Co-cured lap joints

Co-cured lap joints, surface roughness, stacking sequence, manufacturing pressure, tensile load bearing capacity, fatigue characteristics. 

Fig. 2. Photograph of the co-cured lap joint specimens, (a) Co-cured single lap joint (b) co-cured double lap joint.

Figure 1 shows the cure cycle for the co-cured lap joints and table 1 shows the material properties of the carbon fiber-epoxy composite (USN 150) produced by SK Chemicals (Suwon, Korea). After the curing and bonding processes, the co-cured joint should be finished using various abrasive sandpapers to obtain a better joint strength by eliminating sharp edges. A... 

EXPERIMENTAL RESULTS OF THE CO-CURED LAP JOINTS UNDER STATIC TENSILE LOADS... 

Tensile load bearing capacities of the co-cured lap joints with respect to the... 

In this study, residual thermal stresses were also eonsidered because co-cured lap joints generally undergo temperature drop (from 120D to 20D) during the curing process. The stress distributions in the co-cured single and double lap joints were analyzed using ABAQUS i.8 to be commercial finite element analysis software [21],... 

BOND PARAMETERS AFFECTING FAILURE OF CO-CURED SINGLE AND DOUBLE LAP JOINTS SUBJECTED TO STATIC AND DYNAMIC TENSILE LOADS... 

In the case of the dynamic tensile test, co-cured single lap joint specimens selected in this paper... 

The bond length of the specimens under cyclic tensile test was 20mm. Cyclic tensile tests were performed under the condition of stress ratio 7 = 0.1 and a loading frequency / = 5 Hz. Cyclic tensile loads applied to the co-cured single lap joint specimens were 30%, 40%, 50%, 60%, and 70% of the tensile load bearing capacity obtained from the static tensile load test. 

Figure 4 shows typical failure surfaces obtained from tensile tests of the co-cured single and double lap Joint specimens. In the case of the co-cured single lap Joint, as the surface preparation on the steel adherend is better, a greater amount of carbon fibers and epoxy resin is attached to the steel adherend. Failure mechanism is a partial cohesive failure mode at the C ply of the composite adherend. In contrast with the co-cured single lap joint, failure mechanism of the co-cured double lap joint is the partial cohesive failure or interlaminar delamination failure at the 1 ply of the composite adherend because interfocial out-of-plane peel stress... 

Bond Parameters Affecting Failure of Co-Cured Single and Double lap Joints... 

Fig. 8. Coordinate system of the co-cured single and double lap joints for calculating stress distributions in the ply-axis.

The co-cured single and double lap joints were modeled as a three-dimensional solid structure. The resin layer was ignored in this analysis because the average thickness of the resin layer... 

Fig. 10. Interfacial out-of-plane transverse stress distribution, a , of the co-cured single lap joint along the interface between steel and composite adherends. (a) [0]32t stacking sequence and (b) [ 45]4s s stacking sequence.

Fig. 11. Interfacial out-of-plane shear stress distribution, a , of the co-cured single lap joint...

Figures 12 and 13 show interfacial out-of-plane transverse and shear stress distributions of the co-cured double lap joints with [0]i6t and [ 45]4s stacking sequences along the interfaces between steel and composite adherends, respectively. It is important to consider interfacial out-of-plane shear stress rather than interfacial out-of-plane transverse stress because of the compressive stress distribution due to the symmetric configuration of the co-cured double lap...

Based on the failure mechanisms and stress distributions at the interface between steel and composite adherends of the co-cured single and double lap joints, tensile load bearing capacities of the two joints were evaluated. Since failure started at the edge of the interface between steel and composite adherends, it is important to consider the failure criterion using interfacial out-of-plane stress distributions at the interface. Three-dimensional Tsai-Wu and Ye-delamination failure criteria were used to predict partial cohesive failure or interlaminar delamination failure in the co-cured single and double lap joints. 

Equation (1) must be less than 1 failure is predicted when F/ is > 1. Based on the three-dimensional Tsai-Wu failure criterion, tensile load bearing capacities of the co-cured single and double lap joints were calculated. 

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