Session Tu1: Tuesday, June 13, 10:30-12:30
Tuesday Jun 13 2023
10:30 - 11:10
SIMILITUDE A BASIC CORNERSTONE FOR THE ANALYSES OF CRACK PROPAGATION [Keynote]
The similitude concept in fracture mechanics is the base for the understanding the size and loading condition dependent or independent crack propagation resistance. In the present overview few selected examples for monotonic and cyclic loading will be presented and underlying mechanisms are discussed.
11:10 - 11:30
COMPETITION BETWEEN INTERGRANULAR AND TRANSGRANULAR FAILURE IN ALUMINUM ALLOY: EXPERIMENTS AND CRYSTAL PLASTICITY MODELING
Aluminum alloys commonly used in airframe structures have been observed to show orthotropy in fracture when processed through hot rolling or extrusion, while other properties such as yield are more isotropic. Fracture orthotropy is likely due to a competition between damage accumulation within the grains by void growth and cleavage along the grain boundaries. Analysis of the fracture surface indicates varying degrees of dimpled regions (indicating damage by void growth) and quasi-brittle flat regions coinciding with the grain boundary (indicating grain boundary failure). To help determine structure-property relations in such materials, this paper describes a computational model for fracture in ductile polycrystals accounting for both the damage mechanisms. The model is validated by comparing with experiments on a high strength aluminum alloy, AA2139.
11:30 - 11:50
USING DEEP LEARNING TO PREDICT MICROSTRUCTURALLY SMALL FATIGUE CRACK GROWTH PARAMETERS IN POLYCRYSTALLINE MATERIALS
Vignesh Babu RaoWalnut
The ability to rapidly predict the growth behavior of microstructurally small cracks (MSCs) has the potential to significantly advance fracture-based designs and structural prognosis. The difficulties associated with characterizing or predicting MSC growth using experimental and numerical techniques preclude the applicability of such techniques in industrial design approaches, despite their potential benefits. Here, we propose a framework to accelerate high-fidelity MSC growth predictions using deep-learning algorithms, viz. , convolutional neural networks (CNNs). The primary research aim is to train CNNs to predict the rules governing MSC growth and to subsequently apply the trained CNNs to make rapid forward predictions of local crack extension given microstructural neighborhood information along a crack front. The training data are acquired from a large number of “virtual” MSC growth observations enabled by high-fidelity finite-element-based simulations. The MSC-growth-simulation framework, data-extraction strategies, and application of deep-learning algorithms for data-driven model development will be presented, and the resulting advantages will be demonstrated.
11:50 - 12:10
FORWARD AND INVERSE ANALYSIS OF TENSILE PROPETIES OF DUAL-PHASE STEELS
This study proposed a forward analysis method to predict tensile strength and total elongation by considering the three-dimensional microstructure of dual-phase steels. By repeating the forward analysis, an inverse analysis was performed to search for a microstructure with higher tensile properties. The optimal microstructures found by the inverse analysis were consistent with conventional materials engineering findings, demonstrating that the proposed inverse analysis method is effective in solving the structure-properties linkages in the inverse direction.
Session Tu2: Tuesday, June 13, 14:00-16:00
Tuesday Jun 13 2023
14:00 - 14:40
INVESTIGATION OF HIERARCHICAL POROUS STRUCTURES USING PHASE-FIELD FRACTURE MODELING INFORMED BY MOLECULAR DYNAMICS SIMULATION [Keynote]
The mechanical integrity of hierarchical porous structures depends on their pore morphology. To investigate the role of pore morphology on the mechanical and fracture behaviors of these complex systems, a multi-scale approach has been proposed. This paper shows how molecular dynamics simulations provide the means to extract material properties at the atomistic scale to further inform phase-field fracture technique at the continuum scale in an attempt to understand the mechanical response of these porous materials.
14:40 - 15:00
FRICTIONAL CRACK GROWTH INITIATION IN A NATURAL ORTHOTROPIC QUASI-BRITTLE SOLID
The frictional crack is extensively observed in natural phenomena like earthquake fracture, fracture at rock
fault line and in fracture of other geological materials. The contact between the flaw faces alters the stress
field in comparison to the stress field in an open condition or when not in contact. The crack growth
initiation in an open condition have been investigated sufficiently in literature. However, the frictional crack
or closed crack in an anisostropic medium has hardly been addressed. The naturally occurring biological
materials such as bone, wood, cartilage, etc. are anisotropic as well as quasi-brittle in nature. Considering
the vital application of these naturally occurring composites, it calls for a thorough investigation. The
current research work performs compression test on wood with an embedded central pore for different
contact surface conditions and orientation of pore. In addition to that, it carries out numerical simulation of
crack growth initiation and propagation using cohesive zone model (CZM) considering quasi-brittle nature
of wood. Further, it verifies the applicability of classical fracture criteria for friction crack propagation in
15:00 - 15:20
MICROSCALE DISCRETE ELEMENT SIMULATION OF SHOCK WAVE PROPAGATION IN PLASMA SPRAYED CERAMICS
The macroscopic behavior of plasma sprayed zirconia coatings is greatly affected by their microstructure, and phenomena that occur at this scale, such as micro-craking and cracks closure. The present study investigates the effect of micro-porosities and micro-craking on compressive waves mitigation, material compaction, and macroscopic fracture. A procedure to generate 3D digital twins that faithfully represents the microstructure is developped using the discrete element method (DEM) and analysis of scanning electron microscope (SEM) images. Static and dynamic compressive loadings are applied to 3D and 2D twins to identify their macroscopic behavior. Local damage mechanisms and their influence on the waves mitigation and the macroscopic damage are observed and discussed related to the current knowledge in the literature.
15:20 - 15:40
REGULARIZATION OF DAMAGE AND FAILURE USING A NON-LOCAL HARDENING VARIABLE IN AN EULERIAN FORMULATION OF INELASTICITY
It is known that damage or inelastic softening can cause an ill-posed problem leading to localization and mesh-dependence in finite element simulations. Here, a nonlocal hardening variable is introduced in a finite deformation Eulerian formulation of inelasticity. This nonlocal variable is defined over an Eulerian region of nonlocality, which is a sphere with radius equal to a characteristic length, defined in the current deformed geometry of the material. The influence of the nonlocal hardening variable is studied using an example of a plate that is loaded by a prescribed boundary displacement causing formation of a shear band. Predictions of the applied load vs. displacement curves and contour plots of the total distortional deformation of the plate and the hardening variable are studied. It is shown that the characteristic material length controls the structure of the shear band developed in the plate.
15:40 - 16:00
UNRAVELING THE INTERMITTENCY OF DAMAGE EVOLUTION FOR PREDICTING THE FAILURE OF QUASI-BRITTLE SOLIDS
We study the intermittent damage evolution preceding compressive failure using a non-local damage model accounting for material disorder and long-range elastic interactions. Our theoretical predictions are successfully compared with experiments carried on a model elasto-damageable 2D solid where damage evolution is tracked at both the global and local scale. Finally, we show how our understanding of these failure precursors can be harnessed for predicting the remaining lifetime of structures under compression.
Session W1: Wednesday, June 14, 10:30-12:30
Wednesday Jun 14 2023
10:30 - 11:10
QUANTIFYING THE EFFECT OF FIBER BRIDGING ON MODE I QUASI-STATIC AND FATIGUE TESTING [Keynote]
This investigation focuses on mode I delamination propagation in a unidirectional (UD) carbon fiber reinforced polymer (CFRP) composite laminate. Delamination propagation in this type of material may be accompanied by fiber bridging, a phenomenon where fibers from one face of the delamination cross over to the other face, such that the fibers are simultaneously pulled from both faces, thus, bridging the delamination. This increases the material's apparent resistance to further propagation of the delamination. This phenomenon occurs mostly in beam-type test specimens commonly used to characterize failure of composite materials, but does not generally occur in structures with the exception a few structures such as rotor blades. The aim of this investigation is to quantify the effect of fiber bridging for quasi-static and fatigue testing of DCB specimens so as to eliminate it from the fracture and fatigue delamination propagation properties.
11:10 - 11:30
ANALYSIS OF RIGID CURVED INCLUSION EMBEDDED IN A SOFT MATRIX: EXPERIMENTAL INSIGHTS
The role of fiber curvature in short-fiber thermoplastics can be explored by studying a rigid curved inclusion embedded in an epoxy matrix. Although inclusion enhances global stiffness, it also acts as a source of stress singularity, which leads to failure. The current study employs the 2D digital image correlation (DIC) technique to obtain full-field strain fields over a rigid curved inclusion embedded in a soft matrix. The experiment is performed on a rigid curved inclusion specimen subjected to remote tensile loading of 350N. The experimentally obtained strain field is verified using the finite element technique, and a good match is observed. Finally, the stress intensity factor is defined for the rigid curved inclusion, and it is estimated along with the geometric correction factor.
Session W2: Wednesday, June 14, 14:00-16:00
Wednesday Jun 14 2023
14:00 - 14:40
EXAMINING SUB-GRAIN DRIVING FORCES FOR SMALL CRACK GROWTH [Keynote]
High energy X-ray diffraction microscopy (HEDM) techniques and micro-computed tomography were combined with in-situ cyclic loading to examine the evolution of sub-grain-level fatigue crack growth within a Ni-base superalloy at room temperature. A focused-ion beam notch was introduced within the specimen to concentrate damage within the characterized microstructure region of interest. The test specimen was subjected to fatigue cycling with pauses for periodic micro-computed tomography and HEDM measurements to characterize the sporadic growth of the crack front and grain-level strains ahead of the crack front. The HEDM data was used to instantiate a crystal plasticity finite element model and compared to experimentally determined grain-level strains, sub-grain reorientation, and crack path.
14:40 - 15:00
PREDICTING MICROSTRUCTURALLY SENSITIVE FATIGUE-CRACK PATH IN WE43 MAGNESIUM USING HIGH-FIDELITY NUMERICAL MODELING AND THREE-DIMENSIONAL EXPERIMENTAL CHARACTERIZATION
Microstructurally small fatigue-crack growth in polycrystalline materials is highly three-dimensional due to sensitivity to local microstructural features (e.g., grains). One requirement for modeling microstructurally sensitive crack propagation is establishing the criteria that govern crack evolution, including crack deflection. Here, a high-fidelity finite-element modeling framework is used to assess the performance and validity of various crack-growth criteria, including slip-based metrics (e.g., fatigue-indicator parameters), as potential criteria for predicting three-dimensional crack paths in polycrystalline materials. The modeling framework represents cracks as geometrically explicit discontinuities and involves voxel-based remeshing, mesh-gradation control, and a crystal-plasticity constitutive model. The predictions are compared to experimental measurements of WE43 magnesium samples subject to fatigue loading, for which three-dimensional grain structures and fatigue-crack surfaces were measured post-mortem using near-field high-energy X-ray diffraction microscopy and X-ray computed tomography. Findings from this work are expected to improve the predictive capabilities of numerical simulations involving microstructurally small fatigue-crack growth in polycrystalline materials.
15:00 - 15:20
EFFECT OF LOCAL HETEROGENEITY ON FRACTURE DRIVING FORCES
Traditional fracture theories infer the local crack growth driving forces by surveying the mechanical response far from the crack. Although this approach has successfully predicted fracture by assuming isotropic and homogeneous materials, local heterogeneity such microstructural heterogeneity can affect fracture response. This presentation will evaluate the differences between the local and far field driving forces using different microstructure-sensitive modelling approaches. We will demonstrate the effects of grain size and crystallographic orientation gradients on crack tip blunting and microplasticity variability. We will also explore the role of microstructures as a buffer between the local and far fields considering the propagation of uncertainty from constitutive models into fracture prognosis. To conclude, we will discuss the implications for traditional experimental methods based on far field measurements smearing out important crack tip variability.
15:20 - 15:40
CONSIDERATIONS ON THE R-CURVE OF HUMAN CORTICAL BONE
Human bone presents several factors which complicate the evaluation of fracture. Several toughening mechanisms protect humans from health complications, but also contribute to a unique 3D crack geometry. In this study, we combine 3D imaging, in-situ loading (in air and with a waterbath), and computational analysis for the interpretation of the toughness measurements of human cortical bone in the aging human population.