Tensile loading


All plies, all locations experience 100% of maximum stress


100%


For a single ply along the axis of the beam


80% 60% 40% 20% 0% 0% 20% 40% 60% 80% Ply stress level X (% of maximum stress in given ply)


(Top figure shows that all plies experience the maximum stress simultaneously under tensile load. Lower figure shows how vast majority of plies in a beam are stressed well below the maximum stress experienced).


Figure 1: Stress level versus volume of beam which is stressed at that level (various loads and support conditions)


TENSILE TESTS Layup


Nominal fibre volume fraction = 34%


A 8 x 295 E-glass B 8 x 280 Carbon C 8 x 290 Aramid Pfail E.t (N/mm) Schematic Pfail (N/mm)


10 coupons for E Calculated t Calculated + Calculated + 14 coupons for UTS % difference


3.07 2.79 9.0%


3.90 3.66 6.2%


5.24 4.75 9.3%


Calculated Pfail = UTS(N/mm2) x t (mm) (UTS from [1], t by formula [1]) Test Pfail = Test failure load (N) / coupon width (mm)


47562 41779 12.2%


168488 131238 22.1%


97631 96783 0.9%


624 603


3.4% 1749


1296


25.9% 1451


1295 10.8%


** mean + ISO values * de-rated


Table 4: Tensile test results – test values v calculated using Annex C [1]


Test value t** Test value t** Test value t** % difference % difference


100% SS, UDL SS, 4-pt bend SS, 3-pt bend Built-in, UDL


The ply experiences a stress of more than 80-100% of the maximum ply stress for only 7% of the span


Fixed distance from NA


© 2008: Royal Institution of Naval Architects


B-39


Percentage of ply span which experiences a stress of X or greater


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