Numerical simulation of explosively driven metal by material point method

The material point method (MPM) fully takes the advantages of both Lagrangian method and Eulerian method, and can be capable of simulating high explosive explosion problems and impact problems involving large deformation and multi-material interaction of different phases. In this paper, MPM is extended to simulate the explosively driven metal problems, and two typical explosive/metal configurations, open-faced sandwich and flat sandwich, are analyzed in detail using MPM, and numerical results are compared with Gurney solution and its corrections. Based on our MPM results, a new correction to Gurney solution is proposed to account for the lateral effects for flat sandwich configuration. MPM provides a powerful tool for studying the explosively driven metal and other explosive problems.     

Modelling brittle impact failure of disc particles using material point method

Understanding the impact failure of particles made of brittle materials such as glasses, ceramics and rocks is an important issue for many engineering applications. During the impact, a solid particle is turned into a discrete assembly of many fragments through the development of multiple cracks. The finite element method is fundamentally ill-equipped to model this transition. Recently a so-called material point method (MPM) has been used to study a wide range of problems of material and structural failures. In this paper we propose a new material point model for the brittle failure which incorporates a statistical failure criterion. The capability of the method for modelling multiple cracks is demonstrated using disc particles. Three impact failure patterns observed experimentally are captured by the model: Hertzian ring cracks, meridian cracks, and multi-fragment cracks. Detailed stress analysis is carried out to interpret the experimental observations. In particular it is shown that the experimentally observed dependence of a threshold velocity for the initiation of meridian cracks on the particle size can be explained by the proposed model. The material point based scheme requires a relatively modest programming effort and avoids node splitting which makes it very attractive over the traditional finite element method.     

爆炸焊接用低爆速粉状乳化炸药研究

为降低岩石粉状乳化炸药的爆速,选择了一种HW矿物粉,通过筛混方式将该分散剂与炸药混合,并测定了该分散剂加入量和布药厚度对炸药爆速的影响。结果表明,岩石粉状乳化炸药中掺入44.5%⁵0%的HW矿物粉时,爆速为1913m/s50%的HW矿物粉时,爆速为1913m/s²378m/s,经钢与不锈钢板爆炸焊接试验表明,爆炸结合率达100%,可满足金属爆炸焊接用炸药的要求。     

爆炸焊接用低爆速粉状乳化炸药研究

为降低岩石粉状乳化炸药的爆速,选择了一种HW矿物粉,通过筛混方式将该分散剂与炸药混合,并测定了该分散剂加入量和布药厚度对炸药爆速的影响。结果表明,岩石粉状乳化炸药中掺入44.5%~50%的HW矿物粉时,爆速为1913m/s~2378m/s,经钢与不锈钢板爆炸焊接试验表明,爆炸结合率达100%,可满足金属爆炸焊接用炸药的要求。     

Modelling adhesive contact between fine particles using material point method

This paper presents a numerical study on contact law between extremely fine particles taking into account of the effect of adhesion force and surface roughness. The adhesion force between two particles is calculated from the Erkoc inter-atomic potential. This force is incorporated into a material point model for the dynamic impact between the two particles. Unlike a molecular dynamics model, atoms in the model are embedded in the continuum solid such that they can only move relatively to each other as the continuum solid deforms. The model is numerically efficient while taking into account of the adhesion effect at the same time. Numerical study using this model shows that the Maugis theory (Maugis, 1992) is valid for spherical particles as small as 50 nm in size. The numerical study also shows that a slight change in surface roughness can alter the impact behaviour completely. Therefore an uncertainty in using the Maugis contact law for real particles is how to determine the effective specific surface energy for particles of different surface roughness. Because of the uncertainty, full numerical analysis may have to be used to obtain the adhesive contact law.     

钛-钢板爆炸焊接的影响因素及炸药配方

爆炸复合用炸药是影响爆炸焊接效果的最主要因素,不同的材料和工艺参数对炸药的爆速、比冲量和能量有不同的影响,其中炸药的密度直接影响复板斜碰撞基板的速度和角度。选用低合金高强度结构钢Q345B和工业纯钛TA2为实验材料,通过理论计算与实验研究,得到了一种较为适合钛-钢板爆炸焊接用的炸药配方,并对钛-钢爆炸焊接影响因素进行了探讨。     

钛-钢板爆炸焊接的影响因素及炸药配方

爆炸复合用炸药是影响爆炸焊接效果的最主要因素,不同的材料和工艺参数对炸药的爆速、比冲量和能量有不同的影响,其中炸药的密度直接影响复板斜碰撞基板的速度和角度。选用低合金高强度结构钢Q345B和工业纯钛TA2为实验材料,通过理论计算与实验研究,得到了一种较为适合钛-钢板爆炸焊接用的炸药配方,并对钛-钢爆炸焊接影响因素进行了探讨。     

Investigation of explosive welding parameters and their effects on microhardness and shear strength

The aim of this study was to investigate the strength of explosive welded metals with the same chemical compositions. Different welding interfaces (straight, wavy and continuous solidified-melted) were used with changing explosive welding parameters [stand-off distance (s), explosive loading (R) and anvils]. Joined metals were investigated under heat-treated and untreated conditions. Results on the microstructure, microhardness, tensile shear strength and bending tests are reported. According to the experimental results, the effect of the anvil on the explosive welding process was only the joining or not-joining performance. It was shown that the bonding interface changed from a straight to a wavy structure when the explosive loading and stand-off distance were increased. For wavy interfaces, when the explosive loading was increased the wavy length and amplitude increased. Results of tensile shear and bending tests showed that heat-treated specimens have more strength than untreated samples. According to tensile shear test results, straight and wavy interfaces had similar strength. In addition, in bending tests of untreated specimens it was shown that the bending zone had some cracks.     

TNT炸药爆炸场中三波点的数值模拟

准确预测三波点的位置和揭示三波点的规律,对工程防护和实现弹药的高效损伤有着重要作用。基于LS-DYNA有限元软件,利用数值模拟方法研究了TNT炸药在混凝土地面上形成爆炸冲击波的三波点运动轨迹,并初步揭示了炸高、药量和炸药形状等因素对三波点高度的影响。研究表明:在爆炸场中,爆炸冲击波以炸药为中心向四周传播,三波点轨迹的高度均呈现逐渐增高的变化趋势。不论改变炸药的药量还是炸高,三波点高度的增速在中场(4.0⁷.0 m)都较缓,而进入远场(>7.0 m)增速骤增。当炸药的炸高和药量相同,炸药形状不同时,圆柱状炸药在中场爆炸形成的三波点高度比长方体炸药略高,且高度增速都较缓;而在远场三波点的高度基本相等,且增速急剧上升,趋于定值。与炸药形状的影响相比,炸高和药量对TNT炸药爆炸冲击波的三波点高度的影响较大。     

TNT炸药爆炸场中三波点的数值模拟

准确预测三波点的位置和揭示三波点的规律,对工程防护和实现弹药的高效损伤有着重要作用。基于LS-DYNA有限元软件,利用数值模拟方法研究了TNT炸药在混凝土地面上形成爆炸冲击波的三波点运动轨迹,并初步揭示了炸高、药量和炸药形状等因素对三波点高度的影响。研究表明:在爆炸场中,爆炸冲击波以炸药为中心向四周传播,三波点轨迹的高度均呈现逐渐增高的变化趋势。不论改变炸药的药量还是炸高,三波点高度的增速在中场(4.0~7.0 m)都较缓,而进入远场(7.0 m)增速骤增。当炸药的炸高和药量相同,炸药形状不同时,圆柱状炸药在中场爆炸形成的三波点高度比长方体炸药略高,且高度增速都较缓;而在远场三波点的高度基本相等,且增速急剧上升,趋于定值。与炸药形状的影响相比,炸高和药量对TNT炸药爆炸冲击波的三波点高度的影响较大。     

炸药量对爆炸焊接界面波影响的数值模拟

为了保证金属复合材料的爆炸焊接质量,对爆炸焊接过程中的爆轰荷载大小起着决定性作用的炸药量及布药方式进行了探索。应用AUTODYN非线性显式动力学分析软件,模拟了基、复板爆炸焊接复合过程,得到了不同炸药量下爆炸焊接过程中的压力时程,结合理论公式,分析炸药量、爆轰荷载、碰撞速度和界面波状之间的关系,及炸药量对爆炸焊接界面波的影响。并在复板上、下表面等间距各设置了8个关键点,比较了炸药厚度均匀布药方式和厚度递减布药方式产生的波状形态。结果表明,在可焊性窗口内,炸药量多的会产生较大波状结合界面;厚度递减布药方式能够消除均匀布药方式下界面波的不均匀现象,其中方案2的速度波动效果最好。并且已经结合的界面受到后续压力的振动破坏明显降低。     

Testing of explosive welding and welded joints. Wavy character of the process and joint quality

The basic defects occuring in explosive clad plates were properly systemized and the reasons of their formation were explained. Cases of cracks and delaminations in explosive clad plates were examined in this work. Various values of tensile stresses coming from loading and unloading waves were analysed, as they were the main reason of defects. The defects were connected with properties of welded materials in the joint area and beyond it. Some practical aspects of this process were shown as well.     

蒙特卡罗法分析GPS误差对火箭弹落点预测精度的影响

针对火箭弹在落点预测过程中GPS随机误差影响预测精度的情况,从理论和仿真实验上对该影响进行分析。该文将GPS误差作为典型的随机过程,结合火箭弹动力学模型建立数学模型,并利用经典的统计试验法-蒙特卡罗分两种情况进行弹道仿真实验,预测弹丸落点。仿真结果表明:在存在GPS误差的情况下弹道修正的精度大幅降低,因此GPS误差是影响落点预测精度的重要因素。     

基于虚拟介质方法数值模拟应力波穿透水舱

将虚拟介质方法推广到应力波与流固界面的相互作用,基于修正虚拟流体方法(MGFM)思想提出一种适用于流固界面应力波折射问题的界面状态计算法则.以此为基础,用Zwas格式和WENO格式分别离散固体和流体控制方程,数值模拟应力波穿透水舱.数值测试表明:虚拟介质方法推广到模拟流固界面上的应力波时,数值误差具有很好的收敛性;该研...     

双金属爆炸焊接参数设计理论

针对爆炸焊接参数设计问题,从爆炸焊接基本理论出发,分步介绍了飞板爆轰驱动的理论和双金属爆炸焊接窗口理论。首先归纳总结了一维爆轰驱动飞板的终速公式,并详细说明了其应用范围与原因。对于二维滑移爆轰驱动飞板问题,主要针对Richter理论和特征线法进行了介绍,并推导出新的近似计算公式。接着,对于爆炸焊接参数窗口理论,详细比较了以往传统单一金属爆炸焊接窗口理论与公式,并针对部分已有公式进行了重新推导与修正,重新界定了其适用范围。利用这些爆炸焊接窗口的基本理论,作者对所发展的双金属可焊下限、双金属可焊上限、双金属流动限以及声速限构成的双金属爆炸焊接窗口理论进行了系统地介绍。最后,以飞板爆轰驱动和爆炸焊接窗口构建成了整个爆炸焊接工艺技术参数设计理论,并结合二元合金相图进行爆炸焊接设计,针对调控原材料硬度的必要性、焊接界面波纹及气孔的控制方法等问题进行了讨论。     

聚能射流引爆带壳装药数值计算分析

为了分析聚能灭雷装药中的聚能射流速度引爆带壳装药的能力,应用有限元数值计算方法,以金属杆撞击起爆带壳装药模型,模拟聚能装药金属射流引爆带壳装药,分析不同直径金属杆以不同初速的初始条件侵彻不同厚度靶板,引爆带壳装药,并与held理论进行了比较。通过大量的数值计算,得到了不同直径金属杆引爆带壳装药的射流极限速度。分析结果表明,金属杆直径越小,held判据的k值越大,即引爆带壳装药需要的射流速度越大;held判据的k值越小,即引爆带壳装药需要的射流速度越小。所以,要保证射流在具有一定直径的前提下,并提高射流的速度,以达到起爆装药的目的。     

Numerical analysis of thermoplastic composites laser welding using ray tracing method

Laser technology is a good alternative for continuous joining of thermoplastics composites structures. Presence of continuous fibers at a high fiber volume fraction (superior to 30%) does not allow using traditional development as for pure thermoplastic materials, due to the presence of fiber clusters or polymer rich areas. Those heterogeneities induce macroscopic light scattering through the structure, reducing the resulting energy level absorbed at the welding interface. The study proposed here takes into account the real microstructure of the composite in order to evaluate changes in local energy diffusion directly linked with local fiber arrangements. The objective of this work is to develop an affordable numerical simulation of the laser welding process modeled with adapted physics mechanism and taking into account the microstructure heterogeneity of the considered materials regarding optical and thermal properties. To model the optical path of the laser beam through the composite fibrous structure, a simulation tool based on geometrical optic is developed. Weldability is considered on composites with different thicknesses, showing the non linear relationship between welding energy and substrate thickness.     

A selection of material using a novel type decision-making method: Preference selection index method

The aim of the current study is to implement a novel tool to help the decision-maker for selection of a proper material that will meet all the requirements of the design engineers. Preference selection index (PSI) method is a novel tool to select best alternative from given alternatives without deciding relative importance between attributes. In the present study, three different types of material selection problems are examined. A validation and consistency test of preference selection index method is performed in present work by comparing results of PSI method with published results of graph theory and matrix approach (GTMA), and technique for order preference by similarity to ideal solution (TOPSIS) method, respectively. The research has concluded that the PSI method is logical and more appropriate for the material selection problems.     

电子束焊接熔池周期性波动的数值模拟

为了更深入地探究电子束焊接过程中的机理问题,利用数值软件Fluent,对10mm厚的2219铝合金电子束焊接熔池进行三维瞬态模拟。分析电子束焊接进入准稳态后熔池中涡流的变化规律和产生原因,并结合电子束与匙孔壁面相互作用进行讨论。结果表明:电子束焊接进入准稳态后熔池呈周期性波动;根据液态金属流动情况可将焊接熔池分为3个区域,区域Ⅰ中的液态金属维持了熔池体积的稳定,区域Ⅱ中的涡流起到扩大熔池表面的作用,区域Ⅲ中的涡流促使匙孔坍塌;通过对电子束与匙孔壁面的耦合分析可知,电子束在匙孔壁面上并不是均匀分布的,这造成了匙孔底部具有一定的滞后性。     

Computer code for the optimization of performance parameters of mixed explosive formulations

LOTUSES is a novel computer code, which has been developed for the prediction of various thermodynamic properties such as heat of formation, heat of explosion, volume of explosion gaseous products and other related performance parameters. In this paper, we report LOTUSES (Version 1.4) code which has been utilized for the optimization of various high explosives in different combinations to obtain maximum possible velocity of detonation. LOTUSES (Version 1.4) code will vary the composition of mixed explosives automatically in the range of 1-100% and computes the oxygen balance as well as the velocity of detonation for various compositions in preset steps. Further, the code suggests the compositions for which least oxygen balance and the higher velocity of detonation could be achieved. Presently, the code can be applied for two component explosive compositions. The code has been validated with well-known explosives like, TNT, HNS, HNF, TATB, RDX, HMX, AN, DNA, CL-20 and TNAZ in different combinations. The new algorithm incorporated in LOTUSES (Version 1.4) enhances the efficiency and makes it a more powerful tool for the scientists/researches working in the field of high energy materials/hazardous materials.