Seminar: High-Velocity Impact Welding: Past, Present, and Future

Seminar by Ali Nassiri

Research Scientist

Simulation Innovation and Modeling Center

The Ohio State University

In order to meet the increasingly ambitious Corporate Average Fuel Economy (CAFE) standards and reduce CO2 emissions, there is a growing interest in creating lightweight vehicles. One approach relies on the use of lower-density materials such as aluminum, magnesium, and advanced composites. These materials can have increased strength/density ratios and improved section moduli. The philosophy behind this approach is to use each material where it provides the greatest value. For instance, magnesium alloys with the lowest density can be used where energy abortion is not required. Creation of such structures requires joining dissimilar metals. Due to differences in melting points and the tendency to form brittle intermetallic compound (IMCs), many dissimilar metals pairs cannot be joined with traditional fusion-based welding techniques.

One  approach  to  join  dissimilar  metals  is through  high-velocity  impact  welding  (HVIW).  Typically, the HVIW process involves a high-speed, oblique collision between two metals arranged in relatively simple geometries such as parallel plates or coaxial. When carried out at the proper impact angle and velocity, this collision causes the surface oxides and other contaminants to be ejected in the form of a jet, exposing virgin materials beneath. The uncontaminated surfaces are immediately brought into contact by the momentum of one of the joining members and the induced pressure produces metallurgical bond at the interface of two materials where strain rates often reach 10⁶-10⁷ 1/s.

The manufacturing industry often relies on numerical simulations to reduce the number of trial-and-error iterations required during the process development to reduce costs. However, this can be difficult in HVIW process where extremely high plastic strain regions develop. Thus, a traditional pure Lagrangian analysis is not able to accurately model the process due to excessive element distortion near the contact zone. Dr. Nassiri has been involved in developing a variety of computational platforms including Arbitrary Lagrangian-Eulerian (ALE), Coupled Eulerian-Lagrangian (CEL), and Smoothed Particle Hydrodynamics (SPH) capable of capturing the essentials of structure development during HVIW process.

Dr. Nassiri is a Research Scientist in the Simulation Innovation and Modeling Center (SIMCenter) at the Ohio State University (OSU). He joined OSU as a Postdoctoral Researcher at the Center for Design and Manufacturing Excellence (CDME) with a joint appointment in the Department of Materials Science and Engineering. Prior to that, he served as a Postdoctoral Research Associate in the Mechanics, Materials & Manufacturing Lab at University of New Hampshire (UNH). He earned his Ph.D. in Mechanical Engineering from UNH. The overarching goal of his research is to fundamentally understand the materials behavior subjected to large plastic deformation during high-speed manufacturing, in particular, high-velocity impact welding and forming processes. To achieve this goal, he uses a combination of cutting-edge multi-scale multi-physics numerical simulations, mechanical testing, and advanced materials characterization. His other research interests include damage and failure analysis, process simulation, dynamic behavior of materials, and mathematical modeling of manufacturing processes.