Simple Damage Model Research Articles

Monte Carlo damage models of different complexity levels predict similar trends in radiation induced DNA damage.

Ion therapies have an increased relative biological effectiveness (RBE) compared to X-rays, but this remains poorly quantified across different radiation qualities. Mechanistic models that simulate DNA damage and repair after irradiation could be used to help better quantify RBE. However, there is large variation in model design with the simulation detail and number of parameters required to accurately predict key biological endpoints remaining unclear. This work investigated damage models with varying detail to determine how different model features impact the predicted DNA damage.

Methods: Damage models of reducing detail were designed in TOPAS-nBio and Medras investigating the inclusion of chemistry, realistic nuclear geometries, single strand break damage, and track structure. The nucleus models were irradiated with 1 Gy of protons across a range of linear energy transfers (LETs). Damage parameters in the models with reduced levels of simulation detail were fit to proton double strand break (DSB) yield predicted by the most detailed model. Irradiation of the optimised models with a range of radiation qualities was then simulated, before undergoing repair in the Medras biological response model.

Results: Simplified damage models optimised to proton exposures predicted similar trends in DNA damage across radiation qualities. On average across radiation qualities, the simplified models experienced an 8% variation in double strand break (DSB) yield but a larger 28% variation in chromosome aberrations. Aberration differences became more prominent at higher LETs, with model features having an increasing impact on the distribution and therefore misrepair of DSBs. However, overall trends remained similar with better agreement likely achievable through repair model optimisation. 

Conclusion: Several model simplifications could be made without compromising key damage yield predictions, although changes in damage complexity and distribution were observed. This suggests simpler, more efficient models may be sufficient for initial radiation damage comparisons, if validated against experimental data.&#xD.

Hybrid Smoothed-Particle Hydrodynamics/Finite Element Method Simulation of Water Droplet Erosion on Ductile Metallic Targets

Erosion of metallic surfaces due to the permanent impact of high-speed water droplets is a significant concern in diverse industrial applications like turbine blades, among others. In the initial stage of water droplet erosion, there is an incubation regime with negligible mass loss whose duration is strongly dependent on water droplet sizes and velocities, the initial state of the surface, and the material properties of the target. The prediction of the incubation period duration is one of the main topics of research in the field. In this work, the interaction of the water droplets with a metallic surface is simulated using a hybrid Smoothed-Particle Hydrodynamics/Finite Element Method modeling scheme. The effect of multiple random impacts on representative target areas for certain ranges of impact angles and velocities was studied using a combination of simple material and damage models for the target surface of Ti-6Al-4V titanium alloy. The simulation is able to reproduce the main dependencies of the incubation regime and the first stages of water droplet erosion on the impact angle and velocity as reported in the literature. This framework can be considered a foundation for more advanced models with the goal of a better understanding of the physical mechanisms behind the incubation regime in order to devise strategies to extend it in real applications.

A new spectral representation of the strain energy function for linear anisotropic elasticity with a generalization for damage

A new spectral representation of the strain energy function for linear anisotropic elasticity is proposed in the form of a sum of 6 scalar eigen-stiffnesses times the squares of their associated scalar eigen-strains. Since this new representation is general, it is no less or more general than the standard representation. However, the spectral form reveals fundamental coupled eigen-modes of deformation and energy associated with general anisotropic response. Specifically, each eigen-strain is the inner product of the strain tensor with its symmetric eigen-tensor. The 6 eigen-strains are linearly independent and the 6 eigen-tensors are also linearly independent. Moreover, unlike the eigenvectors of a symmetric matrix, distinct pairs of eigen-tensors are not all orthogonal. The 15 constants that define the eigen-tensors together with the 6 eigen-stiffnesses form 21 independent material constants that characterize the fundamental physics of material anisotropy. These 21 constants are invariant to the orientation of the base vectors fixed in the material. This spectral representation also simplifies the restrictions on these material constants which ensure that the strain energy is a positive-definite function of strain. In addition, a simple damage model is proposed based on this spectral representation and a generalization for finite deformations is briefly discussed.

Seismic performance and damage evolution of RC frames retrofitted by the novel GESB system: A numerical study

A novel gapped eccentric steel brace (GESB) system was developed to enhance the seismic performance of existing reinforced concrete (RC) frame structures. To thoroughly investigate the mechanism and damage mode of the novel retrofitting system, numerical analysis was conducted on retrofitted frames with various brace eccentricity configurations, using a comprehensive multi-scale finite element model. Six suitable damage indices were defined to carry out the structural damage evolution study during the whole loading process. On this basis, a simplified damage model was developed. The results demonstrated that GESB effectively modified the mechanical mechanism and failure modes of the frames. The brace eccentricity configuration exerted a significant influence on the structural strength, stiffness, and ductility. With regards to both of strength and ductility requirements, an eccentricity range of 0.3 to 0.4 was recommended. The proposed simplified damage model was used to indicate the allowable drift ratios associated to performance levels, which were found to be very variable with various eccentricity configurations. The outcomes are essential and timely for design decision of RC frames retrofitted by GESB.

Damage in cohesive granular materials: simulations and geophysical implications

The aim of this paper is to test a simple damage model of a cohesive granular medium to study the relationship between the damage and velocity of elastic waves. Our numerical experiments of edometric compression show that the microscopic deformation quickly becomes very heterogeneous, while our simulations of elastic waves propagation show that a small amount of damage induces a dramatic decrease in the elastic velocity. This shows that cohesive discrete media are very sensitive to strain field heterogeneity, and that the wave velocities in these media can measure subtle transient deformation processes, such as earthquake initiation phases.

Ply-Resolved Quantification of Thermal Degradation in Carbon Fibre-reinforced Polymers

This study focuses on thermal degradation of carbon fibre-reinforced polymers depending on the specimen depth. For this purpose, the commercial composite HexPly® 8552/IM7 was thermally irradiated from one side with an infrared lamp at constant heat flux of 50 W/cm2 under varying exposure time. Subsequently, a defined number of plies was removed to prepare micro samples from different depths of the bulk material. Non-destructive and destructive testing methods were used to characterize the thermal degradation mechanism and mechanical properties of these specimens. The results showed that during thermal loading temperature and consequently damage gradients manifest along the material cross-section. Thereby, the damage distribution could be divided into the regions rI with matrix depletion, rII with and rIII without structural damage such as delaminations, cracks and pores. By means of ply-resolved investigations, the influence of these regions and corresponding decomposition processes on the mechanical properties could be determined. As a result, a simple damage model was introduced to calculate the residual strength from the initial strength, region sizes and sensitivity factors representing the effect of thermo-induced damage on strength types.

Mechanical Response of Glass-Epoxy Composites with Graphene Oxide Nanoparticles.

Graphene-based fillers possess exceptional properties that encourage researchers toward their incorporation in glass-epoxy (GE) polymer composites. Regarding the mechanical and wear properties of glass-epoxy composites, the effect of graphene oxide (GO) reinforced in glass-epoxy was examined. A decrease in tensile modulus and increase in tensile strength was reported for 1 wt. % of GO. A shift in glass transition temperature Tg was observed with the addition of GO. The cross-link density and storage modulus of the composite decreased with the addition of GO. The decrease in dissipation energy and wear rate was reported with the increase in GO concentration. A simple one-dimensional damage model of nonlinear nature was developed to capture the stress-strain behavior of the unfilled and filled glass-epoxy composite. Tensile modulus E, Weibull scale parameter σo, and Weibull shape parameter β were considered to develop the model. Finally, to understand the failure mechanisms in GO-filled composites, a scanning electron microscopic (SEM) examination was carried out for tensile fractured composites.

Deformation and damage behavior of the deep concrete cut-off wall in core earth-rock dam foundation based on plastic damage model - A case study

Concrete cut-off walls are widely used as an effective anti-seepage technique in overburden dam foundations all over the world. The deep cut-off wall in a core earth-rock dam foundation is often subjected to complex force conditions, and may have to withstand large stresses and deformations. In certain circumstances, it can even face the risk of cracking damage. Thus, it is of a great importance to clarify the mechanical properties and cracking trend of the deep cut-off wall of core earth-rock dam on the overburden foundation. In this paper, a simple plastic damage model for the damage analysis of deep cut-off wall was proposed under the framework of Lee-Fenves Model. In this model, the tensile and compressive responses of the wall were characterized by employing the tensile and compressive constitutive relations based on fracture energy, and different tensile and compressive damage evolution processes were considered based on the damage factor introduced according to the Sidoroff energy equivalence principle. Further, by taking into account the plastic damage, the wall-soil contact effect and the rock mass plasticity, a numerical model was established to investigate the stress deformation and damage properties of a 92-m-deep cut-off wall of a core earth-rock dam, in order to validate the feasibility and rationality of the proposed model in describing the nonlinear mechanical behavior and failure trend of the cut-off wall. Moreover, the impact of hidden faults and constraints on the mechanical properties of cut-off wall was also discussed in detail.

Application of a simple DNA damage model developed for electrons to proton irradiation

Proton beam therapy allows irradiating tumor volumes with reduced side effects on normal tissues with respect to conventional x-ray radiotherapy. Biological effects such as cell killing after proton beam irradiations depend on the proton kinetic energy, which is intrinsically related to early DNA damage induction. As such, DNA damage estimation based on Monte Carlo simulations is a research topic of worldwide interest. Such simulation is a mean of investigating the mechanisms of DNA strand break formations. However, past modellings considering chemical processes and DNA structures require long calculation times. Particle and heavy ion transport system (PHITS) is one of the general-purpose Monte Carlo codes that can simulate track structure of protons, meanwhile cannot handle radical dynamics simulation in liquid water. It also includes a simple model enabling the efficient estimation of DNA damage yields only from the spatial distribution of ionizations and excitations without DNA geometry, which was originally developed for electron track-structure simulations. In this study, we investigated the potential application of the model to protons without any modification. The yields of single-strand breaks, double-strand breaks (DSBs) and the complex DSBs were assessed as functions of the proton kinetic energy. The PHITS-based estimation showed that the DSB yields increased as the linear energy transfer (LET) increased, and reproduced the experimental and simulated yields of various DNA damage types induced by protons with LET up to about 30 keV μm−1. These results suggest that the current DNA damage model implemented in PHITS is sufficient for estimating DNA lesion yields induced after protons irradiation except at very low energies (below 1 MeV). This model contributes to evaluating early biological impacts in radiation therapy.

Simplified Modelling of Failure in High Strength Bolts under Combined Tension and Bending

Bolted connections are widely adopted in steel structures and their behaviour affects to a large extent the global response of the system. High-strength bolts of type HV are commonly employed. Under pure tension, these bolt assemblies usually fail by thread stripping. However, it was observed experimentally that, under combined tension and bending, the failure mode changes to fracture of the shank. The former loading condition commonly occurs in the case of thick extended end plate connections and the latter in the case of flush end plates. In order to analyse the behaviour of the structure, the finite element method (FEM) is usually employed. While there is a wealth of information on FEM modelling of bolts for standard loading conditions (e.g., tension), the authors are unaware of a model able to replicate both tension-only and combined tension and bending conditions. In this paper, a simplified approach to be used in the framework of FEM is proposed to model the behaviour of high-strength HV bolts which can replicate the failure mechanism of bolts under tension only and combined tension and bending. The bolt assembly is modelled with continuum elements, supplemented by a non-linear spring connecting the nut to the bolt shank. The spring captures the stiffness, resistance, and ductility of the bolt-to-nut threaded connection, reproducing the experimentally observed failure mode in the case of pure tension conditions. A simplified damage model is applied to the continuum finite elements used to model the bolt, which replicates shank failure under combined tension and bending as a result of large local stresses and strains occurring under these conditions. The proposed model captures with good accuracy the actual behaviour of high-strength HV bolts under tension only as well as under combined tension and bending.

Effects of temperature on expansion of concrete due to the alkali-silica reaction: A simplified numerical approach

The effects of temperature on the expansion behavior of concrete due to the alkali-silica reaction (ASR) were assessed through a simplified numerical analysis. Numerical models were constructed based on findings from a literature review. A simplified damage model was implemented to capture interactions between the viscoelasticity of the ASR gel and microstructural damage of the aggregate and paste. The parameters of the damage model were identified by fitting the simulated results to the experimental data. The results indicate that for a given reaction ratio, expansion ability is reduced at higher temperatures during the early and late stages of expansion. The results demonstrate that explicit modeling of chemo-mechanical interactions is important to achieve accurate numerical predictions of expansion behavior.

Multiscale failure analysis of a 3D woven composite containing manufacturing induced voids and disbonds

Multiscale failure simulations of a three-dimensional woven composite repeating unit cell considering six scales, spanning the woven composite mesoscale to the sub-microscale voids, have been performed. The multiscale recursive micromechanics approach, which enables recursive integration of general micromechanics theories over an arbitrary number of length scales, has been employed within the NASA Multiscale Analysis Tool. The multiscale model uses both the generalized method of cells and Mori-Tanaka micromechanics theories and considers failure in the constituent materials using a simple damage model. Baseline results, from a model of a composite containing distributed voids, are compared to uniaxial experimental data for an AS4 carbon fiber/ RTM6 epoxy matrix orthogonal three-dimensional woven composite with good agreement in terms of global stiffness and global failure stress. The multiscale model is then used to examine the nonlinear response of the material to other loading conditions. Case studies, motivated by X-ray computed tomography data, are presented on the effects of manufacturing induced voids and cracks.

Topology optimization of damage‐resistant structures with a predefined load‐bearing capacity

AbstractThis article presents a novel strategy for structural topology optimization considering damage. In engineering practice, structures are typically designed to have a certain load‐bearing capacity, with a minimal material volume or cost. We aim to optimize the topology of a structure to have a minimal weight while guaranteeing a predefined load capacity, considering the softening behavior of quasi‐brittle materials. Two different optimization strategies are presented: a fully nonlinear strategy and a simplified strategy. The fully nonlinear strategy relies on existing nonlinear damage models, which require iterative solution methods, for structural analysis and the computation of the corresponding sensitivities. The simplified strategy uses a simplified damage model, which computes a structure's damage distribution in only one step, greatly reducing computation time. The accuracy of the simplified damage model is controlled by occasional nonlinear simulations—without sensitivity analysis—to calibrate the results. Benchmark tests compare the simplified optimization strategy with the fully nonlinear optimization strategy. While the simplified damage model does not have the same accuracy as nonlinear damage models, results show similar optimized topologies and structural efficiency, with a significant improvement regarding computation time for the simplified optimization strategy.

Fracture prediction in spin forming of anisotropic metal sheets

Fracture often occurs in the spin forming process of thin-walled metal sheets, due to the limited fracture strain and local large plastic deformation of the sheets during the process. However, the accurate fracture prediction is a huge challenge due to the combinations of material anisotropy, complex deformation history and contact boundary conditions in the process. Though there are scattered uncoupled ductile fracture criteria proposed with various deformation mechanisms, reasons for their different fracture prediction abilities remain unclear. Thus in this study, eight popular uncoupled ductile fracture criteria i.e., Freudenthal, C-L, R-T, Brozzo, Oh, Oyane, MMC4 and DF2016, are embedded into an anisotropic constitutive model through VUMAT interface in the ABAQUS simulation software and then realized their fracture prediction in the spin forming process of an anisotropic metal sheet. The results show that the damage accumulation in the spin forming process occurs in a wide range of stress triaxiality, and the most damage accumulation occurs in the stress triaxiality range of 0–1/2. Furthermore, the eight fracture criteria have different prediction abilities in the process and a new deformation history related equivalent fracture strain is proposed to explain these differences. In addition, there exists the abnormal phenomenon that some simple damage models, as Oyane, Oh, etc. provide the more accurate fracture prediction ability than the complex and advanced MMC4 and DF2016 models in the process, and reasons for this phenomenon are explained.

Damage of bond in reinforced concrete: A detailed finite element analysis

AbstractNumerical simulation of the bond is a powerful and versatile tool to analyze different aspects of reinforcement and concrete interaction, such as the formation of internal cracks, damage of concrete around the bar or bond degradation near the cracks. In the present study, a three‐dimensional rib‐scale finite element modeling technique was employed to study the latter phenomena. Numerical models were calibrated using the experimentally measured reinforcement strain profiles in the short tensile reinforced concrete elements reported herein and elsewhere. The selected experimental programs cover a wide range of bar diameters (10–29 mm) that are commonly used in the engineering practice. A parametric analysis was performed to identify the key parameters affecting the bond stress distribution in the vicinity of cracks. Based on the results of the parametric analysis, a simple bond damage model was proposed. Unlike the existing models, which take into account a single parameter, namely, bar diameter, the proposed bond damage model also considers the effect of concrete grade and reinforcement strain in the cracked section.

Ductile Damage Model Based on Void Growth Analysis for Application to Ductile Crack Growth Simulation

AbstractThis study aims to propose the damage model based on of the mechanism for ductile fracture related to void growth and to confirm the applicability of the proposed model to ductile crack growth simulation for steel. To figure out void growth behavior, elastoplastic finite element analyses using a unit cell model with an initial void were methodically performed. From the results of those analyses, it was evident that the relationships between normalized void volume fraction and normalized strain by each critical value corresponding to crack initiation were independent of stress–strain relationship of material and stress triaxiality state. Based on this characteristic associated with void growth, damage evolution law was derived. Then, using the damage evolution law, simple and phenomenological ductile damage model reflecting void growth behavior and ductility of material was proposed. To confirm the validation and application of the proposed damage model, the damage model was implemented in finite element models and ductile crack growth resistance was simulated for cracked components were performed. Then, the simulated results were compared with experimental ones and it was found that the proposed damage model could accurately predict ductile crack growth resistance and applied to ductile crack growth simulation.

Determination of Fracture Limit Line in Principal Strain Space by Shear Tests

The main goal of this paper was to define a new limit line, which expands Forming Limit Curve (FLC) more precisely Fracture Forming Limit Curve (FFLC). The new limit line was defined by damage models transformed from triaxiality-fracture strain space to the major/minor strain space and we focused on the shear area. Because FLC and FFLC have some limitations, for example, some Advanced High Strength Steels (AHSS) fractures before thinning. Another limitation can be seen on the left side of the diagrams in the shear region, where the part can break in the process without crossing the FLC or FFLC. The different shapes of samples were used for finding a new line of the FFLC and Deep Drawing Test (DDT) was used for verification. The fracture points from measurement were used for calibration of simple uncoupled damage models. The simple model means model, which is calibrated based on one or two measurements (tensile test or tensile test + shear test). This paper was used an Advanced High Strength Steel (AHSS) DP1000 sheet with a thickness of 0.8 mm for the experiments.

Development and analysis of composite overwrapped pressure vessels for hydrogen storage

In this study, composite overwrapped pressure vessels (COPVs) for high-pressure hydrogen storage were designed, modeled by finite element (FE) method, manufactured by filament winding technique and tested for burst pressure. Aluminum 6061-T6 was selected as a metallic liner material. Epoxy impregnated carbon filaments were overwrapped over the liner with a winding angle of ±14° to obtain fully overwrapped composite reinforced vessels with non-identical front and back dome layers. The COPVs were loaded with increasing internal pressure up to the burst pressure level. During loading, deformation of the vessels was measured locally with strain gauges. The mechanical performances of COPVs designed with various number of helical, hoop and doily layers were investigated by both experimental and numerical methods. In numerical method, FE analysis containing a simple progressive damage model available in ANSYS software package for the composite section was performed. The results revealed that the FE model provides a good correlation as compared to experimental strain results for the developed COPVs. The burst pressure test results showed that integration of doily layers to the filament winding process resulted with an improvement of the COPVs performance.

A nonlinear BE formulation for analysis of masonry walls considering orthotropy: Fundamentals

In this work, a non-linear Boundary Element (BE) formulation with damage model is extended for numerical simulation of structural masonry walls. The original formulation was presented by other researchers to investigate the concrete material in 2D stress analysis. The formulation proposal is written in terms of domain strain variables and it is based on the consistent tangent operator. A simple damage model is used to represent the material behavior of masonry components and internal variables and cell discretization of the domain are considered. However, for brick masonry it is necessary to take into account the orthotropy in this type of structure. The orthotropy is considered by expressing a residual elastic tensor as the difference of the orthotropic and the isotropic elastic property tensors. The complete integral formulation, using isotropic fundamental solution, and algebraic procedure are developed.

A pragmatic orthotropic elasticity-based damage model with spatially distributed properties applied to short glass-fibre reinforced polymers

This article presents a simple progressive damage model for quasi-brittle materials, combining orthotropic elasticity with a scalar damage model including spatial variation of the damage initiation strain and the crack band method for softening regularization. The model’s performance is first analyzed from a numerical point of view and then demonstrated for tensile tests (0°, 45° and 90°), open-hole tensile tests (0°) and three-point bending (0° and 90°) tests of short fibre-reinforced polypropylene with 15 wt.% and 30 wt.% glass fibres. Despite its simplicity, the model captures the anisotropic elastic and inelastic behaviour observed in experiments. The model is applicable for orthotropic brittle or quasi-brittle materials, where the variability in elastic properties is negligible and the orientation dependency of the fracture strain is small or not relevant for the application.