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Slow Crack Growth (slow + crack_growth)
Selected AbstractsModeling of water absorption induced cracks in resin-based composite supported ceramic layer structuresJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008Min Huang Abstract Cracking patterns in the top ceramic layers of the modeled dental multilayers with polymer foundation are observed when they are immersed in water. This article developed a model to understand this cracking mechanism. When water diffuses into the polymer foundation of dental restorations, the foundation will expand; as a result, the stress will build up in the top ceramic layer because of the bending and stretching. A finite element model based on this mechanism is built to predict the stress build-up and the slow crack growth in the top ceramic layers during the water absorption. Our simulations show that the stress build-up by this mechanism is high enough to cause the cracking in the top ceramic layers and the cracking patterns predicted by our model are well consistent with those observed in experiments on glass/epoxy/polymer multilayers. The model is then used to discuss the life prediction of different dental ceramics. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2008 [source] Delayed Failure of Hi-Nicalon and Hi-Nicalon S Multifilament Tows and Single Filaments at Intermediate Temperatures (500°,800°C)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2009W. Gauthier Previous results have shown that tows of SiC Nicalon fibers are sensitive to the phenomenon of delayed failure, at temperatures below 700°C. The present paper examines the static fatigue of Hi-Nicalon and Hi-Nicalon S when subjected to constant load, at temperatures between 500° and 800°C in air. Multifilament tows and single filaments were tested. Experimental data show that the rupture times of tows depend on the applied stress according to the conventional power law t,n=A. In contrast, the stress-rupture time data obtained on single filaments exhibit significant scatter. A model based on slow crack growth in single filaments shows that the stress-rupture of fiber tows follows the conventional time power law. The dependence on temperature was introduced. The model allowed sound calculations of tow lifetimes and characteristics of the slow crack growth phenomenon to be extracted from the tow stress-rupture time data. [source] High-Temperature Tensile Strength of Er2O3 -Doped ZrO2 Single CrystalsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2006José Y. Pastor The deformation and fracture mechanisms in tension were studied in single-crystal Er2O3 -doped ZrO2 monofilaments processed by the laser-heated floating zone method. Tensile tests were carried out between 25° and 1400°C at different loading rates and the dominant deformation and fracture mechanisms were determined from the shape of the stress,strain curves, the morphology of the fracture surfaces, and the evidence provided by monofilaments deformed at high temperature and broken at ambient temperature. The tensile strength presented a minimum at 600°,800°C and it was controlled by the slow growth of a crack from the surface. This mechanism was also dominant in some monofilaments tested at 1000°C and above, while others showed extensive plastic deformation before fracture at these temperatures. The strength of plastically deformed monofilaments was significantly higher than those which failed by slow crack growth due to the marked strain hardening capacity of this material. [source] Fracture prediction in tough polyethylene pipes using measured craze strengthPOLYMER ENGINEERING & SCIENCE, Issue 5 2008P. Davis In this study, an empirical model is developed that predicts the time to failure for PE pipes under combined pressure and deflection loads. The time-dependent craze strength of different PE materials is measured using the circumferentially deep-notched tensile (CDNT) test. In agreement with previous research, results indicate that bimodal materials with comonomer side-chain densities biased toward high-molecular-weight PE molecules exhibit significantly higher long-term craze strengths. A comparison of currently available PE materials with CDNT samples taken from a PE pipe that failed by slow crack growth in service clearly indicates the superior performance of new-generation materials. Using measured craze strength data from the CDNT test, a simplified model for predicting failure in buried PE pipes is developed. Extending previous research, the reference stress concept is used to calculate an equivalent craze stress for a pipe subjected to combined internal pressure and deflection loads. Good agreement is obtained between the model predictions and observed failure times in an experimental test-bed study of pipes under in-service loading conditions. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Slow crack growth-notches-pressurized polyethylene pipesPOLYMER ENGINEERING & SCIENCE, Issue 11 2007Norman Brown A general method for predicting the lifetime of a polyethylene structure that fails by slow crack growth was applied to the case of externally notched pressurized pipes. An analysis of experimental data indicated that the residual stress must be taken into account. The critical notch depths associated with a given lifetime were calculated as a function of pipe size, PENT value of the resin, and temperature. The results were tabulated to serve as practical guide lines for deciding whether a pipe should be discarded if the notch is too deep. The current 10% of the thickness rule now used by industry was found to be invalid. POLYM. ENG. SCI., 47:1951,1955, 2007. © 2007 Society of Plastics Engineers [source] Intrinsic lifetime of polyethylene pipelinesPOLYMER ENGINEERING & SCIENCE, Issue 4 2007Norman Brown An equation was developed for calculating the time to failure by slow crack growth (SCG) failure in any polyethylene structure. The equation requires the following experimental inputs: (1) the resistance to SCG as measured by the PENT test (ASTM F1473), (2) the stress intensity of the defect from which failure originates, and (3) the temperature. A simple experiment for determining the stress intensity is presented. The equation was applied to SCG failures that are associated with the inherent random defects that occur in the wall of all pipes. The size of the inherent random defect that exists in commercial gas pipes was found to be 0.14 mm. POLYM. ENG. SCI., 47:477,480, 2007. © 2007 Society of Plastics Engineers. [source] | ||||||||||