ABSTRACT
To investigate the mechanical property and failure behavior of laser metal deposited additive manufacturing Ti-6Al-4V (LMD Ti64) in a wide range of stress states and strain rates, different types of specimens were tested at strain rates of 0.001-5000/s. Numerical simulations were conducted to collect the local fracture strain at the critical position where the failure happened for all specimens. By comparing with Ti64 alloy manufactured by different techniques, the failure behavior of LMD Ti64 alloy shows a stronger sensitivity to Lode angle parameter and strain rate. The role of initial defects in failure was discussed. It is found that high laser power and overlap ratio can improve the failure behavior by reducing the number of initial defects. The initial defects on the fracture surface at much higher strain rates were observed, indicating that the initial crack rather than initial void acts as the crack growth point leading to the final fracture at higher strain rates. The scanning electron microscope observation of the fracture surface shows that the failure mechanism of LMD Ti64 alloy varies from different stress states and strain rates. The failure mechanism is characterized by the shear fracture at the negative stress triaxiality, whereas the void growth fracture plays a dominant role in the failure mechanism of LMD Ti64 alloy at a high stress triaxiality on the quasi-static loading condition.
ABSTRACT
Objective: To investigate the species and breeding density of ac aroid mites in the stored rhizomatic traditional Chinese medicinal materials in Anhui province, China, in order to supply evidences for control and prevention of such species. Methods: The stored traditional Chinese medicinal materials of root-stock origins were collected in 30 herb stores and warehouses in 17 cities across Anhui province. Mites were collected by using Tullgren funnel and directicopy, and identified under microscopy. Results: Twenty-two species of acaroid mites, belonging to 15 genera under 5 families, were identified from the total 47 stored samples, in which Tyrophagus putrescentiae, Acarus farinae, Carpoglyphus lactis, and Cologlyplus berlesei were predominant. Conclusion: Breeding density of acaroid mites was high in the stored rhizomatic traditional Chinese medicinal materials in Anhui province. This indicates that the traditional Chinese medicinal herbs of root-stock origins in storage are seriously contaminated by the acaroid mites, and such infestation should be positively controlled to reduce the potential harm to public health (AU)
Objetivo: investigar las especies y densidad de especies de ácaros en los productos a bases de raíces de la medicina tradicional china en la provincia de Anhui, China, con el fin de proporcionar evidencias para el control y la prevención de tal infestación. Métodos: se recogieron muestras de productos procedentes de raíces usados en la medicina tradicional china en 30 tiendas y almacenes de 17 ciudades de la provincia china de Anhui. Se recogieron las muestras mediante el embudo de Tullgren y la directicopia y los ácaros fueron identificados bajo microscopia. Resultados: se identifi caron 22 especies de ácaros, pertenecientes a 15 géneros menores de 5 familias a partir de 47 muestras almacenadas, en las que Tyrophagus putrescentiae, Acarus farinae, Carpoglyphus lactis y Cologlyplus berlesei eran predominantes. Conclusión: la densidad de ácaros fue alta en el las muestras a base de raíces en el material almacenado para usarse como remedio en la medicina tradicional china en la provincia de Anhui. El control de esta infestación puede reducir el daño potencial para la salud pública (AU)
Subject(s)
Medicine, Traditional/methods , Plants, Medicinal , Mite Infestations , Ecosystem/methods , Mites/pathogenicity , Medicine, Chinese Traditional/methods , Medicine, Chinese Traditional/trendsABSTRACT
OBJECTIVE: To study mechanical and cyclic fatigue behavior of IPS Empress2 under cyclic loading, and to establish guidelines for the use and design of all-ceramic crowns. METHODS: A 3-D finit element method model of tooth and crown were established. The strength and lifetime of all-ceramic crowns under cyclic loading in centric occlusion were investigated using computational techniques of the Abaqus and MSC Fatigue software. RESULTS: Most of the fatigue and fracture of all-ceramic crown occurred within the veneering material at cervical marginal of the crown. The number of loading cycles before failure occurred varied within specified limits 2,506,109-6,950,243. The lifetime of the crown decreased significantly as loading increased and decreased gradually as loading time increased as well. CONCLUSIONS: The mechanical and fatigue behavior of ceramic materials and restorations need to be improved before clinical use in order to guarantee clinical long-term success of all-ceramic crown. properly in order to increase the longevity of all-ceramic crowns.
Subject(s)
Dental Porcelain , Denture, Partial, Fixed , Finite Element Analysis , Materials TestingABSTRACT
OBJECTIVE: To study the residual stresses of ceramic-metal bond at viscoelastic and elastic phases during cooling of porcelain-fused-to-metal in order to precisely calculate the ceramic-metal bond strength and improve the restorations. METHODS: The finite element model was set up according the crack initiation test (three-point flexure bond test) based on ISO Standard, elements of viscoelastic and themal-displacement were used to part the model. The result at viscoelastic phases was used as initiation condition of elastic phases to add up. RESULTS: The compressive stress was caused by metal during cooling occurred in the ceramic. The shear stress induced by loading was offset by thermal shear stress. Load tensile stress and the thermal compressive stress vertical of interface concentrated at the end of the bond interface, but the tensile was greatly higher. CONCLUSION: The residual stress is very important to metal-ceramic restorations, and the viscoelastic behavior of porcelain greatly influences it. If the metal and ceramic are compatible,the components stresses of the residual stresses may benefit to ceramic-metal bond, and can be taken as a part of bond stresses.
