2nd International Workshop on Physics-Based Modelling of Material Properties and Experimental Observations with special focus on Fracture and Damage Mechanics: Book of Abstracts

This report covers the book of abstracts of the 2nd International Workshop on Physics Based Modelling of Material Properties and Experimental Observations, with special focus on Fracture and Damage Mechanics. The workshop is organized in the context of European Commission’s Enlargement and Integration Action, by the Joint Research Centre in collaboration with the TOBB University of Economics and Technology (TOBB ETU) on 15th-17th May 2013 in Antalya, Turkey. The abstracts of the keynote lectures and all the technical presentations are included in the book. This workshop will give an overview of different physics-based models for fracture and degradation of metallic materials and how they can be used for improved understanding and more reliable predictions. Models of interest include cohesive zones to simulate fracture processes, ductile-brittle transition for ferritic steels, ductile fracture mechanisms such as void growth or localized shear, fatigue crack initiation and short crack growth, environmental assisted cracking. Experimental studies that support such models and case studies that illustrate their use are also within the scope. The workshop is also an opportunity for scientists and engineers from EU Member States and target countries to discuss research activities that could be a basis for future collaborations.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen

Multi-scale modeling of microstructure evolution induced anisotropy in metals

This paper presents two crystal plasticity based computational constitutive models for the intrinsic evolution of plastic microstructure formation during monotonic loading and its altered evolution under strain path changes in metal forming operations. The formation step is modeled via a nonconvex strain gradient crystal plasticity framework which could simulate the intrinsic evolution of plastic microstructure evolution. The evolution under strain path changes is modeled via phenomenologically based constitutive equations incorporated into crystal plasticity framework. The latter step simulates the transient anisotropy effect (e.g. cross hardening, Bauschinger effect) depending on the change in the strain path. The paper discusses the unification of such models for the continuous modleing of microstructure formation and evolution processes.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen

Synthesis and Characterization of Epoxy/Boron Nitride Composite for Aerospace Applications

Beside extensive successful use of epoxy resins in many applications such as electronic packaging, insulation, adhesives and laminate technologies with various advantages; their low thermal conductivity and high CTE (thermal expansion coefficient) limit their performance. However, the addition of the particles into this material can significantly improve the constitutive and thermal properties. In this context, this study aims to develop an adhesive material where the epoxy resin is considered as the matrix material which is filled with Hexagonal Boron Nitride (h-BN) particles. Moreover, we characterize thermal behavior of the developed composite structure. A facile synthesis method was developed for minimizing the void formation while achieving a homogenous distribution of h-BN particles. SEM analysis has been employed to study the effect of the h-BN particles on the microstructural morphology. In addition, DMA (Dynamic Mechanical Analysis) and DSC (Differential Scanning Calorimeter) techniques were employed to examine the glass transition and viscoelastic mechanical behavior. The obtained results are consistent with the existing ones in the literature

Intragranular deformation patterning through non-convex rate dependent strain gradient crystal plasticity

A rate dependent strain gradient crystal plasticity framework is presented where the displacement and the plastic slip fields are considered as primary variables. These coupled fields are determined on a global level by solving simultaneously the linear momentum balance and the slip evolution equation, which is derived in a thermodynamically consistent manner. The formulation is based on the 1D theory presented in Yalcinkaya et al. (2011), where the patterning of plastic slip is obtained in a system with non-convex energetic hardening through a phenomenological double-well plastic potential. In the current multi-dimensional multi-slip analysis the non-convexity enters the framework through a latent hardening potential presented in Ortiz and Repettto (1999) where the microstructure evolution is obtained explicitly via a lamination procedure. The current study aims the implicit evolution of deformation patterns due to the incorporated physically based non-convex potential.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen

Plastic Slip Patterns through Rate-Independent and Rate-Dependent Plasticity

Plastic deformation induces various types of dislocation microstructures at different length scales, which eventually results in a heterogeneous deformation field in metallic materials. Development of such structures manifests themselves as macroscopic hardening/softening response and plastic anisotropy during strain path changes, which is often observed during forming processes. In this paper we present two different non-local plasticity models based on non-convex potentials to simulate the intrinsic rate-dependent and rate-independent development of plastic slip patterns, which is the simplified mechanism for the intrinsic microstructure development. For the sake of mechanistic understanding, the formulation and the simulations will be conducted in one-dimension which does not exclude its extension to multi-dimensions resulting in a crystal plasticity framework

Plastic deformation induced microstructure evolution through gradient enhanced crystal plasticity based on a non-convex Helmholtz energy

A gradient crystal plasticity model in the framework of continuum thermodynamics and rate variational formulation is presented for the description of plastic deformation patterning in a system with non-convex energetic hardening. The paper focuses on the extension of the 1D deformation patterning analysis of Yalcinkaya et al. (2011) to 2D for monotonic loading histories. Solution algorithm is based on the simultaneous solution of displacement and plastic slip fields, which have been considered as primary variables. The incorporation of non-convexity in the plastic slip potential in the Landau–Devonshire form makes the framework dual to phase field modeling approaches with a strong coupling between the deformation and the plastic slip fields. In the phase field modeling approaches the coupling is rather weak, i.e. fields do not have to be coupled as in the current approach based on the decomposition of the total strain. The numerical examples illustrate the intrinsic formation of (laminate type) microstructures and their evolution under mechanical loading together with the macroscopic hardening–softening–stress plateau response. The effect of different number of slip systems, loading rates and boundary conditions are investigated in detail.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen

Strain Gradient Crystal Plasticity Approach to Modelling Micro-Plastic Flow and Localisation in Polycrystalline Materials

Structural materials in the reactor pressure vessels are exposed to a harsh environment, resulting in a number of material degradation processes. Irradiation generates a number of point defects in the atomic structure of a material. In addition, plastic slip localization occurs on the grain level size where highly-deformed narrow bands of material appear already at the moderate strain levels. These bands are called channels or clear bands, because they are almost empty of irradiation defects, whereas the surrounding matrix is still full of them. Clear bands are very thin with a thickness of a few tens of nm. It is thought that these clear bands contribute significantly to yield-stress increase and loss of work-hardening and ductility under irradiation. Additionally, high stress concentrationsare generated at points where clear bands impinge on the grain boundaries, resulting in grain boundary damage and increasing the possibility of intergranular cracking. Continuum-based structural-mechanics models are not able to predict the initiation or the evolution of grain-level plasticslip localization. New approaches like strain-gradient crystal plasticity are being developed to tackle these issues. In the present work a numerical approach is presented where the application of strain-gradient crystal plasticity is extended to aggregates containing up to tens of grains. Plastic slip localization is demonstrated within the corresponding finite-element model.JRC.F.4-Innovative Technologies for Nuclear Reactor Safet

Patterning in Non-Convex Strain Gradient Crystal Plasticity

During forming processes most metals develop cellular dislocation structures due to dislocation slip patterning from moderate strains onwards. Typical examples of dislocation microstructures are dislocation cells and dislocation walls. Patterning typically refers to the self organization of dislocations with formation of regions of high dislocation density (dislocation walls) which envelop areas of low dislocation density (dislocation cell interiors), also to be regarded as domains of high plastic slip and low plastic slip activity. Due to the induced macroscopic anisotropic effects (the occurrence of dislocation microstructures and their evolution have been an interesting topic for the materials science community for decades. This paper present a non-convex rate dependent strain gradient plasticity framework for the description of plastic slip patterning in metal crystals. The non-convexity is treated as an intrinsic property of the free energy of the material. Departing from explicit expressions for the free energy and the dissipation potential, the non-convex strain gradient crystal plasticity model is derived in a thermodynamically consistent manner, including the accompanying slip law. For the numerical solution of the problem, the displacement and the plastic slip fields are considered as primary variables. These fields are determined on a global level by solving simultaneously the linear momentum balance and the resulting slip evolution equation. The slip law differs from classical ones in the sense that it naturally includes a contribution from the non-convex free energy term, which enables patterning of the deformation field. The formulation of the computational framework is partially dual to a Ginzburg Landau type of phase field modeling approach. The essential difference resides in the fact that a strong coupling exists between the deformation and the evolution of the plastic slip, whereas in the phase field type models the governing fields are only weakly coupled. The derivations and implementations are done in a transparent 1D setting [1], which allows for a thorough mechanistic understanding. The extension to 2D and multiple slip is discussed as well, whereby the non-convexity originates from the slip system interaction.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen

Microstructural patterning in time-dependent non-convex crystal plasticity

Microstructures in materials generally originate from a non-convex free energy, whereby the evolution is controlled by the kinetics underlying the physical processes governing the patterning. Special examples thereof are microstructures in metals and dislocation microstructures in particular, which have been an interesting research topic for the materials science community for decades. This paper analyses the intrinsic role of non-convexity in the formation and evolution of deformation microstructures, in close comparison to classical phase field approaches for microstructure evolution. Special emphasis is given on the role of kinetics that control the time dependent evolution in a deformation microstructure. For this purpose, a non-convex rate dependent strain gradient plasticity framework is used to recover plastic slip patterning in metal crystals. The non-convexity is treated as an intrinsic property of the free energy of the material. Departing from explicit expressions for the free energy and the dissipation potential, the non-convex strain gradient crystal plasticity model is derived in a thermodynamically consistent manner, including the accompanying slip law. For the numerical solution of the problem, the displacement and the plastic slip fields are considered as primary variables. These fields are determined on a global level by solving simultaneously the linear momentum balance and the resulting slip evolution equation. The slip law differs from classical ones in the sense that it naturally includes a contribution from the non-convex free energy term, which enables patterning of the deformation field. The formulation of the computational framework is partially dual to a Ginzburg Landau type of phase field modeling approach. The essential difference resides in the fact that a strong coupling exists between the deformation and the evolution of the plastic slip, whereas in the phase field type models the governing fields are only weakly coupled. The derivations and implementations are first done in a transparent 1D setting [1], which allows for a thorough mechanistic understanding. The extension to 2D and multiple slip is presented as well, whereby the non-convexity originates from the slip system interaction.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen