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63 CHAPTER 9 Glass Foam Arrestor Concept 9.1. Concept Description required for the current EMAS design. Moisture sealing of the vertical sides of individual blocks would be unnecessary. 9.1.1. System Overview Monolithic layups such as this have been used in building Glass foam is a crushable low-density material that has been roof applications. proposed as an arrestor (Figure 9.1). The foam has a closed- cell microstructure that prevents water absorption and makes 9.1.2. Performance Considerations it an excellent thermal insulator. Glass foam has material properties that suggest excellent durability to the environment Because glass foam material is a lightweight crushable foam and good chemical resistance. Typically manufactured in solid bearing many similarities to cellular cement, the list of perfor- mance considerations at the outset was relatively short. Issues blocks of various sizes, the foam can be cut into a variety of for evaluation included: shapes for different applications. Because both materials are low-density crushable foams, · Compression performance of the material in terms of energy the glass foam material exhibited properties similar to cellular absorption and rebound characteristics, cement. However, glass foam in general appeared to be less · Required density/strength for effective arresting, fragile, easier to handle, and potentially more durable than · Balance of compression and shear strengths of the material, the cellular cement. Additionally, adhesives and moisture · Rate dependence of the material, and sealants are available for glass foams that permit joining and · Durability to freezethaw exposure. weatherproofing. Because the glass foam material is generally manufactured in blocks sized at approximately 24 × 18 × 6 inches, two vari- 9.2. Testing and Modeling ants are possible (Figure 9-2): Approach The goal for the performance evaluation was to perform 1. Block Method. The block method would use 4-ft square testing that would allow calibration of high-accuracy computer blocks of the foam, analogous to the current EMAS con- models of the glass foam concept. The testing and modeling struction approach. The blocks would be constructed by approach for the glass foam material was comprehensive in adhering multiple smaller blocks together, followed by the nature, and the final outcome was a well-calibrated numerical potential addition of top and/or bottom cap materials. model for predicting arrestment loads. The sides of the block could potentially be sprayed with a The testing and modeling approach for the glass foam sealant to further weatherproof the blocks. These blocks concept is illustrated by Figure 9-3. Five major stages are would be transported to and installed at a runway in essen- illustrated by the larger process bubbles of the chart: tially the same manner as the current EMAS beds. 2. Monolithic Method. The monolithic method would be 1. Arrestor Material Testing and Modeling. Laboratory and assembled on-site at the runway by stacking and gluing pendulum testing generated test data, and computer blocks into a single large structure. The final assembly would models of the material were calibrated to match it. then be fitted with a continuous top cover layer composed 2. Tire Modeling. Aircraft tire models for the three test air- of a roll/spray-on polymer. This layup would preclude the craft were built and calibrated to match manufacturer need for joint seams, sealants, and maintenance, which are performance specifications.
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64 Figure 9-1. Glass foam material: cylinder test specimen (left) and close-up of cellular microstructure (right). Glass Foam Arrestor Concept 1: Block Method Lid Each Major Block is a Glued Assemblage of Seams Between Blocks, Smaller Blocks Sealed with Tape/Caulk Glass Foam Arrestor Concept 2: Monolithic Method Small Blocks Glued Together in Brick Pattern Monolithic Sealant Top Layer without Joints Figure 9-2. Glass foam arrestor variants: block method (top) and monolithic method (bottom).
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65 (1) Arrestor Material (2) Tire Modeling (3) Aircraft Modeling Testing/Modeling Conduct Material Manufacturer Tire Manufacturer Aircraft Tests Data Data Build Tire Model Develop Estimated Test Data (LS-DYNA) Aircraft Parameters Build Models Calibrate Tire Model Replicating Tests to Match Data Aircraft Library (LS-DYNA) (LS-OPT) Calibrate Model to Develop Arrestor Match Test Data Final Tire Models Prediction Code (LS-OPT) (APC) (MATLAB) Final Material Model (4) Metamodeling Build Combined Tire/Arrestor Models (LS-DYNA) Batch Simulations for Tire/Arrestor Combinations (LS-OPT) Metamodel Data (5) Performance Predictions Predict Arresting Performance for Test Aircraft (APC/MATLAB) Figure 9-3. Testing and modeling process for glass foam arrestor evaluation. 3. Aircraft Modeling. A generalized aircraft model was loads exerted on the different aircraft tires by the arrestor developed to predict the suspension response of the plane bed. Large data sets were generated using simulation batches and its deceleration during a ground roll. This model was for each tire and arrestor combination. These data sets were then incorporated into an APC for determining stopping then accessible by the arrestor prediction code (next step). distances and landing gear loads when an aircraft is driven 5. Performance Predictions. The preceding four development through an arrestor bed. A library of aircraft definitions stages culminated in the final, bottom-most process on the was created to represent the three test aircraft. figure. The APC was used to predict arresting distances, 4. Metamodeling. The arrestor material and tire models were landing gear loads, and ideal arrestor bed designs for the combined to produce an overrun model for determining the different aircraft.