Fatigue in Materials: Fundamentals, Multiscale Characterizations and Computational Modeling: Poster Session
Sponsored by: TMS Structural Materials Division, TMS: Computational Materials Science and Engineering Committee, TMS: Integrated Computational Materials Engineering Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Garrett Pataky, Clemson University; Ashley Spear, University of Utah; Jean-Briac le Graverend, Texas A&M University; Antonios Kontsos, Drexel University; Brian Wisner, Ohio University
Monday 5:30 PM
February 24, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr
Session Chair: Garrett Pataky, Clemson University
G-12 (Invited): Fatigue Crack Growth Behavior in Al-7075 under In-plane Biaxial Loading with Mixed-mode Overloads: Abhay Singh1; S. Datta1; A. Chattopadhyay1; N. Phan2; 1Arizona State University; 2US Naval Air Systems Command
Engineering structures and materials are often exposed to a variety of multiaxial stress state during their service life, yet very limited studies have been conducted on multiaxial fatigue. Most of the existing studies focus mainly on investigating constant amplitude loading; however, in service conditions, the structures are frequently subjected to random or variable amplitude complex loading that can cause significant acceleration or retardation of the crack growth rate, which in turn affects the fatigue live of the structure. Despite this information, there is insufficient research available on the effect of overload excursion in multiaxial loading and there are none on the effects of complex mixed-mode overloads. The primary goal of this research is to characterize the in-plane biaxial fatigue crack propagation behavior of Al-7075 subjected to mixed-mode overloads of varying mode-mixity and to investigate the underlying microscale mechanisms that govern fatigue crack behavior at different lengths.
G-13: A Microstructural Mechanism for Low-cycle Fatigue in NiTi Shape Memory Alloy: Harshad Paranjape1; Thomas Duerig1; 1Confluent Medical Technologies
NiTi shape memory alloy is widely used to manufacture implantable medical devices. Such devices typically undergo cyclic loading and are susceptible to fatigue failure. During cyclic loading, strain localization bands bounded by transformation fronts can form and reversibly propagate in NiTi specimens. Movement of transformation fronts leads to transformation-induced slip and consequently structural and functional fatigue. Thus, intuitively, larger transformation front movements should lead to larger transformation-induced slip accumulation and poorer fatigue lifetimes. In this work, we demonstrate that the fatigue lifetime of NiTi dogbone specimens in the low-cycle fatigue regime is indeed inversely proportional to the volume swept by the transformation front during a load-unload cycle. We elucidate the microstructural mechanism behind this phenomenon by decovoluting the role played by transformation-induced slip and micro-scale inclusions in causing fatigue failure. The understanding gained through this work will aid the development of a microstructural model for high-cycle fatigue in NiTi.
G-14: Analysis of Fatigue Crack Evolution Using In-situ Testing: Susheel Dharmadhikari1; Asok Ray1; Amrita Basak1; 1Pennsylvania State University
Fatigue damage is one of the most ubiquitous sources of structural degradation during both nominal and off-nominal operations in engineering components. While model-based computational methods for assessing structural damage evolution are available, difficulty in achieving the required accuracy due to inadequacy in capturing the dynamical behavior of fatigue damage at the grain level makes them difficult to solely rely on. The objective of the current work is to investigate the evolution of fatigue failure in aluminum parts having varying degree of surface roughness. An in-situ fatigue testing setup integrated with ultrasonic transducers and a confocal microscope allowed for the systematic study of fatigue crack evolution in the presence of different type of notches. The resulting data from experimentation, characterization, and analysis were integrated to gain unprecedented insights into the evolution of fatigue failure in aluminum parts.
G-15: Assessing the Influence of Different Forging Process Parameters on the Local Fatigue Properties of a Precipitation Hardening Ferritic-pearlitic Steel: Matthias Hell1; Rainer Wagener1; Tobias Melz1; 1Fraunhofer Institute for Structural Durability and System Reliability LBF
The use of precipitation hardening ferritic-pearlitic steels for forged components opens up huge potential for the reduction of CO2 emissions and production costs by avoiding additional heat treatment. The material properties are calibrated by a defined cooling process, which utilizes the forging heat still stored in the component. Related to the sensitivity of the material properties to the deformation and temperature gradient, the influence of process parameters on the local properties has to be assessed experimentally by fatigue testing with small scale specimens.With respect to an improved and physically sound numerical modelling for the fatigue assessment of components, the local property distributions have to be examined using a process simulation of the forging and the consecutive cooling process. Based on the process simulation results, a local stress-strain behavior and fatigue properties can be assigned during the numerical evaluation of the local strain-response to an external load-time function.
G-16: Bauschinger Effect and Strain Hardening of Polygonal Ferrite and Granular Bainite Occurring during Pipe-forming of Linepipe Steels: Dae Woong Kim1; Wan-Keun Kim2; Jin-ho Bae2; Hyoung Seop Kim1; Sunghak Lee1; 1Postech; 2POSCO
Linepipe steels complexly consisted of low-temperature transformation microstructures which individually affect the Bauschinger effect and strain hardening occurring during the pipe-forming. In this study, the yield strength of linepipe steels was predicted by competing Bauschinger effect and strain hardening. Yield drop (YD) and yield rise (YR) parameters were defined from cyclic simulation analyses of outer and inner walls of pipes to express more reasonably the Bauschinger effect and strain hardening, respectively. By combining the YD and YR, the variation in yield strength (Δσy) showed a down-and-up behavior and plausibly explained the relationship of Δσy and piping strain used in pipe-forming industries. The polygonal ferrite reduced the yield-strength reduction in the low pre-strain range, whereas the granular bainite expanded it. The yield strength prediction coupled with microstructural analyses provide a good idea for designing the yield strength of various steel pipes.
G-17: Deformation Mechanism of Nickel-titanium-hafnium Alloys Subjected to Rolling Contact Fatigue Experiments: Behnam Aminahmadi1; Sean Mills1; Christopher Dellacorte2; Ronald Noebe2; Aaron Stebner1; 1Colorado School of Mines; 2NASA Glenn Research Center
High hardness and compressive elastic strength of Ni-rich, ternary Ni-Ti-Hf alloys make them attractive candidates for space-age bearing applications since they provide comparable resistance as tool steels to degradation and wear under rolling contact fatigue (RCF) conditions, with superior corrosion and dent damage resistance. Bearing element performance of Ni-Ti-Hf alloys is enhanced by inducing alternative strengthening pathways through complex precipitation sequences, which are dramatically different from that in binary NiTi alloys. In Ni56Ti36Hf8 alloy, new Ni16Ti11 and H-phase precipitates form homogeneously leading to superior hardness (769 HV) and yield stress (3.4 GPa) compared to Ni55Ti45 alloy. Using high-resolution transmission electron microscopy techniques, deformed regions under RCF wear tracks show amorphous bands of nanoscale width in the fatigue condition, eventually leading to fully amorphized regions in the spalled condition. These detailed microstructure attributes are correlated with RCF performance (hardness, strength, life), to provide better understanding of NiTi and NiTiHf bearing alloys
G-18: Development and Validation of an Accelerated Fatigue Test Method Using Model Dental-composite Restoration: Wondwosen Aregawi1; Anqi Zhang1; José Antonio Olivares Treviño2; Ruoqiong Chen3; Conrado Aparicio1; Joel Rudney3; Alex Fok1; 1Minnesota Dental Research Center for Biomaterials and Biomechanics, School of Dentistry, University of Minnesota, United States; 2Facultad de Ingenieria Mecanica Y Electrica, Universidad Autónoma de Nuevo León, Mexico; 3Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota
Dentin-composite disks (ϕ5 mm × 2 mm) made from bovine incisor roots were subjected to diametral compression under: (1) fast fracture, (2) cyclic loading with a constant amplitude and (3) cyclic loading with a continuously increasingly amplitude. Prior to testing, the samples were stored in either deionised water or lactic acid solutions of pH 4.5 for 24, 48 and 120 hours at room temperature. The fracture data were then analyzed by using the Weibull probabilistic failure model.Low pH reduced both the Weibull modulus (from 8.2 to 5.6) and mean bond strength (from 16.6 to 12.2 MPa) of the dentin-composite disks under static and cyclic loading. The longer the challenge, the greater the reduction. The fatigue parameters produced by tests with an increasing load amplitude were similar to those produced by tests with a constant amplitude. This validated the accelerated fatigue test method.
G-20: Effect of Machining and Surface Microstructure in Fatigue Life for Aerospace Titanium Alloys: Daniel Suarez1; Bradley Wynne1; Pete Crawforth2; Katharine Fox3; Martin Jackson1; 1The University of Sheffield; 2Advanced Manufacturing Research Centre; 3Rolls-Royce plc.
Aeroengine parts are subjected to very demanding working conditions, and therefore, it is key to ensure the structural integrity of the critical parts in service. The material of interest is the titanium alloy Ti-6246 used in the IP compressor disks of the new Trent XWB engine. This study is focused in understanding how microstructural or machining induced features affect fatigue life. One technique that can evaluate the fatigue life is the 4-point bend test, which is inexpensive, enables assessment of a range of machining parameters and the ability to analyse different part locations.Material is studied in before and after machining states. Specimens removed by EDM are tested and characterised. The fatigue life of the coupons is compared, as a function of the different surface conditions and the extracted location. Key interests will be to determine the role of upstream induced texture and surface modification through machining on fatigue life.
G-21: Elucidating the Effect of High Altitude Environments on the Fatigue Life of 7075-T651 Aluminum Alloy Determined by Using AFGROW Modeling: Luke Brown1; 1University of Virginia
Aluminum alloy 7075 is used extensively in aerospace applications which undergo fatigue loading in high atmosphere environments. The fatigue life of these parts is generated from laboratory crack growth rates using linear elastic fracture mechanics software, such as AFGROW. Crack growth rates in high altitude environments (low water vapor, low temperature) have been shown to have significantly slower growth rates when compared to standard laboratory environments. By combining FALSTAFF and ENSTAFF (loading and environment spectra for fighter wings) it is possible to determine the increase in fatigue life when laboratory crack growths are used versus when high atmosphere crack growths are used in AFGROW. While this method does not take into account the transient behavior when changing from one environment to another, a 67% increase in fatigue life was predicted and demonstrates that by implementing these growth rates into current fatigue life models, the inspection burden can be significantly reduced.
G-22: Fatigue Behavior and Analysis of Heavy Duty Riveted Steel Grating: Warda Abdulla1; Craig Menzemer1; 1The University of Akron
Heavy duty riveted steel grating is commonly used in bridge construction as it is relatively lightweight and is readily installed. One particular design concern is fatigue, which may affect overall durability and service life of the deck.In this study, the fatigue behavior of the deck focused on the riveted connection between the bearing, intermediate and reticuline bars. Fatigue tests have been conducted and were compared to more recent results from tests on both open-hole and riveted coupons. Lower bound S-N curves are derived for each condition and compared. A fracture mechanics model is used to examine fatigue cracking around a typical rivet hole.
G-23: Fatigue Crack Growth Behavior in Al-7075 under In-plane Biaxial Loading with Mixed-mode Overloads: Abhay Singh1; Siddhant Datta1; Aditi Chattopadhyay1; Nam Phan2; 1Arizona State University; 2US Naval Air Systems Command
Engineering structures and materials are often exposed to a variety of multiaxial stress state during their service life, yet very limited studies have been conducted on multiaxial fatigue. Most of the existing studies focus mainly on investigating constant amplitude loading; however, in service conditions, the structures are frequently subjected to random or variable amplitude complex loading that can cause significant acceleration or retardation of the crack growth rate, which in turn affects the fatigue live of the structure. Despite this information, there is insufficient research available on the effect of overload excursion in multiaxial loading and there are none on the effects of complex mixed-mode overloads. The primary goal of this research is to characterize the in-plane biaxial fatigue crack propagation behavior of Al-7075 subjected to mixed-mode overloads of varying mode-mixity and to investigate the underlying microscale mechanisms that govern fatigue crack behavior at different lengths.
G-24: Influence of the Loading Frequency on the Fatigue Behavior of Different Steels: Karl-Heinz Lang1; Steffen Becker1; 1Karlsruhe Institute of Technology (KIT)
The influence of the loading frequency on the fatigue behavior of steels is contradictorily discussed in literature. Especially for high-strength states often no influence is reported, but for low-strength states, high sensitivity is sometimes observed. Basically, two effects have to be considered: the strain rate dependence of plastic deformation and the heat dissipation due to plastic deformation. To separate these two effects, two different automotive steels, normalized 38MnSiV5 type as well as quenched and tempered 50CrV4 type steel, have been investigated in the high cycle fatigue regime. The tests were conducted at the same stress amplitude at R = -1. The loading frequencies ranged from 1 Hz up to 970 Hz. Additionally, temperature measurements at the surface of the specimens have been carried out to detect self heating effects during testing. The results show a significant frequency effect for both steels, whereas it is more pronounced for the lower strength 38MnSiV5 type steel.
G-25: Low-cycle Fatigue Modeling of Aluminum Landing Mat Connection System: Nolan Hoffman1; 1U.S. Army ERDC
The low-cycle fatigue-life of an extruded 6061-T6 aluminum aircraft landing mat connection system was analyzed through finite element modeling (FEM) and the multi-stage fatigue (MSF) model. The maximum strain was calculated within the joint to predict the strain-life of the connection system based on material properties found in literature. The FEM and MSF results were then validated with laboratory- and full-scale experimental fatigue-life data. Validation of the modeling results allows for a significant reduction in laboratory- and full-scale testing since the performance of the connection system was predictable. Overall, the modeled fatigue-life of the extruded connection system correlated well with the experimental data. The predicted fatigue-life was within 15% of the laboratory results and 9% of the full-scale results. The modeling effort produced a fatigue-life of approximately 1,300 passes while the physical testing resulted in a life of 1,132 cycles and 1,190 cycles for the laboratory- and full-scale experiments, respectively.
Cancelled
G-26: Quasi-in-situ Analysis of the Microstructure Evolution of AZ31B Alloy during Cyclic Deformation: Rong Shi1; 1Chongqing University
The microstructure evolution and deformation characteristics of the rolled Mg-3Al-Zn alloy sheet subjected to uniaxial cyclic loading was explored via quasi-in-situ slip traces analysis and EBSD. The results show that twinning - detwinning process and basal dislocation slip {0001}<11-20> dominated plastic deformation behavior during fully-reversed strain-controlled cyclic loading at a strain amplitude of 1.0% in the normal direction (ND). It is observed that the increased twin volume fraction with loading cycles attributed to the increased twin nucleation sites. Additionally, the accumulated residual twin boundaries, as well as the increased basal dislocation slip activation are responsible for cyclic hardening in both tension and compression reversal. Both grain boundary induced (GB-induced) intergranular and persistent slip band induced (PSB-induced) transgranular crack modes play an important role in final cracking.
G-27: Review of Surface Deformation Strengthening on the Fatigue Behavior of Metal Material: Hongyun Zhang1; Shuangwu Xia1; Shoudong Chen1; Jinbiao Zhang1; 1Tongling University
Fatigue strength is always a major barrier for structural applications of metal material. Many methods have been developed to enhance the fatigue strength of structural components. Compared to other method, surface deformation strengthening is obviously more efficient, which is characterized by the larger improvement in fatigue strength and no pollution to environment. To guarantee the durability and safety of structural components, it is crucial to understand the effect mechanism of surface deformation strengthening on the fatigue behavior. In this review, the research process of surface deformation strengthening is summarized in detail. The effect mechanism of fatigue performance is concluded, which is mainly due to the surface grain refinement, residual compressive stress and surface damage. Moreover, several suggestions is presented to the future research direction.