Integrated Vehicle Health Management

A multidisciplinary design optimization-based sensor placement algorithm for IVHM and prognosis is under development, addressing: (i) integrated airloads, (ii) estimation of damage probability and sensor sensitivity to damage parameters, (iii) sensor/host structure coupling, and (iv) material attenuation

Within NASA, the IVHM program is interested in detecting damage and creating residual useful life estimation (RULE). The current aging aircraft situation is an example of the need for this advanced detection and prognosis of damage. Structures within the airframe develop potentially catastrophic damage that is difficult to detect without vehicle disassembly. Highly specialized, embedded smart sensors coupled with advanced algorithms are being proposed that will perform this task without disassembly. In addition to addressing the current situation, the IVHM program aims to identify and develop new tools for improving the next generation of aircraft.

A category of aerospace materials of particular interest to NASA are advanced composites. Their anisotropic nature makes modeling and damage detection particularly challenging. The goal of this research is to develop a more detailed model for composite structures through a multi-scale effort using NASA’s MAC-GMC code, as well as to develop new techniques for predicting wave propagation within the structure. Damage detection is initially performed on samples with embedded laws and progresses to testing coupons of unknown damage. Highly developed algorithms are developed and used to classify and localize damage. From this detailed understanding of the current status of the structure, a RULE is formed to project the remaining life of the structure.

High-fidelity modeling is needed to help predict possible hot spots and damage propagation at various scales in such structures. In order to address this effectively, models capable of damage classification and analysis at a wide range of scales need to be developed. One approach used here is the use of hierarchical length scales for damage modeling. There are three different length scales within composite materials. The micro damage is on the order of fiber-matrix level within the composite and could be matrix cracking, fiber-matrix debonding, or fiber fracture. The meso damage is on the order of interlaminar effects, such as delamination, and the macro damage is on a working structure and employs all levels of damage. The purpose of the modeling is to apply the basic understanding of the material to develop better damage initiation and propagation throughout the material.