1 Copyright © 2013 by ASME Proceedings of the ASME 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems SMASIS2013 September 16-18, 2013, Snowbird, Utah, USA SMASIS2013-3269 EFFECTS OF ALTITUDE ON ACTIVE STRUCTURAL HEALTH MONITORING Benjamin Cooper Andrei Zagrai Department of Mechanical Engineering, Graduate Studies, New Mexico Tech, Socorro, New Mexico, USA Seth Kessler Metis Design Corporation, Boston, MA, USA ABSTRACT As the field of Structural Health Monitoring (SHM) expands to spacecraft applications, the understanding of environmental effects on various SHM techniques becomes paramount. In January of 2013, an SHM payload produced by New Mexico Tech was sent on a high altitude balloon flight to a full altitude of 102,000 ft. The payload contained various SHM experiments including impedance measurements, passive detection (acoustic emission), active interrogation (guided waves), and wireless strain/temperature sensing. The focus of this paper is the effect of altitude on the active SHM experiments. The active experiment utilized a commercial SHM product for generation and reception of elastic waves that enabled wavespeed measurements, loose bolt detection, and crack detection through the full profile of the flight. Definite deviations were observed in the data through the stages of the flight which included a ground, ascent, float, and descent phases. Several elements of the high altitude environment can have an effect on the measurement such as temperature and pressure. The flight data was compared against a ground altitude baseline and heavy emphasis is placed on comparing changes in the data with the temperature profile of the flight. Conclusions are drawn on the effect of altitude on wavespeed of elastic waves, crack detection, and the sensing of a loose bolt. INTRODUCTION In the past, the New Mexico Institute of Mining and Technology has designed and flown an SHM payload for the purpose of exploring health monitoring sensors and techniques for space applications [1]. This payload focused on impedance type measurements to look for changes in structural dynamics during a sub-orbital rocket launch. The next iteration of the payload included several more experiments, one of which focused on guided waves [2]. Guided waves are a current favorite for SHM applications due to their long range capabilities to detect damage and structural changes in many platforms including aerospace vehicles. SHM techniques have been identified as an important next step for enabling rapid satellite development and deployment. Within that scope, the use of guided waves to identify loose bolts and components has been expressed as an area of need [3]. This payload and its experiments seek to address some of these needs, but with the additional aim of understanding environmental factors. Temperature has been identified as an important element to consider for SHM aerospace applications and an investigation into its effect on Lamb waves (a special set of guided waves applicable to thin plate structures) has been undertaken by Dodson and Inman [4]. Several laboratory tests have been carried out to obtain temperature dependent data and develop strategies to compensate in the SHM techniques [5][6]. The contribution of this paper is to add to the investigation of environmental factors on the use of SHM techniques for space and high altitude application. Sending the payload on a high altitude balloon allows the collection of data in a full high altitude environment which may include extra influences not replicated in laboratory tests. Because temperature is such a strong factor, the first step is to link the temperature profile of the flight with the data collected using guided waves. A temperature profile and elevation of the payload is presented in Figure 1. After understanding the temperature influence on the data, any discrepancies can be explored and attributed to other factors, such as pressure.