High cycle fatigue performance, crack growth and failure mechanisms of an ultrafine-grained Nb+Ti stabilized, low-C microalloyed steel processed by multiphase controlled rolling and forging

The bimodal, equiaxed and Widmanstatten microstructures of TC4 titanium alloy were obtained through different heat treatment processes. The content of primary α phase in the bimodal and equiaxed microstructures was measured to be about 40% and 90%, and the average size was about 9.4μm and 7.9 μm. Three types of microstructure fatigue S-N curves are obtained, which are successively descending type, single-platform descending type and infinite life type. The order of very high cycle fatigue performance is Widmanstatten>equiaxed>bimodal, but the anti-fretting fatigue performance of Widmanstatten is the worst. The grain refinement makes the fatigue performance of the equiaxed better than that of the bimodal. The second process is determined as the best heat treatment method. There is no significant difference in the life of the crack propagation stage. The very high cycle fatigue life mainly depends on the crack initiation stage. In the bimodal and the equiaxed, the crack initiates in the primary α phase of the subsurface, and the crack in the Widmanstatten initiates in the coarse α 'grain boundary of the subsurface.

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Influence of equal channel angular pressing on high cycle fatigue behavior of ultrafine-grained iron: Role of anisotropy

Materials Science and Engineering A ◽

10.1016/j.msea.2017.11.075 ◽

2018 ◽

Vol 711 ◽

pp. 650-658 ◽

Cited By ~ 5

Author(s):

Enrico Bruder ◽

Chandanraj Gangaraju ◽

Rimma Lapovok

Keyword(s):

Equal Channel Angular Pressing ◽

High Cycle Fatigue ◽

Fatigue Behavior ◽

Cycle Fatigue ◽

Angular Pressing ◽

Ultrafine Grained

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High Cycle Fatigue Resistance and Reliability Assessment of Flexible Printed Circuitry

Journal of Electronic Packaging ◽

10.1115/1.1462628 ◽

2002 ◽

Vol 124 (3) ◽

pp. 254-259 ◽

Cited By ~ 9

Author(s):

Elena Martynenko ◽

Wen Zhou ◽

Alexander Chudnovsky ◽

Ron S. Li ◽

Larry Poglitsch

Keyword(s):

Fatigue Resistance ◽

High Cycle Fatigue ◽

Failure Mechanisms ◽

Three Dimensional ◽

Reliability Assessment ◽

Core Layer ◽

High Strength ◽

Multiple Cracks ◽

Material System ◽

Cycle Fatigue

Flexible printed circuitry (FPC) is a patterned array of conductors supported by a flexible dielectric film made of high strength polymer material such as polyimide. The flexibility of FPC provides an opportunity for three dimensional packaging, easy interconnections and dynamic applications. The polymeric core layer is the primary load bearing structure when the substrate is not supported by a rigid plate. In its composite structure, the conductive layers are more vulnerable to failure due to their lower flexibility compared to the core layer. Fatigue data on FPCs are not commonly available in published literature. Presented in this paper is the fatigue resistance and reliability assessment of polyimide based FPCs. Fatigue resistance of a specific material system was analyzed as a function of temperature and frequency through experiments that utilized a specially designed experimental setup consisting of sine servo controller, electrodynamic shaker, continuity monitor and temperature chamber. The fatigue characteristics of the selected material system are summarized in the form of S-N diagrams. Significant decrease in fatigue lifetime has been observed due to higher displacements in high cycle fatigue. Observed temperature effect was however counter-intuitive. Failure mechanisms are discussed and complete fracture analysis is presented. In various FPC systems, it has been found that the changes take place in FPC failure mechanisms from well-developed and aligned single cracks through the width at low temperature to an array of multiple cracks with random sizes and locations at high temperature.

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