Plastics Fractures

A. G. Atkins and Y-W. Mai, Elastic and Plastic fracture, Ellis Horwood, Chichester, U.K., 1985. 

The utility of K or any elastic plastic fracture mechanics (EPFM) parameter to describe the mechanical driving force for crack growth is based on the ability of that parameter to characterize the stress-strain conditions at the crack tip in a maimer which accounts for a variety of crack lengths, component geometries and loading conditions. Equal values of K should correspond to equal crack tip stress-strain conditions and, consequently, to equivalent crack growth behavior. In such a case we have mechanical similitude. Mechanical similitude implies equivalent crack tip inelastic zones and equivalent elastic stress fields. Fracture mechanics is... 

Elastic-plastic Fracture Mechanics Behavior of Graphite... 

As with the purely elastic case, the energy values associated with elastic-plastic fracture may be ascertained from the load versus load-point deflection diagram for a cracked body as shown in Fig. 5. 

M. Sakai, K. Urashima, and M. 1 nagaki, Energy Principle of Elastic-Plastic Fracture and Its Application to the Fracture Mechanics of a Polycrystalline Graphite, Journal of the American Ceramic Society, 1983, 66(12), 868 874. 

In order to supplement micro-mechanical investigations and advance knowledge of the fracture process, micro-mechanical measurements in the deformation zone are required to determine local stresses and strains. In TPs, craze zones can develop that are important microscopic features around a crack tip governing strength behavior. For certain plastics fracture is preceded by the formation of a craze zone that is a wedge shaped region spanned by oriented micro-fibrils. Methods of craze zone measurements include optical emission spectroscopy, diffraction... 

Ernst, H. A., Elastic Plastic Fracture Mechanics Methodology for Surface Cracks, Georgia Inst, of Tech., 1994. 

In the case of thin sections the measure of toughness is given by plane-stress fracture toughness, Kc and elastic-plastic fracture mechanics (EPFM) are used. It is also necessary to bear in mind that plane-stress fracture toughness Kc is higher than plane-strain fracture toughness Xlc. 

V. Kumar, M. D. German and C. F. Shih, An Engineering Approach for Elastic-Plastic Fracture Analysis, EPRI Technical Report NP-1931, Electric Power Research Institute, Palo Alto, CA, 1981. 

E. W. Hart, Stable Crack Extension Rates in Ductile Materials Characterization by a Local Stress-Intensity Factor, in Elastic-Plastic Fracture Second Symposium, Volume I—Inelastic Crack Analysis, eds. C. F. Shih and J. P. Gudas, ASTM STP 803, American Society for Testing and Materials, Philadelphia, PA, 1983, pp. I-521-I-531. 

It must be noted that the fracture mechanics framework described above only applies when plastic deformation of the material is limited. Substantial plastic deformation may accompany propagation of existing defects in structures fabricated from relatively low-strength materials, e.g., carbon steels. In these cases, the linear elastic stress intensity factor, K, does not accurately apply in structural design. Alternately, elastic-plastic fracture mechanics methods may apply. ... 

KEY WORDS J-integral, tearing modulus, crack propagation, plastic fracture... 

It is well known that the methods of elastic-plastic fracture mechanics provide more realistic models of cracked structures with high toughness compared with the methods of the linear elastic fracture mechanics. Ductile materials are used in structural elements not only in piping systems of power plants but in chemical industry, in aircraft propulsion systems and elsewhere [1-8], Evidently, cracked elements in chemical or power plants pose a serious threat to operation of these stmctures. Therefore, it is extremely important that the crack will not spread unstably through the pipe thickness. 

Hutchinson, J.W. and Paris, P.C., (1979), Stability analysis of J-controlled crack growth. In J.D. Landes, J.A. Begley and G.A. Clarke (Eds), Elastic-Plastic Fracture, ASTM STP 668. American Society for Testing Materials, Philadelphia, 37. 

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