Haptic Evaluation of the Prickle of Fabrics: Axial Compression Bending Tests On Ramie Fibers

Although smoothness, softness, and stiffness determine the physical and mechanical behavior of a fabric and the subjective assessment of quality when it is handled, the perceived comfort of clothing is more important to consumers. The sensations perceived from the contact of clothing with the skin can greatly influence our over-all state of comfort and one aspect of this is the unpleasant skin sensation of prickle. Surface prickle of fabrics can be a factor limiting the use of the coarser types of ramie in apparel. And the mechanical stimulus of fabric-evoked prickle underlies our discomfort to fabrics independent in the majority of cases of any chemical or the atopic status of the individual. It is known that the prickle of fabric can be reduced by fabric-finishing treatments, but the assessment of fabric prickle is often done subjectively. This is time consuming, and it is difficult to obtain reliable and reproducible results, since variability between subjects in their sensitivity to prickle, such as skin mechanical properties, effective density of nociceptors and the mood state of the individual. In order to find an objective method of measuring the physical properties of the stiff fiber ends protruding from the fabrics to predict prickle, axial compression bending tests were examined by using single ramie fiber. By comparing analysis, it is found that the critical compressing load (Pcr), the bending modulus (E) are the important parameters. The relationship of the critical load (Pcr) with the length of fiber (L) and the fineness of fiber (Nt) has been investigated.

Post-Buckling Behavior of Laminated Composite Cylindrical Shells Subjected to Axial, Bending and Torsion Loads

In present work, post-buckling behavior of imperfect (of eigen form) laminated composite cylindrical shells with different L/D and R/t ratios subjected to axial, bending and torsion loads has been investigated by using an equilibrium path approach in the finite element analysis. The Newton-Raphson approach as well as the arc-length approach is used to ensure the correctness of the equilibrium paths up to the limit point load. Post-buckling behavior of imperfect cylindrical shells with different L/D and R/t ratios of interest is obtained and the theoretical knock-down factors are reported for the considered cylindrical shells.

Behavior of Reinforced Concrete Columns under Combined Axial Load and Bending in Accordance with a Nonlinear Numerical Model

A nonlinear numerical model was developed to analyze reinforced concrete columns under combined axial load and bending up to failure. Results of reinforced concrete columns under eccentric compression tested to failure are presented and compared to results from a numerical nonlinear model. The tests involved 10 columns with cross-section of 250 mm × 120 mm, geometrical reinforcement ratio of 1.57% and concrete with compression strength around 40 MPa, with 3,000 mm in length. The main variable was the load eccentricity in the direction of the smaller dimension of cross-section. Experimental results of ultimate load and of the evolution of transverse displacements and concrete strains are compared with the numerical results. The estimated results obtained by the numerical model are close to the experimental ones, being suitable for use in verification of elements under combined axial load and bending.

A Non-Linear 3D FEM to Simulate Un-Bonded Steel Reinforcement Bars under Axial and Bending Loads

This paper presents development of 3D non-linear finite element model to simulate the response and predict the behavior of un-bonded mild steel bars under axial and bending loading. The models were successfully analyzed with the finite element software ANSYS, taking into account the nonlinear material properties of the reinforced mild steel bars. A bending strain relationship is derived based on a parametric study involving multiple nonlinear finite element models. A mild steel fracture criterion based on low-cycle fatigue models is proposed to control the total (elastic and plastic) strains in the mild steel bar below a maximum permissible limit. In addition, FE predictions of bar elongation due to strain penetration reasonably agreed with a proposed empirical equation by Raynor and Lehman. It was concluded that the equation proposed by Raynor and Lehman is considered valid for estimating the additional unbounded length and can be used in both analysis and design.

内置工字型CFRP型材高强圆钢管高强混凝土轴压短柱组合效应分析

目的 研究内置工字型CFRP型材的高强圆钢管高强混凝土短柱在轴心压力作用下三种材料的组合效应。方法 采用有限元分析软件ABAQUS对其进行数值模拟,通过相关试验验证模型的准确性,并对典型构件的破坏形态、受力全过程曲线进行分析,揭示构件各组成部分之间的相互作用和工作机理,评估CFRP配置率、钢材屈服强度、混凝土抗压强度、约束效应系数对组合效应的影响。结果 在高强圆钢管高强混凝土柱中内置CFRP型材,对构件的延性及安全裕度有显著提高,并改善了高强圆钢管对高强混凝土的约束,提高了构件的组合效应。结论 CFRP配置率控制在5.9%~8.4%,约束效应系数在1.2~1.4,钢材屈服强度不大于770 MPa时,构件中三种材料组合效应最佳。

外包薄壁夹心钢-混组合管柱层间作用对其受压承载力的影响

为了研究外包薄壁夹心钢混组合管柱层间作用下的力学性能,建立了组合管柱有限元分析模型,通过库伦摩擦定义层间作用力,改变影响参数值,研究了轴压、偏压作用下组合管柱的力学性能。结果表明:当摩擦系数由0.2增大至0.4时,轴心受压柱与偏心受压柱极限承载力分别提高了1.06%、13.35%,由0.4增大至0.6时,分别提高了0.06%、13.61%;随着内外钢管与混凝土之间外力的增加,层间作用力和机械咬合力也相应地增加,增强层间作用力可以明显提高外包薄钢混凝土偏心受压组合管柱的极限承载力。

钢桁架锥形结构轴压力学性能分析

依托青岛虚拟创享中心的实际工程项目,以钢桁架锥形结构为研究对象,提取了单榀主桁架子结构,并利用Abaqus2023有限元软件对其进行了轴压力学性能分析。重点研究了单榀钢桁架锥形结构的破坏模式和传力机理,同时结合钢桁架腹杆内力分布规律,研究了关键位置处腹杆截面类型以及截面壁厚对单榀钢桁架锥形结构承载力的影响规律,分析结果表明:该腹杆发生压弯屈曲,通过与其他杆件相交节点的连接将内力传递给其他腹杆。截面类型由矩形变成H型时,桁架的极限承载力降低1.3%。变成后,该腹杆的屈曲现象得到一定程度的缓解,整体结构的变形程度相对减小,极限承载力提高2.6%。而截面壁厚由8 mm增加到24 mm时,极限承载力提升17.6%。研究成果可为工程实践提供一定参考。

3D打印汽车吸能结构耐撞性分析

3D打印技术由于其耗材成本低、成品多样化的特点,在汽车吸能结构的耐撞性研究中已被研究人员关注与应用。通过3D打印技术针对相同结构尺寸,不同基体材料的防撞梁和蜂窝填充材料等汽车吸能结构,开展了准静态试验研究,对比分析了其力学响应及变形模式,进一步基于有限元仿真,研究了结构参数对其耐撞性指标的影响。研究结果表明,3D打印PLA防撞梁及蜂窝填充结构的载荷-位移曲线与金属结构呈现出相同的趋势,并且能反映汽车吸能结构的变形特征;结构壁厚的增加导致相对密度的增加,提高了防撞梁与蜂窝结构的耐撞性,此外,胞元尺寸的增加也会影响蜂窝结构的耐撞性。提出了基于3D打印技术的汽车吸能结构优化方案,采用试验与仿真相结合的方法系统地研究了结构参数对耐撞性的影响,对于汽车类专业教具设计及汽车吸能结构分析有一定的参考意义。

H形钢构件双向压弯下全过程弯矩计算模型

为探究可发展全截面塑性的H形钢构件在双向压弯加载全过程中塑性应力及两主轴弯矩的发展机制,基于经由已有实验数据校核过的建模方法,采用ABAQUS建立了不同轴压比、腹板和翼缘宽厚比的H形截面构件在不同加载角度下的参数分析模型。结合有限元分析结果,考察了双向压弯下H形截面钢构件的塑性应力发展规律,引入平截面假定,对其应力分布形式进行一定的简化处理。进一步,通过最小二乘法拟合得到相关参数,建立加载位移、塑性发展程度和宏观承载能力三者之间内在联系,构建H形钢构件双向弯矩的理论计算模型。该模型充分考虑了截面尺寸、位移加载方向角、轴压比和加载位移的影响。通过对模型计算结果的分析,验证了该模型可得到构件在加载任意时刻的应力分布形式,并为考虑一定截面塑性发展的双向抗弯设计提供更为简便的设计方法。

钢筋PVA-ECC柱复合受扭性能试验研究及损伤分析

为研究复合受力状态下钢筋PVA-ECC构件的受扭性能,进行了9根PVA-ECC柱和1根普通混凝土(RC)柱的单调加载试验,考虑不同轴压比、扭弯比、剪跨比、纵筋配筋率和箍筋间距等参数,研究其破坏特征、扭矩-扭率曲线特征,并进行了损伤演变分析。结果表明,PVA-ECC试件受力过程均经历了弹性阶段、弹塑性阶段和破坏阶段;PVA-ECC试件在受扭承载能力和扭转变形方面与RC试件相比有很大提升;降低轴压比、增大扭弯比和剪跨比可有效提高试件的扭转延性,减小箍筋间距和剪跨比、增大轴压比可有效延缓试件开裂;采用PVA-ECC材料能有效抑制试件的损伤发展;剪跨比、纵筋配筋率和箍筋间距对复合受扭作用下试件的损伤有较大影响;纵筋配筋率越大和剪跨比、箍筋间距越小,试件复合受扭的损伤程度越小。

内、外侧锁定钢板内固定治疗胫骨远端骨折的有限元分析

目的通过有限元分析法比较内、外侧锁定钢板内固定治疗胫骨远端骨折的生物力学性能。方法对1名健康男性志愿者的胫骨行CT扫描构建正常胫骨模型。使用Solidworks 2013软件制作得到内侧锁定钢板和锁定螺钉的装配体(模型1)、外侧锁定钢板和锁定螺钉的装配体(模型2)。使用Ansys 14有限元分析软件分析在施加轴向力、扭转力、侧向力后,模型1和模型2的承载力及骨折断端的位移情况。结果(1)承载力:施加轴向力后,模型1不足模型2的1/6(P<0.05);施加扭转力后,模型1约是模型2的7倍(P<0.05);施加侧向力后,模型1和模型2比较差异均无统计学意义(P>0.05)。(2)骨折断端平均位移:施加轴向力后,模型1小于模型2(P<0.05);施加扭转力后,模型1大于模型2(P<0.05);施加侧向力后,模型1小于模型2(P<0.05)。结论与外侧锁定钢板内固定模型相比,胫骨远端骨折内侧锁定钢板内固定模型力学分布更均匀、稳定性更好,且骨折断端的微小位移能有效刺激骨痂再生,更利于骨折愈合,在软组织条件允许下更利于治疗胫骨远端骨折。

不同失效模式下皮质骨结构临界能量释放率预测

背景:临界能量释放率是结构在破坏过程中可测得的一个全局断裂力学参数,即使针对同一结构,在不同失效模式下其数值也可能存在差异。目的:提出一种方法预测皮质骨结构在不同失效模式下的临界能量释放率。方法:针对大鼠股骨皮质骨结构进行三点弯曲与轴向压缩实验以及相应断裂仿真。通过对有限元模型赋予不同临界能量释放率进行断裂模拟,并将每次模拟所得载荷-位移曲线与实验数据进行比较,当仿真与实验所得断裂参数差异小于5%时,即代表拟合成功,以此反演预测皮质骨结构在不同失效模式下的临界能量释放率。结果与结论:①结果显示大鼠股骨皮质骨结构在三点弯曲载荷下主要发生拉伸破坏,该失效模式下所预测临界能量释放率为0.16N/mm;②在轴向压缩载荷下主要发生剪切破坏,所预测临界能量释放率为0.12N/mm,这说明同一皮质骨结构在不同失效模式下的临界能量释放率存在差异;③此文通过对结构力学性能与损伤机制进行综合分析,揭示了不同失效模式下皮质骨结构临界能量释放率存在差异的原因,为能量释放率测量以及准确的皮质骨断裂模拟提供理论依据。

哑铃形钢管混凝土柱压弯扭复合作用下力学性能试验研究和有限元分析

以轴压比(n)、弯扭比(γ)为变化参数,开展了四根圆形和四根哑铃形钢管混凝土构件压弯扭复合作用下的试验,对不同轴压比和弯扭比参数下各构件的扭矩-转角曲线、扭矩-剪应变曲线、破坏模态的变化规律进行分析。结果表明:在轴压比一定的情况下,弯扭比较大时,构件以受弯为主,破坏模式接近“弯型破坏”;弯扭比较小时,构件以绕构件中心扭转为主,破坏模式接近“扭型破坏”。抗扭承载力随着轴压比增加而提高;在γ=2.80时,当n=0.00增大至n=0.11时,圆形和哑铃形钢管混凝土构件抗扭承载力分别提高23%和53%,增大到n=0.22时,圆形和哑铃形钢管混凝土构件抗扭承载力分别提高了23%和99%;抗扭承载力随着弯扭比增加而降低,其中γ=0.90增大至γ=2.80时,圆形和哑铃形钢管混凝土构件抗扭承载力分别下降了46%和51%。通过有限元软件ABAQUS,对压弯扭构件的扭矩-转角全过程关系曲线及破坏模态进行分析,有限元计算结果与试验结果吻合良好。

Micro Mechanical Model of 3D Woven Composites

A combined beam model representing the periodicity of the microstructure and micro deformation of 3D woven composites is developed for predicting mechanical properties. The model considers the effects of off axial tension/compression and bending/shearing couplings as well as the mutual reactions of fiber yarns. The method determining microstructure by using woven parameters is described for a typical 3D woven composite material. An analytical cell, constructed by a minimum periodic section of yarn and interlayer matrix, is adopted. Micro stresses in the cell under in-plane tensile loading are obtained by using the proposed beam model and macro modulus is then obtained by the averaging method. Material tests and a 2D micro FEM analysis are made to evaluate this model. Analyses reveal that micro stress caused by tensile/bending coupling effect is not negligible in the stress analysis.

OBSERVATIONS ON DEFORMATION BEHAVIOR OF HIGH PERFORMANCE FIBERS BY POLARIZING OPTICAL MICROSCOPY

By means of polarizing optical microscopy (POM), deformation behavior of four kinds of fibers, i.e, ultra high molecular weight polyethylene (UHMW-PE) fiber, polyvinyl alcohol (PVA) fiber, polyethylene terephthalate (PET) fiber, and wholly aromatic (rho-hydroxybenzoic acid/2-hydroxy-6-naphthoic acid) copolyester [P(HBA/HNA)]/PET (ACPET blend) fiber, in axial compression, axial impacting, and bending was observed. In compression, kink bands formed at an angle of 55-60 degrees ro the fiber axis in 10-times-drawn UHMW-PE fiber, 75-80 degrees in 40-times-drawn sample, 80 degrees in PVA fiber, and 90 degrees in the ACPET blend fiber. In impacting and bending, band angles of UHMW-PE, PVA and PET fibers are nearly the same as those formed in compression, indicating that slip systems do not change. For any of the four kinds of fiber, band spacing exhibits great differences in compression, in impacting, and in bending, which may be attributed to the differences in the degrees of strain or stress concentration.

《钢结构与钢-混凝土组合结构设计方法》的理解与应用——矩形钢管混凝土柱

截面高宽比h/b大于2.0的矩形钢管混凝土柱具有较好的外观优势,能避免室内出现凸柱现象,随着实际应用日渐增多,对其的研究也越发深入。根据《隐式钢管混凝土结构技术规程》(T/CECS 951—2021)和《矩形钢管混凝土结构技术规程》(CECS 159:2004)两本规范给出的条文对构件的计算结果及构造要求进行了对比。计算对比包括截面塑性发展能力、单向压弯荷载作用下的截面强度及单向压弯荷载作用下的平面内稳定承载力等三个方面。计算结果将再与多组实际试验结果进行对比,根据两者计算偏差判断规范公式的合理性。构造方面主要对比截面尺寸、长细比、宽厚比、轴压比及强柱弱梁验算公式和免除强柱弱梁验算的条件。结果表明,相比于CECS 159:2004,T/CECS 951—2021更接近实际试验结果,计算公式更合理,构造要求规定更全面。

Forming Characteristics of Al-alloy Large-diameter Thin-walled Tubes in NC-bending Under Axial Compressive Loads

Tube thinning control without wrinkling occurring is a key problem urgently to be solved for improving the forming qualities in numerical control （NC） bending processes of large-diameter Al-alloy thin-walled tubes （AATTs）. It may be a way solving this problem to exert axial compression loads （ACL） on the tube end in the bending. Thus, this article establishes a three-dimensional （3D） elastic-plastic explicit finite element （FE） model for the bending under ACL and has its reliability verified. Through a multi-index orthogonal experiment design, a combination of process parameters, each expressed by a proper range, for this FE model is derived to overcome the compression instability on tube ends. By combining the FE model with a wrinkling energy prediction model, an in-depth study is conducted on the forming characteristics of large-diameter AATTs with small bending radii and it can be concluded that （1） The larger the tube diameters and the smaller the bending radii, the larger the induced tangent tension stress zones on tube intrados, by which the tube maximum tangent compression stress zones will be partitioned in the bending processes; thus, the smaller the ACL roles in decreasing thinning degrees and the larger the compression instability possibilities on tube ends. （2） The tube wrinkling possibilities under ACL are larger than without ACL acting in the earlier forming periods, and smaller in the later ones. （3） For the tubes with a size factor less than 80, the ACL roles in decreasing thinning degrees are stronger than in increasing wrinkling possibilities.

外包不锈钢管中空夹层钢管混凝土压弯构件N_(u)-M_(u)相关曲线研究

外包不锈钢管中空夹层钢管混凝土构件结合了中空夹层钢管混凝土(CFDST)与不锈钢的优点,在桥墩、海洋平台与输电塔结构中有广泛应用前景。为此,该文基于前期试验,采用自编纤维模型法程序对225个外包不锈钢管CFDST压弯构件进行了系统分析。研究了各参数对该类压弯构件典型N/N_(u)-M/M_(u)曲线的影响,并将相关曲线与普通外包碳素钢管CFDST构件进行了对比,最后提出了该类压弯构件N/N_(u)-M/M_(u)相关曲线方程。分析结果表明:该文自编纤维模型法程序可较好预测外包不锈钢管CFDST构件压弯承载力以及N/N_(u)M/M_(u)曲线的发展;混凝土强度、内管径厚比、钢材屈服强度、空心率、名义含钢率与长细比影响N/N_(u)M/M_(u)曲线的形状;由于不锈钢材料明显的应变强化效应,相比于外包碳素钢管CFDST构件,外包不锈钢管CFDST构件的N/N_(u)-M/M_(u)曲线接近于钢结构;基于试验与参数分析结果以及外包碳素钢CFDST计算公式,得到了外包不锈钢CFDST相关曲线特征点公式和曲线方程,与程序计算结果吻合较好。

地下车站装配式双H型钢支撑设计及应用

目的:为了解决地下车站深基坑工程中钢筋混凝土支撑存在的施工难度大、不可重复使用、经济社会效益低等问题,应深入研究该支撑结构的受力机理及施工使用特点。方法:提出了一种适用于地铁车站工程的新型装配式双H型钢支撑,并对该支撑截面和连接节点进行了设计分析。采用ABAQUS软件建立了装配式双H型钢支撑及其拼接节点的有限元模型,分析了其轴压性能及支撑拼接节点受弯性能。分析了双H型钢支撑的经济效益和社会效益。结果及结论:新型装配式双H型钢支撑及其连接节点承载力满足现行规范和实际工程要求,并已成功应用于无锡至江阴城际轨道交通工程南门站工程项目中。装配式双H型钢支撑与现浇钢筋混凝土支撑相比较,在重复使用5次的条件下,可节约35%的经济成本,同时可以减少68%的碳排放量。

窄翼缘PEC中长柱轴压整体稳定性能试验研究

为研究窄翼缘PEC中长柱轴压整体稳定性能,设计制作9根组合长细比介于76~141(正则化长细比介于0.84~1.55)的窄翼缘PEC中长柱,进行轴压整体稳定性能试验。研究窄翼缘PEC中长柱的初始弯曲、长细比、混凝土强度等因素对其破坏模式和轴压整体稳定承载力的影响。试验结果表明,窄翼缘PEC中长柱在轴压荷载下的破坏模式表现为绕弱轴的弯曲失稳,长细比和初始弯曲显著影响试件的破坏模式和极限承载力。当试件的正则化长细比大于1.0,初始弯曲大于L/1000时,试件的破坏模式表现为整体极值点失稳;当试件的正则化长细比大于1.0,初始弯曲小于L/2000时,试件的破坏模式表现为弹性平衡分岔失稳;当试件的正则化长细比小于1.0,初始弯曲小于L/2000时,试件的破坏模式介于弹塑性极值点失稳和平衡点分岔失稳之间;初始弯曲一致时,试件的极限承载力随着长细比的增大迅速降低。采用ABAQUS有限元软件建立窄翼缘PEC中长柱有限元模型,将计算承载力与现行规范计算结果进行对比。结果表明,试件轴压整体稳定承载力比规范承载力高出20%,按现行规范计算整体稳定承载力时,没有充分考虑混凝土和型钢的协同作用,规范计算结果偏保守。