Evaluation of Fatigue Crack Growth Performance in different Hardmetal Grades based on Finite Element Simulation

AbstractHardmetals (WC-Co) are a group of composite materials exhibiting outstanding combinations of hardness and toughness. Therefore, they are extensively used for highly demanding applications, such as cutting and drilling tools, where cyclic loading is one of the most critical service conditions.The micromechanics of fracture in hardmetals under static loads is well investigated and understood. Studies regarding failure by fatigue on the other hand, is mainly limited to experimental investigations conducted at a component scale and seldom refer to the influence of microstructure on the failure mechanism. Moreover, numerical studies evaluating the mechanisms of fatigue crack growth in hardmetals are also scarce.Experimental observations indicate that, the overall fatigue performance of hardmetals can be predicted from the early stages of the microcrack evolution. Taking this into consideration, a numerical methodology for evaluating the fatigue crack propagation in hardmetals was developed. In this respect, previously a model based on a continuum damage mechanics approach together with an element elimination method was implemented in a commercial finite element software for simulating the crack propagation in hardmetals. In the current study, the model is further extended to artificially generated hardmetal structures in order to simulate and evaluate the overall fatigue crack growth performance of different hardmetal grades.Fatigue crack growth rate diagrams based on the simulations were plotted for different hardmetal grades and the results showed good agreement in comparison to experimental observations. Such an approach is helpful for designing hardmetals at a microstructural scale without going through extensive experimental work

Comparative Study of the Tempering Behavior of Different Martensitic Steels by Means of In-Situ Diffractometry and Dilatometry

Martensitic steels are tempered to increase the toughness of the metastable martensite, which is brittle in the as-quenched state, and to achieve a more stable microstructure. During the tempering of steels, several particular overlapping effects can arise. Classical dilatometric investigations can only detect effects by monitoring the integral length change of the sample. Additional in-situ diffractometry allowed a differentiation of the individual effects such as transformation of retained austenite and formation of cementite during tempering. Additionally, the lattice parameters of martensite and therefrom the tetragonality was analyzed. Two low-alloy steels with carbon contents of 0.4 and 1.0 wt.% and a high-alloy 5Cr-1Mo-steel with 0.4 wt.% carbon were investigated by dilatometry and in-situ diffractometry. In this paper, microstructural effects during tempering of the investigated steels are discussed by a comparative study of dilatometric and diffractometric experiments. The influence of the chemical composition on the tempering behavior is illustrated by comparing the determined effects of the three steels. The kinetics of tempering is similar for the low-alloy steels and shifted to much higher temperatures for the high-alloy steel. During tempering, the tetragonality of martensite in the steel with 1.0 wt% carbon shifts towards a low carbon behavior, as in the steels with 0.4 wt.% carbon

Ultra-Fast High Temperature Sintering (UHS) of Strontium Titanate

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Uso del recibo por honorarios electrónico y la satisfacción percibida de los contribuyentes que prestaron servicio en el Fondo de Cooperación para el desarrollo social en el año 2012

La presente investigación tuvo como propósito establecer la relación entre el Uso del Recibo por Honorarios Electrónico y la satisfacción percibida por los contribuyentes que prestaron servicio en el Fondo de Cooperación para el Desarrollo Social en el año 2012. Obteniéndose una significancia de 0.923** lo cual indica que la relación existente entre ambas variables es muy significativa. El diseño empleado fue no experimental de tipo descriptivo y correlacional, de enfoque cuantitativo y de tipo básico. Se utilizó una muestra censal. Los instrumentos empleados fueron el Cuestionario de Uso del Recibo por Honorarios Electrónico y la Satisfacción percibida de los Contribuyentes que prestaron servicio el Fondo de Cooperación para el Desarrollo Social en el año 2012. Se realizó el análisis psicométrico para ambos instrumentos bajo los criterios de confiabilidad y validez. Los resultados indican que existe una relación significativa entre el Uso del Recibo por Honorarios Electrónicos y la Satisfacción percibida por los Contribuyentes. Asimismo los resultados de correlación indican que el Uso del Recibo por Honorarios Electrónicos están relacionados de manera significativa con la Satisfacción percibida de los Contribuyente y sus dimensiones, en la Hipótesis general se ha obtenido un p-valor 0,915** de nivel de significancia asumido por lo tanto no se rechaza la hipótesis nula. En conclusión: El grado de relación que existe entre el Uso del Recibo por Honorarios Electrónico y la Satisfacción percibida es significativa por los Contribuyentes que prestaron servicio en el Fondo de Cooperación para el Desarrollo Social