TY - JOUR
T1 - Accumulation and evolution of elastically induced defects under cyclic loading
T2 - Quantification and subsequent properties
AU - Indeck, Joseph
AU - Cuadra, Jefferson
AU - Williams, C.
AU - Hazeli, K.
N1 - Funding Information:
Dislocation activity should therefore be the primary active mechanism in the bulk material during both the fatigue and quasi-static tension testing. Feng and Kramer concluded that the yield stress in high purity iron was caused by the interaction of dislocations with the surface and not a bulk dislocation reaction [54] . This conclusion was determined through the use of loading, electrolytic polishing, reloading, and monitoring the yield stress change. Their conclusion is supported by the results of Vesely highlighting the short mean free path of screw dislocations [55] . While Feng and Kramer do not explicitly state there is no bulk dislocation activity, the findings detailed herein show that there is enough bulk dislocation activity to help nucleate and grow internal voids especially later in the fatigue life.
Publisher Copyright:
© 2019 Elsevier Ltd
PY - 2019/10
Y1 - 2019/10
N2 - This article quantifies the evolution of bulk material defects in α-iron during cyclic elastic loading and investigates its subsequent effect on quasi-static and dynamic mechanical response. Fatigue test specimens were cycled at a constant stress amplitude, 70% of the yield stress, to cause microscopic defects throughout the material due to a macroscopic elastic load. Afterwards, wire-cut electrical discharge machining was used to obtain multiple sub-tensile specimens from within the gauge section of the fatigued material. X-ray computed tomography of the sub-tensile specimens was used to quantify distribution and location of voids that were induced at different stages of fatigue life. Then, tension tests were performed on the sub-tensile specimens at low (10−3 s−1) and high (103 s−1) strain rates to study changes in mechanical properties. Yield stress and ultimate tensile stress were found to change under both quasi-static and dynamic strain rates based on the amount of prior cyclic loading. Changes in mechanical behavior were correlated to the characteristics of observed defects that exhibited distinct grouping at a certain point during the fatigue life. Mechanical properties of the sub-tensile specimens after fatigue loading displayed different trends depending on the strain rate. Low strain rate deformation resulted in decreases of approximately 20% in the yield stress, ultimate tensile stress, and ductility due to increased fatigue loading. Conversely, during high strain rate deformation some samples with more fatigue loading displayed higher maximum flow stresses. Results demonstrate the significance of bulk material changes which occur at mechanical loads below the yield stress. The systematic experimental procedures developed here for investigating the accumulation, evolution, and effect on subsequent properties due to elastically induced microscopic defects could potentially be applied to a wide range of material systems.
AB - This article quantifies the evolution of bulk material defects in α-iron during cyclic elastic loading and investigates its subsequent effect on quasi-static and dynamic mechanical response. Fatigue test specimens were cycled at a constant stress amplitude, 70% of the yield stress, to cause microscopic defects throughout the material due to a macroscopic elastic load. Afterwards, wire-cut electrical discharge machining was used to obtain multiple sub-tensile specimens from within the gauge section of the fatigued material. X-ray computed tomography of the sub-tensile specimens was used to quantify distribution and location of voids that were induced at different stages of fatigue life. Then, tension tests were performed on the sub-tensile specimens at low (10−3 s−1) and high (103 s−1) strain rates to study changes in mechanical properties. Yield stress and ultimate tensile stress were found to change under both quasi-static and dynamic strain rates based on the amount of prior cyclic loading. Changes in mechanical behavior were correlated to the characteristics of observed defects that exhibited distinct grouping at a certain point during the fatigue life. Mechanical properties of the sub-tensile specimens after fatigue loading displayed different trends depending on the strain rate. Low strain rate deformation resulted in decreases of approximately 20% in the yield stress, ultimate tensile stress, and ductility due to increased fatigue loading. Conversely, during high strain rate deformation some samples with more fatigue loading displayed higher maximum flow stresses. Results demonstrate the significance of bulk material changes which occur at mechanical loads below the yield stress. The systematic experimental procedures developed here for investigating the accumulation, evolution, and effect on subsequent properties due to elastically induced microscopic defects could potentially be applied to a wide range of material systems.
KW - Damage accumulation
KW - Defects
KW - Dynamic loading
KW - X-ray computed tomography
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U2 - 10.1016/j.ijfatigue.2019.05.025
DO - 10.1016/j.ijfatigue.2019.05.025
M3 - Article
AN - SCOPUS:85068394725
VL - 127
SP - 522
EP - 536
JO - International Journal of Fatigue
JF - International Journal of Fatigue
SN - 0142-1123
ER -