相同喷丸强度条件下喷丸强化效果的数值模拟研究

目的优化喷丸工艺参数的匹配方式,进一步提升喷丸强化效果。方法采用预定义场和基于移动矢量的快速建模方法,实现了受喷构件表面100%表面覆盖率的喷丸模拟,并借助三维喷丸有限元模型研究了不同喷丸工艺参数匹配方式对受喷构件表面粗糙度、弹丸撞击时的能量转变方式的影响。结果当喷丸强度均为0.35 mmN时,四种喷丸工艺参数匹配方式对应的表面粗糙度分别为3.156、2.760、2.249、2.081μm,应力集中系数分别为1.205、1.142、1.103、1.071,动能消耗率分别为89.94%、85.53%、82.86%、80.04%,应变能转化率分别为7.99%、9.67%、11.82%、14.29%。结论与其他喷丸工艺参数匹配方式相比,所用喷丸工艺参数中弹丸直径愈大、喷射速度愈低,对应受喷构件表面粗糙度和应力集中系数愈小,有利于降低喷丸强化效果的削弱程度。在弹丸撞击初始动能大致相当的情况下,尽管"大弹丸直径+低喷射速度"参数条件下对应的动能消耗率较低,但应变能转化率较高,撞击过程中摩擦耗散能较少,有利于大塑性应变和残余压应力的产生,可获得较好的喷丸强化效果。

喷丸方法对不规则构件表面残余应力分布规律的影响

目的优化喷丸强化工艺,提升喷丸工艺的强化效果。方法采用预定义场和基于移动矢量的快速建模方法,实现满足表面全覆盖和不同喷丸方法的有限元模拟。通过对模拟结果中的应力值进行局部坐标转换,分析不同喷丸方法条件下残余应力沿受喷构件表面切线方向的分布规律。结果在喷射方向固定的喷丸方法中(方法-1),弹丸撞击角度在不同区域内的变化范围为60°～90°,且随弹丸撞击角度的增加,弹丸撞击时的动能消耗率和应变能转变率分别由71.6%和5.3%提高到89.0%和7.5%,表面覆盖率也随之增加。在喷射角度固定的喷丸方法中(方法-2),弹丸撞击角度始终为90°,表面覆盖率分布均匀,从而使得在凸圆弧面、斜面和凹圆弧面内采用方法-2获得的表面残余应力比方法-1的大,且两者差值沿+x方向呈现先增加、后保持稳定、再减少的变化规律。结论与喷射方向固定的喷丸方法相比,采用喷射角度固定的喷丸方法,因弹丸撞击角度大,弹丸撞击动能消耗率及应变能转变率高,且表面全覆盖能得以保证,构件在凸圆弧面、斜面和凹圆弧面内能获得较大的表面残余压应力值。

水蒸气法刺竹活性炭的制备工艺及性能表征

以刺竹炭为原料,采用水蒸气活化法制备刺竹活性炭,研究活化温度和活化时间对活性炭性能的影响,并对活性炭得率、灰分含量、碘吸附值和亚甲基蓝吸附值等进行测试和分析。结果表明:当活化温度为840℃、活化时间为120 min时,刺竹活性炭得炭率为48.5%、碘吸附值为1141.56 mg·g^(-1)、亚甲基蓝吸附值为150 mg·g^(-1)、灰分含量为14.63%,微孔率高达88.3%,具有良好的吸附性能;经SEM表征,经活化后的刺竹活性炭,出现大量孔隙结构,具有较大的比表面积。

THE VOID FRACTION DISTRIBUTION IN TWO-DIMENSIONAL GAS-LIQUID TWO PHASE FLOW USING IMAGE PROCESS METHOD

An image processing method for measuring the instantaneous two-dimensional （2D） local void fraction at high bubble number density was proposed. It was based on computing a correlation between the locally averaged brightness of the bubble plume images and the real void fraction. The method was tested using the 2D distribution of local void fraction from visualized image, where a correlation between the locally averaged brightness and the projection void fraction was derived by introducing an ideal of overlapping probability of the bubble-images under various conditions. This research was used to study the behavior of the bubbly flows with aspect ratio of 1.0,1.5, and 2.0. The present method was applied to the instantaneous measurement. The void fraction for bubble plumes of three different aspect ratios with three different bubble generating flow rates were measured for the clarification of the effect of the bubble on the behavior of the bubbly flows. Dependency of the void fraction on the gas flow rate was measured and compared to other results from the literature. In the range of our experiments, it was observed that not only does an aspect ratio of the tank affect the structure of the plume, but also the gas flow rate in the tank affects the structure of the plume.