Finite element analysis for the evaluation of the low-velocity impact response of a composite plate

The low-velocity impact responses of cross-ply CFRP composite plates are investigated experimentally and are simulated using the finite element code LS-DYNA. An experimental test was initially performed and two different modeling approaches were then employed to model the composite plates. In the first numerical modeling approach, solid elements are utilized for the composite layers, whereas in the second, shell elements are used. The numerical model using the shell elements shows a good correlation with the experimental results, while the impact damage in the form of delamination is predicted more precisely using solid elements.     

A local-domain based phase field method for crack propagation

Abstract

The phase field method transfers the crack surface area into a domain integral through a smeared damage parameter. As a result, the fracture energy release rate can be directly incorporated into the energy form without tracking of crack surface, and a minimization approach to optimize the crack shape becomes possible. This nonlocal damage approach requires a fine mesh discretization to capture the damage gradient in the smeared crack zone, which produces a significant degree of freedom problem to optimize over the entire domain. In this research, a local-domain based phase field method is proposed. This method considers only elements in critical regions for energy minimization, whose internal energy are dominant, thus significantly reducing the degree of freedom to be solved. A numerical verification is carried out to demonstrate the feasibility of this approach, and simulations are presented to verify the accuracy of the new method.     

砖烟囱爆破拆除不同切口形状的数值模拟

针对烟囱爆破拆除时爆破切口形状的确定往往按经验确定,没有重视烟囱倒塌过程中一些问题很难通过理论预见的情况,利用ANSYS/LS-DYNA软件数值模拟了常见的长方形切口、正梯形切口、倒梯形切口这3种爆破切口形状对烟囱倒塌拆除过程并进行了对比和分析,研究结果表明:首先从爆破切口闭合时间看到,倒梯形切口闭合时间最长,正梯形切口闭合时间次之,长方形切口闭合时间最短。其次从烟囱顶端着地时间分析,正梯形切口烟囱顶端着地时间最长,而其它两种切口方案次之,并且这两种方案对烟囱倒塌时间差不多相等。再从模拟烟囱倒塌的过程分析,正梯形切口及长方形切口烟囱倒塌过程出现"后座"现象。最后从烟囱倒塌顶端速度变化曲线中看出正梯形切口烟囱倒塌方案对地面的冲击力最小,引起地面的振动强度最小。     

台阶爆破相邻炮孔间损伤范围的数值模拟

采用ANSYS/LS-DYNA建立三合-新站石灰石矿台阶松动爆破模型,以最大拉应力是否超过动态抗拉强度作为判断岩体破坏的依据,对相邻炮孔间的损伤范围进行对比分析。结果表明,两孔间的损伤百分比随孔距的增大而减小,最后逐渐趋于定值;岩石损伤单元数随着孔距的增大先增大后减小,最后趋于定值。     

时间步长对爆破模拟结果的影响研究

为提高LS-DYNA软件模拟工程爆破时的精度,从理论上改进了确定极限时间步长Δte的方法,结合已有的数据对本方法的合理性进行了验证,并通过实例探讨了时间步长Δt对爆破模拟结果的影响。研究表明:Δte仅与炸药的爆速、炸药最小单元的最小边长以及计算时间步长比例因子有关,在网格划分时,炸药单元不能取过小或过于狭长;Δt对土体中爆炸空腔半径形成的影响不大,而对压力峰值的影响显著,且具有一定的规律性;随着比例距离Z的增加,压力峰值误差呈现由小到大,再由大到小的趋势。当计算区域范围在Z<0.5m·kg^(-1/3)时,Δt可取为1(-1/3)时,Δt可取为1³倍Δte;当Z≥0.5m·kg3倍Δte;当Z≥0.5m·kg^(-1/3)时,时间步长Δt可适当放宽,取为3(-1/3)时,时间步长Δt可适当放宽,取为3⁵倍Δte。对于一般的爆破模拟,考虑到经济性,Δt取为15倍Δte。对于一般的爆破模拟,考虑到经济性,Δt取为1³倍Δte即可满足大多数工程计算精度的要求。     

杀爆战斗部相关作用场的毁伤效能研究

破片和冲击波作为杀爆战斗部的两种主要毁伤元素,对目标的毁伤形式不尽相同。以杀爆弹为研究对象,在不同工况下,通过LS-DYNA动力学软件,对杀爆相关作用场的毁伤效能进行研究,并将其毁伤效能与单独冲击波作用进行对比,得到了如下结论:杀爆相关作用场的毁伤效能较单独冲击波作用有较大提升;TNT当量的增加对杀爆相关作用有较大的增益;杀爆战斗部相关作用场的毁伤效能随着预开孔间距的增大而减小。     

Application of a neural network to predict thickness strains and finite element simulation of hydro-mechanical deep drawing

In this paper an artificial neural network (ANN) is used to predict the thickness along a cup wall in hydro-mechanical deep drawing. This model uses a feed-forward back-prorogation neural network. After using the experimental results to train and test the network, the model was applied to new data for the prediction of thickness strains in hydro-mechanical deep drawing. The results are promising. In the present work, we also attempt to perform a finite element simulation of the process for the two dimensional axi-symmetric case using explicit finite element code LS-DYNA 2D. Counter pressure on the blank is applied by specifying the pressure boundary conditions. A comparison was made between simulated, experimental and ANN results of hydro-mechanical deep drawing using low carbon extra deep drawing grade steel sheets of 0.96 mm thickness. It was also found that by hydro-mechanical deep drawing, a higher drawability and a more uniform thickness distribution were obtained when compared to conventional deep drawing.     

AZ31B镁合金和6065铝合金动态压缩行为数值模拟

为了研究帽状试样AZ31B镁合金和6065铝合金在动态压缩变形过程中的温度、应力与应变演变规律,采用Johnson-Cook本构方程和累积塑性损伤方程进行了数值模拟,运用有限元软件ANSYS/LS-DYNA模拟了AZ31B镁合金和6065铝合金帽状试样的动态变形过程.结果表明,两种合金的裂纹萌生和扩展过程相似,局域化变形带内塑性应变由内向外对称分布.相比于AZ31B镁合金,6065铝合金的塑性应变影响区域更为狭小,其应变和应变率硬化效果更强.6065铝合金的变形温度能够达到其动态再结晶临界点,因而易于绝热剪切带的形成.     

弹载硬回收记录器炮击结构侵彻混凝土靶的数值模拟

为了精确记录和存储炮弹从发射到抛洒过程的数据,设计了一种抗高强度、高过载的弹载硬回收记录器炮击结构,并利用有限元软件ANSYS/LS-DYNA模拟该结构以较大速度垂直撞击混凝土靶的过程.结果表明:该结构设计和材料选取合理,能够保证其内部存储设备完好,可作为存储设备的防护结构.     

爆炸冲击技术研究

爆炸冲击波技术在军事和建筑等领域均存在广泛的应用性.通过ANSYS/LS-DYNA软件可进行爆炸冲击建模,而有限元分析方法是进行爆炸冲击问题研究的方法之一.其数值模拟方法包括有限单元法、有限差分法、有限体积法等.有限差分法和动力有限元法是目前冲击载荷作用下,动力结构响应数值计算中应用最多的方法.