Showing papers by "Dongsheng Zhang published in 2009"
TL;DR: Microstructural changes with aging decreased the capacity for near-tip inelastic deformation and microcracking of the tubules, which in turn suppressed the formation of unbroken ligaments and the degree of extrinsic toughening.
Abstract: An evaluation of the crack growth resistance of human coronal dentin was performed on tissue obtained from patients between ages 18 and 83. Stable crack extension was achieved over clinically relevant lengths (0 ≤ a ≤1 mm) under Mode I quasi-static loading and perpendicular to the nominal tubule direction. Results distinguished that human dentin exhibits an increase in crack growth resistance with extension (i.e. rising R-curve) and that there is a significant reduction in both the initiation (Ko) and plateau (Kp) components of toughness with patient age. In the young dentin (18≤age≤35) there was a 25 % increase in the crack growth resistance from the onset of extension (Ko =1.34 MPa·m0.5) to the maximum or “plateau” toughness (Kp = 1.65 MPa·m0.5). In comparison, the crack growth resistance of the old dentin (55≤age) increased with extension by less than 10 % from Ko = 1.08 MPa·m0.5 to Kp = 1.17 MPa·m0.5. In young dentin toughening was achieved by a combination of inelastic deformation of the mineralized collagen matrix and microcracking of the peritubular cuffs. These mechanisms facilitated further toughening via the development of unbroken ligaments of tissue and posterior crack-bridging. Microstructural changes with aging decreased the capacity for near-tip inelastic deformation and microcracking of the tubules, which in turn suppressed the formation of unbroken ligaments and the degree of extrinsic toughening.
115 citations
TL;DR: Both dentin and enamel underwent contraction with water loss, regardless of the patient age, and the degree of deformation shrinkage resulting from dehydration is over a factor of magnitude larger in dentin than enamel.
41 citations
TL;DR: In this article, the mechanical and thermal properties of polymeric films and solder joints used in electronic packaging are investigated using digital image correlation (DIC) to evaluate the inplane deformation.
Abstract: The mechanical and thermal properties of materials used in electronic packaging are of significant importance. This paper presents a novel application of Digital Image Correlation (DIC) to characterise the properties of polymeric films and solder joints used in electronic packaging. A miniature loading frame and a thermal chamber were designed to load the film and solder samples, respectively. The mechanical properties (Elastic Modulus and Poisson's ratio) of the polymeric film were estimated under uniaxial tension, while the thermal expansion of a solder ball was evaluated in a temperature chamber. Digital images of the samples were documented with a microscopic imaging system and DIC was used to evaluate the in-plane deformation. An algorithm that combined the subpixel technique, displacement fitting and correction of lens aberration was developed to improve the precision of the measurements. Results show that micro DIC is an easy-to-use technique and has strong potential as a characterisation methodology for materials and structures in electronic packaging.