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Calibration and Validation of Three Fracture Criteria for Alloy 718 Subjected to High Strain Rates and Elevated Temperatures
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. (Solid Mechanics)ORCID iD: 0000-0002-5351-9338
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. (Solid Mechanics)
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. (Solid Mechanics)
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-62596OAI: oai:DiVA.org:ltu-62596DiVA: diva2:1083695
Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2017-04-05
In thesis
1. Method Development for Characterisation of Superalloy used in Containment Design
Open this publication in new window or tab >>Method Development for Characterisation of Superalloy used in Containment Design
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Metodutveckling för karaktärisering av superlegering med tillämpning i containmentdimensionering
Abstract [en]

Due to the trend of increasing environmental demands put on civil aviation, manufacturersof commercial aircraft engines meet increased pressure to reduce weight. Modernturbofan engines represent up to almost one tenth of an aircraft's total weight, meaning areduction of engine component weight of just 30 kg is estimated to reduce CO2 emissionsby 400 tonnes over the lifetime of a medium sized commercial aircraft. At the sametime turbine casings are required to fully prevent debris to escape in the event of bladefailure, to prevent further damage to critical systems. For new designs to be approvedthe Federal Aviation Regulations (FAR) states that the containment capability of a suggesteddesign solution must be experimentally established, a process associated with highcosts and long lead times. The industry therefore more frequently relies on numericalsimulations as part of all stages in the design process. For simulations to replace theexpensive experiments in nding the nal optimum design regarding weight and safety,the accuracy of the used models have to be improved.This thesis aims to provide increased accuracy in the numerical predictions by developingexperimental procedures to test material close to the operational conditions of thecontainment structure. This is realised by performing experiments at high-strain ratesand elevated temperatures in a high-velocity tensile testing machine combined with aninduction heater. Sheet specimens of varying geometries are loaded in tension to achievedierent stress states for covering dierent failure modes. Furthermore, high-speed photographyand Digital Image Correlation are utilised to track in-plane deformations. Theresulting local deformations are then used to derive the stress-strain hardening relationand the evolution of the stress state from initial loading up to fracture. The obtaineddata are nally used to calibrate strain rate and thermal dependent plasticity and fracturemodels. To validate the calibrated models so-called reverse impact testing was used,where the resulting force of a material sample impacting an instrumented target wasquantied. The experiment was straightforward to model numerically since the specimenies freely without constraints, thereby avoiding complex boundary conditions.The characterisation method was developed and performed on nickel based Alloy 718.This material is known for its high strength and good corrosion resistance at high temperaturesand is therefore commonly used in hot parts of aircraft engines, such as thecontainment structures of the low-pressure part of the engine turbine. All material fortesting and validation was supplied from one single heat and batch, aged using the sameheat treatment conditions, to ensure consistent mechanical properties. The results fromthe characterisation procedure showed that the plastic ow of Alloy 718 is moderatelystrain rate and temperature dependent while the fracture is clearly stress state dependent.

Place, publisher, year, edition, pages
Luleå University of Technology, 2017
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Metallurgy and Metallic Materials Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-62799 (URN)978-91-7583-866-3 (ISBN)978-91-7583-867-0 (ISBN)
Public defence
2017-05-24, A109, LTU, Luleå, 09:00 (English)
Opponent
Supervisors
Funder
VINNOVA
Available from: 2017-04-05 Created: 2017-03-30 Last updated: 2017-05-08Bibliographically approved

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