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Modeling of Microstructural Effects on Fracture Processes at High Loading Rates

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Final technical rept. 1 Feb 1989-31 May 1992

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We extended classical dynamic fracture mechanics to a class of new commercially useful titanium microstructures and demonstrated that their dynamic fracture behavior differs significantly from that of previously studied model materials. By combining continuum measurements obtained using the torsion split Hopkinson bar and one-point-bend fracture test methods and fractogaphic measurements obtained using fracture surface topography analysis, FRASTA, we generated a complete data base on static and dynamic strength and fracture toughness for various microstructures of the alloy Ti-IOV-2Fe-3AI. We determined effects of microstructural features on microfailure behavior and we modeled some of the observed microfailure processes using finite element analysis. Whereas the dynamic initiation toughness was only moderately higher than the static initiation toughness at most 20, a very strong rise was found in the crack propagation toughness with crack extension as much as a 100 increase for velocities as low as 100 ms. This rate dependent resistance curve effect is an intrinsic material property in contrast to a structural effect and a strong function of microstructure. We demonstrated that the formation of shear lips is also a strongly rate dependent phenomenon and that shear lips, when they develop, make only a modest contribution to the propagation toughness on the order of 20 for the case studied here. Our results also showed that, in general, there is not a direct correlation between the dynamic initiation and propagation toughnesses.

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  • Inorganic Chemistry
  • Properties of Metals and Alloys
  • Mechanics

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