Effects of creep feeding and supplemental glutamine or glutamine plus glutamate (Aminogut) on pre- and post-weaning growth performance and intestinal health of piglets

Background： Creep feeding is used to stimulate piglet post-weaning feed consumption.L-Glutamine（GLN） is an important source of fuel for intestinal epithelial cells.The objective of this study was to determine the impact of creep feeding and adding GLN or AminoGut（AG;containing glutamine ＋ glutamate） to pre-and post-weaning diets on pig performance and intestinal health.Litters（N = 120） were allotted to four treatments during 14–21 d of lactation： 1） No creep feed（NC,n = 45）;2） creep fed control diet（CFCD,n = 45）;3） creep fed 1% GLN（CFGLN,n = 15）;4） creep fed.88% AG（CFAG,n = 15）.After weaning,the NC and CFCD groups were sub-divided into three groups（n = 15 each）,receiving either a control nursery diet（NC-CD,CFCD-CD） or a diet supplemented with either GLN（NC-GLN,CFCD-GLN） or with AG（NC-AG,CFCD-AG）.Litters that were creep fed with diets containing GLN or AG also were supplemented with those amino acids in the nursery diets（CFGLN-GLN,CFAG-AG）.Glutamine was added at 1% in all three post-weaning diet phases and AG was added at.88% in phase 1 and 2 and at.66% in phase 3.Results： Feed conversion（feed/gain） showed means among treatment means close to significance（P = 0.056） and Tukey＇s test for pairwise mean comparisons showed that Pigs in the CFGLN-GLN group had the best feed conversion（feed/gain） in the first three-week period post-weaning,exceeding（P = 0.044） controls（CFCD-CD） by 34%.The NC-AG group had（P = 0.02） the greatest feed intake in the last three week of the study,exceeding controls（CFCD-CD） by 12%.CFGLN-GLN,CFCD-GLN and sow reared（SR） pigs had the greatest（P = 0.049） villi height exceeding the CFCD-AG group by 18%,20% and 19% respectively.The CFAG-AG group had the deepest（P = 0.001） crypts among all treatments.CFGLN-GLN,CFCD-GLN and SR groups had the greatest（P = 0.001） number of cells proliferating（PCNA） exceeding those in the NC-CD group by 43%,54% and 63% respectively.Sow reared pigs showed the greatest（P = 0.001） intestinal absorption capacity for xylose and mannitol.Conclusion： Supplementation of creep feed and nursery diets with GLN and/or AminoGut in the first three week improved feed conversion possibly due to improved intestinal health.

EFFECT OF Mg AND Zr ADDITION ON CREEP CRACK GROWTH BEHAVIOUR OF A Ni-BASE SUPERALLOY

The creep crack growth(CCG)and the time to carck initiation and rupture of specimen (t_(rc)and t_r)were measured by means of electrical potential method on single edge notched specimens at 700℃.The field near the crack tip under steady-state creep was represented by energy rate integral(C~*),and the CCG rate as a function of C~* has been obtained.The agreement between the predicted and observed t_(rc)values is quite good.It was found that the addition of small amount of Mg and Zr in the alloys causes t_(rc)and t_r of the specimens to in- crease significantly.

CREEP CRACK GROWTH BEHAVIOR OF ALLOY 718 DURING HIGH TEMPERATURE EXPOSURE

Alloy 718 is a precipitation strengthened nickel-based superalloy based on the precipitation of γ″-Ni3Nb (DO22 structure) and γ′-Ni3(Al,Ti) (L12 structure) phases. Creep crack growth rate (CCGR) was investigated after high temperature exposure at 593, 650 and 677℃ for 2000h in Alloy 718. In addition to the coalescence of γ′/ γ″ and the amount increasing of δ phase, the existence of a bcc chromium enriched α-Cr phase was observed by SEM, and the weight fraction of α-Cr and other phases were determined by chemical phase analysis methods. The CCGR behavior and regulation have been analyzed by means of strength and structure analysis approaches. The experimental results show higher the exposure temperature and longer the exposure time, lower the CCGR. This is probably attributed to the interaction of material softening and brittling due to complex structure changes during high temperature exposure. Therefore, despite α-Cr phase formation and amount enhancement were run in this test range. It seems to us a small amount of α-Cr will be not harmful for creep crack propagation resistance, which is critical for disk application in aircraft and land-based gas turbine.

EFFECT OF SULPHURIZING-OXIDIZING ENVIRONMENT ON CREEP CRACK GROWTH OF Ni-BASE SUPERALLOY GH30

An investigation was made on the creep crack growth behaviour under static load at 1023 K for Ni-base superalloy GH30 exposed to air and air+10% SO_2.The results showed that in the region of low stress intensity factor,the creep crack growth rate is higher in air+10% SO_2 than in air only,while in the high region,it is reverse.The fractograph of specimens has been analyzed,and the mechanism of creep crack growth together with the influences of sul- phur and oxygen has been discussed as well.

Carbide Effects on Creep Crack Growth of Ni-Cr Austenitic Steels

By controlling the carbon content of Fe-15Cr-25Ni alloys,three types of microstructures were obtained:single phase austenite (γ),γ+intergranular carbides, γ+intergranular carbides + intragranular carbides. Creep crack growth behaviour of the three alloys has been compared at 973 K and 1123 K. Intergranular carbides show higher creep crack growth resistance than intragranular carbides.Cav- ities nucleate at the triple junctions of grain bound- aries for single phase alloy,but at intergranular carbides for two-phase alloys.The precipitation of intergranular carbide not only changes the nucleation mechanism of cavities,but also inhibits the growth and coalescence of cavities.The precipi- tation of intragranular carbide obstructs the nucleation and growth of cavities furthermore.

EFFECT OF GRAIN BOUNDARY CARBIDE ON CREEP CRACK GROWTH IN Fe-Cr15-Ni25 ALLOY

Creep crack growth behavior of Fe-Cr15-Ni25 alloys with different grain boundary features has been studied.Cavities nucleate at triple junctions of grain boundaries for the single phase alloy and at grain boundary carbide for the alloy with grain boundary carbide.Grain bounda- ry carbide particles are obstacles to cavity growth and coalescence,and therefore increase the creep crack growth resistance greatly.

CRACK GROWTH,FRACTURE FEATURE AND RUPTURE LIFE DURING CYCLIC CREEP OF SUPERALLOY GH2132

The effects of cyclic loading on crack growth, fracture feature and rupture life of superalloy GH2132 have been studied in the present paper. The crack growth tests were carried out at 550 on compact tension specimens under a wide range of load levels and various periods of hold time, and the fracture surfaces were examined on a scanning electron microscope. The results show that, for both static and cyclic creep, Stage-I of crack growth is related with initial test stress, during which the crack extension is about 0.5mm, and that the final effect of cyclic loading on rupture life depends on the counteraction of its two reversed effects on crack growth rate before and after the point n=0.2.

Creep fracture parameters of polyethylene pipe welded joints

Double edge notched tensile （DENT） tests were carried out to investigate the slow crack growth （SCG） behavior of PESO welded joints. Efforts were made to acquire creep fracture parameters which can characterize creep resistance. Results show that creep compliance indicates an ascending trend with the increase of applied stress. A global creep load parameter is obtained. It has a linear relationship with fkacture time in logarithmic coordinate system and helps to predict the fracture time at any applied load.

Creep Deformation and Rupture in Smooth and Notched Specimens in HK40 Steel

The effects of the eutectic carbides rand secondary carbides on creep deformation and rupture in smooth bars and CT specimens have been studied. The results show that the resistance of the eutectic carbides of skeleton shape to crack growth is larger than that of the blocky shape carbides. The dendritic segregation of secondary carbides promotes the creep ductility. As the secondary carbide particles become coarser, the creep ductility increases and the crack growth rate decreases. However, if the size of secondary carbide is too large, the creep strength decreases too much and therefore crack growth rate increases.

Investigation of average growth stresses in Cr_2O_3 scales measured by a novel deflection method

The stress in the oxide film plays an important role to keep it intact so it is necessary to determine the stress in the oxide scale. Average growth stresses in Cr 2O 3 scales formed on Ni base alloy (Ni80Cr20) at 1?000?℃ in air were investigated by a novel deflection technique. It is found that the growth stress in the oxide scale is basically compressive and its average order is 100?MPa. The stress values are high for the thin scales and become low for thick scales after oxidized for 10?h. The planar stress distribution in metals is complex. It is both compressive and tensile at the beginning of oxidation procedure, and then become only tensile during further oxidation.

考虑蠕变三阶段的哈氏合金X蠕变-疲劳裂纹扩展模拟

结合应变硬化定律和连续损伤力学,提出了一种考虑蠕变3阶段的本构模型,对650℃下的哈氏合金X的CT试样进行了裂纹扩展有限元模拟分析.对比分析了不同蠕变阶段对纯蠕变裂纹扩展的影响,使用考虑蠕变3个阶段的本构模型进行了蠕变-疲劳裂纹扩展模拟,讨论了载荷幅值、载荷比和保载时间对裂纹扩展速率的影响,并分析了每种载荷条件对裂纹扩展期间损伤积累的贡献.结果表明:纯蠕变裂纹扩展模拟结果中,考虑所有蠕变阶段的本构模型计算结果与实验结果一致性最高.载荷从5 kN增加到7 kN,考虑蠕变第Ⅰ、Ⅱ阶段的裂纹扩展速率平均预测差异由0.57增至0.61,考虑蠕变第Ⅱ阶段和考虑蠕变第Ⅱ、Ⅲ阶段分别由0.67减至0.64、由0.16减至0.07.蠕变-疲劳裂纹扩展模拟结果显示,随着载荷幅值从5 kN增大至7 kN,载荷比从0.01增至0.50,裂纹扩展速率前者增大、后者减小,da/dt-C t,avg曲线斜率基本不变,同时蠕变损伤占比增大,疲劳和交互损伤占比减小,各加载情况结果的蠕变损伤均占主导,其次为交互损伤,疲劳损伤占比最小.随保载时间从1 s增加到1800 s,循环相关的裂纹扩展速率增大,时间相关的扩展速率减小,da/dt-C t,avg曲线斜率增大,蠕变损伤增大,疲劳损伤减小,交互损伤先增后减,保载时间为10 s时各损伤占比近似相等,保载时间为1 s时疲劳损伤为83%,保载时间为600 s时蠕变损伤为96%.

CLEAVAGE RUPTURE OF Ti ALLOY TC11 UNDER FATIGUE-CREEP INTERACTION

The cleavage rupture behaviour of the Ti alloy TC11 with various microstructures,i.e., equiaxed,duplex and interweaving,has been studied under fatigue-creep interaction at 520℃.It was found to be not only related to the rate of creep void initiating,but also control- led by the creep strain accumulation on holding under tension test and stress state at crack-tip.This seem to be combinably offected by both value of critic void initiating strain and parameter,V_(GC),of critic void growth.

X12转子钢蠕变-疲劳裂纹扩展行为的研究

在600℃条件下进行蠕变疲劳裂纹扩展速率实验,施加不同的载荷和保载时间,研究力值和保载时间对蠕变疲劳裂纹扩展速率的影响,并通过金相检测观察裂纹扩展路径。结果表明:在低应力条件下,蠕变疲劳裂纹扩展速率随着保载时间缩短而增大;在高应力条件下,蠕变疲劳裂纹扩展速率随保载时间延长而减小;相对含有疲劳成分裂纹而言,蠕变裂纹的扩展路径显得更加圆滑。

汽轮机老化热部件剩余寿命评估方法研究

随着国内大批火电机组达到设计寿命或寿命提前耗尽,如何系统、全面地评估老化机组的安全性与剩余寿命已成为目前亟待解决的问题。通过运行数据分析和理论计算对某电厂联合循环汽轮机中压内缸进行了剩余寿命预测,考虑了蠕变和低周疲劳2种损伤失效机理,分别利用损伤累积理论和断裂力学理论计算了汽缸的裂纹萌生寿命和裂纹扩展寿命。同时,基于金相检查结果评定材料的剩余寿命,现场硬度测试结果也可作为评估的重要补充。研究成果可为汽轮机部件寿命管理和检修周期的确定提供参考。

不同生长调节剂对马蹄金愈伤组织诱导的影响

马蹄金是一种优良的地被兼观赏草坪植物。采用正交设计试验法 ,研究了四种不同生长调节剂对马蹄金子叶、叶片、叶柄和下胚轴愈伤组织诱导的影响。结果表明 :生长调节剂是诱导愈伤组织的关键 ,2 ,4 D对愈伤组织诱导具有显著的影响 ,适宜于马蹄金愈伤组织诱导的培养基及生长调节剂为MS +1 .0mg/L 2 ,4 D +0 .2mg/L 6 BA +0 .2mg/LKT +1 .0mg/Lα NAA。

含裂纹结构时间相关的疲劳断裂理论与剩余寿命评价技术

高温结构的疲劳失效是与时间相关的,建立这一失效机制下的断裂理论和寿命评价技术,进而控制结构失效是人们多年来努力的目标.从裂纹扩展控制参量、裂纹扩展规律和寿命评价技术、材料老化与环境因素影响和结构完整性评定工程方法等几个方面,对近年来这一领域的研究进展进行了总结,并对今后该领域的发展方向进行了预测.

皮肤伸展术中新增皮肤来源的实验研究

目的:研究皮肤伸展术中“额外皮肤”的来源及所占比例。方法:健康的白色家猪9只,采用自身对照的方法,左右侧分别为实验及对照组。实验侧采用自制外向型皮肤牵张装置进行皮肤牵张,对照例不予牵张。分别观察牵张前和牵张1周后皮肤弹性变化和机械蠕变的变化及缝合后1,2,3,4,5,6,7周生物性增长面积,计算三者的比例。结果:实验组牵张前后皮肤弹性由12.32％±2.40％下降至2.64％±0.69％。增生面积中所占比例:机械蠕变51.94％±6.23％,弹性伸展13.65%±5.17%,生物性增长34.44％±2.74％。结论:皮肤伸展术的新增皮肤的来源中不仅有皮肤弹性变化和机械蠕变性变化,还有生物性增长的面积。伸展术引起了皮肤组织的生物性增长,约占新增面积中的34％,在伸展术后2—3周皮肤增生较明显。

紧凑拉伸试样厚度对25Cr2NiMo1V钢高温蠕变裂纹扩展速率的影响

研究了紧凑拉伸(CT)试样厚度对25Cr2NiMo1V钢在566℃时,蠕变裂纹扩展(CCG)速率的影响规律及其机理。结果表明:试样厚度对CCG速率的影响与载荷水平(C*)相关;在低载荷水平区,随试样厚度的增加,面外拘束水平增大,试样趋向于以沿晶蠕变脆性方式断裂,CCG速率增大;在高载荷水平区,不同厚度的试样均以沿晶和穿晶的混合方式发生蠕变延性断裂,CCG速率基本不受试样厚度的影响;CCG速率与载荷水平在双对数坐标中并非呈单一的线性关系,而是由不同斜率的两段直线构成,低载荷水平区的直线斜率低于高载荷水平区的,如果用高载荷水平区的CCG速率数据外推得到低载荷水平区的CCG速率,将得到非保守的结果。

热生长下热障涂层残余应力及失效分析

针对典型热障涂层结构以界面开裂和涂层剥落为主要失效模式,考虑界面凹凸微观形貌特征,借助材料转换的方法实现氧化生长,利用粘弹塑性有限元法,研究了氧化层热生长和蠕变等因素对热障涂层残余应力的影响,并从应力应变循环演化的角度对热障涂层系统中微裂纹的萌生位置进行了预测。结果表明,随着氧化层厚度的增大,垂直于界面方向的残余应力迅速增大;材料蠕变对热障涂层系统应力释放作用显著;从残余应力和应变演化的角度进行评价,结构中的微裂纹会率先出现在粘接层凸峰以及陶瓷层/氧化层/黏结层界面的中间位置,仿真分析结果与试验结果一致。

基于蠕变孔洞长大理论的高温构件蠕变强度设计准则研究

在分析高温构件蠕变失效微观机理的基础上,提出了基于孔洞长大理论的蠕变应变设计准则和蠕变应力设计准则。定义了蠕变等效应力和蠕变等效应变,探讨了蠕变许用应力和蠕变许用应变的确定原则。这些设计准则考虑了蠕变失效的微观机理和时间相关性的影响,能给出比传统设计方法更为稳定和合理的设计结果。分析了在蠕变强度设计上存在的困难,并提出了相应的建议。