爆炸加载下AISI304不锈钢板表面硬化和数值模拟

目的提高AISI304不锈钢板表面硬度。方法利用爆炸加载表面硬化方法对3 mm厚的AISI304不锈钢板进行了表面硬化处理,通过HXD-1000YM型显微硬度计和JEM-2010型透射电子显微镜对爆炸加载处理后试样的不同部位横截面进行了硬度测量和微观组织表征。采用大型有限元数值模拟软件ANSYS/LS-DYNA对爆炸加载表面硬化过程进行了数值模拟,计算了撞击面平均压力和速度。通过对比数值模拟结果与理论计算结果,分析了特征点碰撞压力和速度对爆炸加载处理后表面硬度的影响。结果数值模拟结果表明,撞击面压力平均值为5.5 GPa,撞击面平均速度达到了178 m/s,撞击面压力和速度的理论计算值与数值模拟值误差不超过5%。试验结果与数值模拟结果具有一致性。爆炸加载后,试样近起爆端和爆轰末端的撞击压力和撞击速度小于稳定爆轰阶段,导致前者表面硬度小于后者。横截面硬度分布表明撞击表面硬度大于炸药接触面硬度,撞击表面硬度值从210HV提高至450HV,炸药接触面硬度值从210HV提高至390HV。结论爆炸表面硬化过程中存在边界效应。爆炸表面硬化方法能够显著提高板材表面硬度,同时可以提高板材整体硬度,且硬度提高与变形带和位错阵列形成有关。

爆炸表面处理

本文根据实验研究结果,就表面爆炸处理主要参数、处理前微观组织及疲劳性能的改变、爆轰波作用下零件中裂纹状缺陷的扩展行为,以及用吸能块控制裂纹扩散等问题作一综合介绍。

用动光弹法研究瞬态表面载荷的破坏作用

应用动光弹实验方法,研究了表面爆炸载荷作用在半无限弹性介质边界时,在其内部激发的动态应力场,井着重分析比较了单边集中药包和双边对称药包爆炸两种载荷条件下,在有限板块内形成的瞬态应力分布的差异。结果表明:当使用相同药量时,对称布置药包可在板块内某些部位造成应力集中从而导致板块更易于破裂。

对称表面动载下有限块体的破裂过程

实验表明,受对称布置的表面爆炸载荷的脆性块体,会在通过载荷作用点连线的某一平面上破裂。为解释这一现象并进一步探讨利用类似方法破碎岩块的可能性,本文介绍了应用弹性动力学理论建立的计算模型以及所进行的动光弹和混凝土块模型试验。研究结果表明:在所述载荷条件下,应力波特别是自由界面反射的拉伸波对块体的破碎起重要作用;由于多向拉应力集中,在块体加载端面梭边中部最易产生径向裂隙,此后在侧面反射波的作用下裂隙延伸,与中部可能存在的裂纹贯通,从而将块体破开;对称加载使应力波在块体内多次叠加有利于块体充分破碎。

Effect of Shock Wave on Fabricated Anti-Blast Wall and Distribution Law Around the Wall Under Near Surface Explosion

The loads of shock wave effect on fabricated anti-blast wail and distribution law around the wall were investigated by using near surface explosion test method and FEM. The pressure-time histories and variety law on the foreside and backside of the anti-blast wall were adopted in the tests of variety of different explosion distances and dynamites, as well as in the comparison between the test and numerical calculation. The test results show that the loads of shock wave effect on the anti-blast wall were es- sen-tially consistent with calculation results using criterion under surface explosion when explosion dis- tances exceed 2 m, the distribution of overpressure behind wall was gained according to variety law based on small-large-small. It is also demonstrated that the peak overpressure behind wall had com- monly appeared in wall height by 1.5--2.5 multiples, and the peak overpressures of protective building behind wall could be reduced effectively by using the fabricated anti-blast wall.

Simultaneous investigation of blast induced ground vibration and airblast effects on safety level of structures and human in surface blasting

The significance of studying, monitoring and predicting blast induced vibration and noise level in mining and civil activities is justified in the capability of imposing damages, sense of uncertainty due to negative psychological impacts on involved personnel and also judicial complaints of local inhabitants in the nearby area. This paper presents achieved results during an investigation carried out at Sungun Copper Mine, lran. Besides, the research also studied the significance of blast induced ground vibration and air- blast on safety aspects of nearby structures, potential risks, frequency analysis, and human response. According to the United States Bureau of Mines （USBM） standard, the attenuation equations were devel- oped using field records. A general frequency analysis and risk evaluation revealed that： 94% of generated frequencies are less than 14 Hz which is within the natural frequency of structures that increases risk of damage. At the end, studies of human response showed destructive effects of the phenomena by ranging between 2.54 and 25.40 mm/s for ground vibrations and by the average value of 110 dB for noise levels which could increase sense of uncertainty among involved employees.

Study on the propagation of interface crack of young concrete lining and rock under blasting load

In the construction of water conservancy and hydropower project,young concrete lining structure is often affected by blasting load. Young concrete has a lot of micro-fractures with random distribution,which are easier to propagate and connect under blasting load. This paper focuses on the calculation on dynamic stress intensity factors of bond interface crack of concrete-rock according to concrete age. Result shows that different incidence angles of stress wave lead to different crack propagation mechanisms. Under the normal incidence of impact load,the bonding interface crack propagation of the concrete lining is mainly caused by reflection tensile stress,which forms from the free surface. With horizontal incidence of stress wave,the bond interface crack propagation of concrete lining is affected by concrete age. With the increase of concrete age,the elasticity modulus margin between concrete and rock decreases gradually,and the crack propagation form changes from shear failure to tensile damage.

Blast Pressure Mitigation by Surface Explosion Using Water in a Walled Container

Mitigation of blast pressure using water in a walled container was evaluated. A PETN （pentaerythritol tetranitrate） pellet of 1.4 g near the model wall was detonated on a steel plate. A water-filled container was placed between the explosive and the wall. The pressure histories at six points, which corresponded to Hopkinson scaled distance of from 3.6 m·kg^-1/3 to 21.7 m·kg^-1/3 were evaluated along with dependence of mitigation effects on the amount of water and the position of the container. The presence of the water and the wall mitigated the peak overpressure near the explosion points and the positive impulse along all points. The mitigation effect was equivalent to 20-30% reduction of explosive weight based on discussion of the equivalent ratio. The presence of the water along the wall （not very close to the explosive） also mitigated the blast pressure.