人工裂隙对爆炸裂纹扩展影响的试验研究

为研究与炮孔不同距离节理裂隙对爆炸裂纹扩展的影响机制，以有机玻璃薄板为介质，加工与炮孔距离为￡（20mm、30mm、40mm、50mm、60mm）的人工裂隙进行爆炸实验。试验表明：人工裂隙能够有效阻隔爆炸裂纹的扩展；￡为20mm和30mm时，人工裂隙右端边界能够产生翼裂纹，其起裂角和止裂角度分别为135°和45°，裂纹扩展路径和长度相近；人工裂隙能够有效阻隔爆炸裂纹和模型能够产生爆炸空腔的临界值介于50—60mm之间。研究结果可为节理岩体控制爆破设计及爆破参数优化等提供理论依据。

两组无充填物节理对爆炸裂纹扩展的影响研究

为研究爆炸载荷作用下含有两组节理岩体对爆炸裂纹扩展的影响,试验采用存在两条人工节理的有机玻璃薄板为介质,分别以两组相距10mm、20mm的平行节理及相交角度为45°、135°的节理与炮孔中心的距离为20mm、30mm、40mm作为试验模型,试验采用单发8号数码电子雷管作为爆源,爆炸加载试验模型。由试验结果可知,爆炸荷载作用下试验有机玻璃板会形成明显的分区,与爆炸岩石类似;两组平行节理的相互距离以及两组节理与炮孔中心的距离大小对裂纹总数无明显影响,对分区的有人工节理区、无人工节理区的裂纹数量影响较大;翼裂纹是爆炸应力波沿人工节理绕射形成绕射波作用产生的,两组人工节理的相互角度对翼裂纹的总数量无明显影响;而对翼裂纹的长度有影响。

爆炸应力波作用下分支裂纹动态力学特性试验

应用爆炸加载的透射式动焦散线测试系统,分析了平板中预制贯通裂纹在爆炸应力波作用下端部衍生分支裂纹及爆炸主裂纹的扩展规律。预制贯通裂纹面在压缩应力波及反射拉伸波作用下表现出明显的张开和闭合交替变化,预制贯通裂纹减弱了爆炸主裂纹的动态扩展行为,爆炸主裂纹难以穿过预制贯通裂纹继续扩展。分支裂纹是爆炸应力波在预制贯通裂纹端部衍射效应形成应力集中而衍生、起裂、扩展,其开裂角与预制贯通裂纹、爆炸应力波入射角密切相关,分支裂纹尖端沿着最大能量释放率方向起裂,逐渐平行于最大主应力的方向稳定扩展,中后期扩展多表现为复合型断裂。爆炸分支裂纹的动态应力强度因子、扩展速度低于爆炸主裂纹,获得了分支裂纹起裂韧度为0.50～0.65 MN/m3/2、止裂韧度为0.25～0.35 MN/m3/2。

含一组短裂隙的有机玻璃爆炸实验研究

为研究岩体中的短节理裂隙对爆炸裂纹扩展规律的影响,通过单发数码电子雷管爆炸加载含一组不同方位裂隙的有机玻璃实验,分析实验结果可以得出:爆破产生的裂隙区中,环向裂隙仅出现在靠近空腔的较少区域内,其他区域没有环向裂隙产生;岩体中原有的短裂隙在爆炸作用下,裂隙端部产生了新的裂隙,使爆破破坏范围加大,裂隙与炮孔的距离及裂隙方位对端部裂隙的发展及分布有不同影响。实验结果对相关研究及生产实践有一定指导作用。

爆炸荷载作用下模型介质裂纹扩展试验与分析

为研究爆炸载荷作用下裂隙介质裂纹扩展规律,以含人工裂隙的有机玻璃薄板为介质,分别以炮孔中心到人工裂隙垂直距离L和人工裂隙长度D为变量,采用单发雷管爆炸加载试验模型进行试验。试验结果表明,爆炸荷载作用将使裂隙介质形成径向裂纹、翼裂纹、层裂裂纹和似层裂裂纹;人工裂隙能够阻隔径向裂纹的扩展,径向裂纹的扩展对距离L比长度D更敏感;翼裂纹是爆炸绕射波或绕射波与压缩应力波共同作用产生的,翼裂纹的长度随距离L增加而降低;入射压缩应力波与反射拉伸应力波叠加形成的净拉伸应力拉裂介质形成层裂效应、引起径向裂纹弯曲形成似层裂效应,层裂裂纹和似层裂裂纹几乎平行于人工裂隙。研究结果可为裂隙岩体爆破设计、冲击矿压防治和结构工程防护等提供理论依据。

Caustic study on blast-induced wing crack behaviors in dynamic–static superimposed stress field

This paper studies blast-induced wing crack behavior in a dynamic–static superimposed stress field using high-speed photography in combination with the optical method of caustics. With a static–dynamic loading setup, four PMMA plate specimens with pre-existing cracks under different static loading and the same dynamic loading were tested to observe the mechanical characteristics and the kinematic characteristics of blast-induced wing cracks during the propagation process, including crack length, crack velocity and dynamic stress intensity factor(SIF) at the crack tip. The results show that the behavior of the blast-induced wing crack is affected by the explosion stress wave and initial static stress, and the initial static stress with the direction being perpendicular to the wing crack propagation direction hinders crack propagation. Furthermore, the boundary constraint condition of the specimen plays an important role on the behavior of the crack propagation in the experiment.

Structure and flaws of CuCr alloys by explosive compaction

CuCr alloys are prepared by mechanical alloying and explosive compaction. After we have studied their structure and flaws, the results show that the CuCr alloys have definite strength and toughness, while their fractured surface displays ductile characteristics. In the metallurgical structure, CuCr alloys are composed of two phases of uniform distribution; the SEM morphology is like thin strips with an end arrangement that is bonded to each other and the two-phase distribution of CuCr alloys is more homogenous. It is in only in a very small zone that formation of Cu-rich and Cr-rich phases take place. The flaws of the compaction samples are mainly central-holes and cracks.

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.

Numerical study on crack propagation under explosive loads

Dynamic crack propagation in brittle materials plays an important role in unJerstanding the fracture mechanism.Numerical simulations on crack propagation in the polymethyle methacrylate(PMMA)under explosive loads were carried out through Autodyn 3D code.Although the Johnson-Holmquist(JH-2)constitutive model has been widely treated as an acceptable scheme,it cannot improve the description in the post-failure response of material and reduce the mesh dependency,so the crack softening failure model are introduced in our present work based on two failure criterions.First,material parameters of JH-2 model,failure criterion,and crack softening failure model are determined from available data and calculations.The circular and rectangle thin plates are modeled to explore the fracture mechanisms for single-borehole and dual-borehole explosions.The simulation results well reproduced the entire dynamic evolutionary process of the crushed and fractured zones,crack initiation,propagation and arrest as well as secondary propagation,which successfully proved the relibilities of the combination of JH-2 constitutive model,failure criterion,and crack softening failure model and corresponding material parameters.For dual-borehole explosion,the crack linkage is well performed when borehole distance L is 20 and 30 cm;cracks are failed to link with each other at L=40 cm although main cracks have arrived into the opposite fractured zone.More importantly,it is found that the crack linkage mainly depends on L,which has an important effect on linkage style and its location.Despite a larger L makes more difficult in crack linkage,this difficulty lies not in the shortage of crack length,but in losing control of directional fracture of cracks between two boreholes.