Accumulation Of Structural Damage Research Articles

Ultrasonic Study of Longitudinal Critically Refracted and Bulk Waves of the Heat-Affected Zone of a Low-Carbon Steel Welded Joint under Fatigue

Currently, ultrasonic methods for assessing the fatigue lifetime of various structural materials are being actively developed. Many steel constructions are made by welding. The weld heat-affected zone is the weak point of the construction, as it is most susceptible to destruction. Therefore, it is actually important to search for acoustic parameters that uniquely characterize the structural damage accumulation in the heat-affected zone of a welded joint in order to predict failure. In this work, the specimens were made from the base metal and the welded joint’s heat-affected zone. The specimens were subjected to uniaxial tension–compression under a symmetrical cycle in the region of low-cycle fatigue with control of the strain amplitude. The propagation bulk velocities of longitudinal, shear waves and subsurface longitudinal critically refracted (LCR) waves during cyclic loading were studied. The acoustic birefringence of shear waves was calculated, and a similar parameter was proposed for longitudinal and LCR waves. The dependence of the elastic modulus ratio on the cycle ratio was obtained. It was shown that the acoustic parameters change most intensively in the heat-affected zone. According to the data of the C33/C55 ratio changes measured through the ultrasonic method, a formula for calculating the remaining fatigue life in the heat-affected zone was proposed.

Numerical-Computational Model for Dynamic Nonlinear Analysis of Frames With Semi-Rigid Connection Considering the Damping Effect

Objective: the scope of this work is to present a numerical-computational model for transient dynamic nonlinear analysis of frames with geometric nonlinearity and semi-rigid connection. Methodology: the equation of motion, which describes the structural dynamical system, is solved by the a-Generalized direct integration method associated with the standard Newton-Raphson method. The structures are discretized through the co-rotational formulation of the Finite Element Method considering the Euler-Bernoulli beam theory. The semi-rigid connection of structural members (beam-column and beam-support) is simulated by a connection element with zero length, which is described in terms of axial, translational and rotational stiffness. Results and conclusion: From the numerical results of three structural systems (bi-fixed beam, L-shaped frame, and single-story frame) obtained with the free Scilab program, it is concluded that the definition of the type of connection is an important factor to be considered in the analysis of frames subjected to dynamic loads. Furthermore, structural damping, which is a measure of energy dissipation, drives the structure from a vibrating state to a resting state. Research implications: Structural Engineering has been designing systems that cannot be analyzed and dimensioned without dynamic effects being considered. lack of knowledge of the levels and characteristics of the dynamic response can lead to system failure during the application of repetitive loading due to accumulation of structural damage. In this sense, the numerical model can represent a valuable engineering tool when it comes to the dynamic analysis of plane metallic structures with geometric nonlinearity.

Structural and functional regularities of the damage accumulation and failure in metals under dynamic loading and wear

The effect of damage caused by friction and wear on the accumulation of fatigue damage in the near-surface layers of the material used in technical systems operating under dynamic loading is studied. A comparative study of the samples of carbonized Cr – Mn – Si steel under ultrasonic loading in the range up to 109 cycles and the samples of steel 45 loaded at a permanent frequency of 100 Hz to simulate conditions of tribological tests for frictional fatigue revealed the same types of damage occurring in the characteristic frequency ranges of loading. To assess the effect of friction fatigue on damage accumulation and the probability of operational failures the authors have supposed that the processes of structural damage accumulation in cyclic and frictional fatigue are similar. The analysis of experimental data on the behavior of the friction coefficients and the magnitudes of broadening X-ray lines which characterize changes in the dislocation structure of the metallic structural materials (steels and titanium alloys) upon friction and the friction fatigue curves confirmed that the process of friction fatigue failure occurs via the mechanisms of low and high cycle fatigue that proves the validity of the proposed approach. The calculation results for the probability of the compressor failure are presented as an example. The calculations are based on the friction fatigue curves in a wide range of loading cycles obtained upon testing the crankshaft neck. The use of friction fatigue curves thus obtained provided assessment of the effects of combined action of the dynamic loading and friction, resulting in increased gaps and the dynamic loads (due to the wear of contacting parts) on the fatigue damage accumulation, durability and the reliability of the mechanical systems during operation.

The Effect of the Addition of Aluminum Nitride to the Composition of NiAl2O4 Ceramics on Hydrogenation Processes and the Increase in Resistance to Swelling and Degradation

This work examines the effects of the formation of impurity inclusions in the structure of NiAl2O4 ceramics when aluminum nitride is added to them and the occurrence of a reinforcement effect that prevents hydrogenation processes and the subsequent destruction of conductive and thermophysical characteristics. The appeal of ceramics possessing a spinel crystal structure lies in their potential use as ceramic fuel cells for both hydrogen generation and storage. Simultaneously, addressing the challenges related to ceramic degradation during hydrogenation, a critical aspect of hydrogen production, can enhance the efficiency of these ceramics while lowering electricity production costs. The selection of aluminum nitride as an additive for ceramic modification is based on its remarkable resistance to structural damage accumulation, its potential to enhance resistance to high-temperature degradation, and its ability to bolster strength properties. Moreover, an examination of the alterations in the strength characteristics of the examined samples subjected to hydrogenation reveals that the stability of two-phase ceramics is enhanced by more than three to five times compared to the initial ceramics (those without the addition of AlN). Additionally, it was noted that the most significant alterations in both structure and strength become apparent at irradiation fluences exceeding 1014 proton/cm2, where atomic displacements in the damaged ceramic layer reach over 5 dpa. During the evaluation of thermophysical properties, it was discerned that ceramics featuring an impurity phase in their composition exhibit the highest stability. These ceramics demonstrated a reduction in the thermal conductivity coefficient of less than 1% at the peak irradiation fluence.

Effect of high-stress level loads on the fatigue performance of GFRP-RC beams

GFRP (Glass fiber reinforced polymer) reinforced concrete (GFRP-RC) structures are often used in harsh engineering environments to replace steel bars to resist environmental corrosion. Due to the low fatigue stiffness of the GFRP-RC structure, the structure is prone to failure due to excessive fatigue deformation after experiencing high-stress level loads such as tsunamis and earthquakes. In order to further study the characteristics of the mechanical performance of GFRP-RC beams under high fatigue stress levels, this paper carried out fatigue tests on 10 GFRP-RC beams at fatigue stress levels (S) of 0.85, 0.70, 0.65, and 0.60. The results show that the fatigue stress level can affect the failure mode of GFRP-RC beams, and high-stress loading is prone to inclined section failure. Otherwise, vertical cracking failure will occur. Increasing the fatigue stress level will not affect the damage growth rate during the stable stage of fatigue. However, it will exacerbate the accumulation of structural damage and the degree of fatigue stiffness degradation. In addition, the applicability of three existing fatigue deflection prediction models in GFRP-RC structures was also checked by experimental data, and it was found that only the CEB-FIP model had a higher accuracy.

Damage modelling of a bridge pier subjected to multiple earthquakes: a comparative study

This paper discusses and compares two recently developed methodologies for the prediction of damage accumulation in structures subjected to multiple earthquakes within their lifetime, one based on a regression model and one based on a Markov-chain based approach. A stochastic earthquake hazard model is considered for generating sample sequences of ground motion records that are then used to estimate the probabilistic distribution of the damage accumulated during the time interval of interest using the various methodologies. A simulation-based approach provides a reference solution against which the other methodologies are compared. Besides assessing the effectiveness and accuracy of the two methodologies, some improvements of the regression model are proposed and evaluated. The comparison between the methodologies is carried out by examining a reinforced concrete (RC) bridge pier model and using the Park–Ang damage index to describe the damage accumulation. The study results demonstrate the importance of considering the possibility of occurrence of multiple shocks in estimating the life-cycle performance of structures and highlight strengths and drawbacks of the investigated methodologies.

Mechanical Properties Degradation of Fiberglass Tubes during Biaxial Proportional Cyclic Loading.

Composite structures during an operation are subjected to various types of external loading (impact, vibration, cyclic, etc.), which may lead to a decrease in mechanical properties. Previously, many experimental investigations of the mechanical behavior of composites under uniaxial cyclic loading were carried out. Acquisition of new data on the reduction of composite materials' mechanical characteristics under conditions of multiaxial cyclic loading, as well as verification of existing models for calculation of the residual properties, are relevant. Therefore, this work is devoted to the experimental investigation of the mechanical behavior of fiberglass tubes under proportional cyclic loading. Static and fatigue tests were carried out under tension with torsion conditions. Inhomogeneous strain fields were obtained using a non-contact optical video system VIC-3D. The structural damage accumulation processes were analyzed by an AMSY-6 acoustic emission signals recording system. Surface defects were determined using a DinoLite microscope. Residual dynamic elastic modules were calculated during fatigue tests, and fatigue sensitivity curves were built. Data was approximated using various models, and their high descriptive capability was revealed. Damage accumulation stages were determined. The dependence of the models' parameters on a stress state were observed. It was concluded that multiaxial cyclic loading leads to a significant decrease in mechanical properties, which should be taken into account in composite structure design.

Modeling damage accumulation during ground-motion sequences for portfolio seismic loss assessments

Conventional earthquake risk assessments use fragility and vulnerability models that are based on seismic demands from individual (mainshock) ground motions, and implicitly assume that a structure is intact before an earthquake hits. This study develops a suite of more realistic state-dependent seismic fragility and vulnerability models for a wide range of building taxonomies, leveraging state-of-the-art methods to account for dynamic damage accumulation in structures due to multiple earthquake events (i.e., ground-motion sequences). Models are developed for 561 building classes (i.e., structural types) from the Global Earthquake Model’s global database of fragility and vulnerability models. Four 2010–2012 Canterbury sequence earthquakes are then used to demonstrate an application of the developed models within a portfolio loss assessment, capturing the time-dependent nature of damage and loss in the vulnerability calculations. The results of this application indicate that accounting for damage accumulation across a series of events can significantly increase expected loss ratios compared to a conventional mainshock-only portfolio risk analysis. This work can help analysts to develop and apply state-dependent fragility and vulnerability models for quantifying the potential impact of damage accumulation in portfolio-scale seismic loss assessments.

Disorder and cavity evolution in single-crystalline Ge during implantation of Sb ions monitored in-situ by spectroscopic ellipsometry

Ion implantation has been a key technology for the controlled surface modification of materials in microelectronics and generally, for tribology, biocompatibility, corrosion resistance and many more. To form shallow junctions in Ge is a challenging task. In this work the formation and accumulation of shallow damage profiles was studied by in-situ spectroscopic ellipsometry (SE) for the accurate tracking and evaluation of void and damage fractions in crystalline Ge during implantation of 200-keV Sb + ions with a total fluence up to 1016 cm−2 and an ion flux of 2.1 × 1012 cm−2s−1. The consecutive stages of damage accumulation were identified using optical multi-layer models with quantitative parameters of the thickness of modified layers as well as the volume fractions of amorphized material and voids. The effective size of damaged zones formed from ion tracks initiated by individual bombarding ions can be estimated by numerical simulation compared with the dynamics of damage profiles measured by ion beam analysis and ellipsometry. According to our observations, the formation of initial partial disorder was followed by complete amorphization and void formation occurring at the fluence of about 1 × 1015 cm−2, leading to a high volume fraction of voids and a modified layer thickness of ≈200 nm by the end of the irradiation process. This agrees with the results of numerical simulations and complementary scanning electron microscopy (SEM) measurements. In addition, we found a quasi-periodic time dependent behavior of amorphization and void formation represented by alternating accelerations and decelerations of different reorganization processes, respectively. For the understanding and prevention of adverse void formation and for controlled evolution of subsurface nanocavities or cellular surface texture the in-situ monitoring of the dynamics of structural damage accumulation by the developed SE method is essential.

Peptide Location Fingerprinting Reveals Tissue Region-Specific Differences in Protein Structures in an Ageing Human Organ.

In ageing tissues, long-lived extracellular matrix (ECM) proteins are susceptible to the accumulation of structural damage due to diverse mechanisms including glycation, oxidation and protease cleavage. Peptide location fingerprinting (PLF) is a new mass spectrometry (MS) analysis technique capable of identifying proteins exhibiting structural differences in complex proteomes. PLF applied to published young and aged intervertebral disc (IVD) MS datasets (posterior, lateral and anterior regions of the annulus fibrosus) identified 268 proteins with age-associated structural differences. For several ECM assemblies (collagens I, II and V and aggrecan), these differences were markedly conserved between degeneration-prone (posterior and lateral) and -resistant (anterior) regions. Significant differences in peptide yields, observed within collagen I α2, collagen II α1 and collagen V α1, were located within their triple-helical regions and/or cleaved C-terminal propeptides, indicating potential accumulation of damage and impaired maintenance. Several proteins (collagen V α1, collagen II α1 and aggrecan) also exhibited tissue region (lateral)-specific differences in structure between aged and young samples, suggesting that some ageing mechanisms may act locally within tissues. This study not only reveals possible age-associated differences in ECM protein structures which are tissue-region specific, but also highlights the ability of PLF as a proteomic tool to aid in biomarker discovery.

Exceedance of design actions in epicentral areas: insights from the ShakeMap envelopes for the 2016\u20132017 central Italy sequence

ShakeMap is the tool to evaluate the ground motion effect of earthquakes in vast areas. It is useful to delimit the zones where the shaking is expected to have been most significant, for civil defense rapid response. From the earthquake engineering point of view, it can be used to infer the seismic actions on the built environment to calibrate vulnerability models or to define the reconstruction policies based on observed damage vs shaking. In the case of long-lasting seismic sequences, it can be useful to develop ShakeMap envelopes, that is, maps of the largest ground intensity among those from the ShakeMap of (selected) events of a seismic sequence, to delimit areas where the effects of the whole sequence have been of structural engineering relevance. This study introduces ShakeMap envelopes and discusses them for the central Italy 2016–2017 seismic sequence. The specific goals of the study are: (i) to compare the envelopes and the ShakeMap of the main events of the sequence to make the case for sequence-based maps; (ii) to quantify the exceedance of design seismic actions based on the envelopes; (iii) to make envelopes available for further studies and the reconstruction planning; (iv) to gather insights on the (repeated) exceedance of design seismic actions at some sites. Results, which include considerations of uncertainty in ShakeMap, show that the sequence caused exceedance of design hazard in thousands of square kilometers. The most relevant effects of the sequence are, as expected, due to the mainshock, yet seismic actions larger than those enforced by the code for structural design are found also around the epicenters of the smaller magnitude events. At some locations, the succession of ground-shaking that has excited structures, provides insights on structural damage accumulation that has likely taken place; something that is not accounted for explicitly in modern seismic design. The envelopes developed are available as supplemental material.

Modeling the deformation process of a plate with a stress concentrator taking into account the postcritical stage of material deformation

Postcritical deformation of a material is a process which is characterized by a decrease of stress during growing deformations as a result of accumulation of structural damage. The design becomes unable to withstand the external load only when zones with weakened connections are developed enough. Evolution of postcritical deformation zones can occur with an increase of the external load applied to the construction. It means that taking into account the softening of the material allows determining the strength and deformation reserves of constructions more accurately. The mathematical formulation of the boundary value problem of supercritical deformation mechanics is given in the paper. The features of the experimental study of the postcritical stage of material deformation are listed. Strain curves of various steels with a long section of softening are obtained. Numerical solutions for the problems of deforming a thin plate with stress concentrators of different geometries under kinematic loading are obtained. Piecewise linear approximations and real strain curves of steel 20 and steel 40Cr4 obtained experimentally are considered. The evolution of zones of postcritical deformation in the material is considered. The correspondence between the value of the decline modulus and the nature of the evolution of the softening zones is determined. A stress plot is constructed that reflects how the complete material deformation diagram is realized near the concentrator. The calculated loading diagrams are constructed. It is noted that even after the appearance of softening zones, an increase in external load is possible. The strength and deformation resources of structures are determined, and the influence of the geometry of the stress concentrator on their values is considered. It is noted that the consideration of softening in modeling the behavior of structures with stress concentrators is appropriate.

Strain-dependent shear-band structure in a Zr-based bulk metallic glass

This work presents strong evidence for structural damage accumulation as a function of shear strain admitted by shear bands in a Zr-based bulk metallic glass. Analyzing the shear-band structure of shear-band segments that experienced shear strains covering four orders of magnitude with high-angle annular dark field transmission electron microscopy (HAADF-STEM) reveals strongly scattered data with on overall trend of increasing local volume dilatation with increasing shear strain. Locally, however, a variety of trends is observed, which underlines the strong heterogeneity of structural damage in shear bands in metallic glasses.

The Torsion Problem of a Cylindrical Solid Taking Into Account the Material Weakening

The weakening of the material begins reaching a critical level of stress state, is characterized by a decrease in the level of stress during growing deformations and can develop with an equilibrium accumulation of structural damage. The equilibrium accumulation of damage is possible if the given displacements of the boundary points are provided (that is, with “hard” loading) and if the rigidity of the loading system is sufficient. The design becomes unable to withstand the load only when zones with weakened connections are developed enough. Therefore, taking into account the full deformation diagram in the calculations allows to more accurately determine the load bearing capacity of the design. This paper gives an analytical solution for the problem of a homogeneous cylindrical solid torsion with a circular cross section with its hard loading taking into account the material weakening. Piecewise linear approximations of elastic and elastoplastic medium with a linear weakening at the supercritical deformation stage are considered. The diagrams are plotted regarding stress distribution over the cross section are given; the graphs of the maximum torque value and the extreme value of the relative angle of rotation on the parameters of the deformation diagram. The dependences of the torque on the relative angle of rotation of the sections for the stage of initial supercritical deformation, as well as the stage of supercritical deformation and fracture are determined. The graphs of the dependence of torque on the angle of rotation of the section are given. Reserves of the load bearing capacity of the design are identified. It is noted that taking into account the weakening of the material is expedient in strength calculations and in determination of the system’s safety factor.

Do Chemical Effects Affect the Accumulation of Structural Damage during the Implantation of Fluorine Ions into GaN?

The accumulation of structural damage in GaN under irradiation with accelerated F and Ne ions with energies of 1.3 and 3.2 keV/amu is investigated. It is shown that chemical effects during implantation of fluorine ions within the doses under consideration do not noticeably affect the formation of stable structural damage both in the bulk and on the surface of GaN.

НАКОПИЧЕННЯ УШКОДЖЕНЬ В ОСНОВНИХ НЕСУЧИХ КОНСТРУКЦІЯХ СПОРУД, РЕЗЕРВ ПРАЦЕЗДАТНОСТІ

The article presents the results of experimental studies of the strength and deformability of load bearing structures made of wood under the action of static loads. In most major cities of Ukraine there are a huge number of buildings that have historical and architectural value. To preserve these structures for centuries, it is necessary to constantly receive such information about the state of their supporting structures for making timely decisions about reinforcement, replacement, overhaul, etc. In the materials of building structures, changes occur during the period of operation associated with the appearance, development and accumulation of structural damage. These damages cause submicron and microcracks, which are the result of external mechanical effects on the structure and therefore the transition to the boundary state is the result of a slow accumulation of damage. Having developed a technique for registering damage, you can get a tool that allows you not only to monitor the current state of the structure, but also to predict the change in its bearing capacity over time. In the period of operation there is a change in the structure of materials bearing structures The development of this process consists of several stages, the main of which are: deformation of interatomic bonds, nucleation of a sub-microcrack as a result of breaking macromolecules that form the walls of tracheids. This turns out to be suddenly and is accompanied by weak sound signals, resembling a micro explosion. The interaction of submicrocracks leads to their merging and the occurrence of microcracks, and the merging and increase of microcracks - to the occurrence of macrocracks (trunk crack), which leads to the destruction of the material. This dynamic process, depending on the size, nature and time of action of the load, may stabilize over time or, continuing, lead to the destruction of the structure. Mechanical and electrical devices currently used (indicators, strain gauges and other devices) are not suitable for detecting and recording material damage. For this purpose, it is necessary to use non- destructive research methods that allow continuous observation of submicro- and micro-processes that take place in the structure of the material of the structure. Such methods for estimating the residual life are currently being successfully applied only in aviation and on important equipment (thermal, hydraulic, nuclear power plants, etc.) The processes are obvious. There is a need to comprehensively investigate the issue of damage accumulation in wooden structures under load, and the associated processes of changing the cross-sectional area and carrying capacity and use the results of the study in the calculation of structures. This makes it possible to reduce the consumption of materials and make the sections of wooden structures more economical, and also allows you to avoid excessive margins. The direction of improving the methods of designing and calculating wooden structures and determining the residual life of the main wooden structures of structures are not yet reflected in the technical literature. In this regard, it requires a comprehensive study. To study the processes of damage accumulation in the material of construction, a method was used that does not destroy the structure. This is an acoustic emission method, which is associated with the propagation in the material of elastic waves caused by the dynamic local restructuring of its structure. Acoustic emission signals appear at the onset of micro and macro defects and accompany the entire process of material deformation. This allows you to diagnose the state of the structure, since the emission of sound vibrations can be detected at the stage when the structure as a whole is still operational.

Damage, brittle fracture resistance and working capacity of a KAMAZ vehicle leaf spring when operating in the North

Due to importance of developing the North and Arctic territories, it is essential to ensure working capacity of machinery in cryolithozone. To solve these problems, it is necessary to study accumulation of structural damage and changes in material properties. The purpose of this article is to study influence of operation in the northern roads conditions on fatigue damage, brittle fracture resistance and the working capacity of a leaf spring of a KAMAZ truck widely used in Yakutia. Methods of mathematical statistics, metallography, microindentation, standard mechanical tests, etc. were applied. Results of analysis of distribution of the KAMAZ vehicle springs failures on the months of the year are given, taking into account the seasonal changes in a profile of the typical for Yakutia gravel road. To assess the fatigue damage of metal, the structural and statistical study of microhardness (microdamage) and porosity (mesodamage) was carried out. Impact toughness values were determined and it was found that the accumulated damage did not lead to metal embrittlement at low temperatures. The more significant impact of the cryolithozone road microprofile on the working capacity of the KAMAZ truck springs as compared to the factor of the low temperatures has been substantiated.

Microstructure Analyses and Multiscale Stochastic Modeling of Steel Structures Operated in Extreme Environment

The article primarily is concerned with the problem of damage accumulation and fracture modeling for steel structures operated at low temperature conditions. The inhomogeneity of the weld joints is other issue associated with the need to examining the microstructure and defects in steel at different scale levels. The next problem is that, extreme environment contains not only the extreme temperature conditions but phase transitions also, fluctuations in temperature, inappropriate in service and repair. Last factors have stochastic behavior and are even uncertain in nature. So these problems are observed and discussed in this paper as theoretical and experimental for building the multiscale model of structural damage accumulation, taking into account the following: the inhomogeneity of the weld, the low-temperature brittle-ductile transition for bcc steels, and the uncertainty factors estimation concept. The applications describe the locomotive tire lifetime estimation at low temperature conditions. The modeling approach is based on Kachanov-Rabotnov structural damage accumulation theory and stochastic crack growth modeling. Bayesian probability approach has been used for uncertainty factor estimation. The experimental part includes the internal friction study of low temperature transition mechanism for bcc steel, the mechanical tension and impact toughness tests for locomotive tire steel, and the low-cycling testing and microhardness estimation of mechanical properties for welded steel probes. The experimental testing shows the impact toughness drop at low temperature. The microstructural study for weld joints reveals the small cracks in heat affected zone, so the size and distance between such defects are used for stochastic modeling visualization of crack propagation and crack velocity estimation. The revealing mechanisms and proposed relationships could be used for theoretical and numerical modelling of damage accumulation and fracture in welded steel structures.

Probability-based cumulative damage assessment of structures subjected to non-stationary repeated loads

In-service civil structures are often subjected to repeated external loads (shock events), which may lead to an accumulation of structural damage and further an increase in the probability of structural failure. The shock actions are by nature stochastic with randomness arising from their intensities and occurrence times. A varying trend in future intensity and/or occurrence rate of many types of shock action has been projected in the literature, such as cyclone actions due to the potential impact of climate change. This article proposes a method to assess the structural reliability in the presence of uncertainty and non-stationarity in external shock events, with a limit state that the cumulative damage exceeds the permissible level. The mean value and variance of the cumulative damage are estimated with proposed closed-form solutions, and the gamma distribution is suggested to describe the probabilistic characteristics of the cumulative damage, whose accuracy is verified through a comparison with Monte Carlo simulation. Furthermore, the cumulative density function of structural service life is derived explicitly. Parametric studies are conducted to investigate the impact of non-stationarity in shock actions on structural reliability.

Microstructural MR Imaging Techniques inMultiple Sclerosis.

Due to its sensitivity in the detection of focal white matter (WM) lesions, MR imaging has become a paraclinical tool central to diagnosing multiple sclerosis (MS) and monitoring its evolution. Despite this, the correlation between patients' clinical status and conventional MR imaging measures is weak to moderate. Quantitative MR imaging-based techniques, such as magnetization transfer and diffusion tensor imaging, have a higher specificity toward the heterogeneous pathologic substrates of MS than MR imaging. This article discusses the main insights derived from the application of such MR imaging-based techniques to define MS pathophysiology and to quantify the progressive accumulation of structural damage in the central nervous system.