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Nondestructive Damage Evaluation by Ensyso and Sensuron

Posted on by Pierrick Vulliez

In close collaboration with NASA, Sensuron developed compact fiber optic sensing systems that can provide continuous strain measurements. One major challenge facing the development of prominent nondestructive damage evaluation (NDE) tools has been a lack of fine spatial resolution from sensors. Sensuron’s advanced fiber optic sensing platforms resolve this issue with spatial resolution down to 6.3mm.

Ensyso developed a set of rational procedures that can lead to reliable relationships between damage indices and measurable response parameters. The procedures are based on fundamental mechanics and, therefore, are applicable to arbitrary structures.

Ensyso’s (NDE) expertise combined with Sensuron’s advanced FOS technology offers a fully automated continuous health monitoring tool where local damage detection is possible through the use of global vibration information. By bringing Ensyso’s and Sensuron’s technologies together, a complete NDE system is developed, which could serve as the most prominent NDE algorithm that exists in the market.

Cost Comparison – Fiber Optic Sensing versus Strain Gauges

Posted on by Pierrick Vulliez

Sensuron’s fully distributed fiber optic sensing technology enables a paradigm shift to take place in the areas of structural testing and monitoring. One frequently overlooked aspect of this shift is the potential cost savings when compared with the use of traditional sensors. For example, thousands of fiber optic strain gauges can be installed on an aircraft in a fraction of the time required to install traditional strain gauges. Due to the laborious nature of the installation process, strain gauges are often deployed in limited numbers at probable critical points throughout a structure. Fiber optic sensors are installed using similar methods, but at a significantly faster pace. For the same amount of labor required to install two quarter bridge strain gauges, approximately 85 fiber optic strain gauges can be installed.

Thom Rollins, a principal engineer at Northop Grumman said it best: “ A single fiber allows us to replace thousands of strain gauges, saving significant man-hours of effort on a single project and providing us with new insight we would not have gotten using legacy sensing technology”. For applications that require or can benefit from the use of multiple strain sensors, the cost effectiveness and reduced installation time of fiber optic sensing technology is clearly attractive.
This is demonstrated in much greater detail in a white paper available on our website titled Fiber Optic Sensing vs. Strain Gauges.

We’re All Getting Older: Accelerated Lifecycle and Fatigue Testing

Posted on by Pierrick Vulliez

Shrinking military budgets often necessitate the use of vehicles and aircraft well beyond their service lives. For example, according to STARS and STRIPES, among the Navy’s concerns is a rapidly aging Ready Reserve Force of 46 transport ships, which each average 44 years of age. Similar problems face the Air Force. In 1980, the average age of the Air Force’s bomber force has increased from under 20 years to 39 years and its tanker fleet from about 20 years to 38 years. It’s hard to imagine that Air Force pilots are flying planes designed in the 1970s. What’s more, when these vehicles are decommissioned, many are passed down to the US Forestry Service (as observational or fire-fighting aircraft) or to rural municipalities who need ambulance, police and fire vehicles. People’s lives (and sometimes the outcome of wars) hang on the accuracy and dependability of these vehicles. Being able to predict their fatigue life with accuracy can save time, maintenance costs, and ultimately lives.

Fatigue testing or accelerated-life testing is the process of testing a product by subjecting it to conditions (stress, strain, temperatures, voltage, vibration rate, pressure etc.) in excess of its normal service parameters in an effort to uncover faults and potential modes of failure in a short amount of time. In other words, the simulation of wear and tear over time. By analyzing the product’s response to such tests, engineers can make predictions about their potential service life and recommend maintenance intervals. Two popular methods of fatigue or life-cycle testing include accelerated hardware-in-the-loop simulation and accelerated field testing. Field testing is labor intensive, time consuming and expensive. Hardware in the loop is none of the above, however, not many pilots would feel entirely comfortable relying on the integrity of a plane that had only been tested using a software model. For more advanced testing, many engineers are turning to distributed sensing as the mechanism to help alleviate the guess work in determining an accurate end-of-life scenario. The reason they are embracing this advanced technology is that distributed sensing solutions provide a more detailed picture of the true health of a vehicle. With thousands of sensors contained in a single hair-thin fiber, distributed sensing solutions obtain real-time, spatially continuous information about multiple parameters (strain, temperature, deflection, etc.). All these parameters can be measured simultaneously using a single system – thus saving considerable time and money. In addition, they can also be measured in the actual simulated conditions such a vehicle encounters in the real world, without subjecting them to real-world field testing. This includes, rugged environments with extreme temperature fluctuations, radiation, and high EMI/RFI readings.

Some applications that utilize distributed sensing for end-of-life assessment include crack detection, deformation monitoring, deflection monitoring, composite health, liquid-level monitoring, corrosion sensing, temperature elevation, and more. Each of these assessments allow an engineer to predict – often down to the number of flight hours or miles of service – how long a vehicle will remain safe and functional, enabling decisions to retire or decommission a vehicle or aircraft before a serious accident occurs.

For more information:
View our Applications page about Structural Health Monitoring
View our Case Studies page about Structural Analysis, Structural Health Monitoring, and Nondestructive Evaluation
View our Whitepapers page for an Introduction to Fiber Optic Sensing

New Affordable Distributed Fiber Optic Sensing Platform Now available

Posted on by Pierrick Vulliez

Distributed fiber optic sensing has traditionally been a steep entry price technology to get behind. It has been a common issue for many years that has led many engineers to look for other alternatives when they see the price tag. This has adversely affected the technology’s penetration in the marketplace.

Fortunately, Sensuron is pleased to announce the release of Strain Sense, our low-cost distributed strain sensing platform capable of monitoring strain across thousands of sensing points simultaneously by using a single fiber optic cable. The system replaces single-point solutions such as strain gauges and enables users to measure spatially continuous and finite element-like strain distributions. Provided with a clear picture of deformation, load paths, gradients, and stress concentrations, engineers gain far more insight into the performance of their structures, components, and materials. Additionally, customers who replace single-point sensing solutions with a true distributed sensing platform enjoy significantly reduced installation time as well as labor cost savings. Strain Sense excels in Structural Health Monitoring applications where the ability to continuously observe, assess, and address how a structure or an object reacts under load means the difference between catastrophic failure and safe operation. The technology is especially of interest for the monitoring of critical assets in Civil Engineering, such as bridges, and is becoming a key tool in Nondestructive Testing. With a price point of $15,000 Strain Sense has the potential to revolutionize how Engineers test, monitor, and ensure the safety and reliability of their structures.

Strain Sense offers reduced installation effort compared to traditional strain gauges, increased sensor density, excellent fatigue life, insensitivity to EMI, minimal measurement drift, corrosion resistance, minimal lead cabling, and is available at a much lower price than any other product delivering the same performance! More information about Strain Sense can be found on the product page.

Fatigue – A clear advantage of Fiber Optics Sensing over Strain Gauges

Posted on by Pierrick Vulliez

One widespread application where FOS technology exhibits superior performance over foil strain gauges is in the fatigue testing of components, sub-assemblies, and full-scale structures. Demand for full-scale fatigue testing continues to increase, specifically in the aerospace industry where there is significant interest in extending the service life of aging aircraft well past the intended design life.

In order to extract as much life out of these aging aircraft as possible, new fatigue tests are required to appropriately plan future maintenance schedules.
Strain gauges are not ideal for this purpose as they often fail prematurely when subjected to fatigue or cyclic loading. As strain gauges are sufficiently fatigued, a drift of the zero signal occurs due to permanent damage in the gauge, known as a “zero-shift”. Depending on the stress amplitude and number of cycles that the strain gauge is subjected to, the “zero-shift” can range from ten to several hundred microstrain before the sensor stops working entirely. Regardless of the application, the fatigue performance of FBG optical fiber is vastly superior. For example, the nominal fatigue life (where zero-drift remains below 100 μϵ) of a typical commercial strain gauge is 1500 – 2500 μϵ at 10^6-10^7 cycles [9]. In comparison, optical fiber is essentially insensitive to fatigue. FBG fiber commonly used with Sensuron equipment has proven capable of withstanding over 20,000 μϵ at several million cycles [10]. Thus, FOS strain sensors are ideal for fatigue testing as the fatigue limit for fiber is well above the strain amplitudes witnessed during the testing of common structural materials. 
Summary
Reduced installation effort, increased sensor density, and excellent fatigue life are only a few of the unique advantages of FOS technology. Additional benefits include insensitivity to EMI, minimal measurement drift, corrosion resistance, and minimal lead cabling. Although FOS technology provides a variety of distinct advantages, it is not always optimal for all structural testing applications. For example, hard to reach areas or locations with restrictive space constraints are often best suited for traditional strain gauges. Additionally, traditional strain gauge rosettes are recommended to measure principal strains in areas with limited space. FOS technology has demonstrated its relevance as a critical structural testing tool. When used in conjunction with strain gauges, it provides the ability to thoroughly characterize the behavior of a structure or a component.