DESIGN DETAILS 



3-17 



Threaded Fasteners 



Whenever threaded type fasteners are 

 used in fiberglass laminates, the fastener 

 should always be perpendicular to the plies 

 of reinforcement. Edge fastening should 

 never be used, since this tends to delaminate 

 the fiberglass laminate and has very little strength 

 wrong directions for fasteners. 



Fig. 3-45. Right 

 and Wrong Direction 

 for Threaded Type 

 Fasteners 



Fig. 3-45 indicates the right and 



The strength of threaded fasteners in fiberglass laminates depends on a number of 

 factors including the type of laminate, type of fastener, depth of penetration, diameter of 

 fastener, size of pilot hole, and direction of loading. Tests (1) have been made on two 

 basic directions of loading: axial, which tends to pull the fastener directly out of the 

 laminate; and transverse, which pulls sideways on the fastener. Fig. 3-46 clarifies 

 these loading directions. 



1 ' 



DEPTH OF 

 PENETRAT I ON 



DEPTH OF 

 PENETRAT I ON 



AXIAL LOAD 



b. TRANSVERSE LOAD 



Fig. 3-46. Threaded Fastener Loading Directions 



Also indicated in Fig. 3-46 is the "depth of penetration" as defined for both blind and 

 through holes. 



When used in fiberglass laminates, threaded fasteners should have edge and side dis- 

 tances equal to 2-1/2 times the fastener diameter, and a spacing of 3 times the fastener 

 diameter. Distances are measured as indicated for bolted joints, Fig. 3-44. 



Tables 3-3 and 3-4 give ultimate strengths for axial and transverse loading for three 

 types of threaded fasteners. Table 3-3 gives strengths for fasteners in 10 ounce cloth- 

 polyester resin laminates having the following range of physical properties: 



Tensile Strength 



Edge Compressive Strength 



Shear Strength (Perpendicular) 



30,000 to 45,000 PSI 

 18,000 to 27,000 PSI 

 14, 000 to 17,000 PSI 



Table 3-4 gives strengths for fasteners in mat-polyester resin laminates having the 

 following physical properties: 



Tensile Strength 



Edge Compressive Strength 



Shear Strength (Perpendicular) 



6, 000 to 25,000 PSI 

 10,000 to 22,000 PSI 

 10,000 to 13,000 PSI 



Table 3-4 should also be used for woven roving laminates. 



