The Influence of Loading Protocol in Mechanical Fatigue Tests on - PowerPoint PPT Presentation

The Influence of Loading Protocol in Mechanical Fatigue Tests on Damage Development in Silica Refractories Vahid Tadaion Academic Advisors - Dr. T. Tonnesen & Prof. R. Telle Industrial Advisor - Dr. Kirill Andreev (TATA STEEL) 17.06.2019

Aim Why do we do cyclic fatigue tests? Experimental Part - Loading protocols in Fatigue test Mode I, II and III - Monotonic vs. Cyclic loading - Strain amplitude vs. NO. of cycles to failure - Damage monitoring - NDT methods - mechanical and microstructural analysis Modelling Part - Loading protocol - Results - Linear vs. Nonlinear behavior - Models' vessels Practical Relevance and Future Work Vahid Tadaion, EcerS Conf., 17.06.2019

Aim To investigate the influence of different loading protocols in cyclic loading tests on damage development and the practical relevance of different protocols with respect to service loads. Why do we do cyclic fatigue tests? The refractory lining in applications with batch production nature, often fails after being exposed to repetitive thermal loads , so the failure usually doesn't occur in a single run. Material selection - Long campaign life of silica lining in coke ovens, several decennia. No sufficient in-service performance data is available to establish a correlation with the material properties or to judge new materials. Vahid Tadaion, EcerS Conf., 17.06.2019

Experimental Part - Fatigue Protocols Vahid Tadaion, EcerS Conf., 17.06.2019

Mode I – Constant force limits – Stress-controlled Stress, Stress, Strain, MPa MPa - NO. of Cycles, - Strain, - Advantage Drawbacks  A well-known method to study cyclic fatigue failure Refractory lining predominantly experiences strain- controlled loads [1 ].​  No strain-softening can be seen.  No constant strain amplitude can be applied! Vahid Tadaion, EcerS Conf., 17.06.2019

Mode II – Strain-controlled – Constant displacement limits Stress, Strain, Stress, MPa - MPa Strain, - Strain, - NO. of Cycles, - Advantages Drawback  Has a simple loading protocol The strain amplitude is not constant, it's diminishing.  A more conventional approach Vahid Tadaion, EcerS Conf., 17.06.2019

Mode III – Strain-controlled – Constant displacement amplitude Stress, Strain, Stress, MPa - MPa Strain, - NO. of Cycles, - Advantages Drawback  The strain amplitude is constant Has a complex (not self-explanatory) loading protocol  The method allows gradual damage accumulation (strain softening) Vahid Tadaion, EcerS Conf., 17.06.2019

Results - Monotonic Loading vs. Cyclic Loading Stress, MPa Strain, - ε Peak / ε F ailure Vahid Tadaion, EcerS Conf., 17.06.2019

Results - Strain Amplitude vs. Number of Cycles to Failure Normallised Strain Amplitude, % NO. of Cycles, - Vahid Tadaion, EcerS Conf., 17.06.2019

Results - Strain Amplitude vs. Number of Cycles to Failure Despite large spread of data, Strain Amplitude NO. of Cycles Normallised Strain Amplitude, % NO. of Cycles, - Vahid Tadaion, EcerS Conf., 17.06.2019

Results - Damage Monitoring - NDT - Mechanical Characterisation Stress, E Normallised MPa modulus, Strain, E modulus, GPa Velocity, - % Strain, - NO. of Cycles, - Impulse Excitation technique is more sensitive to d a m a g e . Ultra-sound Velocity can evaluate damage more progressively . Vahid Tadaion, EcerS Conf., 17.06.2019

Results - Damage Monitoring - X-ray Microtomography Before Loading (0 Cycles) Few Cycles After Peak After Peak (970 Cycles) 3 mm 3 mm 3 mm Vahid Tadaion, EcerS Conf., 17.06.2019

Conclusion - Experimental Part  The loading protocol significantly influences the potential to resist crack propagation. Descending order - Mode II, Mode III and Mode I.  Depending on the protocol, the damage accumulation can be either sigmoid (Mode I and III) or exponential (saturation) function (Mode II).  The strain-controlled method allows more gradual, less brittle, failure than the stress- controlled method.  The mechanical tests of various loading schedules can represent different service loads and assist in selecting the optimal refractory material. Vahid Tadaion, EcerS Conf., 17.06.2019

Modelling Part Fatigue Protocol Mode II Vahid Tadaion, EcerS Conf., 17.06.2019

Modelling Part Goal - Is it possible to model fatigue degradation? Two DEM Models - Environment Itasca PFC5 2D - Contact bond Flat-joint - Model shape Cylinder (d=30, H=50mm) - Loading setup Unconfined compressive fatigue - Loading protocol Strain-controlled fatigue - constant displacement limits (Mode II) - ε T = 40% ε Peak - ε T = 95% ε Peak Vahid Tadaion, EcerS Conf., 17.06.2019

Results - Stress-Strain Curves Model A Model B Non-linear behavior Linear behavior ε T = 40% ε Peak ε T = 95% ε Peak - Extensive strain-hardening occurs - No strain-hardening occurs - Significant irreversible strain is developed - No irreversible strain is developed - Fatigue degradation - No fatigue degradation Vahid Tadaion, EcerS Conf., 17.06.2019

Results - Models' vessel at different loading stages Before Loading Model A Model B Vahid Tadaion, EcerS Conf., 17.06.2019

Results - Models' vessel at different loading stages After 10 Cycles * at Peak ** Before Loading Model A Model B * ε T = 95% ε Peak **Monotonic loading Vahid Tadaion, EcerS Conf., 17.06.2019

Results - Models' vessel at different loading stages at Failure *** After 10 Cycles * at Peak ** Before Loading Loosely packed Model A Model B Well-packed * ε T = 95% ε Peak **Monotonic loading ***10% σ Peak Vahid Tadaion, EcerS Conf., 17.06.2019

Conclusion - Modelling Part  It is possible to model fatigue degradation with DEM.  For given loading programs, the degradation patterns are relatively similar to the stress-strain curves observed in Lab experiments.  The degradation process can be judged from the irreversible strains developed in the programs with a similar maximal displacement amplitude. Vahid Tadaion, EcerS Conf., 17.06.2019

What's the Practical Relevance of the Fatigue Protocols? Vahid Tadaion, EcerS Conf., 17.06.2019

Practical Relevance of Fatigue Mode III Repetitive thermal shock events in an unconstrained refractory lining , e.g. silica lining of Coke oven walls Bending Mode III Vahid Tadaion, EcerS Conf., 17.06.2019

Practical Relevance of Fatigue Mode III Repetitive thermal shock events in an unconstrained refractory lining , e.g. silica lining of Coke oven walls Bending Mode III 2015-2016 (TATA STEEL in collaboration with KU Leuven & TU Delft) We conducted cyclic fatigue tests on Silica and Fused Silica [2,3,4] . 2018 (ATHOR project - RWTH Aachen in collaboration with TATA STEEL) We conducted cyclic thermal shock tests [5] . Vahid Tadaion, EcerS Conf., 17.06.2019

Practical Relevance of Fatigue Mode II Compaction of the back-up lining/joint opening in a constrained refractory lining, e.g. Insulation lining in Steel Ladle Comp. Mode II Vahid Tadaion, EcerS Conf., 17.06.2019

Practical Relevance of Fatigue Mode II Compaction of the back-up lining/joint opening in a constrained refractory lining, e.g. Insulation lining in Steel Ladle Comp. Mode II 2019 (ATHOR project - RWTH Aachen in collaboration with TATA STEEL and other partners) We will conduct fatigue tests on Insulation fire-clay brick classes 26 and 28. - Fatigue Mode II - the insulation lining is frequently squeezed between the working lining and ladle shell. - Fatigue Mode III and cyclic thermal shock tests [5,6] - what if the insulation materials are employed as the hot face layer - attractive to reduce energy losses. Vahid Tadaion, EcerS Conf., 17.06.2019

References [1]Schacht, C. (2004). Refractories handbook . CRC Press. [2]Tadaion, V. (2016). Cyclic fatigue resistance of silica based refractories . (master's thesis). Aalto University, Helsinki, Finland. [3]Andreev, K., Wijngaarden, M., Put, P., Tadaion, V., & Oerlemans, O. (2017). Refractories for Coke Oven Wall –Operator’s Perspective. BHM Berg-und Hüttenmännische Monatshefte, 162(1), 20-27. [4]Andreev, K., Tadaion, V., Koster, J., & Verstrynge, E. (2017). Cyclic fatigue of silica refractories – effect of test method on failure process. Journal of the European Ceramic Society , 37(4), 1811-1819. [5]Andreev, K., Tadaion, V., Zhu, Q., Wang, W., Yin, Y., & Tonnesen, T. (2019). Thermal and mechanical cyclic tests and fracture mechanics parameters as indicators of thermal shock resistance – case study on silica refractories. Journal of the European Ceramic Society , 39(4), 1650-1659. [6]Manson, S. S. (1966). Thermal stress and low-cycle fatigue. Vahid Tadaion, EcerS Conf., 17.06.2019

Advanced THermomechanical multiscale mOdelling of Refractory linings Advanced THermomechanical multiscale mOdelling of Refractory linings Thank you for your attention Tadaion@ghi.rwth-aachen.de Acknowledgments: this work was supported by the funding scheme of the European Commission, Marie Skłodowska -Curie Actions Innovative Training Networks in the frame of the project ATHOR - Advanced THermomechanical multiscale modelling of Refractory www.etn-athor.eu linings 764987 Grant. 27