http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Fatigue crack formation and growth from localized corrosion in Al–Zn–Mg–Cu
Kim, Sangshik,Burns, James T.,Gangloff, Richard P. Elsevier 2009 Engineering fracture mechanics Vol.76 No.5
<P><B>Abstract</B></P><P>The effect of precorrosion on the fatigue life of aluminum alloy 7075-T6511 was measured, physical characteristics of corrosion topography plus fatigue damage were established by microscopy, and a corrosion modified equivalent initial flaw size (CM-EIFS) was established using fracture mechanics modeling. Fatigue life is reduced by clustered corrosion pits on the L–S surface from laboratory-EXCO exposure. Cracks initiate from pits clustered as a semi-elliptical surface micronotch rather than the deepest pits, consistent with shape-dependent stress intensity. Marker band analysis establishes that the number of cycles to form a crack about a pit cluster can be a significant fraction of total fatigue life. The CM-EIFS, back-calculated from fracture mechanics analysis of measured fatigue life, equals measured initiating-pit cluster size provided that important inputs are provided; such favorable comparison validates this approach to corrosion-fatigue interaction. Calculated CM-EIFS provides a metric to characterize alloy corrosion damage, and can be used to forward-model the effects of stress and loading environment on fatigue life distribution, critical for efficient alloy development. Use in prognosis of the fatigue performance of a service-corroded surface is hindered by uncertain non-destructive characterization of corrosion topography.</P>
Sumin Kim,Taejin Song,Hyokyung Sung,Sangshik Kim 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10
Pre-straining tends to increase yield/tensile strengths and dislocation density by strain hardening of steel while also, affectingits high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors greatly. The HCF and FCP behaviors of complexphase (CP) steel with different levels of pre-straining from 0 to 9% were examined. It was found that the resistance to HCFof CP steel decreased with 5% pre-straining, while it increased with 9% pre-straining, suggesting that such an abnormal HCFbehavior of CP steel with different levels of pre-straining could be attributed to the nature of dislocation structure formedduring cyclic straining. Based on the detailed micrographic and fractographic analyses, the effect of pre-straining up to 9%on the fatigue behavior of CP steel was discussed.
Soyoung Kim,Hojun Oh,Jung Gi Kim,Sangshik Kim 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.1
Efects of annealing condition and crack orientation on fatigue crack propagation (FCP) behavior of DED (direct energydeposition)-processed Ti–6Al–4V (Ti64) specimens were studied. It was found that the FCP resistance of Ti64 increasedsignifcantly with annealing, particularly above β transus temperature, due to the microstructural coarsening inducing lessdamage accumulation at the tip of crack. The FCP behavior of as-built and as-annealed DED Ti64 specimens was isotropicwith crack direction either parallel or perpendicular to building direction. The detailed micrographic and fractographicanalyses on FCP-tested specimens suggested that the presence of largely elongated β grain boundaries did not afect theadvance of crack.
Sumin Kim,Taejin Song,Hyokyung Sung,Sangshik Kim 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6
Steel sheet is often shaped by straining to form a final product, and deformation process can influence the fatigue resistance. In this study, high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors of precipitation hardened (PH) highstrength steel with pre-straining levels of 0, 5 and 9% were investigated. Regardless of pre-straining level, fatigue crackswere found to be initiated at surface pits formed during pickling. The effect of pre-straining was not significant on the HCFresistance of PH steel, while the FCP rates increased with increasing level of pre-straining only in low and intermediate ΔKregimes. It was suggested that marginal increase on HCF resistance of PH steel was due to the combined effect of enhancedresistance to crack initiation and reduced resistance to crack propagation with pre-straining. The effect of pre-straining onHCF and FCP behavior of PH steel was discussed based on micrographic and fractographic observations.
Microstructural evaluation of oxide layers in CaO-added Mg alloys
Lee, Taeg-Woo,Kim, Hyung-Giun,So, Myoung-Gi,Lee, Jin-Kyu,Kim, Shae K.,Park, Woo-Jin,Kim, Won-Yong,Kim, Sangshik,Lim, Sung-Hwan Elsevier 2015 JOURNAL OF ALLOYS AND COMPOUNDS Vol.635 No.-
<P><B>Abstract</B></P> <P>A transmission electron microscopy analysis was conducted on the oxide layers of Mg–5.5Al–0.25Mn (AM60) alloys with different levels of CaO content formed in a thermogravimetric analyzer (TGA) system at 450°C for 7h. It was found that the oxide layer in AM60+CaO grew as a columnar structure and, resultantly, that the oxide layers had different thicknesses with different levels of CaO content. The columnar oxide grains that were formed on the Mg+CaO alloy grew on the [100]<SUB>MgO</SUB>, resulting in a more compact and thicker initial oxide layer compared to the normal oxide layer. The columnar growth of the oxide layer in AM60+CaO formed due to the Ca, which dissolved from CaO.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Oxidation layer thickness of CaO added AM60 increases with increasing amounts of CaO. </LI> <LI> Effect of CaO is that the columnar grains on AM60 grow along the [100]<SUB>MgO</SUB>. </LI> <LI> A initial oxidation layer thickness and ignition temperature is closely connected. </LI> <LI> The columnar oxide layer formed due to Ca, which dissolved from CaO. </LI> </UL> </P>