Session M1: Monday, June 12, 10:30-12:30
Monday Jun 12 2023
10:30 - 11:00
THE FOURTH SANDIA FRACTURE CHALLENGE - PREDICTING PUNCTURE IN A METAL STRUCTURE [Keynote]
Sharlotte KramerGrand Ballroom A
The fourth Sandia Fracture Challenge (SFC4) investigated the puncture of aluminum structures through comparing various computational predictions to physical experiments. Five teams, internal to Sandia National Laboratories, submitted predictions with mixed success. Qualitatively, many teams were able to predict the deformation and failure modes at the critical velocity for puncture, but the extent of damage was underpredicted by all. Quantitatively, predictions for critical velocity varied widely, though were in the correct order of magnitude. The SFC4 highlighted difficulties in modeling damage and fracture in shear-dominated loading cases.
11:00 - 11:20
PREDICTING DUCTILE FRACTURE FOR MIXED MODE OF LOADING USING THE MODIFIED MOHR-COULOMB CRITERION
Diego Felipe Sarzosa BurgosGrand Ballroom A
Reliable and robust fracture prediction tools are necessary for designing and analyzing critical engineering structures. This paper uses a phenomenological damage model to study the fracture response of a pressure vessel steel under complex loading conditions. Details of the experiments and numerical procedures are provided for calibrating and validating the proposed framework for predicting ductile fracture.
11:20 - 11:40
COUPLED CRYSTAL PLASTICITY PHASE-FIELD MODEL FOR DUCTILE FRACTURE IN POLYCRYSTALLINE MICROSTRUCTURES
Thirupathi MalothGrand Ballroom A
A wavelet-enriched adaptive hierarchical, coupled crystal plasticity - phase-field finite element model is developed in this work to simulate crack propagation in complex polycrystalline microstructures. The model accommodates initial material anisotropy and crack tension-compression asymmetry through orthogonal decomposition of stored elastic strain energy into tensile and compressive counterparts. The crack evolution is driven by stored elastic and defect energies, resulting from slip and hardening of crystallographic slips systems. A FE model is used to simulate the fracture process in a statistically equivalent representative volume element reconstructed from electron backscattered diffraction scans of experimental microstructures. Multiple numerical simulations with the model exhibits microstructurally sensitive crack propagation characteristics.
11:40 - 12:00
A UNIFIED NONLINEAR XFEM-CZM BASED METHODOLOGY TO DEAL WITH DUCTILE FRACTURE
Antonio KaniadakisGrand Ballroom A
The numerical treatment of the whole process of ductile fracture remains a challenging task, particularly when FEM is employed. The main issue regards pathologically mesh dependence of the numerical results, not only in the softening regime but also in the stages of strain localization and further crack propagation. In the literature, non-local approaches are adopted to mitigate these effects but they require a calibrated length scale and mesh refinement, thus being time consuming. This work focuses on the numerical treatment of ductile fracture in metal materials via a three-dimensional unified methodology that combines (i) the GTN model to describe diffuse damage using the standard FEM, the (ii) XFEM to represent the crack and (iii) the coupling of the XFEM with a cohesive zone model to account for the intermediate localization phase. We rely upon the Updated Lagrangian formulation to include large strains and rotations. The methodology, implemented in Abaqus commercial code as a user finite element (UEL), is capable of reproducing numerically the overall response of structures until rupture.
Session M2: Monday, June 12, 14:00-16:00
Monday Jun 12 2023
14:00 - 14:20
VOID SIZE, SHAPE, AND ORIENTATION EFFECTS UNDER INTENSE SHEARING ACROSS SCALES
Kim Lau NielsenGrand Ballroom A
The present work demonstrates how gradient strengthening at the micron scale affects the macroscopic strain at coalescence under intense shearing conditions. The coalescence mechanism relies on severe flattening, rotation, and elongation of the voids causing severe heterogeneous plastic strain to develop near the voids and in the ligament between voids. These gradients are associated with geometrically necessary dislocations, causing a delay in the coalescence process.
14:20 - 14:40
ANALYSES OF DUCTILE FRACTURE USING HUNNY THEORY
Amine BenzergaGrand Ballroom A
We present a theory with a structure that enables analyses of ductile fracture under any type of loading. The theory builds on the standard concept of homogeneous yielding and further proceeds from the concept of unhomogeneous yielding on a (yield) system that depends on the spatial distribution of voids. Depending on the desired level of refinement in analysis, a given simulation employs one or more yield systems with the isotropic limit being reached for an infinite number. We illustrate the predictive capabilities of the theory by considering simulations of three-dimensional crack initiation and growth in a round notched bar, a shear specimen and a compression pin.
14:40 - 15:00
1-TO-1 COMPARISON OF SEM-DIC TO CP STRAIN FIELDS OF ULTRATHIN STEEL FILMS TO UNRAVEL PLASTICITY TO DAMAGE INITIATION
Johan HoefnagelsGrand Ballroom A
In advanced high strength steels, crack propagation and fracture is preceeded by damage initiation and propagation, yet, the nature of the plasticity mechanisms leading to damage are debated. To fully unravel the plasticity-to-damage mechanisms, we present a novel integrated experimental-numerical nanomechanical framework for testing ultra-thin specimens, yielding (i) full 3D reconstruction of grain/phase shapes and orientations, (ii) front&rear-sided, high-resolution, microstructure-correlated SEM-DIC strain fields, and (iii) one-to-one comparison to numerical strain fields computed with (advanced) crytal plasticity. Results on martensite ‘bridges’ show that limited plasticity results in martensite damage whereas significant plasticity prevents damage; analysis reveals the key role of ‘substructure boundary sliding’ in martensite on damage initiation.
15:00 - 15:20
INFLUENCE OF LARGE STRAIN REVERSE LOADING ON DYNAMIC STRAIN LOCALIZATION AND FAILURE OF DUCTILE METALLIC RODS
Longhui ZhangGrand Ballroom A
A bespoke real time strain control setup is constructed to apply the reverse loading directly to the gauge section of 304L stainless steel specimen up to a maximum strain level of ±0.16. The subsequent tensile tests of the reverse loaded specimens are performed from quasi-static to high strain rates of 1000 /s. A higher strain reverse loading significantly influences the development of necking instabilities, with smaller strain to necking inception, higher local stress in the necking zone, and higher local strain rate up to failure. An analysis of the local stress-strain relationship indicates that the reverse loaded 304L rod shows good impact energy absorption up to failure, which agrees with the ductile fracture surfaces of the 304L materials with reverse loading.
Session Tu1: Tuesday, June 13, 10:30-12:30
Tuesday Jun 13 2023
10:30 - 10:50
A GURSON-TYPE LAYER MODEL FOR DUCTILE POROUS SOLIDS CONTAINING ARBITRARY ELLIPSOIDAL VOIDS WITH ISOTROPIC AND KINEMATIC HARDENING
Francois RoubaudGrand Ballroom A
Extensions of Gurson’s model for porous ductile materials have been done by Madou and Leblond (2012) for general ellipsoidal cavities made of rigid-plastic materials, and Morin et al. (2017), for spherical voids with rigid-hardenable matrices. The aim of this work is to provide a homogenized criterion for porous ductile materials incorporating both void shape effects and isotropic and kinematic hardening. A sequential limit-analysis is performed on an ellipsoidal representative volume made of some rigid-hardenable material, containing a confocal ellipsoidal cavity. The overall plastic dissipation is obtained by using the velocity field proposed by Leblond and Gologanu (2008) and that satisfies conditions of homogeneous strain rate on an arbitrary family of confocal ellipsoids. The heterogeneity of hardening is accounted for by discretizing the cell into a finite number of ellipsoids between each of which the quantities characterizing hardening are considered as homogeneous. The model is finally assessed through comparison of its predictions with the results of micromechanical finite element simulations. The numerical and theoretical overall yield loci are compared for various distributions of isotropic and kinematic pre-hardening with a very good agreement.
10:50 - 11:10
A NON-LOCAL GURSON MODEL WITH TWO FRACTURE-MECHANISM ASSOCIATED LENGTH SCALES: SUPPORTED BY NUMERICAL ANALYSES AND EXPERIMENTS
Shuyue WangGrand Ballroom A
An extension of Gurson’s porous plasticity model capable of preventing pathological strain localization, and describing crack initiation and propagation under both shearing and tension is investigated. This paper separates the progression of shear failure and flat dimple rupture based on the assumption that these two failure mechanisms are governed by different characteristic length scales, a deviatoric and a dilatational length scale, respectively. A set of numerical analyses is presented which brings out the effects of these length scales on the development of e.g. cup-cone and slant fracture. Guided by the outcome of the numerical study, a set of tests has been designed and carried out for calibration of these length scales.
11:10 - 11:30
ASSESSMENT OF EXISTING OFFSHORE GAS TRANSIMISSION PIPELINES IN TERMS OF DUCTILE FRACTURE CONTROL USING A MODELING FRAMEWORK
Reiner TrautmannsbergerGrand Ballroom A
A modeling framework is established to describe running ductile fracture in vintage API grade X52 offshore pipelines. For the structural model, the plasticity and ductile fracture properties were characterized by various laboratory scale tests. Tensile tests up to strain rates of 1000 1/s were performed to calibrate the strain rate dependent plasticity model. Using notched tensile specimens with a wide range of stress states, a hybrid experimental-numerical procedure was performed to determine the parameters of a ductile fracture (FL) model. The material model was successfully verified against the instrumented Battelle Drop-Weight Tear (BDWT) test results. The decompression of the CO2-rich gas mixture was described by the GERG-2008 equation of state and implemented as an idealized pressure decay model to reduce the computational cost. Finally, the established modeling framework provides a valuable tool for investigating and evaluating ductile fracture propagation and arrest behavior in the vintage offshore pipelines.
11:30 - 11:50
ESTIMATING PLASTICITY AND DUCTILE DAMAGE MODEL PARAMETERS FOR S355-S690 STEEL FROM MILL TEST CERTIFICATE DATA
Wei Jun WongGrand Ballroom A
Accurate finite-element simulation of the fracture of metals requires the calibration of plasticity and fracture modelling parameters based on mechanical tests on the material. Depending on the complexity of the model, each different material that is modelled requires a number of non-standard tests followed by a calibration process. This paper derives relationships between mill test certificate data and the plasticity and damage model parameters for S355-S690 steel in order to enable the quick application of generally representative plasticity and damage models to these steels without the need for repeated manual calibration of each material. The relationships are obtained by regression analysis between a database of 2597 mill test certificate results (of tensile and Charpy tests) and a parametric finite element study in which the parameters of a Hollomon-type stress-strain model and the Modified Mohr-Coulomb damage model were varied.
11:50 - 12:10
PREDICTING DUCTILE FRACTURE DURING TORSION TESTING USING ELLIPSOIDAL VOID MODEL AND ANALYTICAL MODEL
Kazutake KomoriGrand Ballroom A
Research on ductile fracture under high stress triaxiality has been performed considerably, whereas research on ductile fracture under low stress triaxiality has not been performed sufficiently. In this paper, torsion testing of a bar which is prestrained by drawing is performed using a torsion testing machine, and ductile fracture during torsion testing is predicted using an ellipsoidal void model and an analytical model.
Session Tu2: Tuesday, June 13, 14:00-16:00
Tuesday Jun 13 2023
14:00 - 14:20
EFFECT OF HPT PROCESSING ON FRACTURE BEHAVIOUR OF MARAGING STEELS
Kevin JacobGrand Ballroom A
Maraging steels are a class of precipitation hardened steels wherein different micro-mechanisms of deformation such as planar slip, interaction with coherent/incoherent precipitates, and reverted austenite affecct the overall mechanical behavior of the material. High-pressure-torsion (HPT) processing introduces a large density of dislocations that form sub-grain boundaries within the refined nano-scale structure, leading to changes in precipitate morphology compared to hot-rolled maraging steels. The impact of such nanostructuring on the deformation and fracture micro-mechanisms is being reported for the first time using in-situ characterization techniques along with transmission electron microscopy and atom probe tomography analysis, in this study. Digital image correlation has been used to quantify the full field strain maps in regions of severe strain localization as well as to determine the fracture toughness through critical crack tip opening displacements.
14:20 - 14:40
DUCTILE FRACTURE OF SS-304L MICROTUBE UNDER COMBINED AXIAL FORCE AND INTERNAL PRESSURE
Yannis KorkolisGrand Ballroom A
The fracture behavior of the stainless-steel SS-304L is assessed by loading microtubes of 2.38 mm diameter under combined axial force and internal pressure, using a custom apparatus. The force/pressure ratio is controlled in the experiments, to generate different biaxial stress paths that are proportional or nearly proportional. The results from the experiments are used to calibrate the non-quadratic anisotropic yield function Yld2004-3D. Then, finite element (FE) models of the microtubes are created after incorporating the anisotropic material modeling framework, and compared with the experiments to establish their fidelity. The FE models are then used to probe the fracture behavior under the proportional loading. The failure modes of the microtubes are different depending on the stress state being axial- or hoop-stress-dominant. It is found that the structural instabilities that precede necking are different and appear at different levels of strain. The strains at the onset of fracture, as determined by probing the FE model, reveal significant fracture anisotropy, that can be possibly also attributed to the specimen geometry, beyond the material processing.
14:40 - 15:00
MODELING OF THE ELASTO-PLASTIC BEHAVIOR OF HSLA X140 STEEL: EFFECT OF PRE-STRAIN AND TRIAXIALITY
Asmae ElochiGrand Ballroom A
In this work, a comprehensive experimental campaign is conducted to investigate the effect of pre-strain on the mechanical properties of X140 steel used in high performance threaded connections. Mechanical tests are used to characterize the plastic and fracture behavior of the material. Smooth tensile (ST), notched tensile (NT), plane strain (PE) and shear tests (STC) were performed. Cyclic tension-compression tests are used to characterize kinematic hardening. Initially qualified as isotropic, this material showed an anisotropic behavior after undergoing a pre-strain expansion as its plastic flow becomes loading direction dependent. This pre-strain effect is well reproduced using a phenomenological modeling combining isotropic and kinematic hardening contributions with a Hosford’s criterion.
15:00 - 15:20
MICRO-STRUCTURAL DAMAGE ANALYSIS FOR PREDICTING THE EFFECT OF LOADING PATH ON DUCTILITY OF TWO-PHASE STEELS
Hiroto ShojiGrand Ballroom A
The purpose of this study is to predict the effect of loading path on ductility of two-phase steels based on micro-structural damage analyses. A micro-structural damage model that consists of 3D micro-structural FE-model and ductile damage model is proposed. Isotropic / kinematic hardening model is introduced for considering the mechanical behavior of Bauschinger effect. The effective damage concept for considering micro-scopic behavior of Bauschinger effect which is dislocation behavior in loading path change is introduced into the damage model. Two types of ferrite-pearlite two-phase steels with different volume fraction of pearlite, and ferrite and pearlite single-phase steels are used. Tensile tests using micro-tensile specimen extracted orthogonal to pre-strained direction from tensile pre-strained round-bar specimens are conducted. Ductility is increased due to loading path change, and the effect is greater in the case of higher volume fraction of pearlite. The mechanism of the effect is analyzed by numerical simulation based on the proposed micro-structural damage model. It is presented that the improvement of ductility by loading path change is caused by micro-structural heterogeneity, delay of necking due to mechanical behavior of Bauschinger effect, and non-effective plastic strain for damage evolution due to micro-scopic behavior of Bauschinger effect.
15:20 - 15:40
STRAIN EVOLUTION AND DAMAGE DEVELOPMENT DURING TIGHT-RADIUS BENDING OF ADVANCED HIGH STRENGTH STEELS
Nizia Mendes-FonsecaGrand Ballroom A
Improved vehicle fuel efficiency and driving safety requirements have promoted the development of Advanced High Strength Steels (AHSS) in the last few decades. The mechanical performance of AHSS is commonly characterized by the product of the ultimate tensile stress and total elongation. However, tensile elongation is not suitable for predicting the performance of a material under complex forming operations. This work aims to investigate the effect of the steel microstructure on bending performance and to make a parallel between strain partitioning and damage nucleation in tension and bending.
15:40 - 16:00
THE INFLUENCE OF TRANSFORMATION INDUCED PLASTICITY IN THIRD-GENERATION ADVANCED HIGH STRENGTH STEELS
Concetta PelligraGrand Ballroom A
Considerable research has been invested in developing thin sheet Advanced High Strength Steels (AHSSs) and to metastabilize phases at ambient temperatures; however, little has been done to determine the extent to which the transformation from austenite to martensite (TRIP), can suppress/delay damage. The damage processes that lead to fracture in AHSSs are complex and understanding them requires a careful assessment of the strain partitioning amongst the phases, the evolution of microstructure with strain and how damage accumulates in the form of voids and microcracks. This can only be accomplished by applying a range of methodologies tracked as deformation proceeds, including micro-Digital Image Correlation (µDIC), Electron Backscattered diffraction (EBSD), X-ray microtomography (µXCT) and synchrotron-sourced High Energy X-ray diffraction (HEXRD). Such experiments have also been applied to notched specimen to further understand the response of AHSSs at different states of stress. Data will be presented on a range of ultrahigh strength AHSSs with and without TRIP-assistance (dual phase (DP), quench & partition (Q&P), and Medium-Mn steels). The data suggests that grain refinement, TRIP and decreased mechanical heterogeneity amongst phases can be used to suppress damage. It remains a challenge to quantify these effects separately, opening new avenues for experimental and modeling investigations.
Session W1: Wednesday, June 14, 10:30-12:30
Wednesday Jun 14 2023
10:30 - 10:50
A MODIFIED J-Q CONSTRAINT APPROACH TO ASSESS EFFECTIVE NOTCH FRACTURE TOUGHNESS
Nicolas LarrosaGrand Ballroom A
This paper uses a modified constraint-based fracture mechanics approach to estimate the effective notch fracture toughness . A modified J-Q constraint correction approach is proposed to evaluate the role of the notch tip acuity on the severity of the stress field accounting for two main characteristics, i.e. spread and maximum stress dependence of notch tip acuity. The methodology uses standard pre-cracked specimen toughness and the constraint-based approach in BS7910/R6 procedures to estimate mean values of notch fracture toughness. Experimental notch tests for S355 specimens at -140oC show good correlation with the model predictions
10:50 - 11:10
FRACTURE ANALYSES OF THIN-DUCTILE MATERIALS USING CRITICAL CTOA AND TWO-PARAMETER FRACTURE CRITERION
James NewmanGrand Ballroom A
The critical crack-tip-opening angle or displacement (CTOA/CTOD) fracture criterion is one of the oldest fracture criteria applied to metallic materials. Improved computer-aided photographic methods have been developed to measure CTOA during the fracture process; and elastic-plastic, finite-element analyses (ZIP2D) with a constant CTOA and a plane-strain core have been used to simulate fracture of laboratory specimens. The fracture criterion has been able to link the fracture of laboratory specimens to structural applications. This paper analyzes fracture of cracked thin-sheet 2219 aluminum alloy over an extremely wide range in width, crack-length-to-width ratio, and applied loading. The results from the critical CTOA fracture analyses on the thin-sheet material showed that the stress-intensity factor at failure (KIe) was linearly related to the net-section stress (Sn), as predicted by the Two-Parameter Fracture Criterion (TPFC).
11:10 - 11:30
CHARACTERIZATION AND NUMERICAL SIMULATION OF DUCTILE CRACK INITIATION AND PROPAGATION IN CT SPECIMENS OF DIFFERENT SIZES MACHINED FROM A 316L THICK PLATE
Sihan ChengGrand Ballroom A
Measuring fracture toughness for ductile materials requires the specimen size to be large enough for the tests to be valid. The higher the toughness is, the larger the specimen must be. This paper uses experimental and numerical approaches to study the fracture behavior of as-received and aged 316L(N) steel and the effect of the size and thickness of the specimens on the evaluated toughness.
11:30 - 11:50
APPLICATION OF A NOVEL UNIFIED PARAMETER ON CHARACTERIZING IN-PLANE AND OUT-OF-PLANE CRACK-TIP CONSTRAINTS FOR AL7075 T651 SEN(B) SPECIMENS
Zeng ChenGrand Ballroom A
Crack-tip constraint can have a significant effect on fracture toughness. A loss of crack-tip constraint can cause an increase in fracture toughness. In this paper, a novel unified constraint parameter λ based on the plastic strain energy was proposed to quantify the crack-tip constraint level. The application of this parameter for assessing the in-plane and out-of-plane constraints of Al7075 T651 alloy SEN(B) specimens was investigated with a series of fracture bending experiments and numerical modelling.
11:50 - 12:10
FRACTURE MODELLING AND ANALYSIS OF MULTIPLE SITE CRACKS IN PLATES UNDER LATERAL PRESSURE
Zeljko BozicGrand Ballroom A
Results of experimental and finite element study on fracture behavior of damaged thin plate specimens subjected to lateral pressure are presented. Plate specimens with a single crack or an array of collinear cracks were tested applying lateral pressure load by using a specially designed experimental setup. The elastic plastic fracture mechanics concept (EPFM) was employed in FE analyses, as large scale yielding occurred in ligaments of fractured specimens. The critical J-integral and crack tip opening displacement (CTOD) values associated with fracture onset were inferred from finite element simulation results. Assessed critical pressure loads for considered plate specimens were compared with experimentally obtained results and a good agreement was ob-served.