| 1 | A STUDY OF STRUCTURE AND PROPERTY CHANGES OF BIODEGRADABLE POLYGLYCOLIDE AND POLY(GLYCOLIDE-co-LACTIDE)FIBERS DURING PROCESSING AND IN VITRO DEGRADATION显示文摘Structure and properties of bioabsorbable polyglycolide (PGA) and poly(glycolide-co-lactide) (PGA-co-PLA)fibers were investigated during several industrial processing stages and in vitro degradation by means of wide-angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA) and mechanical property tests. In the orientation stage, the PGA fibers were found to have higher degrees of crystallinity than corresponding PGA-co-PLA samples produced under similar conditions. In the hot-stretching and post-annealing stages, after fibers were braided, PGA samples were found to gain more crystallinity and higher Tg than PGA-co-PLA samples. The higher crystallinity in PGA fibers resulted in a slower rate of degradation. DMA results showed that a great deal of internal stress that was built during orientation and hot-stretching stages was released in the post-annealing stage for all PGA and PGA-co-PLA samples. During earlier stages ofin vitro degradation, both PGA and PGA-co-PLA samples exhibited the typical cleavage-induced crystallization mechanism. The heat shrinkage in the glass transition area was found to disappear after 6-8 days of degradation for all PGA and PGA-co-PLA samples, indicating the amorphous portions of the polymers lost orientation after a short period in the buffer solution, most likely due to relaxation of the cleaved chains. | Bruce X.Fu Benjamin S.Hsiao Gavin Chen Jack Zhou Susan Lin Jenny Yuan Ilya Koyfman Dennis D Jamiolkowski Edward Dormier | 2003 | Chinese Journal of Polymer Science2003，21，2： | 9 |
| 2 | Toward developing Ti alloys with high fatigue crack growth resistance by additive manufacturing显示文摘Fatigue crack growth behaviors were investigated by three-point bending tests for TA19 alloy fabricated by laser metal deposition and four kinds of heat-treated samples.The crack growth resistance of the TA19 samples in the near-threshold regime and Paris regime was evaluated through the experimental characterization and theoretical analysis of the interaction between fatigue crack andα/βphase inter-face,columnar prior-βgrain boundary and colony boundary.The results show that in the near-threshold regime,the fatigue crack propagation threshold and resistance increase with the increase of widths of lamellarαp phases and colonies,and the decrease of the number ofαlaths with an angle(ϕ)relative to the applied stress direction ranging from 75°to 90°.In the Paris regime,the fatigue cracking path can be deflected at colony boundaries or columnar prior-βgrain boundaries.The larger the deflection angle,the more tortuous the cracking path and the lower the fatigue crack growth rate.The angle(γ)of the columnar prior-βgrain growth direction relative to the build direction affects not onlyϕof differentαvariants,but also the fatigue cracking path deflection angle(θij)at columnar prior-βgrain boundaries.An optimal combination ofγ=0°-15°-0°-15°for several adjacent columnar prior-βgrains is derived from the theoretical analysis,and that can effectively avoidϕbeing in the range from 75°to 90°and makeθij as large as possible.Such findings provide a guide for the selection of scanning strategies and process parameters to additively manufacture Ti alloys with high fatigue damage tolerance. | F.Wang L.M.Lei X.Fu L.Shi X.M.Luo Z.M.Song G.P.Zhang | 2023 | Journal of Materials Science & Technology2023，，1： | 1 |
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