﻿ 失效准则在船舶碰撞破坏中的应用研究
 舰船科学技术  2017, Vol. 39 Issue (1): 56-62 PDF

1. 华中科技大学 船舶与海洋工程学院，湖北 武汉 430074;
2. 核动力舰船蒸汽动力系统国防科技实验室，湖北 武汉 430064

An application research on failure criteria of collision damage in ship structures
ZHANG Zhi-qiang1, LI Hua-feng2, ZHANG Yong-ou1, XU Xiao-dong1, LIU Tu-guang1
1. Huazhong University of Science and Technology, School of Naval Architecture and Ocean Engineering, Wuhan 430074, China;
2. National Lab of Science and Technology on Steam Power for NS, Wuhan 430064, China
Abstract: Failure of the ship structure attracts more and more attention recently. Collision is considered to be one of the most common damage for the structure and can sharply shorten its lifespan. Since the weight of the ship is sometimes very large, serious damage can still happen even with a low impact velocity. In order to know whether the failure occurs on a structure or not during the simulation, the failure criteria is always used and affects the analysis a lot. The present paper compares the effect of three different types of failure criterion on numerical results. Firstly, suitable parameters in the finite element method are chosen and validated by comparing with experimental data in modelling the typical double shell collision model. After that, the application of three types of failure criterion, namely the GL, RTCL, and JC models, are discussed. Results show that the triaxiality greatly affect the accuracy of the simulation, while the strain rate has much less effect especially under low impact velocity.
Key words: ship collision     failure criteria     double shell     numerical simulation
0 引言

1 模型验证

1.1 几何模型

 图 1 双层壳结构尺寸 Fig. 1 Structure size of the double shell

 图 2 尖刀型撞头尺寸 Fig. 2 Size of the knife edge indenter

1.2 材料参数

 $\sigma = (A + B{\varepsilon ^n})(1 + C\ln {\dot \varepsilon ^ * })(1- {T^ * }^m)。$ (1)

1.3 结果对比分析

 图 3 双层壳结构变形图 Fig. 3 Deformation of the double shell

 图 4 外板撞击变形图 Fig. 4 Deformation of the outer plate

 图 5 仿真横向肋板变形图 Fig. 5 Deformation of stringers on simulation

 图 6 撞击中心垂向位移曲线 Fig. 6 Vertical displacement curves in impact center

2 失效准则适用性分析 2.1 失效准则概述

1）GL 失效准则。采用单一的等效临界失效应变预测损伤起始，但与常应变准则不同的是临界值的确定方法不一致，GL 根据材料沿厚度方向的应变值来判断单元是否失效。

 ${\varepsilon _f}({l_e}) = {\varepsilon _g} + {\varepsilon _e} \cdot \frac{t}{{{l_e}}}。$ (2)

2）RTCL 准则。以细观损伤力学为基础，通过研究材料内部球形孔洞的生长规律，给出 Rice-Tracey 韧性失效准则失效判据表达式为：

 $\begin{array}{l} D = \int_0^{{{\bar \varepsilon }_f}} {\frac{{{\sigma _1}}}{{{\sigma _m}}}{\rm d}\bar \varepsilon } {\rm{- 0}}{\rm{.33}} < \eta < 0.33,\\[3pt] D = \int_0^{{{\bar \varepsilon }_f}} {\frac{1}{C}\exp (1.5\eta ){\rm d}\bar \varepsilon } {\rm{ }}\eta > 0.33。 \end{array}$ (3)

 图 7 RTCL 失效准则失效应变与应力三轴度曲线 Fig. 7 Strain-stress triaxiality curves of RTCL failure criteria

3）JC 失效准则。综合考虑应变硬化、应变率效应及温度软化效应，其具体形式为：

 ${\varepsilon _f} = ({D_1} + {D_2}\exp {D_3}{\sigma ^ * })(1 + {D_4}\ln {\dot \varepsilon ^ * })(1 + {D_5}{T^ * })。$ (4)

2.2 撞击破坏模型

2.3 结果对比

 图 8 外板撞击破坏图 Fig. 8 Fracture plots of the outer plate

 图 9-1 塑性能、损伤能、撞击力-速度曲线 Fig. 9-1 Curves of plastic dissipation energy damage dissipation energy and force- velocity

1）对于 GL 失效准则。

① 不同网格尺寸下，最终的塑性吸收能一致，但随时间变化的趋势不同，网格尺寸越小，单元进入塑性越快，其塑性吸收能上升越快。

② 损伤耗散能则随着网格尺寸的增大而变大，这也与破裂缺口的尺寸规律一致。

③ 冲击力峰值随着网格尺寸的减小而增大，而最后撞头的反弹速度随网格尺寸的增大而减小，但不同 FN-V 曲线与坐标轴围成的面积基本相当。这表明整个双层壳结构塑性吸收能基本相当，其对网格尺寸敏感性不强。而局部破坏则表现出对网格的依赖性，但损伤能相比塑性能小。而撞头的接触力随着网格尺寸的精细而增大。

2）对于 RTCL 准则。

① 从结构的塑性能和损伤耗散能来看，10 mm 和5 mm 网格下，塑性能和损伤能都基本一致，而 15 mm网格尺寸下，损伤耗损能相对较小。

② 三种网格下，曲线的峰值和趋势都比较吻合。 说明 RTCL 准则，在网格尺寸小于 10 mm 时，已经具有一定的收敛性。这说明：考虑应力三轴度影响的 RTCL 失效准则对双层壳结构的破坏过程描述是较为准则的。且在 10 mm 网格尺寸下，该准则对网格尺寸的影响不是特别敏感。

3）对于 JC 失效准则。

① 塑性吸收能曲线十分吻合。

② 损伤耗散能最终的值基本相当，但上升趋势有所不同，当网格尺寸为 15 mm 时，从破坏图上来看， 损伤单元的数量较少，曲线上升趋势发生了偏折。

③ 撞头的力-速度曲线基本一致，撞击力在峰值附近有一点波动，但峰值大小基本相当。这说明 JC 失效准则对网格敏感度较小，仿真结果较为准确。

2.4 适用性分析

 图 10 中心单元的等效应力-应变曲线 Fig. 10 Equivalent stress-strain curves of the central element

 图 11 撞击区域 3 个单元的应力三轴度 Fig. 11 Stress triaxiality curves of three elements in the impact area

 图 12 撞击区域 3 个单元的应变率曲线 Fig. 12 Strain rate curves of three elements in the impact area

 图 13 撞击中心单元的等效塑性应变曲线 Fig. 13 Equivalent plastic strain curves of the central element
3 结语

1） GL 失效准则对网格尺寸较为敏感，需要较精细网格才能够模拟出外板的失效破坏。而 RTCL 失效准则和 JC 失效准则考虑了应力三轴度对断裂失效应变的影响，对网格尺寸的敏感性较小，更加适用于撞击破坏的仿真计算之中。

2）由于板撞击中心破坏区域的应力三轴度在撞击中心变化较小，不考虑应力三轴度的 GL 失效准则也能较好的模拟板的冲击破坏，但相比 RTCL 和 JC 失效准则，其对网格质量的要求更高。同时，低速撞击中，材料的应变率多在 102 量级以下，JC 失效准则中的应变率参数对结果的影响不是很大。

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