Damage Regime Research Articles

Probing nonlinear excitation conditions: photoluminescence and nonlinear absorption studies in laser-irradiated dielectrics

Understanding the fundamentals of laser-matter interactions is crucial for developing and optimizing ultrafast laser processing strategies. In optically transparent solids, the key event by which energy is deposited in the material is through the generation of an electron–hole plasma via nonlinear excitation mechanisms. As the energy stored in the plasma relaxes, local distortions of the lattice may occur, such as point defects. These defects give rise to new discrete energy states located in the bandgap. In this study, we investigate how the presence of these energy states influences the transmission of ultrashort near-infrared laser pulses in fused silica. Experimental results of laser pulse transmission and photoluminescence from defects are correlated with optical microscopy of the irradiated spots, allowing us to identify different nonlinear interaction regimes. Numerical simulations indicate that photo-induced defects influence the nonlinear losses of ultrashort laser pulses and explain why a non-destructive damage regime with detectable excitation is only observed for a narrow intensity range in multipulse experiments.

Evaluation of neutron radiation damage on gold microstructure using MCNP

The effects of radiation interaction with materials have been studied over the years on metals, semiconductors, and other alloys. The result of these interactions constitutes microstructural effects, like point defects, dislocation loops, and void swellings. The accumulation of these defects results to damage on the macroscopic scale. This study is aimed to predict the magnitude of radiation damage in gold sample due to neutron irradiation. Neutron flux, displacement-per-atom rate, as well as heat deposition, were calculated in MCNP6.2, using the SAFARI-1 reactor model. The total neutron flux and dpa rate in the gold sample were determined to be 2.262 × 1011 n.cm−2.s−1 and 5.209 × 10−7 s−1 respectively. Also, the total heat deposition due to neutrons and photons was 2.515 × 10−6 W.g−1 and 0.513 W.g−1, respectively. Hence, the predicted neutron dpa and flux for the gold sample in this study suggest a heavy damage regime.

Gradient-extended damage modelling for polymeric materials at finite strains: Rate-dependent damage evolution combined with viscoelasticity

While the strong rate-dependent effects of polymeric materials in the elastic regime are well studied, the time-dependent effects that arise in the inelastic damage regime are still difficult to model and are therefore the subject of investigation. In this work, we propose a simple but flexible formulation for the description of rate-dependent damage combined with viscoelasticity at finite strains. This model is based on a finite viscoelastic material formulation combined with a Perzyna-type approach to describe the damage evolution equation. With this formulation we are able to describe both damage due to creep and relaxation of the polymer matrix in both a qualitative and quantitative manner. Besides the main aspects of thermodynamic consistency, we describe the numerical implementation into finite elements and present numerical examples to demonstrate the capabilities of the proposed model. At last, we compare the model with experimental data and show the good predictive capabilities of this newly developed material model.

Digital image correlation analyses of masonry infilled frame: Uncertainty-based mesh refinement and damage quantification

Masonry walls are subjected to cyclic lateral loads to study damage caused by earthquakes. Imaging techniques are useful to quantify crack networks in such tests, where preferential locations for their initiation are not present. However, detecting small cracks in large structures is challenging. It is shown that finite element (FE)-based digital image correlation (DIC) can detect and quantify cracks by combining optical and mechanical information of a cyclic shear experiment performed on a full-size masonry wall. Pixel-wise gray-level residuals and elementary crack opening displacement fields are the key quantities of the proposed framework. Detection criteria based on standard uncertainties guided the application of new DIC strategies (i.e., mechanical regularization, mesh adaption, and damage). Two damage regimes were quantified. Zigzagged cracks were first formed, for which their opening displacements were on average less than 0.5 mm with very limited damage. They were followed by sliding shear cracks, whose mean opening displacements varied between 1 and 3 mm, and damage developed in a more gradual and extended way. Such rich full-field data set may be used for validating damage models up to full-scale simulations.

Liquid–Solid Impact Mechanism, Liquid Impingement Erosion, and Erosion-Resistant Surface Engineering: A Review

Liquid impingement erosion has been known as mechanical degradation, where the original material is removed progressively from a solid surface due to continued exposure to impacts by high-speed liquid droplets. This is a major issue in many industries, including aerospace and aviation and power generation, particularly gas and steam turbines, nuclear power plants, and wind energy. Tremendous numerical and experimental studies have been performed so far to understand the physical phenomena involved in this process and to improve the erosion resistance of different surfaces. In this review paper, first, the liquid–solid impact in a wide range of relative velocities is reviewed fundamentally. Then, the liquid impingement erosion of metals, including damage regimes and damage accumulation mechanisms, as well as the role of solid properties on erosion performance are explained. Finally, promising water droplet erosion-resistant materials and surface treatments are discussed. This review paper is intended to summarize the present knowledge of the different mechanisms involved in the liquid impingement erosion process.

Finite element implementation of the aortic double-dispersion fibre model and development of a predictive damage model

With the development of next-generation cardiovascular prosthesis, the requirement for more advanced simulations for predicting the mechanical response of biological tissue has arisen. Finite-element analysis represents a powerful tool capable of simulating complex behaviours within this framework. The present work proposes the computational implementation of an advanced constitutive model for the fibre-reinforced tissue making up the aortic wall. The formulation available in literature is numerically implemented within the FE software Abaqus© through specific user subroutines, and model predictions are compared with the already available single-dispersion-model results. The influence of each dispersion parameter on the macroscopic behaviour is analysed and discussed. Finally, the model is extended by a damage regime based on strain invariants, which is capable of considering the influence of patient ageing on the mechanical response failure strain. The user subroutines are here provided in the Appendix for applications.

Expected radiation environment and damage for YBCO tapes in compact fusion reactors

We investigate the neutron damage expected in high-temperature superconducting tapes that will be employed in compact fusion reactors. Monte Carlo simulations yield the expected neutron spectrum and fluence at the magnet position, from which the primary knock-on atom energy distributions can be computed for each atomic species comprising the superconductor. This information is then employed to characterize the displacement cascades, in terms of size and morphology, through molecular dynamics simulations. The expected radiation environment is then compared with the neutron spectrum and fluences achievable at the facilities currently available for experimental investigation in order to highlight similarities and differences that could be relevant to the understanding of the radiation hardness of these materials in real fusion conditions. We find that the different neutron spectra result in different damage regimes, the irradiation temperature influences the number of generated defects, and the interaction of the neutrons with the superconductor results in a local increase in temperature. These observations suggest that further experimental investigations are needed in different regimes and that some neutron shielding will be necessary in compact fusion reactors.

Punitive damages for intellectual property infringements in China – A cross-jurisdictional analysis

China’s Civil Code provides for a system of punitive damages. In particular, it affirms the content of punitive damages for intellectual property rights. An analysis of the punitive damages regime for intellectual property rights in China aims to introduce to the reader legal elements for the entitlement of punitive damages, methods of quantification as well as existing problems found in the implementation of relevant provisions in China. A comparison is made between the concept of punitive damages under both common law and civil law jurisdictions with the example of the U.S. and Germany, and some recommendations are provided for foreign rights holders and the Chinese legislators regarding the implementation of punitive damages.

Exploring Ductility in Dental Ceramics

Two damage regimes—“brittle” and “ductile”—have been identified in the literature on ceramic grinding, machining, grit blasting, and wear. In the brittle regime, the damage mechanism is essentially crack formation, while in the ductile region, it is quasiplasticity. Onset of the brittle mode poses the greater threat to strength, so it becomes important to understand the mechanics of ductile–brittle thresholds in these materials. Controlled microcontact tests with a sharp indenter are employed to establish such thresholds for a suite of contemporary computer-aided design/computer-aided manufacturing dental ceramics. Plots of flexural strength S versus indentation load P show a steep decline beyond the threshold, consistent with well-established contact mechanics relations. Threshold dimensions occur on a scale of order 1 µm and contact load of order 1 N, values pertinent to practical grit finishing protocols. The ductile side of ceramic shaping is accessed by reducing grit sizes, applied loads, and depths of cut below critical levels. It is advocated that critical conditions for ductile shaping may be most readily quantified on analogous S(P) plots, but with appropriate machining variable (grit size, depths of cut, infeed rate) replacing load P. Working in the ductile region offers the promise of compelling time and cost economies in prosthesis fabrication and preparation.

Microscopic Kinetics in Poly(Methyl Methacrylate) Exposed to a Single Ultra-Short XUV/X-ray Laser Pulse.

We study the behavior of poly(methyl methacrylate) (PMMA) exposed to femtosecond pulses of extreme ultraviolet and X-ray laser radiation in the single-shot damage regime. The employed microscopic simulation traces induced electron cascades, the thermal energy exchange of electrons with atoms, nonthermal modification of the interatomic potential, and a triggered atomic response. We identify that the nonthermal hydrogen decoupling triggers ultrafast fragmentation of PMMA strains at the absorbed threshold dose of ~0.07 eV/atom. At higher doses, more hydrogen atoms detach from their parental molecules, which, at the dose of ~0.5 eV/atom, leads to a complete separation of hydrogens from carbon and oxygen atoms and fragmentation of MMA molecules. At the dose of ~0.7 eV/atom, the band gap completely collapses indicating that a metallic liquid is formed with complete atomic disorder. An estimated single-shot ablation threshold and a crater depth as functions of fluence agree well with the experimental data collected.

A global–local approach for progressive damage analysis of fiber-reinforced composite laminates

The present work applies the global–local technique to the progressive damage analysis of fiber-reinforced composite laminates. A one-way, loosely-coupled global–local approach is developed as a combination of a low-fidelity linear global analysis and a high-fidelity local nonlinear analysis of specific regions within the structure, where damage is expected to occur. The local model is based on higher-order structural theories derived using the Carrera Unified Formulation (CUF), and specifically, Lagrange polynomials are used to model each ply through its thickness, leading to a layer-wise model. Composite damage is described using the CODAM2 material model, which is based on continuum damage mechanics. Initial assessments compare the relative performance of 3D finite elements (FE), 1D-CUF, and the proposed global–local approach via the free-edge stress analysis of a stiffened composite plate. The proposed technique is then used to predict the tensile strength of an open-hole specimen. The last assessment simulates damage progression within an over-height compact tension specimen using the global–local approach. Verification and validation of results are carried out via refined models and experiments from literature. The results demonstrate the accurate evaluation of 3D stress fields and composite laminates’ mechanical response in the progressive damage regime. A multi-fold improvement in the computational cost is shown when compared to full-scale CUF analyses and indicates this technique’s strong potential towards the computationally-efficient high-fidelity analysis of complex and large-scale composite structures.

Nature-Based Engineering: A Review on Reducing Coastal Flood Risk With Mangroves

Integration of mangroves in projects to reduce coastal flood risk is increasingly being recognised as a sustainable and cost-effective alternative. In addition to the construction of conventional hard flood protection infrastructure, mangroves not only contribute to attenuating flood events (functionality), they also recover in, and adapt to, a changing climate (persistence). The implementation of mangroves in flood risk reduction, however, remains complex. This is because the innate functionality and persistence of mangroves depend on a range of environmental conditions. Importantly, mangroves may collapse when environmental impacts or climatic changes exceed key system thresholds, bringing uncertainty into a situation where failure could endanger lives and livelihoods. The uncertainties in mangrove functionality and persistence can be dealt with by (1) improving insights in how ecological and physical processes affect mangrove functionality and persistence across scales, (2) advancing tools to accurately assess and predict mangrove functionality and persistence, and (3) adopting an adaptive management approach combined with appropriate engineering interventions to enhance mangrove functionality and persistence. Here, we review existing evidence, monitoring techniques and modelling approaches from the viewpoint of mangrove functionality and persistence. Inspired by existing guidelines for Nature-based Solutions (NbS) to reduce flood risk, we provide an operationalization for this new approach. In addition, we identify where further research efforts are required for the practical application of mangroves in coastal flood risk management. Key aspects in the variability and uncertainty of the functionality and persistence of mangroves are their failure and recovery mechanisms, which are greatly site- and storm-specific. We propose five characteristic damage regimes that result in increasing reductions of mangrove functionality as well as post-storm recovery periods. Further research on the quantification of these regimes and their thresholds is required for the successful integration of mangroves in coastal flood risk management. Ultimately, the key challenge is the development of adaptive management strategies to optimise long-term mangrove functionality and persistence, or their resilience. Such adaptive strategies should be informed by continued mangrove functionality and persistence assessments, based on continued monitoring and modelling of key mangrove thresholds, and supported through well-established guidelines.

Tropical Oil Pollution Investigations in Coastal Systems [TROPICS]: A 32-year Review of Response and Recovery

ABSTRACT In 1984, the Tropical Oil Pollution Investigations in Coastal Systems (TROPICS) experiment began in Bahia Almirante on the Caribbean coast of Panama. This study sought to compare the impacts of a severe, but realistic spill of untreated crude oil versus chemically treated (dispersed) crude oil on tropical marine reef, sea-grass, and mangrove ecosystems. The aim of the study was to identify and evaluate the environmental trade-offs of dispersant use in tropical marine and subtidal systems. As a result of continuing research at the site, the study became one of the most comprehensive field experiments examining the long-term impacts of oil and dispersed oil exposures in nearshore tropical communities. Consequently, TROPICS has been the foundational and seminal field study which served as the historical antecedent for Net Environmental Benefit Analysis (NEBA), as well as the basis for follow-on Spill Impact Mitigation Analysis (SIMA) and Comparative Risk Analysis (CRA) for oil spill planning, preparation, and response. From the initial experiment in 1984, through three decades of study and data collection visits, the coral reef, seagrass, and mangrove communities have exhibited significantly different damage and recovery regimes, depending on whether the sites were exposed to non-treated crude oil or dispersed crude oil. While this study does not definitively determine whether or not dispersants should be applied in tropical nearshore environments, it is illustrative of the environmental and ecosystem trade-offs between surface oil impacts to the shoreline, compared to water column exposure from chemically dispersed oil. This paper provides an overview of the results and observations reported in numerous previous TROPICS publications, as a progression of damage and recovery over time. With this perspective, planners and responders can use this study to predict what damages/recoveries may be expected from an oil spill incident in this environment. The results of the TROPICS experiment are examined within the context of this recent parallel research from the perspective of ongoing implications for oil spill preparedness and response.

Antitrust Damages, Consumer Harm, and Consumer Collective Redress

The European Union (EU) Antitrust Damages Directive (Directive) was enacted in December 2014 after nearly a decade of consultations—its implementation was due by 27 December 2016.1 The Directive entails a number of requirements reforming the Member States’ substantive and procedural law, thereby specifying the European damages regime. It seeks to boost private enforcement and, in particular, to enable each purchaser that suffers damage due to infringements of competition law to claim compensation. The main objective of the Directive is the attainment of ‘full compensation’, with ‘deterrence’ being stipulated as an important secondary goal.2 ... This paper brings into focus the harm borne by final consumers. Any infringement which raises prices to final consumers, either directly or indirectly through the supply chain, may harm such consumers in two different ways. First, final consumers who made some purchases during the infringement period (e.g. at the time a cartel was in place) may have done so at inflated prices. We refer to this as the ‘overcharge effect’. Second, final consumers who refrained from purchasing (or reduced their purchase volume) during the infringement period only because of the inflated prices, but who would have purchased (more) absent the infringement, suffered from a so-called ‘lost consumption effect’. This damage component, equivalent, in economic terms, to the deadweight loss generated by the infringement, captures the benefits (the utility) that consumers would have derived from all the purchases which did not effectively take place because of the infringement. No matter how straightforward the existence of the ‘lost consumption effect’ may be from an economic point of view, it is very difficult, from a legal perspective, for individual consumers to prove that they would have made a purchase if the prices were lower but refrained from doing so due to the infringement. Hence, we argue that all necessary actions—in particular enabling consumer collective redress mechanisms—should be taken to facilitate compensation for the harm resulting from the ‘overcharge effect’ in order to guarantee that the final consumers benefit, at least, from viable enforcement mechanisms related to that share of their overall harm. In this paper, we present the economic and legal arguments supporting our views.

Performance of bio-inspired cross-laminated timber under blast loading – A numerical study

Cross-laminated timber (CLT) is recently attracting significant attention due to the high demand for environmentally friendly materials. As a result, the number of buildings and structures comprising CLT is increasing. However, CLT exhibits brittle behavior which can be detrimental to its performance under blast loads. The structure of CLT shows a striking resemblance to that of conch shells, which is also highly composed of brittle materials but exhibits excellent damage tolerance. This paper mimics numerous features from the cross-lamellar structure of conch to enhance the performance of CLT under blast loading. Numerous finite element models were developed to simulate the behaviors of bioinspired conch-like panels under blast loading, and their performance was benchmarked against a traditional CLT panel. The energy dissipation, peak reaction force, and peak displacement and velocity were used as the key performance criteria. The results showed that the conch-like panel can improve the performance of CLT under blast loading through several damage mitigating mechanisms, which increased energy dissipation by up to 82% in the low damage regime, reduced the reaction force by up to 11% in the moderate damage regime and reduced the back face fragment velocity by up to 28% in the high damage regime.

Characterizing and modeling the progressive damage of off-axis thermoplastic plies: Effect of ply confinement

Although the mechanisms of degradation are, overall, quite similar between thermoset and thermoplastic composites, thermoplastic laminates exhibit a higher ductility. Because of that, classical models developed for thermosets fail in predicting accurately the response of thermoplastic-based laminates.Here, we demonstrate that simulations based on the properties identified on isolated thermoplastics unidirectional plies, as usually done for thermosets, result in large errors. This is explained by the significant load-bearing capacity of the ply in the transverse direction that remains even after the first-ply failure, as a result of the confinement provided by adjacent plies. This effect also exists in thermosets, but it is usually limited due to the brittle nature of the resin. We are improving the mesoscale damage modeling in the off-axis direction by introducing this confinement effect in an original way. We are using a pragmatic approach consisting of separating the progressive damage into two parts called the “diffuse damage regime” and the “transverse-cracking regime”, which we describe by two distinct damage parameters. We show that the proposed method accurately predicts the nonlinear damage behavior of the off-axis laminates, and is a viable path to tailor the classical mesoscale damage model to glass fiber-reinforced thermoplastic composites.

Damages Arising from Contraventions of Competition Act 89 of 1998

Persons who have suffered loss or damage as a result of a prohibited practice in terms of the Competition Act 89 of 1998 (the Act) have the right to recover such damage in the civil courts. This right is expressly provided for in section 65 of the Act. To date South Africa has failed to usher in an efficient and effective environment for section 65 civil damages actions, despite growing success being achieved by the competition authorities in uncovering and prosecuting firms for contraventions of the Act, including prohibited practices. Understanding how section 65 rights might be vindicated and whether South Africa's damages regime is adequate to deal with potentially complex damages actions within the realm of competition law contraventions, a starting point would be to gain certainty as to the classification of the nature of section 65 damages. This article seeks to evaluate the arguments of whether these damages actions should be properly classified as statutory or delictual actions by the South African civil courts.
 

Laser damage of silica optical windows with random antireflective structured surfaces

High intensity nanosecond laser pulses induce damage on uncoated optics and antireflection (AR) coated optics with thin film boundaries. Structured surfaces with AR performance have shown higher damage resistance than conventional AR coatings. This work explores laser-induced damage threshold (LIDT) of random antireflective surface structures (rARSS), covering interfaces of planar fused silica substrates, using a 7 ± 1 nanosecond duration, single damaging pulse at 1064-nm wavelength. The rARSS treated windows were optimized for AR at 1064 nm, and transmittance of each treated interface was increased by 3.2% per ISO 13697. Incident fluence was controlled near LIDT for both entry and exit sides. Multiple locations were tested for each fluence setting in accordance with ISO 21254 1-on-1 LIDT testing. Double-sided and single-sided rARSS, orientation with both entrance-side and exit-side treatments, were tested to determine effects random structures have in damage induced by field enhancement on the exit side. Results show that rARSS on a single side of an optic have higher resistance to onset of laser damage when located at entry (structured) side. All tests resulting in damage of polished and single-sided rARSS oriented on exit side were ballistic on beam exit facet, showing surface cracks. Results from rARSS located on beam entry side (both single- and double-side treated) showed nonballistic damage and densification of rARSS features from localized melting or reflow, capping the rARSS but still preserving effective-gradient index and rARSS transmission enhancement. This suggests that the localized melting of the rARSS optic surface does not constitute damage optically, or at least not catastrophically within the prebulk damage regime. Therefore, it is possible to foresee the onset of true damage within an optical system via tracking transmission drop, and swap optics out before catastrophic system failure. The drop in transmission acts as an early warning system, making these rARSS optics an invaluable tool in high-energy laser development.

Bird-striking damage of rotating laminates using SPH-CDM method

Bird strike represents a major hazard to civil aviation. In this paper, impact damage under high velocity is numerically investigated by means of non-linear explicit finite element analysis. We mainly focus the influence of rotational speeds on damage modes and energy variations of bird impact on a circular laminated plate. The Smoothed Particle Hydrodynamics method and an equation of state were employed for the bird projectile. A Continuum Damage Mechanics approach has been applied to simulate failure initiation and damage evolution in unidirectional composite laminates. Hashin's failure initiation criteria have been employed to be able to distinct lamina failure modes. Two damage regimes are identified with respect to the rotational speeds, i.e. impact-dominated damage and rotation-dominated damage. A threshold rotational speed exists for the rotating thin plate in terms of damage regimes. The results can serve as design guidelines in future full-scale or part-scale study of rotating laminated structures.

Damage behaviour of full-scale straight pipes under extreme cyclic bending conditions

Requirements of industrial piping and pipelines to withstand extreme cyclic loading conditions have been motivating increasing interest on a particular extreme fatigue regime: the ultra-low cycle fatigue (ULCF). This damage domain corresponds to a transition between low-cycle fatigue and monotonic ductile damage. Albeit better understanding of this damage regime is required, very few studies are available covering full-scale testing. This study aims at investigating the performance of X60 and X65 piping steels, subjected to extreme cyclic loading conditions resulting in a reduced number of fatigue cycles (Ni<100). Experimental tests were carried out on full-scale straight pipes subjected to cyclic pure bending, which were performed under the framework of the ULCF RFCS/EU project. Additionally to the large-scale tests, plain material was also tested under monotonic and ULCF conditions, supported by small-scale smooth and notched specimens. Large-scale tests were simulated by means of elastoplastic finite element models in order to reproduce the local plastic instability (buckling) where fatigue cracking was verified. Classical Coffin-Mason relation and a modified Xue relation were calibrated using small-scale testing data, the latter relation accounting for triaxiality and Lode angle stress tensor dependencies. The referred models were applied in the damage prediction of the full-scale pipes and results compared with code based procedures such as the ones proposed in the ASME VIII, Div.2. In general, the incorporation of the stress state parameters in the computation of ULCF damage produced improved predictions with respect to the pure strain range based models as the Coffin-Manson or ASME VIII, Div.2 code.