ENGINEERING PROPERTIES OF LAMINATES 5-7 



For each range an average value and a lower limit was established. It can be 

 stated, with 95 per cent confidence, that not more than 5 per cent of the panels made 

 under similar conditions will give values below the lower limit. 



5. A detail discussion of the statistical procedure is given in Appendix B. 

 Results of Investigation of Main Variables 



1. Fabricators - effects of variations in good shop practice. 



This variable has considerable effect on some of the properties. The differences 

 are consistent in the sense that they are the same for all laminate thicknesses and for 

 angles from the warp. 



2. Laboratories - effects of variations in testing techniques and equipment. 



Consistent differences among test laboratories were found in some small areas 

 of the test data. The measurement error between duplicate coupons was not found 

 to be controlling for any property. In most cases, the measurement error was 

 negligible compared to the average random variability of a single fabricator making 

 similar laminates. 



3. Materials - effects of different types of reinforcement. 



As expected, the different types of reinforcement and glass percentage show 

 marked differences in physical and mechanical properties. 



For most properties, and particularly for the thicker laminates, little apparent 

 difference exists between laminates faced with single ply 10 ounce cloth and laminates 

 of equal construction without facings. For these laminates, with and without cloth 

 facings, some differences do exist in glass content and tensile strength within both 

 mat and woven roving reinforcements and in tensile and flexural moduli for mat 

 reinforcement only. 



Laminates of mat reinforcement are generally isotropic or nondirectional for all 

 properties. Laminates of cloth and woven roving reinforcement are orthotropic or 

 directional for most strength and modulus properties, but are isotropic for shear 

 strength properties. Laminates of cloth and woven roving are particularly directional 

 for tensile strength, values at 45 degrees to the warp being much lower than values at 

 degrees and 90 degrees to the warp. 



4. Laminate Thickness - effects of number of reinforcement plies. 



The thickness of the test laminates is a minor factor in the data for some of the 

 reinforcements and properties. There seems to be little consistency in this effect. 

 It is detected in the moduli values for some of the reinforcements and for the 

 strength values for other reinforcements. Thickness effect is particularly apparent 

 in all strengths and moduli for woven roving reinforcement. 



