基于CDM的复合材料缺口强度三维数值仿真模型

层合板受载时在缺口尖端出现的沿纤维方向的基体开裂会使缺口钝化,降低缺口带来的应力集中影响。为了更好地模拟这一现象,建立基于CDM的三维有限元模型,提出一种可以实现层合板中每层网格不同排列的建模方法,使网格边缘与每层纤维方向一致;为了实现每层网格不同的排列,在层间建立内聚力接触模拟分层损伤;对纤维增强复合材料层合板[0/902/0]S和[0/90/±45]S进行开孔拉伸的渐进损伤分析。结果表明:该模型可以模拟不同材料体系和铺层参数的层合板在拉伸载荷作用下的渐进损伤过程,预测其破坏强度;通过已知的试验结果对模型进行验证,证明了该方法的正确性且预测精度较高。     

考虑钉头传载的阶梯搭接钉载分配特性

确定钉载分配比例是机械连接强度分析的基础和关键,也是研究孔周应力分布的前提。以某型飞机铝合金阶梯形搭接板螺栓群连接结构为研究对象,利用应变电测法初步测量了各排螺栓的钉载分配比例。随后通过ABAQUS有限元三维实体建模,考虑钉头传载及接触摩擦、螺栓预紧、材料非线性、防弯夹具等因素,对螺栓群的钉载分配行为进行了模拟。计算发现：阶梯形搭接板多钉连接的钉载分配比例呈两端大中间小的规律,且台阶高度是影响钉载分配比例的重要因素。在此基础上,进一步研究了台阶高度对钉载分配均匀性的影响。分析结果表明：阶梯形搭接板多钉连接处于弹性范围以内时,随着台阶高度的增加,钉载分配趋于均匀;结构产生塑性变形后,随着台阶高度的增加,钉载分配先趋于均匀后随之变差。最后,基于钉载分配与孔边最大应力,对阶梯搭接多钉连接的几何构型进行了优化。优化后阶梯搭接的钉载分配比例极差不超过1.1%,最危险部位的孔边最大应力及螺栓最大剪切应力分别减小了约4.4%与10.2%。     

机翼缘条喷丸强化变形模拟与参数优化

机翼缘条是连接飞机机翼与中央翼盒的重要结构件,其制造精度要求较高.喷丸强化后,该零件在啧丸残余应力的作用下会产生弯曲变形,需要通过优化不同位置的喷丸强化参数以减小弯曲变形量.首先,在喷丸强度的许可范围内进行了喷丸强化试验,并通过X衍射测量,建立喷丸参数与喷丸残余应力场间的函数关系;其次,设计Box-Behnken试验,通过等效喷丸变形模拟方法,得到了不同喷丸参数下机翼缘条的变形量,建立了缘条变形量与喷丸参数间的函数关系,根据Box-Behnken试验分析,结合工程条件得出了一组最优的喷丸强化参数;利用该组最优喷丸参数进行缘条的变形模拟和喷丸强化试验,发现喷丸变形的模拟与试验结果均较小,从而验证了缘条零件变形模拟和喷丸参数优化的有效性.     

TA15四层板结构超塑成形/扩散连接技术研究

进行了TA15合金超塑拉伸试验,在温度920℃和应变速率5.25×104s-1时,TA15合金的最大延伸率约为1100％,其应变速率敏感性指数约为0.57.在较佳超塑变形条件930℃和应变速率5.25×10-4s-1附近,TA15合金的超塑本构方程为σ=949(ε) 0.55.对TA15四层板结构超塑成形过程进行了有限元分析,获得了压力p-时间t曲线.在T =930℃和应变速率5.25×10-4s-1下,成功进行了TA15四层板结构SPF/DB成形试验,试验件的整体质量良好,无沟槽等缺陷,金相组织观测表明,TA15四层SPF/DB试验件扩散连接质量优良.     

三维角联锁机织复合材料剪切性能有限元分析

使用三维绘图软件Pro/E 5.0构建出一种三层角联锁机织复合材料的细观结构模型,借助有限元软件ANSYS对复合材料在剪切力作用下纤维与树脂的应力、应变分布进行数值模拟,并借此分析该复合材料在剪切作用下的力学行为,并预测复合材料破坏模式。结果表明:复合材料在剪切力作用下发生沿剪切力方向程度较均匀的剪切变形;纤维相对于树脂承受更多剪切力作用,产生更大应力,但发生相对较小的应变;纤维中轴向与剪切力方向平行的经纱相对轴向垂直于剪切力的纬纱表现出更大的应力和应变。     

Residual stress indentation model based on material equivalence

A novel residual stress indentation model for conical indentation loading is proposed to describe the relationship between the residual stress, material constitutive parameters, load, and displacement for materials with a uniaxial constitutive relationship that obeys Hollomon’s power law (H-law). The novel model was established based on the principle that the equivalent material without residual stress corresponds to the original material with residual stress, conical indentation theoretical model based on energy density equivalence, and an assumed power-law relationship between the dimensionless residual stress and relative difference of the yield stresses of the equivalent material and original material. Sixty imaginary H-law materials with ten equibiaxial and ten uniaxial residual stresses were investigated by Finite Element Analysis (FEA). The residual stresses predicted by the novel model from the indentation load–displacement curves simulated for the imaginary materials are in close agreement with those applied by the FEA. Finally, indentation tests for Cr12MoV steel, 45 steel, and 6061-T6511 aluminum alloy were carried out on their specimens without residual stress and their bending specimens with equibiaxial and uniaxial residual stresses. The residual stresses predicted by the novel model according to the indentation load–displacement test curves are in good agreement with those applied by the tests.     

Impact of aperture on dynamic response of sandwich plates with aluminium face-sheets and PMI core based on an alternative finite element formulation and experiments

Apertures generally exist in the sandwich structures attributing to mechanical connection and lightweight, which might induce failure of such structures. Thus, it is required to realize the impact of aperture on mechanical behaviors of sandwich structures. If transverse shear deformations are unable to be described accurately, the reasonable prediction of dynamic behaviors of the form-core sandwich plates with apertures will meet severe challenges due to a large difference of transverse shear mo...     

Refined modeling and experimental verification of a torque motor for an electro-hydraulic servo valve

The Permanent Magnet Torque Motor (PMTM) is the key electro-mechanical conversion device in an Electro-Hydraulic Servo Valve (EHSV). In this work, a refined model of a PMTM is developed, considering the non-working air-gaps between the upper or lower yoke and the armature, the fringing effect at the limiting holes, and the nonlinear permeability of soft magnetic material. Based on the refined model, the influences of various factors on the calculation accuracy of the magnetic flux at the pole surfaces of the armature and the output torque are investigated. For verifying the validity of the refined model, a Finite Element Analysis (FEA) of the PMTM is conducted, and a test platform is constructed. Compared with existing models, the refined model can better reveal the intrinsic mechanism of the PMTM, and its calculations are more consistent with the FEA results. The experimental results of the armature deflection displacement show that the refined model can accurately describe the output characteristics of the PMTM.     

广义有限元法计算飞机开口裂纹应力强度因子

机身开口圆角损伤可能逐渐形成裂纹从而严重影响飞机使用安全,为此对圆角裂纹进行剩余强度估算显得十分重要。使用Williams位移场广义有限元法进行裂尖单元加强,并对裂尖区域应用放射形网格划分技术,编写广义有限元法的MATLAB程序,研究并计算飞机舱门开口圆角裂纹的应力强度因子。结果表明：在裂纹分析上,广义有限元法较常规有限元法具有更好的适应性和更高的精度。     

一种舱段快速连接结构设计及承载能力分析

设计了一种新型的舱段间连接装置，分析了其在轴向力载荷作用下的受力情况，并以相对滑动作为失效判据给出了预紧力的计算方法，在此基础上分析了卡箍倾角、摩擦系数以及预紧力等对该结构承载能力的影响。研究结果表明：直径为1 200 mm的连接结构能够满足1 000 kN 轴拉载荷下的使用要求。卡箍与壳体配合面倾角、摩擦系数以及预紧力等均会对该连接结构的承载能力产生影响，其中预紧力的影响主要表现为预紧力增大，卡箍与上下壳体对接面的压力增大，产生的摩擦力增大，因此其轴向承载能力增大。此外，随着配合面倾角增大以及摩擦系数的减小，则会导致该连接装置承载能力产生显著下降。