Resource Library

We have developed this library of resources to provide access to the tremendous amount of content that we have developed over the years. It includes product-specific literature, application-based technical resources, and media presentations of our unique technologies.

If you know which specific product or application you’re looking for, simply click on that link below and you’ll find in-depth content. Alternatively, you can use the search function to connect you to literature and media related to your specific interest.

Published Papers

Title
Product Area
In-Situ Structural Health Monitoring of Composite-Overwrapped Pressure Vessels
  • ODiSI/HD-FOS
Short Summary
Demonstrates integration of fiber sensor into composite overwrapped pressure vessel as a built-in structural integrity assessment system, potentially eliminating the need for hydrotesting recertification.
Abstract

Currently, most composite pressure vessels must be recertified every 2-5 years via hydrostatic testing to confirm the structural integrity of the pressure vessel. The test requires pressurization in a fluid filled chamber with the global volumetric expansion compared to acceptance criteria. This requirement poses significant cost and time out-of-service issues across many industries. In this work, Luna has teamed with Worthington Industries (WI) - a leading commercial and military supplier of composite air flasks and contracted designer of 30 year flasks, with the objective of providing composite flasks with a built-in structural integrity assessment system that will eliminate the need for hydrotesting recertification. High-definition (HD) distributed strain sensing is used to monitor strain along the axis of circumferentially-wrapped embedded fiber optic sensors in composite-overwrapped pressure vessels (COPVs) during qualification testing and following blunt and highly localized damage events. Luna demonstrates that the use of strain sensors embedded in the composite flask during manufacture will allow rapid assessment of the composite flask structural integrity on-site, while the flask is still mounted in the rack. In addition to the potential for replacing hydrotesting, risk associated with the use of 30 year extended service life flasks will be mitigated by utilizing this efficient health monitoring capability to identify damage and weakened flask structure. The core technology behind Luna’s HD strain measurement systems is Optical Frequency Domain Reflectometry (OFDR) technology, which allows continuous strain measurements at hundreds of gage locations per meter of fiber. Application of the sensor is directly integrated into current flask fabrication methods and the technology utilizes standard telecommunication optical fiber. Therefore, the added cost associated with the embedded sensor and interrogation equipment will be minimal when compared to the recertification costs currently required.

Integrated Fiber Optic Structural Health Sensors for Inflatable Space Habitats
  • ODiSI/HD-FOS
Abstract

Inflatable space habitats offer many advantages for future space missions; however, the long term integrity of these flexible structures is a major concern in harsh space environments. Structural Health Monitoring (SHM) of these structures is essential to ensure safe operation, provide early warnings of damage, and measure structural changes over long periods of time. To address this problem, the authors have integrated distributed fiber optic strain sensors to measure loading and to identify the occurrence and location of damage in the straps and webbing used in the structural restraint layer. The fiber optic sensors employed use Rayleigh backscatter combined with optical frequency domain reflectometry to enable measurement of strain every 0.65 mm (0.026 inches) along the sensor. The Kevlar woven straps that were tested exhibited large permanent deformation during initial cycling and continued to exhibit hysteresis
thereafter, but there was a consistent linear relationship between the sensor’s measurement and the actual strain applied.  Damage was intentionally applied to a tensioned strap, and the distributed strain measurement clearly identified a change in the strain profile centered on the location of the damage. This change in structural health was identified at a loading that was less than half of the ultimate loading that caused a structural failure. This sensing technique will be used to enable integrated SHM sensors to detect loading and damage in future inflatable space habitat structures.

Citation
Osgar John Ohanian, Naman Garg, and Matthew A. Castellucci, “Integrated fiber optic structural health sensors for inflatable space habitats”, Proc. SPIE 10172, March 25, 2017. doi:10.1117/12.2260106
Method for Improving the Resolution and Accuracy against Birefringence Dispersion in Distributed Polarization Cross-Talk Measurements
  • Polarization
Polarization Resolved Measurement of Rayleigh Backscatter in Fiber-Optic Components
  • Optical Test
Short Summary
Measuring the distribution of the light scattered in the backward direction as a function of length down a fiber-optic assembly can be useful in identifying breaks, bad spices and non-reflective events. This method has significant advantages in range, resolution, speed and usability when compared to conventional reflectometers.
Abstract

In this paper, we introduce a method for fiber-optic testing and troubleshooting at the assembly level that is based on using OFDR to measure the distributed Rayleigh backscatter along the length of the fiber-optic network. Measuring the distribution of the light scattered in the backward direction as a function of length down a fiber-optic assembly can be useful in identifying breaks, bad spices and non-reflective events. Rayleigh scatter can also be used to measure distributed loss and gain, induced stress and strain, temperature, and local birefringence.

Citation
B. Soller, M. Wolfe, and M. Froggatt, "Polarization Resolved Measurement of Rayleigh Backscatter in Fiber-Optic Components," in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference, Technical Digest (CD) (Optical Society of America, 2005), paper NWD3.
Quadrupling Optical Delay Range Using Polarization Properties
  • Polarization
Residual Strains using Integrated Continuous Fiber Optic Sensing in Thermoplastic Composites and Structural Health Monitoring
  • ODiSI/HD-FOS
Abstract

The evolution of spatially resolved internal strain/stress during the manufacturing of thermoplastic composites and subsequent relaxation from water intake are evaluated using an in-situ fiber optic sensor corresponding to a coated optical glass fiber with a nominal diameter of 160 μm. Unidirectional carbon fiber-polyamide 6 composites are produced using compression molding with an embedded fiber optic for strain measurement. The distributed fiber optic based strain sensor is placed in an arrangement to capture 0, 45, and 90° strains in the composite to resolve in-plane strain tensor. Strains are monitored in the direction of fiber optic sensor along its length at high resolution during the various stages of compression molding process. Results indicate considerable internal strains leading to residual stress at the end of processing step along the off-axis (45°) and transverse (90°) directions, and small strains in the carbon fiber pre-preg (0°) direction. At the end of compression molding process, an average of 7000 and 10,000 compressive micro-strains are obtained for residual state of strain in the off-axis and transverse direction. Since water/moisture infusion affects the mechanical properties of polyamide-6 matrix resin, these composite panels with embedded sensors targeted for marine applications are monitored in a water bath at 40 °C simulating accelerated testing conditions. Using the same fiber optic sensor based technique, the strain relaxation was observed during water uptake demonstrating in-situ strain monitoring during both manufacturing and subsequent composite implementation/application environment. The technique presented in this paper shows the potential of optimizing time-temperature-pressure protocols typically utilized in thermoplastic manufacturing, and continuous life-cycle monitoring of composite materials using a small diameter and inexpensive distributed fiber optic sensing.

Citation
Arhant, M., Meek, N., Penumadu, D. et al. Exp Mech (2017). https://doi.org/10.1007/s11340-017-0339-2
Return Loss Measurement in the Presence of Variable Insertion Loss Using Optical Frequency Domain Reflectometry
  • Optical Test
Short Summary
The capability of measuring localized insertion loss using OFDR presents a unique opportunity to provide consistent
measurements of device RL even in the presence of variable connector loss, even for short lead lengths. This paper outlines the methodology used to establish a value for the scatter in optical fiber, and how this Rayleigh scatter level is used to maintain consistent reflection measurements.
Abstract

The high spatial resolution and high sensitivity inherent to optical frequency domain reflectometery enables precise measurements of distributed insertion loss and return loss events. The ability to compensate return loss for variable insertion loss greatly adds to the accuracy and practicality of measurements. Further, the capability of measuring the Rayleigh backscatter internal to the instrument provides a stable power calibration artifact.

Citation
S. Kreger et al., “Return Loss Measurement in the Presence of Variable Insertion Loss Using Optical Frequency Domain Reflectometry,” NIST SPECIAL PUBLICATION SP, 2006, 1055, 18.
Self-Calibrating Binary Polarization Analyzer
  • Polarization
Small Scale Crack Growth Sensor
Test Method for Monitoring Atmospheric Corrosion Rate by Electrochemical Measurements
Three-Axis Distributed Fiber Optic Strain Measurement in 3D Woven Composite Structures
  • ODiSI/HD-FOS
Short Summary
In the present application optical fiber for distributed sensing was embedded on a commercial weaving loom and used for three-axis strain measurement and subsequent spatial frequency analysis.
Abstract

Recent advancements in composite materials technologies have broken further from traditional designs and require advanced instrumentation and analysis capabilities. Success or failure is highly dependent on design analysis and manufacturing processes. By monitoring smart structures throughout manufacturing and service life, residual and operational stresses can be assessed and structural integrity maintained. Composite smart structures can be manufactured by integrating fiber optic sensors into existing composite materials processes such as ply layup, filament winding and three-dimensional weaving. In this work optical fiber was integrated into 3D woven composite parts at a commercial woven products manufacturing facility. The fiber was then used to monitor the structures during a VARTM manufacturing process, and subsequent static and dynamic testing. Low cost telecommunications-grade optical fiber acts as the sensor using a high resolution commercial Optical Frequency Domain Reflectometer (OFDR) system providing distributed strain measurement at spatial resolutions as low as 2mm. Strain measurements using the optical fiber sensors are correlated to resistive strain gage measurements during static structural loading.

Citation
M.A. Castellucci, S. Klute, E.M. Lally, M.E. Froggatt, D. Lowry. Three-Axis Distributed Fiber Optic Strain Measurement in 3D Woven Composite Structures, SPIE Smart Structures 2013
Tomographic Inspection of Fiber Coils Using Optical Coherence Tomography
  • Polarization
Waveplate Analyzer using Binary Magneto-optic Rotators
  • Polarization
Wireless, Non-invasive, Asset Life-cycle Monitoring System