Finite element simulation of the micromachining of nanosized-silicon-carbide-particle reinforced composite materials based on the cohesive zone model

A finite element method based on the cohesive zone model was used to study the micromachining process of nanosized silicon-carbide-particle(SiCp) reinforced aluminum matrix composites. As a hierarchical multiscale simulation method, the parameters for the cohesive zone model were obtained from the stress-displacement curves of the molecular dynamics simulation. The model considers the random properties of the siliconcarbide-particle distribution and the interface of bonding between the silicon carbide particles and the matrix.The machining mechanics was analyzed according to the chip morphology, stress distribution, cutting temperature, and cutting force. The simulation results revealed that the random distribution of nanosized SiCp causes non-uniform interaction between the tool and the reinforcement particles. This deformation mechanics leads to inhomogeneous stress distribution and irregular cutting force variation.

A Modified Cohesive Zone Model for Simulation of Delamination Behavior in Laminated Composites

Considering the promotion effect of interlaminar normal tensile stress and the inhibition effect of interlaminar normal compressive stress,two kinds of elimination initial criteria were proposed in this paper.Based on these two delamination initial criteria,a modified cohesive zone model(CZM)was established to simulate the delamination behavior in laminated composites.Numerical simulations of double cantilever beam(DCB),mixed-mode bending(MMB)and end notched flexure(ENF)tests were conducted.The results show that the proposed model can do a better job than common ones when it is used to predict laminates’delamination under interlaminar compression stress.Moreover,a factor r,named cohesive strength coefficient,was defined in this paper on account of the difference between cohesive strength and interlaminar fracture strength.With changing factor r,it shows that a moderate variation of cohesive strength will not cause significant influences on global load-displacement responses.Besides,in order to obtain a good balance between prediction accuracy and computational efficiency,there shall be two or three numerical elements within the cohesive zone.

Determination of key parameters of Al–Li alloy adhesively bonded joints using cohesive zone model

The key parameters of the adhesive layer of a reinforcing patch are of great significance and affect the ability to suppress crack propagation in an Al–Li alloy patch-reinforced structure.This paper proposes a method to determine the key parameters of the adhesive layer of adhesively bonded joints in the Al–Li alloy patch-reinforced structure.A zero-thickness cohesive zone model(CZM)was selected to simulate the adhesive layer’s fracture process,and an orthogonal simulation was designed to compare against the test results.A three-dimensional progressive damage model of an Al–Li alloy patch-reinforced structure with single-lap adhesively bonded joints was developed.The simulation’s results closely agree with the test results,demonstrating that this method of determining the key parameters is likely accurate.The results also verify the correctness of the cohesive strength and fracture energy,the two key parameters of the cohesive zone model.The model can accurately predict the strength and fracture process of adhesively bonded joints,and can be used in research to suppress crack propagation in Al–Li alloy patch-reinforced structures.

Progressive Failure Evaluation of Composite Skin-Stiffener Joints Using Node to Surface Interactions and CZM

T shaped skin-stiffener joint are one of the most commonly used structures in aerospace components.It has been proven in various studies that these joints are susceptible to failure when loaded in pull out conditions however,in specific applications these joints undergo pull loading.De-lamination/de-bond nucleation and its growth is one of the most common failure mechanisms in a fiber reinforced composite structure.Crack growth takes place due to the induced interlaminar normal and shear stresses between different structural constituents when a load is applied.In this study,Finite Element Analysis has been performed using cohesive contact interactions on a composite T-joint to simulate the pull out test conditions.A simplified shell based model coupled with CZM is proposed,which can evaluate the failure initiation and progression accurately with lesser computational efforts.The final failure occurred at a displacement of 4.71 mm at the computed failure load of 472.57 kgf for basic configuration.Computed Failure load for the padded configuration is 672.8 kgf and corresponding displacement is 4.6 mm.The results obtained by the proposed numerical model are validated by experimental results and it is observed that predicted failure displacements and failure load calculated were correlating reasonably well with the experiment.

3D Nonlinear XFEM Simulation of Delamination in Unidirectional Composite Laminates: A Sensitivity Analysis of Modeling Parameters

This article presents a three-dimensional extended finite element (XFEM) approach for numerical simulation of delamination in unidirectional composites under fracture mode I. A cohesive zone model in front of the crack tip is used to include interface material nonlinearities. To avoid instability during simulations, a critical cohesive zone length is defined such that user-defined XFEM elements are only activated along the crack tip inside this zone. To demonstrate the accuracy of the new approach, XFEM results are compared to a set of benchmark experimental data from the literature as well as conventional FEM, mesh free, and interface element approaches. To evaluate the effect of modeling parameters, a set of sensitivity analyses have also been performed on the penalty stiffness factor, critical cohesive zone length, and mesh size. It has been discussed how the same model can be used for other fracture modes when both opening and contact mechanisms are active.

Effect of intermittent joint distribution on the mechanical and acoustic behavior of rock masses

The mechanical characteristics and acoustic behavior of rock masses are greatly influenced by stochastic joints.In this study,numerical models of rock masses incorporating intermittent joints with different numbers and dip angles were produced using the finite element method(FEM)with the intrinsic cohesive zone model(ICZM).Then,the uniaxial compressive and wave propagation simulations were performed.The results indicate that the joint number and dip angle can affect the mechanical and acoustic properties of the models.The uniaxial compressive strength(UCS)and wave velocity of rock masses decrease monotonically as the joint number increases.However,the wave velocity grows monotonically as the joint dip angle increases.When the joint dip angle is 45°–60°,the UCS of the rock mass is lower than that of other dip angles.The wave velocity parallel to the joints is greater than that perpendicular to the joints.When the dip angle of joints remains unchanged,the UCS and wave velocity are positively related.When the joint dip angle increases,the variation amplitude of the UCS regarding the wave velocity increases.To reveal the effect of the joint distribution on the velocity,a theoretical model was also proposed.According to the theoretical wave velocity,the change in wave velocity of models with various joint numbers and dip angles was consistent with the simulation results.Furthermore,a theoretical indicator(i.e.fabric tensor)was adopted to analyze the variation of the wave velocity and UCS.

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.

UHPC-RC节段组合梁的抗弯性能分析

为研究低预应力度条件下,不同节段接缝的超高性能混凝土-钢筋混凝土(ultra-high performance concrete-reinforced concrete,UHPC-RC)组合梁的抗弯性能,文章基于ABAQUS有限元软件,建立UHPC-RC节段组合梁的基准有限元模型,并利用已有的试验数据验证该模型的合理性。节段接缝分别为平面干接缝、平面胶接缝、齿键干接缝和齿键胶接缝,在基准有限元模型的基础上,进一步研究节段接缝类型对组合梁抗弯性能的影响。研究发现,在四点受弯加载方式下,接缝的几何特征(平面或齿键)对组合梁的极限荷载和开裂荷载影响较小,环氧树脂胶的使用对组合梁的抗弯性能影响较大。

INTERFACE DAMAGE ANALYSIS OF FIBER REINFORCED COMPOSITES WITH DUCTILE MATRIX

A cohesive zone model is employed to simulate the fiber/matrix interface damage of composites with ductile matrix. The study is carried out to investigate the dependence of the interface damage and the composite tensile strength on the micro parameters of the composite. These parameters contain fiber packing pattern, fiber volume fraction, and the modulus ratio of the fiber to the matrix. The investigation reveals that though the high fiber vo lume fraction, the high fiber′s modulus and the square fiber packing can supply strong reinforcement to the composite, the interface damage is susceptible in these cases. The tensile strength of the composite is dominated by the interface strength when the interface debonding occurs.

基于复合材料Ⅰ型分层损伤机制的解耦内聚力方法

分层损伤是航空航天复合材料结构分层的主要损伤模式之一。Ⅰ型分层具有起始断裂韧性值低,损伤模式复杂的特征,深入分析裂纹尖端损伤区多种损伤机制之间的相互关系及纤维桥接损伤演化过程,对研究Ⅰ型分层损伤起关键作用。本文针对性采用3种不同层间铺层(0//0、0//45、0//90)设计T700级碳纤维/环氧复合材料层合板并开展Ⅰ型分层测试。通过观测分层起始及损伤演化过程,总结标准双悬臂梁(DCB)试验结果载荷位移曲线及R曲线规律,并根据试样断口形貌、SEM等多种表征方法分析,揭示了裂纹尖端的损伤机制。在此基础上提出了一种分层损伤机制解耦的新方法。该方法基于3个双线性内聚力本构叠加,通过建立内聚力单元模型来解耦不同损伤尺度的分层损伤机制,独立表征了不同损伤机制在分层扩展过程中所作的贡献。仿真模拟所需参数均可从试验获得,计算得到的仿真结果与试验结果具有良好的一致性。

基于内聚力模型的气波机振荡管304对接钎焊接头拉伸强度研究

气波机核心部件振荡管采用钎焊连接,钎焊接头拉伸性能对气波机结构强度具有重要影响。为了对钎焊接头界面裂纹扩展过程进行探究,笔者针对气波机振荡管钎焊结构,制备304对接钎焊接头试样进行拉伸试验,并对拉伸断口进行形貌分析,断口处表现为韧性断裂;基于内聚力模型,开发了VUMAT子程序,进行了有限元模拟分析。模拟断裂载荷为5 039 N,试验值为5 242 N,2者误差为3.9%,验证了模拟的准确性,结果表明内聚力模型可以较好地模拟气波机振荡管钎焊接头的裂纹萌生与扩展过程。在此基础上研究焊缝缺陷对钎焊接头断裂载荷的影响,发现缺陷处内聚力单元损伤速率加快,引起断裂载荷显著下降。

Numerical Simulation of Particle/Matrix Interface Failure in Composite Propellant

Interface debonding between particle and matrix in composite propellant influences its macroscopic mechanical properties greatly. For this, the laws of interface cohesive damage and failure were analyzed. Then, its microscopic computational model was established. The interface mechanical response was modeled by the bilinear cohesive zone model. The effects of interface properties and particle sizes on the macroscopic mechanical behavior were investigated. Numerical simulation of debonding damage evolution of composite propellant under finite deformation was carried out. The debonding damage nucleation, propagation mechanism and non-uniform distribution of microscopic stress-strain fields were discussed. The results show that the finite element simulation method based on microstructure model can effectively predict the trend of macroscopic mechanical behavior and particle/matrix debonding evolution process. It can be used for damage simulation and failure assessment of composite propellants.

玻璃钢夹砂管涵夹砂层细观断裂数值模拟

为了提高玻璃钢夹砂管中夹砂层的力学性能,增强其可设计性,借助有限元仿真软件构建代表性体积单元重现树脂夹砂层的细观结构特性,通过全域插设零厚度粘聚单元,实现复杂离散的多裂缝萌生和扩展。对夹砂层试样单轴拉伸断裂过程进行模拟,分析细观断裂损伤演化过程,探究各组分参数对夹砂层断裂力学行为的影响规律。结果表明:构建的细观粘聚断裂模型能较好地表征夹砂层复杂断裂过程,轴向拉伸变形时复合材料主裂缝的形成位置近似垂直于加载方向,伴随界面脱粘和基体内裂纹的萌生与扩展。裂纹扩展方向主要受细观颗粒分布的位置影响,提高颗粒体积分数能显著提高材料刚度;多颗粒粒径分布的增强效果优于单粒径分布,粒径越小,则增强增韧效果越好;粘聚单元的抗拉强度和断裂能的增大均能够提升模型整体抗拉强度,断裂能越大,则裂纹路径分支越少。

Failure load prediction of adhesive joints under different stress states over the service temperature range of automobiles

To predict the failure loads of adhesive joints under different stress states over the service temperature range of automobiles,adhesively bonded carbon fiber reinforced plastic( CFRP)/aluminum alloy joints under shear stress state( thickadherend shear joints,TSJ),normal stress state( butt joints,BJ) and combined shear and normal stress states( scarf joints with scarf angle 45°,SJ45°) were manufactured and tested at-40,-20,0,20,40,60 and 80 ℃,respectively. The glass transition temperature Tgof the adhesive and CFRP,failure loads and fracture surfaces were used to analyze the failure mechanism of CFRP/aluminum alloy joints at different temperatures. A response surface,describing the variations of quadratic stress criteria with temperature,was established and introduced into the cohesive zone model( CZM) to carry out a simulation analysis. Results show that the failure of CFRP/aluminum alloy joints was determined collectively by the mechanical performances of adhesive and CFRP. Besides,reducing temperature or increasing the proportion of normal stress of adhesive layer was more likely to cause fibre tear or delamination of CFRP,resulting in a more obvious effect of CFRP. The validity of the prediction method was verified by the test of scarf joints with the scarf angle of 30°( SJ30°) and 60°( SJ60°) at-10 and 50 ℃.

基于渐进损伤模型的热固性复合材料电阻焊接头强度的尺寸效应研究

研究了拉剪载荷下热固性复合材料电阻焊接头强度的尺寸效应,揭示了不同搭接尺寸对焊接强度和焊接界面渐进损伤行为的影响规律。为了研究焊接界面的渐进损伤行为,引入双线性内聚力单元,进而建立焊接接头的有限元模型,然后通过电阻焊接的拉剪试验验证了模型的准确性。在此基础上,建立了不同搭接尺寸的数值模型并对其进行研究。研究结果表明,增大搭接长度或者宽度可以提高接头结构的承载能力,但是当搭接长度较长时,在搭接区域边缘易发生翘曲失效,降低了接头单搭接剪切强度,而宽度则对接头的剪切强度影响很小。

原位生成界面的第一性原理-内聚力建模

激光熔覆技术制造(TiBw+TiCp)/Ti复合材料时颗粒与基体间为原位生成界面,为探究原位生成界面力学性能,用第一性原理和内聚力模型计算具体的界面结合强度。用Abaqus建立压缩模型,导入计算出的界面结合强度,分析其颗粒形貌的变化,并对不同应变率下的压缩试验进行验证。结果表明:位于剪切带上的TiB颗粒断裂,TiC颗粒尺寸较小且为球形,无显著变化。

挖补修理平纹编织面板蜂窝夹芯结构侧向压缩渐进失效机理

针对单侧面板挖补、单侧面板加芯子挖补、双侧面板加芯子挖补3种修理方式,采用一维阶梯挖补模型代替三维模型研究挖补修理平纹编织面板蜂窝夹芯结构侧向压缩渐进失效机理。建立能够模拟蜂窝壁损伤演化的有限元模型,利用内聚力模型模拟胶层损伤。试验和仿真结果表明,完好件和各种挖补方式试验件的破坏模式均为向非修补面板内凹的屈曲变形;各种挖补方式的侧压强度恢复率均在75%以上,大小排序为:单侧面板挖补、双侧面板加芯子挖补、单侧面板加芯子挖补;完好件和各种挖补方式试验件均未出现面板损伤,均出现蜂窝壁横向损伤和剪切损伤,且横向损伤均先出现,均在与发生大变形的蜂窝芯格相连的胶层处出现应力集中;蜂窝壁纵向损伤仅出现在单侧面板挖补件上,胶层损伤只出现在双侧面板加芯子挖补件上;芯子蜂窝壁损伤均发生在靠近替芯的母体芯材上。

基于统一相场理论和内聚力模型的钢纤维混凝土界面过渡区力学性能研究

为探究数值模拟中界面过渡区不同建模方式对钢纤维混凝土力学性能及其损伤、破坏过程的影响,基于统一相场理论和内聚力模型,针对含单根钢纤维的混凝土拉伸试验,采用2种方法建立钢纤维混凝土界面过渡区的数值计算模型,对比分析不同建模方式对钢纤维混凝土力学性能及其破坏形态的影响,并考察不同因素对含单根钢纤维的混凝土极限抗拉强度的影响。结果表明,对混凝土基体部分采用相场断裂模型、界面过渡区采用内聚力模型,无论是计算结果还是细观破坏形态,都具有较好的准确性和可靠性;初始裂缝位置取30 mm和35 mm的钢纤维混凝土抗拉强度比取25 mm时分别提高30.8%和75.7%,钢纤维埋置角度为15°,30°和45°时的钢纤维混凝土抗拉强度比0°时分别降低12.2%,30.8%和48.9%,钢纤维增强作用受初始裂缝位置及钢纤维埋置角度影响较大,受钢纤维直径影响相对较小。采用统一相场理论可降低分析的难度、保证较高的计算精度,为研究钢纤维混凝土的损伤、断裂过程提供了理论参考。

搭接长度对钢丝绳芯输送带接头承载能力影响的数值模拟

输送带接头区域钢丝绳的抽出力是衡量接头承载能力的重要指标。目前针对钢丝绳芯输送带接头的研究主要集中在接头的结构参数、硫化工艺及胶料的粘合性能,并没有指出搭接长度对接头承载能力的影响。为研究搭接长度对钢丝绳芯输送带接头承载能力的影响,以st1250型钢丝绳芯输送带为研究对象,取输送带接头处单根钢丝绳部分建立接头模型,采用双线型内聚力模型模拟钢丝绳与橡胶的胶接状态,并通过切向拉剪试验与法向拉伸试验获得模型参数。将双线型内聚力模型与钢丝绳-橡胶接触界面相结合,对接头单根钢丝绳从橡胶中脱粘抽出的损伤演化过程进行仿真分析,发现接头损伤演化过程分为线性加载、损伤萌生、损伤扩展与完全失效4个阶段,且接头损伤失效曲线与双线型内聚力模型牵引力-位移曲线具有较好的一致性,验证了双线型内聚力模型可较好地模拟钢丝绳芯输送带接头损伤失效过程。对不同搭接长度的接头模型进行了仿真,得出搭接长度为350~750 mm时,随着搭接长度增大,接头刚度总体呈非线性增大,接头橡胶所受最大剪应力呈递减趋势,从而确定了接头搭接长度范围应控制在350~750 mm。对不同钢丝绳直径下搭接长度对接头承载能力的影响进行了仿真,结果表明:钢丝绳抽出力随搭接长度增大总体呈非线性递增;钢丝绳直径越大,接头钢丝绳抽出力随搭接长度增大的涨幅越大。拟合得到了不同钢丝绳直径下接头搭接长度与单根钢丝绳抽出力之间的函数关系,为不同承载能力要求下接头搭接长度的合理化选择提供了理论依据。

An incremental elastic-plastic cohesive constitutive model with considering damage

The interface has a significant influence on the macroscopic mechanical behaviors of composite materials,with interface cracking being a typical failure event.The ability to precisely describe the mechanical behavior of the interface is critical for analyzing the failure of composite materials.Based on plasticity theory and damage mechanics,an elastic-plastic interface constitutive model is developed to simulate the irreversible plastic deformation at the interface under the cyclic loading condition.Furthermore,by incorporating a damage factor in scalar form,the model is able to simulate mixed loading forms(Modes I and II).The influence of interfacial strength and toughness on the overall mechanical properties of unidirectional fiber reinforced composites under transverse loading is studied with this model.The simulation results are consistent with the experimental data in the literature,demonstrating the model's effectiveness.The model can be used to simulate the mechanical behavior of composites with interfaces under cyclic loading,and it is helpful for understanding the plastic behavior and damage accumulation at the interfaces in the composites.