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Method Development for Characterisation of Superalloy used in Containment Design
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. (Hållfasthetslära)ORCID iD: 0000-0002-5351-9338
2017 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Metodutveckling för karaktärisering av superlegering med tillämpning i containmentdimensionering (Swedish)
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: urn:nbn:se:ltu:diva-62799ISBN: 978-91-7583-866-3 (print)ISBN: 978-91-7583-867-0 (electronic)OAI: oai:DiVA.org:ltu-62799DiVA: diva2:1085783
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
List of papers
1. Calibration and validation of plastic high strain rate models for alloy 718
Open this publication in new window or tab >>Calibration and validation of plastic high strain rate models for alloy 718
2013 (English)In: Computational Plasticity XII / [ed] E. Oñate; D.R.J. Owen; D. Peric; B. Suárez, Barcelona, 2013, 469-479 p.Conference paper, Published paper (Refereed)
Abstract [en]

Alloy 718 (Inconel™ 718), composed mainly of nickel, iron and chromium has properties that are of interest in many high temperature applications. One such application is the containment structure in aero engines which prevents fragments from penetrating the structure in case of blade failure. Impact of blade fragments on the containment structure includes both high strain rates and high temperatures and simulation models must therefore have their base in experimental conditions including transient loading and heating. An experimental method has been developed that utilizes induction heating in a high rate tensile test machine. Strain rates up to the order of 1000 s-1 and temperatures up to 650 °C have been included in the test program. Material parameters for the Johnson-Cook and the Zerilli-Armstrong models are evaluated from experimental data using optimisation. These parameters are then used to simulate a specially designed impact experiment and a direct comparison of a calculated and measured quantity can be made in order to validate model and parameters. The result from the validation experiment showed better agreement for the Johnson-Cook model than the Zerilli-Armstrong model

Place, publisher, year, edition, pages
Barcelona: , 2013
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-27449 (URN)0e719951-985e-4bc7-b1c1-6c0f49130f5d (Local ID)9788494153150 (ISBN)0e719951-985e-4bc7-b1c1-6c0f49130f5d (Archive number)0e719951-985e-4bc7-b1c1-6c0f49130f5d (OAI)
Conference
International Conference on Computational Plasticity. Fundamentals and Applications : 03/09/2013 - 05/09/2013
Note
Godkänd; 2013; 20131217 (tedsjo)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-08-22Bibliographically approved
2. Reverse ballistic experiment resembling the conditions in turbine blade off event for containment structures
Open this publication in new window or tab >>Reverse ballistic experiment resembling the conditions in turbine blade off event for containment structures
2016 (English)In: Thin-walled structures, ISSN 0263-8231, E-ISSN 1879-3223, Vol. 107, 671-677 p.Article in journal (Refereed) Published
Abstract [en]

An experimental technique has been developed which allows loading of heated sheet material under impact conditions with simultaneous measurement of the impact force history. The combined characteristics of impact loading at elevated temperature makes the experiment ideal for validation of models used to simulate the containment structure surrounding aircraft engines. In this paper experimental results for Alloy 718 are presented, a nickel based super alloy commonly used in hot parts of the containment structure. The experimental results are then compared to simulations in order to validate previously calibrated material parameters. The basic principle of the validation experiment is based on reverse ballistics, in which a thin circular specimen with free boundaries impacts the end of an instrumented rod. Using induction heating the specimen is heated to temperatures up to 650 °C and a gun driven by compressed air accelerates the specimens to desired velocity. In the reported work velocities are kept low enough to avoid cracking and thus the study is limited to plastic conditions, even though the technique is applicable also for fracture studies. The free boundaries of the experiment makes numerical modelling and simulation straightforward, making it valuable as a validation tool. All numerical simulations are performed using the commercial finite element code LS-Dyna and plastic behaviour of the material was modelled with the Johnson-Cook material model

National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-14178 (URN)10.1016/j.tws.2016.07.002 (DOI)000383813200054 ()2-s2.0-84982803960 (Scopus ID)d87e4938-9599-407f-9604-78c6dbbcdf41 (Local ID)d87e4938-9599-407f-9604-78c6dbbcdf41 (Archive number)d87e4938-9599-407f-9604-78c6dbbcdf41 (OAI)
Note

Validerad; 2016; Nivå 2; 20160825 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-08-22Bibliographically approved
3. Fracture behaviour of Alloy 718 at high strain rates, elevated temperatures, and various stress triaxialities
Open this publication in new window or tab >>Fracture behaviour of Alloy 718 at high strain rates, elevated temperatures, and various stress triaxialities
2017 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 178, 231-242 p.Article in journal (Refereed) Published
Abstract [en]

A methodology for fracture characterisation at strain rates up to 1000 s−1, temperatures up to 650 °C, and various stress triaxialities is presented. High-speed photography combined with digital image correlation is used to evaluate the strain at fracture. The methodology was successfully demonstrated on aged nickel based Alloy 718, commonly used in the containment structure of aircraft engines. Tensile specimens with four different geometries were loaded to get a wide range of positive stress triaxialities. All specimens originated from one single heat and batch to ensure consistent mechanical properties. The results showed evident stress state dependency on the failure strain, where lower failure strains were observed at higher stress triaxialities for all combinations of temperatures and strain rates. A coupled relationship between the temperature and the stress triaxiality controlling the fracture strain was found. However, any clear dependency on strain rate was hard to detect.

Place, publisher, year, edition, pages
Elsevier, 2017
Keyword
Mechanical testing, Failure mechanism, High strain rate, High temperature, Digital image correlation
National Category
Metallurgy and Metallic Materials Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-62599 (URN)10.1016/j.engfracmech.2017.04.036 (DOI)000403127100016 ()2-s2.0-85019076687 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-06-07 (rokbeg)

Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2017-08-22Bibliographically approved
4. Experimental Characterization of Triaxiality Stress State Evolution for Sheet Metal Materials
Open this publication in new window or tab >>Experimental Characterization of Triaxiality Stress State Evolution for Sheet Metal Materials
(English)Manuscript (preprint) (Other academic)
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-62474 (URN)
Available from: 2017-03-13 Created: 2017-03-13 Last updated: 2017-04-05
5. Calibration and Validation of Three Fracture Criteria for Alloy 718 Subjected to High Strain Rates and Elevated Temperatures
Open this publication in new window or tab >>Calibration and Validation of Three Fracture Criteria for Alloy 718 Subjected to High Strain Rates and Elevated Temperatures
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-62596 (URN)
Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2017-04-05

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