DESIGN OF LAMINATES 



6-19 



of loading should be known so that the most appropriate factor of safety can be 

 established. The following factors of safety for various load conditions should be 

 considered for fiberglass structures: 



Static short term loads 



b. Static long term loads 



FS = 2 minimum 



FS = 4 minimum on reduced values 

 from tests 



c. Variable or changing loads 



d. Repeated loads 



e. Fatigue or load reversal 



f. Impact loads - repeated 



FS = 4 minimum 



FS = 6 minimum 



FS = 6 minimum 



FS = 10 minimum 



6. Service requirement. Where failure of a material can cause personal injury 

 or extensive damage to expensive equipment, a high factor of safety should 

 be used. 



Safety factors are dependent on many variables which only the design engineer can 

 analyze. Every problem presents its own peculiarities and requirements and therefore the 

 judgment and experience of the designer plays a most important part. The final selection 

 of a factor of safety, unless established by a specific code or authority, becomes the re- 

 sponsibility of the designer. 



TENSION 



Members subjected to axial pulling loads are under tensile stress. The magnitude of 

 stress is directly proportional to the load and the resisting area. In isotropic materials the 

 tensile stress distribution is assumed to be uniform throughout the entire cross-sectional 

 area. This assumption is not valid for composite orthotropic materials. 



Isotropic Laminates 



When a member, such as shown in Fig. 6-15, is subjected to an axial tensile load, the 

 stress relationship in its cross-section is indicated by means of the following formulas: 



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Fig. 6-15. Isotropic Tension Member 



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