Abstract
Resins characterized by the properties of light weight and easy molding have become widely applied to the field of engenering materials, such as products with high reliability. Accordingly, it is strongly required to grasp the strength of parts made of resins accurately, and to exactly evaluate the resistance to fracture. Not only tensile and flexural tests, but also many studies have been done on the evaluation of the toughness of resins, after the manner of estimation for life time and reliability of metal goods. But the resins have uniqe characteristics, behaving as glass or materials with plasticity or viscoelasticity. Under certain circumstances, it is necessary to consider these characteristics. Thus at first, the factor on the strengh of resins are explained, next the outline of the method and the relationship of evaluation of toughness, strain energy release rate, stress intensity factor, J-integration, COD and the displacement method are explained. Lastly, the application of these methods is given for examples.
