2.全瓷材料的疲劳损伤及咬合病（2. Fatigue damage and occlusion of all porcelain materials）.docVIP

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2.全瓷材料的疲劳损伤及咬合病（2. Fatigue damage and occlusion of all porcelain materials）.doc

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2.全瓷材料的疲劳损伤及咬合病（2. Fatigue damage and occlusion of all porcelain materials）

2.全瓷材料的疲劳损伤及咬合病（2. Fatigue damage and occlusion of all porcelain materials） And when the stress increases to a certain value, but can not return to the original, after unloading at this time is called the stress of the material beyond its elastic limit, which is more than the removal of external force, its size can be fully recovered when the material on the maximum stress. The stress strain curve describes the strain of the material under different stresses. For elastic materials, at the origin to a middle point P, the curve is a straight line, and then it becomes a curve. This P point becomes the proportional limit, where the stress strain ratio is elastic modulus, and the modulus of elasticity is also called youngs modulus, which is expressed by force in unit area. When choosing a restorative materials, the limit stress of material selection is often greater than using stress several times, even under such conditions the practical work is not safe, the so-called low stress brittle fracture occurs, often in the stress is far lower than the material strength index, and have no obvious plastic deformation occurs under the condition of damage. This presents a new problem for us. We use the traditional calculation method based on ultimate stress to carry out the material design, which can not fully reflect the objective reality. After analysis research, people found on the material internal structure homogeneous continuous assumption is a kind of ideal assumption, in fact material internal always exist some defects such as cracks, and the brittleness damage is caused by the micro crack propagation, the result is a stress intensity factor K, K is described near the crack tip stress and strain of a parameter. Its also the relationship between the stress sigma and the crack size a, K = Y · sigma times the square root of a. Where Y is the stress intensity factor, the unit is MPa square root m, sigma is the stress, the unit is MPa, and Y is constant. The pattern of loading