Reassessment of the Dynamic Thermomechanical Conversion in Metals

Area of Science:

• Materials Science
• Mechanical Engineering
• Thermodynamics

Background:

• Dynamic plasticity under high-rate loading often occurs under nearly adiabatic conditions, where heat dissipation is limited.
• A direct relationship between stored mechanical energy, microstructure, and mechanical properties is often assumed.
• Understanding thermomechanical conversion is crucial for predicting material behavior under extreme conditions.

Purpose of the Study:

• To investigate the relationship between mechanical response, microstructural evolution, and thermal dissipation in metals under high-rate loading.
• To reassess the concept of thermomechanical conversion in dynamic plasticity.
• To explore the strain rate sensitivity of thermal and mechanical behaviors.

Main Methods:

• High-rate experiments using a Kolsky bar.
• In-situ thermal measurements during dynamic loading.
• Characterization of microstructural defects using transmission electron microscopy.
• Analysis using a dislocation-based constitutive model.

Main Results:

• The thermal response of pure nickel and aluminum was found to be strongly dependent on strain rate.
• Mechanical flow behavior and microstructural characteristics remained largely insensitive to strain rate at similar strain levels.
• A discrepancy was observed between the strain rate sensitivity of thermal effects and mechanical/microstructural evolution.

Conclusions:

• The direct one-to-one relationship between stored energy, microstructure, and mechanical characteristics is not straightforward under dynamic plasticity.
• The thermal response is a more sensitive indicator of strain rate effects than mechanical properties or microstructure in the studied materials.
• The concept of thermomechanical conversion requires a more nuanced understanding, particularly concerning the interplay between thermal and mechanical behaviors at high strain rates.