addition, its fracture surface was flatter than halogen material, and it has shown frail fracture morphology. And, there was peeling between resin and glass fiber in the central region of the base of these shell state form. One region of the fracture surface pattern of matrix resin of each material like superscription was named Unit Fracture Area. The difference of this UFA seems to greatly affect the difference in fatigue life of each material. A cause of the difference of size of UFA between halogen material and halogen free material was considered to be due to the difference of a molecular structure of matrix resin. Criteria of fatigue fracture in composite material From this fatigue test result, the fatigue life of each material differs in spite of the equal of mechanical property. This was considered to be due to the difference of criteria of fracture between static fracture and fatigue fracture. Then, sample materials are caught as a resin/glass fiber composite in order to explain criteria of fracture. Fig.9(a) shows a way of list of the element link of each material in static fracture. Each element link seems to parallelly range in static fracture. Therefore, the whole material was not fractured immediately, even if the weakest element was destroyed, because the material strength was kept by the more resistant elements. That is to say, its strength is dependent on the most resistant element in the static destruction. The glass fiber is the most resistant element in this material. So the static strength seemed to be equal, since an equal glass fiber has been used in sample materials. Fig.9 (b) shows a way of list of the element link in fatigue fracture. Each element link seemed to ranks for the series in fatigue fracture. Fatigue fracture is caused by crack generating and developing at repeated stress that is smaller than yield stress (or, tensile strength). Therefore, a crack initiation and propagation is most important role in failure mechanism in fatigue fracture. Since a crack is generated from the weakest element in the material, its element decides the whole life in the fatigue fracture. So, it is considered that the fatigue life was controlled for the weakest link hypothesis. By the consideration to the previous paragraph, a weakest element in this material seemed to be an interface between resin and reinforced fiber or resin. That is to say, it is thought that a difference of the fatigue life of halogen material and halogen free material is based on a difference of the strength of the interface between glass fibers and resin by difference of the kind of resin. Fatigue cracks in halogen material were initiated from the interface of fiber and resin, and in addition, it develops, while the resin was exfoliated from fibers. In the meantime, fatigue crack in halogen-free material develops inside of matrix resin, since adhesive property of the interface of fiber and resin was comparatively good. And since the resistance for fracture of the resin was bigger than halogen material, a fatigue crack comparatively slowly develops on the halogen free material. So, fatigue life of halogen-free materials seemed to be longer than that of halogen materials. Parallel element Element Stress Crack Glass fiber Resin Element Fracture Halogen-free material Halogen material Stress Crack tip Series element Glass fiber Resin Stress Crack tip Glass fiber Resin (a)Static fracture mode (b)Fatigue fracture mode Fig.9 Criteria in static fracture and fatigue fracture , and fracture mechanism
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