﻿ 舰船高强度钢材的裂纹分析和力学特性评估
 舰船科学技术  2023, Vol. 45 Issue (11): 72-75    DOI: 10.3404/j.issn.1672-7619.2023.11.014 PDF

Crack analysis and mechanical property evaluation of ship high strength steel
GE Jun-chao, WANG Li-peng
Hebi Institute of Engineering and Technology, Henan Polytechnic University, Hebi 458030, China
Abstract: In order to improve the strength of ship structure, high-strength steel such as Q460 is often used in ship shell and other positions. A large number of tests and actual ship collision accidents show that the failure form of ship high-strength steel structure is usually not the failure under static strength, but the structural failure and fracture under fatigue load. Therefore, fracture mechanics analysis of high strength ship steel has always been a hot topic. This paper introduces the fracture and elastic mechanics principle of steel in detail, establishes the fatigue load distribution and S-N curve of ship high strength steel, and simulates the mechanical characteristics of ship high strength steel plate with Ansys.
Key words: high strength steel     crack analysis     mechanical properties     finite element     fatigue
0 引　言

1）极限载荷下的塑性屈服或者屈曲变形

2）疲劳载荷损伤

1 舰船高强度钢材的线弹性力学与断裂力学分析

 图 1 高强度钢材3种裂纹形式的示意图 Fig. 1 Schematic diagram of three crack forms of high-strength steel

 ${\sigma _{ij}} = \frac{{{K_1}}}{{\sqrt {2\text{π} r} }}{\phi _i}(\theta ) 。$

 ${K_1} = \sigma \sqrt {\text{π} a} f(a,W, \cdots ) \text{，}$

 ${K_c} = \sigma \sqrt {\text{π} a} f\left(\frac{a}{W}, \cdots \right) 。$

 $\begin{gathered} {\sigma _p} = \frac{1}{{2\text{π} }}{\left( {\frac{{{K_1}}}{{{\sigma _w}}}} \right)^2} ，\\ {\delta _p} = \frac{1}{{2\text{π} }}{\left( {\frac{{{K_1}}}{{{\sigma _{\text{w}}}}}} \right)^2}{(1 - 2v)^2} 。\\ \end{gathered}$

 $R=\frac{1}{\alpha \text{π} }{\left(\frac{{K}_{1}}{{\sigma }_{H}}\right)}^{2}，\alpha =\Bigg\{\begin{array}{l}1\text{，}应力，\\ 2\sqrt{2}\text{，}应变。\end{array}$
2 舰船高强度钢材的疲劳裂纹扩展特性研究

 $\Delta K = {K_{\max }} - {K_{\min }} \text{。}$

${K}_{\mathrm{max}}{\text{和}}{K}_{\mathrm{min}}$ 分别为一个疲劳载荷循环下的应力强度因子最大值和最小值，在对数坐标系下得到裂纹扩展速度与 $\Delta K$ 的关系曲线如图2所示。

 图 2 裂纹扩展速度与 $\Delta K$ 的关系曲线 Fig. 2 The relationship between the crack growth velocity and the curve

1）低速扩展区域

2）中速扩展区域

3）高速扩展区域

3 基于有限元的舰船高强度钢材的裂纹分析与力学仿真 3.1 舰船高强度钢材结构的载荷分布

1）连续型正态/瑞利分布

 $F(\zeta ) = \frac{1}{{\sqrt {2\text{π} {\sigma _x}} }}\exp \left[ { - \frac{{{{\left( {\zeta - {\mu _x}} \right)}^2}}}{{2\sigma _x^2}}} \right] 。$

 $f(y) = \frac{{2y}}{R}\exp \left[ { - \frac{{{y^2}}}{R}} \right],0 \leqslant y < + \infty 。$

 图 3 波浪载荷的连续型正态/瑞利分布曲线图 Fig. 3 Continuous normal/Rayleigh distribution curve of wave loading

2）连续型威布尔分布

 $\begin{gathered} F(\Delta \sigma ) = 1 - \exp \left[ { - {{\left( {\frac{{\Delta \sigma }}{q}} \right)}^h}} \right]0 ，\leqslant \Delta \sigma < + \infty ，\\ f(\Delta \sigma ) = \frac{h}{q}{\left( {\frac{{\Delta \sigma }}{q}} \right)^{h - 1}}\exp \left[ { - {{\left( {\frac{{\Delta \sigma }}{q}} \right)}^h}} \right]0，\leqslant \Delta \sigma < + \infty 。\\ \end{gathered}$

 图 4 浪涌载荷的连续型威布尔分布曲线 Fig. 4 Continuous Weibull distribution curve for surge loads
3.2 舰船高强度钢结构的疲劳累积损伤和S-N曲线

P-miner线性累积损伤理论[4]是目前针对疲劳载荷常用的一种评估方法，定义应力为 ${S_i}$ ，该应力下的材料失效的循环次数为 ${N_i}$ ，经过 ${n_i}$ 次该应力的循环，可得材料的损伤值为：

 ${D_i} = \frac{{{n_i}}}{{{N_i}}} \text{。}$

 $D = \sum\limits_{i = 1}^k {} \frac{{{n_i}}}{{{N_i}}} \text{。}$

D＜1时，证明材料在该疲劳载荷下不发生失效。

 图 5 舰船高强钢的材料S-N曲线 Fig. 5 Material S-N curve of ship high-strength steel
3.3 基于有限元的舰船高强度钢材有限元仿真

1）有限元模型建立

 图 6 舰船高强度钢结构的有限元模型 Fig. 6 Finite element model of high-strength steel structure of ships

2）加载和求解

 ${F_s} = {P_0}{\beta _z}{\chi _0}K 。$

 图 7 舰船高强度钢结构的强度特性仿真结果 Fig. 7 Simulation results of strength characteristics of high-strength steel structure of ships
4 结　语

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