Effect of Strain Rate on the Dynamic Hardness in Metals

Abstract

Traditionally, the hardness of materials is determined from indentation tests at low loading rates (static). However, considerably less work has been conducted in studying the dynamic hardness of materials using relatively high loading rates. In the present work, two models are used to predict strain rate dependency in hardness. The first model is a power law expression that is based on the dependence of the yield stress on the strain rate. This model is relatively simple in implementation, and it is quite easy to determine its parameters from simple uniaxial experiments. The second model is a micromechanical based model using Taylor’s hardening law. It utilizes the behavior of dislocation densities at high strain rates in metals in order to relate dynamic hardness to strain rates. The latter model also accounts for any changes in temperature that could exist. A finite element is also run and compared with the two models proposed in this work. Results from both models are compared with available experimental results for oxygen-free high-conductivity copper and 1018 cold rolled steel, and both models show reasonably good agreement with the experimental results.

An investigation into the dynamic indentation response of metallic materials

“…Considering the special case n = 2 as proposed in references [24,25], it was found that the best fit for h m was obtained when the impact C 1 was much less than the C 1 ind as listed in This contradicts the general understanding that the dynamic resistance of metals is higher than that obtained under quasi-static conditions [49]. For example, Almasri et al [52][53][54] investigated the strain rate dependence of the dynamic hardness of fcc copper and bcc steel finding that the hardness increased with the increase of the strain rate from 10 -5 to 10 5 s -1 . Moreover, Clough et al [55] studied the dynamic hardness using a dropped ball on steels and found the hardness increased with strain rate up to 10 6 s -1 .…”

The mechanical behavior during nanoindentation near the grain boundary in a bicrystal FCC metal

“…Almasri and Voyiadjis [25] developed a physically based temperature and strain rate-dependent expression for microhardness H 0 such that…”

Влияние Малоамплитудных Осцилляций Нагрузки На Наноконтактные Характеристики Материалов В Процессе Наноиндентирования

“…Тестирование осу-ществлялось двумя основными модами нагружения: a) традиционной квазистатической без добавления ос-цилляции, b) посредством метода CSM с наложением дополнительной осцилляции смещения индентора ам-плитудой z = 0.5−8 nm и частотой 45 Hz. Во время проведения всех экспериментов скорость относительной квазистатической деформации поддерживалась постоян-ной (ε = 0.05 s −1 ) с помощью цепей обратной связи в приборе, что позволяло исключить влияние скоростного фактора на величину твердости [33]. Максимальная глубина отпечатков в контрольных образцах (для ко-торых z = 0), устанавливаемая протоколом испытания, составляла 25, 50, 100, 200, 500, 1000, 1500 и 2000 nm.…”