Second-order two-scale computational method for ageing linear viscoelastic problem in composite materials with periodic structure

The correspondence principle is an important mathematical technique to compute the non-ageing linear viscoelastic problem as it allows to take advantage of the computational methods originally developed for the elastic case. However, the correspon- dence principle becomes invalid when the materials exhibit ageing. To deal with this problem, a second-order two-scale （SOTS） computational method in the time domain is presented to predict the ageing linear viscoelastic performance of composite materials with a periodic structure. First, in the time domain, the SOTS formulation for calcu- lating the effective relaxation modulus and displacement approximate solutions of the ageing viscoelastic problem is formally derived. Error estimates of the displacement ap- proximate solutions for SOTS method are then given. Numerical results obtained by the SOTS method are shown and compared with those by the finite element method in a very fine mesh. Both the analytical and numerical results show that the SOTS computational method is feasible and efficient to predict the ageing linear viscoelastic performance of composite materials with a periodic structure.

Distortional buckling analysis of steel-concrete composite box beams considering effect of stud rotational restraint under hogging moment

Restrained distortional buckling is an important buckling mode of steel-concrete composite box beams(SCCBB)under the hogging moment.Rotational and lateral deformation restraints of the bottom plate by the webs are essential factors affecting SCCBB distortional buckling.Based on the stationary potential energy principle,the analytical expressions for the rotational restraint stiffness(RRS)of the web upper edge as well as the RRS and the lateral restraint stiffness(LRS)of the bottom plate were derived.Also,the SCCBB critical moment formula under the hogging moment was derived.Using twenty specimens,the theoretical calculation method is compared with the finite-element method.Results indicate that the theoretical calculation method can effectively and accurately reflect the restraint effect of the studs,top steel flange,and other factors on the bottom plate.Both the RRS and the LRS have a nonlinear coupling relationship with the external loads and the RRS of the web’s upper edge.Under the hogging moment,the RRS of the web upper edge has a certain influence on the SCCBB distortional buckling critical moment.With increasing RRS of the web upper edge,the SCCBB critical moment increases at first and then tends to be stable.

Stochastic Second-Order Two-Scale Method for Predicting the Mechanical Properties of Composite Materials with Random Interpenetrating Phase

In this paper,a stochastic second-order two-scale(SSOTS)method is proposed for predicting the non-deterministic mechanical properties of composites with random interpenetrating phase.Firstly,based on random morphology description functions(RMDF),the randomness of the material properties of the constituents as well as the correlation among these random properties are fully characterized through the topologies of the constituents.Then,by virtue of multiscale asymptotic analysis,the random effective quantities such as stiffness parameters and strength parameters along with their numerical computation formulae are derived by a SSOTS strategy combined with the Monte-Carlo method.Finally,the SSOTS method developed in this paper shows an excellent computational accuracy,and therefore present an important advance towards computationally efficient multiscale modeling frameworks considering microstructure uncertainties.

A PREDICTIVE APPROACH TO THE IN-PLANE MECHANICAL PROPERTIES OF STITCHED COMPOSITE LAMINATES

This contribution attempts to model the alteration of the in-plane elastic properties in laminates caused by stitching, and to predict the in-plane effective tensile strength of the stitched composite laminates. The distortion of in-plane fibers is considered to be the main cause that affects the in-plane mechanical properties. A fiber distortion model is proposed to characterize the fiber misalignment and the fiber content concentration due to stitching. The undistorted region, the fiber distortion region, the resin-rich pocket and the through-thickness reinforcement section are taken into account. The fiber misalignment and inhomogeneous fiber content due to stitching have been formulated by introducing two parameters, the distortion width and maximum misalignment. It has been found that the ply stress concentration in stitched laminates is influenced by the two concurrent factors, the stitch hole and inhomogeneous fiber content. The stitch hole brings about the stress concentration whereas the higher fiber content at the local region induced by stitching restrains the local deformation of the composite. The model is used to predict the tensile strength of the [0/45/0/-45/90/45/0/-45]58 T300/QY9512 composite laminate stitched by Kevlar 29 yarn with different stitching configurations, showing an acceptable agreement with experimental data.

Microstructure and Performance of 2Y-PSZ/TRIP Steel Composites

2Y-PSZ/TRIP steel composites have been sintered by hot-pressing method. Their microstructure and mechanical properties were investigated by means of SEM, TEM, XRD and static tension, split Hopkinson pressure bar method. The results showed that the strength and elastic modulus of 2Y-PSZ/TRIP steel composites at room temperature decreased with the increase of 2Y-PSZ content. The main reason was that the combining strength was quite weak between the grains of ZrO2. Distortion induced martensite transformation and plasticity during the dynamic loading increased the strength and distortion capability of the composites. The transformation was carried out mainly through twins formation. The shape of martensite induced by distortion was lamellate with substructures of twins. The habit plane was near {259}T with no mid-ridge and no explosion phenomena. The interface was straight between the austenite and martensite induced by distortion. The increase of 2Y-PSZ content, on the one hand, made the composite dynamic flow stress improved. Thereby, the fracture strength was improved. On the other hand, it depressed both the distortion capability and the martensite transformation induced by distortion. This resulted in the decrease of dynamic fracture strength.

An R(x)-orthonormal theory for the vibration performance of a non-smooth symmetric composite beam with complex interface

A composite beam is symmetric if both the material property and support are symmetric with respect to the middle point. In order to study the free vibration performance of the symmetric composite beams with different complex nonsmooth/discontinuous interfaces, we develop an R(x)-orthonormal theory, where R(x) is an integrable flexural rigidity function. The R(x)-orthonormal bases in the linear space of boundary functions are constructed, of which the second-order derivatives of the boundary functions are asked to be orthonormal with respect to the weight function R(x). When the vibration modes of the symmetric composite beam are expressed in terms of the R(x)-orthonormal bases we can derive an eigenvalue problem endowed with a special structure of the coefficient matrix A :=[aij ],aij= 0 if i + j is odd. Based on the special structure we can prove two new theorems, which indicate that the characteristic equation of A can be decomposed into the product of the characteristic equations of two sub-matrices with dimensions half lower. Hence, we can sequentially solve the natural frequencies in closed-form owing to the specialty of A. We use this powerful new theory to analyze the free vibration performance and the vibration modes of symmetric composite beams with three different interfaces.

Influence of mandrel-cores filling on size effect of cross-section distortion of bimetallic thin-walled composite bending tube

Two new size factors of cross-section hollow coefficient and bending degree are introduced to reveal the size effect of bending forming of bimetallic composite tube.Hollow coefficient and bending degree can limit the commonly used bent tube to the size description range of(0,2.00).The evolution laws of the cross-section distortion forms in the hollow coefficient-bending degree interval are revealed as well as the action of the mandrel-cores on the size effect.Results show the mandrel-cores filling can expand the forming limit of the bent tube,but also bring two other forming defects of wrinkle and rupture.The identification factor(hollow coefficient multiply bending degree)provides a method for querying the cross-section distortion forms of all composite bending tubes.In the identification factor interval(0,1.00),the distribution area of bending forming defects of the composite tube is continuous.The thin-walled composite bending tube collapses when identification factor in(0,0.39),wrinkles when identification factor in[0.39,0.50),and ruptures when identification factor in[0.50,1.00).The mathematical model of size effect is derived,by which the average cross-section distortion rate is found to distribute like a radial leaf in the hollow coefficient-bending degree qualified forming space.The best forming zone is hollow coefficient 0.46-0.68,and bending degree 0.25-0.47.

Influence of Electrical Field Distortions Induced by Water Droplets on the Contamination Characteristics of an Insulator

When separated water droplets condense on the surface of a composite insulator,the electrical field on the insulator surface is distorted.In turn,such distortions change the trajectories of pollution particles.In this study,the COMSOL software is used to simulate such a process for the FXBW4-10/100 composite insulator with or without water droplets condensation under a 10 kV DC voltage.The influence of the wind speed and particles concentration on the contamination characteristics of the considered 110 kV insulator is analyzed.The results show that:1)in the presence of water droplets on the insulator surface,the ratio of electrical field force and gravity acting on the particles is large;2)the contamination on the insulator surface increases with the wind speed;3)when the wind speed is small,the relationship between the contamination amount and the pollution concentration is essentially linear.

Dynamic thermo-mechanical coupled response of random particulate composites:A statistical two-scale method

This paper focuses on the dynamic thermo-mechanical coupled response of random particulate composite materials. Both the inertia term and coupling term are considered in the dynamic coupled problem. The formulation of the problem by a statistical second-order two-scale （SSOTS） analysis method and the algorithm procedure based on the finite-element difference method are presented. Numerical results of coupled cases are compared with those of uncoupled cases. It shows that the coupling effects on temperature, thermal flux, displacement, and stresses are very distinct, and the micro- characteristics of particles affect the coupling effect of the random composites. Furthermore, the coupling effect causes a lag in the variations of temperature, thermal flux, displacement, and stresses.

Multi-Level Inverter Linear Predictive Phase Composition Strategy for UPQC

The power system is facing numerous issues when the distributed gen-eration is added to the existing system.The existing power system has not been planned with flawless power quality control.These restrictions in the power trans-mission generation system are compensated by the use of devices such as the Static Synchronous Compensator(STATCOM),the Unified Power Quality Con-ditioner(UPQC)series/shunt compensators,etc.In this work,UPQC’s plan with the joint activity of photovoltaic(PV)exhibits is proposed.The proposed system is made out of series and shunt regulators and PV.A boost converter connects the DC link to the PV source,allowing it to compensate for voltage sags,swells,vol-tage interferences,harmonics,and reactive power issues.In this paper,the fea-tures of a seven-level Cascaded H-Bridge Multi-Level idea are applied to shunt and series active filter changeovers to reduce Total Harmonic Distortion and com-pensate for voltage issues.Despite its power quality capacity for common cou-pling,the proposed system can inject the grid’s dynamic power.During voltage interference,it can also provide a piece of delicate burden power.The simulation is carried out with the help of MATLAB/SIMULINK programming,and the results are compared to those of other conventional methods.

新型波形钢腹板组合箱梁畸变效应

为研究新型波形钢腹板(CSW)组合箱梁的畸变效应,以板梁框架法和位移法为基础,建立单箱多室新型CSW组合箱梁的畸变控制微分方程和边界条件,得到畸变正应力解析解,并采用有限元法检验推导结果的正确性。应用推导结果对比分析新型CSW组合箱梁与传统CSW组合箱梁的畸变性能,以及截面高度、箱室宽度和钢底板厚度对新型CSW组合箱梁畸变效应的影响。结果表明:解析解计算得到的畸变正应力与有限元模型计算的结果吻合较好,畸变角的变化规律与有限元模型计算结果一致;与传统CSW组合箱梁相比,新型CSW组合箱梁的畸变翘曲刚度减小了38.89%,畸变框架刚度减小了71.84%,抗畸变能力减弱;随着截面高度和箱室宽度增加,新型CSW组合箱梁跨中畸变角和跨中畸变双力矩均逐渐增大,且箱室宽度的影响更为明显;随着钢底板厚度增加,新型CSW组合箱梁跨中畸变角逐渐减小,跨中畸变双力矩逐渐增大。

Multiscale microstructural consideration of enhanced shear strength in TiAl intermetallic/K4169 alloy composite joints prepared by vacuum brazing with(Ti,Zr)-Ni-based amorphous filler metal

TiAl intermetallic could be used to replace Ni-based alloy in assemblies to generate excellent specific strength.A(Ti,Zr)-Ni-based amorphous filler metal Ti_(21.25)Zr_(25)Ni_(25)Cu_(18.75)(at.%)was designed using a cluster-plus-glue-atom model to successfully vacuum braze K4169 and TiAl bimetallic assemblies.At various brazing temperatures and holding time,the quantitative relationships between lattice distortion,grain boundary,dislocation density,and hardness,elastic modulus,shear strength of the joints were investigated.Meanwhile,the fracture mechanism of the joints was revealed.The brazed seam mainly consisted of solid diffusion reaction layers(ZonesⅠandⅢ)and filler metal residue zone(ZoneⅡ).When the brazing temperature increased to 1030℃,grain refinement occurred in the brazed seam.ZoneⅠwas primarily composed of(Ni)ss[0-11]+TiNi[011]/(Cr,Fe,Ni)ss[0-11]/(Ti,Zr)Ni[0-1-1]+(Cr,Fe,Ni)ss[0-11].The(Ti,Zr)(Ni,Cu)[001]and(Ti,Zr)(Ni,Cu)[101]intermetallic compound-based solid solutions were formed in ZoneⅡ.And the lattice distortion of(Ti,Zr)(Ni,Cu)[101]and(Ti,Zr)(Ni,Cu)[001]was 32.05%and 14.82%,respectively.As a result,the proportion of low angle grain boundaries(LAGBs)and deformed grains in ZoneⅡrose to 38.6%and 38.7%.In ZonesⅠandⅢ,the proportion of LAGBs reduced to 8%and 3.4%,respectively.As the holding time increased,the long-range diffusion of Al in ZoneⅡcaused the(Ti,Zr)(Ni,Cu)[001]with cubic structure to transform into(Ti,Zr)(Ni,Cu,Al)[00-1]with hexagonal crystal system structure,where the lattice distortion was 4.42%and 10.49%for a and c.At 1030℃/10 min,the average geometrically nec-essary dislocation densities(GNDs)in ZonesⅠ,ⅡandⅢwere 9.87×10^(14)m^(-2),8.55×10^(14)m^(-2)and 11.4×10^(14)m^(-2),respectively.Therefore,the shear strength of joints reached 322 MPa due to the lattice distortion,dislocation strengthening and fine grain strengthening.Meanwhile,the plastic and brittle hard phases were generated in ZoneⅡand displayed a mechanical interlocking structure that contributed to the performance of the joint.Both(Ti,Zr)(Ni,Cu)[001]and(Ti,Zr)(Ni,Cu)[101]in ZoneⅡformed along differ-ent low-index cleavage planes during transgranular fracture.The cracks initiated in this region extended to the interface between Zones I andⅡand exhibited bimodal grain characteristics.

考虑滑移的钢-混凝土组合箱梁畸变效应研究

通过引入滑移转角位移函数,建立考虑滑移的畸变翘曲正应力,基于势能驻值原理,推导考虑滑移效应的畸变微分方程。定义了一个畸变的滑移影响系数κ,此系数仅与混凝土与钢材材料特性、栓钉类型及栓钉布置形式有关,并给出均布荷载和集中荷载作用下的微分方程初参数解。建立一个考虑滑移的钢-混凝土组合箱梁的Ansys有限元模型,均布荷载作用下畸变应力与畸变角与本文理论吻合良好,验证了本文理论的正确性。将考虑滑移与不考虑滑移的结果进行对比,分析表明,均布荷载作用下考虑滑移的畸变角与畸变翘曲均小于不考虑滑移的情况,且考虑滑移的畸变角更加接近于有限元计算结果。重新定义了考虑滑移的畸变矩和畸变双力矩且考虑滑移影响的结果均大于不考虑滑移的结果。

波形腹板钢-混组合箱梁畸变效应分析

为研究波形腹板钢-混组合箱梁畸变效应,以桑园子黄河大桥引桥简支箱梁为研究对象,将畸变角重新定义,通过计算畸变中心、畸变总势能,确定初始参数,利用势能驻值原理推导与传统扭转分析理论相一致的畸变效应分析方法。根据工程实例,对车道荷载下波形腹板钢-混组合箱梁畸变翘曲应力变化规律进行研究。结果表明,畸变翘曲应力在组合箱梁应力中占比不容忽视,且随着箱梁顶板混凝土厚度增大,翘曲正应力逐渐减小,在钢底板组合箱梁增设铺底混凝土可有效减少畸变翘曲应力。

Crystal Structure and Chemical Composition of Ludwigite from Vranovac Ore Deposit (Boranja Mountain,Serbia)

The crystal structure of ludwigite from Vranovac ore deposit （Boranja Mt., Serbia） was refined using the X-ray powder diffraction （XRPD） Rietveld method in the space group Pbam to a final RB=7.45% and RF=5.26%. It has the unit cell dimensions of： a=9.2515（2） A; b=12.3109（2） A; c=3.03712 （7） A; and V=345.91（1） A3. The calculated distances and angles are mostly in good agreement with the Mg2＋-Fe2＋ substitutions across the M（1） and M（3） sites, as well as with the Fe3＋-AI3＋ replacement in the M（4） site. However, the mean observed M（2）-O distance is considerably shorter than prescribed, due to a slight increase of the Fe3＋ content in the M（2） site. Such replacement was compensated by slight increase of the Fe2＋ content in the M（4） site, resulting in the （Mg1.4sFe2＋o.46Fe3＋o.osMno.o2）2.o1 （Fe3＋o.94Fe2＋0.04Al0.02）1.00B1.00Os composition. The formation temperature was estimated to be about 500- 600C. The influences of the various chemical compositions to the crystallographic parameters, M-O distances, M（3） and M（4） sites shift, distortion parameters and estimated valences, were also studied and compared with other reference samples.

Second-order two-scale method for bending behavior analysis of composite plate with 3-D periodic configuration and its approximation

This paper considers the bending behaviors of composite plate with 3-D periodic configuration.A second-order two-scale(SOTS)computational method is designed by means of construction way.First,by 3-D elastic composite plate model,the cell functions which are defined on the reference cell are constructed.Then the effective homogenization parameters of composites are calculated,and the homogenized plate problem on original domain is defined.Based on the Reissner-Mindlin deformation pattern,the homogenization solution is obtained.And then the SOTS’s approximate solution is obtained by the cell functions and the homogenization solution.Second,the approximation of the SOTS’s solution in energy norm is analyzed and the residual of SOTS’s solution for 3-D original in the pointwise sense is investigated.Finally,the procedure of SOTS’s method is given.A set of numerical results are demonstrated for predicting the effective parameters and the displacement and strains of composite plate.It shows that SOTS’s method can capture the 3-D local behaviors caused by3-D micro-structures well.

腹板并合双肢冷弯薄壁Σ型钢压弯构件畸变性能试验研究

为研究腹板并合双肢冷弯薄壁Σ型钢拼合钢柱的畸变屈曲性能及其相关作用,并评估现行各国规范计算方法适用性,设计制作了22根构件进行压弯试验。以Σ型加劲、腹板孔位、偏心荷载作用位置、柱长等为主要参数,考察其对试件屈曲行为、破坏特征和极限承载能力的影响。结果表明:试验主要发生畸变屈曲或畸变-整体、畸变-局部相关屈曲,Σ型加劲有效地防止了腹板局部屈曲;腹板开孔不会影响屈曲模式的改变;关于强轴和弱轴的偏压位置及偏心距离对试件畸变屈曲行为有显著影响。采用中美技术标准包括中国规范GB50018-2002、JGJ/T 421-2018以及北美规范NAS 100-2016计算的承载力结果与试验结果进行了对比分析,结果表明:荷载绕强轴偏心作用时,中美规范计算结果均偏于安全;荷载绕弱轴偏心作用时,GB 50018-2002和NAS 100-2016计算结果偏于安全,而JGJ/T 421-2018计算值较为保守,试验与其比值约为1.64,该文建议腹板双肢并合截面整体协同工作下绕弱轴稳定承载力可按全截面计算。

碳纤维复合材料固化变形预报方法对比

碳纤维复合材料固化变形引起复合材料制件装配困难、残余应力等问题。因此,非常有必要建立复合材料构件制造过程引起变形缺陷的准确预报方法。本文对半经验模型与CHILE模型这两种应用最为广泛的固化变形仿真分析方法进行对比,并通过热压罐成型工艺试验对其进行验证。试验结果表明,这两种模型均可准确地模拟复合材料层合板的固化变形行为,其模拟误差均小于10%。基于CHILE模型研究材料参数对固化变形的影响,发现对固化变形影响最大的是玻璃态横向热膨胀系数,其次是橡胶态横向化学收缩系数。

钢桁腹-混凝土组合箱梁畸变效应研究

为研究梯形截面的钢桁腹-混凝土组合箱梁的畸变效应,在薄壁箱梁理论的基础上,考虑钢桁腹杆的力学特性,应用改进的板元分析法建立畸变控制微分方程,并给出畸变解析解。通过ANSYS建立实体模型验证所推公式的正确性。结合数值算例,对比分析在均布畸变荷载作用下相同截面参数的钢桁腹-混凝土组合箱梁和传统混凝土箱梁的畸变翘曲正应力,并分析梁宽和钢腹杆俯角对组合箱梁畸变内力的影响。结果表明,相同截面参数下,由于组合箱梁钢桁腹杆的纵向刚度很小,其畸变翘曲正应力为混凝土箱梁的1.71倍;梁宽对畸变内力影响较大,当梁宽增加至4.5 m时,畸变双力矩和畸变矩分别增大至3.68倍和1.36倍,且前者在纵向上双峰的分布趋势逐渐平缓;腹杆俯角对畸变双力矩影响较大,当腹杆俯角增加至27°时,畸变双力矩减小了约14.3%,但其对畸变矩影响很小。

钢桁腹-混凝土组合箱梁畸变效应分析

为研究钢桁腹-混凝土组合箱梁的畸变效应,根据其结构特性和力学特性,考虑共同工作区对组合箱梁腹杆纵向刚度的贡献,提出一种更适用于该类组合箱梁的畸变扇性坐标分布模式。采用新畸变中心定义符合钢桁腹-混凝土组合箱梁畸变变形特征的畸变角,应用能量变分法建立畸变控制微分方程,并给出包含Krylov函数的初参数解。结合数值算例,分析钢桁腹-混凝土组合箱梁在均布畸变荷载作用下的畸变翘曲正应力,并通过有限元软件ANSYS验证所推导理论的正确性。通过改变腹杆壁厚、俯角等关键参数,探究其对畸变内力的影响规律。结果表明:按该方法揭示的钢桁腹-混凝土组合箱梁的畸变应力分布规律与ANSYS计算结果吻合良好;横向畸变框架刚度是影响此类箱梁畸变效应的主要因素,且其对钢腹杆几何特性参数较为敏感。