Fatigue fracture mechanics

Speidel, M.O., Stress Corrosion Cracking and Corrosion Fatigue - Fracture Mechanics, in Corrosion in Power Generating Equipment, M.O. Speidel, A. Atrens (eds.), Plenum Press, NY, pp. 85-132, 1984. 

The requirements for an FSW tool in high-temperature materials (HTM) are significant. Obviously, the tool must maintain sufficient strength to constrain the weld material at softening temperatures in excess of 1000 °C (1830 °F). Perhaps less apparent, the tool must also be resistant to fatigue, fracture, mechanical wear, and chemical reactions with both the atmosphere and the weld material. To date, two classes of materials have been found that meet these requirements refractory metal tools and superabrasive tools. 

Only a handful of titanium alloys have currently been FSWed. Considerable scope for investigation of other titanium alloys exists. Finally, property databases for first-tier (tensile) and second-tier (fatigue, fracture) mechanical properties are mandatory if designers are to use FSW of titanium alloys in future designs. Corrosion databases are also required for designers. 

Table 8.2 Cyclic fatigue fracture mechanics test methods for FRP composites...

Another basic major advantage is that the cyclic-fatigue fracture-mechanics data may be gathered in a relatively short time-period, but may be applied to other designs of bonded joints and components, whose lifetime may then be predicted over a far longer time-span. Obviously, the fracture-mechanics tests need to be conducted under similar test conditions and environments as the joints, or components, whose service-life is to be predicted. This is important since the fracture-mechanics test specimens do need to exhibit a similar mechanism and locus of failure (e.g. cohesively through the adhesive layer, or interfacially between the adhesive and substrate, or through the oxide layer on the metallic substrate, etc.) as observed in the joints, or components, whose lifetime is to be ranked and predicted. 

Thus, as follows from mentioned above, the data on corrosion fatigue of Mg alloys are very contradictory. The present research is devoted to the correlation analysis of corrosion fatigue behavior of diecast and extruded Mg alloys in 3.5% NaCl (pH 5) and 0. IN Na2B407 solution with a stable pH of 9.3 (buffer solution) and to the investigation of fatigue fracture mechanisms of these alloys depending on chemical composition, e.g, A1 content, environment and microstructure. 

R. Murakami, D. Yonekura, and T. Murayama, "A study on fatigue fracture mechanism of Cr-Mo steel SCM435 in super long life range". International Journal of Modern Physics B, 17(8-9), 2003 pp. 1697-1703. 

During product test and some field conditions, the solder is subjected to temperature extremes of — 55°C to 150°C or higher. These temperature cycles result in the imposition of large cyclic stresses and strains that cause the solder to fail due to complex interactions of creep and fatigue fracture mechanisms. If a chip underfill is employed, the critical interfaces between the underfill and chip and chip carrier are subjected to high alternating stress that can cause fracture, especially in the presence of impurities and contamination. 

The use of fatigue data and crack length measurements to predict the remaining service life of a stmcture under cyclic loading is possibly the most common application of fracture mechanics for performance prediction. In complex stmctures the growth of cracks is routinely monitored at intervals, and from data about crack growth rates and the applied loadings at that point in the stmcture, a decision is made about whether the stmcmre can continue to operate safely until the next scheduled inspection. 

Fracture Mechanics. Linear elastic fracture mechanics (qv) (LEFM) can be appHed only to the propagation and fracture stages of fatigue failure. LEFM is based on a definition of the stress close to a crack tip in terms of a stress intensification factor K, for which the simplest general relationship is... 

A. Ptakash,D. K. Kim, and R. M. Shemeashi, International Conference on Fatigue, Corrosion Cracking Fracture Mechanical andFailure Analysis, ASM... 

Fracture mechanics can be applied to this problem, much as it is to fatigue. We use only the final result, as follows. If the standard test which was used to measure (Tts takes a time f(test), then the stress which the sample will support safely for a time t is... 

Bloom, J. M. (ed.) 1983 Probabilistic Fracture Mechanics and Fatigue Methods Applications for Structural Design and Maintenance. American Society for Testing and Materials. 

C. J. Beevers, R. L. Carlson, K. Bell and E. A. Starke, A Model for Fatigue Crack Closure , Engineering Fracture Mechanics. 

In this book no prior knowledge of plastics is assumed. Chapter 1 provides a brief introduction to the structure of plastics and it provides an insight to the way in which their unique structure affects their performance. There is a resume of the main types of plastics which are available. Chapter 2 deals with the mechanical properties of unreinforced and reinforced plastics under the general heading of deformation. The time dependent behaviour of the materials is introduced and simple design procedures are illustrated. Chapter 3 continues the discussion on properties but concentrates on fracture as caused by creep, fatigue and impact. The concepts of fracture mechanics are also introduced for reinforced and unreinforced plastics. 

The mechanisms by which polymers undergo degradation in the human body are not yet completely understood. Examples of breakdown of these materials are illustrated by the embrittlement and excessive wear of polyester sockets exposed to the mechanical, biochemical and thermal stresses of the physiological milieu, as well as by the fatigue fractures, excessive wear and additional cross-linking (embrittlement) that have been observed in polyethylene sockets. 

The NACE publication Corrosion Fatigue gives a comprehensive account of all aspects of the subject, and in this work a review of the application of fracture mechanics for studying the phenomenon has been presented by McEvily and Wei , whilst Kitagawa has given a detailed account of crack propagation in unnotched steel specimens. This work should be consulted for details of testing and interpretation of results. 

Fracture mechanic The fracture mechanics theory developed for metals is also adaptable for use with plastics. The basic concepts remain the same, but since metals and plastics are different they require different techniques to describe their fatigue-failure behaviors. Some of the comments made about crack and fracture influences on fatigue performance relate to the theory of fracture mechanics. The fracture mechanics theory method, along with readily... 

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