Fatigue in Materials: Fundamentals, Multiscale Characterizations and Computational Modeling: Cyclic Plastic Localization, Crack Nucleation, and Propagation II
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee, TMS: Computational Materials Science and Engineering Committee, TMS: Integrated Computational Materials Engineering Committee, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Additive Manufacturing Committee
Program Organizers: J.C. Stinville, University of Illinois Urbana-Champaign; Garrett Pataky, Clemson University; Ashley Spear, University of Utah; Antonios Kontsos, Drexel University; Brian Wisner, Ohio University; Orion Kafka, National Institute Of Standards And Technology
Wednesday 8:30 AM
March 22, 2023
Room: Sapphire H
Location: Hilton
Session Chair: J.C. Stinville, University of Illinois at Urbana-Champaign
8:30 AM
Fatigue and Inclusions in NiTi Shape Memory Alloy: High-magnification Observations of Damage and Crack Formation at Particle/Void Assemblies: Nathan Rendon1; William LePage1; 1University of Tulsa
The high-cycle fatigue life of NiTi shape memory alloys is limited by nonmetallic inclusions and surrounding voids ("particle/void assemblies," or PVAs). PVAs are the primary sites for crack initiation, increasing the risk of premature/unpredicted failure in key NiTi applications (stents, heart-valve cages, etc.). Unfortunately, the micromechanical understanding of PVAs in NiTi is limited, largely due to their small size (~3 µm). To provide more confident fatigue predictions, this work is zooming in on PVAs and their role in NiTi fatigue, especially with scanning electron microscope digital image correlation (SEM-DIC) to quantify strain around PVAs prior to and after crack initiation. This talk will share our results so far, including details of reliable SEM-DIC speckle patterning for NiTi, along with the initiation and development of damage around inclusions and voids. Ultimately, our work is pinpointing the characteristics of PVAs that most likely lead to failure.
8:50 AM
Role of Non-Metallic Inclusions in the Fatigue Behavior of Superelastic Nitinol: Parisa Shabani Nezhad1; Jacob Rusch1; John Moore1; Dinc Erdeniz2; 1Marquette University; 2University of Cincinnati
Owing to its excellent strength, high corrosion resistance and biocompatibility combined with superelastic strain recovery, nitinol has found many applications in the aerospace and biomedical device industries. In most applications, nitinol components experience cyclic loads and a mixed state of austenite–martensite phases. Unfortunately, due to the complicated nature of the stress-induced martensitic transformations, the existing fatigue theories do not precisely address the fatigue crack nucleation, propagation, and eventual failure of superelastic components. It has been shown that other than surface defects, the internal microstructural inhomogeneities, such as non-metallic inclusions, also play a role in fatigue crack initiation. In this work, advanced non-destructive characterization techniques such as X-ray microtomography (μCT) and far-field high energy diffraction microscopy (ff-HEDM) are utilized to obtain the 3-D map of the inclusions, crystallographic orientation of the grains, and the lattice strain surrounding them before and during the fatigue test.
9:10 AM
On Fatigue Crack Initiation with Fine Granular Area in Metal Matrix without Defect during Very High Cycle Fatigue: Guocai Chai1; 1Alleima
During very high cycle fatigue (VHCF) of high strength steels, fatigue crack initiation at a subsurface inclusion with a fine granular area (FGA) is a typical phenomenon. Local stress or strain concentration at subsurface inclusion is a critical factor. Fatigue crack initiation with an FGA in bulk matrix has rarely been reported. In this paper, a fundamental study on formation of FGA in bulk matrix of an austenitic stainless steel has been done using a novel one single specimen progressive stepwise-load increasing test (PSLIT). With this method, FGA has been observed in the subsurface bulk matrix. With electron microscopy techniques, damage and crack initiation behaviours in the material have been studied. Strain localization and grain fragmentation are the main processes for the formation of FGA. Local plasticity exhaustion leads to crack initiation due to local stress concentration. This method can also be used to predict damage rate in individual specimen.
9:30 AM
Effects of Frequency and Dwell on the Fatigue Crack Propagation in Single Crystal Ni-based Superalloy CMSX-4 at Intermediate Temperatures: Joseph Doyle1; Angelos Evangelou2; Nong Gao1; Edward Saunders3; Jane Woolrich3; Mark Hardy3; Philippa Reed1; 1University of Southampton; 2University of Cyprus; 3Rolls Royce
Ni-based single crystal superalloys are used as turbine blades due to their excellent combination of high temperature mechanical properties and corrosion resistance. The effects of oxidation and dwell will influence fatigue crack propagation rates and damage mechanisms at elevated temperatures. In this work the effects of frequency on the fatigue crack growth rate have been studied on CMSX-4 at intermediate service temperatures (450-550°C) through a series of frequency scan tests to obtain the transition from cycle to time dependent crack growth. Tests were conducted on single edge notched bend bars in air at a load ratio 0.1 at constant ΔK. Frequencies tested range from high frequency 5Hz to low frequency long dwell waveforms. Fatigue crack propagation mechanisms have been compared between each frequency using a combination of optical microscopy, scanning electron microscopy and Alicona IFM to characterise the fracture surfaces and assess fatigue and time dependent failure mechanisms.
9:50 AM
Investigation of the Impact of Residual Stresses on Short Crack Propagation in Martensitic Spring Steel: Anna Wildeis1; Matthias Thimm1; Hans-Jürgen Christ1; Robert Brandt1; Claus-Peter Fritzen1; 1University of Siegen
Herein, the short crack propagation (SCP) in a martensitic steel via in-situ fatigue tests in a confocal laser microscope and additional electron back scattered diffraction analyses to link the local crystallographic orientation of the microstructure with the SCP behaviour are investigated. To determine the effect of residual stresses, samples are tested with and without prior shot peening treatments. The results obtained indicate an early formation of a short crack network, where initiation sites are mainly at or close to prior austenite grain boundaries (PAGBs). The SCP rates exhibit an oscillating behaviour due to a strong interaction of the fatigue cracks with PAGBs. The shot-peened samples show similar SCP mechanisms. However, the shot peening treatment leads to a higher fatigue resistance, which is probably due to a delayed transition from SCP to long crack propagation and a shift of the fatal crack initiation site from the sample surface to the interior.
10:10 AM Break
10:25 AM Invited
Deformation Mechanisms of CoCrNi and CoCrFeMnNi MPEAs under Low-cycle Fatigue Loading: Comparison and Correlation with Lifetime: Kaiju Lu1; Ankur Chauhan1; Aditya Srinivasan Tirunilai1; Alexander Kauffmann1; Martin Heilmaier1; Mike Schneider2; Guillaume Laplanche2; Jens Freudenberger3; Jarir Aktaa1; 1Karlsruhe Institute of Technology; 2Ruhr-Universität Bochum; 3Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden)
Equiatomic CoCrNi and CoCrFeMnNi FCC MPEAs have attracted tremendous attention due to their excellent strength-ductility combinations. However, their low-cycle fatigue (LCF) behaviors are not fully clear yet. In this talk, the LCF behaviors of CoCrNi and CoCrFeMnNi at RT under different strain amplitudes will be given and correlated to their microstructural evolution. Both alloys manifest cyclic hardening followed by softening and a near steady state until failure. CoCrNi exhibits higher strength and longer lifetime than CoCrFeMnNi. TEM characterizations reveal their unique dislocation patterns, including slip bands, high-density dislcoation walls (HDDWs), extended stacking faults, PSB-walls and/or cells for CoCrNi; slip bands, PSB-walls, labyrinth and/or cells for CoCrFeMnNi, which also vary with strain amplitudes. The difference in their deformation mechanisms (including the nature of dislocations involved) is rooted by their distinct SFEs and can explain CoCrNi’s superior lifetime. Furthermore, the reasons for their cyclic stress responses will also be addressed.
10:45 AM
Characterization of Low-Cycle Fatigue Deformation Behavior at RT/200 °C of FeMnAlC Lightweight Steel for Low-Pressure Turbine Blade: Uiseok Ko1; Chi-Won Kim1; Sung-Jun Park2; Hyun-Uk Hong1; 1Changwon National University; 2Korea Institute of Materials Science
Recently, FeMnAlC lightweight steels are being considered a candidate for high-strength steel materials by applying it to economic and social demands of greenhouse gas reduction and material reduction of power generation by improving energy efficiency. Considering the application environment of the low-pressure turbine blade for power generation, fatigue characteristics are essentially required. Accordingly, this study investigated the low-cycle fatigue behavior of FeMnAlC lightweight steel. During low-cycle fatigue, cyclic softening occurred at room temperature and cyclic hardening occurred at 200 °C in all the investigated strain ranges, Δεt=0.6–2.0%. In addition, the serrated flows were observed in the hysteresis loop at 200 °C, unlike at RT. To find out the influence of dynamic strain aging, various fatigue tests with different strain rates were conducted. Therefore TEM observed the interrupted fatigue specimens to make a profound understanding of how dislocation evolutions are developed and their effects on cycle hardening/softening were influenced.
11:05 AM
Correlation Between Microstructure and Fatigue Properties of Complex-phase Steel: Nader Heshmati1; Peter Hedström1; Annika Borgenstam1; Henrik Sieurin2; Joachim Larsson3; 1KTH; 2Scania CV AB; 3SSAB
Complex-Phase (CP) steel with multi-phase microstructures offers an excellent combination of high strength, ductility, and formability. These properties make them an attractive alternative to conventional high-strength low-alloy (HSLA) steel in the automotive industry. However, the relation between microstructure and fatigue properties has not been studied in detail so far. In this work, the effect of microstructure and local hardness on fatigue properties of 8 mm thick commercial CP (800CP) and HSLA (500MC) steels was investigated and compared. The 800CP steel has a 25% higher fatigue limit due to the increased strength of the bainitic-ferritic-martensitic microstructure as compared to the ferritic-pearlitic microstructure in the 500MC steel. Furthermore, microscopy observations indicate more crack branching in the 800CP with blunting of cracks, suggesting that the microstructure more effectively hinders fatigue crack propagation.
11:25 AM
The Influence of Ex-service Steel Turbine Blade Microstructural Variability on Fatigue Behaviour and Lifetime Extension Approaches: Ara Masis Khodavirdi1; Philippa Reed1; Andrew Hamilton1; 1University of Southampton
Ex-service stainless steel (SS) turbine blades from the low-pressure stage of steam turbines are shot peened as a means of fatigue lifetime extension to allow redeployment. The variability of the microstructure within and between blades of a given SS alloy may influence the lifetime prediction models. The study aims to quantify the microstructural variability, in terms of grain size, distribution and orientation in relation to the fatigue crack initiation/propagation processes to incorporate into fatigue lifetime predictive models. EBSD mapping was used to quantify microstructural variability and mechanical testing used to correlate macro-mechanical properties to microstructural changes. Short and long crack fatigue samples were analysed by sectioning and EBSD scanning to study the microstructural variation and subsequent shot peening effect on crack initiation and propagation. A mechanistic understanding of the influence of microstructural variability on the predictive models of life extension of shot peened blades is thereby developed.
11:45 AM
Defect Tolerance of Cu Alloyed and Precipitation Hardened Steels with Different C Contents: David Goerzen1; Hannah Schwich2; Bastian Blinn1; Wolfgang Bleck2; Tilmann Beck1; 1TU Kaiserslautern; 2RWTH Aachen University
Defect tolerance aims at reducing the negative effect of defects on fatigue strength. Previous works showed that Cu precipitates enhance the defect tolerance of steels by inducing an increased cyclic hardening potential and, thus, a higher potential to counteract local stress intensities. Based on this, it was investigated how different Cu precipitation states influence the defect tolerance of two steels with 0.005 (X0.5) and 0,21 wt.% C (X21). The defect tolerance was evaluated by the √area concept, a comparison of the fatigue lifetime, the reduction of fatigue strength at given defect size, and the Kitagawa-Takahashi diagram. These approaches show that for X0.5 a higher cyclic hardening potential, induced by precipitation hardening, correlates with a higher defect tolerance, being dependent on the precipitation state of Cu. However, the defect tolerance of X21 was not increased by Cu precipitates, which might be caused by the additional pearlitic phase present in X21.
12:05 PM
Mitigating Localized Plastic Strain Accumulation in Cyclic Loading of Polycrystalline Shape Memory Ceramics: A Phase-field Study: Amirreza Lotfolahpour1; Mohsen Asle Zaeem1; 1Colorado School of Mines
Deterioration under cyclic loading is the main factor stalling various applications of shape memory ceramics (SMCs). Under cyclic loading, the fatigue cracks form from the accumulation of plastic strains in regions with high stress concentrations such as grain boundaries and phase interfaces. Therefore, the plastic strain accumulation rate can be used to assess the fatigue crack initiation and the cyclic life in these ceramics. We propose a phase-field modeling approach to investigate the localized plastic strain accumulation and cyclic behavior of zirconia-based SMCs by coupling the phase-field phase transformation and a viscoplastic model. We investigate the effects of grain orientation as well as engineered defects on mitigating the localized plastic accumulation and phase transformation induced expansion, and possibly increasing the fatigue life of these ceramics.