5-6 



ENGINEERING PROPERTIES OF LAMINATES 



Test Procedures 



Property 



Tensile strength 



Flexural strength 



Compressive strength 



Shear strength perpendicular 



Shear strength parallel 



Tensile modulus 



Flexural modulus 



Compressive modulus 



Specific gravity 



Per cent glass by volume 



Per cent glass by weight 



Tensile Poisson's Ratio * 



Compressive Poisson's Ratio * 



Mechanical properties specimens were wet-conditioned or immersed in water at room 

 temperature for 30 days. 



* developed specifically for this program, see Appendix A. 



All of the above properties were tested on specimens cut at degrees, 45 degrees and 

 90 degrees from the warp direction of the test panel. 



Statistical Analysis of Test Data 



The test program was developed primarily to study the following four main variables 

 which were considered of primary importance: 



1. 

 2. 

 3. 

 4. 



Fabricators 



Laboratories 



Materials 



- effects of variations in good shop practice. 



- effects of variations in testing techniques and equipment. 



- effects of different types of reinforcement. 



Laminate thickness - effects of number of reinforcement plies. 



To keep the number of test samples to a minimum and still obtain the necessary data 

 for statistical confidence in the results, a balanced fourth of a full set of (4)4 factorial 

 design plus additions was used. One material was added and all thicknesses were 

 studied for one of the materials. 



It was necessary to omit a very small portion of the test data because the pattern 

 of its scatter showed these points to deviate for different reasons, than those determin- 

 ing the normal scatter. Because the data for different fabricators frequently clustered 

 around different averages, it was necessary to establish a high and low range of values. 

 In order to establish reasonable lower limits, few unrealistic test results were ex- 

 cluded in the computation of the data. 



