Frank A. Leone

On the applicability of acoustic emission to identify modes of damage in full-scale composite fuselage structures

The acoustic emission method was applied during the testing of six full-scale sandwich composite aircraft fuselage panels containing through-the-thickness notches. The panels were subjected to different combinations of quasi-static internal pressure, the corresponding hoop loads, and longitudinal loads. The applicability of conventional acoustic emission signal feature analysis to identify the dominant modes of failure and extraneous emission in large composite structures was investigated. It was concluded that no clear distinction could be made among the different failure mechanisms based on the conventional acoustic emission signal features alone. Further, emission generated by fretting, either among fracture surfaces or of loading fixtures, has acoustic emission signal waveform features that are similar to those of damage-generated emission signals.

Fracture-Based Mesh Size Requirements for Matrix Cracks in Continuum Damage Mechanics Models

This paper evaluates the ability of progressive damage analysis (PDA) finite element (FE) models to predict transverse matrix cracks in unidirectional composites. The results of the analyses are compared to closed-form linear elastic fracture mechanics (LEFM) solutions. Matrix cracks in fiber-reinforced composite materials subjected to mode I and mode II loading are studied using continuum damage mechanics and zero-thickness cohesive zone modeling approaches. The FE models used in this study are built parametrically so as to investigate several model input variables and the limits associated with matching the upperbound LEFM solutions. Specifically, the sensitivity of the PDA FE model results to changes in strength and element size are investigated.

Cohesive Laws and Progressive Damage Analysis of Composite Bonded Joints, a Combined Numerical/Experimental Approach

The results of an experimental/numerical campaign aimed to develop progressive damage analysis (PDA) tools for predicting the strength of a composite bonded joint under tensile loads are presented. The PDA is based on continuum damage mechanics (CDM) to account for intralaminar damage, and cohesive laws to account for interlaminar and adhesive damage. The adhesive response is characterized using standard fracture specimens and digital image correlation (DIC). The displacement fields measured by DIC are used to calculate the J-integrals, from which the associated cohesive laws of the structural adhesive can be derived. A finite element model of a sandwich conventional splice joint (CSJ) under tensile loads was developed. The simulations, in agreement with experimental tests, indicate that the model is capable of predicting the interactions of damage modes that lead to the failure of the joint.