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对飞机结构螺接件来说,最主要的强度问题之一,是在疲劳载荷下会产生裂纹并扩展。而目前对含裂纹螺接件的应力强度因子(Stress intensity factor,SIF)分析多以简化的二维有限元模型为主。为此,在考虑螺栓与孔壁间的非线性接触、摩擦和螺栓预紧力等因素影响的基础上,利用非线性有限元软件MSC.Marc构建含裂纹螺接件的三维有限元分析模型,通过分析得到不同损伤模式下的SIF与裂纹长度沿板厚度方向的变化曲线。结果表明,虽然螺接件孔边裂纹是复合型裂纹,但Ⅰ型SIF起主导作用,Ⅱ型和Ⅲ型SIF可忽略不计;在裂纹长度一定时,接触面处的SIF最大,外表面处最小,孔边双侧裂纹对称时的SIF大于孔边单侧裂纹情形;裂纹长度相同时,含沉孔螺接件接触面上的SIF大于直孔情形时相应的SIF,而外表面的SIF趋势则恰恰相反。
One of the most important strength issues for aircraft structural screw connections is cracking and expanding under fatigue loads. At present, stress intensity factor (SIF) analysis of cracked screwdrivers is mainly based on the simplified two-dimensional finite element model. Therefore, based on the nonlinear contact between the bolt and the hole wall, the friction and the preload of the bolt, the three-dimensional finite element analysis model of the cracked screw joint is constructed by using the nonlinear finite element software MSC.Marc, The curves of SIF and crack length along the thickness of the plate under different damage modes were obtained. The results show that type I SIF plays a leading role and type II and type III SIFs are negligible although the crack at the edge of the screw is a composite crack. When the crack length is constant, the SIF at the contact surface is the largest and the outer surface is the smallest , The SIF at the bilateral crack symmetry of the hole edge is larger than that of the unilateral crack at the hole edge. When the crack length is the same, the SIF at the contact surface of the counterbore screw connector is larger than that at the straight hole, while the SIF trend of the outer surface Quite the opposite.