冲击加载条件下金属粉末的动态力学性能分析

为研究金属粉末在冲击加载过程中, 粉末预压力对压坯动态力学响应的影响, 设计了基于分离式霍普金森压杆装置(split Hopkinson pressure bar, SHPB)的金属粉末高应变率冲击加载实验, 并结合一维应力波理论对预压后粉末压坯的力学性能进行分析。结果表明:在冲击过程中, 金属压坯会表现出较为明显的应变率效应; 加载率越大, 材料的应变能越大, 预压力越大, 应变硬化率越大; 在相同的加载条件下, 预压力越大, 压坯临界位移越小。     

热等静压方法制备细晶钨合金及其动态力学性能研究

采用喷雾干燥方法制备了超细90W7Ni3Fe复合粉末,并冷等静压成形,压坯经过低温还原后采用热等静压进行低温压制烧结,得到了晶粒度小于5μm、接近理论密度的钨合金材料.利用Hopkinson压杆装置对细晶钨合金进行了动态力学性能研究,对不同应变率下的应力应变曲线进行分析.结果表明:通过热等静压低温烧结而成的细晶钨合金,在高应变率下表现出明显的应变强化和应变率强化效应,其动态力学性能优于常规液相烧结制备的钨合金.     

TB10钛合金的动态力学性能及绝热剪切分析

利用分离式的Hopkinson压杆,得到了不同组织状态的近β型TB10钛合金在高应变率下的动态压缩应力-应变曲线,结果表明:TB10钛合金的三种组织状态都表现出应变率敏感性。通过光学显微镜分析其显微组织的变化规律,结果表明:两相区固溶 时效、两相区固溶 双重时效的试样中均可观察到明显的绝热剪切带,且沿剪切带出现裂纹;单一固溶态试样金相观察表明晶粒的变形是均匀的,没有观察到绝热剪切带。在单一固溶态试样中出现了应力诱发马氏体相。     

基于J-C模型的TC18钛合金动态本构方程构建

采用电子万能试验机对TC18钛合金进行常温准静态压缩实验,得到该合金在准静态下的实验数据,根据实验数据,选用分离式Hopkinson压杆对TC18钛合金在温度分别为298、523、773、1 023 K,应变率分别为500、1 000、1 500 s~(-1)下进行动态力学性能实验,从而获得TC18钛合金在高温动态压缩条件下的应力-应变曲线,并利用J-C模型对合金在高应变率下的动态塑性本构关系进行拟合,最终建立该合金在高温下的动态塑性本构方程。通过对模型的计算结果分析表明,该模型可以较好地预测TC18钛合金在高温与冲击载荷共同作用下的塑性流变应力。     

高速冲击条件下TWIP钢组织和性能的研究

采用分离式Hopkinson压杆技术分析了TWIP钢在冲击载荷下应变速率对其性能的影响,采用金相(OM)、X射线衍射(XRD)、透射电镜(TEM)等方法对其变形前后的显微组织进行了研究。结果表明:高应变速率下,TWIP钢的应力-应变曲线存在响应时间,并且在中间阶段出现了波浪形的应力起伏。TWIP钢变形前后都是奥氏体单相组织,形变孪晶与静态变形条件下的相比,较易于多个孪晶系生成,孪晶的宽度、数量增加,间距减小。孪晶与位错的交互作用、孪晶与孪晶的相互作用、特别是多次孪晶的出现是使TWIP钢得到强化的主要变形机制。     

基于SHPB试验的岩石应变率效应分析

岩石材料在静荷载和动荷载作用下,其力学特性差异很大。采用直径100 mm分离式Hopkinson压杆试验装置和波形整形技术对岩石进行动态冲击压缩试验,研究应变率范围为10～100 s~(-1)岩石的动态抗压强度、峰值应变及破坏形态的应变率效应。试验结果表明:试件动态抗压强度和峰值应变均随应变率增加而增大,最大动态抗压强度约为静态强度的2倍。试件动态破坏形态从低应变率下径向劈裂破坏到高应变率下粉碎破坏,随着应变率增加碎块数量明显增多而粒径变小,碎块粒径和块度分布变化显示出试件破坏形态具有明显的应变率效应。     

应变率对Mg-Gd-Y合金断裂机制的影响

对Mg-Gd-Y合金分别使用准静态压缩试验机、分离式霍普金森压杆、平头弹丸侵彻加载,研究了该合金在1×10-3,1×103,1×104s-1时,应变率对其断裂机制的影响.研究结果表明,在应变率为1×10-3 s-1时,呈现出脆性解理断裂特征;当应变率增加为1×103 s-1时,动态压缩后断口除了解理片层外,还出现了热软化带,变形局域化是裂纹形核的通道,最终导致材料的失效.在应变率约为1×104 s-1时,稳定侵彻阶段,绝热剪切带是更高应变率下导致材料断裂的原因,特定位置的绝热剪切带为相变带,应变率的提高有利于形成相变带.应变率是通过影响Mg-Gd-Y合金的热软化效果而影响其断裂机制的.     

高温高应变率下EW75镁合金动态压缩性能与组织演变

为了研究EW75镁合金在不同温度、高应变率下的动态力学性能及变形机制,采用分离式Hopkinson冲击压杆装置(SHPB)对挤压态EW75镁合金进行了动态压缩实验,并利用金相显微镜(OM)和透射电子显微镜(TEM)对冲击后的试样进行了显微分析。结果表明:挤压态EW75镁合金沿ED方向在室温(20～25℃), 200和300℃3个温度的动态压缩载荷下,随应变率的提高具有正应变率强化效应,室温下2826 s~(-1)时具有最大动态工程压缩强度为764 MPa,而在300℃3344 s~(-1)时获得最大动态压缩断裂应变为20%;随着应变率和温度的提高,挤压态EW75镁合金的组织中孪晶的数量增加,再结晶晶粒发生增殖和长大,并有异常长大的晶粒和白亮带的形成;挤压态EW75镁合金的动态压缩变形机制为滑移和孪生两种方式进行,并存在绝热剪切变形,随着温度升高,有动态回复和强烈的再结晶发生。     

高温、高应变率下Ti6321合金的力学行为及本构模型

为了研究Ti6321合金在高温、高应变率下的力学行为,采用分离式霍普金森压杆装置对Ti6321合金进行室温(25℃)和高温(200、400、600℃)动态压缩试验,对其在高温和高应变率下的力学性能、应变率敏感性和温度敏感性进行了研究。采用聚类全局优化算法构建了双态组织Ti6321合金在103s-1下的Johnson-Cook本构模型。结果表明,双态组织Ti6321合金在室温和高温下均存在应变率硬化效应,但试验温度对流变应力的影响比应变率的影响更大。随着压缩试验温度升高,流变应力显著降低,温度敏感因子升高。Johnson-Cook模型拟合的曲线与实验曲线吻合良好,可以用于Ti6321合金高应变率下的力学仿真计算。     

粉末冶金60Al–30Fe–10Bi合金在高速冲击下的变形行为与微观组织演化

通过粉末冶金技术制备60Al–30Fe–10Bi合金药型罩材料,采用分离式霍普金森(Hopkinson)压杆测试了铝基合金在变形温度从25~450℃和应变速率从1300~7000 s~(-1)下的动态冲击压缩力学性能,研究了其动态变形前后微观组织的演变规律和断裂机制。结果表明:60Al–30Fe–10Bi合金在动态冲击压缩下的流变应力主要依赖于温度的变化,流变应力随变形温度的升高而降低,而应变速率对流变应力的影响不大;合金在25℃、1300 s~(-1)下的高速冲击载荷作用下的失效原因是发生了绝热剪切。     

转炉炉壳热应力分析

根据实际转炉建立实体模型。以有限元为手段,考虑了炉衬和炉壳材料的物性参数随温度变化的特点和炉衬与炉壳之间膨胀间隙,计算了转炉炉壳在温度载荷和炉衬膨胀压力同时作用下的热应力。所得结果可为转炉炉壳设计提供依据。     

显微维氏硬度测量不确定度评定

对显微维氏硬度测量不确定度进行评定，建立了不确定度计算的数学模型，确定了影响实验结果的各项因素，计算出了各因素的标准不确定度，得出结果的扩展不确定度，并给出最终测量结果的表达式。     

Concept of freedom of infection of animal flocks

Totally negative results of epidemiological investigation of random samples do not prove the absence of the infection as the pathogen may be restricted to only a few animals in the herd for a long time. The statement "absence of infection" is critical for such situations. The question is raised, whether the statement "absence of infection" should be generally avoided. Classification of herds and flocks according to the prevalence of the pathogen would be more valid for the implementation of control measures.     

Quality of life of relatives of mental patients

Usage of quality of life of psychiatric patients' relatives as the parameter of estimation of the quality of psychiatric care is considered. By means of standard questionnaire elaborated by the authors as well as by means of both individual and group conversations the quality of life was analyzed in 40 relatives which lived together with psychiatric patients. Different spheres of their life and difficulties (financial, social-psychologic, production) were examined in families with such patients. The defects of psychiatric care that had direct influence on the quality of life of the psychiatric patients' relatives are outlined.     

Effect of antibiotics of chemotaxis of human leukocytes

The effect of 20 different antibiotics on chemotaxis by human neutrophils was studied. Human leukocytes incubated with chloramphenicol, rifampin, sodium fusidate, and tetracyclines in vitro showed markedly depressed migration. The mechanisms by which these antibiotics affect leukotaxis are discussed.     

The effect of amount of possession of the trait of hostility on accuracy of perception of hostility in others.

Some theories of personality hold that an individual's perception of others is influenced by his own personality characteristics; more specifically, that a trait of low social value will be projected more into others, and that insight into the possession of these characteristics reduces this distortion. These 2 hypotheses were tested by having a group of college students rate each other (including themselves) on degree of friendliness or hostility. Agreement with group rating about self yielded the insight score. In general, the hypotheses were supported; the "friendly" Ss were most accurate in their perception of others, and insight was positively associated with accurate perception. From Psyc Abstracts 36:04:4HL16M. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of rates of infection of two methods of emergency ventricular drainage

The rates of infection of two methods of external ventricular drainage in use at Atkinson Morley's Hospital--namely, (a) percutaneous drainage with Rickham reservoirs and (b) tunnelled ventriculostomies--were compared in this retrospective review. Percutaneous drainage of CSF with Rickham reservoirs was associated with a 27% rate of infection as identified by positive microbiological cultures; tunnelled ventriculostomy catheters had a 10% infection rate. The difference in the infection rate between the two methods was statistically significant (P < 0.015). Other variables examined, including the age and sex of the patients and the reasons for ventricular drainage, were not associated with an increased rate of infection. Most infections from either method were caused by a coagulase negative staphylococcus. The average duration of ventricular drainage before identification of positive cultures was 5.7 days for Rickham reservoirs and 6.0 days for ventriculostomies.