A CATASTROPHE ANALYSIS ON THE STABILITY OF THE CRACK GROWTH IN THREE-POINT BENDING SPECIMENS

This paper presents an attempt at the application of catastrophe theory to the stability analysis of J-controlled crack growth in three-point bending specimens. By introducing the solutions of J-integral in the completely yielding state for the ideal plastic material, the critical condition of losing stability for the crack propagation in the specimen is obtained, based on the cusp catastrophe theory. The process of the crack growth from geometrical sense is described.

Three-point bending of honeycomb sandwich beams with facesheet perforations

A novel square honeycomb-cored sandwich beam with perforated bottom facesheet is investigated under threepoint bending,both analytically and numerically.Perforated square holes in the bottom facesheet are characterized by the area ratio of the hole to intact facesheet（perforation ratio）.While for large-scale engineering applications like the decks of cargo vehicles and transportation ships,the perforations are needed to facilitate the fabrication process（e.g.,laser welding）as well as service maintenance,it is demonstrated that these perforations,when properly designed,can also enhance the resistance of the sandwich to bending.For illustration,fair comparisons among competing sandwich designs having different perforation ratios but equal mass is achieved by systematically thickening the core webs.Further,the perforated sandwich beam is designed with a relatively thick facesheet to avoid local indention failure so that it mainly fails in two competing modes：（1）bending failure,i.e.,yielding of beam cross-section and buckling of top facesheet caused by bending moment;（2）shear failure,i.e.,yielding and buckling of core webs due to shear forcing.The sensitivity of the failure loads to the ratio of core height to beam span is also discussed for varying perforation ratios.As the perfo-ration ratio is increased,the load of shear failure increases due to thickening core webs,while that of bending failure decreases due to the weakening bottom facesheet.Design of a sandwich beam with optimal perforation ratio is realized when the two failure loads are equal,leading to significantly enhanced failure load（up to 60%increase）relative to that of a non-perforated sandwich beam with equal mass.

Numerical analysis of bending property of bi-modulus materials and a new method for measurement of tensile elastic modulus

In nature,there are widely distributed bi-modulus materials with different deformation characteristics under compressive and tensile stress states,such as concrete,rock and ceramics.Due to the lack of constitutive model that could reasonably consider the bi-modulus property of materials,and the lack of simple and reliable measurement methods for the tensile elastic parameters of materials,scientists and engineers always neglect the effect of the bi-modulus property of materials in engineering design and numerical simulation.To solve this problem,this study utilizes the uncoupled strain-driven constitutive model proposed by Latorre and Montáns(2020)to systematically study the distributions and magnitudes of stresses and strains of bi-modulus materials in the three-point bending test through the numerical method.Furthermore,a new method to synchronously measure the tensile and compressive elastic moduli of materials through the four-point bending test is proposed.The numerical results show that the bi-modulus property of materials has a significant effect on the stress,strain and displacement in the specimen utilized in the three-point and four-point bending tests.Meanwhile,the results from the numerical tests,in which the elastic constitutive model proposed by Latorre and Montáns(2020)is utilized,also indicate that the newly proposed measurement method has a good reliability.Although the new measurement method proposed in this study can synchronously and effectively measure the tensile and compressive elastic moduli,it cannot measure the tensile and compressive Poisson’s ratios.

Modelling and Simulation on the Effect of Hot Forming Damage on Three-Point Bending Performance of Beam Components

The effects of forming damage are analyzed,which occur during hot stamping process,on the load-carrying capacity and failure mode of hot stamped beams.A damage-coupled pre-forming constitutive model was proposed,in which the damage during hot stamping process was introduced into the service response.The constitutive model was applied into the three-point bending simulation of a hot stamped beam,and then the influences of forming damage on the load-carrying capacity and cracks propagation were investigated.The results show that the forming damage reduces the maximum load capacity of the hot stamped beam by 7.5%.It also causes the crack to occur earlier and promotes crack to propagate along the radial direction of the punch.

Experimental and theoretical analyses of package-on-package structure under three-point bending loading

High density packaging is developing toward miniaturization and integration, which causes many difficulties in designing, manufacturing, and reliability testing. Package-on-Package （POP） is a promising three-dimensional high- density packaging method that integrates a chip scale package （CSP） in the top package and a fine-pitch ball grid array （FBGA） in the bottom package. In this paper, in-situ scanning electron microscopy （SEM） observation is carried out to detect the deformation and damage of the PoP structure under three-point bending loading. The results indicate that the cracks occur in the die of the top package, then cause the crack deflection and bridging in the die attaching layer. Furthermore, the mechanical principles are used to analyse the cracking process of the PoP structure based on the multi-layer laminating hypothesis and the theoretical analysis results are found to be in good agreement with the experimental results.

Interfacial toughness evaluation of thermal barrier coatings by bending test

Determining the interfacial properties of thermal barrier coatings(TBCs) is imperative for their durability evaluation and further improvements. A ceramic coating(topcoat) and a NiCoCrALY bondcoat were atmospheric-plasma-sprayed(APS) on a stainless steel substrate. A modified three-point bending test was adopted to initiate and propagate the topcoat/bondcoat(TC/BC)interfacial crack. After a complete delamination, the fracture surfaces were examined by an optical microscope, which shows that the cracking plane was merely on the TC/BC interface. Based on the experimental results of load–displacement and crack length–displacement,the strain energy release rate G for crack propagation was calculated, and the averaged magnitude was 77.1 J/m^2.Repeatable results have indicated that the method can be used for the evaluation of interfacial fracture toughness in thermal barrier coatings and other multi-layer structures.

A New Method for Determining J_(IC) of High StrengthHigh Fracture Toughness Steels by SingleThree Point Bend Specimen

A single three point bend specimen compliance method for determining JIC of high strength high fracture toughness steels is presented and a formula for calculatinff J-integral is proposed as follows.It is simple and valid for high strength high fracture toughness steels. The values of JIC and KIC measured by this method are in good agreement with those measured by standard test method.

Bending Analysis of a Filament-Wound Composite Tube

The aim of this paper is to present finite element model of a filament-wound composite tube subjected to three-point bending and bending in accordance with standard EN?15807:2011?(railway applications-pneumatic half couplings) along with its experimental verification. In the finite element model, composite reinforcement plies have been characterized by linear orthotropic material model, while rubber liners have been described by a two-parameter MooneyRivlin model. Force-displacement curves of three-point bending show fairly good agreement between simulation results and experimental data. Reaction forces of FE simulation and experiment of standard bending test are in good agreement.

应力状态对三点弯曲小试样蠕变性能评价的影响

针对大部分小试样技术没有规范化的标准,试样在尺寸上的变化往往会引起所受应力状态的变化,进而影响蠕变参数反演的准确性的问题,采用有限元法,基于三点弯小试样梁弯曲本构模型和Norton蠕变方程,分析试样在不同横截面宽厚比下的应力状态,及其对三点弯小试样蠕变性能的影响。研究结果表明,当横截面宽厚比b:2h<1:2时,试样趋向于平面应力状态;当b:2h>2:1时,试样趋向于平面应变状态;当1:2≤b:2h≤2:1时,试样介于两种应力状态之间。对于加载点稳态位移速率、蠕变应力、转换系数、蠕变参数反演结果,平面应力状态的影响明显大于平面应变状态;与单轴蠕变试验数据的对比结果表明,将试样横截面宽厚比控制在1:1≤b:2h≤2:1范围之内,能够提高蠕变参数反演结果的准确性。研究结果为三点弯小试样试验方法的合理应用提供依据。

Multi-Objective Optimization of Aluminum Alloy Electric Bus Frame Connectors for Enhanced Durability

The widespread adoption of aluminumalloy electric buses,known for their energy efficiency and eco-friendliness,faces a challenge due to the aluminum frame’s susceptibility to deformation compared to steel.This issue is further exacerbated by the stringent requirements imposed by the flammability and explosiveness of batteries,necessitating robust frame protection.Our study aims to optimize the connectors of aluminum alloy bus frames,emphasizing durability,energy efficiency,and safety.This research delves into Multi-Objective Coordinated Optimization(MCO)techniques for lightweight design in aluminum alloy bus body connectors.Our goal is to enhance lightweighting,reinforce energy absorption,and improve deformation resistance in connector components.Three typical aluminum alloy connectors were selected and a design optimization platform was built for their MCO using a variety of software and methods.Firstly,through three-point bending experiments and finite element analysis on three types of connector components,we identified optimized design parameters based on deformation patterns.Then,employing Optimal Latin hypercube design(OLHD),parametric modeling,and neural network approximation,we developed high-precision approximate models for the design parameters of each connector component,targeting energy absorption,mass,and logarithmic strain.Lastly,utilizing the Archive-based Micro Genetic Algorithm(AMGA),Multi-Objective Particle Swarm Optimization(MOPSO),and Non-dominated SortingGenetic Algorithm(NSGA2),we explored optimized design solutions for these joint components.Subsequently,we simulated joint assembly buckling during bus rollover crash scenarios to verify and analyze the optimized solutions in three-point bending simulations.Each joint component showcased a remarkable 30%–40%mass reduction while boosting energy absorption.Our design optimization method exhibits high efficiency and costeffectiveness.Leveraging contemporary automation technology,the design optimization platform developed in this study is poised to facilitate intelligent optimization of lightweight metal components in future applications.

柔度法测算三点弯曲试样疲劳裂纹长度的影响因素

使用柔度法对不同厚度三点弯曲试样的疲劳裂纹长度进行测算,结合有限元仿真分析方法,研究了试样厚度、柔度函数关系式的适用条件、材料的弹性模量、裂纹前缘弯曲程度、引伸计标距等因素对柔度法测算裂纹长度准确性的影响。结果表明:归一化实际裂纹长度不小于0.3是保证柔度法测算结果准确性的必要条件;用有限元方法模拟平直的贯穿型裂纹,归一化模拟裂纹长度不小于0.3时,柔度函数关系式与模拟结果的吻合程度较高;当试样厚度不大于40 mm时,在柔度函数关系式中使用材料的弹性模量可以获得较为准确的测算结果;随着试样厚度的增加,裂纹前缘圆弧角度增大,裂纹平直度降低,导致测算裂纹长度比实际裂纹长度偏小。

Experimental and numerical investigation of mechanical behavior of plain woven CFRP composites subjected to three-point bending

The mechanical behavior of plain woven Carbon Fiber-Reinforced Polymer(CFRP)composites under Three-Point Bending(TPB)is investigated via experimental and numerical approaches.Multiscale models,including microscale,mesoscale and macroscale models,have been developed to characterize the TPB strength and damages.Thereinto,Representative Volume Elements(RVEs)of the microscale and mesoscale structures are established to determine the effective properties of carbon-fiber yarn and CFRP composites,respectively.Aimed at accurately and efficiently predicting the TPB behavior,an Equivalent Cross-Ply Laminate(ECPL)cell is proposed to simplify the inherent woven architecture,and the effective properties of the subcell are computed using a local homogenization approach.The macroscale model of the TPB specimen is constructed by a topology structure of ECPL cells to predict the mechanical behavior.The TPB experiments have been performed to validate the multiscale models.Both the experimental and numerical results reveal that delamination mainly appears in the top and bottom interfaces of the CFRP laminates.And matrix cracking and delamination are identified as the significant damage modes during the TPB process.Finally,the quasi-static and dynamic behaviors of plain woven composites are discussed by comparing the results of Low-Velocity Impact(LVI)and TPB simulations.

木材横纹销槽承压强度研究

设计了3种共计290个木材横纹销槽试件,分析了试验方法、判定方法、有效承压高度、试件尺寸及螺栓直径等因素对木材横纹销槽承压强度的影响,并将试验结果与规范计算结果进行对比.结果表明:现行规范中的木材横纹销槽承压强度试验方法和计算方法均存在一定的局限性;基于本文提出的标准试验方法所得到的木材横纹销槽承压强度,木结构螺栓连接横纹屈服承载力计算结果与试验结果比值的平均值为0.92.

聚乙烯醇纤维混凝土动态断裂过程试验研究

为探究纤维体积掺量对聚乙烯醇纤维增强水泥基复合材料(PVA-ECC)断裂过程的影响,基于50 mm的分离式霍普金森压杆(SHPB)装置对不同纤维体积掺量(0%、0.75%、1.50%、2.25%、3.00%)的PVA-ECC中心切槽半圆盘弯曲(NSCB)试件进行冲击试验,同时结合超高速数字图像(DIC)相关试验系统对PVA-ECC材料的动态断裂过程进行试验研究,得到了预制裂纹尖端张开位移的变化规律以及各组试件的临界裂缝尖端张开位移(CTODC)。结果表明,当不添加PVA纤维或添加较少(小于1.50%)时,裂尖宏观裂纹基本出现在裂尖荷载的峰值时刻处,而随着PVA纤维掺量的增加,裂尖宏观裂纹的出现显著早于裂尖荷载的峰值时刻,并且纤维体积掺量越大,裂尖宏观裂纹出现得越早,裂纹扩展至完全断裂的时间也显著增加。添加聚乙烯醇纤维可以显著提高混凝土试件的CTODC值,提高试件的阻裂能力,相同冲击荷载下,体积掺量为2.25%的聚乙烯醇纤维试件具有较大的CTODC值。

Hopkinson杆式冲击疲劳试验方法研究

在民用与国防领域,装备或结构部件常常受到高加载率的重复冲击,即冲击疲劳问题。冲击疲劳试验装置是研究冲击疲劳问题的基础,该研究提出一种分离式Hopkinson杆式冲击疲劳试验方法。首先通过真空系统使撞击弹复位,在加载过程中通过弹性约束对入射杆进行限位,最后利用电动推杆使透射杆和试样复位,以上过程通过PLC控制器控制。这种方法操作简易,能通过在杆上的信号采集实现冲击波的连续实时显示,并能改变撞击体几何构形以产生不同形状(梯形波、三角波或半正弦波)和不同加载率(8×10^(5)~3×10^(6)MPa/s)的冲击加载波,加载频率范围在0~0.5 Hz。最后利用高强钢圆柱试样和含有工艺缺陷的增材制造316L不锈钢三点弯曲试样对试验方法进行了验证,证明该方法有效可靠。

Effect of layer thickness on the flexural property and microstructure of 3D-printed rhomboid polymer-reinforced cemented tailing composites

For mines with poor ore bodies and surrounding rocks,the general mining method does not allow the ore to be extracted from underground safely and efficiently.For these mines,the downward layered filling mining technique is undoubtedly the most suitable mining method.The downward filling mining technique may eliminate the troubles relating to poor ore deposit conditions,such as production safety,ore loss rate,and depletion rate.However,in this technique,the safety of the artificial roof of the next stratum is of paramount importance.Cementitious tailings backfilling(CTB)that is not sufficiently cemented and causes collapses could threaten ore production.This paper explores a diamond-shaped composite structure to mimic the stability of a glued false roof in an actual infill mine based on the recently emerged three-dimensional(3D)printing technology.Experimental means such as three-point bending and digital image correlation(DIC)techniques were used to explore the flexural characteristics of 3D construction specimens and CTB combinations with different cement/tailings weight ratios at diverse layer heights.The results show that the 3D structure with a 14-mm ply height and CTB has strong flexural characteristics,with a maximum deflection value of 30.1 mm,while the 3D-printed rhomboid polymer(3D-PRP)structure with a 26-mm ply height is slightly worse in terms of flexural strength characteristics,but it has a higher maximum flexural strength of 2.83 MPa.A combination of 3D structure and CTB has more unique mechanical properties than CTB itself.This research work offers practical knowledge on the artificial roof performance of the downward layered filling mining technique and builds a scientific knowledge base regarding the successful application of CTB material in mines.

SiC_(f)/SiC陶瓷基复合材料T型结构件在弯曲载荷下的失效行为研究

为了揭示SiC_(f)/SiC陶瓷基复合材料(CMCs)T型结构件在发动机服役载荷下的失效模式及承载水平,利用数字图像相关技术(DIC)研究了室温及高温环境下T型结构件在弯曲载荷下的失效行为,开展了T型结构件在室温、900℃以及1200℃下的静强度试验。DIC及断口分析结果表明,T型结构模拟件在弯曲载荷下底板首先出现分层,并沿着结合面向外扩展。随着载荷进一步增大,底板和肋板的倒圆位置出现径向裂纹,T型结构件承载能力迅速下降。T型结构件在900℃下的最大承载能力为室温的73.2%,1200℃下的最大承载能力为室温的59.1%。

变桨轴承套圈材料弯扭疲劳载荷谱研究

变桨轴承套圈承受周期性弯扭交变载荷作用,为使用标准试件研究变桨轴承套圈材料的弯扭疲劳失效,需建立与实际工况等效的试验载荷谱。首先建立了风力发电机桨叶系统的整体力学模型,并研究了变桨轴承套圈承受的周期性外载荷;其次建立变桨轴承的整体有限元模型,研究变桨轴承套圈应力、套圈截面弯矩和扭矩的周期性变化规律;最后通过应力和弯扭载荷特性等效,研究了标准试件试验变桨轴承套圈材料疲劳性能的等效载荷谱。

Heterogeneous Fracture Simulation of Three-point Bending Plain-concrete Beam with Double Notches

Plain concrete is regarded as a two-phase material comprising randomly distributed aggregates and mortar matrix. A series of three-point bending concrete beams with symmetric or asymmetric double notches are modeled using the modified random aggregate generation and packing algorithm. The cohesive zone model is used as the fracture criterion and the cohesive el- ements are inserted into both the mortar matrix and the aggregate-mortar interfaces as potential micro-cracking zones. The dead and alive crack phenomena are studied experimentally and nu- merically; and the influences of notch location, aggregate distribution and gradation on fracture are numerically evaluated. Some important conclusions are given.

Numerical Simulation of Sea Ice and Structure Interaction Using Common Node DEM-SPH Model

In this work,a novel fluid-structure coupling method called the common node discrete element-smoothed particle hydrodynamics(DS-SPH)method is introduced.This framework combines the principles of the common node discrete element method(DEM)and smoothed particle hydrodynamics(SPH)to construct DEM-SPH particles situated on the same node.By doing so,the DEM particles can interact with the SPH particles within their support domain,enabling fluid-structure interaction(FSI).To determine the DEM microscopic parameters required for this method,uniaxial compression and three-point bending tests are conducted on sea ice.To verify the proposed model,we select the interaction between sea ice and structures as a case study.Through simulation,the model's capability of accurately depicting sea ice deformation and fracture has been demonstrated.The results indicate that the inclusion of SPH particles with fluid properties in the DEM model has minimal impact on the main mechanical parameters of sea ice.Additionally,it helps prevent the occurrence of particle splashing during cement failure.However,it is observed that the size of DEM particles and the friction between DEM particles and the structure significantly influence the macroscopic mechanical behavior of the common-node DEM-SPH model.Finally,we compare the fracture behavior of sea ice and the ice forces acting on structures obtained from the current model with on-site measured results.The agreement between the two sets of data is excellent,further validating the effectiveness of the proposed model in practical applications.