常压烧结Sialon材料高温性能的研究

研究了添加剂为Y2O3、Al2O3、AlN的Sialon材料的高温性能。晶化处理后,其断裂韧性由4MPa·m1／2提高到6MPa·m1／2;高温强度到1100℃仍不明显降低;抗热震临界温差达△Tth＝473℃。其高温断裂为蠕变机制,符合裂纹准静态扩展机理。裂纹准静态扩展是热震损伤的控制因素。     

混凝土受拉徐变研究

本文用纯弯曲试件，进行了不同高应力水平下受拉徐变破坏试验。得到了应力水平与试件破坏时间的关系，测得了试件的弯曲受拉徐变变形过程，给出了徐变变形的数学表达式，同时，计算了弯曲受拉徐变损伤值。     

小浪底工程高压闸门压紧式止水粘弹性力学性能试验研究

高压闸门止水橡皮属子粘弹性材料，在长期荷载作用下其力学性能会发生怎样的变化是设计部门极为关心的问题。本文结合小浪底工程高压闸门止水的实际工况，对其拟采用的止水橡皮进行了长达一年多的蠕变试验观测，分析研究试验成果，导出了蠕变方程及应力松弛方程，探讨了上水橡皮的粘弹性力学特性，为工程设计提供参考。     

Mechanical and thermal characterization of as-received recycled polyethylene filled with rice husk and their relationship to the end use of these composites

ABSTRACT

Waste can be considered a crisis across the world, especially in the Global South where landfills are collapsing and vector-borne illnesses are increasing. Due to the increase in the amount of waste plastic in the environment, different uses of recycled plastics are being investigated. One such use is roofing tiles. This has been put in place in Sri Lanka through the Waste for Life organization. Here, recycled polyethylene is filled with rice husk particles. Due to the hydrophilic nature of the rice husk, the strength of the polyethylene composites decreased with increasing rice husk filler. Since the roofing tiles do not need to support a large load, the loss in strength should not be too detrimental. However, the creep behavior was improved with 10% and 20% filler. This is important in that the temperature on the roof can reach high temperatures.     

Creep behavior of Bure clayey rock

Clayey rock may be the host medium for a French long-term nuclear-waste storage facility. To gain better understanding of the delayed behavior of this potential host rock, we conducted a testing program that focused on creep tests. Fourteen tests were conducted: short-term multi-step creep tests (six at ambient temperature, four at T=80 °C and four on damaged samples); and four long-term mono-step creep tests (in which a constant load is applied for nearly 2 years). Experimental results are displayed and discussed.     

镍基单晶合金压痕蠕变研究

为了探索用压痕法确定晶体学蠕变应力指数的可行性,采用晶体塑性理论模型对不同取向镍基单晶合金压痕蠕变行为进行了有限元模拟。研究表明,晶体学对称性会导致压痕表面应力呈现特定的对称性;晶体取向对压痕蠕变深度及其扩展速率具有显著的影响。通过开展不同载荷下的压痕蠕变模拟,获得相应的稳态压痕深度扩展速率,再通过线性回归的方法可有效获得晶体学蠕变应力指数。本文提出的确定蠕变应力指数的方法不受晶体取向的影响,有望应用于各向异性高温合金蠕变性能评估。     

Effect of directional solidification and heat treatments on the microstructure and mechanical properties of multiphase intermetallic Zr-doped Ni–Al–Cr–Ta–Mo alloy

The effect of directional solidification and heat treatments on the microstructure and mechanical properties of intermetallic Ni–21.29Al–7.04Cr–1.46Ta–0.64Mo–0.57Zr (at.%) alloy was studied. Increasing growth rate is found to decrease primary dendrite arm spacing and to increase volume fraction of β(NiAl)-based dendrites and low melting point γ′(Ni₃Al)/Ni₅Zr eutectic. Room-temperature tensile yield strength and ultimate tensile strength increase and plastic elongation to fracture decreases with the increasing growth rate. Two types of heat treatments of directionally solidified (DS) specimens including two-step ageing at temperatures of 1273 and 1123 K and two-step solution annealing at 1373 and 1493 K were performed. Ageing at 1273 and 1123 K decreases volume fractions of the dendrites and eutectic regions and leads to a coarsening of spherical -Cr and needle-like γ′ precipitates within the β-phase. Annealing at 1373 K for 100 h is shown to be sufficiently long to completely dissolve the eutectic regions. Compressive yield strength increases with increasing temperature reaching a peak value at about 1023 K and then decreases at higher temperatures. Minimum creep rate is found to depend strongly on the applied stress and temperature according to a power law. The power law stress exponent n is determined to be 5.1 and apparent activation for creep Q_a is measured to be 326 kJ/mol.     

氧化物添加剂对Ag-SnO2电接触材料抗蠕变性能的影响

为研究氧化物添加剂对Ag基电接触材料抗蠕变性能的影响,用粉末冶金法制备了分别含有CuO、WO_3和In_2O_3的Ag-SnO_2材料。室温下对拉伸试样进行蠕变实验,获得蠕变特征曲线及相关参数,构建了Ag-SnO_2材料的蠕变本构方程。借助扫描电子显微镜(SEM)对拉伸断口形貌进行分析,用ABAQUS有限元软件进一步对蠕变行为进行模拟。结果表明:由于SnO_2与Ag基体间的界面强度得到提高,氧化物添加剂可显著增强Ag-SnO_2电接触材料的抗蠕变性能,尤其是CuO添加剂的效果最佳。模拟结果与通过实验获得的蠕变数据基本吻合,误差小于3%。研究结果对预测Ag基电接触材料的蠕变行为及改善力学性能均具有一定参考价值。     

镍基单晶高温合金蠕变-疲劳寿命评估方法进展

论述镍基单晶合金的滑移变形机制和疲劳裂纹萌生机理，分别介绍镍基单晶合金蠕变寿命和低循环疲劳寿命分析评估模型；镍基单晶合金蠕变、疲劳寿命的研究方法可分为应用各向异性张量描述非弹性各向异性变形的宏观力学(唯象)模型和基于晶体学滑移变形理论的微观力学模型；晶体取向、平均应力、环境温度、循环频率、循环应力比是影响单晶合金蠕变-疲劳寿命的主要因素。复杂应力状态下的单晶合金多轴低循环疲劳损伤，单晶合金在疲劳-蠕变交互作用下的疲劳损伤和单晶合金的接触疲劳损伤等问题是需要研究的重要课题。