Advanced LIGO UK G K 1 Blade committee notes Justin Greenhalgh with Norna Robertson, Calum Torrie, Mike Plissi, Caroline Cantley LSC, March 2004 LIGO-G K

Advanced LIGO UK G K 2 Contents Report –Heat treatment – strengthening Strength & stress levels –Heat treatment – stress relieving –Creep –Young’s Modulus –Predict blade performance (blade design equations) –Blade committee conclusions so far Discussion

Advanced LIGO UK G K 3 Heat treatment for strength Unlike most other high-strength steels, maraging does NOT fail in a brittle way Current ageing heat treatment is 4 hours at 480C (gives yield stress around 1800 MPa) VIRGO results: a longer, slightly cooler treatment will give higher strength (100 hours at 435C – gives yeild stress around 2GPa) Two ways to use this: –Higher allowable stress would allow a better combination of low uncoupled mode and high internal modes. Example on next slide. AND/OR –Higher yield strength margin might give better resistance to noisy creep What next?

Advanced LIGO UK G K 4 Effect of increased allowable nominal stress Eg top blades of ITM –Set root width (say 95 mm) –Set uncoupled frequency (say 2.4 Hz with 11 kg mass) –Set shape (alpha = 1.5) –Set total supported mass (say 62kg) –Allowable stress gives thickness/length curve –Uncoupled freq gives thickness/length curve –Which gives internal mode (and ease of fitting in) StressthicknesslengthInternal f 950 Mpa4.2 mm435 mm84 Hz 1500 Mpa2.6 mm275 mm132 Hz

Advanced LIGO UK G K 5 Heat treatment for creep Ricardo suggests a long heat treatment (~1 week at ~100C) under load, to allow full dislocation movement and so effectively remove the noisy creep problem. Alternative – overload the blades briefly at room temperature Is either method –Necessary? –Sufficient? Could make AE measurements on blades under load at RAL and, if detectable results, verify that overloading or heating makes them go away –But no guarantee that what the AE detects is significant in terms of science performance –GEO has never seen blade/clamp creep but may not yet be sufficiently sensitive

Advanced LIGO UK G K 6 Creep questions At what stress level does “noisy” creep start? How is this affected by the ageing heat treatment and by stress-relieving heat treatment? How much “noisy” creep can we stand? What level can we detect with, say, AE?

Advanced LIGO UK G K 7 Young’s modulus - VIRGO results The Maraging Steel Blades of the Virgo super attenuator Meas Sci Tech 11 (2000) Careful measurements of natural frequency of bars One would expect more accurate results than load/deflection tests E = 187*[1-2.54x10-4(T-293)] +/- 1% GPa –Sample cut from blade, error bar derived from known uncertainties E values between 147 and 176 GPa(Table 5) –Thin samples

Advanced LIGO UK G K 8 Yong’s modulus – Mike Plissi results T D Cantilever Blade analysis for Advanced LIGO 176 +/- 2 Gpa 1mm thick samples Error derived how?

Advanced LIGO UK G K 9 Young’s modulus - SEI results –Here is Dennis's . The final figure converts to MPa, and the minimum is which is just outside Mike's cited range 176 +/- 2. –One other tolerance which will effect the stiffness or deflection under –load for the maraging steel blades is the variation in elastic modulus, lot –to lot. FYI, an SEI contractor, HPD, made calculations of elastic modulus –from measurements of 4 coupons of Maraging 300: –26,028,300 psi –26,363,500 psi –25,944,500 psi –26,378,800 psi –for an average of 26,278,775 psi, +/- 0.9% 179 GPa +/0.9 % Error derived how?

Advanced LIGO UK G K 10 Young’s modulus – conclusions Results so far: –VIRGO 186 +/- 1% –Mike P 176 +/- 2GPa –SEI 179 +/- 0.9% E appears to vary batch to batch Propose therefore to use a common supplier and even a common batch

Advanced LIGO UK G K 11 Blade Equations

Advanced LIGO UK G K 12 Blade design equations Recheck of earlier results – alpha and Young’s modulus –Suggests that use of the geometric value of alpha plus measured value of E gives good fit to results. Non-linear FEA to look at initial deflection of blades –Very simple work at RAL, preliminary to transmissibility (T040024) –Some work to look at the relationship between FEA predictions and those of the blade design equations –Need to check RAL results against Russel’s ( T D ) results Is flatness of blades per se a big deal?

Advanced LIGO UK G K 13 Blade committee conclusions Conclusions so far: –E varies between batches of maraging steel, so we should use a common manufacturer or maybe even a single order for the project. –Plan to make two large blades plus test samples at the same time, then measure E of samples and blade performance –Results from Virgo suggest that the heat treatment regime we have used may not be optimal, need to investigate further –Plan some tests at RAL using AE to look for noisy creep and, if found, verify that gentle heating under load removes it

Advanced LIGO UK G K 14 Bullets for discussion Creep questions –At what stress level does “noisy” creep start? –How is this affected by the ageing heat treatment and by stress-relieving heat treatment? –How much “noisy” creep can we stand? –What level can we detect with, say, AE? –Any better ideas than the planned AE tests? Does flatness of blades matter? Is the plan to make test coupons plus blades a good one (order placed already!) Where did the material Janeen gave us come from?