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Seoul, South Korea

Chung C.-S.,Flow Master Co. | Kim H.-K.,Seoul National University of Science and Technology
Journal of Engineering Science and Technology | Year: 2015

Uniaxial and biaxial torsional fatigue specimens were extracted from a railway wheel steel. The fatigue tests were performed with the stress ratio of R= -1 by using uniaxial and biaxial torsional fatigue test specimens at room temperature in air. The ultimate and yield strengths of the steel were evaluated. The uniaxial fatigue limit was 422.5 MPa, which corresponds to 67% of the ultimate tensile strength. The ratio of τee was 0.63. Appropriate parameters to predict the fatigue life of the steel under multiaxial stress states were reviewed. © 2015 School of Engineering, Taylor’s University. Source


Nguyen V.L.,Seoul National University of Science and Technology | Chung C.-S.,Flow Master Co. | Kim H.-K.,Seoul National University of Science and Technology
Microelectronics Reliability | Year: 2015

The present study aims to evaluate the effects of isothermal aging on the mechanical properties of solder joints. To achieve this objective, the tensile impact behavior of lead-free Sn-3Ag-0.5Cu solder ball joints aged at 373. K for times ranging from 24. h to 1000. h was investigated using an altered miniature Charpy impact-testing system. The experimental results showed that the tensile strength, the work-of-fracture and the fracture toughness of solder joints were found to decrease as the effective strain rate (or the loading speed) as well as the aging time increased due to a thicker IMC layer with a coarser nodule under thermal aging. In addition, the joint strength after isothermal aging under a tensile load was more sensitive to the strain rate than those in the shear loading mode. Specifically, equations representing the relationships among the effective stress, the strain rate and the aging time were established for the solder joints aged at 373. K in this study. Furthermore, the mode II fracture toughness values were less than the mode I fracture toughness for each aging time condition of the solder joints. © 2015 Elsevier Ltd. Source


Nguyen V.L.,Seoul National University of Science and Technology | Chung C.-S.,Flow Master Co. | Kim H.-K.,Seoul National University of Science and Technology
Materials Letters | Year: 2016

In this work, nanoindentation tests using a three-sided Berkovich indenter were performed for a Cu6Sn5 intermetallic compound (IMC) in interfacial specimens of lead-free Sn-3Ag-0.5Cu solder ball joints at room temperature to investigate effect of the strain rate on the mechanical properties of this IMC. The fracture toughness was found to have an approximately linear relationship with the logarithmic nanoindentation strain rate, implying that the fracture toughness decreased in a range of (1.64-0.63) MPa m0.5 with an increase in the strain rate ranging from 0.01 s-1 to 0.33 s-1. This characteristic was similar to the KC values of Cu6Sn5 under shear or tensile tests. It was, however, when measured by nanoindentation tests, found to be less sensitive to the strain rate compared to measurements gained through shear or tensile tests. The results here were discussed and compared to those from other studies. © 2015 Published by Elsevier B.V. Source


Nguyen V.L.,Seoul National University of Science and Technology | Chung C.-S.,Flow Master Co. | Kim H.-K.,Seoul National University of Science and Technology
Journal of Electronic Materials | Year: 2015

The tensile impact behavior of lead-free Sn-3Ag-0.5Cu/Cu solder joints aged at 413 K and 453 K for times ranging from 24 h to 1000 h has been investigated in this study. The activation energy for growth of the intermetallic compound (IMC) layer was estimated and compared with literature values. Additionally, the tensile strength of solder joints with IMC thickness of 17.6 μm was found to be more sensitive to the strain rate as compared with solder joints with thinner IMC layers. Equations representing the relationships among the effective stress, strain rate, aging time, and aging temperature as well as IMC thickness were established using matrix laboratory (MATLAB) software. These equations show that the tensile strength decreases with increase in the IMC thickness to about 8 μm, after which it becomes nearly constant when the IMC thickness is between approximately 8 μm and 14 μm, before decreasing significantly when the IMC thickness exceeds 14 μm. The main reason for these characteristics was excessive increase in the IMC thickness of solder joints, causing a change in the stress concentration of the tensile load from the protruding region to the inside of the IMC layer at the same tested strain rate. © 2015 The Minerals, Metals & Materials Society Source


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Flowmaster Inc. | Date: 2010-01-19

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