Department Seminar of Gil Goviazin - Dynamic mechanical characterization of materials by synchronized thermal-optical-mechanical experiments

SCHOOL OF MECHANICAL ENGINEERING SEMINAR

Monday 15.04.2024 at 14:00

Wolfson Building of Mechanical Engineering, Room 206

Dynamic mechanical characterization of materials by synchronized thermal-optical-mechanical experiments

Gleb Gil Goviazin

Ph.D., Mechanical engineering (direct track). Technion, Israel institute of technology.

The mechanics of materials study when subject to dynamic loading is crucial for correct materials’ representation, e.g., impact events, machining, plastic deformation processes and much more. For those dynamic events the thermo-mechanical coupling is a fundamental study, although usually overlooked. In this seminar the importance of that fundamental study will be emphasized, where selected examples of this methodology for various materials will be presented, leading to unexpected results. High-speed infrared (thermal response) and optical cameras, synchronized with Split Hopkinson Bar apparatus (dynamic mechanical response) were used for high strain rate thermomechanical characterization throughout those works.

• Among the many additive manufacturing (AM) methods, wire and arc additive manufacturing (WAAM) is an AM method especially suitable for large parts. The part is built by melting a wire, then driving the melt pool to construct the final geometry. Those layering techniques introduce inherent mechanical anisotropy to the materials. However, the thermo-mechanical coupling of WAAM 316L stainless steel (SS316L) was found to be a material’s property that is isotropic despite the plastic mechanical anisotropy.
• An additional application for AM consists of building a pre-formed shape and then plastically deforming it into a final shape, hence saving material. A significant strength increase after flow-forming (plastic deformation) of WAAM SS316L as opposed to the as-built material was found resulting in an ultra-high-strength SS316L (~1600 MPa).

• Structural reactive materials (SRMs) encompass a broad category of pure substances or compounds, capable of releasing significant energy under specific stimuli (impact), while retaining structural integrity and inert otherwise. However, a compelling question pertains to the initiation mechanism of SRMs, which is the key for applicable use of SRM for applications. The impact ignition mechanism of a Structural Reactive Material (SRM), made of Al + PTFE, was studied, using the same experimental setup. It was found that despite the belief that shear loading causes SRM ignition, it was shown that pressure is the reaction-triggering loading mode, with the potential involvement of a pore collapse mechanism.

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