Performance Evaluation of Out-of-Autoclave Sandwich Structures with K-COR and Nomex Core

Abstract

Composite sandwich structures are being increasingly employed in the aerospace, marine as well as other applications which require high strength, high in-plane and flexural stiffness coupled with a reduction in weight. In the aerospace industry sandwich composites are usually manufactured using the autoclave process which is expensive and time consuming. A viable alternative is the Out-of-Autoclave (OOA) process whose main advantage is the low cost of manufacturing. One of the most dominant failure modes in sandwich composites is the debonding that occurs at the facesheet-to-core interphase. A well-formed adhesive bond at the skin to core interphase and improved adhesion strength are significant factors in preventing bond failure. In this paper honeycomb and K-COR sandwich composites are manufactured using the Out-of-autoclave process. The adhesive bonding strength in each of the manufactured panels is quantified by evaluating the flatwise tensile strength in accordance with ASTM standards. Core-facesheet debonding was observed in K-COR sandwich while core failure was observed in the Nomex sandwich structures. Finite element modeling and simulation of Nomex and K-COR sandwich structures subjected to flatwise tension is conducted using comprehensive three-dimensional finite element models. Cohesive damage modeling approach is used to simulate delamination failure in both Nomex and K-COR sandwich structures. Finite element results are compared with the experimental results for model validation. The ultimate flatwise tensile strength predicted by simulation was found to be in good agreement with the experimental results.