Fatigue in Materials: Fundamentals, Multiscale Modeling and Prevention : Poster Session
Sponsored by: TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Computational Materials Science and Engineering Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Ashley Spear, University of Utah; Jean-Briac le Graverend, Texas A&M University; Antonios Kontsos, Drexel University; Tongguang Zhai, University of Kentucky

Tuesday 6:00 PM
February 28, 2017
Room: Hall B1
Location: San Diego Convention Ctr

L-68: A Strain Energy Based Damage Model for Fatigue Crack Initiation and Growth: Peter Huffman1; 1John Deere
    A strain energy based fatigue damage model is proposed which uses the strain energy from applied loads and the strain energy of dislocations to calculate stress-life, strain-life, and fatigue crack growth rates. Stress ratio effects intrinsic to the model are discussed, and parameterized in terms of the Walker equivalent stress and a fatigue crack growth driving force. The method is then validated using a variety of different metals with strain-life data and fatigue crack growth rate data available on the SAE Fatigue Design & Evaluation subcommittee database.

L-69: Acoustic Induced Vibration and Failure Assessment in Piping; Fluid-Structural-Interface: Bakr Rabeeh1; Mariz Mattar1; 1German University in Cairo, GUC
    One of the key design parameters to a process plant with large capacity is the risk of AIV. However, the key driving micro mechanisms of failure with acoustic phenomena is still need more investigation. This paper introduces failure mechanisms for a case study of AIV based on actual operating condition in a piping systems with different boundary conditions. Modeling and simulation of AIV in actual piping system are introduced via ANSYS considering different external stimuli. Acoustic analysis of AIV is being considered utilizing fluid, structural and fluid structural interface (FSI). Failure micro-mechanisms are illustrated with different failure modes. The synergetic effect of different external stimuli for AIV is also introduced with its weight fraction. This kind of AIV evaluation would be useful to determine the priority of the counter measure to mitigate piping failure caused by AIV in the existing plant.

L-70: Crack Initiation and Propagation Modeling Using Extended Finite Element Method (XFEM): A Review: Mashhour Alazwari1; Singiresu Rao1; 1University of Miami
    For structural components under cyclic loading condition, the crack initiation and propagation analysis is important to ensure a reliable design. The classical finite element method is used in modeling the crack growth. However, an accurate analysis is needed for the crack growth to ensure more reliability. Extended finite element method (XFEM) is the most accurate method used to solve discontinuity issues at this time especially for crack growth modeling. The great potential of XFEM is the ability to analyze discontinuities independently of the mesh. This novel method allows the crack growth to be modeled without re-meshing the crack surface which alleviates the difficulties and inaccuracies associated with the use of the conventional finite element method (FEM). This work gives an extensive review on crack initiation and propagation modeling using Extended Finite Element Method (XFEM). The current state of research and future opportunities are outlined in this work.

L-71: Crack Initiation in a Ni-based Superalloy Studied by Miniaturised Ultrasonic Fatigue Testing: Jicheng Gong1; Isaac Cabrera1; Angus Wilkinson1; 1University of Oxford
    Laser micro-machining has been used to cut meso-scale ~100-200 Ám wide cantilevers in thin metallic foils. Cyclic deflections of the cantilevers were excited through vibration of the sample using a high power ~20 kHz ultrasonic generator. The meso-cantilevers were machined so as to randomly sample relatively small patches of microstructure in polycrystalline Ni-superalloy foils. An optical microscope integrated with the loading system enabled in situ monitoring of the sample surface and fatigue damage was recorded throughout each test. SEM images and EBSD maps of the entire tested region were obtained prior and/or post testing. The formation of localised slip and profuse surface extrusions associated with crack initiation was recorded, and locations correlated with underlying microstructure. Annealing twins were present in large numbers and fatigue damage was associated with those twins where a very high Schmid factor was found on the slip systems parallel to the twin plane.

L-72: Creep, Damage and Fatigue Failure of Sn3.0Ag0.5Cu Solder Joints: Travis Dale1; Dennis Chan1; Chaitra Chavali1; Carol Handwerker1; Ganesh Subbarayan1; 1Purdue University
    SnAgCu alloys exhibit complex microstructural aging that affect both their creep response and fatigue resistance over the life of the joints. We will describe the development of microstructurally adaptive constitutive models for creep response of Sn3.0Ag0.5Cu solder joints. The developed model identifies microstructural parameters that critically influence the mechanical response as a result of aging, and accurately predicts the creep response for a given microstructural state. The foundational physical principle of maximum entropy is used to describe damage accumulation in ductile solids. The theory results in a single parameter exponential damage accumulation model. The damage model parameter is obtained through isothermal cyclic fatigue tests. For both the constitutive model and the life model, a high precision micromechanical tester was used to perform monotonic, creep, and fatigue tests on Sn3.0Ag0.5Cu solder joints under various aging and testing conditions.

L-74: Effect of Laser Ablation Coating Removal (LACR) on the Fatigue Behavior of a Steel Substrate: Md Shamsujjoha1; Sean Agnew1; James Brooks2; James Fitz-Gerald1; 1University of Virginia; 2Newport News Shipbuilding
    The effect of laser ablation coating removal (LACR) on the fatigue performance of a DH36 steel was investigated and compared against abrasive blasting and conventional hand grinding. The fatigue life of LACR and hand-ground samples are similar, while abrasive-blasted samples show a slightly better fatigue life.The metal surface is melted and re-solidified during the LACR process.A high density of embedded abrasive blasting media was observed even after performing LACR and hand grinding. Stylus-based profilometry revealed that LACR reduced the roughness slightly, while hand ground samples exhibited significantly lower roughness values.X-ray diffraction-based measurements of the residual stress show that both LACR and hand grinding induce a tensile shift in the near surface region.SEM fractography revealed that fatigue cracks initiated from the surface defects (e.g. valleys of surface roughness, embedded media). The observed fatigue performance is attributed to the combined effects of surface damage and residual stress.

L-75: Effects of Deformation Behaviors on S-N Fatigue Properties of High-Mn Steels at Ambient and Cryogenic Temperatures: Hyokyung Sung1; Daeho Jung1; Wongyu Seo1; Jehyun Lee2; Sangshik Kim1; 1Gyeongsang National University; 2Changwon National University
    The S-N fatigue property of newly developed austenitic high-Mn steels was investigated at ambient temperature (298 K) and cryogenic temperature (110 K), and the results were compared to STS304L steels. High-Mn steels have quite satisfactory fatigue performance at 298 and 110 K, indicating comparable resistance to fatigue in STS304L. The S-N fatigue behavior of high-Mn steel was dependent on tensile strength, the trend of which well-matched to that of other austenitic steels. The EBSD and micrographic analyses suggested that there is no notable TRIP (transformation induced plasticity) and TWIP (twinning induced plasticity) effects in high-Mn steels under fatigue loading at 298 and 110 K unlike monotonic loading condition. In this talk, the correlation between deformation behaviors and S-N fatigue properties of high-Mn steels will be presented based on the fractographic and microscopic observations.

L-77: Fatigue Crack Initiation and Fatigue Crack Growth Behavior of Pre-Ccrroded AA7050-T7451: Noelle Easter Co1; James Burns1; 1University of Virginia
    A galvanic couple is set-up in aluminum aerospace structures when electrolyte is trapped in between the aluminum substructure and the stainless steel fastener. This research studies the effect of different galvanically induced corrosion morphologies on the fatigue initiation and crack growth behavior in AA7050-T7451. Pre-fatigue corrosion damage are carefully characterized using white light interferometry, optical microscope and x-ray computed tomography. Results show that severe macro-scale corrosion metrics (pit depths, area, volume, density) do not dictate the fatigue crack initiation site leading to possible strong effect of micro-geometry and/or microstructure on the location of fatigue crack formation. Local plasticity at the fatigue initiation site is also investigated by considering the grain orientation and constituent particle distribution. The outcome of this research provides guidance for better structural integrity management and corrosion inhibitor design in the context of pit-to-crack transition.

L-79: Finite Element Analyses of Pure Ni Cold Spray Particles Impact Related to Coating Crack Behavior: Pasquale Cavaliere1; 1University of Salento
    The present paper describes a systematic study of the processing parameters influencing the in-flight and impact velocity of cold sprayed Ni particles through Finite Element Modelling (FEM). The possibility of repairing cracks, in Ni-based superalloy panels panels, through cold spray is demonstrated. IN718 panels with a surface 30░ V notch was filled with pure Ni powders via cold spray. The crack behavior of V-notched panels subjected to bending loading was studied by FEM and mechanical experiments. A good behavior in terms of K factor reduction and crack nucleation and growth behavior of the repaired panels was demonstrated. The way stress concentration was quantified, residual stress field and failure are affected by the mechanical properties of the sprayed materials and by the geometrical and mechanical properties of the interface with particular effect of the adhesion strength and of the local residual stresses.

L-81: Micromechanical Analysis of Acoustically Induced Vibration; Piping Bulging and Thinning: Bakr Rabeeh1; Alaa Mazroua1; Marwa Abdelbaqy1; 1German University in Cairo, GUC
    In gas applications with high-pressure drops, an intense internal vibrations in pipes. The effect of acoustic field generated inside the pipelines is investigated in two different design cases. Micromechanical analysis are introduced via continuous and incremental fatigue testing along with MATLAB modelling. Microstructural banding along with micro-mechanisms of piping failure are introduced. Five different mechanisms are established; localized micro plasticity (slip banding with grain boundary flow), crack initiation, crack propagation, crack evolution and catastrophic failure and correlated with physical acoustic analysis corporation (PAC) system. However, localized micro plasticity are introduced, crack initiation has a circumferential behavior that may induce piping bulging and thinning. MATLAB micromechanical modeling is introduced to illustrate acoustic induced vibration, and failure assessment diagram, with fatigue life estimation. A synergetic effect is established between sound pressure level, design parameters, pre-forming and post-forming seamless piping that has a dominant effect on piping failure mechanisms.

L-83: The Effect of Rare-earth Additions on Low-cycle Fatigue Behavior in Mg Alloys: Aeriel Murphy1; John Allison1; 1University of Michigan
    Wrought Mg alloys are increasingly important for aerospace and automobile applications, necessitating improvement in understanding of the factors affecting fatigue resistance of these materials. Rare-earth (RE) elements are known to reduce the cyclic tension-compression asymmetry found in many Mg alloys through texture weakening and inhibition of dislocation motion during deformation and thus this study has focused on this class of alloys. Cyclic deformation and fatigue damage development of pure Mg, Mg-2.4Nd, and a rare-earth Mg alloy, WE43, were investigated by conducting fully-reversed strain controlled tension-compression experiments.. Four strain amplitudes were investigated in this study: 0.2%, 0.4%, 0.6%, and 0.8% at a testing frequency of 0.5Hz. Both fatigue life as well as tension-compression asymmetry have been characterized. To study fatigue damage evolution fatigue cycling was interrupted and surfaces examined using scanning electron microscopy. The effects of ageing and grain size in Mg-RE alloys were also investigated and will be discussed.

L-84: The Effects of Microstructure on Fatigue in a Polycrystalline Nickel Base Superalloy at Intermediate Temperature: J.C. Stinville1; M.P. Echlin1; P.G. Callahan1; W.C. Lenthe1; E. Marin2; J. Miao3; T.M. Pollock1; 1University of California Santa Barbara; 2GE Global Research; 3University of Michigan
    Robust models for fatigue and the variability in this property could provide substantial enhancements to the design, processing and life prediction of alloy components. A major challenge is the strong dependence of the intrinsic plastic deformation processes that operate during fatigue on the microstructure of the alloy involving localized accumulation of plastic strain and ultimately crack initiation and propagation. In this context, statistically representative measurements of strain localization and damage during cyclic loading that are spatially correlated with the microstructure have been collected through advanced experimental techniques. The specific microstructural configurations that induce crack initiation in a RenÚ 88DT polycrystalline nickel-base superalloy during fatigue at intermediate temperature have been identified. Transmission electron microscopy has been conducted at these specific microstructural configurations to characterize the dislocation sub-structure that promotes fatigue crack initiation. Results are discussed for varying temperatures and in relation to the fatigue life (S-N plot) of the RenÚ 88DT.

L-85: VHCF Strength of Spring Steel with Small Scratches: Yoshiro Nishimura1; Masahiro Endo2; Keiji Yanase2; Yuichi Ikeda2; Yuya Tanaka2; Susumu Miyakawa1; Nobuyuki Miyamoto1; 1Denso Corporation; 2Fukuoka University
    A number of components in the automotive vehicles have various types of compression coil springs. These days, because of the strong demand for better performance of automotive vehicles, the use of high-strength spring steel has been increasing. When the compression coil springs are subjected to high cyclic stress, fatigue crack sometimes propagates from small defect or scratch produced in the manufacturing process. However, there are a limited number of studies on the fatigue behavior of high-strength spring steel in the presence of small defect, especially in very high cycle fatigue regime. In this study, a series of fatigue were systematically conducted by using a resonance-type torsional fatigue machine and ultrasonic torsional fatigue machine. Then, the sensitivity of high-strength spring steel (SWOSC-V) to small artificial defect was qualitatively and quantitatively examined both in high cycle and very high cycle fatigue regimes.