EXPERIMENTAL RESULT A relationship between number of cycles to failure and stress amplitude in halogen free material and halogen material were shown in Fig.3. From Fig.3, it was proven that the fatigue life of halogen-free material is longer than that of conventional halogen material. That is to say, the fatigue life of halogen free material was longer than that of halogen material. Generally, the material of which the static strength shown by the stress-strain chart is similar becomes also similar on fatigue characteristics. However, there was a remarkable difference in fatigue life of both materials in spite of not recognizing the difference of static strength clearly. Then, in the following chapter, fatigue destructive mechanism are considered from a meso-scopic viewpoint, in order to clarify the difference of the fatigue characteristic of both material. CONSIDERATION Relationship between crack initiation life and fatigue fracture life The relationship between crack initiation life and fatigue fracture life of sample materials is shown in Fig.4. Still, number of crack initiation cycles was decided when main crack length became 0.5 (mm) by visual observation. From Fig.4, it was proven that the crack initiation of halogen free material was comparatively an early time in fatigue life. On the other hand , it was proven that the crack initiation of halogen material was late in fatigue life, halogen material was immediately fractured after a main crack was initiated. Then, Fig.5 shows the relationship between crack initiation life ratio (NI ;Number of crack initiation life / Nf ; Number of failure life) and stress amplitude in both materials. From Fig.5, it was proven that the value of crack initiation life ratio of halogen free material was smaller than that of halogen Table 3 Mechanical properties of Halogen- free and halogen material Number of cycles (cycle) Stress amplitude (MPa) 0 10 20 30 40 50 60 70 80 90 100 102 103 104 105 106 107 Halogen-free material Halogen material Item Halogenfree material Halogen material Elastic modulus(GPa) 1.51 1.44 Tensile strength(MPa) 363.7 364.7 Total elongation 3.36 3.32 Fig.3 S-N curves 0 10 20 30 40 50 60 70 80 90 100 102 103 104 105 106 107 Number of cycles (cycle) Stress amplitude (MPa) Halogen-free material Failure Crack initiation Halogen material Failure Crack initiation Stress amplitude(MPa) 0 10 20 30 40 50 60 70 80 90 100 50 60 70 80 90 Life ratio Ni/Nf Halogen-free laminate Halogen laminate Fig.4 Relationship between number Fig.5 Ratio of number of cycles of cycles to failure and crack initiation to crack initiation in fatigue life
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