钛合金TC4制压力容器筒体外压失稳的有限元分析

钛合金TC4材料具有良好的综合力学性能,被用于压力容器产品。对于承受外压的TC4制压力容器除须满足强度要求外,还应满足稳定性要求。由于目前没有TC4材料外压应力系数B曲线,因此常规设计方法不能计算。可通过有限元法,采用非线性屈曲分析,逐步增加外压载荷,求解出相应的变形量,从而求解出其临界失稳点。     

油套管抗挤毁性能的初始后屈曲理论分析

抗挤毁性能是油套管的一项至关重要的性能指标．椭圆度和壁厚不均是存在于油套管中的初始微小几何缺陷．运用Koiter初始后屈服理论分析承受均匀外压力的长薄壁油套管的后屈曲性态及其缺陷敏感性,得出承受均匀外压力的长薄壁油套管具有后屈曲稳定性的结论．     

楔横轧多楔轧制高铁空心车轴壁厚均匀性

在空心轴楔横轧多楔轧制中,控制壁厚均匀性是衡量车轴成形质量的重要标准.本文先分析空心轴楔横轧多楔轧制的稳定轧制条件,得到了确定空心车轴楔横轧压扁失稳的准则.在此基础上,基于DEFORM-3D软件,建立楔横轧多楔同步轧制高铁空心车轴的三维刚塑性有限元模型,分析展宽角、成形角等工艺参数对壁厚均匀性的影响,获得了工艺参数影响轧制空心车轴壁厚变化的规律.结果表明:成形角越大,壁厚均匀性越好;展宽角越大,壁厚均匀性越好,但在展宽角大于10°时,壁厚均匀性反而下降.基于多楔轧制实验,轧制1∶5缩比的空心车轴,测量了轧制力矩和轧制空心轴的壁厚,与仿真结果作比较,相对误差均在10%以内,验证了所建有限元模型的正确性.     

矩形大开孔圆柱壳轴压作用下的屈曲性能

利用数值方法研究了开有矩形大开孔的薄壁圆柱壳在轴压作用下的屈曲性能.首先通过特征值屈曲分析,得到开孔圆柱壳的一阶屈曲模态,并预测屈曲荷载的上限;其次,通过非线性分析,得到结构的荷载位移全过程响应;然后引入正交试验设计方法,分析了矩形开口的周向角度、高度和轴向位置等几何参数对结构稳定性的影响.分析表明,矩形开孔圆柱壳临界屈曲荷载的上限值远小于无开孔圆柱壳的下限值,影响矩形开孔圆柱壳轴压作用下稳定性的主要因素为壳体的径厚比,临界荷载值随径厚比的增大迅速下降.     

6061铝合金带筋圆管在线淬火模拟分析

通过喷水淬火实验获得6061铝合金的冷却曲线,结合数值计算方法获得材料的在线淬火换热系数,运用ABAQUS有限元软件对带筋圆管在线淬火过程进行了动态模拟。结果表明：在淬火开时阶段,换热系数较小,随着淬火温度降低,换热系数逐渐增大至峰值2kW／m。℃,随后又逐渐减小;在圆管筋部外边缘处冷却最快,型材内表面与筋的连接处冷却最慢;淬火开始2s内型材的整体温差近100℃,随后温差显著减小,型材各部分的温度趋于均匀;淬火初始阶段,管外壁及筋外壁表现为拉应力,管内壁和筋内壁表现为压应力,随着淬火的进行,压应力和拉应力互相转变,最大拉应力和压应力分别为21．7MPa和28．7MPa。     

游动芯头圆盘拉伸紫铜圆管工艺规程计算方法

本文作者提出的“在大型卷筒拉伸机上采用游动芯头多道次连续拉伸中小规格紫铜圆管工艺规程计算方法”又称“ZBL法”。其计算程序分为3个步骤：拉伸次数n的计算；各拉伸道次管子壁厚的计算；各拉伸道次管子外径的计算。各道次管子的壁厚减缩系数呈等比数列；各道次管子的外径是通过呈等差数列的径差计算出来的。     

芯棒直径对楔横轧5Cr21Mn9Ni4N空心气门壁厚均匀性的影响规律

楔横轧空心轴类件存在壁厚分布不均问题,特别是在小直径大长径比空心件楔横轧成形中更为突出.本文在Gleeble-1500D热模拟实验机上进行了5Cr21Mn9Ni4N耐热钢的热压缩实验,得到了5Cr21Mn9Ni4N的热变形本构方程.通过改变芯棒直径,采用有限元仿真和实验相结合的方法,研究了楔横轧轧制空心气门过程中的壁厚变化规律.研究结果表明,带芯棒轧制时,芯棒直径存在临界值,在该值下进行轧制,空心气门预制坯壁厚均匀性最优;楔横轧空心件时,金属轴向均匀流动是壁厚均匀的必要条件;轧件轴向拉应变减小,径向压应变变大,周向应变在0附近且为拉应变时,壁厚较为均匀.     

带钢拉伸横向屈曲及拉伸极限载荷的研究

研究了对于在4个边进行了简单支持约束的带钢的临界拉伸横向屈曲应力,并通过修正拉伸横向屈曲应力系数K,得到了不同支撑条件下的临界拉伸应力计算公式,继而对带钢的拉伸横向后屈曲进行了研究,最后引入了"有效宽度"概念来计算带钢不致发生屈服失效的极限载荷。     

钢-混凝土组合板的弹性整体剪切屈曲分析

为了研究钢-混凝土组合板的弹性整体剪切屈曲性能,采用夹层板理论推导了组合板弹性屈曲方程,分析了界面剪切刚度的影响.通过在钢与混凝土之间设置假想的剪切薄层,模拟钢-混凝土组合板界面滑移效应,建立考虑滑移效应的组合板分析模型,推导出四边简支矩形组合板在均匀受剪状态下的弹性屈曲方程,并分析了界面剪切滑移刚度对屈曲荷载的影响.通过参数分析拟合了防止完全剪力连接四边简支组合板整体屈曲所需混凝土板最小厚度的计算公式.结果表明,剪切刚度较小时,屈曲荷载增长较快;剪切刚度较大时,屈曲荷载变化缓慢并逐渐趋于稳定,与完全剪力连接组合板的屈曲值接近.该结果与有限元计算结果吻合较好.     

油套管抗挤毁性能的有限元分析

运用有限单元分析方法详细考察了承受均匀外压力的样本油套管在不同椭圆度、不同壁厚不均(或称偏心度)、以及不同椭圆度和壁厚不均组合等初始几何缺陷的情况下的应力变化及其分布,并作出相应的初始几何缺陷与应力变化的曲线.     

High pressure versus low pressure electromagnetic extracorporeal lithotripsy

A low pressure and an upgraded high pressure electromagnetic lithotriptor were compared for the treatment of calculi within the ureter. The upgrading allows for increased energy density onto the stone surface. We targeted 139 ureteral calculi (average diameter 8.1 mm.) with the low pressure system. The mean number of shock waves was 7,308, 9,226 and 5,304 for calculi in the upper, mid and lower ureter, respectively, and the energy density corresponded to 0.222, mJ./mm.2, 0.224 mJ./mm.2 and 0.223 mJ./mm.2, respectively. Immediate fragmentation was achieved in 39 of 51 upper (77%), 21 of 42 mid (50%) and 22 of 46 lower (49%) ureteral calculi. The upgraded shock wave tube was used in 52 calculi (average diameter 6.1 mm.). The mean number of shock waves was 6,250, 14,150 and 3,400 for calculi in the upper, mid and lower ureter, respectively, and the energy density corresponded to 0.32 mJ./mm.2, 0.33 mJ./mm.2 and 0.30 mJ./mm.2, respectively. Immediate fragmentation was achieved in 11 of 16 upper (69%), 4 of 6 mid (67%) and 7 of 30 lower (23%) ureteral calculi. The comminution rate did not significantly increase, which implies that the focal energy density is not the only decisive parameter in fragmentation by extracorporeal shock wave lithotripsy.     

Assessment of cardiac filling pressure during continuous positive pressure ventilation

Before and after 10 dogs were near-drowned with fresh water, cardiac filling pressures were measured during spontaneous respiration, controlled mechanical ventilation with ambient expiratory airway pressure, continuous positive-pressure ventilation (CPPV) with 20 ml H2O PEEP, and CPPV alone. Pulmonary arterial occlusion and left ventricular end diastolic pressures were measured and compared. Intrapleural pressure was subtracted from values for each of these pressures to calculate respective transmural filling pressures. Mechanical ventilation and CPPV each decreased thoracic venous return, but only CPPV increased pulmonary arteriolar resistance. The increase of both airway pressure and pulmonary arteriolar resistance, in turn, increased both right atrial and pulmonary arterial occlusion pressures, but decreased left ventricular filling. Thus, measurement of pulmonary arterial occlusion pressure alone did not allow accurate assessment of cardiac filling pressure. The authors found that measurement of intrapleural pressure was necessary to obtain an accurate reflection of left ventricular filling pressure during CPPV. Momentary interruption of CPPV to measure any pressure was of no value in assessing vascular filling and caused pulmonary edema in several animals. Therefore, the authors recommend that vascular pressures be measured and evaluated without interruption of positive airway pressure.     

Intra-abdominal pressure monitoring

MOTIVATION: The CloneIt program searches for sub-cloning strategies, in-frame deletions and frameshifts within a plasmid sequence. AVAILABILITY: The program, written in ANSI-C language, is available at http://locus.jouy.inra.fr/soft/cloneit/clonei t.html CONTACT: lindenb@biotec.jouy.inra.fr     

High pressure areas

The study highlighted the extent of occupational distress in a group of nurses in an NHS hospital trust. The levels of distress were similar across settings and similar to levels identified in current NHS-wide studies. Levels of work pressure and emotional exhaustion were higher than previous UK norms. High levels of distress were associated with younger age, high work pressure and low social support. For general mental well-being individual factors, such as satisfaction with social support, were more predictive than organisational factors. For work-specific distress, factors in the work environment, such as work pressure, patient contact and task orientation, were more important. Strategies for addressing the needs identified were reviewed and are now being implemented.     

Metallurgy under pressure

The development of iron and steel production is briefly reviewed. Metallurgy under gas pressure appeared at the end of the twentieth century. Even at this early stage, some significant benefits of metallurgy under pressure over traditional metallurgy and vacuum metallurgy have been established, such as fourfold increase in yield point with reduced consumption or elimination of some expensive alloying elements (Ni, Mo, Co, W, etc.); the possibility of alloying with nontraditional elements (Ca, Zn, Pb, etc.); low environmental impact; and stable development. Metallurgy under pressure may be expected to give rise to breakthroughs in the production of high-quality and special metal. Of the currently existing methods, the most promising is the use of a large steel-smelting bath.     

Blood pressure tracking

Interactions between nitric oxide (NO) and angiotensin (ANG) II in renal vascular beds were examined in anesthetized dogs. The renal blood flow (RBF) response to an intrarenal arterial injection of ANG II was significantly augmented by intrarenal infusion of the NO synthase inhibitor N(G)-nitro-L-arginine (LNA, 50 microg/kg/min). The simultaneous intrarenal infusion of L-arginine (1 mg/kg/min) prevented the potentiating action of LNA. Similar potentiation was also seen in phenylephrine-induced renal vasoconstriction. Moreover, during simultaneous intrarenal infusion of sodium nitroprusside (SNP), an NO donor, the potentiating action of LNA on the renal vasoconstrictor action of ANG II disappeared. Under these conditions, the released NO stimulated by ANG II was still inhibited by LNA, if present, but basally released NO was resupplied by SNP, as indicated by the return of the RBF. During an infusion of phenylephrine, which produced an increase in renal vascular tone similar to that observed during the infusion of LNA, the renal vasoconstrictor action of ANG II was not augmented. These data suggest that basally released NO plays an important role in the regulation of renal hemodynamics by modulating the renal vasoconstrictor actions of ANG II and phenylephrine.