impact energy Flashcards
What is the Ductile-to-Brittle Transition Temperature (DBTT)?
Mechanism: Many materials, particularly body-centered cubic (BCC) metals like steel, exhibit a transition from ductile behavior at higher temperatures to brittle behavior at lower temperatures.
Reason: At higher temperatures, dislocation motion is easier, allowing the material to deform plastically and absorb more energy before fracturing. As the temperature decreases, dislocation motion becomes more difficult, and the material is more likely to fracture in a brittle manner, absorbing less energy.
What is the mechanism behind Thermal Activation of Dislocations?
Mechanism: Dislocation movement is thermally activated, requiring thermal energy to overcome obstacles within the crystal lattice.
Reason: At higher temperatures, atoms vibrate more vigorously, providing the thermal energy necessary for dislocations to move more easily. This enhances plasticity and increases the material’s ability to absorb impact energy. At lower temperatures, reduced atomic vibrations impede dislocation motion, resulting in lower impact energy absorption.
How does Yield Strength change with temperature?
Mechanism: Yield strength typically increases as temperature decreases.
Reason: At lower temperatures, materials generally become stronger and harder but also less ductile. This higher yield strength means that less plastic deformation occurs before fracture, leading to a reduction in impact energy absorption.
What is the significance of Fracture Mode in relation to temperature?
Mechanism: Fracture mode changes with temperature, affecting impact energy absorption.
Reason: Ductile fracture involves significant plastic deformation and energy absorption, while brittle fracture occurs with little to no plastic deformation. At lower temperatures, the tendency towards brittle fracture increases, lowering the impact energy because brittle fractures occur quickly and with minimal energy absorption.
How do Microstructural Changes influence mechanical properties at different temperatures?
Mechanism: Microstructural changes, such as phase transformations, can alter material toughness.
Reason: Phase transformations in alloys, for example, can change a material’s toughness with temperature. A material tough at room temperature may become brittle if a phase transformation occurs at lower temperatures.
What role do Residual Stresses play in impact energy at varying temperatures?
Mechanism: Residual stresses within a material are temperature-dependent and can affect impact energy absorption.
Reason: Changes in temperature alter the distribution and magnitude of residual stresses, influencing the material’s ability to absorb energy during an impact.
How does Strain Rate Sensitivity vary with temperature?
Mechanism: Materials often exhibit temperature-dependent strain rate sensitivity.
Reason: At lower temperatures, materials may become more sensitive to the rate of deformation (strain rate). High strain rates, such as those during impacts, can increase brittleness and reduce impact energy absorption.
