possibility to simulate more complex surface finishing operations. Manufacturing processes based on abrasion material removal, such as the grinding process, will be considered in the future

Laser Shock Processing and Related Phenomena

Laser shock processing (LSP) is a continuously developing effective technology used to improve surface and mechanical properties for metallic alloys. LSP is in direct competition with other established technologies, such as shot peening, both in preventive manufacturing treatments and maintenance/repair operations. The level of LSP maturity has increased in recent years and several thematic international conferences have been organized (i.e., the 7th ICLPRP held in Singapore, June 17–22, 2018) to discuss different developments of a number of key aspects. These aspects include: fundamental laser interaction phenomena; material behavior at high deformation rates/under intense shock waves; laser sources and experimental process implementation; induced microstructural/surface/stress effects; mechanical and surface properties with experimental characterization and testing; numerical process simulation; development and validation of applications; comparison of LSP to competing technologies; and novel related processes. All of these aspects have been recursively treated by well-renowned specialists, providing a firm basis for the further development of the technology in its path to industrial penetration. However, the application of LSP (and related technologies) on different types of materials with different applications (such as the always demanding aeronautical/aerospatial field or the energy generation, automotive, and biomedical fields) still requires extensive effort to elucidate and master different critical aspects. Thus, LSP deserves a great research effort as a necessary step prior to its industrial readiness level. The present Special Issue of Metals in the field of “Laser Shock Processing and Related Phenomena” aims, from its initial launching date, to collect (especially for the use of LSP application developers in different target sectors) a number of high-quality and relevant papers representing state-of-the-art technology that is useful to newcomers in realizing its wide and relevant prospects as a key manufacturing technology. Consequently, in an additional and complementary way, papers were presented at the thematic ICLPRP conferences, and a call was made to authors willing to prepare high-quality and relevant papers to the journal, with the confidence that their work would become part of a fundamental reference collection regarding the present state-of-the-art LSP technology. The Special Issue includes two reviews and nine research papers. Each contribution adds to the reference knowledge of LSP technology and covers the practical totality of open issues, which will lead to present-day research at worldwide universities, research centers, and industrial companies

Understanding the Mechanism of Abrasive-Based Finishing Processes Using Mathematical Modeling and Numerical Simulation

Recent advances in technology and refinement of available computational resources paved the way for the extensive use of computers to model and simulate complex real-world problems difficult to solve analytically. The appeal of simulations lies in the ability to predict the significance of a change to the system under study. The simulated results can be of great benefit in predicting various behaviors, such as the wind pattern in a particular region, the ability of a material to withstand a dynamic load, or even the behavior of a workpiece under a particular type of machining. This paper deals with the mathematical modeling and simulation techniques used in abrasive-based machining processes such as abrasive flow machining (AFM), magnetic-based finishing processes, i.e., magnetic abrasive finishing (MAF) process, magnetorheological finishing (MRF) process, and ball-end type magnetorheological finishing process (BEMRF). The paper also aims to highlight the advances and obstacles associated with these techniques and their applications in flow machining. This study contributes the better understanding by examining the available modeling and simulation techniques such as Molecular Dynamic Simulation (MDS), Computational Fluid Dynamics (CFD), Finite Element Method (FEM), Discrete Element Method (DEM), Multivariable Regression Analysis (MVRA), Artificial Neural Network (ANN), Response Surface Analysis (RSA), Stochastic Modeling and Simulation by Data Dependent System (DDS). Among these methods, CFD and FEM can be performed with the available commercial software, while DEM and MDS performed using the computer programming-based platform, i.e., "LAMMPS Molecular Dynamics Simulator," or C, C++, or Python programming, and these methods seem more promising techniques for modeling and simulation of loose abrasive-based machining processes. The other four methods (MVRA, ANN, RSA, and DDS) are experimental and based on statistical approaches that can be used for mathematical modeling of loose abrasive-based machining processes. Additionally, it suggests areas for further investigation and offers a priceless bibliography of earlier studies on the modeling and simulation techniques for abrasive-based machining processes. Researchers studying mathematical modeling of various micro- and nanofinishing techniques for different applications may find this review article to be of great help

Predictive model of impact-induced bonding in cold spray using the Material Point Method

Cold spray technology has emerged in recent years as a promising method of powder deposition that is inherently different from other processes. Without melting of the particles prior to deposition, powders of a wide range of materials can be deposited onto a substrate primarily through their initial kinetic energy. By keeping particle temperatures below melting, coatings made from cold spray are able to elegantly avoid many temperature-related defects commonly seen in traditional coating methods. The amount of kinetic energy required for successful bonding has been experimentally shown to be defined by a critical velocity, which varies depending on the thermomechanical properties of the powder material. Due to the time duration across which bonding occurs, it is difficult to observe the precise bonding phenomena in experiments leading to an emphasis on numerical simulation. However, most numerical studies have been focused on using mesh-based FEMs and identify bonding during post-processing of results. As such, these models are incapable of properly predicting bonding or bond effects on material behavior. In the current thesis, a bonding model is developed within a Material Point Method (MPM) framework that is able to directly model bonding effects on each body within the simulation. By using the MPM, it is possible to combine the advantages of Lagrangian and Eulerian FEMs while simultaneously minimizing their shortcomings in modeling the extreme strain and strain rate conditions seen in cold spray. This novel, direct bonding model introduces a time-discrete bond parameter whose evolution is based on adhesion energy, similar to the energy release rate seen in damage/fracture modeling. The overall code has been generalized to also provide initial consideration of multiparticle impacts, which is important for modeling the overall build-up and predicting the properties of coatings or structures. With the current model, it is possible to produce accurate predictions of the critical velocity for a range of Al particle sizes. Through use of adhesion energy and regularization techniques, the bonding model is able perform independently of discretization level and accurately capture the material jetting behavior observed experimentally to be related to impact-induced bonding. A linear trend is predicted such that critical velocity decreases as particle diameter increases. Furthermore, the current model also predicts convergence of the percent bonded area with grid size refinement towards a value which aligns with theoretical works. This further suggests that the current model is also able to provide insight on the bond quality and mechanical properties of the final coating/component with sufficient discretization

Cold spraying - A materials perspective

Cold spraying is a solid-state powder deposition process with several unique characteristics, allowing production of coatings or bulk components from a wide range of materials. The process has attracted much attention from academia and industry over the past two decades. The technical interest in cold spraying is twofold: first as a coating process for applications in surface technology, and second as a solid-state additive manufacturing process, offering an alternative to selective laser melting or electron beam melting methods. Moreover, cold spraying can be used to study materials behaviour under extremely high strain rates, high pressures and high cooling rates. The cold spraying process is thus considered to be relevant for various industrial applications, as well as for fundamental studies in materials science. This article aims to provide an overview of the cold spray process, the current understanding of the deposition mechanisms, and the related models and experiments, from a materials science perspective

Peridynamic Modeling of Dynamic Fracture in Bio-Inspired Structures for High Velocity Impacts

Bio-inspired damage resistant models have distinct patterns like brick-mortar, Voronoi, helicoidal etc., which show exceptional damage mitigation against high-velocity impacts. These unique patterns increase damage resistance (in some cases up to 3000 times more than the constituent materials) by effectively dispersing the stress waves produced by the impact. Ability to mimic these structures on a larger scale can be ground-breaking and could be used in numerous applications. Advancements in 3D printing have now made possible fabrication of these patterns with ease and at a low cost. Research on dynamic fracture in bio-inspired structures is very limited but it is crucial for the development of such materials with enhanced impact resistance. In this thesis, we investigate damage in some bio-inspired structures through peridynamic modeling. We first print a 3D brick-mortar structure, 82% VeroClear plastic (a PMMA substitute in 3D printing; the stiff phase) and 18% TangoBlack rubber (a natural rubber substitute in 3D printing; the soft phase). We investigate damage in this 3D printed sample by low-velocity drop test with fixed and free boundary conditions. Under free boundary conditions, at this impact speed no damage was observed, while cracks form when the sample rests on a fixed metal table. A 3D peridynamic model for dynamic brittle fracture is used to first validate it against the Kalthoff-Winkler experiment, in which a pre-notched steel plate is impacted at 32m/s by a cylindrical impactor and brittle cracks grow at a 70-degree angle with the impact direction. A new peridynamic model for a brick-mortar microstructure is created using the properties of PMMA and rubber. Because simulating the supporting table used in the experiments would be too costly, we choose to work with free boundary conditions and a higher impact speed (500m/s), to observe damage in the peridynamic model of the brick-mortar structure. Under these conditions, the damage is limited to the contacting brick only. The soft phase is able to limit its spread. Other boundary conditions are likely to cause wave reflections and reinforcements, which can damage other bricks, far from the impact point, as observed in our experiments. Advisor: Florin Bobar