Damage Model Research Articles

Simulating the onset of damage in DCDC tests using a novel gradient‐extended damage model for tension‐compression asymmetry

AbstractIn the present work, an existing framework for gradient‐extended damage is extended to simulate the damage onset in double cleavage drilled compression (DCDC) tests. The main idea is to consider the different evolution of the damage variable under tensile and compressive loading. More specifically, the star‐convex decomposition is exploited to split the strain energy into an active part and an inactive part, and only the active part drives the evolution of the damage variable in the compressive regime. A parameter adopted in the star‐convex decomposition is applied to calibrate the compressive strength independently from the tensile strength, such that the current model can simulate different types of the damage onset. Furthermore, the strengthening effect induced by damage hardening is discussed in this work.

Protective Mechanism of Sea buckthorn Proanthocyanidins Against Hydrogen Peroxide-Introduced Oxidative Damage in Adult Retinal Pigment Epithelial-19

Retinal pigment epithelial (RPE) is an oxidation-resistant cell. But if it is subjected to various harmful stimuli for a prolonged period, an excessive amount of oxyradical will be generated to cause retinal dysfunction. We investigated and elucidated the protective mechanism of Sea buckthorn proanthocyanidins (SBP) against oxidative damage in RPE. In this study, we established an oxidative damage model of adult retinal pigment epithelial cell line-19 (ARPE-19) using hydrogen peroxide (H2O2), followed by different concentrations of SBP for 24 h. The finding demonstrated that SBP effectively inhibited the generation of malondialdehyde (MDA), restored the activity of superoxide dismutase (SOD) and content of glutathione (GSH), and significantly eliminated the level of reactive oxygen species (ROS) and oxidative stress. It was revealed that 100 µg/mL of SBP was more suitable for restoring oxidative damage in ARPE-19, which enhanced cell activity and migration ability and maintained normal cell morphology. In addition, SBP increased the expression of Bcl-2, decreased the expression of Bax and caspase-3, and activated the Nrf2/HO-1 signaling pathway to protect ARPE-19 from oxidative stress. Moreover, SBP could restore the morphology and quantity of mitochondria and inhibit mitochondrial permeability and swelling. The present results provide a theoretical basis for the protective and restorative effect of SBP in retinopathy caused by oxidative stress.

Analysis of shear creep damage model of slope rock mass under the influence of coupled damage effects (DBSM)

Abstract This article reveals the evolution law of shear creep damage of carbonaceous shale (weak interlayer of slope) under dynamic load from a mechanical perspective by combining indoor experiments and theoretical research. Firstly, a coupled damage variable D BSM was established for the initial damage D 0 and dynamic disturbance shear creep damage D BS of rock mass based on the theory of damage mechanics. Secondly, according to the fractional calculus operator theory and considering the influence of coupled damage variable D BSM on the viscosity coefficient of rock mass in the viscoelasticity and viscoplasticity creep stages, a shear creep damage model of rock mass was established. At the same time, combined with the shear creep test data under the influence of dynamic loads, the damage evolution law of shear creep in carbonaceous shale (weak interlayer of slope) was revealed, and the accuracy of the established shear creep damage model was verified. Finally, the damage evolution law of carbonaceous shale was quantitatively analyzed. Results show that: The shear creep damage model established in this article has unique advantages. The greater the initial damage, the more likely shear creep failure is to occur under the influence of dynamic disturbance and shear creep loads. Dynamic disturbance accelerates the damage of weak interlayers of slope. The cumulative coupling damage of carbonaceous shale (D ma ≤0.18) under dynamic disturbance and multi-stage shear creep loads exhibits an S-like evolution pattern. The shear creep damage mechanism of carbonaceous shale is characterized by obvious initial damage effect, dynamic disturbance damage effect, and stress response characteristics.

Cognitive improvement via cortical cannabinoid receptors and choline-containing lipids.

Recent research linking choline-containing lipids to degeneration of basal forebrain cholinergic neurons in neuropathological states illustrates the challenge of balancing lipid integrity with optimal acetylcholine levels, essential for memory preservation. The endocannabinoid system influences learning and memory processes regulated by cholinergic neurotransmission. Therefore, we hypothesised that activation of the endocannabinoid system may confer neuroprotection against cholinergic degeneration. We examined the neuroprotective potential of sub-chronic treatments with the cannabinoid agonist WIN55,212-2, using ex vivo organotypic tissue cultures including nucleus basalis magnocellularis and cortex and in vivo rat models of specific cholinergic damage induced by 192IgG-saporin. Levels of lipids, choline and acetylcholine were measured with histochemical and immunofluorescence assays, along with [35S]GTPγS autoradiography of cannabinoid and muscarinic GPCRs and MALDI-mass spectrometry imaging analysis. Learning and memory were assessed by the Barnes maze and the novel object recognition test in rats and in the 3xTg-AD mouse model. Degeneration, induced by 192IgG-saporin, of baso-cortical cholinergic pathways resulted in memory deficits and decreased cortical levels of lysophosphatidylcholines (LPC). WIN55,212-2 restored cortical cholinergic transmission and LPC levels via activation of cannabinoid receptors. This activation altered cortical lipid homeostasis mainly by reducing sphingomyelins in lesioned animals. These modifications were crucial for memory recovery. We hypothesise that WIN55,212-2 facilitates an alternative choline source by breaking down sphingomyelins, leading to elevated cortical acetylcholine levels and LPCs. These results imply that altering choline-containing lipids via activation of cannabinoid receptors presents a promising therapeutic approach for dementia linked to cholinergic dysfunction.

Mitochondrial donation as a mechanism of participation by mesenchymal stromal cells in regenerative processes

Mesenchymal stromal cells (MSCs) are universal regulators of regenerative processes due to their ability to secrete regulatory molecules or replace dead cells through differentiation in the appropriate direction. Recently, another mechanism for the beneficial effects of MSCs on damaged tissue has been discovered, such as the transfer of mitochondria into its cells in response to stress signals. MSCs can transfer mitochondria through tunneling nanotubes that form a communication bridge between cells, through gap junctions, by release as part of extracellular vesicles or in free form, and as a result of complete or partial fusion with recipient cells. In damaged cells that received mitochondria from MSCs, impaired energy metabolism is restored and oxidative stress is reduced, which is accompanied by increased survival, and in some cases also increased proliferation or a change in differentiation status. The restoration of energy after the transfer of mitochondria from MSCs has a beneficial effect on the functional activity of recipient cells and suppresses inflammatory reactions. A significant contribution of the MSC mitochondrial donation to the therapeutic efficacy of MSCs has been repeatedly demonstrated in models of damage to various organs in experimental animals. This stimulates the search for methods to enhance the process of mitochondrial donation. However, it should be taken into account that MSCs are able to transfer mitochondria to malignant cells as well, thereby stimulating tumor growth and increasing its resistance to chemotherapy. These data make it necessary to evaluate the prospects for the use of MSCs in cell therapy with caution. On the other hand, they can serve as a basis for the search for new therapeutic targets in the treatment of oncological diseases.

Construction of an intelligent pH-sensitive hydrogel drug delivery system and its application in gastric ulcer treatment

The occurrence of gastric ulcer is mainly due to the damage of gastric mucosa which leads to inward flow of gastric acid to corrode the gastric cavity, thus producing gastric fever, vomiting, loss of appetite and other adverse reactions. Prevention and treatment of such injuries are crucial. In this study, a simple and non-toxic composite hydrogel (PLGA/CMCS) was prepared through Schiff base reaction between poly(lactic-co-glycolic acid) (PLGA) and carboxymethyl cellulose (CMCS). Subsequently, compound 1 was loaded onto it to construct PLGA/CMCS@1. A series of structural characterization and performance experiments were conducted on these novel hydrogel polymers. Furthermore, we detected the gene expression level of Fas/FasL apoptotic pathway after treating the cells with different concentrations of PLGA/CMCS@1 through an ethanol-induced damaged gastric mucosal epithelial cell model. The results showed that the system was able to significantly regulate the expression of genes related to the apoptotic pathway. The system can regulate the Fas/FasL apoptosis pathway to treat gastric ulcer.

Studying the Constitutive Model of Damage for a Stainless Steel Argon–Oxygen Decarburization Slag Mixture

The purpose of this study was to fully explore the mechanical properties of five different doses of an Argon–Oxygen Decarburization slag mixture in an unconfined compressive strength test. The peak stress, elastic modulus, and stress–strain curve of the mixture were studied for 90 days. Based on the experimental data and according to the theory of damage mechanics, the concept of damage threshold (t) was introduced to construct a damage constitutive model. Referring to the damage threshold of concrete, that of the mixture was determined to be 0.7 times higher than the peak strain, and the correlation coefficient between the established model and the test curve was above 0.85. These results indicate that the addition of AOD slag and fly ash can cause hydration reactions, increase the quantity of hydration products, and enhance the peak stress and elastic modulus of the mixture. The maximum increases were 94.9% and 43.1%, respectively. Parameters a and b reflect the peak stress and brittleness of the mixture, respectively. The incorporation of Argon–Oxygen Decarburization slag can make the mixture less brittle and improve its properties. The incorporation of Argon–Oxygen Decarburization slag can protect the mixture from damage. The maximum decrease is 40.2%.

Evaluation and optimization of interventional blood pump based on hydraulic performances and hemocompatibility performances

This study was designed to investigate the effects of hemodynamic environment and design factors on the hydraulic performance and hemocompatibility of interventional blood pumps using computational fluid dynamics methods combined with specialized mathematical models. These analyses assessed how different hemodynamic environments (such as support mode and artery size) and blood pump configurations (including entrance/exit blade angles, rotor diameter, blade number, and diffuser presence) affect hydraulic performance indicators (rotational speed, flow rate, pressure head, and efficiency) and hemocompatibility indicators (bleeding, hemolysis, and thrombosis). Our findings indicate that higher perfused flow rates necessitate greater rotational speeds, which, in turn, reduce both efficiency and hemocompatibility. As the artery size increases, the hydraulic performance of the pump improves but at the cost of worsening hemocompatibility. Among the design parameters, optimal configurations exist that balance both hydraulic performance and hemocompatibility. Notably, a configuration without a diffuser demonstrated better hydraulic performance and hemocompatibility compared to one with a diffuser. Further analysis revealed that flow losses primarily contribute to the degradation of hydraulic performance and deterioration of hemocompatibility. Shear stress was identified as the major cause of blood damage in interventional blood pumps, with residence time having a limited impact. This study comprehensively explored the effects of operating environment and design parameters on catheter pump performance using a multi-faceted blood damage model, providing insights into related complications from a biomechanical perspective. These findings offer valuable guidance for engineering design and clinical treatment.

Effect of initial temperature damage on the static and fatigue performance of all-lightweight shale ceramsite concrete

The effects of initial temperature damage on the static and compressive fatigue properties of LC30 all-lightweight shale ceramsite concrete (ALWSCC) were studied. The curing conditions ranged from -5 °C to -30 °C without antifreeze, with an elevated temperature range of 100 °C to 400 °C applied after 28 days of standard curing. We tested the static strength, elastic modulus, and stressstrain curves of ALWSCC, as well as its uniaxial compression fatigue life and ƐN curves under different stress levels. The credibility of data from only three test samples per condition was statistically analyzed, and we explored how temperature, aggregate properties, and concrete pore structure affect performance. The results indicate that the impact of temperature on the static and fatigue performance of ALWSCC can be described by a unified damage model. The Hillerborg characteristic length effectively captures the brittleness induced by temperature changes. Using the two-parameter Weibull equation and various fatigue equations that account for failure probability and temperature, the fatigue life predictions were accurate. Although low and high temperatures affect ALWSCC differently, temperature effects combined with static and fatigue loads further accelerate its deterioration.

Mito-TEMPO Demonstrates Protective Effect Against Ultraviolet Radiation-Induced Skin Damage in Wistar Rats.

Mitochondria could be an important target for ultraviolet radiation (UVR)-induced skin damage. Therefore, protecting mitochondria using mitochondria-targeted antioxidants may protect skin from UV-induced photodamage. In the present study, UVR-induced skin damage model was developed by irradiating male Wistar rats with UVB at a dose of 120 mJ/cm2, twice a week for a period of 5 weeks. Mito-TEMPO was administered intraperitoneally (0.1 mg/kg b.w.) twice a week for 5 weeks. After 5 weeks of treatment period, animals were sacrificed and the dorsal skin tissues were collected. Physical examinations of the skin for analyzing wrinkle formation and epidermal thickening were carried out. Skin tissues were used for the evaluation of histopathological changes, mitochondrial dysfunction analysis, and mitochondrial membrane potential. Physical and histological examination showed that mito-TEMPO protected from the damaging effect of UVB radiation. A significant increase in mitochondrial reactive oxygen species (mtROS) generation with a concomitant increase in mitochondrial lipid peroxidation (mtLPO) was observed in UV-irradiated groups. UV-induced generation of mtROS and mtLPO formation was effectively reduced by mito-TEMPO. Mito-TEMPO pre-treatment improved mitochondrial complex II activity, which was significantly reduced in the UV-irradiated group. The results suggested that mito-TEMPO effectively protected skin tissue against UV-induced oxidative stress and damage.

Numerical study of delamination process of the CFRP composite

A quasi-static approach for an interface damage model, incorporating Rayleigh damping for viscoelastic carbon fiber reinforced polymer composites, is introduced. The interface traction-relative displacement behavior is modeled using a thin adhesive layer, similar to cohesive zone models. The problem is solved numerically with a semi-implicit time-stepping method. The cohesive interface model, integrated into the Finite Element Method, was applied to determine the critical force away from the crack tip. Results showed that the numerical delamination under mode I conditions aligned well with experimental data for the cohesive zone formulations studied. The numerical example demonstrates the effectiveness of the proposed model.

5-Demethylnobiletin Ameliorates Isoproterenol-Induced Cardiac Fibrosis and Apoptosis by Repressing the Sirt1/FOXO3a/NF-κB and Wnt/β-Catenin Pathways.

Apoptosis and fibrosis are two main factors leading to heart failure. 5-Demethylnobiletin (5-OH-Nob) is a natural polymethoxyflavone derived from the peel of citrus fruits that has many biological effects, such as antioxidative stress and anti-inflammatory effects. Here, we aimed to probe the function and mechanism of 5-OH-Nob in myocardial damage. Primary rat cardiac fibroblasts were exposed to isoproterenol (ISO, 10 µM) to establish an in vitro model of cardiac damage, and ISO (30 mg/kg/d) was used to induce myocardial fibrosis in mice. 5-OH-Nob was used for treatment in vivo and ex vivo. Functional assays revealed that 5-OH-Nob alleviated the apoptosis and fibrosis of cardiac fibroblasts treated with ISO and increased cell viability (p < 0.05). In vivo, 5-OH-Nob treatment ameliorated cardiac injury in ISO-treated mice (p < 0.05). Mechanistically, 5-OH-Nob treatment enhanced Sirt1 expression and suppressed ISO-mediated activation of the FOXO3a/nuclear transcription factor-κB (NF-κB) and Wnt/β-catenin pathways. Furthermore, Sirt1 inhibition attenuated the protective effect of 5-OH-Nob on ISO-induced cardiac apoptosis and fibrosis. Overall, 5-demethylnobiletin mediates the Sirt1/FOXO3a/NF-κB and Wnt/β-catenin pathways to mitigate ISO-induced myocardial fibrosis and apoptosis.

A kidney-specific fasting-mimicking diet induces podocyte reprogramming and restores renal function in glomerulopathy.

Cycles of a fasting-mimicking diet (FMD) promote regeneration and reduce damage in the pancreases, blood, guts, and nervous systems of mice, but their effect on kidney disease is unknown. In addition, a FMD has not been tested in rats. Here, we show that cycles of a newly developed low-salt FMD (LS-FMD) restored normal proteinuria and nephron structure and function in rats with puromycin-induced nephrosis compared with that in animals with renal damage that did not receive the dietary intervention. LS-FMD induced modulation of a nephrogenic gene program, resembling renal developmental processes in multiple kidney structures. LS-FMD also activated podocyte-lineage reprogramming pathways and promoted a quiescent state in mature podocytes in the rat kidney damage model. In a pilot clinical study in patients with chronic kidney disease, FMD cycles of 5 days each month for 3 months promoted renoprotection, including reduction of proteinuria and improved endothelial function, compared with that in patients who did not receive the FMD cycles. These results show that FMD cycles, which promote the reprogramming of multiple renal cell types and lead to glomerular damage reversal in rats, should be tested further for the treatment of progressive kidney diseases.

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.&#xD;&#xD;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.&#xD;&#xD;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. &#xD;&#xD;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.

Compressive resistance of thin-walled pultruded GFRP profiles: The role of delamination examined through experiments and FE simulations

Significant efforts have been made in the last decades to develop design rules and guidelines for composite structures, meeting the increasing interest in pultruded glass fibre reinforced profiles (GFRP) by the construction industry. One aspect that has been difficult to address is the crushing resistance of these profiles, with previous research indicating that the design equations are not conservative, predicting much higher resistances than those obtained in experimental tests. This paper explores the possibility that crushing resistance is governed by tensile failure in the through-thickness direction of the laminates, by Poisson effect, and proposes modifications to a previously presented material damage model to account for this in finite element (FE) simulations. Compressive experimental tests were conducted in stub-column specimens, with 5 different open-section configurations, obtained from three different producers. The test results were compared to analytical and FE simulations, confirming that the former grossly overestimate the resistance, while the latter, with the proposed damage model, compare well with experimental results.

Determination of high‐strength polymer composite reinforcement effect on the armor‐grade aluminum plates' explosion resistance—A computational perspective

AbstractThe selection of highly efficient materials is a crucial task for designing protective structures or armor against extreme explosive loadings. Due to the high strength‐to‐weight ratio of various grades of aluminum alloys and composites, they are mostly preferred for making protective structures. Investigation of their explosion resistance characteristics through experiments is very costly, dangerous, and time‐consuming. Hence, the present work deals with a cost‐effective numerical analysis on explosion resistance performance evaluation of various armor‐grade aluminum alloy plates of the same areal densities under 1–3 kilograms of trinitrotoluene explosions at a 100 mm stand‐off distance. The superior‐performance aluminum alloy plate is further reinforced with a high‐strength carbon/epoxy polymer composite to enhance its performance. The masses of the plates are maintained constant throughout the study. The Johnson‐Cook rate‐dependent material model and a progressive damage model including Hashin with Puck‐Schumann failure criteria were used to determine the realistic failures in the aluminum alloys and polymer composites, respectively. The outcomes of the study showed that the AA7075‐T6 plate has the highest deformation resistance under extreme explosion loadings. Carbon fiber‐reinforced aluminum laminate (CRALL) showed improved deformation resistance and energy absorption than those of the same mass of monolithic plate.Highlights Explosion resistance of various aluminum alloys of equal masses is compared. AA7075‐T6 provides better protection against blast compared with other alloys. To design CRALL, a carbon/epoxy composite used to reinforce the AA7075‐T6. CRALL provides 16.3% smaller peak deflection than the same mass of AA7075‐T6. CRALL improved energy absorption by 29.3% compared with same mass of AA7075‐T6.

Nonalcoholic fatty liver disease worsens cardiac repair after myocardial infarction

Abstract Background There is a strong epidemiological link between nonalcoholic fatty liver disease (NAFLD) and ischemic heart disease such as myocardial infarction (MI). Yet, a causal relationship between liver injury and post-MI cardiac repair remains to be established. Purpose NAFLD impairs post-MI myocardial repair processes. In particular, we hypothesized that the pathological liver could transmit deleterious signals shaping the inflammatory reaction in the infarcted milieu. Methods To characterize post-MI cardiac function and remodeling in three mouse models of liver damage mimicking different stages of NAFLD without cardiovascular (CV) risk factors : i) choline-deficient, L-amino-acid-defined, high fat diet (CDA-HFD) causing severe non-alcoholic steatohepatitis; ii) NEMOLPC-KO mice deficient for NF-κB in liver parenchymal cells, exhibiting liver inflammation and fibrosis, but mild steatosis; and ATGLLPC-KO animals deficient for Adipose Triglyceride Lipase in liver parenchymal cells displaying strong steatosis. Results In our three experimental models, liver damages were characterized by inflammation, steatosis and fibrosis but were not associated with metabolic syndrome. More interestingly, left ventricular ejection fraction were reduced by 1.2-fold, 1.3-fold and 1.3-fold in CDA-HFD, NEMOLPC-KO and ATGLLPC-KO male and female mice, respectively when compared to their respective controls, at 35 days post-MI (n=12-25 per group). NAFLD-induced cardiac dysfunction was not associated with worsen cardiac remodeling as infarct size, fibrosis and vascular density were not significantly affected. On the same note, flow cytometry experiments, at 7- and 14-days post-MI, showed no changes in the number or type of inflammatory cells, particularly that of cardiac resident macrophages, in CDAHFD, ATGLLPC-KO and NEMOLPC-KO mice. We next hypothesized that reduced left ventricular function could be induced by altered cardiomyocyte contractility. To corroborate this hypothesis, we isolated cardiomyocytes from hearts of infarcted mice with or without NAFLD and assessed cell contractility using IonOptix technology. Our preliminary results, in the CDAHFD model, showed that there was a reduction in contraction amplitude, defining by the ratio of the difference in sarcomere length during contraction/relaxation to the sarcomere length at the time of relaxation. The speed of contraction and relaxation were also decreased in CDAHFD mice compared with control animals. Conclusions NAFLD favors cardiac dysfunction post-MI. We now aim to identify molecular and cellular entities participating to such pathogenic dialogue between the dysfunctional liver and the infarcted heart.

Identification of Key Genes Related to Immune-Lipid Metabolism in Skin Barrier Damage and Analysis of Immune Infiltration.

Several physical and chemical factors regulate skin barrier function. Skin barrier dysfunction causes many inflammatory skin diseases, such as atopic dermatitis and psoriasis. Activation of the immune response may lead to damage to the epidermal barrier. Abnormal lipid metabolism is defined as abnormally high or low values of plasma lipid components such as plasma cholesterol and triglycerides. The mouse skin barrier damage model was used for RNA sequencing. Bioinformatics analysis and validation were performed. Differently expressed genes (DEGs) related to immune and lipid metabolism were screened by differentially expressed gene analysis, and the enriched biological processes and pathways of these genes were identified by GO-KEGG. The interactions between DEGs were confirmed by constructing a PPI network. GSEA, transcription factor regulatory network, and immune infiltration analyses were performed for the 10 genes. Expression validation was performed by public datasets. The expression of key genes in mouse skin tissue was detected by qPCR. The expression of differentially expressed immune cell markers in the skin was detected by immunofluorescence. Based on the trans epidermal water loss (TEWL) score, the expression of key genes was detected by qPCR before skin barrier injury, at 4h and 7d, and at recovery from injury. Il17a, Il6, Tnf, Itgam, and Cxcl1 were immune-related key genes. Pla2g2f, Ptgs2, Plb1, Pla2g3, and Pla2g2d were key genes for lipid metabolism. Database validation and experimental results revealed that the expression trends of these genes were consistent with our analyses. The research value of these genes has been demonstrated through mouse datasets and experimental validation, and future therapeutic approaches may be able to mitigate the disease by targeting these genes to modulate the function of the skin barrier.

Evaluation of fatigue damage of structural steel based on attenuation of laser-induced surface acoustic wave

ABSTRACT In this paper, the fatigue damage degree of low-alloy structural steel is evaluated by using the attenuation characteristics of laser-induced surface acoustic wave (SAW) during propagation. Taking the typical structural steel material Q345 as an example, a cracks model of fatigue damage is established, and the finite element method is used to solve the model. The results showed that the attenuation coefficient of SAW can reflect the depth and density of fatigue cracks. The surface measurement experiments of specimens with stress cycles of 0, 50000, 100000, 150000, and 200,000 showed that with the increase of stress cycles, the attenuation coefficient of SAW increases as a whole, indicating that it is feasible to evaluate the fatigue damage degree based on the attenuation of SAW. A method of applying tensile stress to the material to improve the sensitivity of fatigue damage evaluation is proposed. The tensile stress is used to offset the horizontal amplitude of the SAW, keeping the fatigue cracks in an open state and increasing the attenuation coefficient of SAW. The attenuation coefficient measurement experiment shows that this method is feasible.

Experimental Study on Mechanical Characteristics of Stabilized Soil with Rice Husk Carbon and Calcium Lignosulfonate

In cold regions, the extensive distribution of silt exhibits limited applicability in engineering under freeze–thaw cycles. To address this issue, this study employed rice husk carbon and calcium lignosulfonate to stabilize silt from cold areas. The mechanical properties of the stabilized silt under freeze–thaw conditions were evaluated through unconfined compressive strength tests and triaxial shear tests. Additionally, scanning electron microscopy was utilized to analyze the mechanisms behind the stabilization. Ultimately, a damage model for rice husk carbon–calcium lignosulfonate stabilized silt was constructed based on the Weibull distribution function and Lemaitre’s principle of equivalent strain. The findings indicate that as the content of rice husk carbon and calcium lignosulfonate increases, the rate of improvement in the compressive strength of the stabilized silt progressively accelerates. With an increase in the number of freeze–thaw cycles, the deviatoric stress of the stabilized soil gradually diminishes; the decline in peak deviatoric stress becomes more gradual, while the reduction in cohesion intensifies. The decrease in the angle of internal friction is relatively minor. Microscopic examinations reveal that as the number of freeze–thaw cycles increases, the soil pores tend to enlarge and multiply. The established damage model for stabilized silt under freeze–thaw cycles and applied loads demonstrates a similar pattern between the experimental and theoretical curves under four different confining pressures, reflecting an initial rapid increase followed by a steady trend. Thus, it is evident that the damage model for stabilized silt under freeze–thaw conditions outperforms traditional constitutive models, offering a more accurate depiction of the experimental variations observed.