Fracture statistics of dental ceramics: Discrimination of strength distributions

The Weibull distribution is the most widely used function in the reliability analysis and structural design of dental ceramics; however, it is still unclear whether Weibull distribution is always the most suitable one. With wide applications of dental ceramics, a special attention has been paid in discriminating their strength distributions. In this paper, three versatile functions, involving normal, log-normal and Weibull distributions, are applied to the analysis of ten strength data sets of dental ceramics with different compositions and the results are compared in terms of the Akaike information criterion and the Anderson-Darling test. It reveals that various microstructures and compositions in the investigated dental ceramics cause their strength distributions deviated from the Weibull distribution. The influence of microstructure induced fracture properties (multiple-modal flaw size distribution, R-curve behavior and subcritical crack growth) on strength distributions is discussed

Dynamic localization of a helper NLR at the plant-pathogen interface underpins pathogen recognition

Plants employ sensor-helper pairs of NLR immune receptors to recognize pathogen effectors and activate immune responses (1). Yet the subcellular localization of NLRs pre- and post-activation during pathogen infection remains poorly understood. Here we show that NRC4, from the ‘NRC’ solanaceous helper NLR family (1), undergoes dynamic changes in subcellular localization by shuttling to and from the plant-pathogen haustorium interface established during infection by the Irish potato famine pathogen Phytophthora infestans. Specifically, prior to activation, NRC4 accumulates at the extra-haustorial membrane (EHM), presumably to mediate response to perihaustorial effectors, that are recognized by NRC4- dependent sensor NLRs. However not all NLRs accumulate at the EHM, as the closely related helper NRC2, and the distantly related ZAR1, did not accumulate at the EHM. NRC4 required an intact N-terminal coiled coil domain to accumulate at the EHM, whereas the functionally conserved MADA motif implicated in cell death activation and membrane insertion was dispensable for this process. Strikingly, a constitutively autoactive NRC4 mutant did not accumulate at the EHM and showed punctate distribution that mainly associated with the plasma membrane, suggesting that post-activation, NRC4 may undergo a conformation switch to form clusters that do not preferentially associate with the EHM. When NRC4 is activated by a sensor NLR during infection however, NRC4 forms puncta mainly at the EHM and to a lesser extent at the plasma membrane. We conclude that following activation at the EHM, NRC4 may spread to other cellular membranes from its primary site of activation to trigger immune responses

The mechanical strength of a ceramic porous hollow fiber

The mechanical strength of inorganic porous hollow fibers is a critical constraint that limits their wide scale application. Various methods, including 3-point bending, 4-point bending, and diametrical compression are used for the quantification of the mechanical strength. Here, we show that these methods cannot be used in an interchangeable manner. For large sets of alumina hollow fibers, the parameters describing the cumulative probability of failure functions depend on the type of measurement, i.e., 3 or 4-point, the span size, and the measurement geometry. This implies that reporting data on mechanical properties of inorganic hollow fibers requires that extensive information about the experimental details is provided, and that a direct quantitative comparison between datasets is unjustifiable. The mechanical strength of the alumina hollow fibers tends to follow a normal distribution, or log-normal distribution, instead of the often used Weibull distribution. Monte Carlo simulations demonstrate that, especially at small sample set sizes, it is difficult to accurately determine the shape of the probability distribution. However, detailed knowledge of the type and the shape of this distribution function is essential when mechanical strength values are to be used in further design

Effect of sintering temperature on microstructure and strength distribution of alumina ceramic springs

Ceramic coil springs are one of the most widely used components in mechanical systems under harsh chemical conditions and high temperatures. In real applications of ceramic coil springs, knowing the effect of sintering temperature on their microstructure and strength distribution plays a crucial role. In this paper, the microstructure and strength distribution of alumina coil springs sintered at 1550, 1600 and 1650°C are investigated. Strength data of alumina coil springs are fitted by a Weibull distribution and according to the coefficient of determination, the deviation from the Weibull distribution can be determined. It is shown that the Weibull distribution best fits the strength data of alumina coil springs sintered at 1600°C. The probable reasons for deviation from the Weibull distribution are discussed in terms of grain size, porosity, and R curve behaviour