Damage Kinetics Research Articles

The effect of residual mechanical stresses and vacancy defects on the diffusion expansion of the damaged layer during irradiation of BeO ceramics

The paper presents the results of a study on the application of Raman and UV spectroscopy methods to determine the structural damage kinetics in the near-surface layer of BeO ceramics caused by high-dose irradiation with He2+ ions. Interest in this type of ceramics is due to the combination of its structural and thermophysical parameters, making these ceramics one of the promising classes of materials for microelectronics and structural materials for nuclear reactors, with the possibility of operation in conditions of heightened radiation background. According to the conducted studies, it was established that with the irradiation fluence growth, changes in the nature of deformation structural distortions associated with the accumulation of residual mechanical stresses of tensile and compressive types are observed. At irradiation fluences of 1016-5×1016 Не2+/cm2, tensile stresses play a dominant role in structural distortions, while the value of compressive stresses at fluence growth makes up a small share in the overall nature of the deformations. Moreover, an elevation in the irradiation fluence above 5×1016 He2+/cm2 leads to a rise in the concentration of defects caused by the formation of oxygen vacancies, as well as He-VO type complexes, the presence of which is indicated by the halo intensity growth in the Raman spectra, as well as a change in the intensity of the absorption bands. Analysis of changes in thermophysical parameters revealed that a rise in structural distortions associated with the accumulation of complex defects results in thermal conductivity reduction and a deterioration in heat transfer processes associated with partial amorphization of the damaged layer. Moreover, the established direct relationship between the value of residual mechanical stresses and the degradation of thermal conductivity indicates the cumulative effect of destructive changes caused by irradiation, as well as the influence of diffusion mechanisms on the damaged layer thickness growth.

Enhanced radiation damage tolerance in Zr-doped UO2

This study explores the effect of tetravalent Zr doping on the radiation behaviour of UO2 through a combination of experimental and theoretical approaches. The intrinsic changes that Zr introduces in UO2 were quantified using X-ray diffraction and Raman spectroscopy, which reveal a shrinkage of the lattice volume and the formation of ZrO8-type clusters. Heavy-ion irradiation was carried out on both undoped and doped UO2 under conditions similar to the ballistic regime of fission products in nuclear fuels. Empirical data, together with DTF+U simulations, found that Zr doping modifies the irradiation-induced defect mechanisms by enabling recombination pathways, allowing a rapid recovery of the UO2 lattice. The fundamental mechanisms involving the role of dopant in modifying the radiation damage kinetics are discussed in this paper, as well as the subsequent evolution in fluorite-structured materials relevant to nuclear fuels.

Damage kinetics in high-temperature irradiated Ni crystals

High-temperature (∼800 K) ion irradiation with 380 keV Ar ions was used to modify the surface of Ni single crystals in order to generate radiation defects and mimic the effect of neutrons avoiding sample activation. The modified 800 nm thick layer was analyzed regarding structural and mechanical properties utilizing a combination of experimental and simulation techniques. The ion implantation fluence ranged from 1 × 1014 cm−2 up to 1 × 1016 cm−2, which corresponds to values of displacements per atom from 0.25 to 25, respectively. The structural characterization was performed by Rutherford Spectroscopy in Channeling mode (RBS/C) associated with scanning (SEM) and transmission electron microscopy (TEM). The experimental results were supported by Monte Carlo (McChasy) and Molecular Dynamics (MD-LAMMPS) simulations. The simulations performed using the second generation of the McChasy code show that the influence of bubbles formed inside the material is not negligible and affects the quantitative analysis of defects in the simulated spectra. A second step in damage kinetics was revealed for the highest dose (i.e., 25 dpa) as a consequence of the entanglement of dislocations and agglomeration of noble gas bubbles, which was confirmed by TEM analysis. Moreover, nanomechanical results confirm that Ar bubbles deteriorate mechanical properties such as hardness.

222 nm causes greater protein damage and repair inhibition of E. coli than 254 nm for water disinfection

Germicidal ultraviolet (UV) light has been widely used to inactivate pathogens in water. Emerging alternatives to conventional low pressure (LP) mercury lamps emitting at 254 nm, such as krypton chloride (KrCl) excimer lamps emitting at 222 nm, are gaining acceptance and popularity due to advantages in human safety and disinfection mechanisms. Cyclobutane pyrimidine dimer (CPD) formation kinetics and photolyase damage kinetics were quantified in E. coli for 222 nm and 254 nm UV. Molecular damage and cell regrowth were also quantified after UV irradiation under photorepair and dark repair incubation conditions using a standardized photorepair fluence response protocol. CPDs and photolyase were measured using enzyme linked immunosorbent assays (ELISA). A novel ELISA for photolyase was developed for this study. Culture-based log inactivation UV fluence responses were similar for 254 nm and 222 nm, with Geeraerd model estimates for rate constants of 1.18±0.09 and 1.24±0.08 cm2 mJ−1 for LP and KrCl lamps, respectively. Molecular UV fluence kinetics showed that the rate of CPD formation was greater by LP, but the rate of photolyase damage was greater by KrCl, as supported by the intercepts of repair kinetics. Compared to LP irradiated samples, KrCl irradiated samples exhibited less repair overall. For a given lamp, similar repair was observed between light and dark repair incubations. Percent reactivation rates with respect to photorepair fluence were (3.7±1.4)×10−5 and (–1.3±2.5)×10−5 cm2 mJ-1 for LP and KrCl lamps, respectively. CPDs decreased at a higher rate during repair incubations in LP samples than KrCl samples, and photolyase concentration increased in LP samples but decreased in KrCl samples. The results quantify contributions of photolyase protein damage to disinfection and repair prevention mechanism of KrCl lamps. This study mechanistically demonstrates why KrCl lamps can be applied for UV water disinfection to limit photorepair after treatment. Synopsis: This study used a novel photolyase assay to demonstrate photolyase damage inflicted by krypton chloride excimer lamps contributes to disinfection of bacteria to prevent bacterial photorepair of damaged DNA and regrowth in drinking water treatment.

The interplay of DNA damage and repair, gene expression, and mutagenesis in mammalian cells during oxidative stress.

We investigated the interplay among oxidative DNA damage and repair, expression of genes encoding major base excision repair (BER) enzymes and bypass DNA polymerases, and mutagenesis in mammalian cells. Primary mouse embryonic fibroblasts were challenged with oxidative stress induced by methylene blue plus visible light, and formation and repair of DNA damage, changes in gene expression, and mutagenesis were determined at increasing intervals post-treatment (0 - 192 hours). Significant formation of oxidative DNA damage together with upregulation of Ogg1, Polβ, and Polκ, and no changes in Mutyh and Nudt1 expression were found in treated cells. There was a distinct interconnection between Ogg1 and Polβ expression and DNA damage formation and repair whereby changes in expression of these two genes were proportionate to the levels of oxidative DNA damage, once a 3-plus hour lag time passed (P < 0.05). Equally notable was the matching pattern of Polκ expression and kinetics of oxidative DNA damage and repair (P < 0.05). The DNA damage and gene expression data were remarkably consistent with mutagenicity data in the treated cells; the induced mutation spectrum is indicative of erroneous bypass of oxidized DNA bases and incorporation of oxidized deoxynucleoside triphosphates during replication of the genomic DNA. Our findings support follow-up functional studies to elucidate how oxidation of DNA bases and the nucleotide pool, overexpression of Polκ, delayed upregulation of Ogg1 and Polβ, and inadequate expression of Nudt1 and Mutyh collectively affect mutagenesis consequent to oxidative stress.

The Influence of Microstructural Arrangement on the Failure Characteristics of 3D-Printed Polymers: Exploring Damage Behaviour in Acrylonitrile Butadiene Styrene.

This study investigated how printing conditions influence the fracture behaviour of 3D-printed acrylonitrile butadiene styrene (ABS) under tensile loading. Dog-bone-shaped ABS specimens were produced using the fusion filament fabrication technique, with varying printing angles. Tensile tests were conducted on pre-notched specimens with consistent pre-notch lengths but different orientations. Optical and scanning electron microscopies were employed to analyse crack propagation in the pre-notched specimens. In order to support experimental evidence, finite element computation was implemented to study the damage induced by the microstructural rearrangement of the filaments when subject to tensile loading. The findings revealed the simple linear correlation between the failure properties including elongation at break and maximum stress in relation to the printing angle for different pre-notch lengths. A more progressive damage was found to support the ultimate performance of the studied material. This experiment evidence was used to build a damage model of 3D-printed ABS that accounts for the onset, growth, and damage saturation. This damage modelling is able to capture the failure properties as a function of the printing angle using a sigmoid-like damage function and a modulation of the stiffness within the raster. The numerical results demonstrated that damage pattern develops as a result of the filament arrangement and weak adhesion between adjacent filaments and explains the diffuse damage kinetics observed experimentally. This study concludes with a topological law relating the notch size and orientation to the rupture properties of 3D-printed ABS. This study supports the idea of tailoring the microstructural arrangement to control and mitigate the mechanical instabilities that lead to the failure of 3D-printed polymers.

Study of a mechano-electrochemical model: a numerical and experimental approach

The mechanochemical effects of elasticity and plasticity are introduced into a peridynamic (PD) corrosion model. A PD equation that couples the mechanics and kinetics of electrochemistry is proposed for the first time. This clarifies the influence of the mechanical load in governing the occurrence of diffusion during corrosion. The phase changes experienced by a material are used to characterize the movement of the corrosion boundary, and the concentration of material points is used to characterize the degree and extent of damage caused to the chosen metal. Immersion tests and in situ electrochemical tests are carried out, and the results are used to explore the effects of stress and/or load on the kinetics of environment-induced damage to an aluminum alloy. The model predictions are in good agreement with the experimental observations. The results of this study demonstrate that a coupled mechano-electrochemical PD corrosion model can capture corrosion-induced damage and can be used to study damage propagation upon exposure to an aggressive environment.

Damage kinetics and compression behavior of Al alloy foam using in situ SRμCT

Damage kinetics and compression behavior of Al alloy foam using in situ SRμCT

Compression fatigue of elastomeric foams used in midsoles of running shoes

Due to their excellent specific mechanical properties, closed cell elastomeric foams are the main element in the soles of running shoes to absorb repetitive shocks from strides and to release a maximum of the absorbed energy. However, these cellular materials are gradually damaged. To enhance their mechanical durability by slowing their damage kinetics, it is critical to understand their mechanical behaviour in fatigue. The objective of this work is thus to clarify the link between the microstructure and the fatigue properties of five commercial elastomeric foams used in the midsoles of running shoes. The 3D cellular structures of each foam were finely analysed using X-ray microtomography. Foam samples were then subjected to cyclic compression which were close to running conditions. During cycling, samples exhibited a rapid densification associated with noticeable decreases of (i) the stress levels required to deform them as well as (ii) the cushioning and (iii) the rebound properties. We show that the two midsoles filled with micro-sized mineral fillers present the highest specific mechanical properties during the first compression cycle and during fatigue. However, their damage kinetics and rebound properties could probably be improved by tuning the fillers-matrix compatibility. The lightest foam, being very porous and presenting process-induced tortuous cell walls, is the best cushioning system but exhibits high damage kinetics. The densest foam presents poor specific mechanical properties, but very slow damage kinetics. Its double hierarchical architecture probably prevents the occurrence of micro-cracks in the cell walls.

A spatial measure-valued model for radiation-induced DNA damage kinetics and repair under protracted irradiation condition

In the present work, we develop a general spatial stochastic model to describe the formation and repair of radiation-induced DNA damage. The model is described mathematically as a measure-valued particle-based stochastic system and extends in several directions the model developed in Cordoni et al. (Phys Rev E 103:012412, 2021; Int J Radiat Biol 1–16, 2022a; Radiat Res 197:218–232, 2022b). In this new spatial formulation, radiation-induced DNA damage in the cell nucleus can undergo different pathways to either repair or lead to cell inactivation. The main novelty of the work is to rigorously define a spatial model that considers the pairwise interaction of lesions and continuous protracted irradiation. The former is relevant from a biological point of view as clustered lesions are less likely to be repaired, leading to cell inactivation. The latter instead describes the effects of a continuous radiation field on biological tissue. We prove the existence and uniqueness of a solution to the above stochastic systems, characterizing its probabilistic properties. We further couple the model describing the biological system to a set of reaction–diffusion equations with random discontinuity that model the chemical environment. At last, we study the large system limit of the process. The developed model can be applied to different contexts, with radiotherapy and space radioprotection being the most relevant. Further, the biochemical system derived can play a crucial role in understanding an extremely promising novel radiotherapy treatment modality, named in the community FLASH radiotherapy, whose mechanism is today largely unknown.

Viscoelastic-damageable behavior of sheet molding compound (SMC) composites

The variability of microstructures in the SMC composite induced by the manufacturing process is very important. The volumetric fraction and reinforcement orientation distribution significantly affect the material’s mechanical properties in both the elastic and nonlinear phases, associated with the development of damage phenomena. The distribution of local stresses between the reinforcements and the matrix is conditioned by the privileged orientation of the reinforcements. This, in turn, influences both the elastic mechanical properties and the degradation mechanisms, resulting in a degree of anisotropy. Additionally, SMC composites typically exhibit viscoelastic-damageable behavior. Therefore, it is necessary to characterize the microstructure accurately and comprehensively to effectively manage the mechanical behavior and damage of SMC structures. The research process involved investigating the viscoelastic behavior of randomly oriented Sheet Molding Compound (SMC) composites using Dynamic Mechanical Analysis (DMA) in the glass transition zone. By conducting a thorough analysis of the frequency and temperature-dependent behavior of the viscoelastic material, the experimental results obtained from the DMA test have been modeled. To demonstrate the effect of the matrix, two types of SMSs were utilized: standard SMC and Advanced SMC (A-SMC). The Cole-Cole experimental results fit well with the Perez model showing deformed semi-circles denoting the heterogeneity of the material system used in this study. The aim of this study is to link the WLF Law to the Perez model near the transition zone. The results demonstrated that dynamic properties can be plotted against temperature due to the strong correlation between the experimental and numerical data. Additionally, an increase in the strain rate results in a shift in the damage threshold and a reduction in damage kinetics. These effects are directly related to the damage thresholds and kinetics at the fiber-matrix interface.

Experimental investigation of the effect of infill parameters on dynamic compressive performance of 3D-Printed carbon fiber reinforced polyethylene terephthalate glycol composites

The current investigation evaluates the compressive response of 3D-printed carbon fiber-reinforced PETG thermoplastics to optimize different infill parameters when loaded at high impact pressures (strain rates). The selected parameters for the 3D printing of different samples are the filling pattern (rectilinear and honeycomb) and the filling density (25%, 50%, and 75%). Compression-split Hopkinson pressure bars (SHPBs) combined with a high-speed camera were used to monitor the evolution of the mechanical behavior and damage kinetics of 3D-printed samples in real-time with the variation in strain rate. The results revealed a significant improvement in compressive strength and compressive modulus when the filling density was increased from 20% to 75% for both patterns. However, the combination of a honeycomb pattern with 75% filling presented the best compressive strength, stiffness and damage resistance, irrespective of impact pressure. In particular, the highest compressive strengths, ranging from 35.5 to 56.16 MPa for impact pressures of 1.4 to 2.4 bar, respectively, were obtained with this configuration (75% honeycomb pattern). This represents a substantial difference of 25 to 38% compared with the 75% rectilinear pattern, which showed values below 35 MPa. Another significant result was observed for the compressive modulus, which reached 2787.8 MPa for the honeycomb-filled samples, whereas this value remained below 2000 MPa for the rectilinear pattern.

Damage-failure transition in titanium alloy Ti-6Al-4V under dwell fatigue loads

The role of structural mechanisms responsible for the consequent staging of damage-failure transition as the combination and continuity of ductile and creep kinetics of the structure evolution and the modeling in dwell fatigue regime. Damage-failure transition is considered as critical phenomena, the structural-scaling transition, when the damage develops as specific phase with characteristic stages: nucleation of new phase and the phase growth kinetics. In the case of dwell fatigue, the nucleation stage is associated with slip localization, faceting, voids and microcrack initiation; the phase growth kinetics has the relation to specific non-linearity of the free energy release responsible for the staging of damage-failure transition. Statistically based phenomenological model of damage-failure transition specified the links of macroscopic material parameters with structural parameters responsible for the influence of microstructure on the structure sensitive mechanical properties. The developed conception of modeling of Ti alloys based on the duality of damage kinetics in dwell fatigue loads allowed us to propose the strategy of structural study to provide in perspective the links of structural parameters of /phases with phenomenological parameters responsible for different mechanisms of damage accumulation at LCF and stress hold regimes.

The use of acoustic emission in assessing the ductility loss in steel products under the effect of impact

Acoustic emission (AE) diagnostics was carried out during tensile testing of 20KhN2MA steel samples to study the loss of ductility after the impact. We used V-notched samples (3.3 mm in depth) with overall dimensions of 300 × 20 × 6 mm. The impact in the concentrator zone caused the depletion of the plasticity of the material, which was accompanied by a decrease in the partial fraction of ductile fracture and an increase in brittle fracture. The test samples were divided into six batches. The samples of the first batch were not subjected to the impact. In the second batch, the impact energy was 50 J, in the third — 75 J, in the fourth — 100 J, in the fifth — 125 J and in the sixth — 150 J. The rupture tests were carried out at room temperature and at a speed of the movable traverse of 1 mm/min. The kinetics of damage in the notch zone during loading was monitored using the acoustic emission (AE) method and video recording. Processes of brittle and ductile (caused by cleavage and shear, respectively) destruction of the crystal lattice of a metal differ primarily in the speed and duration of stress waves. To separate AE pulses generated by these processes, spectrograms of time-frequency transformations and waveforms were analyzed. Pulse selection was carried out using a complex parameter reflecting the steepness of the amplitude drop at the phase of signal attenuation. Boundary values were determined that allow separation of the recorded pulses into flows caused by ductile and brittle structural damage to structural steels. It is shown that manifestation of the effect of impact on the exhaustion of the plastic properties of steel 20KhN2MA becomes noticeable when the level of specific work exceeds 50 J/cm2. Moreover, with an increase in the specific work up to 150 J/cm2, the weight content of location pulses characterizing the kinetics of brittle destruction of structural bonds increased by 3 – 4 times, relative to that recorded for the samples without impact. This result correlates with the duration of the rupture test of the samples, which was reduced by three times when the level of the specific work increased to 150 J/cm2

Discovery of novel benzimidazole acyclic C-nucleoside DNA intercalators halting breast cancer growth.

Breast cancer continues to be the most frequent cancer worldwide. In practice, successful clinical outcomes were achieved via targeting DNA. Along with the advances in introducing new DNA-targeting agents, the "sugar approach" design was employed herein to develop new intercalators bearing pharmacophoric motifs tethered to carbohydrate appendages. Accordingly, new benzimidazole acyclic C-nucleosides were rationally designed, synthesized and assayed via MTT(3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay to evaluate their cytotoxicity against MCF-7 and MDA-MB-231 breast cancer cells compared to normal fibroblasts (Wi-38), compared to doxorubicin. (1S,2R,3S,4R)-2-(1,2,3,4,5-Pentahydroxy)pentyl-1H-5,6-dichlorobenzimidazole 7 and (1S,2R,3S,4R)-2-(1,2,3,4,5-pentahydroxy)pentyl-1H-naphthimidazole 13 were the most potent and selective derivatives against MCF-7 (half-maximal inhibitory concentration[IC50 ] = 0.060 and 0.080 µM, selectivity index [SI] = 9.68 and 8.27, respectively) and MDA-MB-231 cells (IC50 = 0.299 and 0.166 µM, SI = 1.94 and 3.98, respectively). Thus, they were identified as the study hits for mechanistic studies. Both derivatives induced DNA damage at 0.24 and 0.29 μM, respectively. The DNA damage kinetics were studied compared to doxorubicin, where they both induced faster damage than doxorubicin. This indicated that 7 and 13 showed a more potent DNA-damagingeffect than doxorubicin. Docking simulations within the DNA double strands highlighted the role of both the heterocyclic core and the sugar side chain in exhibiting key H-bond interactions with DNA bases.

Recovery kinetics following sprint training: resisted versus unresisted sprints.

To determine the recovery kinetics of performance and exercise-induced muscle damage following different sprint-training protocols. In a crossover design, ten male and female athletes (20.6 ± 2.4years) performed 2× (3 × 20m: 2min rest) and 1× (3 × 30m: 3min rest) of: (a) unresisted sprints (UST), (b) resisted sprints with 10% of body mass (BM) load (RST10), (c) resisted sprints with 20% BM load (RST20), against a control trial (no-training). Blood lactate (mmol/L) increased post-training versus pre-training in all sprint-training trials (6.7 ± 2.4 vs 1.2 ± 0.2, 5.6 ± 2.4 vs 1.3 ± 0.3, 7.3 ± 2.7 vs 1.2 ± 0.3, in UST, RST10, RST20, respectively), as did creatine kinase (U/L) 24h, 48h and 72h post-training (UST: 251 ± 173, 238 ± 154, 209 ± 115 vs 155 ± 9, RST10: 252 ± 134, 240 ± 83, 218 ± 103 vs 164 ± 106; RST20: 237 ± 133, 323 ± 303, 262 ± 184 vs 179 ± 106, respectively). DOMS of knee-extensors (KE) and knee-flexors (KF) increased post-training up to 72h in all sprint-training trials versus pre-training (ranging from 1.6 ± 1.3 to 3.8 ± 2.8 vs 1.0 ± 0, respectively). Eccentric torque (Nm) of the KE of the non-dominant limb, decreased 24h post-training versus pre-training in all sprint-training trials (UST: 249 ± 49 vs 266 ± 54; RST10: 229 ± 52 vs 273 ± 72; RST20: 253 ± 6 vs 262 ± 56), as did that of the KF of the dominant limb (UST: 135 ± 29 vs 144 ± 26; RST10: 130 ± 29 vs 140 ± 25; RST20: 139 ± 33 vs 142 ± 26). 10-m sprint-time (s) increased 48h post-training versus pre-training (1.81 ± 0.15 vs 1.77 ± 0.11), and 30-m sprint-time increased 24h, 48h, 72h post-training versus pre-training (4.35 ± 0.36, 4.40 ± 0.44, 4.33 ± 0.41 vs 4.21 ± 0.34, respectively), only in RST20. Unresisted and resisted sprint-training induces prolonged reduction of muscle strength (24h), and sprinting performance (72h), associated with prolonged increase of DOMS and CK (72h).

Comparative evaluation of antimicrobial activity of human granulysin, bovine and porcine NK-lysins against Shiga toxin-producing Escherichia coli O157:H7.

Shiga toxin-producing Escherichia coli (STEC) O157:H7 (O157) is a foodborne pathogen causing human disease ranging from hemorrhagic colitis and hemolytic uremic syndrome to kidney failure, while remaining harmless to cattle, its primary reservoir. The severity of the human disease associated mainly with Shiga toxin production and a global emergence of antibiotic resistant STEC highlights the need for effective non-antibiotic, pre-harvest strategies to reduce O157 in cattle, the principal source of human infection. Towards this goal three synthetic antimicrobial peptides (AMPs): human granulysin (hGRNL), bovine NK-lysin (bNK2A), and porcine NK-lysin (pNKL), were tested in vitro against O157 isolates. As expected, circular dichroism spectroscopy findings were consistent with a predominantly α-helical conformation for all three AMPs in an environment mimicking bacterial outer surface or liposaccharides. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations of hGRNL (200 μM), bNK2A (12.5 μM against strain 86-24 and 25 μM against EDL933), and pNKL (6.25 μM) were determined using the Clinical and Laboratory Standards Institute broth microdilution method in Müeller-Hinton broth (cation-adjusted). The bNK2A and pNKL AMPs did not induce Shiga toxin expression in O157 at MIC, as there was a significant decrease or no change in toxin expression following 4- or 20 h incubation with the AMPs; bNK2A p <0.0001 (4 h) and p = 0.4831 (20 h); pNKL p <0.0001 (4 h) and p = 0.0001 (20 h). Propidium iodide uptake assay revealed faster O157 membrane damage or killing kinetics with bNK2A and pNKL compared to hGRNL. Nonetheless, transmission electron microscopy demonstrated that all three AMPs mediated damage to O157 membranes. In contrast, the three AMPs showed minimal cytotoxicity (<2%) against cattle red blood cells at tested concentrations (0.39-50 μM). Overall, our results demonstrate the potential for bNK2A and pNKL to be further developed into novel non-antibiotic agents to reduce O157 shedding in cattle.

Acoustic emission, damage and fracture mechanisms of structural steel under mixed-mode loading

Mechanical and acoustic properties, damage kinetics and fracture mechanisms of 30CrMnSiA structural steel under mixed loading modes (I + II) have been investigated. It is shown that the change in loading mode leads to changes in strength and acoustic parameters, microcrack accumulation kinetics and fracture mechanism. The greatest changes in average frequency (AF) and rise angle (RA) of acoustic emission signal with increase in load are observed when the sample is oriented at an angle of 15°, at which the AF decreases linearly depending on the average values of the signal RA. However, the acoustic emission characteristics are not only determined by the loading mode but also by the fracture mechanism: brittle fracture at an angle of 45° is accompanied by increase in many acoustic characteristics including RA and AF parameters and a change in the type of time dependence of the total number of acoustic signals (ΣNAE), bAE – value and cumulative energy of acoustic emission signals (∑EAE). The frequency analysis showed that the average values of the peak frequency and the frequency centroid at rupture exceed the values of these parameters under mixed loading modes. A change in the failure mechanism under mixed loading modes does not affect these acoustic characteristics.Analysis of the kinetics of microcrack accumulation showed that the rate of damage accumulation decreases as the shear component of the load increases.

On the Emergence of the Deviation from a Poisson Law in Stochastic Mathematical Models for Radiation-Induced DNA Damage: A System Size Expansion.

In this paper, we study the system size expansion of a stochastic model for radiation-induced DNA damage kinetics and repair. In particular, we characterize both the macroscopic deterministic limit and the fluctuation around it. We further show that such fluctuations are Gaussian-distributed. In deriving such results, we provide further insights into the relationship between stochastic and deterministic mathematical models for radiation-induced DNA damage repair. Specifically, we demonstrate how the governing deterministic equations commonly employed in the field arise naturally within the stochastic framework as a macroscopic limit. Additionally, by examining the fluctuations around this macroscopic limit, we uncover deviations from a Poissonian behavior driven by interactions and clustering among DNA damages. Although such behaviors have been empirically observed, our derived results represent the first rigorous derivation that incorporates these deviations from a Poissonian distribution within a mathematical model, eliminating the need for specific ad hoc corrections.

Analysis of the Impact of Rubber Recyclate Addition to the Matrix on the Strength Properties of Epoxy-Glass Composites.

Currently, there is a noticeable trend of modifying new materials by using additives from the recycling of harmful waste. This is to protect the environment by using waste to produce composites and at the same time to reduce the cost of their production. The article presents an analysis of the impact of the use of rubber recyclate obtained from the utilization of car tires as a sandwich layer of epoxy-glass composites and its impact on the strength parameters of the composite. The presented research is an extension of the previously conducted analyses on composite materials modified with the addition of rubber recyclate. The four variants of the materials produced contained the same percentage amount of rubber recyclate, but differed in the way it was distributed and the number of layers. Static tensile tests as well as impact strength and kinetics of damage to samples made with and without the addition of recyclate were carried out. Observation of the structures of the materials with the use of SEM was also performed. A significant influence of the method of distributing the recyclate in layers on the strength parameters of the materials was found. In the case of composites with three and two sandwich layers of recyclate, more favorable results were obtained compared to the blank sample. In addition, the values of the impact strength measurements were subjected to statistical analysis at the significance level of α = 95%. The distributions were tested for normality with the Shapiro-Wilk test, differences between pairs were tested with the Student's t-test for dependent groups, and ANOVA differences were tested for independent groups. Using the Student's t-test, it was confirmed that between the pairs of variables in the configurations reference sample and modified sample, there were significant statistical differences in the distribution of impact strength measurement results for all the analyzed materials. Statistical analysis showed a significant usefulness in the selection of the material with the best strength parameters and a significant role of statistical methods in the study of anisotropic materials.