Submit to Materials Review for Materials Propose a Special Issue

Journal Browser

Micromechanics: Experiment, Modeling and Theory

Special Issue Editors
Special Issue Information
Keywords
Published Papers

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Simulation and Design".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 44630

Share This Special Issue

Special Issue Editor

Prof. Dr. Alexander Hartmaier

E-Mail Website
Guest Editor

Interdisciplinary Centre for Advanced Materials Simulation, Ruhr-Universität Bochum, Bochum, Germany
Interests: micromechanical modeling; fracture; fatigue; crystal plasticity; dislocations
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Miniaturization in mechanical testing can be applied to features on micro and even nanometre scales and enables the characterization of individual microstructural constituents. The smallest experimental length scales are now overlapping with the largest scales reached by atomistic material models, which are quite fundamental descriptions of materials. The combination of experiment, model and theory on different scales has led to new insight about fundamental deformation and failure mechanisms of materials. Furthermore, new understanding of the influence of microstructure on observable macroscopic material behaviour has been gained through combining micromechanical experiments and models. This has inspired new ideas about joining different phases on a microstructural level to obtain materials with purposefully designed properties.

In this special issue, the state-of-the-art in micromechanics is reflected in review articles and new developments are covered in research papers. Contributions focus on the characterisation of microstructures and the assessment of mechanical behaviour of materials and individual microstructural constituents on all relevant length and time scales. In particular, this includes the identification of elementary deformation and failure mechanisms and their relation to microstructure by experimental and numerical methods as well as by theoretical approaches. Material behaviour under harsh conditions, such as elevated temperatures, corrosive environments and cyclic mechanical loads, is investigated and described, and methods to design microstructures to withstand such harsh conditions are laid out.

Prof. Alexander Hartmaier
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

microstructure
mechanical properties
deformation mechanisms
failure mechanisms
micro/nano mechanical testing
microstructure-sensitive modeling

Published Papers (13 papers)

Download All Papers

Research

Jump to: Review

19 pages, 61873 KiB

Open AccessArticle

Lath Martensite Microstructure Modeling: A High-Resolution Crystal Plasticity Simulation Study

by Francisco-José Gallardo-Basile, Yannick Naunheim, Franz Roters and Martin Diehl

Materials 2021, 14(3), 691; https://doi.org/10.3390/ma14030691 - 02 Feb 2021

Cited by 15 | Viewed by 7239

Abstract

Lath martensite is a complex hierarchical compound structure that forms during rapid cooling of carbon steels from the austenitic phase. At the smallest, i.e., ‘single crystal’ scale, individual, elongated domains, form the elemental microstructural building blocks: the name-giving laths. Several laths of nearly identical crystallographic orientation are grouped together to blocks, in which–depending on the exact material characteristics–clearly distinguishable subblocks might be observed. Several blocks with the same habit plane together form a packet of which typically three to four together finally make up the former parent austenitic grain. Here, a fully parametrized approach is presented which converts an austenitic polycrystal representation into martensitic microstructures incorporating all these details. Two-dimensional (2D) and three-dimensional (3D) Representative Volume Elements (RVEs) are generated based on prior austenite microstructure reconstructed from a 2D experimental martensitic microstructure. The RVEs are used for high-resolution crystal plasticity simulations with a fast spectral method-based solver and a phenomenological constitutive description. The comparison of the results obtained from the 2D experimental microstructure and the 2D RVEs reveals a high quantitative agreement. The stress and strain distributions and their characteristics change significantly if 3D microstructures are used. Further simulations are conducted to systematically investigate the influence of microstructural parameters, such as lath aspect ratio, lath volume, subblock thickness, orientation scatter, and prior austenitic grain shape on the global and local mechanical behavior. These microstructural features happen to change the local mechanical behavior, whereas the average stress–strain response is not significantly altered. Correlations between the microstructure and the plastic behavior are established. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Figure 1

17 pages, 3904 KiB

Open AccessArticle

Finding and Characterising Active Slip Systems: A Short Review and Tutorial with Automation Tools

by James S. K.-L. Gibson, Risheng Pei, Martin Heller, Setareh Medghalchi, Wei Luo and Sandra Korte-Kerzel

Materials 2021, 14(2), 407; https://doi.org/10.3390/ma14020407 - 15 Jan 2021

Cited by 12 | Viewed by 2879

Abstract

The behaviour of many materials is strongly influenced by the mechanical properties of hard phases, present either from deliberate introduction for reinforcement or as deleterious precipitates. While it is, therefore, self-evident that these phases should be studied, the ability to do so—particularly their plasticity—is hindered by their small sizes and lack of bulk ductility at room temperature. Many researchers have, therefore, turned to small-scale testing in order to suppress brittle fracture and study the deformation mechanisms of complex crystal structures. To characterise the plasticity of a hard and potentially anisotropic crystal, several steps and different nanomechanical testing techniques are involved, in particular nanoindentation and microcompression. The mechanical data can only be interpreted based on imaging and orientation measurements by electron microscopy. Here, we provide a tutorial to guide the collection, analysis, and interpretation of data on plasticity in hard crystals. We provide code collated in our group to help new researchers to analyse their data efficiently from the start. As part of the tutorial, we show how the slip systems and deformation mechanisms in intermetallics such as the Fe₇Mo₆ μ-phase are discovered, where the large and complex crystal structure precludes determining a priori even the slip planes in these phases. By comparison with other works in the literature, we also aim to identify “best practises” for researchers throughout to aid in the application of the methods to other materials systems. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Figure 1

16 pages, 4646 KiB

Open AccessArticle

Micromechanical Characterisation of Ni/PU Hybrid Foams

by Martin Reis, Kristian König, Stefan Diebels and Anne Jung

Materials 2020, 13(17), 3746; https://doi.org/10.3390/ma13173746 - 24 Aug 2020

Cited by 1 | Viewed by 2021

Abstract

The computer-aided design of individual parts and the desire for weight reduction and material savings require further development of new hybrid materials. Ni/PU hybrid foams as a new hybrid material offer great potential for the production of components that are lightweight and yet can absorb large amounts of energy. The development of this structured material is at its beginning and mechanical characterisation on all scales is necessary. Experimental investigations on individual struts must be carried out on the micro scale to understand the structure-properties-relationship. Inspite of the challenges raising due to the complex geometry of the struts, tensile tests, three-point bending tests and micro sections are presented in this work. Due to the stiff Ni coating on the outer diameter of the struts, the resistance against bending is around five times as high as against tensile loading. The correlation between the behaviour of the struts and the macroscopic material behaviour validates the planned use of the foams as energy absorbers. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Figure 1

25 pages, 38321 KiB

Open AccessArticle

Automated Quantitative Analyses of Fatigue-Induced Surface Damage by Deep Learning

by Akhil Thomas, Ali Riza Durmaz, Thomas Straub and Chris Eberl

Materials 2020, 13(15), 3298; https://doi.org/10.3390/ma13153298 - 24 Jul 2020

Cited by 13 | Viewed by 2737

Abstract

The digitization of materials is the prerequisite for accelerating product development. However, technologically, this is only beneficial when reliability is maintained. This requires comprehension of the microstructure-driven fatigue damage mechanisms across scales. A substantial fraction of the lifetime for high performance materials is attributed to surface damage accumulation at the microstructural scale (e.g., extrusions and micro crack formation). Although, its modeling is impeded by a lack of comprehensive understanding of the related mechanisms. This makes statistical validation at the same scale by micromechanical experimentation a fundamental requirement. Hence, a large quantity of processed experimental data, which can only be acquired by automated experiments and data analyses, is crucial. Surface damage evolution is often accessed by imaging and subsequent image post-processing. In this work, we evaluated deep learning (DL) methodologies for semantic segmentation and different image processing approaches for quantitative slip trace characterization. Due to limited annotated data, a U-Net architecture was utilized. Three data sets of damage locations observed in scanning electron microscope (SEM) images of ferritic steel, martensitic steel, and copper specimens were prepared. In order to allow the developed models to cope with material-specific damage morphology and imaging-induced variance, a customized augmentation pipeline for the input images was developed. Material domain generalizability of ferritic steel and conjunct material trained models were tested successfully. Multiple image processing routines to detect slip trace orientation (STO) from the DL segmented extrusion areas were implemented and assessed. In conclusion, generalization to multiple materials has been achieved for the DL methodology, suggesting that extending it well beyond fatigue damage is feasible. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Figure 1

12 pages, 6169 KiB

Open AccessArticle

Effect of Twin Boundary Motion and Dislocation-Twin Interaction on Mechanical Behavior in Fcc Metals

by Jaber Rezaei Mianroodi and Bob Svendsen

Materials 2020, 13(10), 2238; https://doi.org/10.3390/ma13102238 - 13 May 2020

Cited by 7 | Viewed by 2733

Abstract

The interplay of interface and bulk dislocation nucleation and glide in determining the motion of twin boundaries, slip-twin interaction, and the mechanical (i.e., stress-strain) behavior of fcc metals is investigated in the current work with the help of molecular dynamics simulations. To this end, simulation cells containing twin boundaries are subject to loading in different directions relative to the twin boundary orientation. In particular, shear loading of the twin boundary results in significantly different behavior than in the other loading cases, and in particular to jerky stress flow. For example, twin boundary shear loading along

⟨ 112 ⟩

results in translational normal twin boundary motion, twinning or detwinning, and net hardening. On the other hand, such loading along

⟨ 110 ⟩

results in oscillatory normal twin boundary motion and no hardening. As shown here, this difference results from the different effect each type of loading has on lattice stacking order perpendicular to the twin boundary, and so on interface partial dislocation nucleation. In both cases, however, the observed stress fluctuation and “jerky flow” is due to fast partial dislocation nucleation and glide on the twin boundary. This is supported by the determination of the velocity and energy barriers to glide for twin boundary partials. In particular, twin boundary partial edge dislocations are significantly faster than corresponding screws as well as their bulk counterparts. In the last part of the work, the effect of variable twin boundary orientation in relation to the loading direction is investigated. In particular, a change away from pure normal loading to the twin plane toward mixed shear-normal loading results in a transition of dominant deformation mechanism from bulk dislocation nucleation/slip, to twin boundary motion. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Figure 1

16 pages, 3991 KiB

Open AccessArticle

A Novel Approach to Discrete Representative Volume Element Automation and Generation-DRAGen

by Manuel Henrich, Felix Pütz and Sebastian Münstermann

Materials 2020, 13(8), 1887; https://doi.org/10.3390/ma13081887 - 17 Apr 2020

Cited by 14 | Viewed by 2838

Abstract

In this study, a novel approach for generating Representative Volume Elements (RVEs) is introduced. In contrast to common generators, the new RVE generator is based on discrete methods to reconstruct synthetic microstructures, using simple methods and a modular structure. The plain and uncomplicated structure of the generator makes the extension with new features quite simple. It is discussed why certain features are essential for microstructural simulations. The discrete methods are implemented into a python tool. A Random Sequential Addition (RSA)-Algorithm for discrete volumes is developed and the tessellation is realized with a discrete tessellation function. The results show that the generator can successfully reconstruct realistic microstructures with elongated grains and martensite bands from given input data sets. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Figure 1

22 pages, 8723 KiB

Open AccessArticle

Effect of Sample Size and Crystal Orientation on the Fatigue Behaviour of Single Crystalline Microbeams

by Jorge Rafael Velayarce and Christian Motz

Materials 2020, 13(3), 741; https://doi.org/10.3390/ma13030741 - 06 Feb 2020

Cited by 4 | Viewed by 2237

Abstract

Beam deflection experiments were used to systematically examine size effects on the low cyclic fatigue (LCF) deformation behaviour of micro-sized bending beams of copper (Cu) single crystals oriented for single slip, critical and coplanar double slip. We present cyclic hardening curves and fatigue surface roughness, as well as dislocations structures of the micro-sized beams with sizes between 1 and 15 µm. A clear crystal orientation and size effect on the cyclic hardening curves, surface roughness, and the dislocation microstructures were observed. Based on the experimental results, the fatigue damage in single slip orientations clearly decreased with decreasing the sample size, however, below a critical size regime, the surface damage suddenly increases. Additionally, samples with sizes larger than 5 µm clearly revealed, besides PSBs-like structures, the emergence of kink bands leading to larger surface roughness in comparison to the smaller ones. Fatigue surface damages in microcrystals oriented for critical double slip became more prevalent compared to single slip orientations. Quantitatively, the correlation of the fatigue surface damage was also demonstrated with the formation of PSBs-like structures. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Graphical abstract

23 pages, 15353 KiB

Open AccessArticle

Gradient Crystal Plasticity: A Grain Boundary Model for Slip Transmission

by Xiang-Long Peng, Gan-Yun Huang and Swantje Bargmann

Materials 2019, 12(22), 3761; https://doi.org/10.3390/ma12223761 - 15 Nov 2019

Cited by 4 | Viewed by 3134

Abstract

Interaction between dislocations and grain boundaries (GBs) in the forms of dislocation absorption, emission, and slip transmission at GBs significantly affects size-dependent plasticity in fine-grained polycrystals. Thus, it is vital to consider those GB mechanisms in continuum plasticity theories. In the present paper, a new GB model is proposed by considering slip transmission at GBs within the framework of gradient polycrystal plasticity. The GB model consists of the GB kinematic relations and governing equations for slip transmission, by which the influence of geometric factors including the misorientation between the incoming and outgoing slip systems and GB orientation, GB defects, and stress state at GBs are captured. The model is numerically implemented to study a benchmark problem of a bicrystal thin film under plane constrained shear. It is found that GB parameters, grain size, grain misorientation, and GB orientation significantly affect slip transmission and plastic behaviors in fine-grained polycrystals. Model prediction qualitatively agrees with experimental observations and results of discrete dislocation dynamics simulations. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Figure 1

22 pages, 2681 KiB

Open AccessArticle

Microstructural Influences on Fracture at Prior Austenite Grain Boundaries in Dual-Phase Steels

by Luv Sharma, Ron H. J. Peerlings, Marc G. D. Geers and Franz Roters

Materials 2019, 12(22), 3687; https://doi.org/10.3390/ma12223687 - 08 Nov 2019

Cited by 10 | Viewed by 2141

Abstract

Dual phase (DP) steels provide good strength and ductility properties. Nevertheless, their forming capability is limited due to the damage characteristics of their constituting microstructural phases and interfaces. In this work, a specific type of interface is analysed, i.e., prior austenite grain boundaries (PAGBs). In the literature, prior austenite grain boundary fracture has been reported as an important damage mechanism of DP-steels. The influence of the morphology of phase boundaries near the PAGB and the role of the martensite substructure in the vicinity of a PAGB on damage initiation is analysed. The experimentally observed preferred sites of crack nucleation along the PAGB are assessed and clarified. A finite strain rate dependent crystal plasticity model accounting for the anisotropic elasto-plasticity of martensite (and also ferrite) was applied to an idealized volume element approximating a typical small-scale PAGB microstructure. The boundary value problem is solved using a fast Fourier transform (FFT) based spectral solver. The role of crystallography and geometrical features within the volume element is studied using simulations. Results are discussed considering possibly dominant regimes of elasticity and plasticity. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Figure 1

22 pages, 13534 KiB

Open AccessArticle

Modelling Microstructural Deformation and the Failure Process of Plastic Bonded Explosives Using the Cohesive Zone Model

by Kaida Dai, Baodi Lu, Pengwan Chen and Jingjing Chen

Materials 2019, 12(22), 3661; https://doi.org/10.3390/ma12223661 - 07 Nov 2019

Cited by 21 | Viewed by 3522

Abstract

A microstructure finite element method combining the cohesive zone model (CZM) is used to simulate the mechanical behavior, deformation, and failure of polymer-bonded explosive (PBX) 9501 under quasi-static loading. PBX 9501 consists of Cyclotetramethylene tetranitramine (HMX) filler particles with a random distribution packaged in a polymeric binder. The particle is treated as elastic and the binder as viscoelastic. Cohesive elements with a bilinear softening law are inserted into the particle/binder interface, the HMX particle, and the binder to study the interface’s debonding and failure evolution. Macroscopic stress–strain curves homogenized across the microstructure under tension and compression with different strain rates are basically consistent with the experimental data. The interface debonding approximately vertical to the loading direction is the primary failure mechanism under tension, while shear failure along the interfaces and particle fracture plays a significant role under compression. The effects of interface strengths and strain rates on the performance of PBX 9501 are also evaluated. The tensile and compressive strengths are dependent on the interface strength and strain rate, but the failure paths are insensitive. This model is shown to accurately predict macroscopic responses and improve our understanding of the relationship between the mechanical behavior and microstructure of PBX 9501. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Figure 1

18 pages, 6836 KiB

Open AccessArticle

Studying Grain Boundary Strengthening by Dislocation-Based Strain Gradient Crystal Plasticity Coupled with a Multi-Phase-Field Model

by Waseem Amin, Muhammad Adil Ali, Napat Vajragupta and Alexander Hartmaier

Materials 2019, 12(18), 2977; https://doi.org/10.3390/ma12182977 - 14 Sep 2019

Cited by 14 | Viewed by 4320

Abstract

One ambitious objective of Integrated Computational Materials Engineering (ICME) is to shorten the materials development cycle by using computational materials simulation techniques at different length scales. In this regard, the most important aspects are the prediction of the microstructural evolution during material processing and the understanding of the contributions of microstructural features to the mechanical response of the materials. One possible solution to such a challenge is to apply the Phase Field (PF) method because it can predict the microstructural evolution under the influence of different internal or external stimuli, including deformation. To accomplish this, it is necessary to take into account plasticity or, specifically, non-homogeneous plastic deformation, which is particularly important for investigating the size effects in materials emerging at the micron length scale. In this work, we present quasi-2D simulations of plastic deformation in a face centred cubic system using a finite strain formulation. Our model consists of dislocation-based strain gradient crystal plasticity implemented into a PF code. We apply this model to study the influence of grain size on the mechanical behavior of polycrystals, which includes dislocation storage and annihilation. Furthermore, the initial state of the material before deformation is also considered. The results show that a dislocation-based strain gradient crystal plasticity model can capture the Hall-Petch effect in many aspects. The model reproduced the correct functional dependence of the flow stress of the polycrystal on grain size without assigning any special properties to the grain boundaries. However, the predicted Hall-Petch coefficients are significantly smaller than those found typically in experiments. In any case, we found a good qualitative agreement between our findings and experimental results. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Graphical abstract

25 pages, 10390 KiB

Open AccessArticle

Micromechanical Modelling of the Influence of Strain Ratio on Fatigue Crack Initiation in a Martensitic Steel-A Comparison of Different Fatigue Indicator Parameters

by Benjamin Josef Schäfer, Petra Sonnweber-Ribic, Hamad ul Hassan and Alexander Hartmaier

Materials 2019, 12(18), 2852; https://doi.org/10.3390/ma12182852 - 04 Sep 2019

Cited by 22 | Viewed by 4169

Abstract

Micromechanical fatigue lifetime predictions, in particular for the high cycle fatigue regime, require an appropriate modelling of mean stress effects in order to account for lifetime reducing positive mean stresses. Focus of this micromechanical study is the comparison of three selected fatigue indicator parameters (FIPs), with respect to their applicability to different total strain ratios. In this work, investigations are performed on the modelling and prediction of the fatigue crack initiation life of the martensitic high-strength steel SAE 4150 for two different total strain ratios. First, multiple martensitic statistical volume elements (SVEs) are generated by multiscale Voronoi tessellations. Micromechanical fatigue simulations are then performed on these SVEs by means of a crystal plasticity model to obtain microstructure dependent fatigue responses. In order to account for the material specific fatigue damage zone, a non-local homogenisation scheme for the FIPs is introduced for lath martensitic microstructures. The numerical results of the different non-local FIPs are compared with experimental fatigue crack initiation results for two different total strain ratios. It is concluded that the multiaxial fatigue criteria proposed by Fatemi-Socie is superior for predicting fatigue crack initiation life to the energy dissipation criteria and the accumulated plastic slip criteria for the investigated total strain ratios. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures

Figure 1

Review

Jump to: Research

54 pages, 12220 KiB

Open AccessReview

A Review of Experimentally Informed Micromechanical Modeling of Nanoporous Metals: From Structural Descriptors to Predictive Structure–Property Relationships

by Claudia Richert and Norbert Huber

Materials 2020, 13(15), 3307; https://doi.org/10.3390/ma13153307 - 24 Jul 2020

Cited by 22 | Viewed by 3576

Abstract

Nanoporous metals made by dealloying take the form of macroscopic (mm- or cm-sized) porous bodies with a solid fraction of around 30%. The material exhibits a network structure of “ligaments” with an average ligament diameter that can be adjusted between 5 and 500 nm. Current research explores the use of nanoporous metals as functional materials with respect to electrochemical conversion and storage, bioanalytical and biomedical applications, and actuation and sensing. The mechanical behavior of the network structure provides the scope for fundamental research, particularly because of the high complexity originating from the randomness of the structure and the challenges arising from the nanosized ligaments, which can be accessed through an experiment only indirectly via the testing of the macroscopic properties. The strength of nanoscale ligaments increases systematically with decreasing size, and owing to the high surface-to-volume ratio their elastic and plastic properties can be additionally tuned by applying an electric potential. Therefore, nanoporous metals offer themselves as suitable model systems for exploring the structure–property relationships of complex interconnected microstructures as well as the basic mechanisms of the chemo-electro-mechanical coupling at interfaces. The micromechanical modeling of nanoporous metals is a rapidly growing field that strongly benefits from developments in computational methods, high-performance computing, and visualization techniques; it also benefits at the same time through advances in characterization techniques, including nanotomography, 3D image processing, and algorithms for geometrical and topological analysis. The review article collects articles on the structural characterization and micromechanical modeling of nanoporous metals and discusses the acquired understanding in the context of advancements in the experimental discipline. The concluding remarks are given in the form of a summary and an outline of future perspectives. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

► Show Figures