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This work aims to reveal the effect of rock bridge length (RBL), i.e., 10, 20, 30, or 40 mm, on the fatigue mechanical responses and fracture evolution of marble samples containing stepped fissures under multilevel cyclic loading paths. Comprehensive investigations were conducted on fatigue strength, deformation, damping evolution, and damage propagation. The test results demonstrate that fatigue strength, volumetric deformation, and fatigue lifetime increase as rock bridge length increases. The energy dissipation reflected by the damping ratio indicates that much energy is consumed to drive crack propagation, especially for rock with larger rock bridge segments at the final cyclic loading stage (CLS). An index of strain incremental rate is proposed to predict rock failure development. It is found that volumetric strain rate is a better early warning sign than axial strain rate. Warning time decreases with increasing rock bridge length; it is suggested that rock with large segments has good ability to resist external fatigue loading. [ABSTRACT FROM AUTHOR]

This study presents an innovative numerical model based on the position-based finite element method, utilizing laminated frame elements to predict beam displacements under corrosion-a common challenge in reinforced concrete structures due to chlorides and carbon dioxide penetration. The proposed model addresses both geometric and physical non-linearity, specifically considering the uniform reduction in rebar area, a critical consequence of carbonation-induced corrosion. This reduction significantly influences element inertia and, consequently, the structure's stiffness. Given the expected increase in corrosion problems in reinforced concrete structures due to climate change-induced rising temperatures and heightened carbon dioxide levels, resulting in earlier degradation and reduced stiffness, there is a pressing need for alternative approaches to calculate structure displacement under carbonation-induced corrosion. In response to this concern, our model provides an innovative and alternative methodology, demonstrating promising results when compared with existing literature, even under the constraints of a simplified model. [ABSTRACT FROM AUTHOR]

This study aims to review and highlight the important modelling methodologies used for studying carbon nanotubes (CNTs) and their composites. Understanding appropriate modelling methods for specific applications is crucial as CNTs become integral in achieving lighter, multifunctional composite structures. This paper explores a range of techniques, including finite element modelling (FEM), Molecular Dynamics (MD), Molecular Structural Mechanics (MSM), as well as nonlocal models, and the Cauchy-Born (CB) rule. Emphasis is placed on factors such as interphase effects between CNTs and the matrix, bonding interactions, non-bonded van der Waals (vdW) forces, and dynamic behaviour. Multiscale modelling is extensively discussed as a pivotal approach for efficiently addressing various length scales in nanocomposites. Modelling of failure, damage and its propagation, delamination, and instabilities such as buckling and fracture have been highlighted, and research gaps have been pointed out. [ABSTRACT FROM AUTHOR]

This work aims to reveal the effect of rock bridge length (RBL), i.e., 10, 20, 30, or 40 mm, on the fatigue mechanical responses and fracture evolution of marble samples containing stepped fissures under multilevel cyclic loading paths. Comprehensive investigations were conducted on fatigue strength, deformation, damping evolution, and damage propagation. The test results demonstrate that fatigue strength, volumetric deformation, and fatigue lifetime increase as rock bridge length increases. The energy dissipation reflected by the damping ratio indicates that much energy is consumed to drive crack propagation, especially for rock with larger rock bridge segments at the final cyclic loading stage (CLS). An index of strain incremental rate is proposed to predict rock failure development. It is found that volumetric strain rate is a better early warning sign than axial strain rate. Warning time decreases with increasing rock bridge length; it is suggested that rock with large segments has good ability to resist external fatigue loading.

This paper aims at the development and implementation of an algorithm for the treatment of damage and fracture in smooth particle hydrodynamic (SPH) method, where free surface, crack opening, including its propagation and branching is modelled by weakening the interparticle interactions combined with the visibility criterion. The model is consistent with classical continuum damage mechanics approach, but does not use an effective stress concept. It is a difficult task to model fracture leading to fragmentation in materials subjected to high-strain rates using continuum mechanics. Meshless methods such as SPH are well suited to be applied to fracture mechanics problems, since they are not prone to the problems associated with mesh tangling. The SPH momentum equation can be rearranged and expressed in terms of a particleparticle interaction area. Damage acts to reduce this area, which is ultimately set to zero, indicating material fracture. The first implementation of the model makes use of Cochran-Banner damage parameter evolution and incorporates a multiple bond break criterion for each neighbourhood of particles. This model implementation was verified in simulation of the onedimensional and three-dimensional flyer plate impact tests, where the results were compared to experimental data. The test showed that the model can recreate the phenomena associated with uniaxial spall to a high degree of accuracy. The model was then applied to orthotropic material formulation, combined with the failure modes typical for composites, and used for simulation of the hard projectile impact on composite target. [ABSTRACT FROM AUTHOR]

The influences of variable damages (crack and delamination) and high-strain loading conditions on the elasto-plastic stress–strain characteristics of fiber-reinforced polymeric composite have been evaluated in this research. The desired constitutive behaviour is obtained using the advent of material modelling features of a unanimously accepted commercial finite element (FE) tool (ABAQUS). The effect of damages (individual/combined) is obtained through a Quad element to analyze different specimens considering various strain rate loading (0.001, 0.01, 0.1, 1, 10, 50). The model validity has been established initially by verifying the outcomes (stress–strain data) with those of the open domain results. Furthermore, the relevant mechanical forces and stress–strain characteristics are computed for several new cases of polymeric composite samples by varying the geometry, damages, and testing conditions (strain-rate loading). Additionally, the sensitivity analysis is carried out based on surrogate models (i.e., stochastic constitutive models) to quantify the influence of damages in presence of strain rate. The comprehensive features and the model capabilities are summarized in detail for the variable geometrical configurations. [ABSTRACT FROM AUTHOR]

To promote the use of newhigh-strengthmaterials in the automotive industry, the evaluation of crashworthiness is essential, both in terms of finite element (FE) analysis aswell as validation experiments. Thiswork proposes an approach to address the crash performance through high-speed imaging combined with 3D digital image correlation (3D-DIC). By tracking the deformation of the component continuously, cracks can be identified and coupled to the load and intrusion history of the experiment. The so-called crash index (CI) and its decreasing rate (CIDR) can then be estimated using only one single (or a few) component, instead of a set of components with different levels of intrusion and crushing. Crash boxes were axially and dynamically compressed to evaluate the crashworthiness of TRIP-aided bainite ferrite steel and press-hardenable steel. Acalibrated rate-dependent constitutivemodel, and a phenomenological damage model were used to simulate the crash box testing. The absorbed energy, the plastic deformation, and the CIDR were evaluated and compared to the experimentally counterparts. When applying the proposed method to evaluate the CIDR, a good agreement was found when using CI:s reported by other authors using large sets of crash boxes. The FE analyses showed a fairly good agreement with some underestimation in terms of energy absorptions. The crack formation was overestimated resulting in too high a predicted CIDR. It is concluded that the proposed method to evaluate the crashworthiness is promising. To improve the modelling accuracy, better prediction of the crack formation is needed and the introduction of the intrinsic material property, fracture toughness, is suggested for future investigations and model improvements. [ABSTRACT FROM AUTHOR]

Textile composites are predestined for crash-loaded lightweight structures due to their adjustable energy absorption capacity, but they can exhibit different types of defects that occur during production (voids) and in operation (fatigue). The influence of such defects, especially the interaction of several defect types on the strain-rate-dependent material behaviour, is still insufficiently researched and can represent a safety risk. Therefore, this paper presents a phenomenological model that can be used to mathematically describe the strain-rate-dependent stress-strain behaviour of nominally defect-free and defect-affected textile composites. An adjunctive damage model in the sense of continuum damage mechanics is introduced, which also considers the interaction of both defect types for the first time. For the model validation, extensive experimental tests on glass fibre non-crimp fabrics reinforced epoxy (GF-NCF/EP) composites are performed. The focus is put on the influence of voids and fatigue-related pre-damage under subsequent tensile loading at strain rates up to 40 s − 1 . The theoretical studies show a good coincidence with the experimental results. The novel model provides a method for the efficient generation of material maps for numerical highly dynamic crash and impact analyses for defect-free and defective textile composites. As a result, a flexible and practice-oriented model approach is available, which makes a significant contribution to an improved understanding of materials and enables a future defect-tolerant design of textile composites. [ABSTRACT FROM AUTHOR]

Damage modelling of composite material delamination is an intense field of research to understand the complex composite failure behaviour and predict the residual strength of damaged structures. One of the widely employed methods to simulate delamination is the cohesive zone modelling (CZM) technique. To successfully utilize this approach, accurate characterisation of the interlaminar fracture toughness is crucial, while the composite delamination is dominated by Mode I and Mode II fracture in most cases. Numerous studies have been conducted on composite materials delamination under Mode I loadings using double cantilever beam (DCB) tests. Accordingly, the ASTM standard testing procedure and data reduction scheme to obtain Mode I fracture toughness (GIc) have been well established and widely accepted. However, it is still challenging to characterize the composite Mode II delamination resistance due to the susceptibility problems inherent to the existing testing methods and the lack of robust data reduction schemes to accurately identify the initial crack tip and monitor the crack growth. This study attempts to find a reliable solution to obtain the Mode II fracture toughness (GIIC) and an effective modelling strategy to simulate Mode II delamination in laminated composites. First, we reviewed the existing testing set-ups and surveyed the data reduction schemes conventionally used to obtain GIIC. The advantages and drawbacks of the three most used test methods, and particularly the standard end-notched flexure (ENF) test (ASTM D7905/D7905M) and the end-loaded split (ELS) test (ISO 15114:2014) were examined. Second, the advantages of the effective-crack-length-based data reduction schemes against the classical data reduction schemes were empirically studied with the ENF tests conducted on G40-800/5276-1 carbon-fibre reinforced composite laminate coupons. Although many studies have studied the accuracy of the effective-crack-length-based approaches from different aspects, there is a lack of direct comparison between the numerical results and experimental data. Our modelling study demonstrates that among the five data reduction schemes that are examined, the compliance calibration method (CCM) required by ASTM D7905 yields the most conservative GIIC values, which is suitable for establishing material property for a design purpose. The compliance-based beam method (CBBM) may generate the least conservative GIIC values, which are deemed to be the most accurate ones for modelling and simulation validation purposes. Finite element (FE) modelling of the ENF tests using the CZM technique was carried out and comprehensive parametric studies were conducted to achieve an efficient and robust strategy for delamination modelling of composite laminates under Mode II shear loadings.

Hydrogen can degrade the mechanical properties of steel components, which is commonly referred to as "hydrogen embrittlement" (HE). Quantifying the effect of HE on the structural integrity of components and structures remains challenging. The authors investigated an X70 pipeline steel through uncharged and hydrogen-charged (notched) tensile tests. This paper presents a combination of experimental results and numerical simulations using a micro-mechanics-inspired damage model. Four specimen geometries and three hydrogen concentrations (including uncharged) were targeted, which allowed for the construction of a fracture locus that depended on the stress triaxiality and hydrogen concentration. The multi-physical finite element model includes hydrogen diffusion and damage on the basis of the complete Gurson model. Hydrogen-Assisted degradation was implemented through an acceleration of the void nucleation process, as supported by experimental observations. The damage parameters were determined through inverse analysis, and the numerical results were in good agreement with the experimental data. The presented model couples micro-mechanical with macro-mechanical results and makes it possible to evaluate the damage evolution during hydrogen-charged mechanical tests. In particular, the well-known ductility loss due to hydrogen was captured well in the form of embrittlement indices for the different geometries and hydrogen concentrations. The limitations of the damage model regarding the stress state are discussed in this paper. [ABSTRACT FROM AUTHOR]

Numerical prediction of composite damage behaviour at the microscopic level is still a challenging engineering issue for the analysis and design of modern materials. In this work, we document the application of a recently developed numerical technique based on the coupling between the virtual element method (VEM) and the boundary element method (BEM) within the framework of continuum damage mechanics (CDM) to model the in-plane damage evolution characteristics of composite materials. BEM is a widely adopted and efficient numerical technique that reduces the problem dimensionality due to its underlying formulation. It substantially simplifies the pre-processing stage and decreases the computational effort without affecting the solution's accuracy. VEM is a recent generalization to general polygonal mesh elements of the finite element method that ensures noticeable simplification in the data preparation stage of the analysis, notably for computational micro-mechanics problems, whose analysis domain often features complex geometries. The numerical technique has been applied to artificial microstructures, representing the transverse section of composite material with stiffer circular-shaped inclusions embedded in a softer matrix. BEM is used to model the inclusions that are supposed to behave within the linear elastic range, while VEM is used to model the surrounding matrix material, developing nonlinear behaviours. Numerical results are reported and discussed to validate the proposed method. [ABSTRACT FROM AUTHOR]

Numerical testing is crucial for the design of composite fuselages, which have strict crashworthiness regulations. However, the majority of studies on numerical fuselage impacts do not account for the effects of strain rate in simulations. A damage model considering strain rate dependence has been implemented to accurately predict the impact behaviour of a composite fuselage structure. This model enhances the existing three-dimensional Hashin criterion by incorporating strain rate effects and its implemented numerically using a VUMAT subroutine in ABAQUS/explicit. Validation of the model is done through a low-velocity impact problem, showing a better correlation with experimental data compared to previous numerical analyses available in the literature. The study focuses on high-energy impact on a composite stanchion in the lower lobe of an aircraft fuselage. Results demonstrate that the newly proposed model effectively predicts failure zones and modes, indicating its potential in addressing dynamic composite problems typical of impact scenarios. [ABSTRACT FROM AUTHOR]

Rockfall hazards present significant challenges in modelling the damage behaviour of flexible barrier systems, particularly under repeated impact conditions. In this study, we developed an enhanced model to predict the performance degradation and failure of steel wire ring nets under such impacts. Compared to previous numerical models, this model improves the accuracy of damage analysis from the individual ring scale to the steel wire scale. First, we derived geometric equations for wire winding within a single ring. Furthermore, we coupled ductile and shear damage criteria with the material's constitutive equation to consider stress-state-dependent damage behaviour. Model parameters were calibrated using quasi-static destructive tests and validated through repeated impact tests. Results demonstrate the model's effectiveness in predicting the damage evolution of the ring net and replicating wire redistribution and sectional modulus changes during the impact process. The findings highlight the critical role of frictional interactions in energy dissipation during repeated impacts. This irreversible and repeatable friction significantly enhances the ring net's energy absorption capacity, accounting for 53.1–62.5% of the total and surpassing the energy dissipation from the elastic and plastic deformation of the steel wire. [ABSTRACT FROM AUTHOR]

[Display omitted] • Predicating subsurface butterfly-wing cracking damage due to non-metallic inclusions. • Developing Continuum Damage Mechanics FE modelling under rolling contact fatigue. • Integrating localised plastic deformation and kinematic hardening in damage modelling. • Investigating effect of inclusion boundary separation and internal cracking on damage evolution. Wind turbine (WT) gearbox bearings experience premature failures. Damage characterisation of failed bearings has shown that subsurface micro cracks and butterfly-wing cracks are associated with non-metallic inclusions in the bearing raceways. The existing studies are unable to predict crack propagation under rolling contact fatigue considering shakedown and ratchetting when the material around an inclusion experiences sufficiently high levels of stresses. In this study, a finite element (FE) damage model based on the Continuum Damage Mechanics (CDM) is developed, integrated with the modelling of plastic deformation and kinematic hardening when the material around inclusion is subjected to alternating tension and compression. Two damage types of manganese-sulphide inclusions are investigated, showing significant effects of inclusion boundary separation and internal cracking on the subsurface RCF crack evolution. The modelling results also show that higher surface traction, overloads and varied loading sequences, commonly experienced by WTs in operation, have significant effects on the increase of the subsurface butterfly-wing crack lengths, because of early crack initiation and accelerated crack propagation. The developed CDM FE model has shown its effectiveness in predicting the damage evolution to gain new insights of complex interactions of a number of critical factors that can lead to the premature failure of bearings. [ABSTRACT FROM AUTHOR]

Frequently observed damage in historic masonry vaults has always given rise to concerns on their stability. The effect of present damage on masonry vaults structural response should be taken into consideration during structural analysis as it clearly affects its behavior. The aim is to propose a method to study the safety of vaults, setting up a finite element model with a limited number of discontinuities, based on the consideration of the vault construction and damage observation. A case study from Milan cathedral is adopted where damage is documented. A complex damage mechanism characterized by sliding of voussoirs and detachment of the rib from the web was documented in the 1960s. The results show the possibility to analyze the evolution of the observed mechanism and to evaluate numerically its safety in function of the documented settlements. Technical applications of the present work include interpretations of the causes of observed damage, estimation of the level of settlements based on observed damage, and numerical evaluation of the safety of the current mechanical state. [ABSTRACT FROM AUTHOR]

The Small Punch Test (SPT) method is especially useful for quantifying the mechanical properties of metallic materials in cases where the material available for testing is limited or for in service monitoring. However, the applicability of this method to metal matrix composites has not yet been fully established. In the present study, Al-TiB2 composite billets with TiB2 particle volume fractions of 5%,10% and 15% were manufactured using Spark Plasma Sintering (SPS). Thin specimens with 0.5 mm thickness were cut from the billets, and SPT experiments were conducted until failure. Well-accepted analytical techniques were utilized to determine the Al-TiB2 composite effective yield stress for all TiB2 particle volume fractions. It was shown, that standard analytical methods for characterizing the effective yield stress were adequate only for TiB2 volume fractions of up to 5%. The experimental mechanical response up to and including failure was reproduced for all Al-TiB2 compositions by finite element analysis incorporating a continuum damage mechanics approach. The computational analysis revealed that for high TiB2 volume content, the region of the SPT loading curve which is commonly associated with specimen yielding, may represent a mixture of yielded and damaged areas. Since the damage distribution in the specimen influences the specimen flexural modulus, standard analytical relations cannot be used to determine the composite yield stress and computational methods must be used. This finding may explain the inconsistent results reported in the literature with regard to the accuracy of the SPT method in determining the effective yield stress for metal matrix composites. [ABSTRACT FROM AUTHOR]

To promote the use of newhigh-strengthmaterials in the automotive industry, the evaluation of crashworthiness is essential, both in terms of finite element (FE) analysis aswell as validation experiments. Thiswork proposes an approach to address the crash performance through high-speed imaging combined with 3D digital image correlation (3D-DIC). By tracking the deformation of the component continuously, cracks can be identified and coupled to the load and intrusion history of the experiment. The so-called crash index (CI) and its decreasing rate (CIDR) can then be estimated using only one single (or a few) component, instead of a set of components with different levels of intrusion and crushing. Crash boxes were axially and dynamically compressed to evaluate the crashworthiness of TRIP-aided bainite ferrite steel and press-hardenable steel. Acalibrated rate-dependent constitutivemodel, and a phenomenological damage model were used to simulate the crash box testing. The absorbed energy, the plastic deformation, and the CIDR were evaluated and compared to the experimentally counterparts. When applying the proposed method to evaluate the CIDR, a good agreement was found when using CI:s reported by other authors using large sets of crash boxes. The FE analyses showed a fairly good agreement with some underestimation in terms of energy absorptions. The crack formation was overestimated resulting in too high a predicted CIDR. It is concluded that the proposed method to evaluate the crashworthiness is promising. To improve the modelling accuracy, better prediction of the crack formation is needed and the introduction of the intrinsic material property, fracture toughness, is suggested for future investigations and model improvements.

Natural fibers are capable substitutes to conventional synthetic fibers, primarily because of their economic and environmental advantages, as well as they find widespread applications in textile, construction, and non‐load‐bearing applications in the case of automotive and aircraft industries. This paper presents a comprehensive review of natural fiber‐reinforced composites, focusing on their failure behavior, failure modelling techniques, and associated theories. Finite element modelling is widely applied in the damage modelling of natural fiber as well as natural fiber‐based green composites. Formation of representative volume elements in conjunction with homogenization emerges to be the common and most effective multi‐scale technique used for determining the effect of microstructures on the thermal and mechanical properties of the natural fiber‐reinforced composite. To provide a better understanding of the insight of damage aspects of natural fiber composites an up‐to‐date review catering to various aspects ranging from its manufacturing techniques, failure processes and mechanisms, finite element modelling techniques, and mechanical performance is very much required. This review aims to address the above‐stated issues, challenges, and details of achievements made with them. [ABSTRACT FROM AUTHOR]

This work aims to reveal the fracture the damage evolution characteristics of fissure‐holes containing rock under multistage constant‐amplitude variable‐frequency cyclic loads. Testing results show that the peak strength and fatigue lifetime both increase as the fissure angle increases from 10° to 70°. However, the volumetric deformation, AE activities, and crack network scale get to a maximum for a sample having a 50° fissure angle. More small‐sized cracks were formed for rock having a high fissure angle, and the proportion of low‐frequency signal is relatively high. A damage evolution model was proposed based on AE rate, and an inverted "S"‐shaped curve reflects the damage propagation of the experimental data. Additionally, the highlighted internal crack network reveals the crack coalescence and hole spalling behaviors; three types of rock bridge coalescence modes of single tensile coalescence, double‐tensile coalescence, and double shear coalescence were identified. Highlights: Failure of pre‐flawed granite under multi‐level variable‐frequency (MLVF) cyclic loads was discussed.Fissure angle influences the rock deformation, lifetime, AE activities, and the final crack pattern.A damage evolution model was proposed by AE rate to describe three‐phase damage propagation.The crack coalescence behaviors were visualized and three coalescence modes were identified. [ABSTRACT FROM AUTHOR]

The formability limit in a typical incremental sheet forming (ISF) far exceeds the conventional estimate assuming necking failure. The material subjected to incremental forming fails by fracture. Although damage models have been used to correlate the failure in incremental forming, a detailed understanding of the failure mechanism spanning strain paths is not clear yet. In this work, three parts with varied shapes (hybrid five lobe, pyramid and variable wall angle conical frustum (VWACF)) were developed using ISF to cover a range of possible strain paths. The failure is predicted using established uncoupled phenomenological damage models. Damage models were calibrated for AA1050 aluminium sheet by the method of inverse approach using carefully designed tensile tests and FE simulations. Three different damage models were implemented as user subroutine in commercial software code, ABAQUS/Explicit and the results predicted were compared. The linear damage accumulation used to develop fracture locus under monotonic loading could not predict the failure limit in a benchmark single groove test. Therefore a non linear damage accumulation rule (NLDA) is implemented to simulate ISF. The parameters of the NLDA were calibrated from the single groove test. The fracture forming limits during ISF was established using circular grid analysis near the failure zone of the formed part. A good agreement can be found between the experimental observations and numerical predictions for fracture location and part height. It was observed that the overall predictive capability of Hosford Coulomb (HC) damage model is better among three damage models investigated for the given range of loading conditions. However all the three models under-predicted the experimental fracture strain measured in ISF. The possible explanation for the discrepancy is explored. [ABSTRACT FROM AUTHOR]

A thorough control of the machining operations is essential to ensure the successful postprocessing of additively manufactured components, which can be assessed through machinability tests endowed with numerical simulation of the metal cutting process. However, to accurately depict the complex metal cutting mechanism, it is not only necessary to develop robust numerical models but also to properly characterize the material behavior, which can be a long-winded process, especially for state-of-stress sensitive materials. In this paper, an efficient mechanical characterization methodology has been developed through the usage of both direct and inverse calibration procedures. Apart from the typical axisymmetric specimens (such as those used in compression and tensile tests), plane strain specimens have been applied in the constitutive law calibration accounting for plastic and damage behaviors. Orthogonal cutting experiments allowed the validation of the implemented numerical model for simulation of the metal cutting processes. Moreover, the numerical simulation of an industrial machining operation (longitudinal cylindrical turning) revealed a very reasonably prediction of cutting forces and chip morphology, which is crucial for the identification of favorable cutting scenarios for difficult-to-cut materials. [ABSTRACT FROM AUTHOR]

• Analytical method developed and verified to model impact events on metal plates. • Transition region introduced between local deformation and global deflection. • Deductive process defined for predicting the impactor from damage dimensions. • Model result error was lowest for plates with thickness range of 1.5–3 mm. • Analytical method is faster and accurate (<10% error) compared to FEM. This paper proposes an analytical model that uses historical damage dimension data to deduce physical impactor characteristics (size and energy) that has caused a certain resulting damage. Maintenance tasks occur in operations due to impact, however the source of the damage caused in the event remains in most cases unknown. Consequently, by inferring what has caused a certain type of damage from the distribution of the damage type and severity relative to impactor types, maintainers can be better prepared in terms of what to expect from a given impactor source. The developed model introduces a novel transition deformation region between the local deformation and the global plate deflection, allowing for fast and accurate predictions of the impact event. Using the known aluminium structural properties and damage dimensions, the damage data is converted into impactor data. The model is applied in a case study using 120 fuselage dent damages dimensions (length, width, and depth) from a Boeing 777 fleet. The results show that the model deduces impactor characteristics for 94% of the considered damages, ranging up to 240 J and 110 mm for impactor energy and radius respectively. [ABSTRACT FROM AUTHOR]

In-service masonry arch road bridges, mainly realised before the first half of the last century, represent a wide portion of the entire worldwide infrastructural asset. Given their age, during their service life these structures could have experienced damage due to anthropic (i.e. traffic) and natural (i.e. earthquakes, soil settlements, degradation, etc.) actions which may have inevitably affected their load-bearing capacity. The present study addresses the problem of the residual capacity estimation of damaged bridges by investigating the impact of previous loading on the actual strength of the structure. In particular, reference to a past experimental activity retrieved from the literature on reduced-scale bridges subjected to concentrated vertical loads has been made to calibrate a reliable detailed finite element model in Abaqus software. Then, damage of different extent has been introduced by simulating the transit of vehicles of various weights on the structure and the residual capacities of the bridge have been assessed and compared against the undamaged configuration. The results confirm that pre-existing damage due to traffic loading may significantly influence the capacity of such structures, with peak load reductions up to 60% estimated through the proposed methodology. • Pre-existing damage affects the actual capacity of existing masonry arch bridges. • Numerical models can be profitably adopted to simulate the presence of pre-existing damage. • Damage can be introduced in numerical models by simulating their causes. • Rigid-block analyses can provide conservative estimation of the actual capacity of masonry arch bridges. [ABSTRACT FROM AUTHOR]

Grillage decks made of reinforced concrete (RC) with more than 40–60 years of service life may exhibit localised areas of severe damage or even entire elements exceeding the serviceability limits. In these cases, it is essential to quickly and efficiently assess the structure's safety margins, and, in the worst cases, to also verify whether the damaged deck's residual bearing capacity is sufficient for it to be used as a platform for the repair works. This article proposes an assessment based on a non-linear RC finite element specialised in dealing with systems working in bending and torsion. The damage, measured at a particular time after construction, is modelled by a reduction of the reinforcement section, supposed to be induced by chlorides diffusion and investigated through a Cellular Automata algorithm. Such an approach is applied in studying a bridge deck, having an edge beam damaged by leakage of salted water from the road platform. The results give a thorough description of the structural behaviour and the deformed shapes help in understanding the redistribution process of the internal forces. These results may provide a reliable reference to plan proper maintenance actions as well as to establish a hierarchy of repairing and strengthening interventions. [ABSTRACT FROM AUTHOR]

During the damage evolution of bonded joints, different modes of failure can be detected. These modes include pure modes (Mode I, Mode II, Mode III) or their combinations (Mixed-mode) according to the type and the direction of loading. Some scientifically validated test methods are commonly used to obtain the fracture toughness by loading under pure Mode I, Mode II and their Mixed-mode. Some test methods were established to obtain the fracture toughness by loading under pure Mode III, however further research is required. The aim of this work is to clarify the mode ratio of a tubular lap joint under torsional loading and then to propose a method to determine the cohesive and damage parameters of this joint. The presumed mode of failure is Mode III, or Mixed-mode with a predominance of Mode III. Emphasis is placed on the widespread applicability of the obtained results for similar specimens loaded under similar modes. [ABSTRACT FROM AUTHOR]

This paper presents a method of constructing a mathematical model of a diagnostic station to identify the vibration spectrum of wheel rims in order to identify their technical condition. The method for diagnosing the technical state of a wheel rim is based on comparative analysis of time runs and a change in the natural frequencies in relation to the model runs. During the tests carried out according the developed method, the vibration spectrum was obtained through dynamic excitement of vibrations of the examined rim mounted on the diagnostic station by using a mechanical exciter of known impact energy. As a part of the mathematical model construction, a structural analysis was carried out and the stiffness coefficient, necessary for the description of the phenomenon, was determined using Sobol's grid. The obtained simulation results were compared to the results obtained in empirical tests on the diagnostic station for the wheel rim, which confirmed the correctness of the proposed model, as well as the method for identifying the technical condition of the wheel rim. [ABSTRACT FROM AUTHOR]

Abstract A constitutive model for an interface finite element is proposed to enable simulation of delamination in composite materials with R-curve effects. The constitutive model is formulated in the framework of cohesive zone modelling (CZM). In essence, a multilinear CZ law with an arbitrary number of line segments is developed. The CZ law seeks to enable constitutive modelling of failure mechanisms on multiple scales within the fracture process zone and reduce conventional a priori assumptions regarding the shape of the CZ law. The CZ law relies on damage mechanics, an equivalent one-dimensional formulation, and criteria for mode interactions to simulate delamination under mixed-mode loading. Special emphasis is put on the derivation of interpolation formulas and a constitutive tangent stiffness tensor for the multilinear formulation. The constitutive model is implemented in the commercial FE program ANSYS Mechanical, for implicit finite element analysis (FEA), using user-programmable features. The implementation is verified through single interface element numerical studies, and its applicability is demonstrated by simulating an experiment of quasi-static delamination showing large-scale fiber bridging in pure mode I DCB glass-fiber epoxy specimens. Experimental measurements and simulation outputs using the novel cohesive element is compared to those of the conventional bi- and trilinear CZ laws. [ABSTRACT FROM AUTHOR]

Abstract It is commonly acknowledged that greenhouse gas (GHG) emissions from anthropogenic sources accelerate climate change impacts. Efforts are made by governments and companies to reduce GHG emissions via policies and actions. In order to determine which actions to prioritize among many options, benefits of emission reductions are often monetized, to compare with the costs of action or with benefits that can be obtained from other actions. Life cycle assessment (LCA) is a commonly used tool to assess the amount of GHGs emitted over the life cycle of a service, policy or product system. However, the damage modelling of GHGs in life cycle impact assessment (LCIA) and its monetary values have not been separately evaluated. This hinders the application of LCA in relevant decision contexts. This study evaluates the cause-effect chains and associated monetary values of GHG in three LCIA methods LIME2, EPS2015 and ReCiPe2016. Among these three, EPS2015 covers most damage categories, including the ones on human health, ecosystem and social assets. ReCiPe2016 does not include social assets damages and LIME2 does not consider ecosystem damages in climate change impact. Human health damages are well estimated in all three methods, contributing to 70–97% of the GHG monetary values. The lack of data is a clear obstacle across methods. Further research is needed to develop comprehensive and robust modelling approach for ecosystem damages, which are not well covered in current LCIA methods. Moreover, due to the scope of environmental LCA, there is a lack of consideration on socio-economic consequences, which may not be negligible for climate change. The resulting monetary value of GHG, expressed in per tonne CO 2 -eq are 16, 160 and 140 US$ 2017 respectively in LIME2, EPS2015 and ReCiPe 2016. These monetary values are reasonable for use in decision contexts where LCA is applied. Further research is, however, needed to reduce the current uncertainty of at least 1–2 orders of magnitude. Highlights • Human health damages contribute to 70–97% of the GHG monetary value in assessed methods. • Comprehensive and robust modelling for ecosystem damages is lacking in LCIA. • Monetary values of CO 2 -eq are 16, 160 and 140 US$ 2017 /ton in LIME, EPS and ReCiPe. • GHG monetary values in EPS and ReCiPe are in line with social costs of carbon (SCC). • The uncertainty of GHG monetary values is at least 1–2 orders of magnitude. [ABSTRACT FROM AUTHOR]

Finite Element Simulations in solid mechanics are nowadays common practice in engineering. However, considering uncertainties based on this powerful method remains a challenging task, especially when nonlinearities and high stochastic dimensions have to be taken into account. Although Monte Carlo Simulation (MCS) is a robust method, the computational burden is high, especially when a nonlinear finite element analysis has to be performed behind each sample. To overcome this burden, several "model-order reduction" techniques have been discussed in the literature. Often, these studies are limited to quite smooth responses (linear or smooth nonlinear models and moderate stochastic dimensions). This paper presents systematic studies of the promising Sparse Polynomial Chaos Expansion (SPCE) method to investigate the capabilities and limitations of this approach using MCS as a benchmark. A nonlinear damage mechanics problem serves as a reference, which involves random fields of material properties. By this, a clear limitation of SPCE with respect to the stochastic dimensionality could be shown, where, as expected, the advantage over MCS disappears. As part of these investigations, options to optimise SPCE have been studied, such as different error measures and optimisation algorithms. Furthermore, we have found that combining SPCEs with sensitivity analysis to reduce the stochastic dimension improves accuracy in many cases at low computational cost. [ABSTRACT FROM AUTHOR]

Highlights • The Bayesian method was exploited to assess the uncertainties in damage models. • The developed methodology has been tested by mode-I fracture on four model classes. • The elastic region of the load deflection curve was most sensitive to Young's modulus. • Non-local damage model appeared the best average goodness of fit. • Gradient-enhanced damage model showed the highest model selection probability. Abstract We present a methodology to evaluate the uncertainty in several popular models for modelling damage and material failure, i.e. a gradient damage model, nonlocal model, phase field approach and cohesive zone model; the latter one is used in the context of the phantom node method though it can easily be used in the context of other computational methods for discrete fracture. The objective is to evaluate and compare the uncertainties in the current models and correlate them to practical observations. The Bayesian method is exploited to achieve this purpose based on experimental reference measurements. The developed methodology has been tested on mode-I fracture in concrete beams through well established three point bending test though other benchmark problems can be adopted for the comparison as well. The results from the current study are compared to the published experimental results. The methodology is implemented in three different steps. Firstly, a sensitivity analysis is performed to quantify the influence of uncertainties in the model parameters. Secondly, the coefficient of variation and average goodness of fit are calculated to evaluate the discrepancy of the predictions with respect to the corresponding measured experimental data. Finally, the posterior probability of models are updated to incorporate the uncertainties in both the model and the parameters, leading to an estimation of the model complexity. Based on the results, the gradient-enhanced damage is found to be the most probable model class with the lowest total model uncertainty. The present study can serve as a platform for future investigations on uncertainties associated with damage modelling and hence the concerned countermeasures. [ABSTRACT FROM AUTHOR]

Miniaturised tensile tests coupled with in-situ scanning electron microscopy are used to deduce the grain boundary properties of a nickel-based superalloy at 750 °C. This allows the damage initiation, evolution and failure processes to be observed directly. The significant variation in ductility – consistent with the limited number of grain boundaries being present – is rationalised using a crystal plasticity approach calibrated by experiments on single crystals loaded along the <001>, <011>, and <111> directions. Quantitative strength and toughness values for the grain boundaries are estimated using a cohesive zone method. The modelling approach is used to determine an approximation of the size of the representative volume element (RVE) needed for volume-averaged behaviour. [ABSTRACT FROM AUTHOR]

Computational homogenization has been used extensively over the past two decades for the analysis of masonry structures based on various averaging schemes (periodic homogenization, transformation field analysis,...), focusing on regular periodic masonry. Irregular masonry has subsequently also been scrutinized using multiscale approaches. In such efforts, an efficient strategy is required for the generation and meshing of realistic representative volume elements (RVEs) geometries. In complement to existing generation approaches, the present contribution deals with a level set-based methodology to generate irregular masonry RVE geometries. Starting from inclusion-based RVEs, combinations of distance fields are used to produce typical geometries of irregular masonry RVEs. The resulting geometries are described by implicit functions. Such implicit geometry descriptions are next exploited in an automated procedure for producing high quality conformal 2D finite element meshes on implicit geometries. This automated RVE generation and discretization procedure is then illustrated by producing failure envelopes for irregular masonry, using an implicit gradient damage formulation. The interest of recently developed gradient models with decreasing interaction length parameters is also illustrated on a specific example. [ABSTRACT FROM AUTHOR]

The paper aims to present a novel mathematical formulation for the modelling of damage. In particular, the decay of the mechanical properties of the elastic media is modeled by means of two-dimensional smooth functions, which are the Gaussian and the ellipse shaped ones. Various damaged configurations are obtained as concentrated variations of the elastic properties of the materials by setting properly the parameters that define the distributions at issue. This approach is employed to investigate the dynamic behavior of damaged plates and shells made of composite materials. In particular, a massive set of parametric studies is presented for this purpose. The results are obtained numerically by means of the Generalized Differential Quadrature (GDQ) method and are presented in terms of natural frequencies. Several Higher-order Shear Deformation Theories (HSDTs), which can include also the Murakami’s function to capture the so-called zig-zag effect, are used and compared. [ABSTRACT FROM AUTHOR]

In this work, polymer laminated composites based on Epon 862 Epoxy resin, T300 6 k carbon fibers and carbon nanotubes (CNTs) were tested with the aim to elucidate the effect of CNTs on impact properties including impact force and capacity to absorb impact energy. The polymer matrix was reinforced by a random distribution of CNTs with fraction ranging from 0.5 to 4.wt%. Composite panels were manufactured by using the infusion process. Taylor impact test was used to obtain the impact response of specimens. Projectile manufactured from a high strength and hardened steel with a diameter of 20 mm and 1.5 kg of mass was launched by a compressed gas gun within the velocity of 3 m/s. Impact force histories and absorbed energy of specimens were recorded. A numerical model was employed to simulate the impact performance. This model has been accomplished by forming a user established subroutine (VUMAT) and executing it in ABAQUS software. Finally, the effect of CNTs amount on dynamic properties of laminated composites was discussed. [ABSTRACT FROM AUTHOR]

Embedded fiber Bragg grating (FBG) sensors have been widely used for damage monitoring of fiber composite structures for a few decades. However, many remaining engineering challenges have delayed FBG based in situ structural health monitoring (SHM) systems. One of the major problem associated with FBG based SHM system is the unavailability of reliable data processing algorithms. The present work details a study which has been undertaken for identification of delamination crack propagation in fiber reinforced polymer (FRP) composite plate under uniaxial loading. The strain measured by embedded FBG sensors closer to the crack tip was used to qualitatively and quantitatively analyze delamination damage propagation using recently proposed elasto-plastic model. Strain energy release rate was calculated and compared with the model prediction. The study has concluded that the delamination crack propagation in a FRP composite can be monitored successfully using an integral approach of FBG sensors measurements and the predictions of proposed elasto-plastic model. [ABSTRACT FROM AUTHOR]