SEMI-ELLIPTIC SURFACE CRACK IN AN ELASTIC SOLID WITH FINITE SIZE UNDER IMPACT LOADING

In this paper a semi-elliptic surface crack problem in an elastic solid of finite size under impact loading is investigated. An analysis is performed by means of fracture dynamics and the finite element method, and a three-dimensional finite element program is developed to compute the dynamic stress intensity factor. The results reveal that the effects of the solid＇s boundary surface, crack surface, material inertia and stress wave interactions play significant roles in dynamic fracture.

大尺寸非标碟簧承载性能仿真分析

以某锤击式振打系统中的大尺寸非标碟簧为研究对象,对其在不同载荷作用下的响应特性进行了研究。分别采用理论及仿真模拟方法,对标准碟簧及大尺寸非标碟簧的载荷-变形及载荷-应力状态进行了分析;并采用仿真分析方法,研究了对合状态下重载非标碟簧的响应特征。研究结果表明,对于大变形工况,有限元法能更准确地描述大尺寸非标碟簧的承载性能;大尺寸非标碟簧承受载荷小于额定载荷时,其载荷-变形量呈现线性特征;承受载荷超过额定载荷后,载荷-变形量呈现非线性特征。分析认为,碟簧载荷与变形量的理论计算方法适用于结构的小变形状态,当载荷超过额定载荷时,碟簧的变形较大,小变形的线弹性理论已经不适用于大载荷工况。随着载荷变大,对合状态碟簧接触面的接触状态会发生突变,从面-面接触变成线-面接触,接触状态的改变会造成碟簧局部应力产生变化,影响碟簧的安全使用。

Influence of Specimen Size on Compression Behavior of Cement Paste and Mortar under High Strain Rates

Static and dynamic compression tests were carried out on mortar and paste specimens of three sizes（Ф68 mm×32 mm,Ф59 mm×29.5 mm and Ф32 mm×16 mm）to study the influence of specimen size on the compression behavior of cement-based materials under high strain rates.The static tests were applied using a universalservo-hydraulic system,and the dynamic tests were applied by a spilt Hopkinson pressure bar（SHPB）system.The experimentalresults show that for mortar and paste specimens,the dynamic compressive strength is greater than the quasi-static one,and the dynamic compressive strength for specimens of large size is lower than those of smallsize.However,the dynamic increase factors（DIF）has an opposite trend.Obviously,both strain rate and size effect exist in mortar and paste.The test results were then analyzed using Weibull,Carpinteriand Ba？ant＇s size effect laws.A good agreement between these three laws and the test results was reached on the compressive strength.However,for the experimentalresults of paste and cement mortar,the size effect is not evident for the peak strain and elastic modulus of paste and cement mortar.

Size distribution and diffuse pollution impacts of PAHs in street dust in urban streams in the Yangtze River Delta

Particles of dust washed off streets by stormwater are an important pathway of polyaromatic hydrocarbons （PAHs） into urban streams. This article presented a comprehensive assessment of the size distribution of PAHs in street dust particles, the potential risks of the particles in urban streams, and the sources and sinks of PAHs in the stream network. This assessment was based on measurements of 16 PAHs from the USEPA priority list in street dust particles and river sediments in Xincheng, China. The content of total PAHs ranged from 1629 to 8986 Dg/kg in street dust particles, where smaller particles have a higher concentrations. Approximately 55% of the total PAHs were associated with particles less than 250 μm which accounted for 40% of the total mass of street dust. The PAH quantities increased from 2.41 to 46.86 μg/m2 in the sequence of new residential, rising through main roads, old town residential, commercial and industrial areas. The sediments in stream reaches in town were found to be sinks for street dust particle PAHs. The research findings suggested that particle size, land use and the hydrological conditions in the stream network were the factors which most influenced the total loads of PAH in the receiving water bodies.

Dynamic behavior of single-layer latticed cylindrical shells subjected to seismic loading

The single-layer latticed cylindrical shell is one of the most widely adopted space-fl'amed structures.In this paper,free vibration properties and dynamic response to horizontal and vertical seismic waves of single-layer latticed cylindrical shells are analyzed by the finite element method using ANSYS software.In the numerical study,where hundreds of cases were analyzed,the parameters considered included rise-span ratio,length-span ratio,surface load and member section size.Moreover,to better define the actual behavior of single-layer latticed shells,the study is focused on the dynamic stress response to both axial forces and bending moments.Based on the numerical results,the effects of the parameters considered on the stresses are discussed and a modified seismic force coefficient method is suggested.In addition,some advice based on these research results is presented to help in the future design of such structures.

Attenuation of Salt-Loading Induced Cardiomegaly and Dyslipidemia in Wistar Rats by Aqueous Leaf Extract of <i>Chromolaena odorata</i>

The effect of aqueous extract of the leaves of Chromolaena odorata on body weight, organ sizes, lipid profiles and atherogenic indices was investigated in normal and sub-chronic salt-loaded rats. The normal and treatment control groups were fed 100% of commercial feed, while the test control, reference and test treatment groups received an 8% salt-loaded diet. The extract (at 100 and 200 mg/kg body weight) and moduretics (at 1 mg/kg body weight) were orally administered daily. The normal and test control groups orally received appropriate volumes of water. The extract was screened for bioactive components using gas chromatography-coupled-flame ionization detector. The main glycosides, saponins, allicins, alkaloids, benzoic acid derivatives, terpenes and lignans detected were arbutin, avenacin B-1 (and avenacin A-1), diallyl thiosulphinate, lupanine, ferulic acid (and vanillic acid), limonene and retusin, respectively. Compared to test control, the extract dose-dependently, significantly (P 0.05) lowered the heart size, plasma levels of triglyceride, total density lipoprotein, very low density lipoprotein, low density lipoprotein and non-high density lipoprotein cholesterol and atherogenic indices (cardiac risk ratio, atherogenic coefficient and atherogenic index of plasma). It also significantly increased plasma high density lipoprotein level. These results suggest a protective mechanism of the extract against hypertension induced cardiomegaly and dyslipidemia, thus suggesting that this may underlie its antihypertensive action.

The Online Assessment of Electric Distribution Network Load Capability

To improve the security and reliability of a distribution network, several issues, such as influences of operation con-strains, real-time load margin calculation, and online security level evaluation, are with great significance. In this pa-per, a mathematical model for load capability online assessment of a distribution network is established, and a repeti-tive power flow calculation algorithm is proposed to solve the problem as well. With assessment on three levels: the entire distribution network, a sub-area of the network and a load bus, the security level of current operation mode and load transfer capability during outage are thus obtained. The results can provide guidelines for prevention control, as well as restoration control. Simulation results show that the method is simple, fast and can be applied to distribution networks belonged to any voltage level while taking into account all of the operation constraints.

A CONTRAST ANALYSIS ON THE LOAD CHARACTER OF THE CHANGJIANG RIVER AND THE HUANGHE RIVER

According to the analysis of grain size, mineral composition and inclusion in quartz grain of the suspended and bed load sampled from the Changjiang (Yangtze) River and the Huanghe (Yellow) River, the authors reveal the differentiation of loads between the two rivers. In the Huanghe River the size of suspended load is coarser than that in the Changjiang River, while the bed load is on the contrary. Through heavy mineral analysis, the biotite content of the Huanghe River loads is much higher than that of the Changjiang River, and the monomorillonite content of the former is about two times higher than the latter. All those may be attributed to the effects of different material sources and hydraulic conditions on load. The analysis of inclusion in quartz grain definitely illustrates the environmental difference of material sources between the two rivers. In the meantime, it provides a new method in seeking source of river load.

An Experimental Study on the Effect of Foundation Depth, Size and Shape on Subgrade Reaction of Cohessionless Soil

The modulus of subgrade reaction ks depends on several factors such as the size and shape of the foundation as well as the embedment depth of the foundation. The present study is an experimental analysis using plate load test to determine the effect of foundation depth, size as well as the shape on the modulus of subgrade reaction (ks) of cohesionless soils. It was carried out by using nine rigid steel plates with different sizes and shapes (circular, square and retangular). The tests were carried out on cohessionless soil with different relative densities under different applied pressures. The settlement has been measured at the surface of the plate for different depths of footings. The ultimate bearing capacity [qu] has been determined from the stress-settlement relationships. The allowable bearing capacity (qa) was determined by dividing the ultimate bearing capacity (qu) by F.S. = 3.0, after which the corresponding settlement (Sa) has been obtained. However, ks was calculated based on dividing the allowable bearing capacity (qa) by the corresponding settlement (Sa). From the present study it is concluded that the subgrade reaction ks of cohessionless soil increases with increasing foundation depth as well as foundation size. In addition, subgrade reaction ks of cohessionless soil under rectangular footing is higher than that under square and that under circular one with same equivalent area. An empirical formula is presented to calculate the subgrade reaction ks of cohessionless soil under square foundation taking into consideration foundation depth. Fair agreement has been obtained between values of ks from the empirical formula at depth of footing = 0.00 B and Biot (1937) as well as Meyerhof and Baike (1965).

非对称载荷作用下倾斜区段煤柱稳定性分析及控制技术

为解决工作面回采及巷道掘进影响下倾斜区段煤柱稳定性劣化的复杂问题,运用弹性力学半逆解法及摩尔-库伦准则建立力学模型,结合三维有限元数值模拟,深入分析了倾斜区段煤柱一侧受载结构形态特征,明确了倾斜煤柱失稳致灾力源及载荷的分布特性,探究了采掘扰动下倾斜区段煤柱塑性变形-失稳-破坏的动态演化过程,揭示了非对称载荷作用下倾斜区段煤柱临界失稳致灾机理,以此为基础优化了倾斜煤柱及周围巷道稳定性控制技术。结果表明:区段煤柱因煤层倾角导致的倾斜形态是煤柱所承受载荷呈非对称状的关键诱因,这一特性致使倾斜煤柱最底端区域覆载最大,且当此区域失稳破坏时,呈现由煤柱下端底角塑性区向煤柱上端底角塑性区扩展的运移过程,并因此得出倾斜区段煤柱临界尺寸随煤层倾角增大而增加的演化规律。由此,针对大南湖一矿倾斜区段煤柱及周围巷道变形失稳的问题,采用支护优化及注浆加固等措施,降低了倾斜区段煤柱侧巷道的变形速率,为类似矿井的煤柱稳定性控制提供了借鉴。

机械臂K因子影响因数的研究和扩展寿命计算

基于应力强度因子知识,借助Workbench软件采用子模型技术和奇异单元研究搬运机械臂的断裂强度问题。在搬运机械臂基座关节相贯线处建立椭圆形表面裂纹有限元模型,开展抓取载荷、裂纹相对尺寸对应力强度因子影响的研究并进行裂纹扩展寿命计算。分析结果表明:KⅠ、KⅢ随着抓取载荷的增加而增加,而KⅡ随着抓取载荷的增加而减小;随着裂纹短半轴和长半轴的增加,Ⅰ型、Ⅲ型应力强度因子先增大后减小且相应的应力强度因子逐渐增大,Ⅱ型应力强度因子先减小后增大;裂纹两端与中间段的裂纹扩展速率不同,呈现两端快、中间慢的特点且裂纹长半轴尺寸比短半轴尺寸对裂纹扩展速率的影响更敏感,机械臂的剩余寿命富余。

分级加载下不同骨料粒径的混凝土声发射波速分析

目前利用声发射技术对混凝土结构进行损伤定位时,采用固定表面波速进行损伤定位,没有考虑混凝土声发射信号是从混凝土内部传播出来以及混凝土材料在不同的阶段产生的损伤对声发射波速的影响,导致检测结果与实际产生一定的偏差。以3种不同类型的弹性波速变化将混凝土的损伤化为5个阶段。利用波速的变化结合经典材料损伤力学从而进行材料损伤的定量分析。通过试验结果分析得出:当水灰比一定时,随混凝土粗骨料粒径的增大弹性波波速呈上升的趋势,但波速上升的趋势随粒径的增大而相对减小。随着应力的增加,波速降低时,波速与应力阶段存在一定的线性关系。采用不同加载阶段波速的不同进行变波速定位,定位精度更接近实际损伤位置,可有效提高定位精度。试验得出的结果为混凝土桥梁结构无损检测提供了新的思路方向为其安全检测提供了参考价值。

Improving the Reliability of a Domestic Refrigerator Compressor Subjected to Repetitive Loading

As a reliability quantitative specification, parametric accelerated life testing was used to assess the reliability of a newly designed compressor of a commercial refrigerator subjected to repetitive stresses. A generalized life-stress failure model and new sample size equation with a new load concept were derived starting with the basic refrigeration cycle. The sample size equation with the acceleration factor also enabled the parametric accelerated life testing to quickly evaluate the expected lifetime. The design of this testing should help an engineer uncover the design parameters affecting reliability during the design process of the compressor system. Consequently, it should help companies improve product reliability and avoid recalls due to the product failures in the field. A newly designed compressor in a commercial refrigerator was used as a test case.

装配整体式梁柱节点的抗震性能对比研究

目的 研究预制柱纵筋间距放大后装配整体式T型节点和十字型节点的抗震性能,为工程设计提供依据。方法 对5个足尺梁柱节点试件进行低周往复荷载试验,通过对比各试件的滞回曲线、骨架曲线和位移延性等,研究了节点类型、柱纵筋间距和轴压比对梁柱节点抗震性能的影响。结果 装配式节点均发生梁端弯曲破坏,预制柱和节点核心区未见明显破坏,破坏主要是预制梁端底部纵筋屈服和梁端底部混凝土压碎脱落;楼板加强了叠合梁的抗负弯矩能力,叠合梁上部现浇混凝土和预制混凝土交界面出现明显的水平剪切裂缝;柱纵筋间距放大后,与对比试件相比,T型节点的承载力提高了9.2%,十字型节点的承载力提高了1.3%。结论 柱纵筋间距放大试件的延性和耗能能力与对比试件相差不大,柱纵筋间距放大对梁柱节点的抗震性能影响不大;十字型节点和T型节点位移延性系数相差不大。

轴向荷载作用下小规格拉铆钉和普通螺栓疲劳性能对比研究

拉铆钉因其良好的防松动、抗疲劳和防腐性能以及较强的环境适应性等特点而被广泛应用于航空航天、轨道交通、桥梁建筑等领域。为解决光伏支架中螺栓连接易发生疲劳的问题,现研究一种国产新型拉铆钉的轴向疲劳性能,用以代替普通螺栓连接进而提高光伏支架的疲劳寿命。对LMY8和LMY10小规格拉铆钉及同规格的普通螺栓进行了轴向荷载作用下的静力试验和疲劳试验,并利用ABAQUS软件进行了拉铆钉铆接过程的模拟,利用FE-Safe软件对拉铆钉疲劳寿命进行了模拟。研究结果表明:在同样条件下,铆钉的疲劳性能优于普通螺栓的疲劳性能;拉铆钉在轴向荷载作用下的疲劳断口位于套环和锁紧环槽啮合的第一圈螺纹处,此处应力集中是拉铆钉发生疲劳失效的主要原因;拉铆钉的疲劳寿命会随着最小荷载的增大而提高,随最大荷载的增大而降低;由疲劳云图可知,拉铆钉在承受轴向循环荷载作用时,铆钉头部下方R角过渡处也会产生较大的应力,此区域也是易发生疲劳失效的部位。

高校大科学设施推动高端装备制造业创新研究——以环境与载荷耦合全尺寸试验为例

大科学设施是推动前沿基础科学发展和技术创新的重要条件支撑,越来越多的高校承担了大科学设施的建设运行任务。重大工程材料服役安全研究评价设施通过研制开发能够实现真实服役工况的、复杂环境与载荷耦合的全尺寸试验装置,积极面向高端装备制造开展复杂工况下服役性能试验,对相关学科融合发展,以及国产高端装备制造的材料选型、新材料应用、设计优化和可靠性评价等方面发挥了不可替代的推动作用,在核心技术研发与产品验证等环节中加速国产化进程,是直接面向国民经济主战场的大科学设施。该文在总结环境与载荷耦合全尺寸试验技术创新的基础上,分析了大科学设施服务高端装备制造产业的实际案例。

金属材料超声疲劳试验数据的一致性分析

超声疲劳试验技术已被广泛用于金属材料的超高周疲劳性能测试。超声频率条件下开展试样的超高周循环加载时,需要采用间歇加载控制试样发热,这会影响到试验结果一致性。同时,当循环周次由高周跨越至超高周后,疲劳试验结果对试样形状、尺寸、表面质量和内部缺陷更为敏感。基于大量的试验结果对这些影响因素进行了一致性分析。结果表明,加载间歇比和试样形状、尺寸对试验结果均有影响;试样表面质量与内部缺陷存在竞争效应;通过疲劳S-N曲线可以有效预测内部缺陷对超高周疲劳的影响。

负载下活性粉末混凝土钢筋网加固足尺混凝土柱轴压性能试验研究

为提高负载下钢筋混凝土(RC)柱的轴心抗压性能,使用活性粉末混凝土钢筋网(RPCSM)对负载下的RC足尺柱进行加固,设计制作了7根RC方柱试件,其中1根未加固对比柱、1根端部箍筋加密加固柱、2根RPCSM加固柱、3根端部箍筋加密RPCSM加固柱。考虑加固层厚度、钢筋网配筋率和端部箍筋加密对轴心受压RC柱性能的影响,进行了试验研究并分析了各试件的破坏模式、荷载-变形关系和应变变化规律。结果表明:加固柱的承载力提高了2.81~3.82倍;原混凝土柱与RPCSM加固层界面粘结可靠,共同工作良好;随着钢筋网配筋率的提高以及加固层厚度的增加,端部箍筋加密后整体性的提高,承载力和轴向变形能力提高,但延性有所下降。结合规范和破坏机理,给出了承载力计算公式,以促进该加固技术的推广。

瞬态热流下钨再结晶规律的研究

通过观测钨分别在能量密度3.82MJ⋅m^(−2)/脉宽5ms和能量密度1.5MJ⋅m^(−2)/脉宽1ms的脉冲电子束1~100次的辐照下发生再结晶及晶粒长大的情况,研究了钨在瞬态热流下的再结晶行为及其对脉冲参数的依赖关系。根据非等温匀速加热退火过程的晶粒尺寸表达式推导出了瞬态热流下晶粒正常长大的表达式,再结合实验数据推导出了钨在脉宽ms量级瞬态热流辐照下发生正常长大的晶粒尺寸对脉冲参数的依赖关系。利用该关系计算得到的钨在脉宽5ms、1ms的脉冲电子束辐照下的晶粒尺寸与晶粒只发生正常长大的实验结果相吻合。

考虑油液流变时变特性和深度特征尺寸的静压转台流动分析

转台用液压油的非牛顿特性及随时间推移流变特性的变化,将影响油液在转台内的流动以及承载能力。以双环形静压转台为研究对象,针对油液的流变时变特性,提出了一种虚外力项LBM方法,并利用泊肃叶流的理论解进行了验证,通过仿真分析发现,双环形转台侧边入油口可有效增加中心凹槽的压力,改善承载能力。油液流变时变特性和转台深度特征尺寸是两个重要因素。相对于速度分布,封油边深度及油腔深度对承载能力的影响更加显著。随时间推移,油液黏度增大,使油液的流动减缓,速度减小,承载能力变弱,因此建议定期更换液压油,以保证转台的正常工作。