Multi-scale fatigue damage model for steel structures working under high temperature

In order to better understand the fatigue mechanisms of steel structures working under high temperature, a multi-scale fatigue damage model at high temperature is developed. In the developed model, the macroscopic fatigue damage of metallic materials due to the collective behavior of micro-cracks is quantified by using the generalized self-consistent method. The influence of temperature on fatigue damage of steel structures is quantified by using the previous creep damage model. In addition, the fatigue damage at room temperature and creep damage is coupled in the multi-scale fatigue damage model. The validity of the developed multi-scale damage model is verified by comparing the predicted damage evolution curve with the experimental data. It shows that the developed model is effectiveness. Finally, the fatigue analysis on steel crane runway girders (CRGs) of industrial steel melt shop is performed based on the developed model.

Multi-scale elastoplastic mechanical model and microstructure damage analysis of solid expandable tubular

We present an in-depth study of the failure phenomenon of solid expandable tubular (SET) due to large expansion ratio in open holes of deep and ultra-deep wells. By examining the post-expansion SET, lots of microcracks are found on the inner surface of SET. Their morphology and parameters such as length and depth are investigated by use of metallographic microscope and scanning electron microscope (SEM). In addition, the Voronoi cell technique is adopted to characterize the multi-phase material microstructure of the SET. By using the anisotropic elastoplastic material constitutive model and macro/microscopic multi-dimensional cross-scale coupled boundary conditions, a sophisticated and multi-scale finite element model (FEM) of the SET is built successfully to simulate the material microstructure damage for different expansion ratios. The microcrack initiation and growth is simulated, and the structural integrity of the SET is discussed. It is concluded that this multi-scale finite element modeling method could effectively predict the elastoplastic deformation and the microscopic damage initiation and evolution of the SET. It is of great significance as a theoretical analysis tool to optimize the selection of appropriate tubular materials and it could be also used to substantially reduce costly failures of expandable tubulars in the field. This numerical analysis is not only beneficial for understanding the damage process of tubular materials but also effectively guides the engineering application of the SET technology.

Research on Fatigue Damage Behavior of Main Beam Sub-Structure of Composite Wind Turbine Blade

Given the difficulty in accurately evaluating the fatigue performance of large composite wind turbine blades(referred to as blades),this paper takes the main beam structure of the blade with a rectangular cross-sectionas the simulation object and establishes a composite laminate rectangular beam structure that simultaneouslyincludes the flange,web,and adhesive layer,referred to as the blade main beam sub-structure specimen,throughthe definition of blade sub-structures.This paper examines the progressive damage evolution law of the compositelaminate rectangular beam utilizing an improved 3D Hashin failure criterion,cohesive zone model,B-K failurecriterion,and computer simulation technology.Under static loading,the layup angle of the anti-shear web hasa close relationship with the static load-carrying capacity of the composite laminate rectangular beam;under fatigueloading,the fatigue damage will first occur in the lower flange adhesive area of the whole composite laminaterectangular beam and ultimately result in the fracture failure of the entire structure.These results provide a theoreticalreference and foundation for evaluating and predicting the fatigue performance of the blade main beamstructure and even the full-size blade.

Progressive Failure Analysis of Composite/Aluminum Riveted Joints Subjected to Pull-Through Loading

Out-of-plane mechanical properties of the riveted joints restrict the performance of the wing box assembly of airplane.It is necessary to investigate the pull-through performance of the composite/metal riveted joints in order to guide the riveting design and ensure the safety of the wing box assembly.The progressive failure mechanism of composite/aluminum riveted joint subjected to pull-through loading was investigated by experiments and finite element method.A progressive damage model based on the Hashin-type criteria and zero-thickness cohesive zone method was developed by VUMAT subroutine,which was validated by both open-hole tensile test and three-point bending test.Predicted load-displacement response,failure modes and damage propagation were analysed and compared with the results of the pull-through tests.There are 4 obvious characteristic stages on the load-displacement curve of the pull-through test and that of the finite element model:first load take-up stage,damage stage,second load take-up stage and failure stage.Relative error of stiffness,first load peak and second load peak between finite element method and experiments were 8.1%,-3.3%and 10.6%,respectively.It was found that the specimen was mainly broken by rivet-penetration fracture and delamination of plies of the composite laminate.And the material within the scope of the rivet head is more dangerous with more serious tensile damages than other regions,especially for 90°plies.This study proposes a numerical method for damage prediction and reveals the progressive failure mechanism of the hybrid material riveted joints subjected to the pull-through loading.

Failure analysis of crush hammers based on damage fracture energy

To prolong the life-span of crush hammers in the pyrite concentrate workplace of Ganbazi Coal Preparation Plant of Chongqing Nantong Mining Ltd., we used a progressive damage constitutive model based on the ductile and shear damage fracture energy to analyze the hammer wear failure caused by the impact and abrasion on the hammer surface by pyrite, and carried out simulation analysis with the explicit algurithm on hammer leftovers from the plant during the process of coarser pyrite comminution. The simulation results are consistent with hammer wear failure caused by pyrite impact. Then we proposed corrective measures to prolong hammer life-span. Results of the production test in the Ganbazi Coal Preparation Plant showed that non-clearance hammers can avoid wear erosion, and adding steel bonded tungsten carbides F3002 prolonged the hammer life- span. The effect of austenitic manganese steel work-hardening was not prominent. Therefore, the hammer failure was mainly caused by superficial abrasion instead of fatigue cracks appearing when grains acted on the hardening layer.

微细金属Z-pin对复合材料开孔板压缩性能的影响

通过开孔板压缩试验和建立的参数化多尺度有限元模型,获得微细(φ0.11 mm)金属Z-pin植入体积分数和排布方式对开孔板压缩力学性能和失效行为的影响规律.采用离散实体单元代表Z-pin,选用3D Hashin失效准则判断面内起始损伤,可以有效地模拟结构失效过程中扭结现象的不稳定扩展.结果表明,所有加Z-pin开孔板的压缩强度均低于无Z-pin试样.随着Z-pin植入体积分数的增加,Z-pin与层合板之间的桥联作用增强,加Z-pin开孔层合板压缩强度增加,开孔周围分层损伤区域受到抑制,损伤区域面积最高减小了67%.在相同的体积分数下,Z-pin排布变化对开孔板压缩强度没有显著影响.加Z-pin开孔板有限元模型的模拟结果与试验结果之间的最大相对误差为8.6%.

Damage and progressive failure of concrete structures using non-local peridynamic modeling

Peridynamics (PD), a recently developed theory of solid mechanics, which employs a non-local model of force interaction and makes use of integral formulation rather than the spatial partial differential equations used in the classical continuum mechanics theory, has shown effectiveness and promise in solving discontinuous problems at both macro and micro scales. In this paper, the peridynamics theory is used to analyze damage and progressive failure of concrete structures. A non-local peridynamic model for a rectangular concrete plate is developed, and a central pairwise force function is introduced to describe the interior interactions between particles within some definite distance. Damage initiation, evolution and crack propagation in the concrete model subject to in-plane uni-axial tension, in-plane uni-axial compression and out-of-plane impact load are investigated respectively. The numerical results show that discontinuities appear and grow spontaneously as part of the solution to the peridynamic equations of motion, and no special failure criteria or re-meshing techniques are required, which proves the potential of peridynamic modeling as a promising technique for analyzing the progressive failure of concrete materials and structures.

沉头螺接复合材料接头失效预测强度包线法

多钉连接复合材料接头设计分析中,常用强度包线来预测其强度与失效模式。目前所使用的强度包线法只适用于凸头螺接结构,无法应用于沉头螺接结构。该文建立了带衬套沉头螺接复合材料接头有限元模型,对3钉连接结构进行了拉伸性能分析,并通过试验结果验证了模型的有效性,然后用该模型对衬套的作用进行了研究。在此基础上,提出了适用于沉头螺栓复合材料连接结构强度和失效模式预测的强度包线法。结果表明:使用衬套比仅采用螺杆过盈装配能够明显减慢孔边损伤扩展速率,避免接头各钉载的比例在拉伸过程中剧烈变化;引入衬套能提高接头的承载能力和刚度,其2%偏移载荷、极限载荷和刚度比不带衬套接头分别提高了14.08%、5.21%和6.04%。通过计算少量单钉螺接接头的损伤情况,便可以绘制出相应参数多钉连接结构的新型强度包线。利用新型强度包线,能准确预测沉头和凸头螺接接头的强度和失效模式。

碳纤维复合材料车门防撞梁多尺度高效变形模拟及实验验证

以碳纤维复合材料车门防撞梁为例,开发了一种面向工程零部件的多尺度高效变形模拟技术,建立了自洽聚类分析方法及多尺度渐进损伤本构模型,通过多尺度单元与唯象单元混合建模,有效降低了模型的求解成本,通过将有限的计算资源分配在恰当的位置,结果表明计算资源的利用效率得到显著提升,实现了工程零部件损伤行为的高效预测,实际计算时间缩短至原来的1/4。对三点弯状态下复合材料防撞梁的宏微观渐进损伤过程进行了分析。基于真空袋成形工艺进行了防撞梁样件试制以及三点弯破坏实验,验证了仿真结果的准确性。

基于局部均匀化多尺度方法的机织复合材料单轴拉伸力学行为研究

机织碳纤维增强树脂基复合材料在厚度方向存在纤维的相互交织,拥有较复杂的纤维空间结构,因此具有优异的比刚度和比强度。本文建立了平纹机织复合材料的“微观-介观-宏观”的多尺度有限元渐进损伤模型,并对介观模型中的各成分进行具有等效性能的局部均匀化简化。基于微观力学失效理论判断纤维/基体损伤起始,通过ABAQUS有限元分析平台,开发用户自定义的子程序VUMAT,对平纹机织复合材料进行拉伸力学行为和损伤机理分析。结果表明:在拉伸载荷模拟中纤维束树脂损伤最为严重,纤维失效发生在经向纤维束中,且外层损伤相较于内层更加严重。试验和数值分析的结果误差均在2%以内,表明多尺度渐进损伤模型的可靠性。

考虑边坡渐进破坏特性的新型条分法及其应用

为了分析边坡的渐进破坏过程,以剩余推力法为例,应用剪应力—应变本构模型对传统条分法进行改进。分析了新型条分法的基本原理,提出基于临界状态的滑坡稳定性评价系数。根据稳定系数的变化可以判断滑坡不同阶段的滑体稳定情况。应用新型条分法对西北地区的一个滑坡进行稳定分析,并将分析结果与监测位移对比,证明了新条分法的可行性。

Homogenization-based multi-scale damage theory

The research of modern mechanics reveals that the damage and failure of structures should be considered on different scales. The present paper is dedicated to establishing the multi-scale damage theory for the nonlinear structural analysis. Starting from the asymptotic expansion based homogenization theory, the multi-scale energy integration is proposed to bridge the gap between the micro and macro scales. By recalling the Helmholtz free energy based damage definition, the damage variable is represented by the multi-scale energy integration. Hence the damage evolution could be numerically simulated on the basis of the unit cell analysis rather than the experimental data identification. Finally the framework of the multi-scale damage theory is established by transforming the multi-scale damage evolution into the conventional continuum damage mechanics. The agree- ment between the simulated results and the benchmark results indicates the validity and effectiveness of the proposed theory.

复合点阵结构强爆炸冲击载荷下的损伤机理与动态响应特性

基于碳纤维增强复合材料面板与金属芯层,设计出金字塔型复合点阵夹芯结构。利用地面爆炸冲击实验,研究复合点阵结构在强爆炸载荷作用下的损伤机理和失效模式。基于材料的细观损伤机理,构建复合材料面板的三维渐进损伤模型和金属芯层的Johnson-Cook损伤模型,并结合有限元方法发展了复合点阵结构的爆炸冲击响应预报模型。开展了不同载荷工况下结构的动态响应特性分析,结合实验测试结果分析了结构抗爆性能的主要影响因素。研究表明,在近距离强爆炸载荷作用下,复合点阵结构整体构型基本保持完好,仅局部出现失效现象,主要失效形式为边缘区域面芯脱粘和局部芯层杆件断裂,但结构整体上仍具有较好的承载能力。探讨了考虑多种载荷条件和结构参数相关变量的毁伤函数,给出了结构的可行设计域。研究结果可为装备关键部件轻量化/抗爆设计提供参考。

复合材料Ω形加筋壁板低速冲击渐进损伤及剩余强度分析

研究复合材料Ω形加筋壁板结构在不同能量及位置的低速冲击作用下的渐进损伤及其冲击后剩余强度具有重要意义。通过编写VUMAT子程序,将选择的三维Hashin失效准则及刚度退化模式加入渐进损伤模型中并与文献中试验进行对照,进一步研究不同冲击位置及不同冲击能量对于模型冲击载荷、渐进损伤及剩余强度的影响。结果表明,在加强筋中央位置处冲击对结构剩余强度影响最大;相同冲击位置处,冲击能量越大,结构损伤越严重,剩余强度越小。这为复合材料Ω形加筋壁板的结构设计提供了参考。

复合材料径向和轴向螺栓连接失效预测方法及失效模式分析

大型火箭舱段间的复合材料端框连接主要由径向螺栓连接和轴向螺栓连接组成,设计了不同铺层和几何尺寸的连接试验件,并通过试验获得了失效载荷和失效形式。然后,选择了3种渐进损伤方法进行了连接结构的失效预测,并将预测结果与试验结果进行比较,结果表明:采用基于细观力学的复合材料渐进损伤方法,15组径向连接试验件失效载荷计算误差最大为17.3%;4组轴向连接失效载荷计算误差最大7.4%;预测的失效形式与试验结果接近,为连接结构确定了合适的失效预测方法。采用数值分析结果揭示了复合材料单向层的主要失效模式。为复合材料端框连接的设计研究提供了可用的失效预测方法及详细的失效模式分析结果。

金属/复合材料混合连接结构高温承载特性与失效行为研究

针对3种不同搭接板厚度的铝合金和碳纤维增强树脂(Carbon fiber reinforced polymers,CFRP)复合材料三钉螺栓连接结构,分别进行了常温(25℃)和高温(150℃)环境下的准静态拉伸力学性能测试。同时建立有限元三维模型,结合Hashin失效准则和渐进损伤准则进行数值模拟分析,获得了结构的高温承载特性与损伤演化规律。研究结果表明,对于D_(1)、D_(2)、D_(3)这3种不同铝合金厚度的连接结构,在150℃时的极限载荷试验值相对25℃分别降低6.63%、13.07%、8.48%,且常温环境下3种结构破坏模式分别为铝合金拉伸断裂、复合材料挤压失效、复合材料拉伸断裂,而在150℃高温环境下,3种结构损伤模式都为复合材料孔边的挤压剪切失效。

干法/湿法挖补修理层合板力学性能的对比研究

挖补修理是一种常用的受损复合材料结构修复方法,主要可分为干法(预固化补片)修理和湿法(湿铺贴)修理。通过开展静力拉伸实验,研究了不同损伤尺寸的预固化补片挖补修理和湿铺贴挖补修理层合板的极限强度、破坏模式以及补片脱粘情况,实验结果表明采用预固化补片修理的结构其强度恢复率更高,补片提前脱粘概率更低,修理效果更好。在力学实验的基础上,通过有限元计算准确预测了挖补修理层合板的极限强度、应力应变分布和损伤演化过程,计算结果表明预固化补片修理结构的胶层应力分布更加均匀,应力水平和应力集中程度更低,出现界面失效和胶层内聚失效的载荷也更高。

基于多尺度模型的编织复合材料圆管扭转行为有限元模拟

为进一步探究编织复合材料圆管在扭转加载过程中的力学响应,在前期试验研究的基础上,以具有45°编织角的碳纤维/树脂复合材料圆管为例,采用了综合考虑圆管的细观结构和全尺寸模拟计算成本的多尺度方法构建了编织复合材料圆管有限元模型,系统模拟了其扭转加载过程,并分别讨论了圆管单胞的剪切和圆管的扭转渐进损伤过程。结果表明:模拟结果与试验结果具有较高的一致性;圆管单胞在剪切失效之前的损伤分布基本呈对称状态,纤维束早于基体形成损伤,承担主要载荷;纤维束编织路径对圆管的扭转损伤扩展有一定的影响,从损伤出现至结构完全失效的用时很短,损伤单元在扭转加载末期产生于圆管中部,并沿纤维束编织路径扩展,最终形成空间螺旋型损伤剪切带。

拉伸载荷下开孔层合板的渐进损伤分析

建立拉伸开孔层合板的渐进损伤模型,研究层合板的失效模式,并分析了不同孔径对开孔层合板极限载荷的影响。通过编写VUMAT子程序将Hashin失效准则和材料退化模型加入渐进损伤分析中。首先将不同网格数量的开孔层合板模型的位移-载荷曲线和试验结果进行对照,然后将仿真分析得到的失效模式与试验结果进行对照,验证模型和选用的失效准则的正确性,最后研究了不同孔径对开孔层合板拉伸极限载荷的影响。结果表明:本文建立的渐进损伤模型能够较准确地预测层合板的位移-载荷曲线和失效模式,纤维拉伸失效首先发生在孔边,并沿着45°方向进行扩展,随着孔径的增大,开孔层合板的拉伸极限载荷逐渐减小,且下降速度首先呈线性下降,然后又逐渐增大。

含孔碳纤维增强镁合金层合板拉伸性能和失效模式研究

基于渐进失效模型有限元数值模拟并结合试验,研究在拉伸载荷的作用下不同开孔直径对复合材料层合板的损伤演化过程和剩余强度影响,用扫描电子显微镜对断口形貌和微观损伤模式进行分析。结果表明:随孔径增大,带孔碳纤维增强镁合金层合板强度下降。在拉伸载荷作用下,其失效模式为金属层塑性破坏、纤维层拉伸断裂和层间分层为主的混合失效模式。试验和数值模拟结果吻合,验证了该模型的正确性,对实际工程具有参考价值。