Von Misses Pure Shear in Kirchhoff’s Plate Buckling

The pure shear strength for the all-simply supported plate has not yet been found;what is described as pure shear in that plate, is, in fact, a pure-shear solution for another plate clamped on the “Y-Y” and simply supported on the long side, X-X. A new solution for the simply supported case is presented here and is found to be only 60-percent of the currently believed results. Comparative results are presented for the all-clamped plate which exhibits great accuracy. The von Misses yield relation is adopted and through incremental deflection-rating the effective shear curvature is targeted in aspect-ratios. For a set of boundary conditions the Kirchhoff’s plate capacity is finite and invariant for bending, buckling in axial and pure-shear and in vibration.

Shear deformation and grain refinement in pure Al by asymmetric rolling

Asymmetric rolling(ASR), as one of severe plastic deformation(SPD) methods, was widely used to make ultra-fined materials with enhanced performance. Internal marks were used to show the shear deformation during asymmetric rolling with pure aluminium as a model material. Effects of reduction ratio and mismatch ratio on the shear deformation were studied. With the observed shear deformation results, equivalent strain was calculated. For lager shear deformation, rolling equipment was modified to increase friction between specimen and the rollers. Consequently, extremely fine grains with size of 500 nm are obtained in pure aluminium. With improved asymmetric rolling, the ability of grain refinement of ASR is greatly improved.

Dynamic Mechanical Behavior and Adiabatic Shear Bands of Ultrafine Grained Pure Zirconium

Dynamic compression tests were carried out to investigate dynamic mechanical behavior and adiabatic shear bands in ultrafine grained(UFG)pure zirconium prepared by equal channel angular pressing(ECAP)and rotary swaying.The cylindrical specimens were deformed dynamically on the split Hopkinson pressure bar(SHPB)at different strain rates of 800 to 4000s^-1 at room temperature.The temperature distribution of the shear bands was estimated on the basis of temperature rise of uniform plastic deformation stage and thermal diffusion effect.The results show that the true stress-true strain curves of UFG pure zirconium are concave upward trend of strain in range of 0.02-0.16 due to the effects of strain hardening,strain rate hardening and thermal softening.The formation of the adiabatic shear bands is the main reason of UFG pure zirconium failure.A large number of micro-voids are observed in the adiabatic shear bands,and the macroscopic cracks develop from the micro-voids coalescence.The fracture surface of UFG pure zirconium exhibits quasi cleavage fracture with the characteristic features of shear dimples and river pattern.The highest temperature within the shear bands of UFG pure zirconium is about 592 K.

Spring-Value in Kirchhoff-Love Plate: Displacement, Buckling, Pure-Shear, Vibration

The stiffness model of the finite element is applied to the Kirchhoff-love closed-form plate buckling;buckling is always in focus in plate assemblages. The useful Eigen-value solutions are unable to separate a square plate from a much weaker long one in the most commonly-used all-simply supported plate (SSSS), among others. Spring-values of the Kirchhoff-Love plate are sought;once found, displacement-factors can be determined. Comparative displacements allow an easier and better evaluation of buckling-factors, pure-shear, vibration and so are termed “buckling-displacement-factors”. In testing, many plates in mixed boundary conditions are evaluated for displacement assisted buckling-solutions, first. The displacement-factors made from fundamental Eigen-vectors, in a single-pass, are found to be within about one-percent of known elastic values. It is found that the Kirchhoff-Love plate spring and the finite-element spring, demonstrated, here, in the assemblage of beam-elements, are equivalent from the results. In either case, stiffness is first assembled, ready for any loading—transverse, buckling, shear, vibration. The simply-supported plate draws the only exact vibration solution, and so, in an additional new effort, all other results are calibrated from it;direct vibration solutions are made for comparison but such results are, hardly, better. In the process, interactive Kirchhoff-Love plate-field-sheets are presented, for design. It is now additionally demanded that the solution Eigen-vector be developable into a recognizable deflection-factor. A weaker plate cannot possess greater buckling strength, this is a check;to find stiffness the deflection-factor must be exact or nearly so. Several examples justify the characteristic buckling displacement-factor as a new tool.

Work hardening of adhesively bonded pure copper single lap joints

To explain the reason why work hardening occurs in epoxy adhesive bonded zone of pure copper adherends after tensile shear strength testing, an elasto-plastic finite element model was established to analyze the effect of different adherends thickness of 2mm and 4mm on the shear strength as well as the level of work hardening in copper adherends of single lap joint. The numerical simulation results show that the axial or equivalent stress overrun the yield strength of the pure copper adherend is the main reason why the work hardening occurs on the bonded zone of the adherends after the shear strength testing. The elasto-plastic finite element simulation results are agreed with the experimental ones. The thicker its adherends are, the more serious the work hardening is.

The Early Mesozoic NE-SW Extensional Model and Exhumation Processes at the Southeastern Margin of the Central Asian Orogenic Belt:Insights from the Strain and Kinematic Vorticity Analysis of the Sonid Zuoqi Ductile Detachment Zone

The Sonid Zuoqi ductile detachment zone is located at the southeastern margin of the Central Asian orogenic belt(CAOB),striking EW and dipping to the S.The major rock type of the Sonid Zuoqi ductile detachment zone is mylonite derived from granite.The sequence of mylonite features is:(1)S and C foliations of mylonite,and(2)extensional crenulation cleavage(ecc)or C′and the kinematic vorticity(Wk)value changed from 0.70 to 0.95 and from 0.37 to 0.69,respectively;the strain type of the mylonites within the Sonid Zuoqi ductile detachment zone is compressional to planar strain.The strong deformation mylonite and Halatu plutons yielded a zircon U-Pb age of 244 Ma and a zircon(U-Th)/He age of 214 Ma,respectively.Based on the strain and kinematic vorticity analysis,together with the zircon U-Pb and zircon(U-Th)/He ages and the regional tectonic background,the study area experienced three stage evolution:tangential simpleshear(244 Ma),simple-shear-dominated general shear represented by upper crustal extension(224 Ma)and pure-shear-dominated general shear represented by the Halatu pluton doming(214 Ma),which constrained the early Mesozoic NE-SW crustal extension at the southeastern margin of the CAOB.This NE-SW extension probably originated from the postorogenic extensional collapse of the CAOB,subsequent exhumation being controlled by the far afield effects of the closure of the Mongol-Okhotsk belt.

弯-剪-扭复合受力CFRP布加固RC梁抗扭性能细观数值分析

为了研究弯-剪-扭复合受力条件下碳纤维增强复合材料(carbon fiber reinforced polymer, CFRP)布加固钢筋混凝土(reinforced concrete, RC)梁的抗扭性能,建立体现混凝土材料非均质性、钢筋-混凝土黏结滑移关系和CFRP布-混凝土相互作用关系的细观数值分析模型。由于缺乏CFRP布加固RC梁在弯-剪-扭复合受力作用下失效破坏的典型物理试验,采用复合对比验证法对数值模型的合理性进行验证,即分别与单独受剪、单独受扭以及受弯-扭复合作用下RC梁和CFRP布加固RC梁的试验结果进行对比验证。进而,基于建立的细观数值分析模型探究了配纤率和扭弯比对CFRP布加固RC梁在弯-剪-扭复合受力作用下抗扭力学性能的影响。结果表明:1)采用CFRP布加固能够显著提高RC梁的峰值扭矩;2)随配纤率增加,RC梁损伤分布范围逐渐变大,CFRP布应变逐渐减小,梁整体峰值扭矩增大,但其增大幅度减小;3)随扭弯比增加,RC梁裂缝分布愈加集中,裂缝与水平方向夹角逐渐减小,梁整体峰值扭矩增大,CFRP布应变减小。建立的考虑弯-剪-扭复合受力作用的数值模拟方法可为后续研究复杂应力状态下CFRP布加固RC梁尺寸效应行为等奠定基础。

基于数字图像技术的致密砂岩纯剪裂缝断裂过程实验

纯剪应力状态下致密砂岩断裂过程是理解致密砂岩破坏失效机理的关键,然而在纯剪应力状态下,初始裂缝是发育扩展为I型裂缝或II型裂缝却一直有所争议。本文基于新型光学测量技术数字图像相关法和双切边压缩实验理论方法,开展了双切边压缩实验并通过数字图像相关法得到了位移和应变场。实验结果表明:双边开槽压缩实验能在槽尖(预制裂缝尖端)产生纯剪应力状态;致密砂岩试件起裂过程包含2个阶段的I型裂缝,第一阶段裂缝从槽尖起裂,第二阶段裂缝从试件中心两槽尖相连区域起裂。本文研究成果为数字图像技术应用在岩石断裂力学领域提供了新思路,对分析水力压裂中致密砂岩纯剪裂缝的演化规律有一定参考价值。

TA1纯钛绝热剪切行为及变形机制

利用分离式霍普金森压杆实验装置,对TA1纯钛帽形试样进行高应变速率下的动态冲击实验,并利用金相显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和电子背散射衍射(EBSD)技术研究了不同应变速率下纯钛的绝热剪切行为及变形机制。结果表明:在动态加载下,纯钛帽形试样的强迫剪切区出现明显的绝热剪切带。随着应变速率的增加,绝热剪切带宽度变窄,长度增加,表现出较大的绝热剪切敏感性。纯钛绝热剪切带中心区的变形机制是由绝热温升和剧烈塑性变形的共同作用而发生的几何动态再结晶,过渡区的变形机制以位错滑移为主,孪生变形辅助,而基体的塑性变形机制为位错滑移和孪生共同主导。

冷喷压力对不同基板上单道单层冷喷纯铜涂层的影响

在不同喷涂压力下,采用冷喷涂技术将纯铜颗粒沉积到AZ31B镁合金板和6061T6铝合金板上,形成单道单层纯铜涂层。通过扫描电子显微镜观察涂层横截面和显微组织,借助光学显微镜测量涂层厚度,利用三维轮廓仪检测涂层表面粗糙度和形貌,使用剪切强度测试装置测量涂层与基板之间的剪切强度,研究不同喷涂压力对涂层厚度、表面粗糙度和剪切强度的影响。结果显示:随着喷涂压力的增加,AZ31B镁合金基板和6061T6铝合金基板上的涂层厚度都逐渐增加,且铝合金基板上的涂层厚度高于镁合金基板上的涂层厚度;涂层表面粗糙度值也随着喷涂压力的增加而逐渐增加,铝合金基板上的涂层表面质量更好。此外,涂层与基板之间的剪切强度也随着喷涂压力的增加而逐渐增加,AZ31B镁合金基板与纯铜涂层结合强度高于6061T6铝合金基板与纯铜涂层结合强度。

纯剪状态下蜂窝梁腹板的弹性屈曲分析

该文利用有限元软件建立正六边形孔蜂窝梁腹板在纯剪应力状态下的有限元模型,研究四边简支开孔板在纯剪状态下的屈曲模式,分析孔洞尺寸对蜂窝梁腹板屈曲临界应力的影响,提出纯剪状态下开孔板的屈曲系数计算公式,得到蜂窝梁开孔腹板在纯剪状态下的高厚比限值。研究表明,单孔板和双孔板的最大屈曲平面外位移处的连线均与水平方向呈45°,四孔板和六孔板则有2种屈曲模式;蜂窝梁腹板孔高比和距高比是影响开孔板屈曲临界应力的主要因素,建议对于剪力作用较大的蜂窝梁腹板取孔高比γ<0.5,距高比0.4<β<0.5的孔洞尺寸,使得容易实现稳定性和经济性要求;拟合的开孔板屈曲系数公式误差不超过5%,具有良好的精度。

等通道转角挤压变形超细晶纯铜的组织与性能

在室温下采用BC路径(每道次挤压时将试样绕其轴线沿同一方向旋转90°)对T2纯铜进行4道次等通道转角挤压(ECAP),研究了不同道次ECAP变形前后纯铜的显微组织、力学性能和耐腐蚀性能。结果表明:经过1道次ECAP变形后,纯铜内部形成粗大的条带状组织,与剪切应力方向呈30°~45°;经过4道次ECAP变形后,纯铜晶粒发生显著破碎与细化,出现了大量的超细等轴晶组织,平均晶粒尺寸约为0.96μm;4道次ECAP变形后纯铜的显微硬度与抗拉强度较未变形显著提高,增幅分别为43.8%和51.5%;随着ECAP道次的增加,纯铜的溶液电阻、电荷转移电阻和极化电阻均增大,开路电位和自腐蚀电位均升高,自腐蚀电流密度减小,耐腐蚀性能提升。

武汉某超高层纯剪力墙结构的墙厚能效比研究

超高层纯剪力墙结构,其墙厚的选取一直是结构设计的重点和难点。论文结合国家节能减排的政策理念,创新地提出了结构墙厚设计的能效比概念,根据剪力墙结构的受力特点,详细介绍了能效比的指标选取及结果分析。

超细晶纯钛动态力学响应及变形机制

采用分离式霍普金森压杆技术在应变速率为2000~3000 s^(-1)和温度为300~450℃条件下对超细晶纯钛进行了动态冲击实验,研究了其动态力学响应及变形机制,并利用扫描电子显微镜和透射电子显微镜对变形后的微观组织进行了表征。结果表明:超细晶纯钛的真应力-真应变曲线呈现出明显的“双应力峰”特征,随着应变速率的增加和温度的降低,其屈服强度和流变应力提高,表现出正应变速率敏感性和负温度敏感性。在应变速率为2000~3000 s^(-1)的范围内,超细晶纯钛的应变速率敏感性指数m为0.12~0.17。当应变速率大于2500 s^(-1)时,超细晶纯钛试样出现绝热剪切带,绝热剪切带产生的临界应变为0.316。在动态冲击载荷下,超细晶纯钛的变形机制由低温时的位错密度增加和位错胞形成转变为高温时的几何动态再结晶和晶粒粗化。

纯应力主轴旋转下固有各向异性砂土力学特性

【目的】进一步揭示固有各向异性和偏应力q对砂土力学特性的影响,深化对土应力方向依赖性的认识。【方法】利用新型制样装置制备具有固有各向异性的砂土空心圆柱试样,结合空心圆柱扭剪仪,开展一系列不同沉积面倾角a3和q条件下的不排水纯应力主轴旋转试验。【结果】在纯应力主轴旋转条件下,砂土临界周数随着a3和q的改变而改变,其数值最大可相差9倍;孔压前期累积速率也与a3和q有关,但中期稳定后的孔压数值受两者的影响较小;随着a3和q增大,剪应变累积速度加快,滞回圈面积及倾角也会发生变化。【结论】砂土的应变发展规律、孔压变化、剪应力-剪应变关系等动力学特性均与固有各向异性和q密切相关,且q的改变也会引起固有各向异性与动力学特性之间关系的变化。

设置少量剪力墙的框架结构设计分析

以某6层办公楼为例,分析了设置少量剪力墙框架结构体系的工作原理,并给出了设计思路。这种结构体系设置的少量剪力墙主要为结构提供刚度,以满足弹性层间位移角限值,但其不能成为第一道防线,故框架结构承载力设计应采用纯框架结构和框架–剪力墙结构包络设计。

拉伸模式对介电弹性体发电机性能影响的研究

为探究介电弹性体发电机发电量与其拉伸变形的关系,采用单轴、纯剪切与双轴3种拉伸模式进行介电弹性体发电机发电性能的实验研究。分析了介电弹性体发电机在3种拉伸模式下电压、电容、电极涂覆面积与拉伸率的关系,实验研究了3种拉伸模式下介电弹性体发电机输出电压、实际产生电能、拉力与其变形量的关系及介电弹性体的破裂极限。实验和研究结果表明,双轴拉伸模式下介电弹性体的破裂极限最大,在面积变换率大于4倍时电能出现大幅度提升,可实现介电弹性体的能量密度最大化。

CFRP的剪切力阻效应

自制装置构造构件的平面纯剪切变形,将薄层状的树脂基碳纤维复合材料(CFRP)粘贴在构件的纯剪切区域表面,在弹性范围内分析了CFRP的电阻对平面纯剪切变形的响应。实验结果表明,剪应变导致单向连续碳纤维增强的CFRP的纵向电阻变化不明显,其剪切力阻效应灵敏度约为0.16;碳纤维毡增强的CFRP具有显著的剪切力阻效应,其电阻表现出随剪应变线性的可恢复的增加,其剪切力阻效应灵敏度约为2.58。结合线应变致力阻效应产生机制,并通过CFRP细观结构的分析得出,纤维的随机乱向分布及纤维搭接形态的多样性是碳纤维毡增强的CFRP存在剪切力阻效应的主要原因。

铝合金在三种应力状态下的力学性能研究及断口分析

通过对铝合金(6063)进行平板拉伸试验、带缺口的平板拉伸试验及纯剪切试验,研究了铝合金在三种应力下的力学性能.宏观试验结果发现:平板拉伸时的断裂应变大于带缺口拉伸时的断裂应变,而平板拉伸时的屈服应力及峰值应力小于带缺口拉伸时的屈服应力和峰值应力,剪切时材料的断裂剪应变远远大于平板拉伸时的断裂应变.三种应力状态下试样的断口也明显不同:缺口试样根部明显发生了颈缩现象,而且断面上存在着大量的韧窝;平板拉伸几乎没有发生颈缩现象,断面上的韧窝和剪切唇各占一定的比例;纯剪切试样断口上几乎以剪切唇为主.

伸展盆地地表热流值的模拟计算——以渤海湾盆地济阳坳陷为例

伸展盆地的大地热流值可以认为是由地幔热流、地壳内部和盆地沉积物生热效应以及岩石圈和沉积物导热性质等多个因素综合叠加的结果。本文根据传热学理论,分析了纯剪切模式条件下伸展盆地内的地表热流值贡献的分布规律及其与伸展因子的理想关系,认为深部热源的能量、伸展因子大小、地壳浅层的生热性质以及盆地构造位置是控制盆地热流高低和展布的关键因素。结合沉积地层的导热性质、放射性元素的生热效应、岩浆底侵和火山作用等因素对大地热流的影响,对纯剪切模型进行了改进,并以渤海湾盆地济阳坳陷为例,计算了研究区的现今地表热流分布,得到了与正演模拟相接近的结果,验证了该方法思路的有效性。同时对该地区幕式伸展裂陷过程中的地表热流值变化趋势进行了模拟,认为在不同的伸展裂陷幕地表热流值表现为阶段式的升高,在末期达到最大值。