Heat stress affects dairy cow health status through blood oxygen availability

Background Rises in global warming and extreme weather occurrence make the risk of heat stress(HS)induced by high ambient temperatures more likely in high-yielding dairy cows,resulting in low milk quality and yield.In ani-mals,oxygen is involved in many physiological and metabolic processes,but the effects of HS on oxygen metabolism remain unclear.Thus,the current study aimed to investigate how oxygen metabolism plays a role in health status of dairy cows by measuring the milk yield,milk composition,and blood biochemical variables of cows under different levels of HS:none(No-HS),mild(Mild-HS),and moderate HS(Mod-HS).Results The HS significantly increased rectal temperature(Ptreat<0.01)and respiration rate(Ptreat<0.01).Under Mod-HS,greater Na+(P<0.05)and lower total CO_(2),and pH(P<0.05)were observed relative to those under No-HS and Mild-HS.Oxygen concentrations in both coccygeal artery and mammary vein(Ptreat<0.01)were lower under Mod-HS than under No-HS.Coccygeal vein concentrations of heat shock protein 90(HSP90)(P<0.05)increased during Mod-HS compared with those in cows under No-HS.Malondialdehyde increased during Mod-HS,and glu-tathione peroxidase(P<0.01)increased during Mild-HS.Coccygeal vein concentrations of vascular endothelial growth factor(P<0.01),heme oxygenase-1(P<0.01),and hypoxia-inducible factor 1α(P<0.01)were greater in cows under Mod-HS than those under No-HS.Red blood cell count(P<0.01)and hemoglobin concentration(P<0.01)were lower in the coccygeal vein of dairy cows under Mild-and Mod-HS than those of cows under No-HS.Conclusions Exposure to HS negatively impacts the health status and lactation performance of dairy cows by limit-ing oxygen metabolism and transportation.However,the specific mechanism by which HS affects mammary function in cows remains unclear and requires further exploration.

Supplementation of vitamin E or a botanical extract as antioxidants to improve growth performance and health of growing pigs housed under thermoneutral or heat-stressed conditions

Background Heat stress has severe negative consequences on performance and health of pigs,leading to significant economic losses.The objective of this study was to investigate the effects of supplemental vitamin E and a botanical extract in feed or drinking water on growth performance,intestinal health,and oxidative and immune status in grow-ing pigs housed under heat stress conditions.Methods Duplicate experiments were conducted,each using 64 crossbred pigs with an initial body weight of 50.7±3.8 and 43.9±3.6 kg and age of 13-week and 12-week,respectively.Pigs(n=128)were housed individually and assigned within weight blocks and sex to a 2×4 factorial arrangement consisting of 2 environments(thermo-neutral(21.2℃)or heat-stressed(30.9℃))and 4 supplementation treatments(control diet;control+100 IU/L of D-α-tocopherol in water;control+200 IU/kg of DL-α-tocopheryl-acetate in feed;or control+400 mg/kg of a botanical extract in feed).Results Heat stress for 28 d reduced(P≤0.001)final body weight,average daily gain,and average daily feed intake(-7.4 kg,-26.7%,and-25.4%,respectively)but no effects of supplementation were detected(P>0.05).Serum vitamin E increased(P<0.001)with vitamin E supplementation in water and in feed(1.64 vs.3.59 and 1.64 vs.3.24),but not for the botanical extract(1.64 vs.1.67 mg/kg)and was greater when supplemented in water vs.feed(P=0.002).Liver vitamin E increased(P<0.001)with vitamin E supplementations in water(3.9 vs.31.8)and feed(3.9 vs.18.0),but not with the botanical extract(3.9 vs.4.9 mg/kg).Serum malondialdehyde was reduced with heat stress on d 2,but increased on d 28(interaction,P<0.001),and was greater(P<0.05)for antioxidant supplementation compared to control.Cellular proliferation was reduced(P=0.037)in the jejunum under heat stress,but increased in the ileum when vitamin E was supplemented in feed and water under heat stress(interaction,P=0.04).Tumor necrosis factor-αin jejunum and ileum mucosa decreased by heat stress(P<0.05)and was reduced by vitamin E sup-plementations under heat stress(interaction,P<0.001).Conclusions The addition of the antioxidants in feed or in drinking water did not alleviate the negative impact of heat stress on feed intake and growth rate of growing pigs.

Effect of organic mineral supplementation in reducing oxidative stress in Holstein calves during short‑term heat stress and recovery conditions

Background This study investigated the effects of inorganic and organic minerals on physiological responses,oxidative stress reduction,and rumen microbiota in Holstein bull calves(123.81±9.76 kg;5 months old)during short-term heat stress(HS)and recovery periods.Eight Holstein calves were randomly assigned to four treatment groups:no mineral supplementation(Con),inorganic minerals(IM),organic minerals(OM),and high-concentration organic minerals(HOM)and two thermal environments(HS and recovery)using 4×2 factorial arrangement in a crossover design of four periods of 35 d.Calves were maintained in a temperature-controlled barn.The experimental period consisted of 14 d of HS,14 d of recovery condititon,and a 7-d washing period.Results Body temperature and respiration rate were higher in HS than in the recovery conditions(P<0.05).Selenium concentration in serum was high in the HOM-supplemented calves in both HS(90.38μg/dL)and recovery periods(102.00μg/dL)(P<0.05).During the HS period,the serum cortisol was 20.26 ng/mL in the HOM group,which was 5.60 ng/mL lower than in the control group(P<0.05).The total antioxidant status was the highest in the OM group(2.71 mmol Trolox equivalent/L),followed by the HOM group during HS,whereas it was highest in the HOM group(2.58 mmol Trolox equivalent/L)during the recovery period(P<0.05).Plasma malondialdehyde and HSP70 levels were decreased by HOM supplementation during the HS and recovery periods,whereas SOD and GPX levels were not significantly affected(P>0.05).The principal coordinate analysis represented that the overall rumen microbiota was not influenced by mineral supplementation;however,temperature-induced microbial structure shifts were indicated(PERMANOVA:P<0.05).At the phylum level,Firmicutes and Actinobacteria decreased,whereas Fibrobacteres,Spirochaetes,and Tenericutes increased(P<0.05),under HS conditions.The genus Treponema increased under HS conditions,while Christensenella was higher in recovery conditions(P<0.05).Conclusion HOM supplementation during HS reduced cortisol concentrations and increased total antioxidant status in Holstein bull calves,suggesting that high organic mineral supplementation may alleviate the adverse effects of HS.

Changes of Water Status and Different Responses of Osmoregulants in Jatropha Curcas L. Seedlings to Air-drought Stress

[Objective] The study aimed to investigate the changes of water status and different responses of osmoregulants during air-drought stress,to better understand mechanisms of drought resistance in Jatropha Curcas L. [Methods] The 12-day-old J. curcas seedlings were held in a climate chamber at 25/20 ℃（day/night）,16 hours illumination,and 75% of relative humidity for air-drought treatment,and the changes of water potential,osmotic potential and the content of soluble sugar,proline,betaine were measured. [Results] Water potential and osmotic potential in leaves of J. curcas seedlings dropped significantly,pressure potential lost during air-drought stress,and the contents of osmoregulants soluble sugar,proline and betaine rose significantly to different extent in the leaves and stems. [Conclusion] Osmoregulants in the leaves and stems respond differently to air-drought stress,and in general leaves are much more responsive to the drought than stems of J. curcas seedlings.

Effect of Soil Drought Stress on Leaf Water Status, Membrane Permeability and Enzymatic Antioxidant System of Maize

A simulation experiment on the responses of maize (Zea mays L.) from the third leaf stage to maturity for different soil water levels (well-watered, moderately stressed, and severely stressed) was conducted by controlling irrigation and using a mobile rain shelter in a neutral loam, meadow soil to determine the effects on leaf water status, membrane permeability and enzymatic antioxidant system for different growth stages. The results indicated that drought stress relied on drought intensity and duration, with more severe drought stress creating more serious effects on maize. Compared with well-watered conditions, during the silking and blister stages moderate stress did not significantly change the relative water content (RWC) and did change significantly the relative conductivity (RC) (P < 0.05) of the leaves; however, severe stress did significantly decrease (P < 0.01) the leaf RWC and increase (P < 0.01) membrane permeability (leaf relative conductivity). Furthermore, under severe drought stress antioxidant enzyme activities declined significantly (P < 0.01) in later stages, namely for superoxide dismutase (SOD) the tasseling and blister stages, for peroxidase (POD) the milk stage, and for catalase (CAT) during the tasseling, blister, and milk stages. Meanwhile, membrane lipid peroxidation (measured as malondialdehyde content) significantly increased (P < 0.01) in all stages.

Size effects on flow stress of C3602 in cylinder compression with different lubricants

Micro parts are more difficult to be formed than macro parts because of size effects. The size effects on the flow stress of copper alloy C3602 with different lubricants were studied. Specimens were heat treated at 350℃ for 1 h and 700℃ for 3 h in nitrogen atmosphere, respectively. The initial diameters of the specimens were varied from 5 to 1 mm with a height-to-diameter ratio h0/D0 = 1.5. Cylinder compression was carried out in the lubrication condition with talc powder, without lubricant, with petroleum jelly, and with vegetable oil. The experiment was carried out at room temperature on a universal testing machine INSTRON 5569 with a strain rate of ε = 0.0025 A. The results show that with the same lubricant, the yield strength decreases with a decrease in specimen size for the specimens annealed at 350℃ for 1 b; however, it increases with a decrease in specimen size for the specimens annealed at 700℃ for 3 h. The yield strength decreases with an increase in grain size. The influences of lubricants on yield strength become larger with miniaturization of the specimens.

Growth performance,oxidative stress and immune status of newly weaned pigs fed peroxidized lipids with or without supplemental vitamin E or polyphenols

Background:This study evaluated the use of dietary vitamin E and polyphenols on growth,immune and oxidative status of weaned pigs fed peroxidized lipids.A total of 192 piglets(21 days of age and body weight of 6.62±1.04 kg)were assigned within sex and weight blocks to a 2×3 factorial arrangement using 48 pens with 4 pigs per pen.Dietary treatments consisted of lipid peroxidation(6%edible soybean oil or 6%peroxidized soybean oil),and antioxidant supplementation(control diet containing 33 IU/kg DL-α-tocopheryl-acetate;control with 200 IU/kg additional dl-α-tocopheryl-acetate;or control with 400 mg/kg polyphenols).Pigs were fed in 2 phases for 14 and 21 days,respectively.Results:Peroxidation of oil for 12 days at 80°C with exposure to 50 L/min of air substantially increased peroxide values,anisidine value,hexanal,and 2,4-decadienal concentrations.Feeding peroxidized lipids decreased(P<0.001)body weight(23.16 vs.18.74 kg),daily gain(473 vs.346 g/d),daily feed intake(658 vs.535 g/d)and gain:feed ratio(719 vs.647 g/kg).Lipid peroxidation decreased serum vitamin E(P<0.001)and this decrease was larger on day 35(1.82 vs.0.81 mg/kg)than day 14(1.95 vs.1.38 mg/kg).Supplemental vitamin E,but not polyphenols,increased(P≤0.002)serum vitamin E by 84%and 22%for control and peroxidized diets,respectively(interaction,P=0.001).Serum malondialdehyde decreased(P<0.001)with peroxidation on day 14,but not day 35 and protein carbonyl increased(P<0.001)with peroxidation on day 35,but not day 14.Serum 8-hydroxydeoxyguanosine was not affected(P>0.05).Total antioxidant capacity decreased with peroxidation(P<0.001)and increased with vitamin E(P=0.065)and polyphenols(P=0.046)for the control oil diet only.Serum cytokine concentrations increased with feeding peroxidized lipids on day 35,but were not affected by antioxidant supplementation(P>0.05).Conclusion:Feeding peroxidized lipids negatively impacted growth performance and antioxidant capacity of nursery pigs.Supplementation of vitamin E and polyphenols improved total antioxidant capacity,especially in pigs fed control diets,but did not restore growth performance.

Performance of dynamically loaded journal bearings lubricated with couple stress fluids considering the elasticity of the liner

To take into account the couple stress effects, a modified Reynolds equation is derived for dynamically loaded journal beatings with the consideration of the elasticity of the liner. The numerical results show that the influence of couple stresses on the bearing characteristics is significant. Compared with Newtonian lubricants, lubricants with couple stresses increase the fluid film pressure, as a result enhance the load-carrying capacity and reduce the friction coefficient. However, since the elasticity of the liner weakens the couple stress effect, elastic liners yield a reduction in the load-carrying capacity and an increase in the friction coefficient. The elastic deformation of the bearing liner should be considered in an accurate performance evaluation of the journal bearing.

Baseline Iron Status and Indices of Oxidative Stress in a Cohort of Pregnant Women in Kinshasa, DR Congo

Objective: To determine baseline iron and oxidative status in a cohort of pregnant women before iron supplementation in our setting. Background: Screening of iron deficiency before supplementation during pregnancy has been scarce. Therefore, following routine iron supplementation confounding results might be found in outcomes of groups of patients considered. Taking in account that body/serum iron status is reportedly linked to maternal oxidative status, we aimed to associate assessment of baseline iron and oxidative status of women in need of oral supplementation during pregnancy. Methods: This is a cross-sectional study concerning 74 women attending antenatal care at the University Clinics of Kinshasa from September 2017 throughout June 2018, with a singleton pregnancy not exceeding 19 weeks, regardless of age and parity. Variables of the study included sociodemographic and anthropometric ones along with parameters of iron status (hemoglobin, hematocrit, ferritin, serum iron, transferrin and iron saturation capacity). Oxidative status was assessed using superoxide dismutase (SOD) and uric acid as antioxidants, while oxidant agents were oxidized LDL and blood glucose (beside serum iron and ferritin). According to local standards anemia was defined as hemoglobin 10 g/L and pathologic serum ferritin as 15 ng/ml. For statistical calculations we used t-test, chi-square test and Pearson’s correlation test, the significance being stated at p ≤ 0.05. Results: At recruitment (15.9 ± 1.7 9 week gestational age) mean hemoglobin value of the overall study group was 10.3 ± 1.5 g/dl. Anemia was diagnosed to 39 women that represented 52.2% of the study group, most of anemic women belonging to low socioeconomic sub-group (69.2% vs 29%;P < 0.001). The majority was para 2, with average weight of 70.2 ± 14.5 Kg (P not significant between sub-groups) and BMI of 26 ± 5.2 Kg/m2 (P < 0.01). The proportion of obeses was 18.9%. The proportion of intestinal parasitosis was significantly higher among anemic women (61.5% vs 34.3%;P < 0.02) that had lower alimentary iron intake (22.8 ± 4.9 gr/day vs 31.4 ± 9.5 gr;P < 0.001). Of markers of iron status serum ferritin and iron were lower in anemic women (7.5 ± 3.9 ng/ml vs 35.7 ± 17.1 ng/ml;P < 0.001 and 52.7 ± 38.9 μg/dl vs 96.2 ± 41.8 μg/dl, respectively. Both sub-groups were similar in serum transferrin. As of markers of oxidative stress anemic women had significantly higher superoxide dismutases (SOD) (1056.4 ± 762.1 UI/L vs 682.6 ± 543.9 UI/L (P < 0.02) and oxidizedd anti LDL Ac (439.6 ± 209.5 UI/L vs 192.8 ± 136.3 UI/L (P < 0.001). Serum iron, ferritin, SOD and oxidized LDL were more likely to assess iron and oxidative status in our setting. Conclusion: The rate of anemic mothers found in our study (52.2%) has been quite constant in our setting for years, meaning endemicity. Serum iron and ferritin were significantly lower in anemic women, which is supportive of routine iron supplementation during pregnancy. Significantly higher level of SOD and oxidized LDL in anemic women suggests that maternal anemia may count into oxidative stress likely to be found in these women.

LUBRICATION ANALYSIS OF A CELL SLIDING INTO A CIRCULAR PORE

The resistance to the blood cells at the entrance to capillaries and membrane pores contributes considerably to the peripheral resistance in the blood circulation. This paper proposes, for the first time, a simplified mechanical model in an attempt to treat the axisymmetric motion of a cell sliding into a circular pore. In this model, the shape of the cell is taken as given according to the microvideograph and the cell membrane is assumed to slide over its surface. The lubrication theory is applied to the thin layers of plasma between the membrane and the pore wall, yielding the pressure and shear stress distributions over the membrane as well as the resultant drag exerted on the cell. Our computations have simulated the process of the cell entering the pore, which is in qualitative agreement with the microvideographic observations.

A new general rheological model for rheological lubrication

Limitation and deficiency of main thcoogical models at present are descrital and analyzed, and seteralgeneral rheological models are discussed and compared with each other, and basic demands for a general model aresummarized. The constitutive eqUation is proposetl for a new general theobocal model. The general medel feaaressimple structure and wide coverage, and can take the Place of many edsting thcofogical ed. The whel has suc-cessfully been used for Elastohydrodynamic lubrication calculation.

Pig Social Status and Chronic Cold or Crowd Stressors Differentially Impacted Immune Response

The objectives of this study were to determine the effects of 4-day of cold and crowding stressors and social status on pig immune responsiveness to these stressors. Three unfamiliar white crossbred female pigs were mixed and assigned to ambient temperatures of either 8°C (COLD) or 22°C (control;TN) and floor-space of either 0.26 m2/pig (reduced, CROWD) or 0.45 m2/pig (adequate, CONT) over six blocks (n = 72). Pigs were identified as dominant (DOM), intermediate (INT), or submissive (SUB) based on aggressive encounters that occurred during the first 24-h post-mixing. There were no interactive effects of temperature × floor-space on immune indices. There was social status × stressor for body weight, natural killer (NK) cell cytotoxicity and phagocytosis (P < 0.05). DOM pigs that were COLD or CROWD gained the least amount of body weight compared to either INT or SUB pigs (P < 0.01). INT and SUB pigs subjected to CROWD stress gained more weight compared to their counterparts subjected to COLD temperature or CONT floor-space (P < 0.05). NK cytotoxicity was greater among CROWD-INT pigs and phagocytosis was greater among COLD- and CROWD-SUB pigs. Also, INT pigs had lower T and B cell proliferation regardless of the stressor. COLD stress significantly reduced NK cytotoxicity, total Immunoglobulin-G, and B-cell proliferation and enhanced total WBC counts and T-cell proliferation. These data imply that various immune indices were either enhanced or suppressed by COLD stress, but concurrent exposure to CROWD stressor did not exacerbate these effects. Moreover, social status played a role in determining a pig’s immune responsiveness as it modulated differential homeostatic stress response as the pig attempted to cope with stress.

Unbalanced biotransformation metabolism and oxidative stress status: implications for deficient fatty acid oxidation

The concept of accumulating xenobiotics within the human body as a health risk is well known. However, these compounds can also be endo-genous, as in the case of inborn errors of me-tabolism, and lead to some of the same symp-toms as seen in xenobiotic intoxication. Bio-transformation of both exogenous and endo-genous toxic compounds is an important function of the liver, and the critical balance between these systems is of fundamental importance for cellular health. We propose a novel model, to describe the critical balance between Phase I and Phase II biotransformation and how a disturbance in this balance will increase the oxidative stress status, with resulting pathological consequences. We further used deficient fatty acid oxidation to verify the proposed model, as deficient fatty acid oxidation is associated with the accumulation of characteristic metabolites. These accumulating metabolites undergo both Phase I and Phase II biotransformation reactions, with resulting depletion of biotransformation substrates and co-factors. Depletion of these important biomolecules is capable of disturbing the balance between Phase I and Phase II reactions, and disturbance of this balance will increase oxidative stress status. The value of the proposed model is illustrated by its application to a clinical case investigated in our laboratory. In this case the possibility of deficient fatty acid oxidation only became evident once the critical balance between Phase I and Phase II biotransformation was restored with oral replenishment of biotransformation substrates. In addition to bio-chemical improvement, there was also significant clinical improvement. The significance of this model lies within the treatment possibilities, as the assessment of biotransformation metabolism and oxidative stress status can lead to the development of nutritional treatment strategies to correct imbalances. This in turn may reduce the chances of, or delay the onset of certain disease states.

Increased oxidative stress and altered antioxidants status in patients with chronic allergic rhinitis

Background: Allergic rhinitis is an inflammatory disorder of the upper airways. Although several oxidants and antioxidants are likely to be involved, alterations in only limited parameters have been studied. Objective: In this study an attempt has been made to study the oxidant-antioxidant imbalance by investigating changes in a wide range of oxidants and antioxidants in the blood. Methods: Blood samples were obtained from 39 chronic allergic rhinitis patients (males 24, females 15), aged 20-70 (mean age 36.33 ± 2.03) years and 53 individuals (36 males, 17 females);aged 24 to 64 (mean age 45.42 ± 1.36) years. Duration of allergic rhinitis was 1.77 ± 0.237 years. In the study group, nasal symptoms were scored and the results were recorded. The patients were classified as having perennial Allergic rhinitis (PAR) if they had had at least 2 rhinitis symptoms (sneezing, rhinorrhea, nasal obstruction, itching) for at least 6 months a year in the previous 2 years and if they had a positive skin prick test response to at least 1 clinically significant perennial allergen (e.g., house dust mites, molds, cockroach, cockroach excrement grass and tree pollen, cat and dog epithelia and molds, or animal dander). They had no other allergic diseases except persistent allergic rhinitis diagnosed by the physical and history examination. Erythrocyte lipid peroxidation, erythrocyte antioxidants viz., glutathione, glutathione reductase, superoxide dismutase, catalase and plasma antioxidants viz., ceruloplasmin, glutathione-S-transferase, vitamin C, total antioxidant activity were estimated in the above two groups. Results: Erythrocyte lipid peroxidation (0 hour, p < 0.01) and superoxide dismutase (p < 0.01) were significantly higher, whereas plasma vitamin C (p < 0.001), ceruloplasmin (p < 0.05) and total antioxidant activity (p < 0.001) were significantly lower in chronic allergic rhinitis patients when compared to controls. Plasma Glutathione S transferase and erythrocyte catalase, glutathione, and glutathione reductase remained unchanged from normal subjects. Conclusion: The changes in different parameters indicate an imbalance in the oxidant and antioxidant status in chronic allergic rhinitis patients. Further studies are required to investigate the potential for antioxidant supplements to be used as routine therapy in chronic allergic rhinitis patients. Capsule summery: The study shows that the body is trying to cope for the oxidative stress by altering the enzyme levels. But external supplement may also be required as the total antioxidant levels are very much depleted.

Cinnamon Attenuates Cognitive Dysfunction,Hippocampal Oxidative Stress and Neurodegeneration Following Status Epilepticus in Young Male Rats

The present study explores the neuroprotective effects of the natural food product Cinnamomum cassia or Cinnamon(CIN)on lithium pilocarpine(Li-Pc)induced SE in experimental rats to look into a possibility of it being used as antiepileptic drug.Recent studies have shown significant potential of pharmacological,prophylactic or therapeutic use of CIN in many beneficial activities in the body.The animals received CIN pre-treatment before induction of SE.Besides the severity of the seizures,other parameters like cognitive behavioral dysfunction,hippocampal oxidative stress and histological abnormalities in the hippocampus of animals induced with SE by lithium(Li)in 3 mEq/ml/kg dose,i.p.followed 20 h later by pilocarpine(Pc)in 20 mg/ml/kg dose,s.c.CIN was administered intraperitoneally at the doses of 25 and 50 mg/mL/kg,30 minutes before Pc injection.Mortality(if any)within 24 hours was also recorded.Ethical approval was obtained from the Ethics Committee Review Board of the College of Pharmacy of King Saud University,Riyadh,Saudi Arabia.Treatment with CIN significantly ameliorated the frequency and severity of epileptic seizures in a dose-dependent manner.The cognitive dysfunctions were improved,hippocampal oxidative stress was ameliorated and neuronal cell loss in the hippocampus were also attenuated significantly and dose-dependently by CIN.Possible therapeutic application of CIN as an antiepileptic and as an antioxidant for the treatment of SE has a great potential and warrants further studies.

激光熔覆碳化物增强镍基涂层组织与性能的热处理调控

基于激光熔覆技术成形了Ni35-WC-MoS_(2)-CeO_(2)自润滑耐磨涂层,研究了热处理对涂层的物相组成、显微组织、显微硬度、残余应力以及摩擦磨损性能的影响,揭示了涂层的磨损机理.结果表明,激光熔覆层质量良好,没有出现明显气孔和裂纹,涂层与基体呈致密的冶金结合.物相组成主要包括γ-(Fe,Ni),Cr_(7)C_(3),M_(7)C_(3)以及MoS_(2)和CrS两种润滑相等,显微组织主要为柱状晶和等轴晶,在基体中包含了块状硬质相和球形润滑相,平均显微硬度为904 HV,表面残余拉应力为304.6 MPa.涂层的摩擦系数和磨损率分别为0.51和3.64×10^(-4)mm^(3)/(N·m),磨损机理为磨粒磨损和疲劳磨损;经300℃和600℃热处理之后,涂层中没有发生相变,但固溶体和碳化物发生分解,同时晶粒组织长大并呈现出分解现象,导致显微硬度和残余拉应力幅值均降低,磨损率进一步降低,摩擦过程更稳定,磨损机理转变为粘着磨损和磨粒磨损.因此,对激光熔覆Ni35-WCMoS_(2)-CeO_(2)自润滑涂层进行热处理,使显微组织更加均匀并释放残余热应力,碳化物硬质相不易于从涂层中被剥离,使涂层保持较高的硬度和韧性,有助于提高摩擦磨损性能.

超高桥塔混凝土泵送性能优化试验研究

以常泰长江大桥工程为背景,采用一种基于流变仪摩擦计测试流变性能的试验方法,研究了水胶比、同胶凝材料总量、砂率对超高桥塔混凝土工作性及泵送性能的影响,并分析了泵管管径、泵送排量对泵送性能的影响。结果表明:适当提高水胶比、增加胶凝材料总用量、增加砂率均对改善混凝土的工作性与泵送性能有利;流变改性材料的掺入可大幅降低润滑层的黏度系数与混凝土的泵送阻力。

表面粗糙度对滚珠式三叉杆万向联轴器弹流润滑性能的影响

为揭示表面粗糙度对滚珠式三叉杆万向联轴器润滑性能的影响机制,利用高斯随机粗糙表面来表征摩擦副实际接触表面,建立考虑表面粗糙度的等效点接触弹流润滑模型,采用有限差分法和多重网格技术求解Reynolds方程得到油膜压力和接触区弹性变形;通过ANSYS软件建立次表面应力有限元求解模型,分析表面粗糙度参数和表面纹理方向对联轴器弹流润滑性能的影响。结果表明:随着表面粗糙度均方根的增大,接触区内的油膜压力和膜厚波动幅值增大,同时次表面高应力区域逐渐向上表面移动接近接触表面层;随着波长因子的增大,接触区内的油膜压力呈现明显的纹理方向分布,次表面应力出现明显的波动;相较于横向表面纹理方向,纵向表面纹理方向对联轴器润滑性能的影响较大。

自润滑关节轴承在不同应力下的摩擦磨损特性

为了研究应力对自润滑关节轴承摩擦磨损性能的影响,依据SAE AS 81820对EN2584R12轴承在常温下分别进行了50%、100%和150%标准应力条件下的全寿命摆动磨损测试,并对粘贴衬垫的平板样件进行静应力承载测试。采用三维白光干涉形貌仪与金相显微镜(OM)观察静应力承载后衬垫的变形情况,采用体视显微镜(SM)、光学显微镜(OM)和扫描电子显微镜(SEM)观察不同应力下轴承全寿命摆动磨损后内外圈磨损形貌与磨屑形貌。结果表明:全寿命周期内,三种应力下的自润滑衬垫均已磨穿,磨损规律和摩擦因数差异不大,应力越大,轴承表面温度越高,磨屑颜色越深、尺寸越大,失稳期来得更早,破坏更为剧烈;应力对轴承的寿命有显著影响,低应力和中应力条件下的摆动磨损寿命分别是高应力条件的17.95倍和7.86倍;三种应力下的磨损机理均为磨粒磨损与黏着磨损的混合磨损,直接受力区的黏着磨损随载荷的增大而加剧,非直接受力区的磨粒磨损随载荷的增大而减弱。

沟道表面纹理对滚动轴承热弹流润滑的影响

为研究沟道表面纹理对轴承润滑性能的影响,建立了滚动轴承的热弹流润滑模型并与动态接触模型进行耦合分析,仿真结果表明该模型可以模拟角接触球轴承在不同表面下的润滑状态并直观反映其润滑特征的变化。通过对比横向、纵向和各向同性3种表面纹理发现:纵向纹理表面形成油膜的能力较好,平均膜厚和最小膜厚均高于光滑表面,且对表面压力、温度和应力的影响较小,相对于光滑表面可以明显改善润滑的效果;横向纹理和各向同性纹理会引起表面压力、温度和应力的剧增;另外,增大纹理波长或减小纹理幅值均会降低接触区压力,增大膜厚,减小温升,降低最大Von Mises应力,选择合适的纹理波长和幅值有利于提升轴承润滑性能。