Scale and manufacturing effects on tensile strength of marine grade sandwich composite panel joints

In this article, scale and manufacturing effects on the tensile strength of marine grade sandwich composite panels and joints are investigated to aid in the fabrication of large modular ship hulls. This is done by researching transverse sandwich composite joint design, experimental tension methods, and scale and manufacturing effects on tensile strength. Three scales are utilized in this investigation of tension characteristics: coupon scale, table-top single panel fabrication scale, and in position mock-up full-size fabrication scale. First, material properties are gathered through industry standard coupon scale fabrication and testing. Next, a single-infusion baseline panel along with two ship hull transverse joint designs are chosen, fabricated, tested, and compared at single panel scale. These tests include individually fabricated hull panels, as well as secondary structural stiffener sandwich composite web panels, and stiffener flange components. The highest performing joint design is then utilized in a mock-up full-size fabrication scale structure. This structure includes both a transverse hull joint, as well as joints in the secondary structural stiffener web and flange. This mock-up fabrication scale component was then cut apart and tested in tension. The novel sandwich composite panel joint tension experimentation methods used indicate the methods studied are reliable for determination of characteristic tensile properties, and that the joints selected are effective. Investigations concerning scale effects comparing baseline fiber failure mode tension results from the coupon scale to the single panel scale, and manufacturing effects comparing joint interlaminar shear failure mode from the single panel scale to the mock-up fabrication scale, show decreased ultimate tensile strength with increased overall part size and manufacturing complexity. These factors, applied to a reference strength to achieve a nominal strength, were found to range from 0.796 to 0.846.