5-14 ENGINEERING PROPERTIES OF LAMINATES 



MECHANICAL PROPERTIES 



Tensile, Flexure, Compression and Shear 



Tables 5-6 to 5-14 present tensile, flexural, compressive and shear strengths with 

 corresponding moduli for the laminates tested. Also included are values for Poisson's 

 ratio for tension and compression. An over-all average value is given for perpendicular 

 shear modulus since there was insufficient data to determine any level of variability for 

 this property. 



The effects of the different types of reinforcements on these properties have been pre- 

 viously discussed in the section; Results of Investigation of Main Variables. 



Impact Strength 



Non-laminated plastics and similar homogeneous materials are often tested for impact 

 strength by an Izod test in which a small notched or unnotched sample about 1/2 inch x 1/2 

 inch square is clamped as a vertical cantilever beam and struck by a swinging pendulum. 

 The test is run on a series of samples under standard conditions and the impact necessary 

 to break the test sample is determined. 



The Izod impact test is less applicable to laminate materials than to homogeneous 

 materials except when used as a rough screening method. The Izod impact method gives 

 the energy absorbed at failure and not a partial failure as usually occurs in laminated 

 materials ( 1). 



Large areas of fiberglass laminates when struck perpendicular to the direction of lami- 

 nation tend to distribute the impact force due to the arrangement of the reinforcement and 

 due to their relatively low moduli. Therefore, under impact they deflect readily and are 

 capable of absorbing heavy blows. Failure of a laminate under heavy impact involves 

 complex shearing and delamination effects. 



To determine the relative impact resistance of laminates with various reinforcements, 

 a test simulating actual service conditions as nearly as possible was developed. This test 

 consists of dropping a cylindrical impacter through a smooth steel tube to strike the simply 

 supported test panels. The impact testing machine consists of a 4 inch inside diameter, 

 seamless steel tube, 20 feet long, mounted vertically with a cylindrical impact striker having 

 a hemispherical head 3 inches in diameter, Fig. 5-4. The striker could be varied in weight 

 from 7 to 150 pounds by the addition or subtraction of cylindrical increments. This test 

 provides a realistic, comparative test of large panels of fiberglass laminates for resistance 

 to impact or heavy blows. 



Laminated fiberglass panels fail under impact by delamination, puncturing, tearing and 

 crushing. These complex effects are difficult to evaluate. Under standardized conditions the 

 following method is considered a reasonable and practical approach to the problem. After 

 receiving a single blow from the dropped impacter, the panels are tested for leakage under a 

 2 foot head of water. For comparison, panels which are damaged to approximately one-half 

 their thickness and which leak more than 3 but less than 6 gallons per hour under the 2 foot 

 head of water are judged to be in a critical condition. The impact force necessary to produce 

 a critical condition of leakage is expressed as the weight of the impacter in pounds multiplied 

 by the height of drop in feet. A series of panels were tested for each of the types of lami- 

 nates, Ml, M2, M3, M4 and M5 previously discussed. Comparative evaluation of the 



