Damage Processes In Materials Research Articles

Truss-like Discrete Element Method Applied to Damage Process Simulation in Quasi-Brittle Materials

This paper discusses the combined application of the lattice discrete element method (LDEM) and the acoustic emission (AE) technique to analyze damage in quasi-brittle materials. These methods were used to study the damage in a concrete slab under pure-shear stress and a pre-fissured sandstone beam subjected to three-point bending. The first test was restricted to simulation results, whereas the second included experimental data. The discrete element method was used to perform the simulations for both tests, whereas the corresponding results and the information from the experiments were assessed using AE analysis tools. It was shown that the synergistic use of these two methods led to a comprehensive understanding of the two analyzed cases and offered an effective, generalizable approach for assessing damage processes in quasi-brittle materials.

Thermodynamics of Ba(NO3)2(aq) to 393 K and solubilities in the reciprocal system Na+–Ba2+–Cl−–NO3−−H2O with implications for salt damage

This paper reports on an ion interaction (Pitzer) model for the calculation of solution properties and phase equilibria in the binary system Ba(NO3)2–H2O valid in the temperature range (273–393) K. The interaction parameters were determined after critical assessment of available thermodynamic data of the system. In addition, the model parameters for the calculation of solubilities and activities in the quaternary reciprocal system Na+–Ba2+–Cl−–NO3−–H2O at near ambient temperatures are provided. New ternary interaction parameters are reported for the Na+–Ba2+–NO3−–H2O, Na+–Ba2+–Cl––H2O and Ba2+–Cl−–NO3−–H2O systems. Predicted solubility diagrams in the full reciprocal quaternary systems are compared to available experimental data yielding good agreement. Finally, the impact of additional ions on the solubility and deliquescence behavior of Ba(NO3)2(cr) in terms of its contribution to crystallization damage processes in wall paintings and other porous materials is discussed.

Efficient and robust numerical treatment of a gradient‐enhanced damage model at large deformations

AbstractThe modeling of damage processes in materials constitutes an ill‐posed mathematical problem which manifests in mesh‐dependent finite element results. The loss of ellipticity of the discrete system of equations is counteracted by regularization schemes of which the gradient enhancement of the strain energy density is often used. In this contribution, we present an extension of the efficient numerical treatment, which has been proposed by Junker et al. in 2019, to materials that are subjected to large deformations. Along with the model derivation, we present a technique for element erosion in the case of severely damaged materials. Efficiency and robustness of our approach is demonstrated by two numerical examples including snapback and springback phenomena.

Virtual Element Method: Micro-Mechanics Applications

In this contribution we present an application of the lowest order Virtual Element Method (VEM) to the problem of material computational homogenization. Material homogenization allows retrieving material properties through suitable volume averaging procedures, starting from a detailed representation of the micro-constituents of the considered material. The representation of such microstructure constitutes a remarkable effort in terms of data/mesh preparation, especially when there is not evident microstructural regularity. For such a reason, computational micromechanics may represent a challenging benchmark for showing the potential of VEM. In this contribution, polycrystalline materials are considered as an application. The proposed technique constitutes a first step towards modelling of damage processes in micro-structured materials

Experimental Relationship Between Compressional Wave Attenuation and Surface Strains in Brittle Rock

AbstractLinear ultrasonic testing (LUT) has been extensively used as a tool for the evaluation of damage processes in various materials ranging from synthetic metals to natural geomaterials, such as rocks. A key limitation of LUT‐based damage studies to date is the lack of explicit evidence used in associating material damage with the changes in measured LUT attributes (e.g., ultrasonic wave amplitude and velocity). In this study, the evolution of the full‐field strains in brittle rock specimens (Lyons sandstone) subjected to failure are analyzed in real time and linked with the changes in the ultrasonic wave amplitude in localized areas illuminated by ultrasonic beams, termed as the ultrasonic image areas. The noncontact optical full‐field displacement measurement method of 2‐D digital image correlation is implemented in combination with the LUT procedure to continuously track changes in the ultrasonic wave amplitude with the evolution of strains across the surface of the uniaxially loaded intact rock specimens. The ultrasonic amplitude showed near‐linear correlation with the intensity of inelastic tensile strain recorded in the rock specimens. The results from the study corroborate that the ultrasonic changes are in fact influenced by the regions of tensile cracking, which is the primary inelastic deformation mechanism in brittle rocks.

Scientific Ground of a New Optical Device for Contactless Measurement of the Small Spatial Displacements of Control Object Surfaces

It is proposed the computational-experimental ground of newly developed optical device for contactless measurement of small spatial displacements of control object surfaces based on the use of new methods of laser interferometry. The proposed device allows one to register linear and angular components of the small displacements of control object surfaces during the diagnosis of the condition of structural materials for forced elements of goods under exploring by using acoustic non-destructive testing methods. The described results are the most suitable for application in the process of high-precision measurements of small linear and angular displacements of control object surfaces during experimental research, the evaluation and diagnosis of the state of construction materials for forced elements of goods, the study of fast wave propagation in layered constructions of complex shape, manufactured of anisotropic composite materials, the study of damage processes in modern construction materials in mechanical engineering, shipbuilding, aviation, instrumentation, power engineering, etc.

Modeling and simulation of non-isothermal rate-dependent damage processes in inhomogeneous materials using the phase-field approach

We present a continuum model that incorporates rate-dependent damage and fracture, a material order-parameter field and temperature within a phase-field approach. The models covers partial damage as well as the formation of macro-cracks. For the material order parameter we assume a Cahn Larche-type dynamics, which makes the model in particular applicable to binary alloys. We give thermodynamically consistent evolution equations resulting from a unified variational approach. Diverse coupling mechanisms can be covered within the model, such as heat dissipation, thermal-expansion-induced failure and crack deflection due to inhomogeneities. With help of an adaptive finite element code we conduct numerical experiments of different complexity in order to study the possibilities and limitations of the presented model. We furthermore include anisotropic linear elasticity in our model and investigate the effect on the crack pattern.

Damage processes in thermoviscoelastic materials with damage‐dependent thermal expansion coefficients

In this paper, we prove existence of global in time weak solutions for a highly nonlinear PDE system arising in the context of damage phenomena in thermoviscoelastic materials. The main novelty of the present contribution with respect to the ones already present in the literature consists in the possibility of taking into account a damage‐dependent thermal expansion coefficient. This term implies the presence of nonlinear coupling terms in the PDE system, which make the analysis more challenging. Copyright © 2015 John Wiley & Sons, Ltd.

Complete damage in linear elastic materials: modeling, weak formulation and existence results

In this work, we introduce a degenerating PDE system with a time-depending domain for complete damage processes under time-varying Dirichlet boundary conditions. The evolution of the system is described by a doubly nonlinear differential inclusion for the damage process and a quasi-static balance equation for the displacement field which are strongly nonlinearly coupled. In our proposed model, the material may completely disintegrate which is indispensable for a realistic modeling of damage processes in elastic materials. Complete damage theories lead to several mathematical problems since for instance coercivity properties of the free energy are lost and, therefore, several difficulties arise. For the introduced complete damage model, we propose a classical formulation and a corresponding suitable weak formulation in an $SBV$-framework. The main aim is to prove existence of weak solutions for the introduced degenerating model. In addition, we show that the classical differential inclusion can be regained from the notion of weak solutions under certain regularity assumptions which is a novelty in the theory of complete damage models of this type.

On the application of the continuum damage mechanics to multi-axial low-cyclic damage

The paper is devoted to continuum damage mechanics with applications to low-cyclic multi-axial loadings. The development of this solid mechanics branch started more than 50 years ago with the pioneering works of Miner, Palmgren, Kachanov and Rabotnov among others. The investigations in this field are supported by results derived in material science and physics of materials and have great practical importance since cyclic loading is a typical loading case in mechanical engineering. The reason for this is the well-known fact that damage and fracture occur under cyclic loading conditions even if the values of the applied stresses are much lower in comparison with the limit stresses estimated for the static case. Three problems for metallic materials will be discussed below. The first one is related to the experimental investigation of the damage behavior. The main open question is what kind of tests is suitable and result in acceptable data sets. The second problem is connected with the modeling of the damage processes in structural materials. The last one is what kind of conclusions can be drawn structural safety. The present paper gives an overview concerning the contributions of Russian and Ukrainian scientists in this field. A review of various approaches to the damage description at static and cyclic loading is presented.

Radiation damage and point defects

Sir Alan Cottrell has made huge seminal contributions to our basic understanding of radiation damage processes in both fissile and non-fissile materials. Much of this ground-breaking work was accomplished in the mid-1950s when Cottrell was working at Birmingham University and later at Harwell Laboratory. It is interesting to relate the earlier progress in the 1950s to our present understanding of the phenomenon.

Mechanics of damage processes in series and in parallel: a conceptual framework

A conceptual framework for damage processes in materials is presented. In this framework, the mechanics of damage processes in materials is investigated. These processes are categorized into either damage processes described in terms of stiffness degradation or damage processes described in terms of cross-sectional area reduction. Furthermore, the damage processes are visualized to occur as sequences either in series or in parallel. Schematic diagrams are used to illustrate these processes in a similar way to what is done with elastic springs and electric circuits. Different kinds of combinations and interactions of the damage processes are illustrated with various examples. The generalization to three-dimensional states of deformation and damage is also presented. This work is currently limited to linear elastic materials. The concepts presented in this work could be linked to homogenization methods. It is hoped that this work will lay the groundwork to open new areas of research in damage mechanics.

Damage Development During Superplasticity of Light Alloys

Superplastic forming (SPF) of metallic alloys allows the production of components with particularly complex shapes since in this regime, due to the predominance of grain boundary sliding (GBS), the material exhibits a high plastic stability. However, in many light alloys (i.e., Al or Mg alloys), superplastic deformation induces damage leading to premature fracture. Despite extensive work in the past, the mechanisms of damage induced by superplastic deformation remain under debate. In particular, due to the important contribution of GBS, voids with very irregular shapes frequently develop, resulting in a difficulty to obtain reliable experimental data from conventional quantitative metallography. It is the reason why the use of X-ray microtomography, providing 3D images of material bulk, is a particularly fruitful technique to investigate damage processes in superplastic materials. Thanks to this technique, damage development during superplastic deformation of Al and Mg alloys is investigated and the three main steps of damage development (nucleation, growth, and coalescence) are discussed.

A coupled discrete-continuum approach to simulate moisture effects on damage processes in porous materials

In the present paper, a coupled model for the prediction of damage under hygro-mechanical loading is developed. The model combines a mechanical and a moisture transport model within a poromechanical framework. Damage is incorporated by embedded displacement discontinuities, allowing an accurate prediction of the crack path within a coarse finite element mesh. To simulate the preferential wetting around a crack, a discrete front tracking method to predict the fluid transport through cracks is incorporated in a continuous moisture transport model. The computational features and capabilities of the coupled model and the effects of moisture on dimensional stability, crack opening evolution and cracking behaviour are illustrated with different examples of combined mechanical and moisture loading during three point bending tests on a fictitious sandstone.

Impact damage processes in composite sheet and sandwich honeycomb materials

The research interest of this study is the impact toughness of different lightweight sandwich panels and composite sheet materials. This is as to the degrees of damage inflicted on the contact surface, through-thickness and rear surface of the materials when subjected to different impacts. For this study, specimens were prepared from sheet moulding compound (SMC), glass mat thermoplastic (GMT) and honeycomb sandwich panels employing different skin and core materials. For all experiments, drop-weight impact facilities were used and for some experiments a servo-hydraulic impact machine was also employed. The reason for this study is that very much needed for the next generation of more advanced aircraft, marine-craft, road and rail vehicles are improved lightweight stiff materials that can absorb higher impact energy and retain a higher degree of structural integrity.

Theory and Modeling of Radiation Damage Processes in Materials

Present knowledge is reviewed of radiation damage processes in materials. These processes cover various time- and length-scales, from ballistic binary collision process to collective atomic motion in the thermal spike stage, followed by the thermally activated processes involved in defect aggregation. It is emphasized that greater researches are required to understand these processes and their interplay in the multiscale modeling approach, before a prediction of a given material’s response to fusion irradiation conditions is possible. In addition, a predictive capability is also needed to develop new, advanced materials.

Thermal Stability of Helium-Vacancy Clusters and Bubble Formation - Multiscale Modeling Approach for Fusion Materials Development

The recent progress on our multiscale modeling to understand radiation damage processes in materials during irradiation is reviewed. The energies of He-V cluster formation in Fe were evaluated using a molecular dynamics (MD) simulation technique that employed interatomic potentials partially developed by first-principle (FP) calculations. Using the calculated energies, the longer timescale behavior of He-V clusters in Fe was investigated using a kinetic Monte-Carlo (KMC) simulation technique. The FP-MD-KMC scheme provided us significant information on the thermal stability of a He-V cluster in Fe as a function of the helium-to-vacancy ratio of the cluster.

Damage and failure processes in structural materials

At large plastic strains consideration must be given not only to the descriptions of work hardening and texture evolution but also to the process of damage accumulation and the documentation of the various modes of failure which may terminate the plastic history. In this presentation consideration is given first to documenting the various modes of failure and their dependence on stress state. It is then shown that damage accumulation can be studied in a quantitative manner by using model systems in conjunction with FEM calculations. Finally consideration is given to complex forming processes such as ironing to show how studies of damage initiation and accumulation relate to practical engineering problems

Damage and failure processes in structural 347H SS materials

The relationship between microstructure and high temperature strength of 347H SS welded joints was investigated. The materials studied correspond to two preheated furnaces of the petrochemical industry, working at 700 o C and 45 atm (called furnaces A and B). Furnace A presented failures, hot fissure in the Heated Affected Zone, after 60 h operation, whereas furnace B operated for 70000 h. The microstructure research was made by a non conventional replica technique [1], which allowed more accuracy in the nature, quantity, morphology and distribution of the different phases. The probable cause of the remarkable different behaviour of the two materials, although both fulfil the A213/TB/347 H, ASTM standard requirements, has been discussed taking into account the chemical composition of the steels, matrix characteristics, nature of the inclusions, carbides, intermetallic particles and N/Mn, Al/N, C/Nb relationships

Ultrasonic-image evaluation of microstructural damage accumulation in materials

Ultrasonic imaging techniques for portraying and evaluating cumulative internal microstructural damage in engineering materials are described. A quantitative delineation of the damage is made in terms of acoustic attenuation obtained from computer analyses of digitized ultrasonic images. Acoustic attenuation data are a basic ingredient in previously developed models of damage processes in materials. The ultrasonic imaging methodology has been developed using filled polymer (inert solid rocket-propellant) samples subjected to progressive uniaxial tensile strain. Successive ultrasonic images taken at various levels of applied strain display dewetting and the evolving microvoid formation/growth which occurs. Both initially intact material and that with pre-existing cracks are of interest. Changes in acoustic attenuation with strain, derived from the processing of digital images, have provided results as to the degree of preferential damage accumulation at sites of filler particle agglomerations appearing on the ultrasonic images. Also, the quantitative extent of an asymmetry in the damage-field distribution near the tips of an extending crack was determined in precracked material. Iso-attenuation type contours generated by computer reveal that kidney-shaped damage zones occur in the neighborhood of the propagating crack tips, reminiscent of the plastic-zone shapes near crack tips in ductile metals under strain. Ultrasonic images of precracked samples show that before crack extension begins, the material damage in the neighborhood of the crack already extends over a relatively large volume of the specimen.