The newly derived dynamic crack branching criterion is verified by dynamic photoelastic analysis of dynamic crack branchings in thin polycarbonate, single edged crack tension specimens. Successful crack branching was observed in four specimens and unsuccessful branchings in another. Crack branching consistently occurred when the necessary condition of KIb = 3.3 MPa miind the sufficient condition of r o = rc = 0.7 m were satisfied simultaneously.In the unsuccessful branching test the necessary conditon was not satisfied since K 1 was always less than Kib.

A load-based multiple-partial unloading microindentation technique has been developed for evaluating mechanical properties of materials. Comparing to the current prevailing nano/micro-indentation methods, which require precise measurements of the indentation depth and load, the proposed technique only measures indentation load and the overall indentation displacement (i.e. including displacement of the loading apparatus). Coupled with a multiple-partial unloading procedure during the indentation process, this technique results in a load-depth sensing indentation system capable of determining Young's modulus of metallic alloys with flat, tubular, or curved architectures. Test results show consistent and correct elastic modulus values when performing indentation tests on standard alloys such as steel, aluminum, bronze, and single crystal superalloys. The proposed micro-indentation technique has led to the development of a portable loaddepth sensing indentation system capable of on-site, in-situ material property measurement.

A 16 spark-gap camera was used to record the dynamic photoelastic patterns of ten centrally cracked, Homalite-100 specimens which fractured under ten biaxial stress ratios ranging from 3.7 to 0.The dynamic photoelastic patterns of curved cracks were used to verify the previously developed dynamic crack curving criterion. Cracks, which immediately curved upon propagation in three specimens under high biaxial loadings, were used to verify the static counterpart of the dynamic crack curving criterion. A previously developed dynamic crack branching criterion was verified by the dynamic photoelastic results involving cracks which eventually branched under low biaxial loadings.,

Two types of powder processing techniques, Mechano-Chemical-Bonding (MCB) and MCB plus ball-milling (BM) with reduced time, have been employed to process the nickel-based oxide-dispersion-strengthened (ODS) alloy powders with composition of Ni-20Cr-5A1-3W-1.5Y 2 O 3 to explore the alternate routes for fabricating, homogenizing and mechanical alloying (MA) the ODS alloy powders, which are usually processed by a prolonged ball-milling or rod-milling technique. In order to examine and evaluate the microstructure, morphology, blending homogeneity and MA effect of alloying powders, the commercial ball-milled ODS MA 956 alloy powders and experimental alloy powders processed by MCB only and MCB plus BM were subjected to microscopic and spectroscopic characterization and analysis using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A FIB (focus ion beam) lift-out technique was employed to prepare the TEM cross-section samples of processed powders. The results showed that the MCB plus BM with reduced time could produce the ODS alloying powders with homogeneous lamellate structure similar to MA 956 powders processed by conventional BM technique with a prolonged period of time. The ODS alloy powders processed by MCB plus BM are to be utilized to fabricate the bulk ODS alloy product in the further research phase.