PSI - Issue 17

Waleed H. Alhazmi et al. / Procedia Structural Integrity 17 (2019) 292–299 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Table (1) Elastic Properties in GPa of The Present CFRP* E 11 E 22 E 33 G 12 G 13 G 23  12  13  23 165 11 11 5.3 5.3 3.9 .26 .5 .5 * Estimated values

4. EXPERIMENTAL WORK Epoxy reinforced with 68 volume percent carbon fiber, v f =68%, composites, Sika  CarboDur  S512, were selected for this study. The majority of the plates had the final dimensions of 150 mm x 50 mm x 1.2 mm. Some of bolt-Loaded Holes plates had width of 20 or 30 mm. Aluminum 6061-T6 end tabs of w x 30 x 2 were bonded onto both ends of open-hole specimens and onto the fixed end of bolt-loaded hole specimens using a high strength Araldite  epoxy adhesive. Circular holes were carefully drilled and the specimens were completed without inducing any visible damage. Static and fatigue tests were carried out in a MTS 810 TestStar TM II s test systems in laboratory air and room temperature. The plates were loaded along the fiber direction. The material properties are listed in Table 2. Table (2) Epoxy, Carbon Fiber, Composite Properties Data Epoxy CFRP 4.1. Open-Hole Tension Tests Hole sizes of 5, 10, and 15 mm diameter, d H /w = 0.1, 0.2, and 0.3, were considered. Notched and unnotched specimens were subjected to static load at a rate of 0.2 mm/min to determine the modulus of elasticity in the fiber direction, E 11 , and both notched and unnotched strength of CFRP. Both notched and unnotched specimens were subjected to cyclic load. All fatigue tests were performed under load control at an approximately zero stress ratio, i.e. min. stress = 0. The max. stress to the ultimate tensile stress ratios,  f-max /  ult , were 0.6, 0.7, and 0.8. Each test was performed for 500,000 cycles, and then, the specimens were subsequently loaded statically up to failure to determine the residual stresses and the degradation in the modulus of elasticity. The frequency of the load cycles was 10 Hz which is believed to give a negligible temperature rise during tests. Further, 4.2. Bolted Joint Tensile Test Double lap single-bolt tension joint tests were conducted to evaluate the strength of bolted composite joints and mode of failure in the present unidirectional CFRP. Three different hole sizes, d H = 7, 10, and 13 mm, and three different specimen widths, w = 20, 30, and 50 mm, were considered. Two steel bolts with nominal diameter of 6 and 8 mm were used. The end distance ( e ) from the center of the hole to the free edge of the plate was varied from 10 to 30 mm. The specimen was placed between two flat steel plates and the bolt was tightened by hand. Bolted joint tensile tests were conducted at a crosshead speed of 0.5 mm/min. High Strength Carbon Fiber E f = 220 - 235 3790 - 4825 Modulus of Elasticity, E 11 (GPa) E m = 12.8 165 Tensile Strength (MPa) Elongation at break % 30 3050 -- 1.5 1.7

5. Results And Discussion 5.1. Open-Hole Tension Tests

The measured value of the modulus of elasticity of the present CFRP, E c , is equal to 155 GPa, i.e. equals 93% of the mean value found in the technical data sheet of the supplier or 97% of the calculated value from the rule of mixtures type relation, i.e. E c = v f E f + v m E m = 0.68 x 230 + 0.32 x 12.8 = 160.5 GPa. A rule of mixtures type relation is adequate to predict the modulus of elasticity of a such CFRP plate. This may be attributed to the high mechanical properties and high volumetric content of the fibers compared with the matrix, i.e. there is a marginal contribution of