strain - MUCOOL - LH2 Absorber window - Pressure test...

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Ch. Darve 06/03/01 1 MUCOOL - LH2 Absorber window - Pressure test Measurement of the strain 1 Goal This memorandum describes the techniques considered and the measurements performed with the strain gages installed on the LH2 absorber window. We use the strain gages in order to measure the behavior of the absorber window while a water pressure is applied to the concave side of the absorber window. In addition to the measurement of the strain, we will measure the deflection of the window with the photogrammetry technique. Both deflection and strain measurements will be compared to the finite element analysis results that were performed for the R15 cm absorber window - 130 micron thick. The strain gages were also installed on aluminum specimen simulating the window thickness and finishing. This first test permits us to check the precision of our measurement. 2 Definitions 2.1 Material properties Aluminum 6061 T6, was chosen as the absorber window material (low Z). The Young's modulus of this material is equivalent to 68 GPa and was used in the FEA. The poisson ratio is 0.3. 2.2 Strain The strain, ε , is defined by the deformation per unit length, measured when an uniaxial force is applied to this body. The strain is dimensionless ratio and of the order of the 10 -6 therefore often expressed as με . ε = L/L 2.3 Stress-strain relationship and Young's modulus The relationship between the strain, ε , and stress, σ , permits us to introduce the Young's modulus (or modulus of elasticity), which is one of the main characteristic of the material. σ = εΕ 3 Choice of the strain gages 3.1 Composition The strain gages that we have chosen are bonded resistance strain gage types. The gages are chosen regarding the following parameters: - thickness (as thin as possible to minimize the influence of the gage itself in the measurement) - strain range (we mainly focus on the elastic range of the Aluminum) - filament material (the most stable material is requested) The best fitted products are 1 mil thick (backing film thickness). They are composed of constantan filament. Their strain range is ± 5% (50,000 με ).
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Ch. Darve
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strain - MUCOOL - LH2 Absorber window - Pressure test...

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