FEATURE / BONDED JOINTS failure load. Load vs. end shortening curves are presented in Figure 11. One can notice in this figure that the delamination grew gradually starting from 87.41 kN. Delamination plots as a function of load are also presented in Figure 11. The typical failure mode (delamination between the face sheet plies) of the test coupons and the modes simulated by PFA are in excellent agreement as can be noticed in Figure 12. Hoop Edge-Wise Tension (HEWT) Coupons The test stand for the HEWT coupon tests at Southern Research is shown in Figure 13. The sub-element coupons were gripped in the test machine and pulled under tension loading until failure. The joint testing included 10 pristine HEWT sub-element test coupons. Progressive Failure Analysis of Pristine Coupon Progressive failure analysis of HEWT was performed by adopting the damage model mentioned in sub-section A for predicting in-plane failure modes such as fiber and matrix damages. After closer examination of loading and geometric configuration of the coupon, it was inferred that delamination between plies or any sub-assemblies would be the primary mode of failure. Hence, the finite element model was developed to simulate fiber and matrix damages in the face sheet plies as well as delamination between face sheet plies and splice (doubler) plate plies. The finite element model is presented in Figure 14 showing various components of the joint and boundary conditions. Delamination damage mode is simulated with the help of built-in cohesive zone model (CZM) in Abaqus. Solid elements (C3D8) were used to discretize core, adhesive and gap filler regions. Face sheet and splice plate were discretize using shell continuum (SC8R) elements and the cohesive layers are discretized using COH3D8 elements. Figure 11. Load vs. end shortening of HEWC PFA. (a) Typical failure mode of HEWC coupon Figure 12. Typical failure mode of HEWC coupon. Pristine Coupon Testing & PFA Correlation Ten HEWT sub-element coupons were tested under a tensile load. Table 3 reports the failure modes and failure load of all the 10 HEWT coupons along with the axial strain at center of the joint before failure. The failure modes of the tested coupons were "Delam" (delamination between face sheet plies) and NSF (net-section failure of doubler plate). Four of the coupons failed due to "Delam" on one side and NSF on the other side. Four of the coupons failed due to NSF on both sides and two of the coupons failed due to "Delam" on both sides. The average failure load of the joint in tension is 66.785 kN. Additional information on the HT cou- 18 | SAMPE JOURNAL | (b) Failure mode predictions from PFA M AY/J U N E 2 0 2 0 Table 3. Test data of HEWT coupons. Specimen ID Test Failure Load (kips) Failure Mode CTE-300-1-HT-P-1 71.692 Delam/NSF CTE-300-1-HT-P-2 61.239 Delam/NSF CTE-300-1-HT-P-3 69.321 Delam/NSF CTE-300-1-HT-P-4 57.840 Delam CTE-300-1-HT-P-5 61.817 Delam CTE-300-3-HT-P-1 69.686 NSF CTE-300-3-HT-P-2* 67.595 NSF CTE-300-3-HT-P-3 66.803 Delam/NSF CTE-300-3-HT-P-4 70.687 NSF CTE-300-3-HT-P-5 71.172 NSF Average 66.785 w w w. s a m p e . o r ghttp://www.sampe.org