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Although striations are often used in evaluating fatigue crack growth in engineering materials, they have not been used in studying the mechanics of fracture in hard tissues. The primary objective of this study was to evaluate the striations resulting from fatigue crack growth in the dentin of human teeth. Compact tension (CT) specimens obtained from the coronal dentin of molars from young (17 < or = age < or = 37 years) and senior (age > or = 50 years) patients were subjected to cyclic Mode I loads. Striations evident on the fracture surfaces were examined using a scanning electron microscope (SEM) and contact profilometer. Fatigue crack growth striations that developed in vivo were also examined on fracture surfaces of restored molars. A power spectrum analysis of surface profiles from the CT specimens showed that the striation spacing ranged from 50 to 170 microm. The average spacing in the dentin of seniors (130 +/- 23 microm) was significantly larger (p < 0.001) than that in young dentin (88 +/- 13 microm). Fatigue striations in the restored teeth exhibited features that were consistent with those that developed in vitro and a spacing ranging from 59 to 95 microm. Unlike metals, the striations in dentin developed after a period of cyclic loading that ranged from 1 x 10(3) to 1 x 10(5) cycles. A quantitative evaluation of the striation spacing using the Bates-Clark equation suggested that cyclic crack growth within the restored teeth occurred at a stress intensity range near 0.7 MPa x m(0.5), and a stress range of approximately 12 MPa.

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An experimental study of fatigue crack growth in dentin was conducted, and the influence of stress ratio (R) on the crack growth rate and mechanisms of cyclic extension were examined. Double Cantilever Beam (DCB) fatigue specimens were sectioned from bovine molars and then subjected to high cycle fatigue loading (10 5 Ͻ N Ͻ 10 6 ) under hydrated conditions. The evaluation consisted of Mode I loads with stress ratios that ranged from Ϫ0.5 to 0.5. The fatigue crack growth rates were measured and used to estimate the crack growth exponent (m) and coefficient (C) according to the Paris Law model. The fatigue crack growth rates for steady-state extension (Region II) ranged from 1E-7 to 1E-4 mm/cycle. It was found that the rate of cyclic extension increased significantly with increasing R, and that the highest average crack growth rate occurred at a stress ratio of 0.5. However, the crack growth exponent decreased with increasing R from an average of 4.6 (R ϭ 0.10) to 2.7 (R ϭ 0.50). The stress intensity threshold for crack growth decreased with increasing R as well. Results from this study suggest that an increase in the cyclic stress ratio facilitates fatigue crack growth in dentin and increases the rate of cyclic extension, both of which are critical concerns in minimizing tooth fractures and maintaining lifelong oral health.

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Many experimental and numerical works have been done on different configurations of solar stills to optimize the design by investigative the effect of climatic, operational and design parameters on its performance. One of the most important of the operational parameters that has received a considerable attention in the literature is the brine depth. A study was subsequently conducted to verify this trend by an experimental investigation on three types of solar still that was fabricated with an area of 1 m2 and tested in the composite climate of Coimbatore, Tamilnadu, India, (Latitude: 11°N; Longitude; 77°E and an altitude of 409 m above sea level) with five different brine depths, namely 1, 4, 6, 8 and 10 cm. The present study clearly validated that the decreasing trend in productivity with the increase of brine depth.

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