7 Prototype parts of each configuration were fabricated and evaluated against two criteria. The first criterion was simply evaluating the tensile strength of the joint as was performed in the screening experiment. The second criterion involved examining the performance of the composite links in compression after being buckled and axially compressed to a preset deflection. Doing so revealed that under certain circumstances, the pultruded material tends to delaminate on long-transverse planes with the delamination initiating at the root of the groove. Analyzing the data using the Taguchi approach once again allowed for the contribution to the joint strength of each control factor and control level, and interactions of the control factors and control levels to be determined. From this analysis and delamination considerations, it was found that numerous small, closely-spaced grooves provided the optimal combination of joint strength in tension and delamination resistance after buckling. 1.2.3 Parameter Selection Stage 3: Final Design Once the groove optimization designed experiment was completed, a third and final designed experiment was constructed to examine various processing methods to produce the grooves. Additionally, surface finish was once again considered and the use of adhesives was revisited. An additional six configurations were added to the experiment for checking purposes. Table 1.3 depicts the L18 Orthogonal Array that was constructed for this final investigation. Table 1.4 contains six additional configurations of interest that were included in the experiment. Prototype parts representing the 24 configurations specified in Tables 1.3 and 1.4 were fabricated and evaluated for tensile strength per the procedure used in the previous experiments. Notice that four different processes were considered to produce the grooves both across the grain (cross grooves) and axially—machining (i.e. cutting), grinding, grit blasting, and laser ablation, as well as, a control case of no grooves. Table 1.3 L18 Orthogonal array for stage 3 (final design) 1&2 3 4 A C D Grooves Surface finish Attachment method 1 Smooth Smooth Insert mold 2 Smooth Ground axial fiber exposure Adhesive assy W/o surface primer 3 Smooth Laser axial fiber exposure Adhesive assy W/surface primer 4 Ground axial grooves Smooth Insert mold 5 Ground axial grooves Ground axial fiber exposure Adhesive assy w/o surface primer 6 Ground axial grooves Laser axial fiber exposure Adhesive assy W/ surface primer 7 Ground top-bottom grooves Smooth Adhesive assy W/o surface primer 8 Ground top-bottom grooves Ground axial fiber exposure Adhesive assy W/ surface primer 9 Ground top-bottom grooves Laser axial fiber exposure Insert mold 10 Ground side-side grooves Smooth Adhesive assy W/surface primer 11 Ground side-side grooves Ground axial fiber exposure Insert mold 12 Ground side-side grooves Laser axial fiber exposure Adhesive assy W/o surface primer 13 Laser axial grooves Smooth Adhesive assy W/o surface primer 14 Laser axial grooves Ground axial fiber exposure Adhesive assy W/ surface primer 15 Laser axial grooves Laser axial fiber exposure Insert mold 16 Cut top-bottom grooves Smooth Adhesive assy W/ surface primer 17 Cut top-bottom grooves Ground axial fiber exposure Insert mold 18 Cut top-bottom grooves Laser axial fiber exposure Adhesive assy W/o surface primer Table 1.4 Six additional configurations of interest 19 Ground cross grooves Plasma axial fiber exposure Insert mold 20 Ground cross grooves Plasma axial fiber exposure Adhesive assy W/o surface primer 21 Grit blast cross grooves Smooth Adhesive assy W/o surface primer 22 Grit blast cross grooves Laser axial fiber exposure Insert mold 23 Laser cross grooves Smooth Adhesive assy W/o surface primer 24 Laser cross grooves Laser axial fiber exposure Insert mold 1 How to Join Fiber-Reinforced Composite Parts: An Experimental Investigation
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