FEATURE / BONDED JOINTS [1] The failure indices df & dm represent damage status of fiber and matrix material system. Damage index df will be zero up until failure and attains a value of 0.8 upon failure. However the damage index dm will be zero up until failure and attains a value of 1.0 upon failure. The Hooke's law along with failure indices is presented below. [2] Once a material point reaches the failure limit, the stresses are degraded as show in Figure 5. The area under the stress-strain curve equates to the fracture energy of fiber (GFc) and matrix (GMc) of the material system. The strain scale factor N determines the ultimate strain that equates to the fiber fracture energy toughness. Failed elements were removed from the model to simulate virtual crack growth when in-plane strain reaches a value of 0.25. The failure load provided by this damage model is independent of finite element size as long as the edges are within 0.254 mm to 4.06 mm length. Additional information on mesh regularization procedure and its validation is presented in reference8. Figure 5. Stress degradation profiles for damage simulation. Axial Edge-Wise Compression (AEWC) Coupons The test stand & compression test setup for the AEWC coupons is shown in Figure 6. The coupon is placed between a flat square platen at the bottom and a thick rectangular steel block, covering the entire width and thickness of the coupon, on the top. Above the thick steel block, a circular cross-section steel block is placed. The AEWC sub-element coupons were instrumented with strain gages and a digital image correlation (DIC) system to obtain full field, displacement and strain contours. The joint testing included 10 pristine AEWC sub-element test coupons. 14 | SAMPE JOURNAL | M AY/J U N E 2 0 2 0 Figure 6. Test setup & strain gauge configuration of AEWC coupon. w w w. s a m p e . o r ghttp://www.sampe.org