Search query: Quantifying physical parameters to predict brittle/ ductile behavior

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abstract: Abstract The brittle to ductile transition (BDT) is difficult to predict without extensive fitting parameters or tuning to a particular material. Currently, predicting fracture through extensive fitting or computationally expensive algorithms is high in both cost and time required to capture the relevant deformation physics. Presented here is analysis using a comparatively high throughput analytical model to predict fracture behavior using relatively few key experimentally determined parameters: activation volume, shear stress, and activation energy. This approach could reduce the time scale to predict fracture and thus accelerate new materials discovery. The current work utilizes seminal studies to provide the inputs for validating our approach via two single crystal materials, Si and W, which both have marginal toughness at low temperatures. It is shown that knowledge of underlying deformation mechanisms (still in progress) coupled to rapid determination of physical quantities (shear stress, activation volumes, and dislocation shielding) promotes unique discovery and opportunities, including future application to polycrystalline materials and phenomena. The technique, using literature values for physical parameters, correlates well to experimental fracture behavior for these two different classes of materials, semiconductors and metals, offering new opportunities for broader study.
author_names: William W Gerberich

Kevin M Schmalbach

Youxing Chen

Eric Hintsala

Nathan A Mara
title: Quantifying physical parameters to predict brittle/ ductile behavior
venue: Materials Science and Engineering: A
year: 2021

abstract: Abstract Two German ferritic pressure vessel steels are examined in the brittle to ductile transition regime as a function of temperature and irradiation. The experiments are done by a miniaturized Small Punch Test in hot cells within the temperature range of 185 degC up to 70 degC. From the load displacement curve of the SPT, the yield curves and parameters of both a non local G urson T vergaard N eedleman ductile damage model and a modified B eremin model are identified. The influence of temperature and irradiation on the model parameters is analyzed. All parameters are verified by comparison with results from standard test methods. The parameters, identified from SPT, are used to simulate the failure behavior in standard fracture mechanics specimens. In the upper shelf, the non local GTN model is applied to simulate crack resistance curves, from where the fracture toughness data could be successfully predicted. In the lower shelf, the W eibull stress of the specimens was computed to find out the statistics of fracture toughness values. Finally, the modified B eremin model and the non local ductile damage model were combined to evaluate the failure of fracture specimens in the brittle ductile transition region. This way, an acceptable agreement with Master curve data for non irradiated steels could be achieved in the whole temperature range.
author_names: Thomas Linse

Meinhard Kuna

H W Viehrig
title: Quantification of brittle ductile failure behavior of ferritic reactor pressure vessel steels using the Small Punch Test and micromechanical damage models
year: 2014

abstract: A broad classification of solids in terms of their mechanical behavior would characterize them as brittle or ductile. While there is no doubt that ultimately this behavior is due to processes at the atomistic level, the link between these processes and their macroscopic manifestation is difficult to establish. Phenomenological theories that try to address this link must rely on microscopic parameters, the values of which are beyond their scope. Here we review recent efforts to employ first principles electronic structure calculations in order to determine important physical quantities which, in conjunction with phenomenological theories, can provide insight into brittle versus ductile behavior. We apply this approach to cases of intrinsic interest, such as silicon, the prototypical brittle solid, as well as in cases of practical interest, such as the improvement of ductility in molybdenum disilicide, a material of potential usefulness in improved turbine blades. Current indications are that this combination of techniques can serve as powerful qualitative predictive tool for the dependence of mechanical behavior on the microscopic structure and chemical composition of a solid.
author_names: Umesh V Waghmare

Efthimios Kaxiras

Michael S Duesbery
title: Modeling Brittle and Ductile Behavior of Solids from First Principles Calculations
year: 2000

abstract: Radiation effects lead to significant reduction in ductility during the life of the components used in nuclear reactors. Sharp change in fracture toughness at lower temperature in Body Centered Cubic (BCC) materials as compared to Face Centered Cubic (FCC) materials is a major concern restricting their application in nuclear reactors in spite of having better thermal properties, excellent resistance to helium embrittlement and void swelling under higher dpa levels. In the present paper such strong temperature dependence of strain rate and flow stress in BCC materials is investigated numerically for both non irradiated and irradiated conditions. The BCC materials subjected to radiation would undergo embrittlement which raises the ductile to brittle transition (DBT) temperature up to or above the room temperature. In view of dislocations mobility being a fundamental property to determine the plastic behavior, a dislocations based material model is proposed which has a physical rather than phenomenological basis. This material model accounts for both thermally activated and athermal regime dislocation mobilities in BCC materials and is capable of predicting the effect of irradiation induced defects on the mobility of the dislocations which in turn directly affect the behavior of such materials. The relative change in stress field due to presence of irradiation defects in comparison to non irradiated case provides a valuable input for brittle fracture model to develop advanced materials for nuclear application.
author_names: Kulbir Singh

Christian Robertson

Arun Kumar Bhaduri
title: Brittle Fracture Model Parameter Estimation for Irradiated BCC Material through Dislocation Based Crystal Plasticity Model
venue: Frattura ed Integrita Strutturale
year: 2019

abstract: Fracture properties of Reactor Pressure Vessel (RPV) steels show large variations with changes in temperature and irradiation levels. Brittle behavior is observed at lower temperatures and/or higher irradiation levels whereas ductile mode of failure is predominant at higher temperatures and/or lower irradiation levels. In addition to such temperature and radiation dependent fracture behavior, significant scatter in fracture toughness has also been observed. As a consequence of such variability in fracture behavior, accurate estimates of fracture properties of RPV steels are of utmost importance for safe and reliable operation of reactor pressure vessels.A cohesive zone based approach is being pursued in the present study where an attempt is made to obtain a unified law capturing both stable crack growth (ductile fracture) and unstable failure (cleavage fracture) The parameters of the constitutive model are dependent on both temperature and failure probability. The effect of irradiation has not been considered in the present study. The use of such a cohesive zone based approach would allow the modeling of explicit crack growth at both stable and unstable regimes of fracture. Also it would provide the possibility to incorporate more physical lower length scale models to predict DBT. Such a multi scale approach would significantly improve the predictive capabilities of the model, which is still largely empirical.Copyright (c) 2013 by ASME
author_names: Pritam Kishore Chakraborty

Suleyman Bulent Biner
title: Modeling the Ductile Brittle Fracture Transition in Reactor Pressure Vessel Steels Using a Cohesive Zone Model Based Approach
year: 2013

abstract: Both scientists and engineers are very much concerned with the study of ductile to brittle transition (DBT) in ferritic steels. For historical reasons the Charpy impact test remains widely used in the industry as a quality control tool to determine the DBT temperature. The transition between the two failure modes, i.e. brittle cleavage at low temperature and ductile fracture at the upper shelf occurs also at low loading rate in fracture toughness tests. Recent developments have been made in the understanding of the micromechanisms controlling either cleavage fracture in BCC metals or ductile rupture by cavity nucleation, growth and coalescence. Other developments have also been made in numerical tools such as the finite element (FE) method incorporating sophisticated constitutive equations and damage laws to simulate ductile crack growth (DCG) and cleavage fracture. Both types of development have thus largely contributed to modeling DBT occurring either in impact tests or in fracture toughness tests. This constitutes the basis of a modern methodology to investigate fracture, which is the so called local approach to fracture. In this study the micromechanisms of brittle cleavage fracture and ductile rupture are firstly shortly reviewed. Then the transition between both modes of failure is investigated. It is shown that the DBT behavior observed in impact tests or in fracture toughness specimens can be reasonably well predicted using modern theories on brittle and ductile fracture in conjunction with FE numerical simulations. The review includes a detailed study of a number of metallurgical parameters contributing to the variation of the DBT temperature. Two main types of steels are considered (i) quenched and tempered bainitic and martensitic steels used in the fabrication of pressurized water reactors, and (ii) modern high toughness line pipe steels obtained by chemical variations and optimized hot rolling conditions. An attempt is also made to underline the research areas which remain to be explored for improving the strength toughness compromise in the development of steels.
author_names: Andre Pineau
title: Modeling ductile to brittle fracture transition in steels micromechanical and physical challenges
year: 2008

abstract: In the context of the third Sandia Fracture Challenge (SFC3) the details of the blind predictions performed by the University of Texas team are provided in this article. Over the past two decades, the peridynamic theory has shown great promise in modeling autonomous crack nucleation and growth in materials. While peridynamics has been commonly applied to simulate failure of brittle materials, its ability in predicting ductile fracture has remained mostly untested. This fracture challenge was seen as an opportunity to assess the state of the art of the peridynamic theory in predicting the response of an additively manufactured 316L stainless steel bar with a complex geometry under the dynamic tensile experiments performed by Sandia National Laboratories. The performance of a recently proposed, generalized, ordinary finite deformation constitutive correspondence model, coupled with a recent state based damage correspondence model was explored over this problem. For finite deformation material modeling, the classical elastoplastic framework of Simo was implemented within the ordinary correspondence theory. Damage modeling was achieved by incorporating the Johnson Cook failure criterion using the damage correspondence framework. An iterative inverse technique was applied to calibrate the model parameters using the longitudinal and notched tensile tests data provided by Sandia National Laboratories. A blind prediction of the deformation and failure behavior of the SFC3 geometry was performed by embedding the calibrated model in a peridynamic simulation. Uncertainty was introduced into the model parameters to quantify material variability. The results are compared to the experiments conducted at Sandia National Laboratories. While our modeling approach led to qualitatively good results and a correctly predicted crack path, it underpredicted the load carrying capacity of the structure and simulated an early fracture. Our post experiment analysis identifies material instability issues associated with the model as the primary sources of error.
author_names: Masoud Behzadinasab

John T Foster
title: The third Sandia Fracture Challenge: peridynamic blind prediction of ductile fracture characterization in additively manufactured metal
venue: International Journal of Fracture
year: 2019

abstract: Abstract The structural, mechanical, and electronic properties of perovskite molybdates are a topic of frequent study in materials science. In this study, the influence of Mg doping on the physical metallurgy of perovskite molybdates is investigated using first principles calculations based on density functional theory (DFT) and molecular dynamics (MD) simulation. Our calculated optimized lattice parameters (3.9945, 3.8964, 3.8634, 3.8440, and 3.7952 A [mentioned only DFT data, MD data listed in Table 2 for x 0, 0.1, 0.2, 0.3, and 0.4 respectively) of SrMo1 xMgxO3 are highly consistent with other experimental results (3.9762, 3.9695, and 3.9649 A for x 0, 0.1, and 0.2 respectively) and some available theoretical results (3.9720 A for x 0, no previous data available for Mg doped systems) The calculated elastic constants satisfied the Born stability criteria, indicating that our studied materials are mechanically stable at all doping concentrations, which was also confirmed by the calculated negative values of Cohesive energy. The mechanical behaviors of perovskite, including elastic constants, elastic moduli, ductility, and elastic anisotropy, were investigated and discussed. Our computed results suggest that Mg doping can increase elastic moduli. The calculated Pugh's ratio increased from 0.42 to 0.71 [DFT] and from 0.47 to 0.75 [MD] as well as the Poisson's ratio decreased from 0.31 to 0.21 [DFT] and from 0.30 to 0.21 [MD] which transformed the compound from ductile to brittle due to the addition of Mg at Mo site. The band structures, density of states, and charge density redistributions of the undoped and Mg doped materials were predicted. Our simulation outputs clearly illustrated the importance of accounting for Mg doping's influence in theoretical simulations of the physical properties of the presently studied perovskite material.
author_names: Khandaker Monower Hossain

M Zahid Hasan

Md Lokman Ali
title: Understanding the influences of Mg doping on the physical properties of SrMoO3 perovskite
year: 2020

abstract: Fused depositional modeling (FDM) is one of the common methods for 3D printing of polymers, which is expanding in various industrial applications, scientific researches, and engineering applications due to its ability to make complex parts. In this research, molecular dynamics (MDs) simulation has been used to predict the physical and mechanical properties. Then, the mechanical properties of the printed parts were determined. The mechanical properties of 3D printed parts strongly depend on the correct selection of processing parameters. In this study, the effect of three important parameters such as infill density, printing speed, and layer thickness were investigated on the tensile properties of PLA specimens. For this purpose, standard specimens with four infill densities of 20% 40% 60% and 80% two speeds of 20 mm/s and 40 mm/s, and two thicknesses of 0.1 mm and 0.2 mm were printed and tested under quasi static tensile test. In all printed specimens, the print angle is 45deg. The obtained experimental outcomes from the tensile test revealed that with increasing the infilling density, the mechanical properties of the parts improve and increase significantly. However, at very high infilling densities, the samples behave more brittle, so in cases where the strength of the part is less important than its shape and appearance, a density of 40% is more suitable in terms of cost, material, and time savings. It was also noted that the printing speed has less effect on the mechanical properties of PLA parts. It was also observed that reducing the thickness of the layer, while slightly increasing the stiffness of the parts, makes the part extremely brittle, and on the other hand, it leads to increase in the dimensional accuracy and surface quality of the specimens. At infill density of 80% the specimens had the highest stiffness and strength, but it exhibits a brittle behavior. Moreover, it can be deduced that by reducing the layer thickness although the modulus of elasticity increases a little, ductility is greatly affected.
author_names: Ashkan Farazin

Mehdi Mohammadimehr
title: Effect of different parameters on the tensile properties of printed Polylactic acid samples by FDM: experimental design tested with MDs simulation
year: 2021

abstract: Abstract The size dependent brittle to ductile transition of silicon has been observed with nanowire structures in experiments and many research efforts have focused on revealing its underlying physical mechanisms through both experimental and simulation approaches. While most simulation studies using molecular dynamics have considered the influence of various factors such as strain rate, temperature, and size, etc. little is known about the effect of boundary conditions and simulation types, i.e. constant energy vs. constant temperature simulations. In this work, we study the effects of boundary conditions and thermostats on the failure behavior of silicon nanowires by performing the molecular dynamics simulation of the uniaxial tensile test with three modified embedded atom method potentials. The nanowires are subjected to either periodic boundary conditions or fixed end boundary conditions and the simulation is conducted under either the constant energy or constant temperature conditions by Langevin thermostat. The simulations reveal that Young's modulus and tensile strength exhibit little dependence on the boundary condition and thermostat while the failure strain of the nanowires increases with fixed boundary conditions compared to the nanowires subjected to periodic boundary conditions. The failure behaviors, which are quantified by our novel ductility failure probability parameter, exhibit larger, but limited variations depending on the boundary condition, but the trend is mixed and not conclusive.
author_names: Wen-ting Xu

Woo kyun Kim
title: Role of boundary conditions and thermostats in the uniaxial tensile loading of silicon nanowires
year: 2020