Session W3: Wednesday, June 14, 16:30-18:00
Wednesday Jun 14 2023
16:30 - 17:10
RELATING NANOSCALE STRUCTURE AND PROPERTIES TO MACROSCALE FRACTURE TOUGHNESS FOR BULK METALLIC GLASSES [Keynote]
Jamie KruzicGrand Ballroom B
Bulk metallic glasses (BMGs) can range from exceptionally tough to brittle depending on their structural state; however, quantifying their structure-property relationships has been an unresolved challenge. Our findings revealed that local hardness variations within the BMG microstructure strongly affect the fracture behavior. Moreover, the hardness heterogeneities are controlled by the size and volume fraction of FCC-like medium-range order (MRO) clusters. We have proposed a model of ductile phase softening whereby relatively soft FCC-like MRO clusters sit in a matrix of harder icosahedral dominated ordering, while micropillar compression testing has revealed how the activation of these clusters into shear transformation zones can be negatively affected by oxygen impurities which in turn lower the fracture toughness.
17:10 - 17:30
IN SITU SEM HIGH-THROUGHPUT CYCLIC TESTING OF FREESTANDING THIN FILMS
Alejandro BarriosGrand Ballroom B
This work presents a small-scale high-throughput technique to characterize the cyclic behavior of freestanding thin films. The technique consists of the microfabrication of a Si carrier composed of an array of grips and freestanding dogbone thin films and of the automated in situ Scanning Electron Microscope (SEM) fatigue testing of the microfabricated carrier. The Si carrier functions as a nanomechanical testing device in which multiple dogbones can be simultaneously and independently tested under the same applied mechanical conditions. As a proof-of-concept, the fatigue behavior of nanocrystalline Al thin films was investigated. The technique allows for the simultaneous evaluation of crack nucleation and propagation across the fatigue life of several dogbones, facilitating the understanding of deformation mechanisms in nanocrystalline metals and providing statistically significant data. This technique reduces total testing time by orders of magnitude and allows for the investigation of the stochastic variability in fatigue failure. The current technique can be further expanded to account for different materials, new geometries and different loadings modes.
17:30 - 17:50
UNDERSTANDING FATIGUE DAMAGE PROGRESSION IN A STRUCTURAL STAINLESS STEEL THROUGH CYCLIC BALL INDENTATION TESTING
Raghu V. PrakashGrand Ballroom B
Understanding fatigue damage progression and estimating remaining life of dynamically loaded components has been a major challenge for several safety critical in-service components. Towards this, a few small specimen fatigue test methods are available, such as, cyclic ball indentation, cyclic small punch test and cyclic bulge test etc. Cyclic ball indentation has the potential to be deployed in-situ during plant maintenance to record fatigue response of localized spots. The method uses a spherical indenter of 1/16” (~1.58 mm) diameter which applies cyclic compression-compression loading on the material at selected location and monitors the load-displacement response continuously to identify failure event due to fatigue.
To capture a complete picture of this, controlled experiments using carefully prepared dog bone fatigue specimens of SS 304 have been conducted. The dog bone specimen is fatigue cycled under tension-tension uni-axial loading till failure, with Acoustic Emission (AE) signature capture during fatigue cycling. the fatigue cycling is interrupted periodically and cyclic ball indentation tests are carried out again at some locations of gage length to identify failure life cycle data of fatigue cycled specimen through displacement sensing and hysteresis area. Data obtained from cyclic ball indentation is then correlated with loss of stiffness.
17:50 - 18:10
DETERMINING THE RATE-CONTROLLING, GRAIN-BOUNDARY-MEDIATED MECHANISMS IN ULTRAFINE GRAINED AU AND AL FILMS
Olivier PierronGrand Ballroom B
The active grain boundary (GB) mediated mechanisms in ultrafine grained (ufg) Au and Al metallic films, and the extent to which they dictate plastic flow kinetics, are investigated in this work. The approach consists of a synergistic integration of in situ transmission electron microscopy (TEM) deformation experiments, nanomechanical testing, and transition state theory based atomistic modeling, in order to provide a linkage between GB-mediated dislocation processes and their deformation kinetics. The in situ TEM nanomechanical testing experiments are employed to simultaneously identify plastic deformation mechanisms, obtain key details, and measure the sample-level true activation volume in ufg thin films. The activation of relevant GB mediated dislocation mechanisms is modeled using the atomistic free-end nudged elastic band (FENEB) method as a function of representative, experimentally observed GB characters and local stress. Proper integration of experiments (sample-level true activation volume) and atomistic simulations (activation volumes of dislocation processes) to determine strength/rate-controlling mechanisms requires linking the applied stress to the local stress. To that end, a model of grain-size-dependent activation volume previously developed by Conrad is extended to account for the competition between various GB mediated mechanisms.
Session Th1: Thursday, June 15, 10:30-12:30
Thursday Jun 15 2023
10:30 - 11:10
11:10 - 11:30
IN SITU TRANSMISSION ELECTRON MICROSCOPY STUDY OF NANOMECHANICAL DEFORMATION AND ATOMIC-SCALE FRACTURE IN HIGH ENTROPY ALLOYS
Qi ZhuGrand Ballroom B
Intergranular fracture plays an important role in polycrystalline materials including high entropy alloys, but the atomic scale fracture mechanisms of individual grain boundaries (GBs) are still not fully understood. In this work, we selectively investigate the fracture behaviors of individual GBs in a single-phase face-centered cubic CoCrFeNi high entropy alloy via in situ transmission electron microscopy (TEM) nanomechanical testing supported by molecular dynamics (MD) simulations. With this set up, the classic mode I crack propagation along GBs can be dynamically visualized and quantitatively analyzed.
11:30 - 11:50
EFFECTS OF IRRADIATION DAMAGE LEVELS ON ACTIVATION VOLUME AND DEFORMATION MECHANISMS IN IRRADIATED GOLD THIN FILMS USING IN SITU TEM STRAINING
Lina DazaGrand Ballroom B
The plastic deformation mechanisms of ultrafine-grained gold thin films (average grain size ~150 nm) irradiated with 2.8 MeV Au+ ions at three different levels (0.1, 1 and 5 dpa) have been studied using quantitative in-situ transmission electron microscopy (TEM) nanomechanical testing. This technique allows for the simultaneous observation and comparison of the active deformation mechanisms, measurement of mechanical properties and true activation volume. Some of the observed deformation mechanisms include dislocation nucleation at grain boundaries (GB), dislocation pinning/de-pinning at irradiation induced defects, and stress-induced GB migration. During the early stages of deformation, dislocation nucleation and GB migration occur simultaneously. However, the dense populations of irradiation-induced defects prevent transgranular dislocation motion. As the deformation levels increase, GB migration leads to defect-free zones which then provide avenues for unimpeded dislocation glide. The true activation volume increases from ~10b3 in unirradiated specimens, to ~22b3 in irradiated specimens at 1dpa, for flow stresses ranging from 400 to 550 MPa. The experimentally measured activation volume values are compared with values determined from atomistic simulations (grain size ~10 nm) for different unit dislocation processes to determine the controlling deformation mechanism, using Conrad’s model that provides a Hall-Petch-type relationship of grain size dependent activation volume.
11:50 - 12:10
QUANTIFICATION OF INTERFACE STRENGTH OF A THIN FILM USING A NEW MICROCANTILEVER GEOMETRY.
Eloho OkoteteGrand Ballroom B
Interfaces failure occurs not only in structural materials but also in functional material systems including systems for energy conversion and storage. Such failures lead to degradation of mechanical and functional properties, such as battery capacity or electrical conductivity. In bulk scale, there are various experimental methods to investigate the interface strength and its failure mechanisms, for instance, peeling test, superlayer test, or indentation test. One of the disadvantages of these approaches is that it can be applied only to relatively thick coatings [1,2]. Small-scale mechanical testing is a powerful tool for studying interface properties because it can quantify micro- and nanometer-sized thin films, and individual interfaces of interest can be tested by isolating them using focused ion beam (FIB). Single and double cantilever beams have been used to investigate fracture/delamination properties of single interfaces [3,4], however, these methods are prone to experimental imperfections arising from testing geometries.
In this talk, we propose a new in situ scanning electron microscope (SEM) microcantilever design that provides reliable and quantitative interface toughness. In addition, the optimized geometry can promote a pre-notch (or crack) to propagate in a stable manner, which is important to generate a natural crack front without FIB-induced damage/artifacts.
12:10 - 12:30
EVALUATING THE INTERFACIAL TOUGHNESS OF GAN-ON-DIAMOND USING BLISTERING METHOD WITH NANO-INDENTATION
Dong LiuGrand Ballroom B
An improved analysis of the interfacial toughness using nanoindentation induced blistering of thin films on stiff substrates is demonstrated on GaN-on-diamond. The Hutchinson-Suo analysis requires accurate measurement of blister dimensions, conventionally measured using 2-D line-scans from 3-D topographical maps. The new meteorology overcomes shortcomings of this technique by fitting the 3-D analytical solution of a clamped Kicrchoff plate to the topological map of the blister. This allowed for quantification of interfacial toughness of smaller blisters in GaN-on-diamond, previously assumed invalid for analysis due to inadequacies of the line-scan analysis. Three samples were investigated and found to have interfacial toughness ranging from 0.6–1 J m−2. Additionally, the relationship between residual stress in the GaN and interfacial toughness was investigated using photoluminescence spectroscopy. In all cases, the GaN was found to be under increased compression at the diamond interface by up to -0.81 GPa, although no correlation with interfacial toughness was observed.
Session Th2: Thursday, June 15, 14:00-16:00
Thursday Jun 15 2023
14:00 - 14:40
IMPACT OF GRAIN BOUNDARY MODIFICATIONS ON FRACTURE TOUGHNESS OF TUNGSTEN BASED NANOMATERIALS [Keynote]
Daniel KienerGrand Ballroom B
Nanostructured materials commonly excel with respect to their strength, but their ductility and toughness remain limiting factors for deployment in safety related applications. In this work, using grain boundary engineering concepts in conjunction with severe plastic deformation for microstructural refinement, we aim to develop nanostructured and nanocomposite materials that overcome these limitations. Since material volumes are limited, we utilize small scale testing approaches to examine the respective material properties such as strength, ductility and fracture toughness. We detail on the one hand challenges and recent advancements in small scale fracture experiments, and on the other hand the effectiveness of the mentioned grain boundary engineering approaches to design outstanding nanomaterials overcoming strength-ductility-toughness limitations.
14:40 - 15:00
A NOVEL SMALL-SCALE BEND GEOMETRY CREEP TEST TO EVALUATE DEFORMATION AND CAVITATION DAMAGE IN POLYCRYSTALLINE AND BI CRYSTAL COPPER
Elsiddig ElmukashfiGrand Ballroom B
Understanding the mechanisms of creep deformation and damage (cavitation) in engineering components materials is important, but despite the significant research that has been conducted over the past 50 years, there is still a lack of understanding of the microstructural processes that influence and control the development of damage. To provide further insights into this, in the present work a novel small-scale constant load cantilever beam geometry test specimen is used. The materials selected for the tests are polycrystalline and bi-crystals of high purity copper. The copper provides a simple model material for exploring initiation and early growth of creep cavitation and allows comparison with crystal-based model predictions.
In this study, both creep deformation and creep cavitation were measured. For the latter, a range of higher spatial resolution techniques were adopted including scanning electron microscopy, electron backscattered diffraction and focused gallium ion beam serial section milling. Creep cavity number density and size measurements were made using advanced image analysis procedures. Polycrystalline and bi-crystal results are compared, with particular attention given to the role of Schmid factor and misorientation on the initiation and early growth of the creep cavities. These experimental results inform the development of microstructural based models of cavitation.
15:00 - 15:20
ANALYSIS OF FRACTURE BEHAVIOUR OF MULTILAYERS BY CANTILEVER AND CLAMPED BEAM BENDING GEOMETRY
Nagamani Jaya BalilaGrand Ballroom B
Multilayering of metal/ceramic combinations can help to achieve better strength and toughness than the individual material constituents. The effect of elastic-plastic mismatch in multilayers on the crack driving force and eventually on fracture resistance has been analyzed in this work. The enhancement in fracture toughness by decreasing layer spacing has been predicted from finite element calculations and verified by micro-cantilever fracture tests. Further, calculations have been carried out for a more stable clamped beam bend geometry to determine R-curve behavior in such multilayers.
15:20 - 15:40
OPTIMIZATION AND USE OF HIGH-THROUGHPUT MICROMECHANICAL TESTING DESIGN FOR 3D-PRINTED POLYMERS
Stanislav ZakGrand Ballroom B
Modern materials behave differently on a micro-scale level than in bulk applications. Therefore, with ever present miniaturization, the materials’ testing on a micron-level is gaining importance. 3D printing with a sub micron precision, such as direct laser writing by two-photon lithography, allows for relatively fast manufacturing of miniaturized specimens for micromechanical testing. In combination with precise loading by a nanoindenter tip, high throughput micromechanical testing is enabled. Presented research shows design process of miniaturized cantilever and push to pull device specimens for fracture mechanics testing, aided finite element modelling, together with high throughput testing of polymeric materials with varied printing parameters and loading conditions. Such in situ and ex situ experimental setup allows for systematic fracture mechanics testing on the small scale for common materials used in small-scale 3D printing.
15:40 - 16:00
MICRO-BENDING FOR MULTI-SCALE FRACTURE CHARACTERIZATION OF CEMENT-BASED MATERIALS AND CERAMICS
Santiago El AwadGrand Ballroom B
The last few years have seen the development of several testing techniques at the micro-scale to characterize the mechanical properties of multi-scale materials. One such novel methods are micro-cantilever bending tests to assess mechanical properties of materials. Micro-cantilever tests allow for a variety of test configurations, including scaled chevron-notch geometry allowing controlled crack-growth prior to critical failure load. Chevron notches are convenient at such length scales since they allow for ex-situ measurements of crack length – avoiding the need to directly measure crack length, which could be a challenge at such scale. The test approach provides access to R-curve behavior for quasi-brittle materials on the micro-scale and opens the door to investigate more sophisticated topics, i.e., creep crack growth. Moreover, the technique complemented with visualization and scanning tools, such as Scanning Electron Microscopy and Microtomography, allows for a proper and extensive analysis of the crack growth phenomena.
The motivation of this work revolves around expanding currently available knowledge on multiscale characterization of cement-based materials with the focus on fracture testing at the micro- and mesoscale through the novel micro-bending technique. This test opens the door to understanding fracture, toughening mechanisms, and evolution of these properties regarding processing variables.
Session Th3: Thursday, June 15, 16:30-18:00
Thursday Jun 15 2023
16:30 - 17:10
HIGH-CYCLE FATIGUE IN THE TEM: NANOCRYSTALLINE METALS [Keynote]
Brad BoyceGrand Ballroom B
In-situ TEM high-cycle fatigue experiments on electron transparent thin films of nanocrystalline Pt and Cu have revealed not only microstructural-sensitive crack propagation, but also unexpected microstructural-scale crack healing. Based on the experimental observations, atomistic modeling, and continuum-scale microstructural modeling, the mechanism appears to be crack flank cold welding facilitated by local compressive microstructural stresses and/or grain boundary migration. While these observations are specific to pure nanocrystalline metal thin films under a high-vacuum environment, there are potentially much broader ramifications. The existing observations can be used to help rationalize suppressed fatigue crack propagation rates in vacuum, subsurface, or under contact-inducing mixed-mode stresses; and even the precipitous decline in propagation rates near the fatigue threshold.
17:10 - 17:30
17:30 - 17:50
Session F1: Friday, June 16, 10:30-12:30
Friday Jun 16 2023
10:30 - 11:10
EFFECT OF ELECTRIC CURRENT ON PRE-CRACKED THIN METALLIC SHEETS: FROM CRACK PROPAGATION TO CRACK HEALING [Keynote]
Praveen KumarGrand Ballroom B
Both scientifically and technologically, it is important to study the effects of electric current pulses on the structural integrity of metallic components. As an electric current reverses its direction across a crack, massive current crowding occurs at the crack tip, thereby generating a non-uniform temperature field sourcing away from the crack tip, and considerable electromagnetic forces are generated on the crack faces that open the crack in Mode I. Recent studies have shown that due to the synergistic effects of the above two stimuli, a pre-existing flaw may grow as well as heal upon application of an electric current pulse of high density. While one is a bane for structural integrity, the other one is a boon to in-service components. Here, we will discuss the reasons behind crack propagation upon application of an electric current and then explore the attributes responsible for a transition from flaw propagation to flaw healing upon passage of an electric current pulse. Furthermore, the synergetic role of mechanical load and magnetic field in the propagation of a pre-existing flaw will be discussed. We will establish the complementary roles of electric current, magnetic field and mechanical load in the failure of pre-cracked metallic sheets.
11:10 - 11:30
FRACTURE AND FATIGUE BEHAVIOR OF ADDITIVELY MANUFACTURED MAR-M 509 CO-BASED SUPERALLOYS
Nagamani Jaya BalilaGrand Ballroom B
Mar-M 509 is a Cobalt-based superalloy suitable for elevated temperature applications like nozzle guide vanes and blades in aero engines and gas turbines. Short cycle aging heat treatment of laser powder-bed-fusion processed Mar-M 509 is a novel route explored in this study to enhance the mechanical properties of this alloy, especially tensile ductility and fracture toughness, while retaining room and elevated temperature strengths. A detailed microstructural analysis is carried out using advanced characterisation tools and correlated to miniature, small volume, room temperature tensile tests and fracture toughness and fatigue tests using clamped beam geometry combined with digital image correlation-based in-situ strain mapping across the longitudinal and transverse directions, before and after heat treatment. Mechanisms leading to corresponding changes in fracture and fatigue properties will be discussed.
11:30 - 11:50
INTEGRATING SIMULATION, MACHINE LEARNING, AND EXPERIMENTAL APPROACHES FOR HIGH-THOUGHPUT SMALL-SCALE FRACTURE INVESTIGATIONS
Xing LiuGrand Ballroom B
From Da Vinci to Galileo to modern experimentalists a variety of characterization methods have been introduced for investigating the fracture of materials. Determining fracture properties of materials at small length scales, with complex shapes, under extreme environmental conditions, is still extremely challenging. We will show how this gap is addressed by introducing two novel methods to investigate fracture. The first one involves light for contactless mechanical testing, while the second method integrates experiments with data-driven approaches to address issues related to complex shapes.
11:50 - 12:10
OPERANDO EXPERIMENTS TO CHARACTERISE BRITTLE FRACTURE-LIKE EVENTS IN CERAMIC ELECTROLYTES VIA PHOTOELASTICITY
Christos AthanasiouGrand Ballroom B
Solid electrolytes at current densities that are relevant to real battery operating conditions are prove to the penetration of lithium metal protrusions, also known as “dendritic” events, that are formed during battery charging. In this work, we show via operando photoelasticity experiments that the dendritic events at high current densities can be understood by the classic Griffith - Irwin fracture theory.